Feasibility study of a diesel-powered hybrid DMU

Matteo Magelli; Giuseppe Boccardo; Nicola Bosso; Nicolò Zampieri; Pierangelo Farina; Andrea Tosetto; Francesco Mocera; Aurelio Somà

doi:10.1007/s40534-021-00241-2

Feasibility study of a diesel-powered hybrid DMU

Magelli, Matteo; Boccardo, Giuseppe; Bosso, Nicola; Zampieri, Nicolò; Farina, Pierangelo; Tosetto, Andrea; Mocera, Francesco; Somà, Aurelio 2021-09-01 00:00:00 Rail. Eng. Science (2021) 29(3):271–284 https://doi.org/10.1007/s40534-021-00241-2 1 1 1 1 • • • • Matteo Magelli Giuseppe Boccardo Nicola Bosso Nicolo` Zampieri 2 2 1 1 • • • Pierangelo Farina Andrea Tosetto Francesco Mocera Aurelio Soma` Received: 5 February 2021 / Revised: 14 May 2021 / Accepted: 14 May 2021 / Published online: 11 June 2021 The Author(s) 2021 Abstract Nowadays, the interest in hybrid vehicles is on dynamic simulations performed on the Turin under- constantly increasing, not only in the automotive sector, ground track section, and the results demonstrate the fea- but also in other transportation systems, to reduce pollution sibility of the hybridization process. and emissions and to improve the overall efﬁciency of the vehicles. Although railway vehicles are typically the most Keywords Hybrid railway vehicle Energy saving eco-friendly transportation system, since commonly their Regenerative braking Diesel multiple unit Lithium primary energy source is electricity, they can still gain battery beneﬁts from hybrid technologies, as many lines world- wide are not electriﬁed. In fact, hybrid solutions allow ICE- powered (internal combustion engine) railway vehicles, such as diesel multiple units (DMUs), to operate in full- electric mode even when the track lacks electriﬁcation. The 1 Introduction possibility to switch to full electric mode is of paramount importance when the vehicle runs on urban or underground At present, the concerns about global warming and envi- track sections, where low or zero emission levels are ronmental pollution demand a great research effort and the required. We conduct the feasibility study of hybridization involvement of government policies in order to battle cli- of an existing DMU vehicle, designed by Blue Engineering mate change and its tragic consequences. The transport S.r.l., running on the Aosta–Torino Italian railway line, sector has become largely responsible in terms of CO which includes a non-electriﬁed urban track section and an emissions and energy consumption. Rail transport is one of electriﬁed underground section. The hybridization is the most eco-friendly modes of transportation, and the obtained by replacing one of the diesel generators installed speciﬁc energy consumption in rail transport has decreased on the original vehicle with a battery pack, which ensures by 37% between 1990 and 2013 [1]; however, it still has a the vehicle to operate in full-electric mode to complete its great potential for emission reductions and energy savings mission proﬁle. The hybridization is also exploited to [2], as the European Rail Industry (UNIFE) conﬁrms that a implement a regenerative braking strategy, which allows an huge amount of energy can be saved in the railway sector, increase in the energetical efﬁciency of the vehicle up to especially in light rail vehicles (LRVs) and in diesel mul- 18%. This work shows the sizing of the battery pack based tiple units (DMUs) trains [3]. Due to the low electriﬁcation of railway networks, some countries widely adopt diesel- electric railway vehicles since they are the most diffused & Nicola Bosso technical solution to run along non-electriﬁed sections. nicola.bosso@polito.it However, dual-mode railway vehicles can work in full Department of Mechanical and Aerospace Engineering, electric mode only in track sections where a catenary or a Politecnico di Torino, Corso Duca degli Abruzzi 24, Turin, third rail is available. Although over the last years, electric Italy railway vehicles have been increasingly introduced Blue Engineering S.R.L., Via Albenga 98, Rivoli, Turin, Italy 123 272 M. Magelli et al. worldwide, it is important to improve their efﬁciency and Yuasa, able to travel in the non-electriﬁed section of the to reduce losses of power supply grids because a large part Japanese Sanin Main Line [16], as well as the vehicles of that electricity is still produced using conventional fossil developed from the collaboration between Hitachi Ltd. and sources. According to a UIC-UNIFE technical document the East Japan Railway Company, namely the JR Kyushu [4], the following remarkable energy efﬁciency improve- Series BEC819, based on a battery drive system, and the JR ments can be applied on DMU trains, namely (i) energy East Series HB-E210 and HB-E300, exploiting a hybrid efﬁciency train operation (EETROP) system, (ii) trackside drive system [17]. Furthermore, the collaboration between energy storage systems (ESS), (iii) on-board ESS, Bombardier Transportation and UK Network Rail led to (iv) waste heat recovery and (v) hybrid propulsion with the design of the new Electrostar class 379, running on the permanent magnet synchronous motors. From the vehicle- Essex line [18], which is the ﬁrst UK battery-powered side perspective, different options are available to improve train, also called independently powered electric multiple the efﬁciency of railway vehicles, with regenerative brak- unit (IPEMU) since it can be powered from catenary in ing (RB) seeming the most promising and effective one electriﬁed sections and from a large battery pack in non- since it can theoretically provide up to 30% of the overall electriﬁed tracks. traction-energy demand, resulting in higher efﬁciency of With respect to batteries, supercapacitors (or electric rail vehicles and lower greenhouse gas (GHG) emissions double-layer capacitor, EDLC) feature higher energy den- [5, 6]. RB is a process able to harvest the part of the vehicle sity, capacity and charge/discharge speed, as well as a high kinetic energy, saving it for later use, for example for re- lifecycle and efﬁciency [19]. From 2003 to 2007, a accelerating the vehicle or feeding auxiliary equipment, by remarkable application of supercapacitors for the recovery taking advantage of an electric motor behaviour to act as a of braking energy involved Bombardier Transportation that generator [7]. According to Jiang et al. [8], CO emissions developed the MITRAC Energy Saver, an OESS that can be reduced by 15% and 30% when RB is applied to enabled a prototype LRV, operative in Mannheim (Ger- intercity trains and suburban commuter trains, respectively. many), to save up to 30% of traction energy [20]. Some On the other hand, RB is not very effective at low speeds vehicles of the existing Series 313 operating on the Japa- and mechanical braking is still required, especially in nese Chuo line were retroﬁtted and equipped with 570 emergency operations [9]. EDLC cells, achieving 1.6% of energy saving compared to To perform regenerative braking, a suitable ESS must be the non-retroﬁtted vehicles [21]. Moreover, Alstom and identiﬁed and adopted. Both stationary (SESS) and on- RATP (a public transport operator) have collaborated in the board (OESS) solutions are currently used in the railway STEEM project that aims to improve the energy efﬁciency ﬁeld; however, OESS systems seem the most promising, of railway vehicles. As result of the project, an EDLC- equipped Citadis vehicle was launched on the tramway T3 effective, feasible and valuable method. Currently, the most common ESS technologies for of Paris, in late 2009. The STEEM vehicle is normally braking energy recovery in the railway ﬁeld are batteries, powered by overhead contact line and uses EDLC bank for supercapacitors, and ﬂywheels [10], although interest in a distance of 300 m, achieving daily energy reduction of fuel cells (FC) and superconducting magnetic energy 13% [22]. A more detailed list of EDLC-equipped railway storage (SMES) is growing, but these last two technologies vehicles can be found in the work by Swanson and Smatlak are still not widely adopted. [15], which shows that most applications concern vehicles Ni-MH batteries were installed on twenty catenary-free running on tracks no longer than some hundreds of metres. Alstom Citadis-302 LRVs operating in Nice [11, 12], while Despite the simple design and the maturity of the 16 GIGACELL Ni-MH battery modules developed by technology [23–25], ﬂywheels are not widely adopted as Kawasaki Heavy Industries were tested on the battery- ESS in the railway ﬁeld, but a few applications and fea- driven SWIMO-X running on the experimental track in sibility studies are still witnessed. Advantages of ﬂywheel Sapporo from December 2007 to March 2008, proving that technology are long lifecycle (hundreds of thousands of 10 km could be covered in battery mode [13]. SIEMENS cycles), very low maintenance, long calendar life and high developed the SITRAS-HES power unit comprising a capability to transfer high power within few seconds. In GIGACELL module and supercapacitors, which found addition, since power and energy ratings of the ﬂywheel are its application in AVENIO vehicles running in Lisbon and independent, each of them can be optimized taking into Doha, able to operate without being supplied from other account speciﬁc application requirements. On the other power sources [14, 15]. hand, ﬂywheels have high self-discharge and up to 20% of Another type of battery adopted in the railway ﬁeld is the stored energy can be lost within one hour; furthermore, Li-Ion battery (LIB). Applications include the so-called ﬂywheel rotors can be hazardous if not well designed. A Twilight Express Mizukaze, equipped with LMO (lithium remarkable ﬂywheel trackside application is proposed in manganese oxide) battery from the LIM series by GS [26] showing improvements of energy efﬁciency up to Rail. Eng. Science (2021) 29(3):271–284 Feasibility study of a diesel-powered hybrid DMU 273 21.6% and 22.6% for single and multiple trains, respec- Both car types are equipped with electro-dynamic (ED) tively, while in South Korea ﬂywheels were installed for and pneumatic braking systems: the former operates in peak power reduction purposes on the Panam–Banseok normal braking operation, whereas the latter is activated at line, achieving peak reduction up to 36.7%, an energy a very low speed, in emergency operations or in case of saving of 48 MWh, as well as ﬁnancial improvement of failure of ED braking system. In fact, during braking 24,000 $/month [27]. Feasibility simulations showed that manoeuvres, the control unit sends a braking signal to a the installation of ﬂywheels on LRVs can bring beneﬁts in traction converter that enables the motor to act as a gen- terms of energy savings and reduction of fuel consumption erator, applying a resistant torque to the wheelsets of the and CO emissions [28, 29]. motor bogie. The existing vehicle was designed so that, The present paper is a feasibility study for the during the braking phase, the part of the ED braking power improvement of the energy efﬁciency of an existing DMU feeds auxiliary equipment, while the exceeding part is vehicle designed by Blue Engineering S.r.l. Several options wasted through the brake resistor bank. Each brake resistor were investigated, including heat recovery from exhaust bank has a rated power of 340 kW and a mass of about gases either for electrical energy production through steam 360 kg. Once the vehicle reaches a very low speed (i.e., in or organic rankine cycle (ORC) or to produce hot water, the proximity of the station), the control unit activates which may feed thermal loads such as HVAC (heating, pneumatic braking system ensuring short braking distance ventilation and air conditioning) units or a radiant ﬂoor despite its high operational costs in terms of pad and disc system. Nevertheless, these solutions were discarded wear and energy waste. The main data of the original DMU because they would allow a limited energy recovery are summarized in Table 1. despite requiring signiﬁcant changes in the current DMU Each car of the DMU is equipped with its own diesel train conﬁguration. Therefore, the most suitable solution to generator, and there are not any other external power obtain remarkable energy savings was RB. The existing supply systems; thus, the diesel engine plays an essential DMU train uses dynamic braking to slow down from high role for the proper functioning of the whole system. speeds; however, the surplus of kinetic energy of the However, because of safety issues, the vehicle is developed vehicle that does not feed auxiliary equipment is dissipated so that it is capable of completing its mission even in case into heat through resistor banks (rheostatic banking). The of failure of two of the four diesel engines. The power pack proposed upgrade deals with the replacement of the origi- weighs about 8 tons and includes a diesel engine coupled to nal power pack with a new power unit including an OESS. the electric generator (diesel generator), a control and The chosen OESS is an LTO (lithium titanate oxide) bat- monitoring system, a ﬁre ﬁghting system and a cooling tery, due to the high C-rates, life cycle of more than 5000 system. cycles, fast charging time and a large range of operating The power pack provides power to the following ele- temperatures. Therefore, the proposed changes lead to a ments: the traction converter, an auxiliary converter hybridization [30–33] of the original vehicle, which differs (medium voltage (MV) loads) and to a battery charger (low from typical dual-mode trains in its capability to work in voltage (LV) loads). More in detail, the diesel generator full electric mode even when no catenary or third rails are supplies power to a rectiﬁer that converts alternating cur- installed on the track, also reducing emissions and fuel rent (AC) into direct current (DC). Then, power ﬂows to consumptions, as required in underground and urban sec- traction and auxiliary converters and to the battery charger. tions. Moreover, the proposed hybridization can be The traction converter again converts DC–AC, supplying exploited in very cold areas, where extremely low tem- power to traction motors. The control unit is based on a peratures can damage the electrical contacts. PID controller and sends a signal to the traction converter that regulates ED braking and traction efforts by means of a VVVF inverter. The auxiliary converter feeds and regulates 2 Case study the power of the MV loads such as HVAC units, com- pressors and other auxiliary systems, whereas the battery The reference vehicle adopted in this work is an existing charger supplies power to the existing backup battery pack DMU train designed by Blue Engineering S.r.l. The vehicle used in start-up and emergency operational mode. comprises four wagons distinguished into two types called Figure 2 shows vehicle power ﬂow in different opera- car 2 and car 4, head and body of the trainset, respectively. tional modes synthetized as follows: The diesel generator, HVAC units and brake resistor bank • Traction: the vehicle accelerates until reaching cruise are roof-mounted as shown in Fig. 1. Essentially, the speed. During this phase, electric motors need to heating/cooling system of car 2 differs from the one of car provide the maximum torque, and thus, they demand 4 in the HVAC unit installed in the driver’s cabin. the maximum power because of the inrush current. Rail. Eng. Science (2021) 29(3):271–284 274 M. Magelli et al. Car 2 Car 4 Car 4 Car 2 HVAC HVAC Diesel Traction Auxiliary Brake HVAC compartment compartment generator converter converter resistor driver Car 2 Trailer Motor bogie Traction Auxiliary HVAC bogie HVAC Diesel Brake converter converter compartment compartment generator resistor Car 4 Motor Trailer bogie bogie Fig. 1 Roof-mounted equipment in head and body wagons Table 1 Heads and body wagon characteristics Characteristics Head Body Length/height/width (m) 27.18/4.28/2.82 25.72/4.28/2.82 Wheel diameter (mm) 920 920 Track gauge (mm) 1,435 1,435 Boogie wheelbase (mm) 2,500 2,500 Nominal Boogie centre spacing (m) 19 19 Axle load (t/axle) 18 18 Number of axles 4 4 Primary power source: diesel engine (kW) 560 560 Transmission system: electric motor (kW) 180 9 2 units 180 9 2 units Maximum speed (km/h) 120 Wheel arrangement (2B)(22) (22)(B2) Layout Driver’s cabin and passenger compartment Passenger compartment Capacity (persons) 228 201 Electric motors (kW) 2 9 180 2 9 180 Compressors (kW) 7.5 7.5 Compartment HVAC units (kW) 24 9224 9 2 Driver HVAC unit (kW) 5.8 – 220 V sockets (kW) 2 2 Power pack cooling system (kW) 18 18 Total (kW) 435.5 441.3 Once the vehicle reaches cruise speed, electric motors • Coasting: vehicle runs by inertia and slowly decreases only need to overcome drag force and their power its velocity. The diesel generator provides power to demand decreases. In this phase, the diesel generator auxiliary equipment only (see Fig. 2b). needs to provide power to auxiliary equipment and • Braking: when the vehicle is decelerating, initially ED electric motors (see Fig. 2a). braking energy is applied by means of the VVVF (variable voltage and variable frequency) inverter that Rail. Eng. Science (2021) 29(3):271–284 Feasibility study of a diesel-powered hybrid DMU 275 Brake Brake (a) (b) resistor resistor E.M. E.M. Diesel Traction Traction Diesel Generator Generator engine converter converter engine E.M. E.M. Auxiliary HVAC HVAC Auxiliary converter converter units units Auxiliary Auxilliary equipment equipment Auxiliary Auxiliary Auxiliary Auxiliary battery charger battery battery charger battery Brake (c) resistor E.M. Diesel Traction Generator engine converter E.M. Auxiliary HVAC converter units Auxiliary equipment Auxiliary Auxiliary battery charger battery Fig. 2 Power ﬂow of the single car: a acceleration phase, b coasting operation, and c ED braking enables electric motors to act as generators. In this case, vehicle presented in this work. In fact, dual-mode vehicles a fraction of the generated energy is used by HVAC use diesel generator in non-urban areas, whereas in the units and auxiliary equipment (see Fig. 2c). Since the proximity of urban stations or in underground tracks, they original vehicle does not include an ESS system for use an electrical power supply, such as a pantograph that energy storage, the surplus of energy is wasted by the powers the vehicle through overhead catenary. This dou- resistor bank. ble-power supply system is relatively new and quite dif- fused in the railway sector, but the vehicle is still The hybridization of the existing vehicle essentially dependent on the presence of a track electrical grid that is deals with the substitution of one of the four existing diesel generally not ensured everywhere. On the contrary, the engines with the OESS. Besides allowing ED braking proposed retroﬁtted hybrid vehicle will be capable of energy recovery, this choice enables the vehicle to operate travelling independently in non-electriﬁed urban and in a wider operation range (i.e., underground section) and underground areas thanks to the OESS. In addition, in dual- to reduce pollutant emissions in critical areas, such as not mode vehicles, regenerative braking takes place only when electriﬁed urban stations. Based on these considerations, a close vehicle requires power at the same time, and this the OESS was designed to satisfy the power demand of the scenario is almost impossible in systems different from vehicle during the entire urban track described next. funicular railway or similar. Moreover, the retroﬁtted Figure 3 conceptually shows the hybridization idea, vehicle, through the OESS, could use the engine at optimal which is applied to the existing DMU model. The retro- efﬁciency point, reducing its pollutant emissions. ﬁtted trainset will then have three diesel generators and one The vehicle was designed to operate the service on the battery pack that shall allow the vehicle to recover ED Aosta–Torino railway line, which is partially electriﬁed. In braking energy as well as to reach non-electriﬁed urban particular, the Aosta railway station is not electriﬁed, and it stations and to operate in underground tracks where diesel is in proximity of the city centre. For this reason, the generator use is forbidden. adoption of a hybrid railway vehicle can signiﬁcantly Dual-mode vehicles are already available on the market reduce pollution, especially during the winter months. and exploit the same operating principle of the retroﬁtted Moreover, the railway line includes underground and non- Rail. Eng. Science (2021) 29(3):271–284 276 M. Magelli et al. Diesel HVAC Power HVAC Brake generator compartment pack resistor compartment Car 4 Trailer Motor bogie bogie HVAC HVAC Brake Energy compartment compartment resistor storage system Car 4 Motor bogie Trailer bogie Fig. 3 Conceptual scheme of the hybridization process underground sections in the urban area of Turin for a length battery pack lifecycle, power density, energy density, and of about 20 km, in the track section connecting the stations charging/discharging times. of Torino Rebaudengo Fossata, Torino Porta Susa and Torino Porta Nuova. In these sections, the use of the diesel generator is forbidden, and the vehicle must work in full 3 Battery pack sizing electric conﬁguration. This condition is used to design and size the battery pack. Speed and slope proﬁle of the track in To calculate the vehicle power and energy demand, which the urban area of Turin are shown in Fig. 4. Once the are essential for the battery pack sizing, a longitudinal train vehicle reaches Porta Nuova railway station, acceleration dynamic (LTD) model is developed, considering slope, and slope proﬁles are reversed because the track involves a acceleration and speed proﬁle of the given track shown in round trip starting from the beginning of the underground Fig. 4. As previously explained, the battery module is sized section, located at the entrance of Turin (station of in order to guarantee the running of the vehicle in full Rebaudengo Fossata), to the central station of Porta Nuova. electric mode in the urban area of Turin, which has a length Therefore, the vehicle stops twice at each station, i.e., of about 20 km. Rebaudengo Fossata (Reb), Porta Susa (PS) and Porta Among other considerations, it should be highlighted Nuova (PN), with the way back highlighted in Fig. 4 using that RB power represents part of the total braking effort the contraction ‘‘(R)’’. The departure from each station in since ED braking use is limited by the maximum braking both ways is identiﬁed by the abbreviation ‘‘Dep.’’ As a power of motors and vehicle speed. The proposed LTD side note, it should be known that the speed proﬁle is model is 1D, as common to most LTD simulators [34, 35] imposed and controlled by the railway operator; thereby, and as suggested by the recently established international the vehicle power demand can be easily calculated, as benchmark of LTD simulators [36, 37]. The model con- explained in the next section. siders both the gravitational force due to track slope and the Based on the considerations exposed in the introduction propulsion resistance, which is the sum of rolling resis- section and on the proposed case study, the best choice for tances and air resistances. The curving resistances can be the OESS proved to be an on-board battery, which com- neglected in this work since the considered track line can bines good power and energy density, while supercapaci- be regarded as an approximately straight line in the urban tors were discarded due to their low power density and area of Turin with no tight curves. The gravitational force ﬂywheels were not considered suitable for the selected is easily calculated by means of application since this technology is not commonly used in F ¼ M g sin #; ð1Þ slope veh hybrid vehicles. More in detail, the LTO battery was selected since it guarantees a good compromise in terms of Rail. Eng. Science (2021) 29(3):271–284 Feasibility study of a diesel-powered hybrid DMU 277 (a) 0 0 0 5 10 15 20 25 30 Time (min) (b) 3 0.6 2 0.4 0.2 0 0 -1 -0.2 -0.4 -2 -3 -0.6 0 5 10 15 20 25 30 Time (min) Fig. 4 Proﬁles of the track in the urban area of Turin, a speed and b slope completely rigid links, so that the speed and acceleration of where # is the track angle of inclination, M is the total veh each car are equal to the speed and acceleration of the mass of the DMU train, and g is gravity (9.81 m/s ). whole train. Propulsion resistance F is typically expressed by Res Table 2 shows the main results obtained from the means of second-order polynomial equations as a function application of Eqs. (1)–(4) in the case study described by of the vehicle speed S , and among different expressions veh the track slope, train speed and acceleration proﬁles pre- witnessed in the literature [38–40], the Davis’ formula is sented in the previous section (see Fig. 4). Please note that adopted in this work: the table also includes other quantities that are essential for F ¼ 6:4M þ 129N þ 0:091M S þ 0:051A S ; Res veh ax veh veh front veh the battery pack sizing. Due to the high power demand of ð2Þ the considered application, the module chosen for this application is the Toshiba battery module type 3–23, whose where N is the total number of train axles and A the ax front main technical data are summarized in Table 3, while its train cross-sectional area. charging and discharging curves are presented in Fig. 5. Since the vehicle speed and acceleration proﬁles are A preliminary sizing of the battery pack is performed known in advance, the tractive and braking effort F can Tr according to the four steps suggested by Linden and Reddy be calculated as the sum of the forces previously described: [41]; for a ﬁrst approximation of the number of modules to F ¼ M a þ F þ F ; ð3Þ Tr veh veh slope Res put in series (n ) and in parallel (n ), see Eqs. (5)–(8): s p P ¼ F S ; ð4Þ V Dem Tr veh des n ¼ ; ð5Þ mod where a is the vehicle acceleration and P is the veh Dem dem power demand. E ¼ ; ð6Þ BP DOD Please note that for the sake of simplicity, the proposed model considers the vehicle coupling elements as Rail. Eng. Science (2021) 29(3):271–284 Speed (km/h) Slope (‰) Start Stop Reb Dep. Reb Stop PS Dep. PS Stop PN Dep.PN Stop PS (R) Dep.PS (R) Stop Reb (R) Dep. Reb (R) End Acceleration (m/s ) Distance (km) 278 M. Magelli et al. Table 2 Data for battery pack design Parameter Value Note Total energy demand E (kWh) 196 Including auxiliary equipment dem Maximum tractive power (kW) 1,614 Electrical power Maximum ED braking power (kW) 1,584 Electrical power Maximum braking power (kW) 4,088 Pneumatic and electric braking Desired voltage V (V) 950 Based on electrical requirements des Minimum voltage (V) 850 Based on electrical requirements Power pack mass (kg) 800 _ Diesel generator power (kW) 560 One diesel generator each car conﬁguration includes 38 series modules and 12 parallel Table 3 Battery module technical data branches, which lead to a total energy of the battery pack Parameter Value equal to 566 kWh, a maximum discharge power (at 3C-rate Nominal voltage V (V) 27.6 mod and 80% state of charge, SOC) of 1,775 kW and a total Capacity at C/5 C (Ah) 45 mass including auxiliary equipment equal to 7,660 kg. mod Minimum/maximum voltage (V) 18.0/32.4 Please note that the replacement of the original power Maximum charge/discharge 160 continuous pack (diesel engine and accessories) with the new battery current (A) 350 peak pack leads to a variation in the train mass. Calculation of the traction force and of the demanded traction power using Operative temperature range (C) - 30–45 Dimensions (mm) 190 9 361 9 125 Eqs. (1)–(4) was performed on the retroﬁtted vehicle; however, due to the limited mass change, below 1.5%, the Mass M (kg) 15 mod demanded power is substantially unchanged. As the project is in its feasibility phase, parameters such BP as battery thermal management and internal resistance are C ¼ ; ð7Þ BP n V s mod not considered. However, to estimate the dynamic beha- C viour of the battery pack and the amount of recovered BP n ¼ ; ð8Þ braking energy, a dynamic measure of battery pack SOC is mod required during vehicle operations. Scientiﬁc literature where V is the desired voltage, V the voltage of a des mod proposes various SOC measure methods and battery single battery module, E the energy of the battery pack, BP mathematical models [42–46], but these methods are typ- E the demanded energy (calculated in Table 2), DOD is dem ically based on many parameters that are still not known at the battery pack depth-of-discharge, assumed equal to this preliminary stage of the activity. Therefore, the fol- 80%, C the battery pack capacity, and C the capacity BP mod lowing main assumptions hold: of the single module. 1. Braking power ﬁrstly feeds auxiliary equipment and Once the number of parallel n and series n modules is p s secondarily battery pack, according to its SOC. determined, the mass of the battery pack M is easily BP 2. If braking power is smaller than auxiliary power calculated by means of Eq. (9), in which the 1.2 multipli- demand, the battery pack should supply that power cation factor considers the mass of auxiliary systems and difference. M is the mass of the single module, mod 3. The internal resistance value is not provided by the M ¼ 1:2n n M : ð9Þ BP s p mod battery manufacturer, so it is neglected. By Eqs. (5)–(8), a preliminary sizing of the battery pack 4. Battery efﬁciency is assumed to be 90% for a charge/ is obtained; however, the sizing process must ensure that discharge cycle. during operation the required current is always below the 5. It is assumed that electric motor efﬁciency does not maximum current withstood by the battery and that the change when it acts as a motor or as a generator. system voltage is above the minimum voltage. This aspect 6. Auxiliary power demand is assumed to be constant and is considered by increasing the number of parallel branches equal to 191 kW for the whole trainset. of the initial battery pack conﬁguration until discharging/ To assess the battery pack SOC during operation, charging current complies with the battery limits, by means dynamic simulations are performed on the case study of a MATLAB-dedicated script. The ﬁnal battery pack described in the previous section, which includes four main Rail. Eng. Science (2021) 29(3):271–284 Feasibility study of a diesel-powered hybrid DMU 279 (a) 3C 1C C/5 0% 20% 40% 60% 80% 100% Capacity (b) 30 3C 1C C/5 0% 20% 40% 60% 80% 100% Capacity Fig. 5 Characteristics of the selected battery module for different C-rates, a charge and b discharge Table 4 Vehicle operational modes in full electrical condition Traction Coasting Station stop Braking Operational The vehicle requires the The vehicle has already reached When the vehicle is In proximity of the stations, the mode maximum power since cruise speed, and relatively stationary, the vehicle initially brakes description electrical motors need very small amount of power is battery pack is through the ED braking high current in order to required to the battery pack discharging because system and the battery pack is provide the maximum for powering auxiliary of auxiliary power charged according to its SOC. tractive efforts necessary in equipment and electric demand At very low speed, the the acceleration phase motors pneumatic braking system is activated, and the vehicle rapidly reaches stationary mode Battery pack Discharging Discharging Discharging Charging when braking power is phase larger than auxiliary power Positive power in the dynamic Positive power in the dynamic Positive power in the Negative power in the simulation simulation simulation dynamic simulation Rail. Eng. Science (2021) 29(3):271–284 Module voltage (V) Module voltage (V) Y 280 M. Magelli et al. operational modes, namely traction, coasting, station stop power is negative. Same considerations are still valid for and braking. Please note that the battery sizing is per- current. Therefore, the sign of ‘‘?’’ in Eq. (10) applies formed considering the vehicle working in full electric during battery charging, while that of ‘‘–’’ is used for mode. Table 4 gives an overview of these four operational battery discharging. modes and of the related battery pack phases. The initial values of battery pack SOC as well as the The MATLAB algorithm for the battery SOC evaluation power demand during the simulation are known in is based on the simple Coulomb’s counting method, which advance. The simulations consider different values of ini- performs the integration of charging/discharging current tial battery pack SOC. During the simulation, the battery over time: pack voltage can be determined as a function of the current battery SOC, but the battery features a hysteretic behaviour t þDt SOC ¼ SOC I dt; ð10Þ in charging and discharging operations, which is managed i i1 i in the MATLAB script by means of a proper approach based on the energy conservation principle, allowing the I ¼ ; i ð11Þ V ðÞ SOC logic switch between the charging (f ) and discharging BP;i i crg (f ) functions. Figure 6 shows a ﬂowchart of the discrg where subscript i refers to the ith considered time step, P is MATLAB algorithm implemented for the evaluation of the power, V is the battery pack voltage, and I is the battery BP battery pack SOC during dynamic simulation, where SOD pack current. denotes battery of discharge, I charging current, and crg Please note that in Eqs. (10)–(11), traction and auxiliary I maximum allowed charging current. maxallowed power demands have positive value, whereas braking Initial conditions: - SOC (t=0) -V (t=0) BP -P dem Mission failure: P < 0 N return to sizing SOC > SOC ? i min Braking srage Battery SOC < SOC i max discharging Battery charging & |P |>P N i aux P P i i I = i I = V V BP,i Battery BP,i Pneumatic braking discharghing I =min [I ; I ] crg,i i maxallowed |I |<I i max Coulomb method SOC =SOC + i+1 i I dt crg,i Coulomb method SOC = SOC - i+1 I dt V =f (SOC ) BP,i crg i+1 State of discharge SOC = SOC -SOC i+1 t=0 i+1 SOC < SOC i+1 max V =f (SOC N BP,i discrg i+1 Stop charging: ED braking power flows to brake resistor bank Fig. 6 Flowchart of MATLAB algorithm for dynamic simulations Rail. Eng. Science (2021) 29(3):271–284 Feasibility study of a diesel-powered hybrid DMU 281 (a) -500 -1000 45 -1500 0 5 10 15 20 25 30 Time (min) (b) 1120 2000 -500 -1000 1000 -1500 0 5 10 15 20 25 30 Time (min) Fig. 7 Dynamic simulations: a SOC and power, and b battery pack voltage and total current As expected, the SOC value drastically decreases when 4 Results and discussion the vehicle departs from each station, since in traction mode the vehicle requires the maximum power from the The dynamic simulations aim to estimate the amount of regenerative energy recovered through the battery pack and battery pack that, consequently, is forced to provide a high current. The results of the dynamic simulation presented in to evaluate the evolution of the electrical parameters for Fig. 7 also demonstrate that the SOC level remains in the ensuring the compliance with basic electrical requirements, range of acceptable values since the vehicle terminates its such as maximum current and minimum voltage. Since the mission with battery pack SOC about 50%, considering an performed dynamic simulation neglects factors that, in the real application, could negatively affect battery pack per- initial SOC of 75%. The initial value of SOC strongly affects the amount of formance, it is essential to satisfy at least electrical, size and weight requirements for the hybridization project to be recovered energy as well as charging time; in fact, SOC values higher than 90% should be avoided; otherwise, considered feasible. As shown in Fig. 7a, the SOC level slightly increases at charging time could take too long. On the contrary, if the battery reaches a very low SOC level, the voltage dra- every braking event and linearly decreases in the rest of the journey when no braking effort is applied. Additionally, in matically drops, thus jeopardizing the compliance with the basic electrical requirement and exceeding the maximum the graph of Fig. 7b, it is possible to identify regenerative current allowed by the battery pack. Additionally, the high braking events that take place when the current becomes currents could generate heat so quickly that the battery negative and the voltage has a quick rise, due to the acti- thermal management system might not be able to handle it, vation energy required by the battery to reverse the lithium- ions ﬂow when the transition from discharging to charging thus leading to battery pack failure. Several simulations were performed considering differ- mode occurs. Moreover, it should be noted that the current essentially has the same trend of power demand because of ent values of the initial SOC, and the corresponding regenerative energy calculated for each scenario is pre- the calculation method. sented in Fig. 8, which shows that the total amount of Rail. Eng. Science (2021) 29(3):271–284 Battery pack voltage (V) SOC (%) Start Stop Reb Dep. Reb Stop PS Dep.PS Stop PN Dep. PN Stop PS (R) Dep. PS (R) Stop Reb (R) Dep. Reb (R) End Power (kW) Total current (A) 282 M. Magelli et al. 90% 85% 80% 75% 70% 65% 60% 55% 50% Initial battery pack SoC Fig. 8 Regenerative energy as a function of initial SOC regenerative energy has an upper limit due to vehicle’s the considered case study proves to be the energy recovery kinetic energy, as the amount of recovered energy is by means of regenerative braking, which is possible thanks approximately constant below a certain value of the initial to the electrical transmission system ﬁtted on the vehicle. SOC. On the other hand, the recovered energy decreases as However, since the vehicle is not equipped with a sec- the initial SOC level increases, due to the battery restriction ondary power supply system (i.e., third rail or pantograph), to accept high current above a certain SOC value. the only way to recover ED braking energy is the instal- The results of the simulations performed considering lation of an OESS that, also, allows the vehicle to handle different values of initial SOC highlighted that the regen- regenerative energy with no regard to grid capacity of erative braking can lead to recover up to 18% of the total accepting power. As a result of the research activity done, energy demand, which corresponds to approximately 85% the lithium battery seems to be the most suitable energy of the total ED braking energy, thus proving to be a very storage technology for this type of application character- promising strategy for enhancing the energy efﬁciency of ized by very high-power demand and current. Among the the railway vehicle. Additionally, the best compromise wide range of lithium battery chemistries, the LTO-based between energy recovery and charging time was achieved battery proves to be the most suitable because of their short for the initial SOC values in the range of 65%–75%. In charging time, long lifecycle, wide range of operating fact, large depth-of-discharge values should be avoided, temperatures and high C-rate. The replacement of the since they strongly affect the battery life and state of original power pack with a battery pack also enables the health. vehicle to operate in full electric mode. Therefore, the A second set of dynamic simulations was run to assess retroﬁtted vehicle is a hybrid vehicle, which differs from the vehicle performance in case of absence of regenerative typical dual-mode trains since it has no need for external braking operations, to obtain a safe range of SOC level electrical power supply in underground and urban tracks. within which the vehicle is able to complete its mission. Dynamic simulations performed on the round trip The results showed that the vehicle should have an initial between the stations of Torino Rebaudengo and Torino battery charge higher than 55% to guarantee the mission Porta Nuova on the Aosta-Torino Italian line led to completion, while for the initial SOC levels below 55%, encouraging outcomes, as the retroﬁtted vehicle can the battery pack would reach an unacceptable SOC value at recover up to 18% of the total energy demand and almost the end of the mission. 85% of the total ED braking energy. Moreover, the results Finally, from the two sets of dynamic simulations, it can showed that the vehicle energetical performance is strictly be concluded that an initial SOC value between 55% and dependant on the initial SOC of the battery pack, as the 75% ensures the completion of vehicle mission as well as vehicle can complete the mission if the initial SOC is optimal braking energy recovery. above 55%, with a good compromise between the maxi- mum recovered energy and recharging time when the ini- tial SOC is in the range of 55%–75%. 5 Conclusions The proposed hybrid architecture gives an important contribution for the reduction of local concentration of This work deals with the retroﬁtting and hybridization of particulate and CO2 emissions, which are a major concern an existing DMU to improve the vehicle energetical efﬁ- in the city of Turin. Furthermore, the retroﬁtted hybrid ciency. 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Publisher: Springer Journals
Copyright: Copyright © The Author(s) 2021
eISSN: 2662-4753
DOI: 10.1007/s40534-021-00241-2
Publisher site: See Article on Publisher Site

Abstract

Rail. Eng. Science (2021) 29(3):271–284 https://doi.org/10.1007/s40534-021-00241-2 1 1 1 1 • • • • Matteo Magelli Giuseppe Boccardo Nicola Bosso Nicolo` Zampieri 2 2 1 1 • • • Pierangelo Farina Andrea Tosetto Francesco Mocera Aurelio Soma` Received: 5 February 2021 / Revised: 14 May 2021 / Accepted: 14 May 2021 / Published online: 11 June 2021 The Author(s) 2021 Abstract Nowadays, the interest in hybrid vehicles is on dynamic simulations performed on the Turin under- constantly increasing, not only in the automotive sector, ground track section, and the results demonstrate the fea- but also in other transportation systems, to reduce pollution sibility of the hybridization process. and emissions and to improve the overall efﬁciency of the vehicles. Although railway vehicles are typically the most Keywords Hybrid railway vehicle Energy saving eco-friendly transportation system, since commonly their Regenerative braking Diesel multiple unit Lithium primary energy source is electricity, they can still gain battery beneﬁts from hybrid technologies, as many lines world- wide are not electriﬁed. In fact, hybrid solutions allow ICE- powered (internal combustion engine) railway vehicles, such as diesel multiple units (DMUs), to operate in full- electric mode even when the track lacks electriﬁcation. The 1 Introduction possibility to switch to full electric mode is of paramount importance when the vehicle runs on urban or underground At present, the concerns about global warming and envi- track sections, where low or zero emission levels are ronmental pollution demand a great research effort and the required. We conduct the feasibility study of hybridization involvement of government policies in order to battle cli- of an existing DMU vehicle, designed by Blue Engineering mate change and its tragic consequences. The transport S.r.l., running on the Aosta–Torino Italian railway line, sector has become largely responsible in terms of CO which includes a non-electriﬁed urban track section and an emissions and energy consumption. Rail transport is one of electriﬁed underground section. The hybridization is the most eco-friendly modes of transportation, and the obtained by replacing one of the diesel generators installed speciﬁc energy consumption in rail transport has decreased on the original vehicle with a battery pack, which ensures by 37% between 1990 and 2013 [1]; however, it still has a the vehicle to operate in full-electric mode to complete its great potential for emission reductions and energy savings mission proﬁle. The hybridization is also exploited to [2], as the European Rail Industry (UNIFE) conﬁrms that a implement a regenerative braking strategy, which allows an huge amount of energy can be saved in the railway sector, increase in the energetical efﬁciency of the vehicle up to especially in light rail vehicles (LRVs) and in diesel mul- 18%. This work shows the sizing of the battery pack based tiple units (DMUs) trains [3]. Due to the low electriﬁcation of railway networks, some countries widely adopt diesel- electric railway vehicles since they are the most diffused & Nicola Bosso technical solution to run along non-electriﬁed sections. nicola.bosso@polito.it However, dual-mode railway vehicles can work in full Department of Mechanical and Aerospace Engineering, electric mode only in track sections where a catenary or a Politecnico di Torino, Corso Duca degli Abruzzi 24, Turin, third rail is available. Although over the last years, electric Italy railway vehicles have been increasingly introduced Blue Engineering S.R.L., Via Albenga 98, Rivoli, Turin, Italy 123 272 M. Magelli et al. worldwide, it is important to improve their efﬁciency and Yuasa, able to travel in the non-electriﬁed section of the to reduce losses of power supply grids because a large part Japanese Sanin Main Line [16], as well as the vehicles of that electricity is still produced using conventional fossil developed from the collaboration between Hitachi Ltd. and sources. According to a UIC-UNIFE technical document the East Japan Railway Company, namely the JR Kyushu [4], the following remarkable energy efﬁciency improve- Series BEC819, based on a battery drive system, and the JR ments can be applied on DMU trains, namely (i) energy East Series HB-E210 and HB-E300, exploiting a hybrid efﬁciency train operation (EETROP) system, (ii) trackside drive system [17]. Furthermore, the collaboration between energy storage systems (ESS), (iii) on-board ESS, Bombardier Transportation and UK Network Rail led to (iv) waste heat recovery and (v) hybrid propulsion with the design of the new Electrostar class 379, running on the permanent magnet synchronous motors. From the vehicle- Essex line [18], which is the ﬁrst UK battery-powered side perspective, different options are available to improve train, also called independently powered electric multiple the efﬁciency of railway vehicles, with regenerative brak- unit (IPEMU) since it can be powered from catenary in ing (RB) seeming the most promising and effective one electriﬁed sections and from a large battery pack in non- since it can theoretically provide up to 30% of the overall electriﬁed tracks. traction-energy demand, resulting in higher efﬁciency of With respect to batteries, supercapacitors (or electric rail vehicles and lower greenhouse gas (GHG) emissions double-layer capacitor, EDLC) feature higher energy den- [5, 6]. RB is a process able to harvest the part of the vehicle sity, capacity and charge/discharge speed, as well as a high kinetic energy, saving it for later use, for example for re- lifecycle and efﬁciency [19]. From 2003 to 2007, a accelerating the vehicle or feeding auxiliary equipment, by remarkable application of supercapacitors for the recovery taking advantage of an electric motor behaviour to act as a of braking energy involved Bombardier Transportation that generator [7]. According to Jiang et al. [8], CO emissions developed the MITRAC Energy Saver, an OESS that can be reduced by 15% and 30% when RB is applied to enabled a prototype LRV, operative in Mannheim (Ger- intercity trains and suburban commuter trains, respectively. many), to save up to 30% of traction energy [20]. Some On the other hand, RB is not very effective at low speeds vehicles of the existing Series 313 operating on the Japa- and mechanical braking is still required, especially in nese Chuo line were retroﬁtted and equipped with 570 emergency operations [9]. EDLC cells, achieving 1.6% of energy saving compared to To perform regenerative braking, a suitable ESS must be the non-retroﬁtted vehicles [21]. Moreover, Alstom and identiﬁed and adopted. Both stationary (SESS) and on- RATP (a public transport operator) have collaborated in the board (OESS) solutions are currently used in the railway STEEM project that aims to improve the energy efﬁciency ﬁeld; however, OESS systems seem the most promising, of railway vehicles. As result of the project, an EDLC- equipped Citadis vehicle was launched on the tramway T3 effective, feasible and valuable method. Currently, the most common ESS technologies for of Paris, in late 2009. The STEEM vehicle is normally braking energy recovery in the railway ﬁeld are batteries, powered by overhead contact line and uses EDLC bank for supercapacitors, and ﬂywheels [10], although interest in a distance of 300 m, achieving daily energy reduction of fuel cells (FC) and superconducting magnetic energy 13% [22]. A more detailed list of EDLC-equipped railway storage (SMES) is growing, but these last two technologies vehicles can be found in the work by Swanson and Smatlak are still not widely adopted. [15], which shows that most applications concern vehicles Ni-MH batteries were installed on twenty catenary-free running on tracks no longer than some hundreds of metres. Alstom Citadis-302 LRVs operating in Nice [11, 12], while Despite the simple design and the maturity of the 16 GIGACELL Ni-MH battery modules developed by technology [23–25], ﬂywheels are not widely adopted as Kawasaki Heavy Industries were tested on the battery- ESS in the railway ﬁeld, but a few applications and fea- driven SWIMO-X running on the experimental track in sibility studies are still witnessed. Advantages of ﬂywheel Sapporo from December 2007 to March 2008, proving that technology are long lifecycle (hundreds of thousands of 10 km could be covered in battery mode [13]. SIEMENS cycles), very low maintenance, long calendar life and high developed the SITRAS-HES power unit comprising a capability to transfer high power within few seconds. In GIGACELL module and supercapacitors, which found addition, since power and energy ratings of the ﬂywheel are its application in AVENIO vehicles running in Lisbon and independent, each of them can be optimized taking into Doha, able to operate without being supplied from other account speciﬁc application requirements. On the other power sources [14, 15]. hand, ﬂywheels have high self-discharge and up to 20% of Another type of battery adopted in the railway ﬁeld is the stored energy can be lost within one hour; furthermore, Li-Ion battery (LIB). Applications include the so-called ﬂywheel rotors can be hazardous if not well designed. A Twilight Express Mizukaze, equipped with LMO (lithium remarkable ﬂywheel trackside application is proposed in manganese oxide) battery from the LIM series by GS [26] showing improvements of energy efﬁciency up to Rail. Eng. Science (2021) 29(3):271–284 Feasibility study of a diesel-powered hybrid DMU 273 21.6% and 22.6% for single and multiple trains, respec- Both car types are equipped with electro-dynamic (ED) tively, while in South Korea ﬂywheels were installed for and pneumatic braking systems: the former operates in peak power reduction purposes on the Panam–Banseok normal braking operation, whereas the latter is activated at line, achieving peak reduction up to 36.7%, an energy a very low speed, in emergency operations or in case of saving of 48 MWh, as well as ﬁnancial improvement of failure of ED braking system. In fact, during braking 24,000 $/month [27]. Feasibility simulations showed that manoeuvres, the control unit sends a braking signal to a the installation of ﬂywheels on LRVs can bring beneﬁts in traction converter that enables the motor to act as a gen- terms of energy savings and reduction of fuel consumption erator, applying a resistant torque to the wheelsets of the and CO emissions [28, 29]. motor bogie. The existing vehicle was designed so that, The present paper is a feasibility study for the during the braking phase, the part of the ED braking power improvement of the energy efﬁciency of an existing DMU feeds auxiliary equipment, while the exceeding part is vehicle designed by Blue Engineering S.r.l. Several options wasted through the brake resistor bank. Each brake resistor were investigated, including heat recovery from exhaust bank has a rated power of 340 kW and a mass of about gases either for electrical energy production through steam 360 kg. Once the vehicle reaches a very low speed (i.e., in or organic rankine cycle (ORC) or to produce hot water, the proximity of the station), the control unit activates which may feed thermal loads such as HVAC (heating, pneumatic braking system ensuring short braking distance ventilation and air conditioning) units or a radiant ﬂoor despite its high operational costs in terms of pad and disc system. Nevertheless, these solutions were discarded wear and energy waste. The main data of the original DMU because they would allow a limited energy recovery are summarized in Table 1. despite requiring signiﬁcant changes in the current DMU Each car of the DMU is equipped with its own diesel train conﬁguration. Therefore, the most suitable solution to generator, and there are not any other external power obtain remarkable energy savings was RB. The existing supply systems; thus, the diesel engine plays an essential DMU train uses dynamic braking to slow down from high role for the proper functioning of the whole system. speeds; however, the surplus of kinetic energy of the However, because of safety issues, the vehicle is developed vehicle that does not feed auxiliary equipment is dissipated so that it is capable of completing its mission even in case into heat through resistor banks (rheostatic banking). The of failure of two of the four diesel engines. The power pack proposed upgrade deals with the replacement of the origi- weighs about 8 tons and includes a diesel engine coupled to nal power pack with a new power unit including an OESS. the electric generator (diesel generator), a control and The chosen OESS is an LTO (lithium titanate oxide) bat- monitoring system, a ﬁre ﬁghting system and a cooling tery, due to the high C-rates, life cycle of more than 5000 system. cycles, fast charging time and a large range of operating The power pack provides power to the following ele- temperatures. Therefore, the proposed changes lead to a ments: the traction converter, an auxiliary converter hybridization [30–33] of the original vehicle, which differs (medium voltage (MV) loads) and to a battery charger (low from typical dual-mode trains in its capability to work in voltage (LV) loads). More in detail, the diesel generator full electric mode even when no catenary or third rails are supplies power to a rectiﬁer that converts alternating cur- installed on the track, also reducing emissions and fuel rent (AC) into direct current (DC). Then, power ﬂows to consumptions, as required in underground and urban sec- traction and auxiliary converters and to the battery charger. tions. Moreover, the proposed hybridization can be The traction converter again converts DC–AC, supplying exploited in very cold areas, where extremely low tem- power to traction motors. The control unit is based on a peratures can damage the electrical contacts. PID controller and sends a signal to the traction converter that regulates ED braking and traction efforts by means of a VVVF inverter. The auxiliary converter feeds and regulates 2 Case study the power of the MV loads such as HVAC units, com- pressors and other auxiliary systems, whereas the battery The reference vehicle adopted in this work is an existing charger supplies power to the existing backup battery pack DMU train designed by Blue Engineering S.r.l. The vehicle used in start-up and emergency operational mode. comprises four wagons distinguished into two types called Figure 2 shows vehicle power ﬂow in different opera- car 2 and car 4, head and body of the trainset, respectively. tional modes synthetized as follows: The diesel generator, HVAC units and brake resistor bank • Traction: the vehicle accelerates until reaching cruise are roof-mounted as shown in Fig. 1. Essentially, the speed. During this phase, electric motors need to heating/cooling system of car 2 differs from the one of car provide the maximum torque, and thus, they demand 4 in the HVAC unit installed in the driver’s cabin. the maximum power because of the inrush current. Rail. Eng. Science (2021) 29(3):271–284 274 M. Magelli et al. Car 2 Car 4 Car 4 Car 2 HVAC HVAC Diesel Traction Auxiliary Brake HVAC compartment compartment generator converter converter resistor driver Car 2 Trailer Motor bogie Traction Auxiliary HVAC bogie HVAC Diesel Brake converter converter compartment compartment generator resistor Car 4 Motor Trailer bogie bogie Fig. 1 Roof-mounted equipment in head and body wagons Table 1 Heads and body wagon characteristics Characteristics Head Body Length/height/width (m) 27.18/4.28/2.82 25.72/4.28/2.82 Wheel diameter (mm) 920 920 Track gauge (mm) 1,435 1,435 Boogie wheelbase (mm) 2,500 2,500 Nominal Boogie centre spacing (m) 19 19 Axle load (t/axle) 18 18 Number of axles 4 4 Primary power source: diesel engine (kW) 560 560 Transmission system: electric motor (kW) 180 9 2 units 180 9 2 units Maximum speed (km/h) 120 Wheel arrangement (2B)(22) (22)(B2) Layout Driver’s cabin and passenger compartment Passenger compartment Capacity (persons) 228 201 Electric motors (kW) 2 9 180 2 9 180 Compressors (kW) 7.5 7.5 Compartment HVAC units (kW) 24 9224 9 2 Driver HVAC unit (kW) 5.8 – 220 V sockets (kW) 2 2 Power pack cooling system (kW) 18 18 Total (kW) 435.5 441.3 Once the vehicle reaches cruise speed, electric motors • Coasting: vehicle runs by inertia and slowly decreases only need to overcome drag force and their power its velocity. The diesel generator provides power to demand decreases. In this phase, the diesel generator auxiliary equipment only (see Fig. 2b). needs to provide power to auxiliary equipment and • Braking: when the vehicle is decelerating, initially ED electric motors (see Fig. 2a). braking energy is applied by means of the VVVF (variable voltage and variable frequency) inverter that Rail. Eng. Science (2021) 29(3):271–284 Feasibility study of a diesel-powered hybrid DMU 275 Brake Brake (a) (b) resistor resistor E.M. E.M. Diesel Traction Traction Diesel Generator Generator engine converter converter engine E.M. E.M. Auxiliary HVAC HVAC Auxiliary converter converter units units Auxiliary Auxilliary equipment equipment Auxiliary Auxiliary Auxiliary Auxiliary battery charger battery battery charger battery Brake (c) resistor E.M. Diesel Traction Generator engine converter E.M. Auxiliary HVAC converter units Auxiliary equipment Auxiliary Auxiliary battery charger battery Fig. 2 Power ﬂow of the single car: a acceleration phase, b coasting operation, and c ED braking enables electric motors to act as generators. In this case, vehicle presented in this work. In fact, dual-mode vehicles a fraction of the generated energy is used by HVAC use diesel generator in non-urban areas, whereas in the units and auxiliary equipment (see Fig. 2c). Since the proximity of urban stations or in underground tracks, they original vehicle does not include an ESS system for use an electrical power supply, such as a pantograph that energy storage, the surplus of energy is wasted by the powers the vehicle through overhead catenary. This dou- resistor bank. ble-power supply system is relatively new and quite dif- fused in the railway sector, but the vehicle is still The hybridization of the existing vehicle essentially dependent on the presence of a track electrical grid that is deals with the substitution of one of the four existing diesel generally not ensured everywhere. On the contrary, the engines with the OESS. Besides allowing ED braking proposed retroﬁtted hybrid vehicle will be capable of energy recovery, this choice enables the vehicle to operate travelling independently in non-electriﬁed urban and in a wider operation range (i.e., underground section) and underground areas thanks to the OESS. In addition, in dual- to reduce pollutant emissions in critical areas, such as not mode vehicles, regenerative braking takes place only when electriﬁed urban stations. Based on these considerations, a close vehicle requires power at the same time, and this the OESS was designed to satisfy the power demand of the scenario is almost impossible in systems different from vehicle during the entire urban track described next. funicular railway or similar. Moreover, the retroﬁtted Figure 3 conceptually shows the hybridization idea, vehicle, through the OESS, could use the engine at optimal which is applied to the existing DMU model. The retro- efﬁciency point, reducing its pollutant emissions. ﬁtted trainset will then have three diesel generators and one The vehicle was designed to operate the service on the battery pack that shall allow the vehicle to recover ED Aosta–Torino railway line, which is partially electriﬁed. In braking energy as well as to reach non-electriﬁed urban particular, the Aosta railway station is not electriﬁed, and it stations and to operate in underground tracks where diesel is in proximity of the city centre. For this reason, the generator use is forbidden. adoption of a hybrid railway vehicle can signiﬁcantly Dual-mode vehicles are already available on the market reduce pollution, especially during the winter months. and exploit the same operating principle of the retroﬁtted Moreover, the railway line includes underground and non- Rail. Eng. Science (2021) 29(3):271–284 276 M. Magelli et al. Diesel HVAC Power HVAC Brake generator compartment pack resistor compartment Car 4 Trailer Motor bogie bogie HVAC HVAC Brake Energy compartment compartment resistor storage system Car 4 Motor bogie Trailer bogie Fig. 3 Conceptual scheme of the hybridization process underground sections in the urban area of Turin for a length battery pack lifecycle, power density, energy density, and of about 20 km, in the track section connecting the stations charging/discharging times. of Torino Rebaudengo Fossata, Torino Porta Susa and Torino Porta Nuova. In these sections, the use of the diesel generator is forbidden, and the vehicle must work in full 3 Battery pack sizing electric conﬁguration. This condition is used to design and size the battery pack. Speed and slope proﬁle of the track in To calculate the vehicle power and energy demand, which the urban area of Turin are shown in Fig. 4. Once the are essential for the battery pack sizing, a longitudinal train vehicle reaches Porta Nuova railway station, acceleration dynamic (LTD) model is developed, considering slope, and slope proﬁles are reversed because the track involves a acceleration and speed proﬁle of the given track shown in round trip starting from the beginning of the underground Fig. 4. As previously explained, the battery module is sized section, located at the entrance of Turin (station of in order to guarantee the running of the vehicle in full Rebaudengo Fossata), to the central station of Porta Nuova. electric mode in the urban area of Turin, which has a length Therefore, the vehicle stops twice at each station, i.e., of about 20 km. Rebaudengo Fossata (Reb), Porta Susa (PS) and Porta Among other considerations, it should be highlighted Nuova (PN), with the way back highlighted in Fig. 4 using that RB power represents part of the total braking effort the contraction ‘‘(R)’’. The departure from each station in since ED braking use is limited by the maximum braking both ways is identiﬁed by the abbreviation ‘‘Dep.’’ As a power of motors and vehicle speed. The proposed LTD side note, it should be known that the speed proﬁle is model is 1D, as common to most LTD simulators [34, 35] imposed and controlled by the railway operator; thereby, and as suggested by the recently established international the vehicle power demand can be easily calculated, as benchmark of LTD simulators [36, 37]. The model con- explained in the next section. siders both the gravitational force due to track slope and the Based on the considerations exposed in the introduction propulsion resistance, which is the sum of rolling resis- section and on the proposed case study, the best choice for tances and air resistances. The curving resistances can be the OESS proved to be an on-board battery, which com- neglected in this work since the considered track line can bines good power and energy density, while supercapaci- be regarded as an approximately straight line in the urban tors were discarded due to their low power density and area of Turin with no tight curves. The gravitational force ﬂywheels were not considered suitable for the selected is easily calculated by means of application since this technology is not commonly used in F ¼ M g sin #; ð1Þ slope veh hybrid vehicles. More in detail, the LTO battery was selected since it guarantees a good compromise in terms of Rail. Eng. Science (2021) 29(3):271–284 Feasibility study of a diesel-powered hybrid DMU 277 (a) 0 0 0 5 10 15 20 25 30 Time (min) (b) 3 0.6 2 0.4 0.2 0 0 -1 -0.2 -0.4 -2 -3 -0.6 0 5 10 15 20 25 30 Time (min) Fig. 4 Proﬁles of the track in the urban area of Turin, a speed and b slope completely rigid links, so that the speed and acceleration of where # is the track angle of inclination, M is the total veh each car are equal to the speed and acceleration of the mass of the DMU train, and g is gravity (9.81 m/s ). whole train. Propulsion resistance F is typically expressed by Res Table 2 shows the main results obtained from the means of second-order polynomial equations as a function application of Eqs. (1)–(4) in the case study described by of the vehicle speed S , and among different expressions veh the track slope, train speed and acceleration proﬁles pre- witnessed in the literature [38–40], the Davis’ formula is sented in the previous section (see Fig. 4). Please note that adopted in this work: the table also includes other quantities that are essential for F ¼ 6:4M þ 129N þ 0:091M S þ 0:051A S ; Res veh ax veh veh front veh the battery pack sizing. Due to the high power demand of ð2Þ the considered application, the module chosen for this application is the Toshiba battery module type 3–23, whose where N is the total number of train axles and A the ax front main technical data are summarized in Table 3, while its train cross-sectional area. charging and discharging curves are presented in Fig. 5. Since the vehicle speed and acceleration proﬁles are A preliminary sizing of the battery pack is performed known in advance, the tractive and braking effort F can Tr according to the four steps suggested by Linden and Reddy be calculated as the sum of the forces previously described: [41]; for a ﬁrst approximation of the number of modules to F ¼ M a þ F þ F ; ð3Þ Tr veh veh slope Res put in series (n ) and in parallel (n ), see Eqs. (5)–(8): s p P ¼ F S ; ð4Þ V Dem Tr veh des n ¼ ; ð5Þ mod where a is the vehicle acceleration and P is the veh Dem dem power demand. E ¼ ; ð6Þ BP DOD Please note that for the sake of simplicity, the proposed model considers the vehicle coupling elements as Rail. Eng. Science (2021) 29(3):271–284 Speed (km/h) Slope (‰) Start Stop Reb Dep. Reb Stop PS Dep. PS Stop PN Dep.PN Stop PS (R) Dep.PS (R) Stop Reb (R) Dep. Reb (R) End Acceleration (m/s ) Distance (km) 278 M. Magelli et al. Table 2 Data for battery pack design Parameter Value Note Total energy demand E (kWh) 196 Including auxiliary equipment dem Maximum tractive power (kW) 1,614 Electrical power Maximum ED braking power (kW) 1,584 Electrical power Maximum braking power (kW) 4,088 Pneumatic and electric braking Desired voltage V (V) 950 Based on electrical requirements des Minimum voltage (V) 850 Based on electrical requirements Power pack mass (kg) 800 _ Diesel generator power (kW) 560 One diesel generator each car conﬁguration includes 38 series modules and 12 parallel Table 3 Battery module technical data branches, which lead to a total energy of the battery pack Parameter Value equal to 566 kWh, a maximum discharge power (at 3C-rate Nominal voltage V (V) 27.6 mod and 80% state of charge, SOC) of 1,775 kW and a total Capacity at C/5 C (Ah) 45 mass including auxiliary equipment equal to 7,660 kg. mod Minimum/maximum voltage (V) 18.0/32.4 Please note that the replacement of the original power Maximum charge/discharge 160 continuous pack (diesel engine and accessories) with the new battery current (A) 350 peak pack leads to a variation in the train mass. Calculation of the traction force and of the demanded traction power using Operative temperature range (C) - 30–45 Dimensions (mm) 190 9 361 9 125 Eqs. (1)–(4) was performed on the retroﬁtted vehicle; however, due to the limited mass change, below 1.5%, the Mass M (kg) 15 mod demanded power is substantially unchanged. As the project is in its feasibility phase, parameters such BP as battery thermal management and internal resistance are C ¼ ; ð7Þ BP n V s mod not considered. However, to estimate the dynamic beha- C viour of the battery pack and the amount of recovered BP n ¼ ; ð8Þ braking energy, a dynamic measure of battery pack SOC is mod required during vehicle operations. Scientiﬁc literature where V is the desired voltage, V the voltage of a des mod proposes various SOC measure methods and battery single battery module, E the energy of the battery pack, BP mathematical models [42–46], but these methods are typ- E the demanded energy (calculated in Table 2), DOD is dem ically based on many parameters that are still not known at the battery pack depth-of-discharge, assumed equal to this preliminary stage of the activity. Therefore, the fol- 80%, C the battery pack capacity, and C the capacity BP mod lowing main assumptions hold: of the single module. 1. Braking power ﬁrstly feeds auxiliary equipment and Once the number of parallel n and series n modules is p s secondarily battery pack, according to its SOC. determined, the mass of the battery pack M is easily BP 2. If braking power is smaller than auxiliary power calculated by means of Eq. (9), in which the 1.2 multipli- demand, the battery pack should supply that power cation factor considers the mass of auxiliary systems and difference. M is the mass of the single module, mod 3. The internal resistance value is not provided by the M ¼ 1:2n n M : ð9Þ BP s p mod battery manufacturer, so it is neglected. By Eqs. (5)–(8), a preliminary sizing of the battery pack 4. Battery efﬁciency is assumed to be 90% for a charge/ is obtained; however, the sizing process must ensure that discharge cycle. during operation the required current is always below the 5. It is assumed that electric motor efﬁciency does not maximum current withstood by the battery and that the change when it acts as a motor or as a generator. system voltage is above the minimum voltage. This aspect 6. Auxiliary power demand is assumed to be constant and is considered by increasing the number of parallel branches equal to 191 kW for the whole trainset. of the initial battery pack conﬁguration until discharging/ To assess the battery pack SOC during operation, charging current complies with the battery limits, by means dynamic simulations are performed on the case study of a MATLAB-dedicated script. The ﬁnal battery pack described in the previous section, which includes four main Rail. Eng. Science (2021) 29(3):271–284 Feasibility study of a diesel-powered hybrid DMU 279 (a) 3C 1C C/5 0% 20% 40% 60% 80% 100% Capacity (b) 30 3C 1C C/5 0% 20% 40% 60% 80% 100% Capacity Fig. 5 Characteristics of the selected battery module for different C-rates, a charge and b discharge Table 4 Vehicle operational modes in full electrical condition Traction Coasting Station stop Braking Operational The vehicle requires the The vehicle has already reached When the vehicle is In proximity of the stations, the mode maximum power since cruise speed, and relatively stationary, the vehicle initially brakes description electrical motors need very small amount of power is battery pack is through the ED braking high current in order to required to the battery pack discharging because system and the battery pack is provide the maximum for powering auxiliary of auxiliary power charged according to its SOC. tractive efforts necessary in equipment and electric demand At very low speed, the the acceleration phase motors pneumatic braking system is activated, and the vehicle rapidly reaches stationary mode Battery pack Discharging Discharging Discharging Charging when braking power is phase larger than auxiliary power Positive power in the dynamic Positive power in the dynamic Positive power in the Negative power in the simulation simulation simulation dynamic simulation Rail. Eng. Science (2021) 29(3):271–284 Module voltage (V) Module voltage (V) Y 280 M. Magelli et al. operational modes, namely traction, coasting, station stop power is negative. Same considerations are still valid for and braking. Please note that the battery sizing is per- current. Therefore, the sign of ‘‘?’’ in Eq. (10) applies formed considering the vehicle working in full electric during battery charging, while that of ‘‘–’’ is used for mode. Table 4 gives an overview of these four operational battery discharging. modes and of the related battery pack phases. The initial values of battery pack SOC as well as the The MATLAB algorithm for the battery SOC evaluation power demand during the simulation are known in is based on the simple Coulomb’s counting method, which advance. The simulations consider different values of ini- performs the integration of charging/discharging current tial battery pack SOC. During the simulation, the battery over time: pack voltage can be determined as a function of the current battery SOC, but the battery features a hysteretic behaviour t þDt SOC ¼ SOC I dt; ð10Þ in charging and discharging operations, which is managed i i1 i in the MATLAB script by means of a proper approach based on the energy conservation principle, allowing the I ¼ ; i ð11Þ V ðÞ SOC logic switch between the charging (f ) and discharging BP;i i crg (f ) functions. Figure 6 shows a ﬂowchart of the discrg where subscript i refers to the ith considered time step, P is MATLAB algorithm implemented for the evaluation of the power, V is the battery pack voltage, and I is the battery BP battery pack SOC during dynamic simulation, where SOD pack current. denotes battery of discharge, I charging current, and crg Please note that in Eqs. (10)–(11), traction and auxiliary I maximum allowed charging current. maxallowed power demands have positive value, whereas braking Initial conditions: - SOC (t=0) -V (t=0) BP -P dem Mission failure: P < 0 N return to sizing SOC > SOC ? i min Braking srage Battery SOC < SOC i max discharging Battery charging & |P |>P N i aux P P i i I = i I = V V BP,i Battery BP,i Pneumatic braking discharghing I =min [I ; I ] crg,i i maxallowed |I |<I i max Coulomb method SOC =SOC + i+1 i I dt crg,i Coulomb method SOC = SOC - i+1 I dt V =f (SOC ) BP,i crg i+1 State of discharge SOC = SOC -SOC i+1 t=0 i+1 SOC < SOC i+1 max V =f (SOC N BP,i discrg i+1 Stop charging: ED braking power flows to brake resistor bank Fig. 6 Flowchart of MATLAB algorithm for dynamic simulations Rail. Eng. Science (2021) 29(3):271–284 Feasibility study of a diesel-powered hybrid DMU 281 (a) -500 -1000 45 -1500 0 5 10 15 20 25 30 Time (min) (b) 1120 2000 -500 -1000 1000 -1500 0 5 10 15 20 25 30 Time (min) Fig. 7 Dynamic simulations: a SOC and power, and b battery pack voltage and total current As expected, the SOC value drastically decreases when 4 Results and discussion the vehicle departs from each station, since in traction mode the vehicle requires the maximum power from the The dynamic simulations aim to estimate the amount of regenerative energy recovered through the battery pack and battery pack that, consequently, is forced to provide a high current. The results of the dynamic simulation presented in to evaluate the evolution of the electrical parameters for Fig. 7 also demonstrate that the SOC level remains in the ensuring the compliance with basic electrical requirements, range of acceptable values since the vehicle terminates its such as maximum current and minimum voltage. Since the mission with battery pack SOC about 50%, considering an performed dynamic simulation neglects factors that, in the real application, could negatively affect battery pack per- initial SOC of 75%. The initial value of SOC strongly affects the amount of formance, it is essential to satisfy at least electrical, size and weight requirements for the hybridization project to be recovered energy as well as charging time; in fact, SOC values higher than 90% should be avoided; otherwise, considered feasible. As shown in Fig. 7a, the SOC level slightly increases at charging time could take too long. On the contrary, if the battery reaches a very low SOC level, the voltage dra- every braking event and linearly decreases in the rest of the journey when no braking effort is applied. Additionally, in matically drops, thus jeopardizing the compliance with the basic electrical requirement and exceeding the maximum the graph of Fig. 7b, it is possible to identify regenerative current allowed by the battery pack. Additionally, the high braking events that take place when the current becomes currents could generate heat so quickly that the battery negative and the voltage has a quick rise, due to the acti- thermal management system might not be able to handle it, vation energy required by the battery to reverse the lithium- ions ﬂow when the transition from discharging to charging thus leading to battery pack failure. Several simulations were performed considering differ- mode occurs. Moreover, it should be noted that the current essentially has the same trend of power demand because of ent values of the initial SOC, and the corresponding regenerative energy calculated for each scenario is pre- the calculation method. sented in Fig. 8, which shows that the total amount of Rail. Eng. Science (2021) 29(3):271–284 Battery pack voltage (V) SOC (%) Start Stop Reb Dep. Reb Stop PS Dep.PS Stop PN Dep. PN Stop PS (R) Dep. PS (R) Stop Reb (R) Dep. Reb (R) End Power (kW) Total current (A) 282 M. Magelli et al. 90% 85% 80% 75% 70% 65% 60% 55% 50% Initial battery pack SoC Fig. 8 Regenerative energy as a function of initial SOC regenerative energy has an upper limit due to vehicle’s the considered case study proves to be the energy recovery kinetic energy, as the amount of recovered energy is by means of regenerative braking, which is possible thanks approximately constant below a certain value of the initial to the electrical transmission system ﬁtted on the vehicle. SOC. On the other hand, the recovered energy decreases as However, since the vehicle is not equipped with a sec- the initial SOC level increases, due to the battery restriction ondary power supply system (i.e., third rail or pantograph), to accept high current above a certain SOC value. the only way to recover ED braking energy is the instal- The results of the simulations performed considering lation of an OESS that, also, allows the vehicle to handle different values of initial SOC highlighted that the regen- regenerative energy with no regard to grid capacity of erative braking can lead to recover up to 18% of the total accepting power. As a result of the research activity done, energy demand, which corresponds to approximately 85% the lithium battery seems to be the most suitable energy of the total ED braking energy, thus proving to be a very storage technology for this type of application character- promising strategy for enhancing the energy efﬁciency of ized by very high-power demand and current. Among the the railway vehicle. Additionally, the best compromise wide range of lithium battery chemistries, the LTO-based between energy recovery and charging time was achieved battery proves to be the most suitable because of their short for the initial SOC values in the range of 65%–75%. In charging time, long lifecycle, wide range of operating fact, large depth-of-discharge values should be avoided, temperatures and high C-rate. The replacement of the since they strongly affect the battery life and state of original power pack with a battery pack also enables the health. vehicle to operate in full electric mode. Therefore, the A second set of dynamic simulations was run to assess retroﬁtted vehicle is a hybrid vehicle, which differs from the vehicle performance in case of absence of regenerative typical dual-mode trains since it has no need for external braking operations, to obtain a safe range of SOC level electrical power supply in underground and urban tracks. within which the vehicle is able to complete its mission. Dynamic simulations performed on the round trip The results showed that the vehicle should have an initial between the stations of Torino Rebaudengo and Torino battery charge higher than 55% to guarantee the mission Porta Nuova on the Aosta-Torino Italian line led to completion, while for the initial SOC levels below 55%, encouraging outcomes, as the retroﬁtted vehicle can the battery pack would reach an unacceptable SOC value at recover up to 18% of the total energy demand and almost the end of the mission. 85% of the total ED braking energy. Moreover, the results Finally, from the two sets of dynamic simulations, it can showed that the vehicle energetical performance is strictly be concluded that an initial SOC value between 55% and dependant on the initial SOC of the battery pack, as the 75% ensures the completion of vehicle mission as well as vehicle can complete the mission if the initial SOC is optimal braking energy recovery. above 55%, with a good compromise between the maxi- mum recovered energy and recharging time when the ini- tial SOC is in the range of 55%–75%. 5 Conclusions The proposed hybrid architecture gives an important contribution for the reduction of local concentration of This work deals with the retroﬁtting and hybridization of particulate and CO2 emissions, which are a major concern an existing DMU to improve the vehicle energetical efﬁ- in the city of Turin. Furthermore, the retroﬁtted hybrid ciency. 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Railway Engineering Science – Springer Journals

Published: Sep 1, 2021

Keywords: Hybrid railway vehicle; Energy saving; Regenerative braking; Diesel multiple unit; Lithium battery

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Feasibility study of a diesel-powered hybrid DMU

Feasibility study of a diesel-powered hybrid DMU

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Feasibility study of a diesel-powered hybrid DMU

Feasibility study of a diesel-powered hybrid DMU

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