1、Energy management of a plug-in fuel cell/battery hybrid vehicle with on-board fuel processing Laura Tribioli a, Raffaello Cozzolinoa, Daniele Chiappinia, Paolo Iorab aDept. of Industrial Engineering, Universit di Roma Niccol Cusano, Italy bDept. of Mechanical and Industrial Engineering, Universit di

2、 Brescia, Italy h i g h l i g h t s ?Model-based simulator for energy management of parallel fuel cell/battery vehicle. ?Fuel processor optimization for on-board hydrogen production and storage. ?Electrochemical model of a HT-PEMFC for performance curves determination. ?Design of real time Pontryagi

3、ns Minimum Principle-based adaptive controller. ?Results comparison against the same vehicle with conventional and hybrid powertrain. a r t i c l ei n f o Article history: Received 22 April 2016 Received in revised form 9 September 2016 Accepted 2 October 2016 Available online 12 October 2016 Keywor

4、ds: Energy management HT-PEMFC On-board fuel processor Pontryagins Minimum Principle Adaptive controller a b s t r a c t This paper describes the energy management controller design of a mid-sized vehicle driven by a fuel cell/battery plug-in hybrid powertrain, where an experimentally validated high

5、t temperature polymer electrolyte membrane fuel cell model is used. The power management strategy is derived by the appli- cation of the Pontryagins Minimum Principle, where the control parameter is adapted by using feedback information on the state of charge and total trip length forecast as a func

6、tion of a moving average of past information about the driving cycle speed. The strategy we propose aims at achieving a real time sub- optimal solution of the control problem which is cast into the minimization of the consumed fuel. The vehicle is also equipped by an auto-thermal reformer and, in or

7、der to minimize the hydrogen buffer size, the control algorithm is subject to constraints on the maximum hydrogen buffer level. A comparative analysis of the proposed strategy against the optimal one is conducted and results are reported. The obtained fuel consumptions are also compared to those obt

8、ained by the same vehicle, powered by an internal combustion engine and by a plug-in hybrid electric powertrain. ? 2016 Elsevier Ltd. All rights reserved. 1. Introduction Road transportation and, particularly, road vehicles are nowa- days proved to be one of the main contributors to pollutant and gl

9、obal green-house gas emissions 1. This, together with the rising of fuel price, is striving the automotive sector research towards innovative solutions, aimed at reducing costs and emissions 2. Electric Vehicles (EVs) are still too far from being a valid solution for the problem, both for reduced dr

10、iving range and long charging time. Promising solutions - already widely proposed and analyzed - are plug-in hybrid electric vehicles (PHEVs), characterized by high overall effi ciency, short transients, long range and low road- load-dependency 3,4. The same advantages apply for fuel cell vehicles (

11、FCVs), which generally make use of polymer electrolyte membrane fuel cells (PEMFCs), with the possibility of further reducing pollutant emissions, giving a satisfactory range without the need of an internal combustion engine (ICE) 5. In fact, when compared to ICE-propelled vehicles, both conventiona

12、l or hybrid electric ones, FCVs are, locally, zero-emission vehicles and, in prin- ciple, if the fueling hydrogen could be derived from renewable energy sources, these vehicles could allow for zero pollutant emis- sions also at a global level. Therefore, these vehicles can give a valid contribution

13、to make the transportation sustainable in the long termandgovernmentsarestronglystrivingtowardsthese solutions 6,7. Nonetheless, even being a relatively mature tech- nology, there are still some disadvantages related to the use of fuel cells for vehicles, such as high costs, low power density, and l

14、ack of /10.1016/j.apenergy.2016.10.015 0306-2619/? 2016 Elsevier Ltd. All rights reserved. Corresponding author. E-mail addresses: laura.tribioliunicusano.it (L. Tribioli), raffaello.cozzolino unicusano.it (R. Cozzolino), daniele.chiappiniunicusano.it (D. Chiappini), paolo. ioraunibs

15、.it (P. Iora). Applied Energy 184 (2016) 140154 Contents lists available at ScienceDirect Applied Energy journal homepage: hydrogen infrastructures 6. The latter issue could be solved by using an on-board fuel processor for on-site hydrogen production from hydrocarbon fuels. This solution has been o

16、ften investigated for the use of hydrogen-enriched fuel directly in internal combus- tion engines 8,9. Early prototypes for fuel processors to be used directly in vehicles were obtained by scaling down already existing industrial technologies. In this case, gasoline, ethanol and other automotive fue

17、ls could be successfully processed, but the proto- types still required volume and mass not suitable for automotive applications. In the US, on 2004, these issues and the competition with more mature technologies, such as gasoline/battery hybrid vehicles, have convinced the DOE On-Board Fuel Process

18、ing Go/NoGo Decision Team to terminate the research on on-board fuel processing for FCVs 10. In Europe, in the early 2000s, Daimler Chrysler started testing methanol processors for the fueling of fuel cell vehicle prototypes. NeCar 5, based on the A-Class Mercedes design, was the last launched proto

19、type, which used a 75-kW Ballard fuel cell showing impressive performance 11. In 2004, Renault/Nuvera presented a four-year project for a fuel processor for on-board hydrogen production small enough and powerful enough for use on a vehicle, but also this program ended in 2008 with no further develop

20、ments 12. In these early projects, on- board fuel processing had been considered for fuel cells providing 100% of vehicle traction power, with reformer size and system costs which made this solution unworthy. Afterwards, on-board fuel processing was investigated again for coupling with fuel cells us

21、ed as auxiliary power units (APUs). In fact, when a fuel cell is used as APU, its power is reduced, the system can be more compact and hydrogen storage unit is not required. Technological features and challenges of on-board reforming of heavy hydrocarbon fuels to feed solid oxide fuel cells (SOFCs)

22、as APUs have been summa- rized by 13, underlining the benefi ts of autothermal reforming (ATR) over partial oxidation (POX) and steam reforming (SR). ATR has been again coupled to SOFCs by 14, who evaluated the effect of off-gas recycle on overall system effi ciency. Albeit the lower effi - ciency a

23、nd poorer fuel quality 15, ATR is recognized to be the best solution for transportation applications. In fact, reactions are con- sidered to be thermally self-sustaining, and therefore, they do not produce or consume external thermal energy, unlike POX or SR. In the automotive sector, though, polyme

24、r electrolyte mem- brane fuel cells are preferred to SOFCs being more reliable and hav- ing faster transients. On-board fuel processing for an APU based on alow temperature polymer electrolyte membranefuelcell (LT-PEMFC) has been investigated by 16. However, these devices are affected by CO poisonin

25、g 15,1719 and require high-purity hydrogen, which can ask for more than one water gas shift units and for a preferential oxidation reactor or separation membranes. Such a complex and space consuming system is rather unsuitable for applications like small or medium-size cars. Instead, high tem- perat

26、ure PEM fuel cells (HT-PEMFCs) are more tolerant to carbon monoxide and may cope with an increased CO level in the syngas 20, avoiding the need of water gas shift units and preferential oxidation reactor. HT-PEMFCs can also be operated without exter- nal gas humidifi cation - further simplifying sys

27、tem complexity and management - and have the advantage of a more effi cient heat dis- sipation and of a better integration in the system thermal manage- ment 21. Moreover, the increased electrode kinetics resulting from the higher operating temperatures allow using alternative catalysts for the elec

28、trodes, thus reducing costs 22. The result is a signifi cant reduction in system complexity, size and cost. An extensive review of HT-PEMFC-based auxiliary power units has been proposed by 22 for diesel-powered road vehicles, showing their great potential. Beside these applications, recent developme

29、nts in autothermal reactors are justifying the comeback to the use of on-board proces- sors in vehicles where the fuel cell is used for traction purposes 23,24. In particular, as mentioned above, early projects failed because they focused on the on-board fuel processing for fuel cells providing 100%

30、 of vehicle traction power. Nevertheless, the coop- eration with an energy storage system, such as a battery, can reduce the fuel cell size and, consequently, the reformer size. Fuel cell size can be further reduced by employing a plug-in solution, which gives the possibility of charging the battery

31、 by means of an external source, extending its operating range. However, the real benefi ts of such a solution can only be emphasized with a proper energy management of all the in-vehicle power sources 25. Several energy management control strategies have been already proposed for fuel cell vehicle,

32、 such as heuristic strategies 2628, equivalent consumption minimization strategy (ECMS) 29,30 and strategies based on optimal control theory 3135. Nonetheless, these analyses are all applied to fuel cell vehicles with hydrogen produced offl ine and stored on board, while the energy management of veh

33、icles with on-board fuel processing is usually based on operation of the fuel cell at constant power, derived from the stand-alone optimization of the ATR/FC system effi ciency. A system effi ciency of 25.1% has been evaluated for a methanol based on-board reformer for PEM fuel cell by 23, while 36

34、obtained a system effi ciency up to 41%, for a fuel cell system with auto- thermal ethanol reformer. Even claiming the possibility of using the system on-vehicle, those results were obtained with a stand- alone system. Also in 24, a stand-alone hydrogen production unit from reforming of ethanol for

35、LT-PEMFC is simulated for on-board purposes. There is no evidence of studies on the energy manage- ment of fuel cell vehicles with an on-board processor and variable fuel cell load. Constraints derived from the hydrogen availability must be considered in the energy management in this case. In this p

36、aper, the design of a controller for the energy manage- ment of a parallel fuel cell/battery vehicle with an on-board fuel processor is proposed. The application is a vehicle equipped by an autothermal reformer producing a syngas from isooctane, con- sidered as gasoline surrogate. Aspen PlusTMhas be

37、en used for the fuel processor modeling, in order to fi nd the operating point which maximizes the conversion effi ciency and properly evaluates the syngas composition. The fuel cell is a HT-PEMFC, whose perfor- mance as a function of the syngas composition have been carefully evaluated by means of

38、a self-made semi-empirical code, realized by the authors and presented in 37,38. As the fuel cell load can vary, the fuel processor can not satisfy the hydrogen demand in real time and, therefore, a syngas buffer is placed between the fuel processor and the fuel cell. The strategy derives from the a

39、pplication of the framework pro- posed in 39 to fuel cell vehicles and considers the dynamic of the syngas buffer and the constraints derived from the hydrogen avail- ability. Moreover, the adaptation law proposed in the previous algorithm has also been improved by using the information on the drivi

40、ng cycle average speed, averaged on past driving condi- tions, for pattern typology recognition. In order to demonstrate the effectiveness of the proposed algo- rithm, a comparative analysis of the algorithm against the optimal one is conducted and main results are reported. The model has been valid

41、ated by comparing the results to the fuel consumption of the original conventional vehicle, namely the Chevrolet Malibu, and to a plug-in hybrid electric powertrain implemented on the same vehicle chassis in a past work 40. 2. Vehicle model The simulator used for the study is a quasi-static forward-

42、 looking simulator, developed in Matlab Simulink and derived from a past study 40. The driver model is based on a PID controller, L. Tribioli et al./Applied Energy 184 (2016) 140154141 that compares the actual velocity of the vehicle (which is a conse- quence of the equilibrium between the torque de

43、livered by the powertrain to the wheels and the resistances to the vehicle motion) with the desired velocity. The controller outputs the accel- erator or the brake pedal position, with the simulator choosing the fi rst or the second if the torque at the wheels is positive or nega- tive. The actual v

44、ehicle speed is computed by solving the longitu- dinalvehicledynamics,whichtakesintoaccountallthe resistances to the vehicle motion, such as rolling resistance at tires, aerodynamic resistance and road slope. The main parameters used for the vehicle dynamics calculations are given in Table 1. An equ

45、ivalent vehicle mass is involved to take into account the rota- tional inertia of all the components of the driveline and is approx- imatively estimated in an increase of 10% of the overall vehicle mass, evaluated from the main components masses and the car shell and frame. The FCV powertrain, sketc

46、hed in Fig. 1, consists of a HT-PEMFC, a DC/DC converter and a Li-Ion 105S 2P battery pack, linked together to an electric motor by means of a DC/AC inverter. Thanks to the specifi c effi ciency map, the motor can be directly linked to the front wheels without any transmission ratio. The FC supplies

47、 power directly to the electric motor or to the battery and, if required, the battery and the FC can provide power to the front motor, together. The front motor is a GVM210-150 permanent magnet electric machine and has been modeled by means of its effi ciency map, depicted in Fig. 2, and other perfo

48、rmance data available from the manufacturer 41. The powertrain specifi cations are listed in Table 2. Unlike 40, where the fuel cell was a LT-PEMFC, now the stack is composed by 325 cells in series, each of an effective area of 120 cm2. A storage buffer is placed between the ATR and FC stack, where

49、the hydrogen produced by the ATR is stored to be used by the fuel cell when it is required. This way, the ATR can work at a fi xed optimized operating point. The ATR has been properly mod- eled in order to evaluate the isooctane-derived syngas composition and the model is described in Section 2.1. A

50、fterwards, a zero- dimensional electrochemical model of a HT-PEMFC, proposed in 37,38 and briefl y described in Section 2.2, makes use of the obtained syngas composition for the determination of the FC stack effi ciency and the voltage-current density curve for a single cell. 2.1. ATR model The aim

51、of this section is to defi ne the operating conditions that maximize the effi ciency of ATR-based fuel processor fed by isooc- tane. Aspen PlusTMhas been used for the fuel processor modeling, in order to fi nd the operating point which maximizes the conver- sion effi ciency. The general reforming re

52、action mechanism can be written as: C8H18aH2O cO2 3:77cN2! Products1 whereaandc are the stoichiometric coeffi cients of water and air respectively. The only products considered in the global reaction (1) are H2;CO;CO2;CH4;Cs and H2O. In order to obtain maximum hydrogen production, the reforming reac

53、tion has to be carried out in two steps: ? High-temperature step (reforming reaction), in which isooctane is converted into a gaseous mixture of H2;CO;CO2;CH4;Cs and unreacted H2O; ? Low temperature step (water gas shift reaction), in which CO is reacted with H2O towards H2and CO2. The main componen

54、ts of the process, represented in Fig. 3, are: ? Autothermal Reactor (ATR): reforming reactor in which the isooctane is converted into a gaseous mixture of H2;CO;CO2, and H2O. The ATR is fed by isooctane, steam and oxygen and it is maintained under adiabatic conditions. ? Water Gas Shift Reactor (WG

55、SR): water gas shift reactor (low temperature water shift reactor WGSR) in which CO reacts with H2O;H2and CO2are the products considered. ? Heat Recovery Line: since the thermal effi ciency of the fuel pro- cessor unit depends strongly on reactants preheating tempera- tures, as reported in 42, a hea

56、t recovery line is defi ned by cooling the syngas stream temperature in two heat exchangers. In particular, the water and isooctane required by the steam reforming reaction are pre-heated in HEX2by cooling the syngas stream, and then heated in the HEX1; the oxygen sent to the autothermal reactor is

57、already heated up to 351 ?C as the mem- brane separation process requires compressed air at 10 bar, and the compression heats the oxygen. ? Separation Unit (SEP1): membrane separation unit where the pure oxygen is produced. Here the air is compressed up by C1 to 10 bar and then through the membrane

58、the oxygen is sepa- rated from nitrogen with a 95% removal effi ciency 43. ? Inter-Refrigerated Compression Line (IRCL): last stage of the syngas production line. This is equipped with three compres- sors and two heat exchangers and it is needed in order to increase the syngas pressure up to the hyd

59、rogen buffer pres- sure, i.e. 250 bar, represented as IC Compression section in Fig. 3. Table 1 Main parameters for vehicle dynamics calculations. Curb weightFrontal area Drag coeffi cient Rolling resistance coeffi cientWheel radius 1500 kg2 m20.350.0130.2 m Fig. 1. Vehicle powertrain schematic. 142L. Tribioli et al./Applied Energy 184 (2016) 140154 Due to the complexity of the reaction system, the thermody- namicequilibriumanalysisisdeterminedbythenon- stoichiometric approach 15. In this approach the equilibrium composition of the system is found by the direct minimization of the Gibbs