© EVS-25 Shenzhen, China, Nov. 5-9, 2010 The 25th World Battery, Hybrid and Fuel Cell Electric Vehicle Symposium & Exhibition
Design and Implementation of Power Management System for Fuel Cell and Battery Powered Buses Zhuoneng Hu1, Qinglian Ren2, Dave Crolla2, Adrian Morris2, Dirk Kok2, and Mingjie Hu1 1
Shanghai Shen-Li High Tech Co.,Ltd, No.27, Guoji Yi Av, Longyang Industrial Garden, Industry Synthesize Zone, Shanghai, China 2 AMAP, University of Sunderland, the Industry Centre, Enterprise Park West, Sunderland, SR5 3XB, UK E-mail:
[email protected]
Abstract—With the pressure from global warming, oil crisis and carbon emissions, great effort has been put in to reducing carbon emissions and improving efficiency for the transport sector. Many new technologies have been developed to find an alterative to the traditional internal combustion engine. Ultra low carbon vehicles, including hybrid vehicles, pure electric vehicles and fuel cell vehicles are considered to be not only the ways to solve the environmental problems, but also a boost to the receding economy. While hybrid and electric vehicles are the more popular developments at the moment, fuel cell vehicles are considered to represent the best long term solution. Keywords— Fuel cell bus, power management, EV simulator
1. Introduction Vehicles with internal combustion engines (ICEs) have existed for more than a decade and the development of ICE vehicles is considered to be one of the greatest achievements of modern technology [1]. The position of ICE vehicles are challenged by the newer technologies such hybrid vehicles, battery electric vehicles and fuel cell electric vehicles. This is because of the increased pressures from environment deterioration and energy crisis, etc, which are partly caused by the ICE vehicles. The transportation sector accounts for around 21 percent of current global fossil fuel CO2 missions to the atmosphere—second only to emissions from power production [2]. According to the Technology Strategy Board (TSB), in the UK it is estimated that transport accounts for 24% of the UK‘s carbon emissions. Road transport accounts for 80% of this figure [3]. The automotive industry has been very responsive to both legislation and growing consumer demands to reduce emissions. Almost all the main car manufacturers are in the process of developing hybrid vehicles or electric vehicles. Parallel developments are underway in academic organizations in response to the need for educating engineers in these new areas of technology. Some American universities, e.g. Wayne State, Texas A&M University, have started the academic discipline of advanced vehicle technologies in both undergraduate and graduate programs. In Asia, a pioneering course, Electric Vehicle Technology, has been introduced at the University of Hong Kong for electrical engineering undergraduate students in about 1998[4]. In Europe, for example, University of Sunderland will start a Masters course in ‗Low Carbon Vehicle Technology‘ in autumn 2010. The program is aimed at meeting the needs of the automotive sector involved in the Low Carbon Vehicle Technology sector. It is the first of its kind in the UK and has been developed through extensive discussions with the local low carbon vehicle industry in the North East [5].
The worldwide interests about low carbon vehicles have led to a proliferation of research in analyzing and predicting vehicle performance. This in turn has led to the development of several software packages specifically aimed at modelling the energy management in hybrid and electric drivelines [6]. The best known of these is probably ADVISOR [7], developed in 1999 by the US NREL. Other well-known codes include the QSS-Toolbox [8] and PSAT (Powertrain system analysis toolkit) sponsored by the US Department of Energy [9], both of which use Matlab/Simulink. Further codes include PSIM, Simplorer and V-ELPH [6]
2. Simulation for electric vehicles 2.1 EV Simulator Several projects on low carbon vehicles have been conducted in AMAP, University of Sunderland. As the result of one of the projects, a software package called ‗EV Simulator‘ was developed to simulate and predict the performance of battery or fuel cell electric vehicles. The main function of the software is to help EV manufacturers and research institutes to simulate the performance of an electric vehicle or a fuel cell vehicle before manufacture. The functions of the EV Simulator include: Simulate acceleration performance, such as acceleration vs. time, speed vs. time, distance vs. time, etc; Simulate electric/fuel cell vehicle range; Calculate gradeability; Simulate the vehicle under different driving cycles; Other simulations – motor power, motor efficiency, current in/out of the battery and so on; Generate a report for the simulation report automatically. The software was used in the project called Ecotrans, in which two battery powered electric buses were converted into fuel cell electric buses. The software package was a
© EVS-25 Shenzhen, China, Nov. 5-9, 2010 The 25th World Battery, Hybrid and Fuel Cell Electric Vehicle Symposium & Exhibition
key element in the design and development process for the novel, prototype bus. The aim behind the new software package to simulate the performance of electric vehicles was to support the work of AMAP and other Low Carbon Vehicle companies on the North East region of England in their programmes to design, develop and test new vehicles. This industrial region is seen as the UK leader in Ultra Low Carbon Vehicle Technology, and this is linked to its selection as the location for Nissan‘s production of the Leaf vehicle and the associated new battery manufacturing plant. 2.2 Vehicle model The purpose of the Ecotrans project is to develop the model and simulation of the fuel cell bus; design the power management and controller of the bus, and convert two buses into fuel cell buses. The challenge for the project is to use a relative small fuel cell system (10kW) together with battery on a 9 seater bus. The reason for choosing a small fuel cell was to reduce the cost of the bus, while maintaining reasonable levels of performance in urban duty cycles. Hence, the overall design target was to a use small fuel cell system and battery to drive a bus with a novel, intelligent power control strategy. The data related to the buses are shown in Table 1.
Table 1: Vehicle parameters data
Parameter, units
Value
Total vehicle mass
5676 kg
Wheel diameter 215/75 R16
0.728 m
Aerodynamic drag coefficient
0.55
Frontal area
4.61 m2
Rolling resistance coefficient
0.017
Motor maximum torque
235 Nm(950 rpm)
Motor maximum power
24.8 kW(1039 rpm)
Final drive ratio
1:4.73
Reduction ratio
1:2.94
The schematic diagram of the vehicle model is shown in Figure 1. This includes the driving cycle model, vehicle model, gear box model, electric motor model, power management system model, etc. The designed maximum speed for the buses before conversion is 20 mph (32km/h). So a special driving cycle, with a maximum speed of 32 km/h and maximum acceleration of 0.4m/s 2, was designed to fit these special requirements.
Figure 1 Simulation model for the bus
2.3 Simulation results 2.3.1 Performance prediction Table 2 Performance results
Performance, units
Value
Maximum speed, km/h
32
0-100m acceleration time,s
15
Hill climbing capacity, %
12.6
Range before refilling, km
18.9
The EV Simulator was used to simulate the performance of the bus, as shown in Table 2. For example, the total traveling range without refilling the hydrogen is 18.9km. The traveling range with different usage of hydrogen can also be easily calculated from the software (see Figure 2).
Figure 2 Range simulation results
2.3.2 Simulation under one cycle Simulations under the special designed driving cycle were conducted for the fuel cell bus model. The vehicle
© EVS-25 Shenzhen, China, Nov. 5-9, 2010 The 25th World Battery, Hybrid and Fuel Cell Electric Vehicle Symposium & Exhibition
speed, required power and energy consumption are shown in Figure 3.
to accelerate. After acceleration, when the required power drops, the fuel cell system will drive the bus and charge the batteries.
3. Power management system The powertrain of the bus includes a PEM fuel cell system, a DC/DC converter, a battery and a DC motor, as shown in Figure 4. This kind of powertrain is called energy hybrid structure, compared to power hybrid structure, where the DC/DC converter is connected to the battery rather than to the fuel cell system [10].
Figure 4 Energy hybrid powertrain structure
Figure 3 Simulation results in one cycle
From Figure 3, it can be seen that the maximum required power is about 20kW. Because the peak power for the fuel cell system is 10kW, so the required peak power for the battery have to be at least 10kW. This must be taken into consideration when selecting the battery pack. The voltage for the original batteries is 72V, which is kept unchanged in the new powertrain system. For the new battery pack, 6 units of batteries were connected parallel together. Each unit of the battery is 12V. The data for the battery pack is shown in Table 3. Table 3 Battery discharge data
Discharge duration (min) 5 10 15 30 60
The role of the power management system is to balance the power requirement from the fuel cell system and the batteries; to protect the fuel cell system; to charge the batteries when the wheel required power is less than the rated fuel cell power. The rated power of the fuel cell system is 10kW. To protect the system, it is recommended that power drawn from the system should be no more than 8.5kW for too long. The batteries and Fuel Cell are connected in parallel. The Fuel Cell will increase its output until it has reached its maximum after which any additional (peak) power will be drawn from the batteries. When the required power is less than the maximum fuel cell power, the fuel cell will charge the battery. In summary, the fuel cell is almost always working at its maximum power, either driving the vehicle together with the battery, or driving the vehicle and charging the battery. This is because the 10kW fuel cell is relative small for a 9 seater bus. The fuel cell is the only power source for the vehicle, if keep the battery SOC at the same level at the end of the bus daily duty. The principle of the control strategy used is to keep the battery SOC to a certain level, 0.6 to 0.9 here, to avoid charging the battery externally too frequently. This control strategy emphasizes the advantage of fuel cell vehicles compared to electric vehicles: the hydrogen can be refueled quickly while the batteries need to be charged for a long time. The fuel cell vehicles are arranged to charge the batteries by themselves rather than having to plug the vehicle into the grid.
Number of batteries
Current (amp)
Power (watts)
1 unit
340
3720
6 units
2040
22320
1 unit
230
2550
6 units
2380
15300
1 unit
175
1800
6 units
1050
10800
1 unit
103
1188
6 units
618
7120
4. Experimental results
1 unit
57
672
6 units
342
4032
A control system, including the hardware and the software, was developed to monitor and record related data. The data that collected and stored are: run time, vehicle power, fuel cell voltage, fuel cell current, water in
Table 3 shows that the selected battery pack can deliver 10 kW for about 15 minutes, which is enough for the bus
© EVS-25 Shenzhen, China, Nov. 5-9, 2010 The 25th World Battery, Hybrid and Fuel Cell Electric Vehicle Symposium & Exhibition
temperature, water out temperature, water pump pressure, DC-DC voltage, DC-DC current, vehicle current etc. The data collection from the bus shows that the performance of the bus is poorer than the simulation results. This is because that the bus and its driveline components are approximately 15 years old – and their efficiencies have deteriorated compared with modern electrical components. This was not seen as a major drawback to the project, because the main aim was to prove the principle of the bus design with a relatively small fuel cell linked to an intelligent power management and control strategy. For example, the range before refilling is only about 15km, rather than 18.9km in the simulation. Figure 5 and 6 show the data collected from the experiments. Figure 5 shows the fuel cell output voltage, current and output power. It can be seen the output voltage is kept at about 90V, the output power and current of the fuel cell increase gradually when the vehicle is accelerating. The extra power needed for the acceleration comes from the battery. When the vehicle is driving at a constant speed, the output power is kept at about 10kW, both used for driving the vehicle and charging the battery. 12
10
100
8
80
6
60
4
40
FC voltage FC current FC power
20
0
0
200
400
600 800 Step (0.1s)
1000
FC power (kW)
FC voltage (V), FC current (I)
120
2
1200
0
Figure 5 Fuel cell voltage, current, and power 70 60
Temperature (C)
50 40 30 20 Water in temperature Water out temperature
10 0
0
200
400
600 800 Step (0.1s)
1000
1200
Figure 6 Water temperature of in and out of the fuel cell stack
Figure 6 shows the temperature control for the cooling water in and out the fuel cell stack. The best working temperature for the fuel cell stack is around 60 oC. The PID control algorithm in the controller is designed to
ensure that the temperature is kept within a reasonable range.
5. Conclusions A software package – EV Simulator was developed to simulate the performance of battery or fuel cell electric vehicles. The functions of the package include calculating the top speed, acceleration, gradeability, range per charge etc. and also the simulation of different driving cycles can be performed with the software. A small 9 seater bus was converted into a fuel cell bus successfully and a power management system was designed to balance the power between the fuel cell system and the batteries. An energy hybrid power train structure was used in the power management system. The performance of the prototype fuel cell buses was somewhat lower than the results from the simulation, due mainly to the degradation of the efficiencies of some of the electrical driveline components on the buses. Nevertheless, the Ecotrans project has been successful in two key areas: i. The development of a new software package which is a future valuable asset to the design and development of Ultra Low Carbon Vehicles. ii. The development of a prototype small bus to prove the principle of using a modest sized fuel cell together with an intelligent power control strategy for practical, urban applications.
6. References [1] Ehsani, M., Y. Gao, et al. (2004). Modern electric, hybrid electric and fuel cell vehicles. Florida, CRC Press. [2] IPIECA (2004). Transportation and climate change: opportunities, challenges and long-term strategies. AN IPECA workshop, Baltimore, USA. [3] IME (2009). Brochure for Integrating Technologies for Low Carbon. Integrating Technologies for Low Carbon, Norfolk, Institution of Mechanical Engineers. [4] K.T. Chau, Y.S. Wong and C.C. Chan, ―EVSIM –– a PCbased simulation tool for electric vehicle technology course,‖ International Journal of Electrical Engineering Education (IJEEE), Vol. 37, No. 2, April 2000, pp. 167-179. [5] MSc Low Carbon Vehicle Technology, http://centres.sunderland.ac.uk/amap/lcv/msc-lcvt/ [6] Gao, D. W., C. Mi, et al. (2007). "Modeling and Simulation of Electric and Hybrid Vehicles." Proc IEEE 95(4). [7] Wipke, K. B., M. R. Cuddy, et al. (1999). "ADVISOR 2.1 A user-friendly advanced powertrain simulation using a forward/backward approach." IEEE Trans Vehicular Tech 48(6): 1751-7-1761. [8] Rizzoni, G., L. Guzzella, et al. (1999). "Unified Modelling of Hybrid-Electric Vehicle Drivetrains." IEEE/ ASME Trans. Mechatronics 4(3): 246-257. [9] Argonne (2007). Power Systems Analysis Toolkit (PSAT), Argonne National Laboratory. 2007. [10] M. Ouyang, L. Xu, J. Li, L. Lu, D. Gao, Q. Xie, Performance comparison of two fuel cell hybrid buses with different powertrain and energy management strategies. J. Power Sources 163 (2006) 467–479.
© EVS-25 Shenzhen, China, Nov. 5-9, 2010 The 25th World Battery, Hybrid and Fuel Cell Electric Vehicle Symposium & Exhibition
7. Authors Mr. Zhuoneng Hu Shanghai Shen-Li High Tech Co.,Ltd, No.27, Guoji Yi Av, Longyang Industrial Garden, Industry Synthesize Zone, Shanghai, China Tel: +86-21-67104458 Fax: +86-21-67100832 Email:
[email protected] Mr. Zhuoneng Hu is a technical manager in Shanghai Shen-Li High Tech Co.,Ltd, in charge of fuel cell systems and VRB (Vanadium Redox Battery) products. His main duties also include software development and system design. Dr. Qinglian Ren AMAP, University of Sunderland, The Industry Centre, Enterprise Park West Sunderland, SR5 3XB, UK Tel: +441915153374 Fax: +441915153377 Email:
[email protected] Dr. Qinglian Ren works as a researcher in AMAP (the Institute for Automotive and Manufacturing Advanced Practice) at the University of Sunderland. Her research interests include transmissions, low carbon vehicles and electric vehicle simulation models. Prof. Dave Crolla AMAP, University of Sunderland, The Industry Centre, Enterprise Park West Sunderland, SR5 3XB, UK Tel: +441915153388 Fax: +441915153377 Email:
[email protected] Prof. Crolla was appointed to the academic staff in the School of Mechanical Engineering at the University of Leeds from 1979 to 2004, and was Head of School from 1996 to 2001. I have been a Visiting Professor at the University of Sunderland since 2004 and I contribute to a wide range of activities within the Automotive Technology Academic Area. Mr. Adrian Morris AMAP, University of Sunderland, The Industry Centre, Enterprise Park West, Sunderland, SR5 3XB, UK Tel: +441915153374 Fax: +441915153377 Email:
[email protected] Mr. Adrian Morris is the operation manager for AMAP and also involved with teaching and researching. His teaching interests are project management, Low Carbon Vehicle Technology, Automotive Engineering, Supply Chain, Quality Assurance. His research interests are Low Carbon Vehicles, Power management and Control Systems, Batteries, Fuel Cells, Project management Mr. Dirk Kok AMAP, University of Sunderland, The Industry Centre, Enterprise Park West, Sunderland, SR5 3XB, UK Tel: +441915153374 Fax: +441915153377 Email:
[email protected] Mr. Dirk Kok is a researcher at the University of Sunderland, where he is part of the Low Carbon Vehicle research and development group, which aims to train and provide teaching to the region and in the
University to promote and introduce Low Carbon Vehicle technologies. Mr. Mingjie Hu Shanghai Shen-Li High Tech Co.,Ltd, No.27, Guoji Yi Av, Longyang Industrial Garden, Industry Synthesize Zone, Shanghai, China Tel: +86-21-67104458 Fax: +86-21-67100832 Email:
[email protected] Mr. Mingjie Hu is a technical manager in Shanghai Shen-Li High Tech Co.,Ltd, in charge of fuel cell assembly and test. Also he is experienced in fuel cell vehicle integration and vehicle test.
