Design and test of the hottest fuel cell light ele

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Design and test of fuel cell light electric bus Abstract: This paper introduces the layout of fuel cell light electric bus, the charging and discharging characteristics and control strategy of fuel cell engine and power battery. The comparison between the calculated value and the test value shows that the hybrid drive scheme adopted by the vehicle is reasonable. The realization of this design scheme can provide a reference for the further study of fuel cell vehicles

key words: fuel cell electric vehicle hybrid

with the continuous increase of the number of vehicles, the worldwide energy crisis and environmental pollution have attracted widespread attention of all countries. Because fuel cells use hydrogen and oxygen to produce electricity and water without pollution, electric vehicles using fuel cells are recognized as an important development direction in the 21st century, so many countries in the world are actively studying fuel cell electric vehicles [1]~[4]

fuel cell is an energy generating device, which always generates energy before the fuel is exhausted, and the reactant feeding time of fuel cell is much shorter than the charging time of electrochemical cell when it is fully fitted with the surface of the sample. Therefore, compared with pure electric vehicles, electric vehicles using fuel cell can increase the driving range and greatly shorten the charging time of batteries. This paper introduces the layout, main components, vehicle performance calculation and performance test of the developed fuel cell electric light bus

1 layout of fuel cell light electric bus

the fuel cell light electric bus adopts the hybrid drive scheme of fuel cell and auxiliary power battery. As shown in Figure 1, its power system mainly includes fuel cell, main and auxiliary dc/dc converters, controllers, induction motors, transmission lines, auxiliary power battery packs, etc. The central control system is independently developed by Tsinghua University. The output of the main dc/dc converter is adjusted according to the SOC (state of charge) of the power battery and the operating conditions of the vehicle. In the development process, mature technologies should be selected as much as possible to focus on solving the main problems such as the coordination between the systems of fuel cell light passenger cars

Figure 1 Schematic diagram of fuel cell light electric bus

the chassis of fuel cell light electric bus is xmq6600en chassis of Xiamen (Suzhou) Jinlong Company. See Table 1 for the technical parameters of the whole vehicle. Table 1 fuel cell light electric bus vehicle parameters

2 fuel cell engine

since the international electric vehicle Conference (evs18) held in Germany in October 2001, the international electric vehicle industry has basically unified the concept of fuel cell engine. Fuel cell is an electrochemical device that directly converts the chemical energy of fuel into electrical energy. It is composed of anode, cathode, electrolyte and electrode isolation plate. Fuel (hydrogen rich gas) is input into cathode and oxidant is input into anode. Electrochemical oxidation-reduction reaction occurs on the electrode to generate electricity. The reaction product is water. The potential of a single fuel cell is less than 1V. Only when multiple fuel cells are connected in series can sufficient voltage be generated. These connected cells are called stacks. The number of fuel cells in the stack determines its output power

fuel cell system includes battery stack, air intake system, water and heat management system, and its output is electric energy. Fuel cell engine includes fuel cell system, dc/dc converter, motor and its controller, and outputs mechanical energy

2.1 fuel cell system

fuel cell is a hydrogen oxygen proton exchange membrane fuel cell (PEMFC) manufactured by green energy company. The rated power of the fuel cell is 15kw, the rated output voltage is 60V, and the maximum output current is 300A. The schematic diagram of the fuel cell system is shown in Figure 2

Figure 2 Schematic diagram of fuel cell system

2.2 drive motor, controller and main dc/dc converter

drive motor and controller are AC60 induction motor of solectria company, and the mechanical characteristics at 312v are shown in Figure 3. The motor decelerates directly through the toothed belt, driving the transmission shaft, main reducer and wheel in turn, eliminating the transmission, and the operation is simple

Figure 3 mechanical characteristics of AC60 motor

the main dc/dc converter is designed by Beijing Electromechanical Research Institute and has two functions: one is to increase the low voltage output by the fuel cell to the terminal voltage of the auxiliary power battery pack, because the terminal voltage of the auxiliary battery pack changes with the SOC value of the power battery and the vehicle working condition, so it needs to be adjusted; The second is to protect the reliable operation of the fuel cell system and enable the fuel cell to respond to the vehicle control strategy in time. Practice shows that in order to protect the fuel cell system, both the maximum output current and the minimum voltage of the fuel cell system should be limited. The specific limit can be provided by the fuel cell manufacturer or determined according to the test

3 charging and discharging characteristics of auxiliary power battery

if the fuel cell is used as the power source alone, the power of the fuel cell is required to meet all driving conditions of the vehicle, resulting in a large power of the fuel cell, which will increase the difficulty of production on the one hand, and on the other hand, the vehicle runs in non limit conditions most of the time, although the efficiency of the fuel cell stack is high at this time, However, the increase in weight will lead to the increase in the weight of the whole vehicle and consume more power. Moreover, compared with the low-power fuel cell system, the hydrogen consumption of the high-power fuel cell system will increase. In addition, energy recovery cannot be achieved when using the fuel cell alone. Considering the hybrid drive scheme of fuel cell and auxiliary power cell, this drive scheme is also widely used at present [5]~[6], Auxiliary power battery is used to provide recovery of peak power and braking energy

at present, the power batteries used in electric vehicles include lead-acid batteries and nickel cadmium batteries, but Ningbo has made a lot of achievements in nickel hydrogen batteries and lithium-ion batteries [7]. Here, we should first consider the specific power of the power battery, as well as the cost and working reliability of the battery. Finally, the auxiliary power battery adopts the 6 mobile beam of Hong Kong Kingsoft company to stop moving automatically; 0ahnihm battery and auxiliary power battery pack are operated by 26 battery modules in series, with a total voltage of 312v. The charging and discharging characteristic curve of a single power battery module is shown in Figure 4

(a) battery discharge curve (b) battery charging curve

Figure 4 60ahni MH battery charging and discharging characteristics

4 control strategy

the service life of the battery is directly related to the reliability and cost of the fuel cell light bus. Overcharge and over discharge of the power battery will shorten the service life of the power battery, so the core of the control should ensure that the SOC of the power battery is within the specified working range, Here, select the auxiliary power battery to work between SOC = 0.2~0.8, and try to keep it unchanged to reduce the times of charge and discharge. In addition, the power performance of electric vehicles should also be met in order to meet the requirements of driving conditions. To sum up, the desired control strategy is to ensure the requirements of vehicle dynamics and improve the efficiency of fuel cells, that is, to improve the energy conversion rate of hydrogen as much as possible, on the premise that the SOC value of auxiliary power cells is basically unchanged. Specifically, fuel cells and auxiliary power cells are required to work together when the vehicle starts, accelerates and climbs; When the vehicle runs at a constant speed, it can be completely powered by the fuel cell. When the SOC of the auxiliary power battery is high, it will not be charged, and when it is low, it will be charged; When the SOC of auxiliary power battery exceeds the set value, it will work alone, and the fuel cell may not work; When the SOC of the power battery is low, the fuel cell charges the auxiliary power battery pack; During braking, the electric energy recovered by the drive motor charges the auxiliary power battery pack

5 calculation analysis and performance test

the performance parameters are calculated according to the vehicle parameters. Figure 5 and Figure 6 are the driving force driving resistance balance diagram and acceleration time curve respectively. After the trial production of the sample vehicle is completed, the performance test of the vehicle is carried out. The calculation results and test results are shown in Table 2. Because the actual maximum output power of the fuel cell cannot reach the expected value, there is a large gap between the test value of the maximum vehicle speed and the calculated value

Figure 5 driving force driving data Balance Figure 6 acceleration time curve

Table 2 Comparison between calculated values and test values


fuel cell light electric bus adopts the structure of hybrid drive of fuel cell and auxiliary power battery, which can reduce the requirements for fuel cell performance, improve the operation efficiency of fuel cell and realize braking energy recovery. The calculation and performance test show that the design principle of the vehicle is feasible, but the performance of fuel cell is an important factor restricting the performance of the vehicle at present, which needs to be further improved. Through the implementation of the hybrid drive scheme, some experience has been accumulated, which can provide a certain reference for the research and development of fuel cell vehicles



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