Fuel cell design scheme for transmission system of

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Hybrid electric vehicle transmission system fuel cell design scheme

fuel cell vehicle is a kind of electric vehicle. The electricity generated by the fuel cell supplies power to the motor through the inverter, controller and other devices, and then drives the wheels to rotate through the transmission system, drive axle and so on, which can make the vehicle drive on the road. The energy conversion efficiency of the fuel cell is times higher than that of the internal combustion engine. The chemical reaction process of fuel cells will not produce harmful products, so fuel cell vehicles are pollution-free vehicles. With the requirements of vehicle fuel economy and environmental protection, the automotive power system will gradually transition from gasoline and other fossil fuels to hybrid power, and will eventually be completely replaced by clean fuel cell vehicles

in recent years, fuel cell system and fuel cell vehicle technology have made significant progress. World famous automobile manufacturers, such as Toyota, Honda, general motors, DaimlerChrysler, Nissan and Ford, have developed several generations of fuel cell vehicles and announced various strategic goals to invest fuel cell vehicles in the market

at present, the prototype of fuel cell car is being tested, and the fuel cell powered transport bus is being demonstrated in several cities in North America. Among them, Honda's fcx clarity has a maximum speed of 160 km/h [8]; Toyota fuel cell vehicle FCHV adv has run 360000 km of road test, can start at minus 37 degrees, and can drive from Osaka to Tokyo (560 km) with one hydrogenation [7]. With the support of the Ministry of science and technology, fuel cell vehicle technology has developed rapidly. In 2007, China successfully developed the fourth generation fuel cell car, with a maximum speed of 150 km/h and a maximum driving range of 319 km. In 2008, the 20 fuel cell demonstration vehicles were demonstrated in Beijing Olympic Games. In 2010, a total of 196 fuel cell vehicles, including SAIC, Chery and other domestic automobile enterprises, were demonstrated in the Shanghai WorldExpo park

there are still technical challenges in the development of fuel cell vehicles, such as the integration of fuel cell packs, improving the commercialization of electric vehicles, fuel processors and auxiliary automobile manufacturers are working towards the direction of integrating components and reducing component costs, and have made significant progress. However, compared with traditional diesel cars, fuel cell electric vehicles use "fuel cell + motor" to replace the "heart" of traditional cars - engine and fuel system. Great changes have taken place in the power transmission system of fuel cell cars, mainly in the following aspects: the electric motor has replaced the internal combustion engine as the driving power source; Clutch and torsional shock absorber are omitted; Multi speed transmission is usually replaced by reducer. Therefore, the overall powertrain of fuel cell vehicles is simplified. However, when driving, fuel cells are the main source of power, and batteries are the auxiliary source of energy. The power required by cars is mainly provided by fuel cells. It can be said that the selection of vehicle fuel cells is very important for the performance of fuel cell vehicles

this paper introduces the development of traditional technology of fuel cell vehicle power, and discusses in detail the key technologies such as power transmission topology, multi-source system management, power system configuration and simulation optimization technology of fuel cell electric vehicle

The operation of fuel cell vehicle is not a steady state. Frequent starting, acceleration and climbing make the dynamic working condition of the vehicle very complex. The dynamic response of fuel cell system is relatively slow, and the output characteristics of fuel cell can not meet the driving requirements of vehicles when starting, accelerating rapidly or climbing steep slopes. In the actual fuel cell vehicle, it is often necessary to use the design method of fuel cell hybrid electric vehicle, that is, the auxiliary energy device (battery, supercapacitor or battery + supercapacitor) is introduced to combine with the fuel cell through the power electronic device to provide peak power to supplement the insufficient output power capacity of the fuel cell when the vehicle accelerates or climbs. On the other hand, under idle, low-speed or deceleration conditions, when the power of the fuel cell is greater than the driving power, it stores surplus energy, or absorbs and stores braking energy during feedback braking, so as to improve the energy efficiency of the whole powertrain

1. Direct fuel cell hybrid system structure

the power electronic device used in the direct fuel cell hybrid system structure is only the motor controller, and the fuel cell and auxiliary power device are directly connected in parallel at the inlet of the motor controller. For example, Toyota's fchv-4[16], Fiat elettra[17] and Nissan x-trailfcv[12] all adopt this similar structural design

the auxiliary power unit expands the total energy capacity of the power system and increases the driving range of the vehicle after one-time hydrogenation; The power range of the system is expanded and the power load borne by the fuel cell is reduced. Many plug-in hybrid fuel cell vehicles also often adopt such a framework, such as the edge plug in fuel cell car of Ford company and the volt plug in fuel cell car of GM company [18]. This plug-in hybrid vehicle will effectively reduce the consumption of hydrogen fuel. In addition, the existence of auxiliary power unit makes the system have the ability to recover braking energy, and increases the reliability of system operation. The reasonable distribution of load power between fuel cell and auxiliary power unit can also improve the overall operating efficiency of fuel cell [4]

in the system design, a bidirectional dc/dc converter can be added between the auxiliary power unit and the DC bus of the power system. It makes the control of charging and discharging of auxiliary power device more flexible and easy to realize. Because the bidirectional dc/dc converter can better control the voltage or current of the auxiliary power unit, it is also the third part of the system control strategy

2. Parallel powertrain structure

another framework is the structure of parallel fuel cell hybrid powertrain. In this construction, a dc/dc converter is usually installed between the fuel cell and the motor controller. The terminal voltage of the fuel cell is matched with the voltage level of the DC bus of the system through the step-up or step-down of the dc/dc converter. The difference between this system and the above architecture is that the design of this power system does not consider the feedback recovery of energy, so although the system is simple, its efficiency is relatively low

although there is no coupling relationship between the voltage of the system DC bus and the power output capacity of the fuel cell, the dc/dc converter must maintain the voltage of the system DC bus at the voltage point (or range) that is most suitable for the operation of the motor system. For the AC motor drive system, it is usually necessary to install a dc/ac converter. At present, this kind of framework system is only used on some small or experimental vehicles. For example, the autonomy and hy wire vehicles developed by General Motors in 2002 are based on this framework [10]. In 2008, Tongji University ThyssenKrupp joint laboratory adopted this architecture to develop small fuel cell vehicles [19], and studied the impact of fuel cell stack system on vehicle performance

fuel cell vehicle multi energy system management and optimization

fuel cell is not suitable to be used as a single driving energy of the power system. It is necessary to select an auxiliary energy system to reasonably supplement the energy required to drive electric vehicles, cover power fluctuations, increase peak power, absorb feedback energy, and improve the transient characteristics of fuel cell output power. At present, major auto developers have adopted auxiliary power to improve the performance of fuel cell vehicles (as shown in Table 1)

1. Power battery auxiliary energy system

at present, lead-acid batteries [20] have been eliminated due to their low specific energy and specific power. The commonly used power batteries in automobiles mainly include nickel metal hydride batteries and lithium-ion batteries

Ni MH battery is an alkaline battery, which has the advantages of not easy aging, no pre charging and good low-temperature discharge characteristics. Its energy density can exceed 80 wh/kg, the driving distance of one-time charging is long, and it can discharge smoothly when working with high current. The power systems of fchv-4[6], high lander FCHV adv[7] and general Chevrolet equinox[9] are integrated with fuel cells and nickel metal hydride batteries. However, in the high temperature environment, the charge of Ni MH battery will drop sharply, and it has the problems of memory effect and charging heating. In the fuel cell hybrid system, the SOC of Ni MH battery should be kept between 40%-60%, the charging and discharging current should be in the range of a, and the temperature should be maintained near room temperature to ensure the safety and economy of the system

lithium ion batteries have the advantages of small size, high energy density (120wh/kg), high safety and pollution-free. Honda fcxclarity[8], general Chevrolet sequel[10] lithium and Nissan X-Trail fcv[12] all use lithium-ion batteries as 2 Oscilloscope is the auxiliary energy system of fuel cell vehicle. The energy density of ion battery is 1. 5% of that of Ni MH battery Times. The average voltage of the single battery is 3.2V, which is equivalent to the voltage value of three nickel zinc or nickel hydrogen batteries connected in series, so it can reduce the number of battery combinations, reduce the probability of battery failure caused by the voltage difference of the single battery, and improve the service life of the battery pack

lithium ion battery has the advantage of low self discharge (only 5%-10%). When stored in non use state, it is quite stable internally, and almost no chemical reaction occurs [4,5]. Since lithium-ion batteries do not contain heavy metals such as cadmium, mercury and lead, they will not pollute the environment during use. For electric vehicles, lithium-ion batteries are easy to be installed on vehicles and are ideal energy storage media. Simulink, Dymola and other tools are often used to simulate and analyze the battery system [23] to improve the service efficiency and life of the battery

2. Supercapacitor system

supercapacitor is a new type of energy storage element, which has both high discharge power like electrostatic capacitor and great charge storage capacity like battery [23,25]. Because its discharge characteristics are closer to electrostatic capacitance, it is still called "capacitance"

if only the super capacitor is used as the only auxiliary energy, there are still many deficiencies, such as: the electric vehicle starts again after a long-term shutdown. Due to the self discharge effect of the super capacitor, the power supply of the on-board auxiliary system will not be guaranteed when the energy output of the fuel cell is not stable [5]. Moreover, the energy density of the super capacitor is very low, and if it wants to achieve a certain energy reserve capacity, its equipment volume is bound to increase. At present, supercapacitors are used in fuel cell vehicles when purchasing auxiliary power supply systems with other power batteries [4,25,26]. In order to accurately describe the characteristics of supercapacitors, impedance method can be used to model instead of simple RC loop model [23]. The current SOC of super capacitor is mainly based on the output voltage of super capacitor:

3 Combination and control of multi-source energy

fuel cell electric vehicles can achieve better results by installing the above two topological configurations and combining them with power cells and supercapacitors. At present, there are three main energy combination methods: 1) fuel cell + power cell, which is adopted by general Chevrolet equinox [9,10,12]; 2) Fuel cell + supercapacitor, such as Honda fcv-3 and Mazda fc-ev [4]; 3) Fuel cell + power cell + supercapacitor, such as Honda FCHV-4 [8]. Tadaichi[6] studied the flow mode of energy under different conditions. By comparing the three kinds of energy for vehicles, the Swiss based manufacturer is looking for a portfolio with higher profit margins,

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