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　　Research on system integration design of fuel cell range extender for electric vehicles

　　1 Introduction to electric vehicles and range extenders

　　Electric vehicles refer to vehicles that use all or part of electric energy to drive an electric motor as the power system. It includes three types: fuel cell electric vehicles (FCEV), hybrid electric vehicles (HEV) and pure electric vehicles (BEV). Due to the current limited energy storage of batteries, pure electric vehicles have the problem of short driving range after a single charge. Consider installing a range extender on a pure electric vehicle to cooperate with the on-board power battery to work under different working conditions and increase the driving range of the pure electric vehicle.

　　The range extender is an additional energy storage component installed on pure electric vehicles in order to increase the driving range of pure electric vehicles. Usually users can choose to install or not install it according to their mileage requirements when traveling (reducing vehicle weight can reduce energy consumption). Range extenders usually come in the form of small generators, batteries, fuel cells, etc. Due to the working characteristics of the range extender, its performance usually has the following requirements: the system is required to be reliable and can immediately enter the working state after a long standby; due to the single working condition, the working point is required to be better optimized to reduce system costs. Improve efficiency.

　　Compared with pure electric vehicles, electric vehicles with range extenders have great advantages in terms of driving range. Compared with traditional gasoline-electric hybrid vehicles, electric vehicles with range extenders have outstanding advantages in terms of emissions. Compared with new models, Electric-electric hybrid vehicles and electric vehicles with range extenders are mainly driven by batteries and are more inclined to pure electric drive. Therefore, they can also be regarded as a transition method from hybrid drive to pure electric drive.

　　2Select the range extender

　　Commonly chosen range extender types are small generators or fuel cells. Based on the original intention of avoiding the use of fuel as much as possible and striving to achieve zero emissions, it is recommended to use batteries or fuel cells as the range extender. The output voltage and storage capacity of the range extender can be determined based on the charging voltage of the power battery and the vehicle mileage requirements. By selecting ready-made products currently on the market based on the output voltage and storage capacity of the range extender, the development cycle can be shortened and development costs can be saved. This article introduces the solution of using fuel cells as a range extender, and mainly introduces the integrated design solution of the fuel cell range extender.

　　Example analysis assumes that a stadium vehicle is developed. The vehicle parameters are shown in Table 1.

　　2.1 Select power performance indicators

　　The following power performance indicators can be selected according to its purpose of use and common working conditions. Maximum speed: Vmax=35km/h; Climbing ability: Climb a 15% slope at Vb=12km/h; Acceleration ability: less than 6 seconds from 0 to 30km/h; Cruise speed: Vn=25km/h.

　　2.2 Calculation

　　After calculation, and taking into account the initial design goals, future mass production selection and cost requirements, one of the power supplies was selected as a lithium iron phosphate battery power supply. Its discharge voltage is between 2.5 and 3.5V, so 20 discharge cells can be selected. Lithium iron phosphate batteries with a voltage of 3V are connected in series. Considering the safety factor, the battery parameters can be selected as follows: the battery voltage is 60V, the capacity is 80Ah; the SOC is expected to be 0.2~0.9; and the product is a component that has been mass-produced and mature.

　　2.3 Select range extender

　　The range extender is required to provide energy for the vehicle to travel 45km. Considering the battery charging efficiency, the storage capacity of the range extender should be slightly larger than that of the battery. The charging voltage of the lithium iron phosphate battery is between 3.5 and 4V, so the range extender output is selected. The voltage is 80V. In order to achieve the original intention of zero emissions and prepare for future mass production, a small fuel cell is chosen as the range extender, and this small fuel cell is a relatively mature product currently on the market.

　　3. Arrangement of range extender

　　3.1 Technical background of fuel cell range extender system integration design

　　Starting from the installation structure of the range extender assembly, by changing the range extender system assembly structure to a quickly replaceable structure, the problem of insufficient driving ability in electric vehicles can be solved by adding a range extender assembly system.

　　3.2 Mechanisms and key components of the fuel cell range extender assembly

　　Working principle: The entire range extender assembly achieves rapid positioning through the tapered positioning element at the front end, the locking positioning pin at the rear end, the buckle and the auxiliary baffle on the side. When the range extender starts to be installed, the pulley on the bottom plate contacts the guide rail. After pushing to the end, the pulley slides into the chute. At this time, it is supported by the guide rail. Then pin the positioning locking pin and buckle the locking buckle to complete the extension. Mechanical installation of the programmer. When the range extender is being demonstrated, you can pull the range extender out and support it with the supporting legs. After the demonstration, you can close the supporting legs and put it into the support frame.

　　3.3 Arrangement of each sub-module of the range extender

　　There are many ways to arrange the range extender sub-modules, some of which are commonly used including proximity method, minimum space method, and modularization method. Each of these layout methods has advantages and disadvantages. The nearby layout can reduce the length of the wiring harness and the length of the hydrogen pipeline. But it may not be easy to centrally manage, and it feels like the range extender does not have a sense of integrity and system. The minimum space layout method can compress the envelope space to the maximum extent, making the entire space more compact. However, if the components are too close together, they may produce some negative effects such as thermal radiation and electromagnetic interference, which will lead to a decrease in the reliability of the entire system and make the system extremely unstable. When a problem occurs in a certain sub-module, it is not easy to find the relevant fault. The modular layout method can divide each sub-module into several modules according to relevant functions, so that the corresponding modules can be better managed and some heat radiation and electromagnetic interference can also be reduced. When a problem occurs in one of the modules, it can be quickly discovered and solved.

　　At the same time, it also facilitates the overall installation. The relevant modules are used as an assembly, which can quickly replace the assembly and shorten the installation time of the range extender on the vehicle.

　　After comprehensive comparison and consideration, the electric mini-car in this example gave priority to the third layout plan, subject to space permitting. In this example, after subdivision, the fuel cell range extender can be divided into three modules, including the hydrogen system sub-module, the fuel cell system and its management system sub-module, and the power supply system and its management system sub-module.

　　Among them, the hydrogen system sub-module, the fuel cell system and its control system sub-module are finally integrated into the bracket of the power conversion system and voltage stabilizing system sub-modules through quick buckles and auxiliary positioning mechanisms, thus forming the entire fuel cell range extender assembly.

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