Abstract This paper briefly describes the necessity of bench testing for proton exchange membrane fuel cell electric vehicle engines. It comprehensively discusses the main contents of bench testing for fuel cell electric vehicle power drive systems. Finally, it briefly introduces the main structure and functions of the fuel cell power drive system test bench. Keywords Electric vehicle, proton exchange membrane fuel cell, engine test I. Introduction For over a century, the development of the automotive industry has made tremendous contributions to humanity, and the impact of automobiles on social progress is profound. However, with the large increase in the number of automobiles, the harm caused by automobile exhaust to the human living environment has gradually become known and valued. To achieve the sustainable development of the automotive industry, people have been exploring and developing electric vehicles with advantages such as zero pollution, low noise, easy maintenance, and ease of operation. Since the 1980s, relevant institutions and automobile manufacturers in many industrialized countries have invested heavily in developing various types of electric vehicles. These include rechargeable battery electric vehicles, hybrid electric vehicles, and fuel cell electric vehicles, etc. In recent years, proton exchange membrane fuel cell technology has made breakthrough progress, especially its high specific power and the characteristic of not requiring charging, making it highly competitive as a power source for electric vehicles and showing good application prospects. Proton exchange membrane fuel cells (PEMFCs) operate using hydrogen as fuel and air (O2) as oxidant. They differ significantly from secondary batteries in fuel supply and operating condition control. Therefore, the testing methods for PEMFC power drive systems must be given special consideration in the development of electric vehicles powered by fuel cells. Based on automotive engine testing standards and specifications, and drawing on experience in developing PEMFC mobile power supplies, this paper provides a preliminary discussion of bench testing issues for PEMFC electric vehicle engine assemblies. II. The Necessity of Bench Testing for Fuel Cell Power Drive Systems 1. The Meaning of Fuel Cell Electric Vehicle Power Drive System Based on the concept of an automotive engine, an engine assembly is a comprehensive power system capable of independently generating mechanical power and torque to drive the wheels of a vehicle. Similarly, a fuel cell electric vehicle engine assembly should include two main parts: the fuel cell stack and its auxiliary systems that convert fuel into electrical energy, referred to as the "power source," and the power converter and electric motor that convert electrical energy into torque, referred to as the "power drive system." The power drive system of a fuel cell electric vehicle mainly includes: a fuel processing and supply unit, a fuel cell stack and its operation support system and auxiliary equipment, a power controller, a variable frequency drive, an electric motor and a reducer, etc. (see Figure 1). Figure 1. Block diagram of the power drive system of a fuel cell electric vehicle. 2. Necessity and special characteristics of bench testing of fuel cell power drive system. According to the automotive engine testing specifications, a newly developed or redesigned vehicle should undergo two comprehensive tests before road testing: first, the "engine (assembly) bench test" before engine installation; second, the "vehicle bench test" after engine installation. Regardless of the power source of the vehicle, the "vehicle bench test" can be conducted on a universal "chassis dynamometer" (also known as a drum dynamometer). The purpose of bench testing of the automotive engine (assembly) is to comprehensively test the engine characteristics and various performance aspects to evaluate and predict whether the vehicle's overall power performance and various indicators can meet the design requirements after engine installation. This is an indispensable and extremely important part of the automotive development process. Therefore, bench testing of the power drive system is also necessary for the development of electric vehicles. For "engine (assembly) bench testing," different engine test benches must be used depending on the engine fuel type, operating mode, and the nature of the measured parameters. Currently, in addition to general automotive engine test benches, there are also dedicated test benches for the power drive systems of rechargeable battery electric vehicles. Given the special characteristics of fuel cell electric vehicles in terms of hydrogen fuel supply, fuel cell operation support systems, and their measured parameters, proton exchange membrane fuel cell electric vehicles must use dedicated test benches. III. Main Test Contents of Proton Exchange Membrane Fuel Cell Power Drive Systems 1. Composition of the Proton Exchange Membrane Fuel Cell System: The composition of a proton exchange membrane fuel cell (PEMFC) system is shown in Figure 2. Figure 2. Block Diagram of Proton Exchange Membrane Fuel Cell System 2. Main Test Contents of the PEMFC Power Drive System An automotive internal combustion engine performs work through the combustion of fuel and converts mechanical force into torque through a mechanical transmission system. A proton exchange membrane fuel cell is an electrochemical power generation device; the electrical energy it generates is converted into torque by a power converter driving an electric motor. It is easy to see that the working principles of an internal combustion engine and a PEMFC power drive system are very different. However, as automobile engines, they still have commonalities and similarities: ① Both have fuel storage and supply units; ② Both need to deliver air with a certain pressure; ③ Both engines need to maintain an appropriate operating temperature; ④ The energy generated by the engine must be converted into torque. Based on the working principle and system operation characteristics of PEMFC, and referring to the test standards and specifications for automobile engines, the following two aspects should be considered for bench testing of PEMFC electric vehicle power drive system: First, test items that are the same as or similar to those of internal combustion engines; Second, test items that are unique to PEMFC power drive system. (1) Test items that are the same as or similar to those of internal combustion engines: power test: including total power, net power, rated power and effective power test, as well as no-load characteristic test and load characteristic test. In addition, the power curve of the power drive system (engine) should also be measured. The power curve is the most important curve representing the performance of the power drive system. It describes the maximum power that the fuel cell power source may generate at different speeds. Adjustment test: In order to study and improve the performance of the power drive system, various comparative or adjustment tests are often carried out on the bench. Change a certain operating parameter of the system, observe its impact on engine performance, and select the optimal value based on the test results. Noise Test: Noise level is an important indicator of automotive engines, and low noise is a major advantage of electric vehicles. Proton exchange membrane fuel cells (PEMFCs) themselves are noiseless. The noise of PEMFC electric vehicles mainly comes from the electric motor, power drive, and auxiliary systems of the fuel cell. The purpose of the noise test is to identify the noise sources and reduce the overall noise level of the power drive system. Road Load Test: The road load test is a simulated test of the power drive system (engine) on a test bench, simulating the load applied to the engine when the vehicle is fully loaded and traveling at a constant speed on a flat road after the engine is installed. Fuel Economy Test: There are two methods for testing the fuel (methanol, hydrogen) economy of electric vehicles: road tests and indoor tests. Indoor tests can be conducted using a rotary drum test bench or an engine test bench. Standardized tests on the test bench have good repeatability and can accurately determine the hydrogen consumption of the PEMFC electric vehicle power drive system and evaluate "hydrogen fuel economy." This provides a basis for improving the design of electric vehicle hydrogen storage systems. Reliability test: There are two ways to test the reliability of automobile engines: one is to conduct on-site inspection after the engine is installed in the vehicle, that is, to conduct a 25,000 km road test. The other is to conduct a test on the engine bench to simulate the operating conditions of the vehicle, according to the reliability test procedures specified in the professional standards. Durability test: The durability test is a test conducted on the bench to make the engine work under high speed and high load conditions. The purpose of this test is to assess the fatigue resistance of the various stressed components (including thermal stress, electrical stress and mechanical stress, etc.) of the engine (power drive system), as well as the stability of wear resistance, economy and power indicators. (2) Test items or test contents unique to PEMFC power drive system Starting performance test: The starting performance test contents of fuel cell electric vehicles are different from those of internal combustion engine vehicles. Through this test, the starting performance of the electric vehicle fuel cell power source under different conditions such as no load, load, normal temperature and low temperature is checked. Regenerative braking test: When electric vehicles use three-phase induction motors or DC motors, there is a regenerative braking state. Reasonable use of the regenerative braking function of the motor can save energy. Therefore, when a fuel cell electric vehicle is equipped with a secondary battery, regenerative (power generation) braking tests can be conducted on the drive system and motor. Thermal balance test: In a fuel cell power drive system, the fuel cell stack, power driver, compressor, etc., are heat-generating components that require cooling during operation. Components such as the metal hydrogen storage tank and air preheater also require heat during operation. Therefore, several heat exchangers are installed in the fuel cell power drive system. To save energy and improve system efficiency, a scientific thermal balance design of the power drive system is necessary. To verify and improve the system's heat exchange performance, a thermal balance test is required during engine bench testing. Efficiency test: The efficiency test content for fuel cell electric vehicles differs from that of internal combustion engine vehicles. Electric vehicle efficiency tests include system efficiency tests and component efficiency tests. The purpose is to determine the fuel utilization rate and energy efficiency of the fuel cell power drive system. For the power drive system, it measures the electrical energy transfer and conversion efficiency of the components. Power source power response test: During operation of the fuel cell power drive system, due to changes in the vehicle's operating state and environment, the output power of the power source—the fuel cell stack—must also change accordingly. The power source power response test measures the fuel cell system's output power response capability to rapid load changes. Single-cell uniformity test: The power source of a fuel cell electric vehicle—the fuel cell stack—is composed of many single cells connected in series. To ensure the consistency of performance of all single cells, a single-cell uniformity test must be performed on the battery stack. Protection test: Fuel cell electric vehicles use hydrogen energy, and the power drive system is a high-power power electronic device. For these reasons, protection tests for fuel cell electric vehicles are particularly important. The main aspects of the protection test are the safe operation of the fuel cell stack and the short circuit and overload of the power drive system. There are many sub-items in the bench test of the power drive system of fuel cell electric vehicles. More detailed content can be discussed when formulating test standards and test specifications for fuel cell electric vehicles, and will not be elaborated here. IV. Proton Exchange Membrane Fuel Cell Power Drive System Test Bench The device used for bench testing of automobile engines is called an "engine test bench." Similarly, the device that can conduct bench testing of fuel cell power drive systems is called a "fuel cell power drive system test bench." To complete the test content of the PEMFC electric vehicle system, this test bench should have the following functional units: Fuel storage and supply unit function: It can provide fuel with a certain pressure and flow rate, such as methanol and hydrogen, required for fuel cell power drive system testing for a long time. Control and Protection Unit Functions: Enables automatic adjustment and control of various operating conditions of the fuel cell drive system. It provides alarm, load reduction, and emergency shutdown functions for fault phenomena occurring in the fuel cell drive system during testing. Measurement and Parameter Display Unit Functions: Capable of cyclically monitoring all performance parameters of the fuel cell drive system. It has functions for storing, processing, displaying, and hard copying measured values. Power Electronic Load Functions: The power electronic load is an intelligent, programmable energy-consuming load. It converts the torque generated by the fuel cell drive system into electrical energy. Furthermore, by inputting the vehicle's driving equations, the power electronic load can simulate the force conditions of an electric vehicle driving on the road. Therefore, bench testing can evaluate and predict the actual performance of the tested fuel cell drive system after installation. Engine Lifting Platform Functions: Facilitates the placement and movement of the engine-fuel cell drive system and is equipped with standard gas, water, electricity, and measurement and control system output and input interfaces. Under the management of the central microprocessor, the above functional units can automate the testing of the fuel cell electric vehicle drive system. V. Conclusion Developing fuel cell electric vehicles is an interdisciplinary and multi-professional systems engineering project. The development process of fuel cell electric vehicles (PFMFCs) is far more complex than that of rechargeable battery electric vehicles (RBEVs). To ensure that the research and experimentation of PEMFCs are based on sound science, it is essential to develop key testing equipment as soon as possible, and simultaneously establish corresponding testing specifications and technical standards. This will allow my country's nascent PEMFC electric vehicle program to be built on a solid foundation.