Analysis of the technical status and development prospect of hybrid electric vehicles Abstract: The social concern for environment and energy saving has strongly promoted the development of hybrid electric vehicles. This paper analyzes the research status of hybrid electric vehicles at home and abroad, introduces the main structural forms and working characteristics of hybrid electric vehicles, points out the main problems to be solved at present and the key technologies adopted, and looks forward to its development prospect. Key words: motor control of internal combustion engine of hybrid electric vehicle 0 Introduction With the rapid development of global automobile industry and the increasingly tight supply of petroleum resources, countries all over the world actively seek alternative fuels or reduce fuel consumption, and vigorously develop new energy-saving and environmental-friendly vehicles. Before solar energy, electric energy and other alternative energy sources really enter the practical stage, hybrid electric vehicles have attracted more and more attention because of their advantages of low fuel consumption and low emissions. 1 Development status of HEV technology at home and abroad 1. 1 Overview of HEV development abroad 2 1 After the 20th century, countries have accelerated the process of HEV concept productization, and launched different forms of HEV products one after another. Toyota Prius, Honda Insight, General Precept, Ford Prodigy, DaimlerChrysler ESx3 and Nissan Tino are all representative models, among which Prius and Insight are mature products. By the end of February 2008, Toyota Prius had sold more than 654.38 million vehicles worldwide. 1.2 current situation of HEV research and development in China China also attaches great importance to the research and development of hybrid electric vehicles, and related work began in the 1990s. During the Tenth Five-Year Plan period, the Ministry of Science and Technology organized Beijing Institute of Technology, Tsinghua University, Dongfeng Motor Corporation and other domestic enterprises, universities and scientific research institutions to jointly tackle key problems, and determined that fuel cell vehicles (FCEV), hybrid electric vehicles (HEV) and pure electric vehicles (BEV) are "three verticals", including multi-energy powertrain control system, drive motor and its control system, and power storage battery and its management system. Later, the research and development of energy-saving and new energy vehicles was included in the "Eleventh Five-Year Plan" 863 major project. 2 Composition and working characteristics of hybrid power system The hybrid power drive system adopts two power devices, one is the traditional internal combustion engine, and the other is the motor. The whole system consists of engine, motor, power distribution device, generator, storage battery and current inverter. Generally speaking, the hybrid power system has three power transmission modes: series, parallel and series. Their structural forms and characteristics are as follows. 2. The 1 series hybrid power system is shown in figure1. In series hybrid drive (SHEV) system, all engine mechanical energy is converted into electrical energy to drive the motor. This system makes the engine work in the most efficient speed range, so it can maximize fuel economy and reduce emissions. 2.2 parallel hybrid power system parallel (PHEV) structure has two sets of drive systems, namely internal combustion engine and motor (see figure 2). The parallel connection of the engine and the motor can drive the wheels of the vehicle, and the motor can also be used as a generator to charge the battery without an additional generator. The system takes the engine as the main power source when the vehicle is running, and makes the motor work as the auxiliary driving force when the vehicle starts or accelerates. When the engine is in a low-efficiency and low-load state, the motor function is converted into a generator function to charge the battery. Secondly, when the vehicle brakes or decelerates downhill, the braking energy is recovered by the braking energy recovery system. 2.3 series-parallel hybrid power system The series-parallel hybrid drive system (PSHEV) is a combination of series and parallel, and its structure is shown in Figure 3. The control strategy of series-parallel drive system is: when the car is driving at low speed, the drive system mainly works in series; When the car runs stably at high speed, it mainly works in parallel. 3 Problems and key technologies to be solved for hybrid electric vehicles At present, the problems to be solved for hybrid electric vehicles include the following aspects: First, the research on power distribution device and energy management system. Second, develop economical and practical batteries with high specific energy and high specific power. Thirdly, the hybrid power system has complex structure, high cost, difficult maintenance and relatively high price. Fourthly, a more advanced mathematical model of the drive system (including static and dynamic) is established and analyzed by computer simulation. Specifically, the following key technologies should be studied: 3. 1 hybrid power unit technology In hybrid electric vehicles, heat engines are also called hybrid power units. In order to improve the fuel economy, it is necessary to put forward more requirements for the hybrid power unit, for example, the hybrid power unit can be started and shut down quickly. At present, the research on hybrid power unit mainly focuses on: first, the optimization of combustion system; The second is the tail gas treatment technology, which mainly studies the efficient tail gas catalytic system; The third is the research on alternative fuels. 3.2 Control Strategy Technology The key link of HEV product development is to formulate and optimize its control strategy according to different hybrid drive systems, and a lot of matching theory research has been carried out abroad through system simulation. The development of control system is to calculate the corresponding required output power according to the collected data such as speed and load, and calculate the power value allocated to internal combustion engine and motor based on the highest efficiency, that is, to realize the optimal power distribution ratio between internal combustion engine and motor; Then according to the power distribution ratio, the power value of the driving motor and other related data are obtained, and the control parameters of the internal combustion engine and the motor are given. At the same time, the actuator is driven to complete these two levels of work control. In the design of actuator, the design of power distribution device and its integration with transmission device are the key parts of the design work. Because it must correctly decompose the power of the internal combustion engine into the power to drive the vehicle and the power to drive the generator according to the instructions of the controller. 3.3 Energy storage technology In electric vehicles, the development of storage batteries and the study of charging and discharging characteristics are the key. Now, Ni-MH battery and Li-ion battery can meet the requirements of hybrid vehicles, but they still have some defects such as high price or short life. From the development point of view, the research of energy storage device should include the following aspects: First, study the internal connection, inspection and monitoring of batteries. Second, the improvement of battery design and manufacture has reduced the manufacturing cost, improved the performance of the battery core and extended the service life. Batteries suitable for hybrid electric vehicles need to have high specific power, and the goal to be achieved is that the power-energy ratio is greater than 20 W/Wh; Service life reaches 10 year; It can be recycled at least 6.5438+0.2 million times. The third is the thermal energy management and residual power management of the battery. In addition, the remaining battery power directly affects the economy and emissions of hybrid electric vehicles, so effective testing methods and control devices are needed. 4 Analysis of development prospects From the current development, the gradual application of computer technology and automatic control technology, including the application of various intelligent control systems including adaptive control technology, fuzzy control technology, expert control system and neural network in hybrid electric vehicles, will further promote the development of hybrid electric vehicles. Compared with traditional cars, hybrid cars fully absorb the biggest advantages in the electric/thermal system, and are superior in energy saving and emission. Compared with pure electric vehicles, the voltage and power ratio of HEV is similar to that of electric vehicles, but the battery capacity is greatly reduced, so its manufacturing cost is lower than that of electric vehicles. At present, there are still many main technical problems faced by hybrid electric vehicles. Although it is only a transitional model in the long run, there is no doubt that HEV will have a bright future in the next 20-30 years. Experts in the automotive industry predict that in the near future, hybrid vehicles will account for more than 40% of newly produced cars. China automobile industry should conform to the development trend of science and technology, seize the HEV market, concentrate scientific research and develop its own products quickly before the influx of foreign products. 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