Abstract: This paper reviews the development and basic structure of hybrid electric vehicles. On the basis of this, combined with Toyota Motor Corporation's latest generation hybrid electric vehicle Prius THS II, the specific application of power electronics technology in hybrid electric vehicles is introduced. . Finally, combined with the actual situation of hybrid electric vehicles, the problems that need to be solved are put forward. This article refers to the address: http:// Keywords: electric vehicle hybrid power electronics AC drive inverter 1 Introduction Power electronics technology is a discipline that studies power semiconductor devices to achieve power conversion and control. It is an emerging discipline in which electronic, power semiconductor devices and control cross each other. It studies a wide range of topics, including power semiconductor devices, magnetic materials, power electronics circuits, control integrated circuits, and power conversion devices. At present, the main directions of power electronics research are: (1) Design, testing, model analysis, process and simulation of power semiconductor devices; (2) Circuit topology, modeling, simulation, control and application of power switching converters; (3) Power inverter technology and its applications in industrial fields such as electric drive and power systems. As a clean, efficient and sustainable means of transportation, electric vehicles (EVs) are of great significance for improving air quality and protecting the environment, and provide solutions for the increasingly serious oil charter. Meanwhile, electric vehicles are used as power electronics technology. A new application area, covering all transformations of DC/DC and DC/AC, is a very practical application area. 2. Introduction to hybrid electric vehicles At present, the world automobile industry is in the development stage of technological revolution and industrial adjustment. Safety, environmental protection, energy conservation and intelligence have become major issues of common concern in the automotive industry. In order to sustain the development of human society and the automotive industry, countries around the world, especially developed countries and some developing countries, are studying new technologies to improve the coordination of automobiles and the environment. As the main direction of the transformation and development of the automobile industry in the 21st century, electric vehicles have now transitioned from the experimental development test phase to the commercial trial production stage. Many well-known automobile manufacturers in the world have introduced high-tech safety or environmental protection model cars. The purpose is to guide the trend of the world's automotive technology. 2.1 Characteristics and development of various types of electric vehicles Depending on the power source used, electric vehicles can be broadly classified into three categories: electric storage electric vehicles or battery electric vehicles, fuel cell electric vehicles (Fuel Cell Electric Vehicle) and hybrid electric vehicles. Hybrid Electric Vehicle. Pure electric vehicles are powered by batteries alone, but the performance and price of power batteries have not yet made a major breakthrough. Therefore, the development of pure electric vehicles has not achieved the intended purpose; Fuel cell electric vehicles have unparalleled advantages such as high energy conversion rate, no pollution to the environment, and long service life. However, due to the current breakthrough in fuel cell technology and research, the development of fuel cell electric vehicles has also been limited. Hybrid electric vehicles use electric motors and engines as their power units. The advanced control system enables the two power units to work together to achieve optimal energy distribution, achieving new vehicles with low energy consumption, low pollution and high automation. Since 1995, the world's major automakers have shifted their research focus to the research and development of hybrid electric vehicles. Large auto companies in Japan, the US and Germany have developed hybrids including cars, vans and trucks. electric car. For example, Toyota Motor Corporation, which is the frontier of hybrid electric vehicle research and development, has developed a hybrid electric vehicle that has reached a practical level. Since the launch of the world’s first mass-produced hybrid electric vehicle Prius in 1997, its Later, in 2002, the hybrid van was introduced. The hybrid power system of the car adopts the electric multi-wheel drive and four-wheel drive/braking force integrated control system that was first mass-produced in the century. In 2003, Toyota introduced a new generation of Prius, also known as the “New Age Toyota Hybrid System – THS II†(see Figure 1). The energy saving effect can reach 100km and the fuel consumption is less than 3L. Since 2004, Toyota has introduced a new Lexus RX luxury hybrid sedan to the European market. Toyota plans to use gasoline-electric hybrid engines in 2012 to improve fuel economy and reduce emissions. 2.2 Hybrid electric vehicle classification and characteristics According to different combinations of engine and motor, hybrid electric vehicles can be divided into three categories: series, parallel and hybrid. The basic structure is shown in Figure 2. Figure 3 shows the power distribution of the motor and engine in different hybrid types: In a series hybrid system, a generator is driven by an engine to drive the wheels by an electric motor using the emitted electrical energy. That is, all the kinetic energy emitted by the engine must first be converted into electrical energy, and the electric energy is used to drive the vehicle. The parallel hybrid system uses the engine and the electric motor to drive the wheels. The two power sources are used according to the situation. Since the power sources are parallel, they are called parallel hybrid systems. The hybrid type is also called series-parallel type, which can maximize the advantages of both series and parallel. This is how the Toyota Prius series hybrid system works. In operation, the power splitter is used to distribute the power of the engine: on the one hand, the wheels are directly driven, and on the other hand, the power generation is controlled autonomously. Since the electric motor is driven by electric energy, the usage ratio of the electric motor is increased as compared with the parallel type. 3. Power electronic technology and devices commonly used in HEV This paper combines Toyota's new generation hybrid system THS II to specifically study the application of power electronic technology in HEV. THSII's complete vehicle electrical drive system (see Figure 4) consists mainly of high-efficiency engines with AtkinSon cycles, permanent magnet AC synchronous motors, generators, power splitters, high-performance nickel metal hydride (NI-MH) batteries, and control management units. And the components of the DC-DC converter of each related inverter. High-voltage power supply circuits, various inverters, and auxiliary DC-DC converters for 14V batteries form a power control unit (see Figure 5) that integrates DSP controllers, drive and protection circuits, DC stabilized capacitors, and semiconductors. Insulators, sensors, liquid cooling circuits, and CAN bus interfaces to automotive communications. 3.1 Motor/generator inverter unit In the Prius THS II main drive system, the three-phase voltage inverters (powers 50kW and 30kW) used in motors and generators are integrated into one module (as shown in Figure 6, the electrical structure of the inverter is shown in Figure 7)), the maximum supply voltage of the DC bus is set to 500V. The power device uses a commercial IGBT (850V/200A) with an anti-parallel freewheeling diode that has the ability to withstand a maximum 500V backpressure and other capabilities such as avalanche breakdown and transient short circuit. Each bridge arm of the motor inverter is composed of two IGBT modules and a diode module in parallel. Each IGBT chip has an area of ​​133 mm 2 (13.7 mm × 9.7 mm), and the emitter uses a 5 μm thick aluminum film; and each diode chip has an area of ​​90 mm 2 (8.2 mm × 11 mm). At present, electric vehicles generally adopt PWM-controlled voltage-type inverters. This inverter has the characteristics of simple circuit and high efficiency, and the PWM inverter exhibits the following development trends: (1) IGBT devices are usually used, the operating frequency is high, and the low-frequency harmonic components and the current shock of the starting are reduced. The highest switching frequency of current foreign applications has reached 20 kHz; (2) The rated frequency of the motor is correspondingly increased, and the speed regulation range is expanded to reduce the volume and weight of the motor and improve the power ratio while better meeting the operation requirements. At present, the highest rated frequency of foreign electric motor-specific motors has reached 500Hz; (3) The DSP-based computer control system can realize reliable vector control and calculation. The motor can achieve fast constant torque starting and weak magnetic high-speed operation. This control system is stable, the current impact is small, and the control efficiency is high. In addition to the above traditional PWM control technology, a resonant DC link converter and a high frequency resonant AC link converter have recently appeared. Resonant converters with zero-voltage or zero-current switching technology have the advantages of low switching loss, low electromagnetic interference, low noise, high power density and high reliability, which have attracted wide interest of researchers. The commonly used electronic switching devices currently used in power converters mainly include GTO, BJT, MOSFET, IGBT and MCT. Due to the characteristics of IGBT set BJT and MOSFET, the high-impedance voltage-controlled gate can significantly reduce the gate drive. The power can be integrated into the gate drive circuit; and the IGBT has a very short switching time, which enables the system to have fast response, reduces switching losses, and reduces noise, so the IGBT is a good switching device. MCT is also a potential choice device, although the current commercial MCT rating has yet to be improved; but because MCT has a low voltage drop, so with the new MCT manufacturing process and the use of new materials, the future MCT is There will be good application prospects in electric vehicles. 3.2DC-DC boost converter unit In THS, the battery is directly connected to the motor and generator through the inverter (see Figure 8); in THSII, the output voltage of the battery pack is first boosted by the DC-DC boost converter, and then with the inverter. The devices are connected, so the DC bus voltage of the inverter is increased from 220V of the original THS to the current 500V. Figure 9 is a schematic diagram of energy exchange in the THSII system. The power of the generator in Figure 9 is 30 kW, and the instantaneous power of the battery pack is 20 kW. The two combine to provide energy for the 50 kW motor. The capacity of the boost converter in Figure 9 is also Designed to be 20kW. This system has the following advantages: (1) Since the maximum output power capability of the motor is proportional to the DC bus voltage, compared with the 202V power supply condition of the original THS system, the motor in the THSII system is powered by 500V without increasing the drive current. Its maximum output power and torque output capacity is 2.5 times that of the original THS system; in addition, the same volume of motor can also avoid outputting higher power; (2) Due to the use of DC bus supply voltage variable system, THSII can freely adjust the DC bus supply voltage according to the actual needs of the motor and generator, so as to select the optimal supply voltage to reduce the inverter switching loss and Energy saving purpose of copper loss of electric motor; (3) For a battery pack with a constant supply voltage, the actual demand of the motor and the generator can be satisfied by adjusting the output voltage of the step-up transformer, so that the number of batteries can be reduced to some extent. , to reduce the quality of the entire vehicle. The DC-DC boost converter shown in Figure 9 has two IGBT modules and a freewheeling diode module in parallel for each branch, wherein each IGBT chip has an area of ​​255 mm2 (15 mm × 15 mm), and each freewheeling diode chip The area is 117 mm 2 (13 mm × 9 mm). The circuit topology shown in FIG. 9 can ensure the instantaneous conversion of the charging and discharging of the battery without interrupting the normal operation of the system. Due to the function of the DC-DC boost converter, the system voltage on the main capacitor is different from the output voltage of the battery pack, thereby ensuring that the motor and the generator operate at a high voltage without being affected by the low voltage of the battery pack. Limitation of output capabilities. 3.3DC-DC buck converter unit Usually, various electric equipment in the car is powered by a 14V battery pack (rated voltage is 12V). The Prius also uses a 14V battery pack as a power supply for controlling on-board electrical equipment such as computers, lights, brakes, etc., and charging the battery. The operation is completed by DC 220V through a DC-DC buck converter. The circuit diagram of the converter is shown in Figure 10. The converter has a capacity of 1.4kW (100A/14V), and the power device uses a voltage-controlled commercial MOSFET (500V/20A). Each MOSFET chip has an area of ​​49mm2 (7mm×7mm). 3.4 Inverter unit for other AC equipment The Prius THSII air conditioning system uses a motor-driven air compressor to replace the traditional air compressor driven by the engine. In order to drive the motor for the air compressor, a low power inverter (DC202V, 1.6 kW) was designed. The power device uses a commercial IGBT (600V/30A) with an anti-parallel freewheeling diode. The area of ​​each IGBT chip is 22.1mm2 (4.7mm × 4.7mm), and the area of ​​each freewheeling diode chip is 9mm2 (3mm × 3mm). 4HEV requirements for power electronics technology Limited by the actual operating conditions, power electronic technology and devices for hybrid electric vehicles are required to have the characteristics of low cost, small size, large specific power, and easy installation. In addition, the following technical details need to be considered: (1) Power electronic device sealing problem Various automotive power electronics must be effectively sealed to withstand the effects of temperature and vibration and to prevent the ingress of various automotive fluids. (2) Electromagnetic compatibility / electromagnetic interference (EMC / EMI) problem Hybrid electric vehicle is a relatively small space, which contains various control chips and weak current circuits. Therefore, in the design of on-board power electronic devices, in order to eliminate future accidents, it is necessary to study and solve EMC/EMI. problem. (3) DC bus voltage utilization problem The voltage of a hybrid electric vehicle energy storage system is variable. The magnitude of the voltage depends on the actual load of the vehicle, the operating conditions (electric or power generation), and whether the motor is weakly magnetically operated. The typical bus voltage fluctuation range is the standard. The value is -30%~+25%. Therefore, how to make full use of the DC bus voltage in the case of frequent changes in vehicle operating conditions has become a problem that the control strategy designer needs to solve. (4) Power electronic device control problem “High switching frequency†and “high sampling rate†are currently widely used in power electronic devices and AC drive systems for hybrid electric vehicles. Objectively “double high†requires high-precision encoders and solvers, so this means How to reduce the parameter sensitivity to meet the control requirements when there is a wide temperature gradient and saturation in the motor. 5 Conclusion This paper combines Toyota Motor Corporation's latest generation hybrid electric vehicle Prius THSII, summarizes the application of power electronics technology in hybrid electric vehicles, and puts forward technical issues that need to be considered and solved. With the development of power electronics technology, microelectronic technology and control technology, digital AC drive systems are widely used in commercial electric vehicles; and the development of hybrid electric vehicles using AC motor drive systems has been sustainable in the automotive industry. One of the important ways. With the improvement of human requirements for the living environment, the rational use of energy awareness has increased. 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