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Research on the Technology Development Trend of High and Low Voltage Platform Products for Pure Electric Vehicles

by:Shenmao     2021-04-22
After years of state support, China's new energy vehicles, especially electric vehicles, have developed rapidly in recent years and have become an important part of major cities. In terms of public transportation, Shenzhen, Beijing, Guangzhou, Taiyuan, Foshan and other large cities have all adopted new energy vehicles. Also due to policy support, more and more users in cities such as Beijing, Shenzhen, and Shanghai have chosen electric vehicles as private cars. In addition to the influence of policies, electric vehicles also have their natural advantages over fuel vehicles, such as excellent acceleration performance, no engine noise when driving, and low usage costs. At the same time, electric vehicles also have obvious shortcomings, such as pure electric vehicle driving range. Short, long charging time, poor insuring ability, etc. This paper studies the advantages and disadvantages of high and low voltage platforms from the aspects of user needs, drive system and charging system technology and cost, analyzes the respective advantages of high and low voltage platforms, and the future development trend of pure electric vehicles. The high-voltage platform defined in this article refers to a voltage platform with a maximum operating voltage of more than 500V, and a low-voltage platform is a voltage platform with a maximum operating voltage of less than or equal to 500V. According to the relationship between the highest operating voltage of the battery and the rated voltage, this article defines a low-voltage platform with a rated voltage less than or equal to 438V. 1 The application status of electric vehicle voltage platform. With the development of electric vehicle technology, electric vehicle manufacturers are also focusing on making up their strengths, such as strengthening the pursuit of stronger power. Porsche mission E advertises that its 0-100km/h acceleration time can reach 3.2s/2.8s, peak power 500kW/560kW. The 0-100km/h acceleration time of BYD 'Tang' is 4.4s. The power performance of electric vehicles will be stronger in the future. The increase in power performance is due to the increase in voltage, which increases the power of the drive motor and taps the potential of electric vehicles in terms of power performance. Porsche mission E advertises its voltage platform as 800V, and BYD Tang's rated voltage has reached 613V. The rated voltages of pure electric vehicles announced by BYD, Geely and BAIC New Energy are shown in Figure 1. Among the three major domestic new energy manufacturers, only BYD announced a small number of high-voltage platform models. 2 Evaluation of the pros and cons of the high and low voltage platform of the power system Among the factors that users purchase pure electric vehicles, price is a very important factor, so in the design of pure electric vehicles, price factors should be considered. When choosing a high-voltage platform or a low-voltage platform, it will also affect the price of the vehicle's high-voltage system, and ultimately affect the cost of the vehicle. Based on two models of different levels, this chapter designs the power system of different voltage platforms and evaluates their cost comparison. 2.1 Cost comparison of high and low voltage platforms for A-class models 2.1.1 Evaluation ideas The high and low voltage evaluation is a qualitative evaluation. This evaluation is based on a certain A-class pure electric vehicle and sets a number of assumptions and limiting conditions: a) Speed u200bu200bratio 9.3; b ) 0-100km/h acceleration time is about 9s; c) the power module of the controller is based on IGBT; d) the motor is based on the same rotor diameter, and the scattered wire winding scheme; e) the battery rated voltage evaluation 3 values, respectively: 328V, 438V , 650V; f) Other vehicle demand parameters and resistance refer to the parameters of a specific A-level pure electric vehicle; the evaluation idea is shown in Figure 2. Power performance is based on 0-100km/h acceleration as the only indicator, which can be achieved through different torques and peak powers. The advantages of high voltage cost are: a) the higher the voltage, the greater the power of the motor with the same volume, that is, the higher the voltage, the lower the cost of the motor with the same performance; b) the contactor and high-voltage wiring harness, as the voltage increases, the current decreases, Cost reduction; c) The overcurrent capacity of the charging port is restricted by the national standard, and the charging pile follows the national standard, and the maximum current does not exceed 250A. Under the existing national standard DC charging standard, the higher the voltage, the higher the DC charging power can be achieved; d) For the same vehicle type, when the drive power of the motor is increased, the demand for torque can be reduced. That is, different torque/power combinations can achieve the same 0-100km/h acceleration time requirement. The advantages of low-voltage cost include: a) The IGBT market used by the existing motor controllers for low-voltage platforms is more mature and lower in cost; b) DCOBC, air conditioners, PTC, MOS or IGBT devices and diode devices used in low-voltage platforms Lower cost; c) Currently, the charging piles on the market are mainly low-voltage, and high-voltage platform models need to solve the problem of charging in low-voltage charging piles, which may increase the cost. This part will be expanded later. 2.1.2 Torque/power demand simulation is based on a certain vehicle model parameter with a speed ratio of 9.3. The simulation can meet the power and torque demand for about 9s of acceleration from 100 kilometers. Since it is a qualitative evaluation, 4 sets of torque/power combinations were selected from a variety of combinations for the cost evaluation of the electric drive assembly, as shown in Figure 3 and Table 1. 2.1.3 Accounting for the cost of electric powertrain and drive shaft torque increases, transmission input and output shafts will increase costs, and drive shafts will also need to be strengthened. For different torque/power combinations of motors, the optimal design plan will also have cost differences. Voltage affects the cost of IGBT and capacitor selection.
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