Research On Control System Of Range Extender For Electric Vehicle Powered By Lithium Battery

Range extender is an auxiliary power generation system for electric vehicles.It can effectively increase the mileage of electric vehicles on a single charge,reduce the cost and weight of on-board lithium batteries,and realize a smooth transition from fuel vehicles to pure electric vehicles.The core component of the range extender is the motor.The brushless DC motor has the advantages of small size,light weight and high efficiency.It is an ideal choice for the motor in the range extender.This paper studies the range extender control system of a lithium battery powered electric vehicle powered by a brushless DC motor as a starter/generator motor.The brushless DC motor determines the stator winding commutation information according to the rotor position information,so rotor position detection is a prerequisite for the operation of the brushless DC motor.Brushless DC motors usually use a position sensor to detect the rotor position and provide commutation information for the motor,but it is not suitable for electric vehicles that have limited space and run in various environments and road conditions for a long time.Therefore,this paper studies the position sensorless technology,using the terminal voltage back EMF zero-crossing method to obtain the rotor position,and complete the control of the brushless DC motor.Aiming at the start-up problem of range extender in low temperature environment,a composite cold start scheme of range extender is proposed.In the traditional three-stage open-loop start brushless DC motor control,closed-loop control is added.In the rotor positioning stage,six different voltage vectors are applied to detect the rotor position at rest.After positioning is completed,a new six voltage vectors are added.Combine with the original six groups of detected rotor position voltage vectors to complete acceleration control,and finally complete self-synchronized operation;for the engine,take air intake,fuel,and body warm-up measures to increase the reliability of the engine under cold start;for on-board lithium batteries,add The insulation barrier improves the battery discharge capacity of the lithium battery.Finally,the brushless DC motor,engine,and external lithium battery are combined to complete the overall composite starting scheme.The experimental results show that the range extender can start normally and stably at low temperature after the overall compound start-up optimization.In order to make the range extender generate electricity reliably and solve the problem of rapid heat dissipation in the limited space,the main circuit of the electric vehicle range extender controller with three-phase inverter start and three-phase rectifier power generation is proposed to achieve long-term high-power and high-power Separate operation of heat generation operation and short-time low-power and low-heat start-up operation circuits;when designing the mechanical structure of the range extender controller,the inverter and the rectifier are respectively assembled on different metal shell bottom plates.The dual PI power generation control strategy of the range extender is studied,which can ensure the reliable power generation of the range extender.In order to meet the power supply requirements of electric vehicles under different road conditions,the output voltage must have excellent dynamic characteristics.Because the direct torque control technology controls the output power by controlling the electromagnetic torque of the motor,it has an excellent voltage dynamic response.Therefore,the basic principle of direct torque control is studied,and its application is added to the electric state,power generation state,and start/generation conversion process of the brushless DC motor,so that the range extender can quickly and reliably power the main drive motor and supply it to the vehicle.Lithium battery charging.The hardware circuit and software program of the 4k W/72 V range extender control system are designed.Using ARM’s micro-control chip STM32F051C8T6 as the core,the main power circuit,control circuit,and power supply circuit are designed,and the whole process control of the range extender from start-up to power generation is completed.