Study On Electric Vehicle LLC Resonant Charging Power Supply System Based On STM32

With the trend of low carbon sweeping the globe, electric vehicle charging power supply has become a hot research topic. Due to the stable performance and the low price, most of the domestic electric vehicle batteries are lead-acid batteries. The traditional electric vehicle lead-acid battery charging mode is more obsolete as their charging mode is constant voltage or constant current, which does not conform to the battery charging curve and is easy to damage the battery. And the charging power supply works in the traditional PWM control mode that their switching devices work in hard-switching state in most of the time, limiting the charging power supply efficiency and also brings serious electromagnetic pollution. In order to overcome the shortcomings of traditional electric vehicle charging power supply, this paper supported by the Science and Technology Planning Project of Guangdong Province(2013B010402002) proposes a LLC resonant charging power supply system of electric vehicles based on STM32, and its characteristics and application were studied.Firstly, the characteristics of electric vehicle lead-acid battery and charging method were analyzed. The LLC resonant charging power supply system and its control scheme were described, then the overall technical program of charging power supply system was improved. The LLC resonant as main circuit topology and the four stages positive and negative pulse control scheme were selected which was suitable for electric vehicle lead-acid battery charging power supply.Secondly, the main circuit of the power supply system of the LLC resonant charging was designed. The main circuit used the full-bridge LLC resonant circuit, so that the charging power supply had always been working with primary side MOSFET zero voltage turning on and secondary side rectifier zero current turning off. According to the demand of charging power supply, main circuit parameters were calculated and components were selected, and using the Saber simulation, the feasibility of the main circuit was verified.Thirdly, the hardware control circuit and time sequence control program of the digital control system based on STM32 was designed. Charging power supply used the digital PFM with anti-windup PI control. The LLC resonant primary circuit achieved digital control with the voltage and current feedback circuit, MOSFET power drive circuit, positive and negative pulse generating circuit, anti-reverse battery circuit auxiliary circuit. Control system used small electric current activateâ†'positive and negative pulsesâ†'constant voltage to reduce electric currentâ†'trickle floating timing of the four stages, as well as timing of the positive and negative pulses to generation and the fault protection, which realized digital control of LLC resonant charging power supply system of electric vehicle based on STM32.Finally, the LLC resonant charging power supply was simulated, and the test of lead acid battery charging was carried out. The experimental results showed that the developed electric vehicle charging LLC resonant power supply system based STM32 could achieve the soft-switching state of LLC resonant primary circuit in the entire process and the conversion efficiency was improved. With the battery charging curve and using the four stages positive and negative pulse charging method, the overcharge and gas evolution polarization phenomenon could be reduced, the battery was protected, and the charging speed was increased.