Design Of Multi-input On-board Charger System

As a low-carbon and environmentally friendly new energy vehicle,electric vehicles can solve the environmental and energy crisis problems caused by fuel vehicles.The application as an on-board charger for charging electric vehicles is becomed more and more widespread.Most traditional car chargers use single-phase input,which has low output power and long charging time.With the increase in battery capacity and the need for shorter charging time,the demand for vehicle chargers with higher power levels using three-phase input is also increasing.Aiming at this problem,a multi-input vehicle charger compatible with single-phase and threephase input is designed in this dissertation.Aiming at the multi-input requirements of single-phase and three-phase compatibility,the topology design of the multi-input on-board charger is completed.Two-stage structure of the cascaded DC-DC converter using the APFC converter is adopted in this dissertation,which realized a wide range of input and output voltage characteristics under multiple input conditions through two-stage independent control and mutual cooperation.Comprehensive analysis and comparison of single threephase PFC circuit topology.Three-phase six-switch PFC and interleaved parallel totem pole PFC circuit topology is adopted in the front stage.The input voltage sampling is used to identify single-phase and three-phase input conditions,and used relays to achieve single-phase and three-phase switching The characteristics of the topology were high device utilization,good power factor correction effect and high power density.The rear stage adopted full-bridge LLC converter to achieve the requirements of high efficiency,high power density and high power.To solve the problem of uneven current in two-phase interleaving,the single and three-phase parameter optimization design is completed.A detailed analysis of the two-phase current imbalance caused by the difference in the inductance parameters of the two-phase interleaved PFC circuit is carried out,and the two current-sharing strategies of master-slave current sharing and external characteristic droop are compared and analyzed.An improved optimized control strategy for independent control of the two-phase current loop is proposed,and it is verified by simulation that it can achieve a good current sharing effect within 10% of the inductance parameter difference.The three-phase six-switch PFC circuit is modeled and analyzed,and the mathematical model in its static and rotating coordinate systems is established.Used the current feedforward decoupling method to achieve the decoupling of active and reactive power.According to the performance index of the charger,the single and three-phase circuit is parameter-designed and the circuit parameter optimization design suitable for two working conditions is completed.Finally,the simulation circuit was built to simulate the dynamic and static characteristics,and the electrical parameters of the converter and the rationality of the loop design were verified and analyzed.The operating characteristics of the full-bridge LLC converter in the time domain and the frequency domain are analyzed respectively,and the gain curve is drawn.According to the charging characteristics of the power battery,a converter control strategy that can achieve constant voltage and constant current charging is designed,and the design of the electrical and control parameters of the converter is completed.Finally,a simulation circuit model is built for analysis and verification,and also for actual engineering design.Provide a certain theoretical reference.