Research On Design And Control Technology Of High-Power LLC Digital Power Supply

It is an inevitable trend for electric vehicles to replace traditional fuel vehicles.High-power DC-DC is one of the key technologies of electric vehicles.It is widely used in vehicle chargers,vehicle DC-DC converters,and electric vehicle drive motor test platforms.Full-bridge digital LLC resonant circuit is the main topology of high-power DC-DC power supply.This paper designed a fully digital LLC resonant power supply with a rated power of3 kW and an output voltage of 100 V.It used a semi-bridgeless power factor correction circuit and a full-bridge LLC resonant circuit topology,and the STM32 full digital control method.The working principle and design method of the semi-bridgeless power factor correction circuit and the full-bridge LLC resonant circuit are studied in detail.The circuit model of the LLC resonant circuit is established based on the first harmonic analysis method,analyzed the gain characteristics of the LLC resonant circuit.The main circuit parameters of the semi-bridgeless PFC circuit and the full-bridge LLC resonant circuit are calculated.In order to improve the stability of the power supply,a PI control strategy based on average current control is adopted for the semi-bridgeless PFC circuit.The full-bridge LLC resonant circuit implements double closed-loop PI control;in order to further reduce circuit switching losses and improve working efficiency,a synchronous rectification scheme is used.In the case of lower than the resonant frequency,in order to ensure that zero-voltage switching can still be achieved,optimized and improved the traditional synchronous rectification scheme,a strategy is adopted in which the secondary-side MOSFET and the primary-side MOSFET are turned on at the same time but not turned off at the same time.A simulation model of the designed circuit parameters and control strategy is established in MATLAB/Simulink environment,which verifies the effectiveness of the synchronous rectification scheme and ensures that the circuit can still achieve ZVS below the resonant frequency.