A Planar Transformer Switching Control And Design Of LLC Charging Power Supply

As a key device to connect the on-board energy storage battery with the external charging power supply,the on-board charger has become one of the research focuses in the power electronics industry.The LLC resonant converter topology is widely used in DC-DC modules of on-board charging power supplies.It can not only realize the Zero Voltage Switch(ZVS)of the primary side switch tube,but also the Zero Current Switch(ZCS)of the secondary side rectifier diode,with low switching loss.However,LLC resonant converter has the disadvantage of low efficiency in the light load stage,which is more prominent in the application environment of electric vehicle on-board charger such as unsteady power.To solve the problem of low efficiency in the light load stage,this paper proposes to use the advantage of high consistency of planar transformer parameters to realize the half-bridge LLC resonant converter with precise variation of actual inductance ratio k by controlling planar transformer switching,so as to improve the overall efficiency level of the converter.Firstly,the topology of the proposed resonant half-bridge LLC converter controlled by Switching Parallel Planar Transformer(SPPT)is introduced,and its working modes are analyzed in detail for different working frequencies.The First Harmonic Analysis(FHA)was used to model the converter equivalently,and the idea of control variable was used to compare and analyze the effects of different parameters on the voltage gain characteristics of the converter,and the optimal operating range was obtained.The system control idea of the converter and the specific closed-loop control process are described in detail,as well as the selection of the output power point of the control planar transformer switching.The complete resonant parameter calculation process of the converter is given,and the parameter calculation of an experimental prototype of a charging power supply with rated power of 1k W is completed according to the process.Secondly,the structure characteristics,types and advantages of planar transformer are introduced,and the circuit model of planar transformer with actual parasitic parameters is analyzed.The core loss and winding loss of planar transformer under working condition are analyzed,and the complete parameter design process of planar transformer is given.The planar transformer was modeled by ANSYS Maxwell finite element analysis software,and the different arrangement modes of multilayer PCB windings were compared and analyzed to determine the optimal arrangement mode.Finally,based on the PSIM simulation software platform,the circuit resonance parameter design of the SPPT half-bridge LLC charging power supply and the planar transformer switching control scheme were simulated and verified.The hardware design and manufacture of charging power supply prototype and the design of DSP digital control system are introduced in detail.The experimental platform of the charging power supply prototype was built under laboratory conditions.The experimental results show that the charging power supply controlled by planar transformer switching works in the optimal operating frequency range during the entire charging process of constant current and then constant voltage.The charging power supply can realize the ZVS turn-on of the primary side and the ZCS turn-off of the secondary side.The work efficiency measured in the light load stage is significantly improved,which further verifies the correctness and feasibility of the planar transformer switching control scheme.