Three-phase LLC Resonant DC/DC Converter Based On DSP

The LLC resonant converter is mostly in single-phase form and has a wide output range.It can realize zero-voltage turn-on of the primary switching transistor in the full load range,and the overall switching transistor loss is low,which can help improve power efficiency and power density.However,single-phase LLC resonant converters also have problems such as large ripple current and weak power expansion capability,which affect the power supply structure and overall layout,and reduce power density.Although the two-phase LLC resonant circuit can be used in a staggered parallel manner to improve the current ripple,the actual effect is limited and the phase-to-phase current sharing capability is weak.To this end,this thesis studies the three-phase LLC resonant converter to obtain a smaller output ripple current and phase-to-phase current sharing capability.In this thesis,the topology of the three-phase LLC resonant converter is analyzed in detail,and the working principle of the three-phase LLC resonant converter is clarified.The steadystate DC gain of the three-phase LLC resonant converter is obtained by the Fundamental Harmonic Approximation(FHA).The steady-state characteristics are analyzed,and the resonant element parameters and operating frequency range are determined.Based on the Extended Describing Function(EDF),this thesis determines the single-phase equivalent circuit of the three-phase LLC resonant converter,and combines the single-phase circuit state equation and harmonic balance principle to establish a large-signal model of the three-phase resonant converter;The small-signal disturbance variable near the steady-state operating point is linearized,and the small-signal model and its transfer function of the threephase LLC equivalent circuit are obtained.The loop compensation design is completed on the basis.The voltage closed-loop and current closed-loop simulation models of the three-phase LLC resonant converter are built.The steady-state characteristics of the three-phase LLC resonant converter and the rationality and reliability of the control loop design are verified by the waveform of the three-phase LLC resonant converter in different working areas and the dynamic response waveform during load switching.Finally,a prototype of a three-phase LLC resonant converter with DSP chip TMS320F28069 as the core is built.According to the theoretical analysis and simulation parameters,this thesis designs and debugs the main power circuit: MOSFET,resonant circuit,transformer and rectifier diode and control circuit.The experimental results of the zero-voltage turn-on capability of different operating frequency ranges and dynamic performance of the converter are verified and the experimental waveforms are given.The experimental results further verify the correctness of theoretical analysis and simulation.