The Control Loop Design Of The Half-bridge LLC Resonant Converters

With the development of power electronic technology and power semiconductor devices,the operating frequency of switching power converter is becoming increasingly higher.Resonant converter adopts soft switch method,compared with PWM converter using hard switching mode,can effectively solve the problem of low efficiency at high frequency.However,for the realization of soft switch to join the resonant components,brings the difficulties in stability of the control loop.So the design of resonant converter'control loop causes the researchers attention at home and abroad.At first,the working principle of the half-bridge LLC resonant converter is studied,especially the soft switching process of the primary switch transistor' ZVS and secondary rectifier diode' ZCS are analyzed in detail.Then the fundamental wave equivalent(FHA)method is used to simplify the LLC resonant circuit,the equivalent circuit is simulated to analyze the characteristics of steady state in use of Matlab software.Then gives the design steps of the resonant tank resonant component parameter,and makes the complete design parameters.Based on it,selecting the extension description function(EDF)method to establish the small signal model of the half-bridge LLC resonant converter,based on the dynamic characteristic curve of the small signal model,and control loop is guided to design well.Finally using PSIM software builts the closed loop system of the half-bridge LLC resonant converter,simulating and analysising the converter'steady state performance and dynamic performance,and verifying the validity and effectiveness of the control loop design.Simulation shows that:the designed voltage loop and current loop double-loop control half-bridge LLC resonant converter has the control loop which bandwidth is 10kHz?12kHz and phase margin is greater than 45°.In range of the whole load,it realizes soft switch of the switch transistor and the rectifier diode.The load from no-load to full load' response time is less than 2.8 ms,undershoot voltage is small than 1.2%,from full load to no-load' response time is less than 2.9 ms,overshoot voltage is small than 1.2%.The input voltage from 420V to 360V' response time is less than 2.4 ms,undershoot voltage is small than 0.88%,from 360V to 420V' response time is less than 3.0 ms,overshoot voltage is small than 1.0%.Compared with the single traditional voltage loop control,the designed double-loop control has better dynamic performance.