The Research On Fuzzy PID Control Strategy For Anti-drift Of LLC Resonant Converter

LLC resonant converter does not need to add any auxiliary circuits to realize the zerovoltage turn-on(ZVS)of the primary side switching transistor and the zero-current turn-off(ZCS)of the secondary side rectifier diode in the full load range.It can achieve high power density while maintaining high efficiency,which makes it become a research hotspot.On the other hand,the LLC resonant converter is a complex high-order system,the open loop gain of which varies with working conditions,which would easily deteriorate the control performance.Aiming to solve this problem,this paper analyzes the variation law of the open-loop gain,and proposes an anti-drift fuzzy PID control based on this.This paper first analyses the working mode and voltage regulation principle of LLC resonant converter,analyzes the key parameter characteristics of LLC resonant converter,and introduces the zero-pole drift characteristics of the small-signal transfer function of LLC resonant converter.According to the parameter characteristics analysis,the power circuit parameters of the experimental platform were designed.Secondly,an anti-drift fuzzy PID control is proposed.According to the variation law of the open-loop gain,the control method uses the switching frequency and load current as input variables to adjust the proportional coefficient online to achieve the effect of canceling the openloop gain drift.The open-loop gain drift characteristics of LLC resonant converter are introduced.The variation law of open-loop gain and the harm of open-loop gain drift are introduced and analyzed,which provides the theoretical basis for the following.The smallsignal modeling of the LLC resonant converter is performed,and accordingly,the initial PID coefficients are set.Then designs the fuzzy controller,including membership function design,input and output subset design,fuzzy rule design and defuzzification method design.Then,the compensation effect of the fuzzy controller is analyzed,and it is verified that the anti-drift fuzzy PID control can offset the effect of open loop gain drift.According to the above design,the fuzzy model toolbox is used to build the corresponding model in MATLAB,and the simulations compared with conventional PID control are carried out to verify the superiority of the antidrift fuzzy PID control proposed in this paper.Finally,the software and hardware design of the experimental platform control system are introduced.An 800 W experimental platform is built to perform open-loop testing,load step response comparison test,load regulation test,voltage regulation test,and efficiency test.The experimental results verify the superiority and feasibility of the anti-drift fuzzy PID control applied to the LLC resonant converter.