Research On Fractional Order PID Controlled SWISS Rectifier With Large Transformation Ratio

With the innovation and development of power electronic technology,people have higher and higher requirements for the performance of power electronic converters.Compared with the traditional six switch PWM rectifier,SWISS rectifier has a unique harmonic injection circuit,which not only reduces the harmonic distortion rate of the network side current,but also improves the efficiency of the rectifier.Therefore,it is of great research significance and practical value to deeply study the principle and control strategy of SWISS rectifier and build a topology with better performance on its basis.As a non isolated step-down converter,the traditional SWISS rectifier works under the condition of large transformation ratio,which will lead to too small duty cycle of high-frequency switch and large device loss and stress.In order to avoid the limit duty cycle of high-frequency switch,a large transformation ratio SWISS rectifier based on coupled inductor is taken as the research object in this thesis.Firstly,the control strategy of harmonic injection network of SWISS rectifier with large transformation ratio is improved,so as to realize the freewheeling ability of coupling inductance to the output DC side;The working principle of large transformation ratio SWISS rectifier is analyzed.According to its principle,the duty cycle expression and input-output voltage transformation ratio of high-frequency switch are calculated,and then its equivalent circuit model is deduced;The stress of diode and switch tube of SWISS rectifier with large transformation ratio is analyzed;According to the stepdown ratio and switching duty cycle of the rectifier,the parameters of the coupling inductance are designed.Then,the state space average method is used to model the small signal of SWISS rectifier with large transformation ratio,and the transfer function of the model is obtained.In order to improve the steady-state and dynamic performance of large transformation ratio SWISS rectifier,fractional order PID controller is applied to large transformation ratio SWISS rectifier instead of integer order PID controller;Particle swarm optimization(PSO)is used to adjust and optimize the parameters of fractional PID controller of SWISS rectifier with large transformation ratio;By comparing the Bode diagram and step response curve of the two control systems,the advantages of fractional order PID controller in steady-state and dynamic performance are verified.Finally,the input filter of the rectifier is improved,and the LLCL filter is used instead of the traditional LC filter to suppress the harmonics at the switching frequency and reduce the harmonic distortion rate of the current at the grid side.The simulation model of large transformation ratio SWISS rectifier based on coupled inductor is built on Simulink platform.The steady-state and dynamic simulation results of the two controllers are compared and analyzed to verify the feasibility and effectiveness of fractional PID controller applied to rectifier system.The simulation results of coupled inductor SWISS rectifier with large transformation ratio are verified by experiments.