Research On Passivity-based Adaptive Control Strategy For Fractional Order SWISS Rectifiers

With the rapid development of electrification in our country,the supply and demand of DC equipment,especially the number of rectifiers is increasing rapidly,but a large number of rectifier application brings serious harmonic pollution to the power network.Power Factor Correction(PFC)technology has been widely used because it can suppress harmonics from the root,which effectively improves the harmonic pollution of rectifiers.As a new type of PFC rectifier,the SWISS rectifier can realize single-stage step-down output,which is extremely suitable for the application of electric vehicle charging piles,uninterruptible power supply,and other occasions requiring low DC voltage,and has a huge application prospect.In addition,capacitors and inductors in actual circuits are passive devices with fractional order characteristics,and ideal integer order capacitors and inductors do not exist.Therefore,when constructing circuits containing capacitors or inductors,it is necessary to design fractional order inductance and capacitance models to more accurately describe the dynamic behavior in the circuit.Therefore,it is of great theoretical significance and application value to study the fractional circuit model of the SWISS rectifier and its control strategy,to improve the overall performance and promote the wide application of SWISS rectifier in electric vehicles and other industries.This dissertation mainly studies the fractional order circuit model and passivity-based control strategy of the SWISS rectifier,in order to improve its input current quality,improve the system power factor and the anti-interference ability of output voltage.Specific research contents are as follows:Firstly,the dissertation analyzes working principle and derives the basic current control strategy of the traditional integer order SWISS rectifier.Compared with the classical double closed-loop PI control strategy,this scheme further simplifies the controller structure.After that,the dissertation analyzes the range of DC side filtering inductor and voltage stabilizing capacitor,laying the foundation for the subsequent construction of fractional order inductor and capacitor equivalent circuit.Secondly,the dissertation selects Charef rational approximation algorithm to construct an equivalent circuit of 0.9 order inductor and capacitor.The effectiveness of the equivalent circuit of fractional order element is verified by the amplitude-frequency characteristics in the frequency domain,and the fractional order SWISS rectifier circuit model is obtained by replacing it with the integer order circuit.Thirdly,the dissertation derives reactive power generation mechanism and proposes reactive power compensation control strategy of fractional order SWISS rectifier,so that the rectifier can operate at unity power factor.Then,based on the dynamic model,the dissertation proposes a passivity-based adaptive control scheme based on parallel damping injection,and derives the range of parallel damping values,and the stability of the scheme is proved.Compared with the traditional passivity-based controller based on series damping injection,this scheme can realize the adaptive control of the output voltage when the load changes or the load is unknown.So far,combined with the reactive power compensation strategy,a fractional order passivity-based adaptive controller capable of achieving unity power factor control is obtained.Finally,the simulation model is built based on MATLAB/Simulink.The dissertation compares the control performance first of fractional order passivity-based adaptive controller and integer order passivity-based adaptive controller.The simulation results verify that the performance of the fractional order controller is better than that of the integer order controller,and prove that the fractional order circuit model can describe the dynamic behavior of the circuit more accurately than the integer order circuit model.Thereby enabling the fractional order controller to more accurately control the circuit state and improve the input and output performance of the rectifier.Then,the control performance of the integer order passivity-based adaptive controller and the basic current controller is compared,verifying that the performance of the passivity-based adaptive controller is superior to the basic current controller.It is proved that the passivity-based control strategy is more suitable for the nonlinear characteristics of the rectifier compared to the basic current controller which is centered on PI controller,further improving the performance of the rectifier.After the reactive power compensation function is started by the fractional order passivity-based adaptive controller,the rectifier can work at per unit power factor,which verifies the feasibility of the reactive power compensation strategy.