Research On The Stability Of Three-phase PWM Rectifier With Converter Load

Pulse Width Modulation(PWM)rectifier is widely used in electric vehicle charging,DC micro grid and multi electric aircraft because of low harmonic pollution,unit power factor,and bidirectional energy flow.Because of the wide applications,the stability issues of it have attracted more and more attention.In the above applications,the load of the three-phase PWM rectifier is usually no longer an idealized resistance,but a variety of power electronic converters with nonlinear characteristics.This paper focuses on the three-phase PWM rectifier with converter loads,and discusses the stability issues,including the stability of the three-phase PWM rectifier,the small-signal stability and the large-signal stability caused by converter loads.Firstly,the stability of three-phase PWM rectifier is studied.Based on the analysis of the harmonic generation in the three-phase PWM rectifier,a harmonic suppression method based on the cosine internal model control is proposed.The Jacobian matrix of the rectifier with internal model control is deduced,and the constraints of the controller parameters are obtained by Lyapunov stability theory.The strat-up inrush current of the three-phase PWM rectifier is analyzed.Based on this analysis,a piecewise curve slow given method is proposed,which effectively inhibits the inrush current of the converter from uncontrolled rectification to controlled rectification,and ensures the stability of the starting process.The experimental results verify the effectiveness of the above analysis and control methods.Secondly,the theoretical analysis of the three-phase PWM rectifier with converter load is carried out by small-signal method and large-signal method respectively,and quantitative results on stability are obtained.Besides,the theoretical analysis is helpful to find the way to improve the stability and provide the theoretical support.The open loop output impedance of three-phase PWM rectifier is derived by small-signal analysis,and then the exact expression of closed loop output impedance is obtained by combining with the control loop.Then the stability of the three-phase PWM rectifier with converter load under large-signal disturbance is discussed,and the stability boundary of the system is derived by mixed potential function theory.The simulation results verify the correctness of small-signal output impedance expression and large-signal stability analysis respectively.Thirdly,when the load of the three-phase PWM rectifier is a power electronic converter,the small-signal stability problem may occur due to the mismatch of impedances.This phenomenon is particularly prominent when the film capacitor is used as the bus capacitor to improve the life of the device.A series of output impedance reconstruction methods are proposed,and three forms are given,which are output impedance reconstruction based on bus voltage feedback,output impedance reconstruction based on d axis current feedback and composed output impedance reconstruction.The series methods reduce the output impedance of the three-phase PWM rectifier and avoid the intercepting of the input impedance of the load converter,thus improving the small-signal stability of the system.The experimental results verify the effectiveness of the output impedance reconstruction method,and performance comparisons are given.Finally,the method of improving the large-signal stability of three-phase PWM rectifier with converter load is studied.The interaction between the three-phase PWM rectifier and the load converter leads to serious stability problems under large-signal disturbances such as power sudden increase and so on.The proposed small-signal stability improvement methods are based on the stability theory near the operation point,which are incapable for large-signal disturbances.This paper proposes two methods to improve the large-signal stability of three-phase PWM rectifier with converter load based on auto disturbance rejection control(ADRC): 1)voltage loop ADRC method,which improves the ability of voltage loop to reject disturbance,expands the large-signal stability boundary of rectifier,and is proved by mixed potential function theory.2)The unified ADRC method,which enhances the synergistic control ability of voltage loop and d-axis current loop,gives full play to the advantages of ADRC,while requires a high system bandwidth.The experimental results verify the effectiveness of the two methods.