Research On Large Signal Stability Analysis And Improvement Method Of PWM Rectifier Cascade System

With the increasing use of distributed power sources in aerospace,warships,and microgrids,stability issues caused by their complex structures have become increasingly prominent.To solve this problem,most people start with the most typical structure of a distributed power system,the cascade system,using small signal analysis method to study its stability near the steady-state operating point.But few people study the large signal stability of the system.In order to analyze the stability of the system more fully and improve the reliability of the system operation,it is necessary to study the large signal stability of the cascade system.The object of this paper is a three-phase voltage type PWM rectifier cascade DC/DC converter system.To simplify the analysis,the subsequent DC/DC converter will be equivalent to a constant power load.For the most common large-signal perturbation form of load power jump of the subsequent stage DC/DC converter,this paper uses the third stability theorem of the theory of hybrid potential function to deduce the stable boundary of the cascade system under large signal disturbance in detail.Using Plecs simulation software to build a simulation model verifies the correctness of the theoretical derivation.In addition,this paper elaborates the response process of the cascade system under large signal disturbances,and determines four key factors that affect the stability of the cascade system under large signal perturbation,in order to seek the compensation method of the cascade system under large signal disturbance.In order to improve the stability of the cascade system under large-signal perturbation,and to enlarge the stable boundary of the cascade system under large-signal perturbation,this paper proposes a method to improve large-signal stability based on linear auto-disturbance rejection controller.Combining the d-axis current equation with the DC-side voltage equation and designing a second-order auto-disturbance-rejection controller to control it,the traditional double-closed-loop control method is solved.The difference in response speed makes the current loop unable to fully track the voltage ring oscillation process.Designing a first-order auto-disturbance controller to control the q-axis current eliminates the adverse effects of the integral link and coupling control on the large-signal stability of the cascade system.This article gives detailed controller parameters and design steps for the ADRC.The Plecs simulation software is used to simulate the cascade system under the control of the auto-disturbance rejection controller.The simulation results demonstrate the effectiveness and feasibility of the proposed method.Finally,on the basis of theoretical analysis and simulation verification,a three-phase voltage type PWM rectifier cascade system experimental platform is built to verify the proposed large signal stability improvement method.The experimental results show that the auto-disturbance rejection controller has better resistance to large-signal interference than the traditional PI controller.