Stability Analysis Of Three-Phase Four-Leg Inverter System With Rectifier Load

With the national policy of "carbon neutrality and carbon peaking" and the implementation of the "whole county photovoltaic" policy,the proportion of distributed energy and new energy generation in the overall power system is gradually increasing.However,due to the high switching frequency,negative resistance and small inertia of power electronic converters,the large number of new energy sources can cause oscillations in small micro-grid systems,so it is particularly important to establish a mathematical model of the system and analyze the stability of the system under the corresponding operating conditions.In this thesis,the impedance model of a mini-microgrid consisting of a three-phase four-bridge-arm PWM inverter and a three-phase PWM rectifier is modeled based on the linearized small signal modeling of the dq0 axis.Based on this,the influence of different control parameters and system variables on the system input and output impedance is discussed.The problem of matching the theoretical and actual values of the impedance model is addressed.Based on the principle of orthogonal decoupling in Hilbert space,this thesis proposes a method for separating the sine and cosine components of the system response under frequency excitation.Firstly,the control law for the separation of the sine and cosine components is designed,and the initial value of the measurement system is set to improve the speed of the system impedance measurement,and secondly,the system output impedance at a specific frequency is fitted to the measured sine and cosine components based on Euler’s formula,and the validity of the theory is verified by simulation in MATLAB/Simulink,which provides a simple and This provides a simple and effective solution for the measurement of the system output impedance.The generalized Nyquist stability criterion is used to analyze the stability of the proposed three-phase four-bridge-arm PWM inverter with three-phase PWM rectifier load.Finally,an experimental platform for cascading a single three-phase four-bridge-arm PWM inverter with a three-phase PWM rectifier is built,and the hardware and software design of the experimental platform are briefly introduced.The experiments are conducted to verify the feasibility and validity of the theory presented in this thesis.