Equivalent Small Parameter Symbolic Analyzing Method Of Three-phase PWM Rectifier

Three-phase voltage-source converter has bunch of advantages such as unity power factor, low input current harmonics and so on. However, three-phase rectifier system is difficult to analyze because the switching devices in circuit lead nonlinearity into the system. Existing simulation methods cannot explain the principle of operation of the system while cost lots of computational resource and time. Averaging methods only approximate the low-frequency of the system, which makes it difficult to analyze the high-frequency harmonics of the system. Ripple methods are complicated and not intuitive. In this thesis, equivalent small parameter method(ESPM) is adopted to analyze three-phase voltage-source rectifier. ESPM combines the advantages of the perturbation method and harmonic balance method such as simple usage, intuition, high precision and that analytical solution of the state variables can be obtained to reveal the mechanism of the system. This thesis mainly completed the following work.1) Mathematical model of the three-phase voltage source rectifier, SPWM modulation module and double-loop control module are constructed. Matlab/Simulink model of the system is set up. The parameters of the circuit are obtained.2) ESPM is used to analyze the open-loop three-phase voltage source rectifier, which verifies the feasibility and accuracy of the ESPM to analyze multi-switch rectifier system. ESPM is used in three-phase static coordinate system and the two-phase synchronous rotating coordinate system, which proves that ESPM can be used in different coordinate system.3) Double Fourier series is adopted to linearize the switching function, to pave the way for using ESPM to analyze the system.4) The duty cycle matrix equation described by state variables through mathematical model of control circuit is obtained. ESPM is used to analyze the closed-loop three-phase voltage source rectifier system. The analytical solution to state variables is obtained, which laid the foundation for future system analysis.