Research And Design Strategy Of Three-Level Rectifier Based On Direct Current Control

With the development of power electronics and the continuously improved performance of power semiconductor, the technology of power elecreonic converter device has been rapidly promoted. Three-level neutral-point-clamped PWM rectifier has been widely applied in industry because it can achieve a large-capacity, high-voltage power conversion, has a good sinusoidal input current, and fast dynamic response and adjustable DC voltage and power fantor of the frid side. PWM rectifier and PWM inverter can constitute a double-PWM converter, which can achieve the four-quadrant operation of the motor.The main subject of this thesis is the three-level neutral point clamped PWM rectifier on which we get the derivation of the mathematical model in three-phase stationary coordinate system. The mathematical model in three-phase stationary coordinate system and synchronized rotating coordinate system have been reduced by introducing the concept of coordinate transformation, and in that process, the design of PLL control system with a feed-forward control, which is used to obtain voltage phase angle, has been given.Three-level PWM modulation algorithm has always been the research focus on three-level converter. In the frist part of this thesis, the writer discussed the three-level rectifier and the impacts of every vector on it in condition of fixed alternating current direction, and then developed a simplified algorithm of the three-level SVPWM in the g-h coordinate which had been given under the idea of previous scholars.This thesis chooses outer voltage and inner current double closed loop control structure.In fact, this method is used in most of the practical rectifiers. The main features of the double closed loop control are explicit physical meaning, simple control structures and good control performance. On basis of the discusses in the theory of direct current control system and the optimal engineering parameter design method, this thesis comes up with the design procedure and the method of three-level rectifier controller parameters.Finally, using the Matlab/Simulink and Prototype testing to conduct the system simulation in order to study the performance of three-level rectifier at rated load and power feedback. And the results of the simulation testified the validity and feasibility of the control system which includes phase-locked loop, SVPWM algorithm and double closed loop rectifier control system.