Research And Design Of Three-level PWM Rectifier Based On A New Control Strategy

With the development of power electronics, power semiconductor switching devices continuously improve performance, and promote the rapid development of the technology of power electronic converter device. Three-level neutral-point-clamped PWM rectifier has been widely studied and applied in industry because it can achieve a large-capacity, high-voltage power conversion, and has a good sinusoidal input current, fast dynamic response, and DC voltage and power factor of the grid side can be adjusted. PWM rectifier and PWM inverter can constitute a double-PWM converter, which can make the motor achieve four-quadrant operation, and energy can flow in both directions.According to the relations between topologies of the three-level PWM rectifier in different switching instants, the mathematic models in abc three-phase stator coordinate and in dq two-phase rotating coordinate are established, which provide the theoretical basis for the study of control strategy. Based on derivation of the mathematical model, the steady-state solutions are calculated in this paper, which are the control value of the system in the steady-state conditions, and lay the theoretical foundation for experiments of the control system.Zero cross detection circuit is omitted due to the software PLL designed in this paper. By using a SVPWM strategy in60°coordinate, the algorithm is simplified to make the system easier to digital implementation. The three-level rectifier voltage and current double closed loop control theory is studied, and the parameters design of current regulator and voltage regulator is carried out in this paper.The conventional voltage oriented vector control system of PWM rectifier uses lots of sensors, which not only increases the cost of system, but also has the problem of additional circuits and tesingt error. The virtual flux oriented control strategy is applied in three-level PWM rectifier in this paper. Then a novel decoupling control strategy for three-level PWM rectifier without line voltage sensors is proposed, which combins virtual flux oriented control with traditional double closed loop control theory based on the decoupling d-q frame. A modified virtual grid flux observer and a grid voltage estimation method are presented, which solves the DC drift problem caused by a wrong initial value selecting of integer in virtual flux oriented vector control for PWM rectifier.The system model of virtual flux-oriented three-level PWM rectifier is established in the MATLAB/Simulink environment, and a lot of simulation experiments are carried out in this paper. The simulation results can verify the correctness and the effectiveness of the proposed design. This can provide a theoretical basis for the design of the actual circuit.According to the work present above, three-level PWM rectifier experiment prototype controlled by TMS320F28335DSP is designed. At last, the design of the hardware circuit and software of the whole control system are present in this paper. The results of experiments indicate that the proposed control system of PWM rectifier can work stably and has good dynamic performance.