The Study Of Three-level PWM Rectifier

With the rapid development of modern power electronics technology, multilevel converter has become a hot research topic of power electronics technology in high-voltage and high-power field, because of the advantages of its little voltage stress afford by power device, high equivalent switch frequency, low switching loss and good output waveform, and has been widely used in medium and high voltage frequency conversion speed regulation system, AC and DC power conversion system, new energy power generation system, power quality analysis and other fields.This paper takes the most widely used diode-clamped three-level PWM rectifier as the research object, describes its topology and operating principle in the first, and then establishes its mathematical model of the three phase stationary coordinate system and the synchronous rotating coordinate system. The mathematical model provides a theoretical basis for the design of the control system. The voltage and current double closed-loop control strategy based on direct current control for three-level PWM rectifier is described in detail in this paper, and this control method is simple and excellent. According to the characteristics of DSP control chip, an improved carrier modulation algorithm is adopted, which is simple to implement in DSP. Neutral-point balance problem is an inherent problem of diode-clamped three-level PWM rectifier. In order to effectively restrain the fluctuation of neutral point potential, this paper adopts neutral point potential balancing method based on zero-sequence voltage injection.The control strategy, modulation algorithm and neutral point potential balancing method of three-level PWM rectifier are all simulated by Matlab/Simulink, and results of simulation verify the correctness and feasibility of these control methods in theory. On the basis of theoretical analysis and simulation verification, experimental platform of diode-clamped three-level PWM rectifier based on TMS320F2812 has been constructed, and the hardware circuit and software program of the experimental prototype are designed. Experimental results verify the feasibility and effectiveness of the designed experimental prototype, which shows that the prototype has achieved the design requirements.