Research On PWM Control Methods Of Three-Level Neutral-Point-Clamped Inverter

The research on three-level Neutral Pointed Clamped (NPC) inverter has been the hot spot in the area of power electronics technology and electric power drive for its advantages of high switching frequency, low voltage for each switch device, and the good export waves. The Pulse Width Modulation (PWM) control method is one of the key techniques on three-level inverter. This dissertation researched on carrier disposition and space vector PWM control method of three-level NPC inverter. The main contents of this paper are as follows:1. The principles of three-level NPC inverter and PWM control methods are introduced. The advantages and disadvantages of carrier modulation, space vector and virtual space vector control method are analyzed.2. The output voltage equation of the three-level NPC inverter with carrier disposition PWM control method is derived by means of Dual Fourier Transforms and Bessel theorem. Simulation and experimental results are proposed to verify the exactness of theoretic analysis.3. It is discussed that space vector PWM scheme is limited to balance the neutral-point potential. A hybrid modulation method based on the traditional space vector and virtual space vector is proposed for the neutral-point balancing in the three-level NPC inverter, and proved by MatLab / Simulink simulation and experiment.This dissertation researched on the methods of carrier disposition PWM and the neutral-point potential balancing of three-level NPC. The results of simulation and experiment show that the performance of three-level NPC inverter is improved, which provide theoretical foundation for engineering application.