Research On PWM Technique And Snubber Circuit For Medium Voltage Large Capacity Three-Level NPC Inverter With IGCT Devices

The combination of new high voltage high power switching devices, advanced control (?)ategies and multilevel topology is an effective approach and tendency to make medium or high voltage and large capacity converters for the applications such as ASD, traction drive, FACT systems and so on. This paper focused research work on the three-level Neutral Point Clamped (NPC) inverter with IGCT devices, and investigated its optimum PWM technique, the minimum pulse elimination and dead-time compensation, the square wave control method, the IGCT simulation model and the snubber circuits for the 10MVA three-level NPC inverter.This paper analyzed and compared the SPWM and SVPWM control methods, and pointed out that the SVPWM was more suitable for the three-level NPC inverter because it had less harmonic components of the output line voltage of the inverter. Additionally, this paper optimized the space voltage vector pattern with the minimum transformation of the switching state in every PWM period, therefore, the switching frequency and the switching loss were reduced, and the life-time of the power electronic device was increased accordingly. The SVPWM with optimized the space voltage vector pattern was successfully used in 10MVA IGCT converter and 50KVAIGBT converter respectively.For low modular index of the output voltage, the output performance of the inverter is degraded for the existence of minimum pulse width and the dead-time effect. In order to improve the output performance of the inverter in these cases, a method for the elimination of the minimum pulse width based on SVPWM was provided, which could produce...