A Simplified Synchronous Pulse-Width Modulation Method for Three-level Inverter of High-speed Train

Abstract

The synchronous Pulse-Width Modulation (PWM) is quite complex for three-level neutral point-clamped (NPC) inverter. A simple central 60° synchronous modulation method is presented in this paper for three-level NPC inverter used in the multi-mode PWM strategy. For the fundamental voltage command, the switching angle could be real-time calculated based on this modulation method with different carrier frequency ratios. The switching strategy between these modes is discussed for multi-mode PWM. According to this method, a simulation model of the drive system with three-level inverter and induction motor is built. The simulation results at asynchronous modulation, central 60° synchronous modulation and square wave area, show that the output voltage values can meet the requirements with a good symmetry even in the case of low carrier frequency ratio. The smooth switching among different modes is also accomplished with low impulse current.