A novel SVPWM overmodulation technique for three-level NPC VSI

This paper proposes a simple space vector pulse width modulation (SVPWM) scheme for operating a three-phase three-level neutral-point clamped (NPC) voltage source inverter (VSI) at higher modulation indexes, including overmodulation region. Generally, the overmodulation techniques for SVPWM inverter need to store lots of data in the controller beforehand, which produces a huge memory while the control resolution is not perfect. Based on the study of existing overmodulation techniques published in literatures, a novel two-mode strategy and single-mode feed-forward carrier-based simplified SVPWM overmodulation algorithms are proposed which can manage smooth transition from the linear control range to six-step operation. The proposed overmodulation techniques make continuous control of the output voltage up to the maximum voltage with a smooth linear transition characteristics and minimum distortions. The strategy is simple and suitable for practical digital implementation. Simulation results demonstrate the effectiveness of the proposed SVPWM overmodulation algorithm.