A SVPWM Method With Reduced Switching Frequency Suitable for High Power Three-level NPC Rectifiers

Abstract

The high power three-level NPC rectifier should reduce the switching frequency as much as possible under the premise of satisfying the current harmonic performance of the grid side and the stability of the DC neutral-point potential. Under the even carrier ratio, the existing SVPWM method that begins with the same type of small vector in each 60-degree sector has a lower switching frequency but a higher even harmonics content, and is not conducive to neutral-point potential balancing. However, P type and N type small vector selected alternatively as starting vector in different sectors has a lower even harmonics content and neutral-point potential self-balancing capability but a higher switching frequency. To address this deficiency, this paper presents a new SVPWM method, which chooses P type small vector as starting vector in the corresponding half fundamental period of three phases, and N type small vector as starting vector in the other half period, thus obtaining three different switching sequences. The three-phase average switching frequency is reduced and the even harmonics are eliminated by cycling three switching sequences. Established a three-level NPC rectifier experimental platform and the experimental results verify the effectiveness of this new SVPWM method.