Analysis of Carrier Overlap Modulation and Space Vector Modulation Equivalence in NPC Inverters

Carrier overlapping pulsewidth modulation (COPWM) is proposed to address the level degradation issue in carrier-based pulsewidth modulation (CBPWM) at low modulation index. Due to its unique frequency multiplication band, COPWM has widespread application in industrial scenarios where long-term operation at low modulation index is required. Similarly, space vector pulsewidth modulation (SVPWM) exhibits more switching states at low modulation index, and the output performance can be enhanced by increasing the number of modulation segments. Numerous literature studies have analyzed the equivalence relationship between CBPWM and SVPWM methods. However, there is no research on the equivalence relationship between COPWM and SVPWM methods. Investigating the relationship between the two methods is beneficial for us to draw upon the strengths of both modulation techniques and develop more effective modulation methods. This article analyzes the relationship between COPWM and SVPWM methods under different modulation index and overlap ratios. It is concluded that as the modulation index and overlap ratio increase, the synthesis method of the reference vector in the equivalent SVPWM method for the COPWM method tends to become irregular. Subsequently, by adjusting the active time of redundant states of space vectors, the SVPWM method achieves output equivalence to the COPWM method. Finally, experimental results confirm the correctness and effectiveness of the proposed approach.