Research on the Equivalent Relationship between Space Vector Modulation and Carrier Modulation of Parallel NPC-3L Inverters

To improve the power capacity of power system, several inverters are usually used in parallel. At present, global space vector modulation (SVPWM) of parallel inverters has been studied. However, when more inverters are in parallel, the implementation of SVPWM is very complicated and its calculation amount is greatly increased. Carrier-based pulse width modulation (CBPWM) is simple to operate and implement. The traditional study on the equivalent relationship between CBPWM and SVPWM in multilevel inverters is only applicable to monotonically increasing or decreasing sequences in half cycle. The SVPWM sequence of parallel NPC-3L inverter exists the condition of increasing and decreasing or two-level jump in half cycle, which has not been solved at present. Therefore, a new method is proposed to analyze the equivalent relationship between SVPWM and CBPWM modulation in parallel inverters. In new method of modulation wave decomposition, the choice of carrier is determined by switching states of vector sequence, and the number of sub-modulated waves is determined by the number of switching tubes and vector sequence of inverter. Through strict theoretical derivation and experiment, the equivalence of SVPWM sequence and CBPWM sequence of multiple arbitrary segments in parallel inverter is achieved successfully, and N parallel inverters are derived.