Control of a four-level active neutral point clamped converter with neutral point voltage balance

In this paper, a carrier-based modulation method with optimal zero-sequence signal injection has been devised to modulate the converter and regulate the DC-link neutral points' voltages of a four-level active neutral point clamped (ANPC) converter. With the proposed control strategy, the two neutral points' voltages can be well controlled with a back-to-back structure even under high modulation indices and high power factor conditions. Simulation of a back-to-back four-level ANPC configuration has validated the modulation and control strategy.