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A Novel Carrier-Overlapped PWM Method for Four-Level Neutral-Point Clamped Converters

Neutral-point clamped (NPC) multilevel converters with more than three voltage levels are hard to balance the dc-link capacitor voltages, which limits their application in the industry. In order to solve the neutral-point potential balancing problem of four-level NPC converters, a novel carrier-overlapped pulsewidth modulation (PWM) method is proposed in this letter, which satisfies the volt-second balance principle and can achieve the natural voltage balance of three dc-link capacitors under ideal and steady states. Experimental results are presented to confirm the validity of this PWM method.