A Carrier-Based PWM Technique for Capacitor Voltage Balancing of Single-Phase Three-Level Neutral-Point-Clamped Converters

In this paper, a pulsewidth-modulation (PWM) technique with neutral point capacitor voltage balancing in single-phase neutral-point-clamped converters is presented. The technique is based on the injection of a common-mode voltage signal into the sinusoidal modulating signals of the conventional carrier-based PWM. Although several strategies have been reported for such a problem by using the voltage signal injection, the proposed method is very simple with easy implementation. A set of equations is presented to demonstrate how the injected voltage signal introduces a dc component on the neutral-point current, which can be controlled in order to allow the capacitor voltages balancing.