Voltage-Balance Compensator for a Carrier-Based Modulation in the Neutral-Point-Clamped Converter

This paper presents an optimal voltage-balancing compensator for a specific modulation technique applied to a neutral-point-clamped converter. The technique uses two modulation signals per phase, and it is called double-signal pulsewidth modulation. It completely eliminates low-frequency oscillations in the neutral-point voltage. However, it does not provide natural voltage balancing; therefore, a compensation loop is required. The proposed control generates a feedback compensation signal that correctly modifies the three-phase modulation signals. The optimal compensation signal is calculated by a dynamic limiter according to the intrinsic limitations of the system related to the variability range of the modulation signals. It significantly improves the voltage balancing under all operating conditions of the converter. In addition, this compensation strategy does not increase the switching frequencies of the power devices. The algorithm is tested and verified using both simulation and experimentation.