PWM Method of a Three-Level Neutral-Point-Clamped Converter under Neutral Point Imbalance Condition

Imbalance of the neutral-point potential in three-level neutral-point-clamped converter may appear in some operating conditions. This paper analyzes the voltage distortion caused by the imbalance of the neutral point potential in a three-level neutral-point-clamped converter, and also describes the PWM method to generate the low-frequency harmonics-free output voltages even under the imbalanced condition. Furthermore, the proposed PWM method has the advantages in terms of the high-frequency harmonics, since three voltage vectors near to the reference vector are used. Simulation and experimental results verify the feasibility of the proposed method.