Adjustable Proportional Hybrid SVPWM Strategy for Neutral-Point-Clamped Three-Level Inverters

Neutral-point (NP)-clamped three-level inverter, which is a widely used topology of multilevel converters, suffers from the NP voltage drift as its main technical drawback. The nearest-three-virtual-vector (NTV²) modulation method can control the NP voltage balance for any load over the full range of inverter output voltage. However, compared with the nearest-three-vector (NTV) modulation method, NTV² increases the switching frequency. This paper combines NTV² with NTV, and the two methods are used alternately in a fundamental cycle. The duty-cycle coefficients of the redundant small vectors are analyzed to explore the intervals where NTV can control the NP voltage balance in a fundamental cycle. The proportional parameter, which represents the combination of the two methods in hybrid space vector pulsewidth modulation, can be selected to achieve a high-performance NP balance control and low switching frequency. The steady- and transient-state behaviors of the proposed strategy are analyzed in this paper. The experimental results verify the validity of the proposed strategy.