A Carrier-Based Approach for Overmodulation of Three-Level Neutral-Point-Clamped Inverter with Zero Neutral-Point Current

In a voltage source inverter, overmodulation is required to extend the range of operation and enhance the dc-link voltage utilization. A carrier-based implementation of a modulation strategy for the three-level neutral-point-clamped inverter is proposed for the overmodulation region. The modulation strategy ensures zero average neutral-point current in a switching period. A newly proposed boundary compression is used to regulate the dc-link voltage at all operating points. A description of the algorithm to implement the modulation strategy is also presented. The main advantage of the proposed algorithm is its simplicity. The reference signals for the PWM can be calculated using maximum six steps and does not require knowledge of the reference vector angle. The modulation strategy has been implemented in a three-level neutral-point-clamped inverter, and experimental results are presented.