Optimised Operations and Modulation Scheme for Simplified Seven‐Level Hybrid‐Clamped Converters

ABSTRACT Seven‐level hybrid‐clamped (7L‐HC) converters are new and promising candidates for high‐power medium‐voltage applications. Their configurations can be simplified further by reducing one of the two flying capacitors per phase. However, such simplification significantly reduces the available redundant states, making it hard for dc‐link capacitors balancing and operation optimisation. In this article, the optimised operations and a low switching frequency modulation scheme are proposed for S7L‐HC converters. Various new switching states are explored to help reduce the switching frequency, facilitate the balance of switching frequency distributions and reduction of the dynamic voltage stress on switches. The proposed modulation based on an improved selective harmonic elimination pulse width modulation (PWM) can achieve voltage balancing for all capacitors under a low switching frequency. Simulation and experimental results verify the proposed operations and modulation scheme.