Capacitor Voltage Ripple Reduction of A 4-Level Hybrid Clamped Converter Using Switching State Redundancy for Medium-Voltage Drive

A four-level Hybrid Clamped Converter (4L-HCC) is a novel promising DC/AC multilevel converter for high-efficiency medium-voltage drives. This paper presents a new control method of the 4L-HCC using the switching state redundancy to reduce the DC-link capacitor voltage ripples at low frequencies (<=30 Hz). The new switching state selection algorithm and flying capacitor balancing method are introduced and analyzed. Both of a 3.6 kV 1MW 4L-HCC simulation model and a SiC-based 4L-HCC prototype is established to verify the proposed method. Simulation and experimental result shows that the maximum DC-link capacitor ripple can be reduced effectively from over 50% to less than 5% at low frequencies with the new method. Meanwhile, load voltage and current distortion caused by the excessive capacitor ripple is also mitigated significantly.