Soft Precharging Method for Four-Level Hybrid-Clamped Converter
A four-level hybrid clamped converter(4L-HCC) is one of the next-generation multilevel converters for medium voltage motor drives without transformers. However, dc-link and flying capacitors in 4L-HCCs must be charged to their nominal voltage. Due to the distinctive structure of capacitors in a 4L-HCC, few papers have made an explicit solution on the safe start-up process without inducing large inrush currents. This paper presents an effective soft precharging method using the selected switching states. A straightforward algorithm is developed to control the switching states to build different precharging circuits properly. All capacitors are precharged through internal elements rapidly with suppressed and controllable charging current. The effectiveness of the proposed method is confirmed with the simulation.