Multiphase-Leg Coupling Current Balancer for Parallel Operation of Multiple MW Power Modules

Parallel operation of multiphase bridge legs can reach high current in application to megawatt (MW) power conversion systems. However, direct parallel operation without any current balancing circuit may result in huge circulating current and short circuit because of differences of time delay and parameter tolerance in control circuits and switching speed difference in IGBTs. This paper proposes a multiphase coupling current balancing technique for parallel operation of multiphase legs to achieve multiple MW power converter/inverter modules. Multiphase coupling current balancer (CB) circuit modeling, analysis, and design demonstrate in detail how to implement such CBs. A 4.3-MW/3600-A inverter module is prototyped to illustrate the proposed scheme´s implementation and validation. Six phase legs are operated in parallel to achieve the 3600-A rms inverter current rating. Each phase leg employs 1200-A IGBTs to provide 600-A rms output current. To achieve compactness and light weight, a very high permeability magnetic core with no air gap is used for the CB. Simulation and experimental results verify the excellent current balancing ability in parallel operation of multiple MW power modules.