Current balancer for parallel operation of multiple MW power modules

This paper deals with current balancing techniques for parallel operation of multiple mega-watt (MW) power converter/inverter modules. A compact and reliable current balancer is needed in many high current mega-watt power conversion systems. Detailed current balancer circuit design, implementation, and validation with a 4.3-MW/3600-A inverter module are presented. To achieve the 3600-A rms inverter current rating, six phase legs have to be operated in parallel. Each phase leg employs 1200-A IGBTs to provide 600-A rms output current. Because of differences of time delay and parameter tolerance in control circuits and switching speed difference in IGBTs, direct parallel operation without any current balancing circuit may result in huge circulating current and short circuit to the IGBTs. A current balancer is indispensable in practice. To achieve compactness and light weight, a very high permeability magnetic core with no air gap is used for the current balancer. Circuit modeling, design, and experimental validation with the 4.3-MW/3600-A inverter module demonstrate in detail how to implement such current balancers. Experimental results obtained show an excellent current balancing ability with circulating current limited below 2.6% of the rated current.