Three types of current imbalance between IGBT modules of over a 1 MW inverter were found, which composed of the parallel-connected IGBT modules in double-pulse switching test. The mechanisms of these current imbalances were investigated by circuit analysis with newly developed circuit models considering the bus bar topology of the inverter. The analysis results indicated that the current imbalance was strongly affected by the coupling coefficient of the inductances between the converter or filter capacitor and the IGBTs. In order to suppress the current imbalance, a new bus bar topology with uniform coupling coefficients was developed by using circuit simulation considering a bus-bar equivalent circuit model calculated by electromagnetic-field analysis.
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