Analysis of 1200V 7kW SiC-IGBT and Cascaded GaN-IGBT Hybrid Switches

Wide-bandgap (WBG) devices are replacing IGBTs in high power density applications due to their ability to significantly reduce switching power losses and enable higher switching frequencies. However, for applications above 7kW, IGBTs remain the mainstream power device due their low cost and conduction losses. To combine the benefits of both semiconductors, hybrid devices have been proposed as an alternative to power stages that use only SiC devices. This approach enables low-loss WBG devices to be switched on sooner than IGBTs, which eliminates the reverse recovery problem. This study proposes a new hybrid switch that combines an IGBT with two cascaded 600VGaN devices and compares it with other solo and hybrid switch alternatives in an attempt to find the best switching structure with the minimum power loss and cost product. The faster switching device not only reduces switching losses but also can handle a portion of the load current depending on the generated power losses and thermal resistance of the package and cooling system. In addition to the thermal limitations, the parasitic capacitance currents of IGBTs discharging on WBG devices are considered to properly select the on-state of the WBG devices. Based on these analysis, the optimal size for the hybrid switch structure and the maximum allowed conduction time of the secondary switch are determined.