Elimination of reverse recovery effects associated with CoolMOS devices employing current source inverter topology

MOSFET transistors are continuously being an essential part of power electronic converters due to their low switching losses at high switching frequencies. However, the traditional power MOSFET suffers from a relatively low breakdown voltage. In the late 1990´s, the CoolMOS transistor was launched by Infineon Technologies based on the super junction technology. This device is capable of blocking a considerably higher source to drain voltage and virtually combines the low on-state resistance of the IGBT with the low switching losses of the MOSFET. The main problem associated with this device is that the reverse characteristics of its internal body diode are found to be snappier than that of the conventional MOSFET. This makes it difficult to use this device in hard switched inverters employing Voltage Source Inverter (VSI) topology. In this paper different factors affecting the reverse recovery behaviour of the internal body diode of CoolMOS power switch are studied. Moreover, a technique to eliminate high reverse recovery peak currents in CoolMOS-based inverters is proposed based on Current Source Inverter (CSI) topology accompanied with silicon carbide Schottky diode. Simulation and experimental tests are carried out to compare between the peak current and the switching losses of CoolMOS employed in both VSI and CSI topologies. The experimental results confirm the improvement achieved using CSI.