Hybrid Voltage Balancing Approach for Series-Connected 10 kV SiC MOSFETs for DC-AC Medium-Voltage Power Conversion Applications

This paper focuses on voltage balancing control of series-connected 10 kV SiC MOSFETs for medium-voltage dc-ac power conversion applications. Under ac load current conditions, gate delay time control is used as an example to analyze the limitation of active voltage balancing control methods: 1) active voltage balancing control has a limitation to adjust delay time accurately under a wide-range of load current; 2) the voltage unbalance of body diodes cannot be solved by active voltage balancing control for MOSFETs. For two series-connected 10 kV SiC MOSFETs realized by one half bridge module, the analysis indicates that the unbalance parasitic capacitors inside the power module is the dominant factor causing the voltage unbalance. To achieve voltage balancing control of series-connected SiC MOSFETs and body-diodes, a hybrid approach is proposed in this paper: 1) one small compensation capacitor is applied to balance the non-uniform distribution of package parasitic capacitors inside the power module; 2) close-loop gate signal turn-off time adjustment is applied to compensate the gate signal error. To verify the proposed balancing approach, a single phase pump-back test is conducted to show the improvement of voltage sharing of both MOSFETs and body-diodes.