A Super-Junction MOSFET-Based 99%+ Efficiency T-Type Multilevel Converter

High-efficiency (e.g. 99
^%
+) converters bring benefits in terms of lower energy consumption, reduced cooling requirements (e.g. smaller heatsinks), high power density and potential material cost saving. Super-junction MOSFETs have low on-state resistances and low switching losses, which are essential for high-efficiency operation. However, the reverse recovery behavior of their intrinsic diodes and their output capacitances make their deployment in freewheeling locations challenging. The non-linear output capacitance of SJ MOSFETs may cause significant voltage overshoot, EMI and switching loss. This paper proposes using a novel combination of snubber circuitry and intrinsic diode deactivation circuitry for a three-level T-type converter to address the non-linear capacitance and poor intrinsic diode issues. Benefits of multilevel conversion include reduced harmonic currents for a given switching frequency and filter component size, and a lower switched voltage giving a lower switching loss. Results are given for a 600-V converter supplying a 3-kVA load. Intended applications are in small machine drives and UPS systems. No forced cooling is needed and efficiency is calculated in excess of 99%. A step-by-step approach to locating snubber elements in voltage source converters is elucidated and the power device and ancillary circuit requirements for three-level NPC and T-type circuits are compared.