Design of Insulation System in High-Frequency Auxiliary Power Supply for Medium Voltage Applications

The auxiliary power supply (APS) for medium voltage (MV) SiC based converter systems requires to achieve high insulation capability, low common-mode coupling capacitance (C-cm) in a very compact form-factor. However, these features are difficult to realize at the same time. To achieve a low C-cm value and small size, a high frequency GaN based APS system with single-turn transformer operating at Megahertz is presented. Eight different insulation system designs with different electric-field (E-field) stress control methods are presented with either air or silicone as the insulation materials. 3D E-field shielding, as one important stress-control technique, is introduced. Each design approach is evaluated based on the insulation capability, manufacturability and C-cm. Considering the fabrication process and overall performance, two designs using air and silicones as insulation materials are selected and evaluated by experiments. The partial-discharge inception voltage (PDIV) level for the air-insulation solution reach 6 kV AC with 1.2 pF coupling capacitance. The silicones-insulation solution reaches up to 16 kV PDIV level with 3.9 pF coupling capacitance.