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Insulation Design of Wireless Auxiliary Power Supply for Medium Voltage Converters

FEA simulation result
Fig. 1. FEA simulation result of maximum E-field intensity in air with different geometrical parameters of coils.
  Auxiliary power supply (APS) that provides reliable power and voltage for gate drivers, controllers, and sensors is a critical component in medium voltage (MV) converter. Compared to being fed from the power-cell dc-link, APS fed from an external earthed system has its own benefits. However, with the power-cell number scaled up, the insulation design of the externally-fed APS becomes a significant challenge. Partial discharge (PD) can cause accumulative irreversible damages of insulation, which further lead to auxiliary power circuit fault and eventually cascaded failures of the whole converter system. Therefore, a PD-free APS system ensuring the reliability of MV converter is required. Among different technologies for building APS, wireless power transfer (WPT) becomes an attractive method because of its mechanical design flexibility and inborn insulation capability. In this paper, in order to design a PD-free WPT converter, insulation design criterion and electric field distribution under different coil geometries are analyzed, compared, and tested. Subsequently, a comprehensive insulation design including the influence of ferrite shielding layer is shown. Finally, an optimized WPT prototype with 120 W output power, 92.78 % full-power efficiency, 2.76 pF isolation capacitance, and 27 kV insulation capability is validated experimentally. Fig. 1 shows the FEA simulation resulf of the maximum E-field intesnsity of the coil pair with different outer radius ro, distance between two coil d, and coil winding thickness rw. Fig. 2 shows the test bed designed to verify the insulation design of the coil pair.
Test bed
Fig. 2. Test bed for insulation verification.

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