High Frequency Transformer Insulation in Medium Voltage SiC enabled Air-cooled Solid-State Transformers

The high frequency transformer is a critical component of the isolated DC-DC converters in high-frequency, medium-voltage solid-state transformer. The adoption of wide band gap semiconductor allows for devices to switch at much higher frequencies. The size-reduction potential enabled by the high frequency is limited by the loss, cooling rate, and insulation level. The insulation plays an especially important role when high isolation level is needed. In this paper, the design and impact of the insulation on the performance of the high-frequency, medium-voltage transformers will be analyzed. A high-frequency transformer insulation design will be proposed, which can be used in SiC-based solid state transformers for 13.8 kV AC grid. With a shielded, partial-discharge-free design, polymer/inorganic insulation system, basic insulation level (BIL) of ±95 kV have been demonstrated and the effective thermal conductivity at least 0.8 W/m-K, which is about 2-3 times higher than polymer materials capable of reaching similar BIL levels.