Insulation Design on High-Frequency Transformer for Solid-State Transformer

A Solid-state transformer (SST) directly reduces medium voltage to low voltage (e.g. 1.1 kV) with minimized power conversion stages. High-frequency transformer plays an important role in the DC/DC module of the SST from insulation and power density points of view. Thanks to wide bandgap semiconductors, the switching frequency can be pushed higher to shrink transformer volume. However, for safety reasons, insulation also has a significant impact on volume, and thus limits the power density majorly. In this paper, compact insulation designs are proposed to achieve high power density while meeting the insulation requirement of overvoltage and partial discharge. The manufacturing process and some manufacturing considerations affecting the partial discharge level are also listed. The high-frequency transformer designed for 13.2 kV input voltage systems is evaluated with partial discharge inception voltage (PDIV) level over AC 17.2 kVrms and Applied voltage test over 34kVrms.