Development of Solid-state Transformer for 6.6-kV Single-phase Grid with Automatically Balanced Capacitor Voltage

抄録

This paper proposes a solid-state transformer (SST) for a 6.6-kV single-phase grid using multiple cells, which have a power factor correction stage and an isolated DC-DC converter. In the SST, the capacitor voltage of each cell is automatically balanced on the primary side owing to the use of a resonant DC-DC converter. The main focus of this study involves calculating the fundamental loss of the proposed topology assuming a 6.6-kV single-phase grid. The calculations show that the maximum efficiency of the full model of the SST reaches 99%. The scaled model with an input voltage of 1320V, which is 1/5th that of the full model, is tested to confirm the calculation of the power loss and the fundamental operation. The results confirms that the input current is sinusoidal and the total harmonic distortion is 4.3%. Moreover, the automatic capacitor voltage balancing capability is tested. The capacitor voltage on each cell is automatically balanced without any control. Further, the bidirectional operation is verified. Finally, the power loss of the proposed topology is separated into values for each conversion part. The power loss shows good agreement with the calculation with an error of less than 5%.