DAB Based DC-DC High Frequency Link PET for Interconnecting MVDC-LVDC Grids

Abstract

This paper proposes dual active bridge (DAB) based high frequency power electronic transformer (PET) for interconnecting medium voltage dc (MVDC) and low voltage dc (LVDC) grids for dc power distribution. The above proposed concept works on dual active phase shift principle and square wave HF modulation technique for bidirectional power transfer. Compared to the traditional dc transformer scheme, The proposed power electronic transformer (PET) can disconnect from LVDC distribution grid effectively as a dc breaker when a short circuit fault occurs in the distribution grid. The isolated DC-DC PET topology with a wide range of voltage conversion ratio is useful for High Voltage DC tapping. The DAB based on switched capacitor is connected to the medium voltage DC side and acts as an inverter. The proposed topology has the ability to transfer higher power, and lower circulating power, lower high frequency link voltage, and RMS current and peak values with the same transmission power in the MVDC side. This paper analyzes the topology, voltage and power characterization, control strategy in detail. Increase in the intermediate AC frequency will reduce the size of the transformer and other passive elements significantly in the circuit. The theoretical analysis is supported by MATLAB simulation.