Improvement of DC Voltage Control Dynamics with Bipolar DC Circuits Using a Zigzag Transformer

This paper presents a voltage source converter employing a zigzag transformer for improving bipolar DC voltage control dynamics. The proposed circuit provides a bidirectional power flow by configuring two converter modules in parallel and sharing the neutral point of a zigzag transformer. The zigzag transformer provides low zero-squence impedance which is in the same range of the leakage components of the transformer. By utilizing this characteristics of the zigzag transformer, the converter can independently control each pole voltage in a bipolar structure and also has a fast dynamic response for controlling DC-link voltages. Therefore, it is advantageous for dealing with different loads on each pole and DC-side fault. The feasibliy of the proposed circuit and its operations is verified by both the simulation and the 10kVA experimental prototype.