A Practical Approach to Eliminating DC Magnetic Flux from the Series Transformer of a Dynamic Voltage Restorer

This paper proposes a control method for eliminating dc magnetic flux from the series transformer of a DVR. The method is characterized by intentionally injecting no compensating voltage during a one-sixth line cycle (=3.3 ms at 50 Hz). The control sequence is independent of an initial phase angle of a voltage sag, thus requiring no flux detection. The period, during which no compensating voltage is injected, is one-third as short as that of an existing method. This paper verifies the effectiveness and viability of the proposed method, using a 200-V, 5-kW laboratory system. The proposed method brings no dc magnetic flux to the series transformer.