Vector-Controlled Voltage-Source-Converter-Based Transmission Under Grid Disturbances

Voltage-source converter (VSC)-based transmission systems have attractive potential features in terms of power flow control and stability of the network. Although relatively low switching frequency operation of high-power converters (9-15 times the line frequency) is desirable, it makes them sensitive to power network imbalances when they may be needed the most. This paper specifically proposes a control structure to improve the performance of high-power vector-controlled back-to-back VSC systems for conventional and emerging utility applications. The main improvement is to suppress the possible dc-link voltage fluctuations under power line faults and unbalanced conditions. The proposed controller structure is designed based on regulating the converter system's states locally in dq synchronous reference frame without sequence components extraction or resonant notch compensator. RTDS results verify the validity of the proposed control architecture during normal and unbalanced power system conditions.