A dynamic model and control strategy for the voltage source converter based HVDC transmission system under fault AC conditions

This paper proposes a dynamic model and control strategy for the voltage source converter based high voltage direct current transmission (VSC-HVDC) under fault AC conditions. After simplify the equivalent circuit of the VSC transmission system, a VSC-HVDC electromagnetic transient model which considering the loss of the phase reactors has been built. To restrain the DC voltage double line-frequency ripple that induced additional stresses of the VSC valves and DC capacitor, both positive-sequence and negative-sequence currents should be controlled simultaneously. Based on the inner loop dual current control and outer loop DC voltage control, a new control strategy is introduced. We demonstrate the effectiveness of the proposed control scheme by using computer simulation, and verify the validity of the mathematical model.