Cooperative Control of FFM-CSC Using Positive and Negative Trigger Angle for Offshore Wind Power Transmission

The current source converter (CSC) is a competitive solution for offshore wind grid integration. The fundamental frequency modulation-based current source converter (FFM-CSC) effectively solves the shortcomings of pulse width modulation CSC (PWM-CSC), in which DC voltage ripple is drastic and electrical stresses are high. The independent control of offshore AC voltage and frequency requires two degrees of control freedom for the converter. Nevertheless, this is not possible for the FFM-CSC since it has single control degree of freedom. To solve this problem, a positive and negative trigger angle cooperative control method is developed for CSC-HVDC connected offshore wind farms. The positive and negative trigger angles of the high and low valves are adopted to stabilize the offshore AC grid and achieve independent control of voltage amplitude and frequency. Next, by exploring the monotonicity of the offshore voltage amplitude and frequency, the laws affecting the control objectives were analyzed. Then, the AC fault characteristics are analyzed, whilst the ride-through methods are investigated accordingly. Finally, experimental prototypes and simulation models are built to confirm the designed control strategy and fault ride-through mechanism.