Control Strategies for Wind Farm Integration by Hybrid HVDC Transmission

Wind farm integration by voltage source converter can mitigate negative influence by fluctuating output wind power. Besides, voltage source converter can provide the wind farm with necessary voltage support by controlling the AC voltage for normal operation of wind farm. Wind power integration by high voltage direct current transmission can be further researched, which includes islanded wind farm integration and bundled wind-thermal power integration. In a comparison among voltage source converters, hybrid modular multilevel converter is selected at sending end of the system and is connected with the wind farm. Line commutated converter is used at the receiving end with a comprehensive consideration of economy and technology. The wind farm integration by hybrid high voltage direct current system has obvious advantages when the receiving end is strong. Structure and operation principle of the system are introduced, and feasible control strategies of converters are devised. The hybrid system needs cooperation of voltage source converter and line commutated converter, especially during the startup procedure. A three-stage startup control strategy of the system is designed and verified by simulation. The startup process is smooth and stable, and after that, the system can track respective setting values accurately. Response of the system to fluctuating wind speed is studied. Output power of the wind farm changes with the wind speed, and power of the system will change accordingly. The system can operate normally under fluctuating wind speed.