A Frequency Response Control Strategy for Medium Voltage Wind Turbines With Multiple Rotors

In a medium voltage wind turbine with multiple rotors, multiple rotors are used for the wind energy capture and directly drive permanent magnet synchronous generators (PMSGs). The medium voltage grid is coupled with a cascaded H-bridge (CHB) inverter. Advantages, such as more wind energy capture, higher reliability, and easy extension to higher power and grid connection voltage ratings, can be achieved. In this article, a novel frequency response control strategy for the wind turbine is proposed. Under the normal operation condition, all rotors are controlled individually to extract maximum wind energy. During the deloading operation, the coordinated control on all rotors is executed to obtain the required power reserve. In case the grid frequency sudden dip occurs, the power reserve is released quickly to provide the wind turbine frequency response. A novel control scheme to maintain the utmost transmitted power equilibrium between three phases, between modules in one phase, and three-phase grid connection current equilibrium at both deloading and frequency response modes is proposed, leading to the H-bridge inverter overmodulation risk reduction and grid connection current quality improvement. Simulation and experimental results have validated the proposed frequency response control strategy for the medium voltage wind turbine with multiple rotors.