During power generation, wind turbine generators must ensure a constant output electricity frequency. This is essential for both grid-connected wind power generation and wind-solar hybrid power generation. To maintain a constant frequency in wind power, one method is to ensure the generator operates at a constant speed, i.e., constant speed and frequency operation. Since the generator is driven by the wind turbine through a transmission device, this method requires the wind turbine's speed to be constant, which can affect the conversion efficiency of wind energy. Another method is to adjust the generator's speed with the wind speed, while using other means to ensure the constant frequency of the output electricity, i.e., variable speed and constant frequency operation.