Wind power plant emergency power reduction control method considering ultimate unloading capacity of draught fan

The invention discloses a wind power plant emergency power reduction control method considering the ultimate unloading capacity of a fan. The method comprises the following steps: firstly, analyzing a rapid active power control method of a double-fed fan containing a direct current unloading circuit; the limit unloading capacity of the doubly-fed wind turbine generator containing the direct-current unloading circuit is analyzed by combining the capacity constraint of the converter and the mechanical constraint of the fan, and the controllable domain of the emergency power reduction of the fan is determined; station control strategies suitable for different emergency power reduction control instructions are provided, and comprise a regulation-to-switching strategy and a regulation-to-switching strategy. According to the method disclosed by the invention, the emergency power reduction controllable domain of the wind turbine generator is defined, an active power control strategy of replacing switching by regulat