Virtual Synchronization Control Strategy of Direct Drive Permanent Magnet Wind Turbine under Load Shedding Operation Mode In terms of the problems of insufficient interia supporting capacity of the system and loss of stable performance of grid frequency caused by increased wind power gridconnected capacity, virtual synchronous generator technology to simulate the operation characteristics of synchronous generator has become an effective solution. In this paper, the directdrive permanent magnet wind turbine, one of the mainstream wind farm models, is taken as the research object, and a virtual synchronous control strategy is introduced into the gridconnected control to improve the equivalent inertia of the directdrive permanent magnet wind turbine and make it deliver smooth power to the grid. The spare capacity is provided by the coordinated control of overspeed and pitch change of the unit itself, and the active power output is increased through the inertia response control link of the virtual synchronous generator, thus improving the primary frequency modulation capability of the system. The simulation results show that the coordinated control strategy proposed in this paper can make full use of the load shedding operation of wind turbines and the virtual synchronous generator technology andeffectively improve the frequency stability and intertia support effect of the gridconnected system, contributing to the safe and stable operation of the power system.

Active and Frequency Control Strategy of Improved Droop Control in Islanded Microgrid The traditional droop control will reduce the frequency of the system, and will seriously affect the power quality in an independent microgrid consisting of a variety of distributed power sources. However, if the frequency recovery time is too long, the frequency does not return to the power frequency and will drop seriously and deviate from the rated value when the next load disturbance occurs. In order to solve these problems, this paper proposes a fuzzy PI active and frequency control strategy based on the traditional droop control. The degree of frequency offset is taken as the reference amount, and its control parameters are dynamically adjusted to quickly restore the frequency to the stable value. In addition, the first function term of the power and droop coefficient is established to replace the fixed droop coefficient to prevent the frequency from crossing the boundary. Finally, the effectiveness of the proposed strategy is verified by MatlabSimulink simulation. The improved control strategy can make the system frequency stable in power frequency and improve the dynamic performance of the system.