Study on Secondary Non-Differential Frequency Modulation Control Strategy of VSG in Islanding Mode

The microgrid under VSG control is conducive to the security and stability of the microgrid system. However, it still belongs to the primary regulation of frequency, and the microgrid in islanding mode has the problem that the frequency cannot be stabilised at the rated value after the load change. To address this problem, in order to eliminate the steady state error caused by the primary frequency regulation structure of the traditional VSG control technique and keep the load-induced frequency offset near the rated value, this paper proposes a fractional-order self-resilient-based secondary frequency regulation control strategy. Firstly, a three-phase circuit topology based on VSG is established, and the mechanism of primary frequency regulation is analysed with it as the research object. Then, the proposed fractional-order self-resilient control algorithm is applied to the rotor equations of the active frequency regulation characteristics of the VSG, so as to achieve the quadratic non-differential regulation of the frequency, and to eliminate the frequency error caused by frequency fluctuation of the virtual synchronous generator in the islanding mode. Finally, for the case of sudden load change, the VSG-based islanded microgrid model is constructed in Matlab/Simulink and compared with other control strategies, which verifies the effectiveness of the control strategy proposed in this paper. The control strategy in this paper can effectively eliminate the steady state error caused by the primary frequency modulation and improve the response speed.