Enhanced Grid-Forming Control Strategy for DFIG Participating in Primary Frequency Regulation Based on Double-Layer MPC in Microgrid

To enhance the frequency support capability of the doubly fed induction generator (DFIG) system in microgrid while improving the control effect, a double-layer model predictive control (MPC)-based grid-forming control of DFIG (GFM-DFIG) is proposed for primary frequency regulation (PFR). Firstly, a top-layer MPC is designed to enhance the PFR capability by optimizing control coefficients and power commands of the virtual synchronous generator (VSG) controller. This layer utilizes the predicted frequency deterioration trend as reference to adaptively regulate control coefficients in both grid-connected and islanded mode. Then, the quadratic optimization algorithm is employed to calculate the additional power that can suppress frequency degradation in modifying power commands combined with the system frequency response (SFR) model. Meanwhile, a damping ratio constraint mechanism for VSG controller is designed to avoid the impacts of coefficient adjustment. Secondly, a finite-set min-beat tracking-based bottom layer MPC combined with a VSG inner electrical circuit reconstruction is designed to improve the control effect and dynamic response of DFIG's stator voltage and current. The top-layer and bottom-layer together can enhance the overall control effect and frequency support capability of the DFIG system. Finally, the effectiveness and advantages of the proposed GFM-DFIG is displayed in a simulation system.