A comprehensive coordinated frequency control scheme for double- fed induction generator wind turbine, battery, and diesel generators in islanded microgrids

This paper proposes a comprehensive strategy for the coordinated frequency control of a low-inertia islanded microgrid (MG). The main components of the MG include a double-fed induction generator (DFIG)-based wind turbine, a battery energy storage system (BESS), and diesel synchronous generators (DGs). In the proposed control framework, effective but simple coordination between the DFIG and the BESS is developed to handle the responsibility of fast-primary frequency support (PFS) and compensate for the deficiencies of DGs in providing the fast frequency response during sudden load disturbances. To minimize the consumption of BESS energy, the proposed coordinated control utilizes the maximum support capacity of the DFIG bound by the over-deceleration (OD) and overload (OL) constraints. The coordinated BESS prevents the OD and OL issues of DFIG during the support period, and compensates the shortages of the DFIG wind system for the certain frequency support under any wind condition. It also prevents the secondary frequency drop issue during the DFIG rotor speed recovery. To return to the normal condition after fulfilling the PFS functions, the DFIG and BESS support powers are brought back to zero via a secondary frequency control (SFC) applied in the DGs. In normal conditions, to optimally manage the MG energy efficiency, the BESS exchanged power is set to zero, and the DFIG is controlled in the maximum power point tracking (MPPT) operation through an efficient algorithm. A test system with a 33% load disturbance is modeled in a detailed time-domain simulation environment to evaluate and verify the effectiveness of the proposed design methodology. The simulation results show the superiority of the proposed coordinated control strategy compared with only DFIG or only BESS control under various wind conditions.