Modified stepwise inertial control using the mechanical input and electrical output curves of a doubly fed induction generator

A stepwise inertial control (SIC) scheme of a wind turbine generator (WTG) rapidly increases its constant output to support the frequency control if a large disturbance such as a generator trip occurs in a power grid. This helps to significantly arrest the frequency nadir, but causes significant reduction in the kinetic energy (KE) of a WTG. Thus, the output of a WTG should be rapidly reduced to restore the rotor speed. This might cause a second frequency dip. This paper presents a modified SIC scheme of a doubly fed induction generator (DFIG) to prevent a second frequency dip. The modified SIC scheme generates a reference signal that consists of the constant reference and the reference for maximum power point tracking operation. The former is analytically determined by considering the mechanical input power and electrical output power curves of a DFIG. The output of the proposed SIC scheme decreases with the KE of the DFIG and thus no second frequency dip occurs. The performance of the proposed SIC is investigated for a 100MW aggregated DFIG wind power plant using an EMTP-RV simulator. The results clearly show that the proposed SIC scheme significantly increases the frequency nadir without causing a second frequency dip.