Virtual inertia optimisation control of DFIG and assessment of equivalent inertia time constant of power grid

Due to decoupling between mechanical part and electrical part of doubly fed induction generator (DFIG), the DFIG has no natural frequency response capability, which results in decreasing of total rotary inertia of power grid, and the frequency stability of power grid will face larger challenges. This study proposes an assessment method of equivalent inertia time constant, further gives the assessment value of equivalent inertia time constant of DFIG. Then, a virtual inertia optimisation control of DFIG using rotor current direct control based on status assessment value is proposed, which includes conventional function, status assessment and additional virtual inertia control. The assessment values of equivalent inertia time constant of wind farms, synchronous generator and power grid connected with multi-type generators are calculated, which are related to penetration of wind power and control strategies. The simulation results verify the efficacious of the proposed virtual inertia optimisation control and the accuracy of assessment method of equivalent inertia time constant, and the frequency stability of power grid is improved in the condition of different active power of wind farms and penetration of wind power.