Power smoothing of the DFIG wind turbine using a small energy storage device

The active power produced by wind generators is subject to fluctuations due to the stochastic nature of wind. Depending upon the size of the wind farm and the network to which it is connected, active power variations may result in frequency deviations. This can trigger frequency protection devices and lead to undesirable unit trippings. This paper proposes the addition of a small supercapacitor at the DC link in the power converted of a doubly fed induction generator (DFIG). Based on this, a new method is proposed which simultaneously balances the MPPT as well as output power smoothing objectives. Frequency variations in the range of 0.1-1 Hz are investigated considering variations in wind speed, tower shadow and wind shear effects. Numerical simulations are carried out in PSCAD/EMTDC to illustrate the effectiveness of the proposed method in limiting frequency deviations.