Grid-tied control of variable speed wind turbines for enhanced inertial support

Despite being inherently non-responsive to system frequency events, variable speed wind turbines (VSWTs) can be configured to emulate inertial responses by adding a supplementary control loop to the torque control scheme of the turbine. In such control systems, typically, the change in power output to synthesise the inertial response is scaled with reference to the rate of change of frequency (ROCOF) and/or the deviation of frequency from a set level. This paper presents an alternative method of scaling the inertial response by tying the rotor speed to the grid frequency. Considering that the link between the grid frequency and the rotor speed is the cause for inertial responses by conventional synchronous generators, the responses associated with the proposed method is expected to resemble real inertia more closely than with other methods currently being employed to emulate inertia.