Participation of wind power plants in power system stability

The integration of large amounts of wind power in power systems coupled with the increasing replacement of large conventional synchronous generators by wind power plants (WPPs) presents a considerable impact on power system stability. This is partly because most WPPs, particularly variable speed wind turbine (VSWT) types, are connected to the network via power converters which decouples their output power from the grid frequency, and this results in considerable loss of system inertia. Also, VSWTs are in general operated at the maximum power point tracking, which makes them unable to increase their output power beyond the maximum power level for long-term frequency support. For this reason, it is important to develop control techniques that enable WPPs to participate in power system stability improvement. In literature, several studies have been reported on the frequency control provision of a wind turbines (WT), mainly classified into two categories: inertial response (IR) and primary frequency response (PFR). This work investigates the IR and PFR capabilities of VSWTs; the control schemes are presented in detail and the required energy buffers also discussed. For the IR, the electrostatic energy stored in the dc-link capacitors and the kinetic energy reserve of the WT rotors are utilised. The PFR service is guaranteed by a deloading scheme that reserves a portion of the maximum available power of the WT. Also, the possibility of providing both IR and PFR using external energy storage systems, in this work supercapacitors and battery energy storage system, has been considered. For each support scheme analysed, this work provides a comprehensive survey. This dissertation further proposes two coordinated control strategies that exploits the full potential of VSWTs to participate in power system frequency response enhancement and small-signal stability support. All the control schemes are developed and simulation studies performed on DIgSILENT PowerFactory simulation environment