Wind Turbine Contribution to Ancillary Services under Increased Renewable Penetration levels

Abstract

Wind constitutes a dominant form of sustainable energy that is expected to grow rapidly in the years to come. Increased inverter-based wind power penetration may however endanger grid stability and reliability, if not enriched with the capability to provide crucial ancillary services to the grid, such as frequency regulation. In order for the wind turbine technology to participate in the ancillary service provision, a more in depth understanding of the wind turbine dynamic behavior is acquired. Therefore, this Master Thesis Project was formulated to study how the wind turbine technology can assist in providing ancillary services under increased renewable penetration levels with a concentration on the frequency support. This project proposes the frequency controllers both at the single wind turbine level and the wind farm level to facilitate the provision of ancillary services. The power system transient simulation package PSCADTM/EMTDCTM V4.6.2 is used for the controller design and the simulation study. The single wind turbine frequency controller enables the provision of the necessary positive or negative active power reserves in proportion to the measured grid frequency, via the kinetic energy stored in the rotating masses and pitch control. Thus, the wind turbine generator power output is enabled to increase or decrease respectively. The full potential offered by the technology is exploited, while the limitations associated with the provision of active power reserves are identified and respected by the implemented controller. The wind farm controller allows for the coordination and control of the available wind turbines within a wind farm, despite several barriers identified in this project. A list of parameters is used to this end, which can be varied to achieve a more sustained frequency response, despite the barriers introduced by the available limitations of the electrical and mechanical components of the wind energy conversion system. An offshore wind farm case study was performed to test the performance of the implemented controllers and investigate the impact of the wind farm frequency response on the grid frequency, in various scenarios. The successful response of the implemented controllers is proven, while no violation of physical or safe limits is identified thanks to the frequency controller designed in this project. The allowable ranges within which the controller parameters can be varied without unwanted situations are analytically discussed and summarized as important lessons learned. Finally, the active power product that can be provided within the Ancillary Service Market is quantified and described, while recommendations are made at the Ancillary Service Market level that reflect the capabilities of the wind turbine technology, if enriched with the designed controller. Overall, a positive effect of the frequency response provided by the wind turbine technology on the grid frequency is observed. Significant improvements have been achieved on the frequency nadir and the rate of change of frequency by the wind farm controller parametrization under different severity of the frequency deviations. In general, the frequency response that can be achieved through the wind turbine technology is in any case proportional to the amount of power that is generated by a certain wind farm (i.e. proportional to the wind speed conditions). The response provided can last for several seconds, thus constituting a “Fast Frequency Response” service the most appropriate option for the wind turbine technology. A trade-off between the maximum reserves provided and the duration of the response provided is seen. However, in the cases that a certain wind turbine needs to recover following a period of reserves provision, a compromise between the aggressiveness and the duration of the recovery period is also observed.