Demonstration project 1 System services provided by wind farms (SYSERWIND)
- Clustered provided wide area voltage control, reducing voltage deviation from 9 kV to 0.7 k V.
- Wind farms can work in a coordinated way to provide secondary frequency control in the same way as conventional units.
- Secondary frequency control involves many challenges, including the need for very accurate wind forecasting in order to avoid curtailing large amounts of power.
- A high amount of energy has to be curtailed for providing the upwards power reserve service, so it is not currently attractive from the economical point of view.
The first demonstration project in TWENTIES aimed to show that wind power facilities already in operation can be upgraded to provide services like wide area voltage control and secondary frequency regulation to the system, with limited changes in IT systems at wind turbine and wind farm level. The demonstration was carried out in 15 of Iberdrola's wind farms in the south ofarranged in three clusters: Arcos de la Fron-tera (111 MW), Tajo de la Encantada (122 MW) and Huéneja (248 MW), with a total capacity of 481 MW.
In order to meet the objective, new control regulators were developed and installed in the control centres and the wind farms, making 240 wind turbines work in a coordinated fashion in order to control the voltage in a 350 kilometre-long 400 kV AC corridor. It was also necessary to develop a very short-term wind forecasting algorithm due to the challenging requirements of providing a secondary frequency regulation band with the necessary precision. Most importantly, these tools were fully integrated into the system operation and the transmission system operator's (TSO) tools.
Results in detail
The wide-area voltage control test started with initial voltage differences of up to 9 kV and following the TSO's instruction the response provided by the 15 wind farms reduced the voltage deviation to 0.7 k V.
The main challenges that were faced during these tests were the fact that controlling thecapabilities of the wind turbines meant taking into account the behaviour of the medium voltage grid of the wind farms as well as other installations that were not part of the demonstration but were connected to the same nodes, and the on-load tap changer of the transformers, which reacted to the modifications in the voltage profle.
Providing secondary frequency services with wind farms has proven to be even more challenging. The wind farms were integrated into the TSO's automatic generation control (AGC) system and, in this case, the main problem was the fact that, in order to provide a regulation band with sufficient reliability during the whole time span of the test, a very accurate and reliable forecast was needed. Other issues that made the demonstration difficult were the need to respond quickly to the set points that the TSO sends every four seconds and controlling the pitch in all the wind turbines in such a way that a reduction in power generation was achieved without stopping any machine, which would slow the overall response of the clusters.
Despite the challenges, the demonstration showed that voltage control and secondary frequency regulation can be successfully carried out by wind farms.