Blackstart and Islanding capabilities of Wind turbines

Background

The rising demand for power has led to an increase in the installed generation capacity, along with a need for higher reliability in grid operation due to sensitive & critical loads. Additionally, environmental problems like global warming, sustainability concerns and energy security make renewable energy systems (RES) crucial for future power systems. The European Commission has proposed a target of at least 27% renewables in the final energy consumption in the EU by 2030, along with other international players such as USA, China and India for a more secure, sustainable and low-carbon economy.

Amongst RES, wind energy is the fastest growing due to its abundance & cleanliness. Moreover, the increasing size & number of wind turbines (WT), to achieve a lesser price per kWh, have made large offshore wind power plants (OWPP) with high power WTs more popular due to onshore space constraints.

Motivation

With the recent increase in the integration of RES far from load-centers and replacing conventional power plants, maintaining reliability, robustness and stability of grid operation, has become more complex due to more variable trans-national power exchanges and operation closer to system limits. Moreover, the shift towards power electronics (PE) interface poses a risk to the power system dynamic stability. All of the above factors along with stronger linking of national power systems can result in cascaded tripping of generation and potentially trigger wide-area blackouts.

Thus, with the growing share of wind power, more advanced grid requirements like black-start & restoration services, usually targeted to large thermal power plants, can be addressed by the large OWPPs that are integrated through voltage-source converter (VSC) based high-voltage direct-current (HVDC) transmission.

Large VSC-HVDC connected OWPPs, far from the shore and composed of state-of-the-art WTs, can provide fast & fully-controlled, high-power environment-friendly blackstart capability with low availability uncertainty, due to absence of near-shore wake effects and thus steadier wind conditions. Additionally, having blackstart capability in OWPPs could significantly reduce the restoration time & the unserved load, and thus the overall impact of blackout events.

Blackstartable WTs can produce power to sustain themselves and avoid the risk to their health, as long as there is wind, especially when offline for long durations due to a transmission line outage or a regional black-out. This also helps minimize the use of the offshore-substation diesel-generator backup-power for supplying the auxiliaries thus providing cost-benefits.

Moreover, advanced voltage and frequency control functionalities of VSCs enable modern WT’s with state-of-art PE-interface, to be controlled as grid-forming units. This allows the OWPP to do controlled islanded operation (CIO) without having to wait for completion of the network reconstruction, and thus ensure the continuity of power supply, facilitating bottom-up grid-recovery and participating in defense against blackout. Grid forming WTs also allow the use of diode rectifier unit (DRU) or thyristor-based line commutated converter (LCC), preferred at higher power levels, further reducing installation & operational costs, and increasing efficiency, system reliability and robustness.

Objectives

  • Literature review for technical challenges and state-of-art control solutions in the scope of blackstart and islanding capabilities of WPPs.
  • Design of an energization sequence for providing blackstart and restoration services to the grid.
  • Identification of the target states and challenges in each stage of the energization process.
  • Development of detailed EMT models for transient studies.
  • Dynamic simulations to test & validate controls for grid-forming, network energization and grid-synchronization.
  • Studies for enhancing stability & robustness to faults & harmonic instabilities.
  • Capability assessment for determining compliance with grid-codes for blackstart units.
  • Introduce terminology for use in future research in this area.

This work is part of the InnoDC-project that has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 765585.

Contact

Anubhav Jain
PhD student
DTU Wind Energy
+4544 80 50 99