DRU connected offshore wind power plant operation

Deliverable 3.4 (“Operation of WPPs connected to DR- HVDC”) and deliverable 3.5 (“Performance of ancillary services provision from WPPs connected to DR-HVDC”) complement each other. The fundamental operation and fault response of diode-rectifier unit (DRU) connected offshore wind power plants are presented in D3.4, whereas higher level ancillary services operation of DRU connected offshore wind power plants is presented in D3.5 as an add-on.

The first part of D3.4 covers all aspects of fundamental operation of DRU connected offshore wind power plants; sequential startup of wind turbines via umbilical AC line, switching the DRU transformers and filters, disconnecting the umbilical AC line, and grid-forming operation of wind turbines with the DRU, as well as islanded operation of the wind turbines without any AC or DC connection to the onshore grid. Performance of wind turbines for dynamic offshore voltage and frequency control is presented as well. Moreover, backup operation of the DRU link with a reduced number of DRU units (e.g. when one out of three DRU is out of order) is described in the first part of D3.4.

In the second part of D3.4, all aspects of DRU connected offshore wind power plants with regard to short-circuit faults are presented; such as response of the DRU link and the offshore wind power plant to onshore AC symmetrical and asymmetrical faults, DC pole-to-pole and pole-to-ground faults, and offshore AC symmetrical and asymmetrical faults. The backup operation during internal DRU faults and DC pole-to-ground faults with limited power transfer to the onshore grid is described as well.

It is demonstrated that the DRU link and the connected offshore wind power plant can successfully survive these studied faults. Despite the probability of a fault in the AC umbilical line being low, since it is connected only during startup, these fault scenarios on the umbilical line are studied and presented in D3.4 for the sake of completeness.

Going beyond the fundamental operation and fault responses in D3.4, deliverable 3.5 presents higher level ancillary services functions by the DRU connected offshore wind power plants, such as frequency support and power oscillation damping for the onshore AC grid. It is shown that the DRU connected offshore wind power plant can support the onshore grid stability without any degradation by modulating its active power accordingly. In summary, all details of DRU connected offshore wind power plant operation are presented in D3.4 and D3.5.

For the next deliverable, D3.6, compliance test procedures for DRU and VSC connected wind power plants are being prepared for publication in March 2018. A review of existing evaluation and model validation procedures for offshore wind turbines and wind power plants on the regional and national levels (e.g. available standards and grid codes) will make up the first part of D3.6. In the second part, new compliance evaluation procedures for DRU connection, as well as the required enhancements for compliance evaluation procedures of VSC connected wind power plants, will be presented.


Deliverable 3.4: Results on control strategies of WPPs connected to DR-HVDC (Download PDF 2 MB)

Deliverable 3.5: Performance of ancillary services pro-vision from WFs connected to DR-HVDC (Download PDF 850 KB)