Stabilizing control for HVDC connected offshore wind farm

Bulk power supply from offshore wind farms via voltage-sourced-converter (VSC) based HVDC systems poses several challenges for design and operation. Besides the fundamental requirement of low voltage ride through (LVRT) weak AC grid conditions affecting transmission angle stability is a further issue. This work develops controls stretching from the wind farm to the onshore AC grid to handle major load changes and weak grid conditions. A particular crucial situation is given when grid weakening occurs unobserved. Considering the complexity of wind farm and HVDC controls, for the present work an AC grid connection via radial AC lines is used. The studies are performed on the PSCAD/EMTDC digital simulator in conjunction with plausibility checks using PQ-diagrams. Results obtained so far prove the capability of wind farm and HVDC controls to operate under weak grid conditions. Included in the study are preliminary investigations on an AC grid containing mechanical synchronous generators.