Fault Ride-Through Strategies for VSC-Connected Wind Parks

High-voltage direct-current transmission based on voltage-sourced converters (VSC-HVDC) is an economic connection technology for large remote wind parks. Wind power plants that are connected through a VSC-HVDC link are subjected to the same technical connection requirements as conventional generators. The requirement that these installations have to remain synchronously connected to the network during faults, is particularly challenging. Power electronic converters have no over-loading capabilities and during faults they can only supply a fault current up to the rated current. Since the wind park that is connected to the link does not directly notice the fault, a power imbalance is caused across the link that results in uncontrollability of the direct voltage. Such an uncontrollability might lead to tripping of the link and must be prevented. Three strategies are described to keep the direct voltage controllable during network faults. The first strategy is formed by overdimensioning of the GSVSC. The second is formed by dissipation of the excess wind power during the fault in a braking resistor. The third strategy is the fast reduction of the wind power production, and can be achieved by direct communication, voltage reduction and frequency increase. A reliable and costeffective solution combines over-dimensioning and/or power dissipation with one of the power reduction methods. An optimal system design can be found with the help of an optimization procedure, in which the system costs are minimized.