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This paper analyzes the voltage stability of a control scheme proposed for a large offshore wind farm of DFIGs and linked to the grid using an HVDC system. HVDC rectifier control is set to regulate the local frequency and deliver the real power that is captured by the generator. The generator reactive power is controlled by keeping the stator flux linkage constant. Comparison is made with a more conventional way in which the DFIG reactive power is set explicitly. The study illustrates the reactive power-voltage (Q-V) characteristic of the HVDC system and the requirement on DFIG reactive power or excitation control in order to maintain the voltage stability of the overall system. Analysis based on the dQ/dV criterion is verified by time domain simulation. Effect of the bandwidth of generator control is evaluated.
Date of Conference: 28-31 March 2006