Multi-terminal DC transmission system for wind-farms

Optimal acquisition of power in wind farms requires the speed of each individual turbine-generator to converge automatically to the optimum speed corresponding to the local wind velocity. As the optimum speeds differ with turbine locations, the AC voltages of their generators will have different frequencies and voltage magnitudes. Their powers are rectified and aggregated at a common regulated DC bus. PWM-rectifiers match the different voltage magnitudes and produce near sinusoidal current waveforms which minimize torque pulsation in the generators. The aggregated wind power should be automatically made available to the AC utility grid in a form which meets frequency, voltage regulation and total harmonic distortion standards. This paper shows that the multi-terminal DC transmission system based on voltage-source converters can meet all the complex requirements