Small-signal stability analysis of offshore wind farms with LCC HVDC

Stability of the offshore ac collection bus in offshore wind farms employing high-voltage dc (HVDC) transmission has to be maintained through control of all converters connected to the bus - wind turbine inverters, HVDC rectifiers, and STATCOM. This paper addresses the stability and control of such ac buses when the HVDC rectifier is implemented by using line-commutated converters (LCC). A small-signal impedance model is developed for each of the converters involved, and a system small-signal model is formulated by modeling each wind turbine inverter as a current source, the STATCOM as a voltage source, and the HVDC rectifier as a load. Impedance-based stability criteria are then applied to determine control requirements for the wind inverters and the STATCOM that ensure system stability while minimizing hardware cost.