Alternatives for Primary Frequency Control Contribution from Wind Power Plants Connected to VSC-HVDC Intertie

With the increasing share of renewables in the electric power systems, the transmission system operators (TSOs) need more balancing power to even out short- and long-term variability of the intermittent electric power sources such as solar and wind power. In light of this, this paper investigates how a large offshore wind power plant (OWPP) with high voltage direct current (HVDC) intertie connection to two asynchronous onshore AC power systems can be part of the solution in providing short-term mutual active power balancing.
The primary frequency control is investigated for four different study cases. Both a centralized and distributed DC voltage control strategy have been successfully implemented, each with two communication methods: either direct AC frequency communication to the OWPP or coordinated control of onshore AC frequencies and onshore DC voltages, then communicating the offshore DC voltage to the OWPP.
Independent of the communication method, the implemented distributed DC voltage control has proven to provide a superior frequency stability and limitation of the maximum deviation in onshore AC frequencies during large load events. This control strategy results in a sharing of the primary reserves and rolling inertia between the two onshore AC power systems connected to the HVDC intertie, whilst also exploiting the OWPP in the primary frequency control scheme.