Mención Internacional en el título de doctorThere is an increasing interest in the use of line-commutated converter (LCC) technology
to connect large offshore wind farms (OWFs) placed far from the coast by means
of a high voltage direct current (HVDC) link. This is due to the better features of LCCs
compared to voltage-source converters in terms of cost, reliability and efficiency. However,
this technology requires a frequency control in the OWF to allow the operation
of both the wind turbine generator systems (WTGSs) and the LCC rectifier. Therefore,
this Thesis presents two frequency control proposals. First, a centralized voltage
and frequency control for an OWF connected through LCC-rectifier-based HVDC
link is proposed. It is derived from an enhanced LCC-rectifier station average-value
model which indicates that the active power balance at the point of common coupling
drives the OWF voltage while the corresponding reactive power balance drives the
OWF frequency. Even though voltage control cannot be applied in case of using a
diode rectifier, the voltage magnitude variation is clamped between acceptable values.
As a second proposal, a decentralized frequency control for the diode-rectifier-based
HVDC link connection of OWFs is also presented. This control is based on a reactive
power / frequency droop which allows the WTGSs to reach synchronous operation
and equally share the reactive power without the need of communications among the
WTGSs. Moreover, the control proposals do not rely on a phase-locked loop, so controls
are not subject to grid disturbances or measurement noise. Another important
specification of the proposed control strategies is that they do not modify the active
power control channel of the WTGSs. Finally, the stability and the simulation results to
assess the performance of both control proposals are studied.Programa Oficial de Doctorado en Ingeniería Eléctrica, Electrónica y AutomáticaPresidente: Alireza Nami.- Secretario: Oriol Gomis Bellmunt.- Vocal: Ana Belén Morales Martíne
