RT Dissertation/Thesis
T1 Centralized control strategies for HVDC connection of offshore wind farms based on diode rectifier units.
A1 Nami, Ashkan
AB The possibility of using diode rectifier in the offshore substation for high voltage directcurrent (HVDC) connection of offshore wind farms (OWFs) has recently receivedan increasing interest due to its lower cost and losses together with its higher reliabilitycompared with the voltage source converter (VSC) based HVDC link. However,the main drawback of the diode rectifier solution is that the system frequency has tobe controlled to guarantee the diode rectifier commutation, given that the isolated offshoreAC-grid can not generate the required frequency with the wind turbine generatorsystems (WTGSs) conventional control systems. This Thesis presents a direct frequencycontrol for such an application whose principles are derived from the AC-side dynamicsof a diode rectifier (DR) based HVDC system indicating that the frequency controlcan be achieved by reactive power balance at the rectifier station without a capacitorbank placed at the diode rectifier station. The proposed control system is implementedby a VSC connected to the rectifier station that is always needed for the centralized frequencycontrol where the WTGSs conventional control systems are not changed. A hybridHVDC system consisting of the DC-parallel connection of a low-power VSC withthe rectifier station is also proposed in this Thesis, which is compared with the traditionalVSC-HVDC connected OWFs. Besides the frequency control and diode rectifierharmonic currents compensation, the OWFs start-up is addressed in the centralizedhybrid topology, overcoming all the DR-HVDC link drawbacks. Finally, a centralizedcontrol strategy of the parallel operation of the DR-HVDC and VSC-HVDC links forOWFs connection is presented. The VSC-HVDC controls the voltage and frequencyof the offshore AC-grid needed for the OWFs start-up. The proposed centralized gridforming control is based on controlling the OWFs voltage by controlling the activepower balance at the VSC-HVDC AC-bus. This leads to an onpitimized system wherethe VSC-HVDC can be sized just to support the system energization; while once theOWFs are in operation, the DR-HVDC will be loaded automatically. Stability analysisand simulation results provided throughout this Thesis verify the performance of theproposed control systems.
YR 2020
FD 2020-07
LK https://hdl.handle.net/10016/31887
UL https://hdl.handle.net/10016/31887
LA eng
NO This Thesis work has been financed by: • Pre-doctoral research training contract (PIPF) supported by Univerisdad Carlos III de Madrid, from 01/04/2016 to 31/03/2020. • Mobility Scholarship for researchers in foreign research centers (Industry or Academia) supported by ABB AB. Destination: ABB Corporate Research Center, Västerås, Sweden. From 14/08/2017 to 12/02/2018. • Autonomous Community of Madrid under the PRICAM research project (S2013-ICE-2933). • ABB Corporate Research Center, Västerås, Sweden (10.13039/501100013902).
DS e-Archivo
RD 1 sept. 2024