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This article proposes a unified power-flow controller (UPFC) to suppress subsynchronous resonance occurred in a hybrid power-generation system connected to an infinite bus through a series-capacitor compensated line. The hybrid power-generation system contains a steam-turbine generator (STG) and an offshore wind farm (OWF) based on doubly-fed induction generator (DFIG). The d–q axis equivalent-circuit model under three-phase balanced loading conditions is derived to establish the complete system model including the STG set, the DFIG-based OWF, the series-capacitor compensated line, the UPFC, etc. A damping controller of the proposed UPFC is designed by using pole-assignment approach based on modal control theory to effectively damp out unstable STG modes of the studied system. Both small-signal stability and transient simulation results of the studied system are systematically performed. The simulation results show that the proposed UPFC joined with the designed damping controller can effectively suppress unstable STG modes of the studied power system. [ABSTRACT FROM AUTHOR]

Submarine cables are indispensable for offshore wind farms (OWFs) connected to a power grid. The submarine cable can cause certain degrees of impact on the system performance due to its different lengths, characteristics, electrical parameters, etc. This paper employs the power-system simulation software of Power System Simulator for Engineering (PSS/E) for modeling a future-scheduled OWF, i.e., a large-scale doubly-fed induction generator-based OWF of 200 MW, connected to Jang-Bin distribution substation of Taiwan Power System through five feeders, five circuit breakers, two step-up power transformers, a commercial submarine cable, and an underground cable. This paper simulates and compares the electrical quantities of the studied OWF with different operating capacities under various lengths of three types of commercial submarine cable. The transient surge peak voltages at the common bus of the OWF and the bus of Jang-Bin distribution substation subject to the switching of one of the five circuit breakers of the studied OWF under different lengths of the three types of commercial submarine cable are also compared using the power-system simulation software of ATPDraw in Alternative Transients Program (ATP) version of Electromagnetic Transients Program (EMTP). [ABSTRACT FROM AUTHOR]