This paper presents a new operational strategy for a large-scale wind farm\n(WF) which is composed of both fixed speed wind turbines with squirrel cage\ninduction generators (FSWT-SCIGs) and variable speed wind turbines with\npermanent magnet synchronous generators (VSWT-PMSGs). FSWT-SCIGs\nsuffer greatly from meeting the requirements of fault ride through (FRT), because\nthey are largely dependent on reactive power. Integration of flexible ac\ntransmission system (FACTS) devices is a solution to overcome that problem,\nthough it definitely increases the overall cost. Therefore, in this paper, a new\nmethod is proposed to stabilize FSWT-SCIGs by using VSWT-PMSGs in a\nWF. This is achieved by injecting the reactive power to the grid during fault\ncondition by controlling the grid side converter (GSC) of PMSG. The conventional\nproportional-integral (PI)-based cascaded controller is usually used\nfor GSC which can inject small amount of reactive power during fault period.\nThus, it cannot stabilize larger rating of SCIG. In this paper, a suitable fuzzy\nlogic controller (FLC) is proposed in the cascaded controller of GSC of PMSG\nin order to increase reactive power injection and thus improve the FRT capability\nof WF during voltage dip situation due to severe network fault. To evaluate\nthe proposed controller performance, simulation analyses are performed on a\nmodified IEEE nine-bus system. Simulation results clearly show that the proposed\nmethod can be a cost-effective solution which can effectively stabilize the\nlarger rating of SCIG compared to conventional PI based control strategy.
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