Fault Ride Through Capability Of Wind Turbine Generator And Its Impact On Power System Transient Stability

The development of renewable energy has raised the proportion of wind power in power system. The integration of large-scale wind power generation into power system has brought new challenges to the safety and stability of the power system. The stability of the power system with high penetration of wind power under large disturbances is one of the most urgent problems that is needed to be solved. From the power grid's perspective, wind turbine must have fault ride through capability to remain in connection, which is a basic guarantee for the safe and stable operation of power grid. From the wind turbine's perspective, the safety and stability of the wind turbines during faults is the precondition for its fault ride through. Hence, this paper studies the fault ride through capability of wind turbine generator and its impact on power system transient stability..A detailed simulation model of PMSG was established in PSCAD/EMTDC based on its working principle and common control strategy.On the basis of this model, the problems were analyzed including DC bus over-voltage and AC side converter over-current, which are caused by the unbalance of the input and output power of the DC side during faults.The functions and characteristics of three low voltage ride-through techniques and the respective transient characteristics of the wind turbines were studied through simulation aimed at transient problem of the low voltage fault of PSMG. The three low voltage ride-through techniques include crowbar protection on the DC-side, reactive power compensation on the AC-side and the generator output power reduction. On the above basis, a new low voltage ride-through technique based on coordinated control was proposed. The proposed control strategy can keep the rotational speed of the generator and the voltage on the DC-side within safe limits under all sorts of voltage drops, and therefore the low voltage problem of PSMG wind turbines can be effectively solved.The equivalent model of wind farms was connected to a IEEE three machines nine nodes system. The impact of wind power penetration, interconnected location and the electrical distance to the fault locations of wind farms on the transient stability of power system were investigated. The results show that it's more beneficial to the system's stability when the critical generators rather than the rest generators are replaced by the wind farms with the same capacities. Furthermore, the transient stability of power system improves as the wind power penetration increases when the critical generators are replaced. Simultaneously, when the interconnected location gets closer to thecritical generator, the transient stability gets worse. The increase of the electrical distance of the wind power integration weakens transient stability.For further study, a research on the methods for improving transient stability of wind power system by diffirent reactive compensation devices has been done. With comparing the SVC and STATCOM which install in wind farm on reactive power dynamic characteristics, analysis shows that both SVC and STATCOM can improve power system transient stability. Furthermore, STATCOM is superior to SVC with the same capacity on reactive power adjustment ability and response speed.