Research On Transient Control Strategy Of Wind Farms

As the rapid development of wind power technology, making the capacity of gridintegration of wind power increase, which is bound to the grid safe and stable operationand scheduling adversely affected. Since the majority of wind farms in the world areconnected to the end of the grid, so most of the wind farms far from the load centers.This grid structure is relatively weak, prone to volatility, which affects wind farm safeand stable running. More serious situation is when the grid voltage drastic drop, if thegrid wind power penetration is high, large-scale wind turbines will cause a chainreaction of splitting, a serious threat to the safe operation of the grid. In order to ensurethe stable operation of the grid, the current large-scale wind power technology, powerfailure no longer allow automatic off-grid wind turbine, you need to have some lowvoltage ride through (Low Voltage Ride Through, LVRT) capability. China has alsoissued a wind farm for low voltage ride through aspects of the relevant policies of thewind turbine LVRT made hard and fast rules. Therefore, the study of wind turbine lowvoltage ride through characteristic has important theoretical and practical significance.This paper focuses on doubly-fed wind power generation system in the transientgrid voltage drop mechanism, control and reactive power compensation and otheraspects of in-depth research. First of all, established in DFIG stationary coordinatesystem and the two-phase synchronous rotating coordinate system relative to thesteady-state model. Deduced using the vector method symmetrical three-phase powergrid failure, DFIG in flux and voltage change process, analyzes the grid voltage on theDC bus drop impact is DFIG in the subsequent analysis of the theoretical basis.Research on the Crowbar protection circuit for DFIG based on low voltage ridethrough issues. Propose the Crowbar resistance selection principle. Quantitative analysisof the input Crowbar circuit after the reactive absorption of DFIG. Detailed analysis bysimulation grid failure Crowbar resection time low voltage ride through injury. And forthe moment the wind farm voltage sharp drop fault situation, this paper propose a newtype of reactive coordinated control strategy. This strategy maintains the PCC voltagelevel, enhance the wind farm voltage ride-through capability, and fully mobilize thereactive power regulation ability of DFIG. So that the wind farm showed a flexiblereactive power and voltage regulation characteristics.Finally, the analysis based on Crowbar protection system model with wind farmslow voltage ride through properties. For different fault locations and different types offailures LVRT characteristics analysis and the results showed that the impact of differentfaults on the system are not the same. The analysis of the wind farm inputs Crowbarinfluencing factors as well as improved protection strategies, including appropriate toreduce the current protection settings, using strategies such as self-sustaining circuit toensure reliable fault removal. This paper is sponsored National High-tech R&D Program of China (863Program)High Penetration of Intermittent Energy Research and Demonstration of the KeyTechnologies of the Regional Power Grid (Project ID：2011AA05A105).