Studies On Grid-voltage Support Rules With Wind Power Integration

With the continuous expansion of power grid, the control means to ensure voltage level have become more and more complex, and the integration of renewable resources and AC-DC transmission systems furtherly increases the complexity of control strategy. In this context, how to study in depth the rule of power grid voltage support, and how to make full use of the potential reactive power resources to realize high efficient voltage control, are both issues we must face at present.This thesis mainly discusses about the law of power grid voltage support and the question of reactive power optimization with wind power integration. By taking the integration of Doubly Fed Induction Generator (DFIG) wind farms as a clue, the interaction between wind parks and the power grid is first analyzed. Then, on the basis of that, this thesis researches some problems like the small signal stability and reactive power capacity of wind farms, reactive power optimization with wind power integration in Automatic Voltage Control (AVC), and so on,in order to ease the negative influence caused by the wind farms and to furtherly improve the operation of the power system.First of all, taking DFIG wind farms as the object of study, an explicit expression for static stability region under specific active-power mode is derivated by applying the small signal model of wind power system considering grid-side operation state. On the basis of this expression and taking other steady-state operation constraints into consideration, the DFIG mathematical model for reactive power capacity is proposed which provides a foundation for setting the valid adjusting range for reactive power.Secondly, by analyzing the influence of DFIG wind farms integration to the system voltage, this thesis researches leading static reactive power optimization and dynamic reactive power optimization respectively which both belong to AVC system reactive power optimization. Subsequently, a static reactive power optimization model including the effect of synchronous generator AVR and a dynamic reactive power optimization model based on wind farm scenes are both proposed. By taking into consideration of wind power fluctuation, the optimization models make full use of the reactive power regulation of the grid and wind farms and can determine the operation time and gear of the discrete regulation devices reasonably, which enables the cooperation of the discrete regulation and the continuous regulation. The simplified solution strategy is also given in this thesis according to the characteristics of each model, which can reduce the complexity effectively.Finally, according to the practical operation of wind farms in Yantai, this thesis studies in detail the operating performance of power grid after wind farms integration, from the aspect of power flow, network loss, voltage level and short-circuit capacity. After that, effective suggestions are given for improvement of grid operation, in order to make full use of wind power and reduce the adverse effect of its uncertainty.