Research On Automatic Voltage Control Of Grid-connected Wind Farm

Because of the intermittence and fluctuation, the integration of large-scale wind power into the power system will cause voltage fluctuations, especially at the grid-connecting point. At present, the doubly-fed induction generator (DFIG) -based variable speed constant frequency wind turbine has become the main choice of wind farms. For the active and reactive power can be decoupling controlled through the generator stator flux oriented vector control technology, it has a flexible capacity of reactive power regulation and voltage support. This paper mainly studies on the grid-connecting point oriented automatic voltage control of a DFIG-based wind farm. And two voltage control strategies are proposed, which are the rapid control strategy and the coordinated control strategy. The rapid control strategy only uses the DFIG wind turbines as flexible and controllable source of reactive power to regulate the voltage and reactive power of the wind farm. By calculating the voltage difference of the grid-connecting point between the measured value and the target value, real-time reactive power balance of the wind farm is set and then distributed among the DFIG wind turbines, in order to achieve the initial steady state voltage value or to track the setting voltage value given by the dispatching center. At the same time, sensitivity analysis is introduced into the reactive power distribution. And based on the order of sensitivity, the DFIG wind turbines which will be involved in the regulation of voltage or reactive power are determined. Thus, the accuracy of reactive power control of the wind turbines is improved and the power loss of wind power system is effectively reduced as well. While the coordinated control strategy regulates the voltage and reactive power of the wind farm by not only DFIG wind turbines but also the shunt capacitor banks, which are switched according to the optimized results given by an improved genetic algorithm based on the wind power prediction data and its segment information. After that, the DFIG wind turbines are used to regulate and control the real-time reactive power balance. In this way, the coordinated control problem between the discrete variable and the continuous variable has been solved. And it shows that the wind farm is able to provide more dynamic reactive power and voltage support for the grid.