Active Power Compensation And Stability Control For Grid-connected Wind Farms

High penetration of distributed generation into the power system will result in some deteriorative influences such as poor power quality and stability issues. With the increasing share of the wind power in the power system, the impact of its integration is becoming more widespread. To reduce the detrimental effect of wind farms on power grids and meet the need of technical regulations for connecting wind farms to power systems, the active power compensation strategy and stability issues of grid-connected wind farms are investigated in this paper. The main content of study covers the following:An active power compensation (APC) model for grid-connected distributed generation systems is proposed. This model is based on a hybrid energy storage system (HESS) to compensate the power fluctuation caused by distributed generation, such as wind power. HESS takes advantage of different energy storage technologies to provide satisfying compensation capability with both high energy density and high power density. A novel dynamic energy optimization algorithm based on energy prediction (DEOEP) is also proposed that considerably improves the efficiency of HESS, and the compensation power control value tracked by HESS is calculated using a fuzzy control strategy. The HESS approach and DEOEP strategy are verified effective with simulation studies. This APC model allows higher overall performance with less energy required for HESS, and therefore the cost can be reduced. There is an opportunity for retrospective enhancement of existing energy storage devices due to the practicality of this model.Considering that the low voltage ride-through (LVRT) capability of wind farms has a great impact on power system stability, a novel alternative technology is also proposed that improves the low voltage ride-through capability of wind farms using the series dynamic braking resistor (SDBR) which can boost generator voltage and dissipates active power. A switching scheme of SDBR is introduced based on the dynamic stability margin of speed-voltage. This paper uses a representative wind farm model based on fixed speed wind turbines to study the transient LVRT stability. Both detailed analysis and simulation results of its performance show that SDBR can significantly improve the low voltage ride-through performance of wind farms, and the switching scheme of SDBR is simple and effective. The LVRT's dependence on pitch control systems and other state-of-art alternatives can be reduced with SDBR.