Analysis of active power control algorithms of variable speed wind generators for power system frequency stabilization

A modified control algorithm of a variable speed wind generator (VSWG) for supporting power system frequency stabilization is presented in this paper. A comparison of the performance of this algorithm with active power control algorithms of VSWGs for supporting power system frequency stabilization, as published in the scientific literature, is also presented. A systematic method of analysis of the modified control algorithm is described in detail. It has been shown that by using the modified control algorithm, the VSWG "truly" emulates the inertial response of a conventional steam-generating unit with synchronous generators during the initial/inertial phase of primary frequency control, following loss of active power generation when wind speed is between cut-in (i.e. 4 m/s) and rated speed (i.e. 12 m/s). By the inclusion of a signal proportional to the frequency deviation as a power reference to the torque controller feedback loop of the modified control algorithm, it is ensured that the contribution of the VSWG to frequency stabilization is independent of the initial wind speed. This independence is kept as long as the wind speed is above the cut-in wind speed and slightly below the rated wind speed (i.e. 12 m/s). One of the important features of the modified control algorithm, namely a near-proportional relationship between the initial wind turbine speed and the maximum wind turbine speed variation during the inertial response, has been identified. The results of the analysis provide a solid basis for further research in the area of VSWG contribution to frequency stabilization.