Impact of Wind Power Plants with Full Converter Wind Turbines on Power System Small-Signal Stability : Inherent Characteristics and Potential for Power Oscillation Damping Control

Abstract

Wind power is being developed in power systems all around the world, and already today wind power covers more than 20 % of the electricity consumption in some countries. As the size of each wind power plant (WPP) increases and as the levels of penetration reaches certain magnitudes, the inclusion of the dynamic properties of the WPPs in the power system stability studies become important. The work presented in this report deal with the impact of WPPs based on full converter wind turbines (WTs) on the power system small-signal rotor angle stability. During small disturbances in the power system, the rotor speed of the synchronous machines will eventually return to its steady state if the power system is small-signal stable. The dynamic properties of a WPP are fundamentally dierent from those of a synchronous machine, and the interaction of WPPs with the synchronous machines in power system oscillations has not yet been fully claried. The participation of the WPP in the power system oscillations was investigated for a number of WPP penetration levels and for dierent WPP modes of operation. It was generally found that the inter-area modes were largely unaected by the WPP penetration level and mode of operation. The participation of the WT mechanical system in the inter-area modes were found to be orders of magnitudes smaller than the participation of the synchronous generators. The reactive power controller of the WPP and the WT were found have the highest participation among the WPP and WT states. WPPs based on converter interfaced WTs oer a high degree of controllability due to the rapid response of the converter and the ability to control both the active and the reactive power output. During this project, it has been explored how these properties could be utilized to actively contribute to the modal damping of weakly damped power oscillations through WPP power oscillation damping control (POD). Emphasis has been put on WPP level PODs due to its simplicity as compared to individual WT PODs, and since this oers a single point of access if the operation of the POD is to be controlled by a wide-area measurement system. The ndings encourage that a WPP level POD is feasible, since the WTs in a 150 WT WPP required very similar control signals to optimally contribute to an increased modal damping, and since time domain simulations showed that the interaction between the WTs did not adversely eect the ability of the WTs to generate an aligned WPP response. The theoretical ndings are supported with eld test results on a small 13 WT WPP that has been subject to open-loop tests of both active and reactive power modulations in the frequency range of 0:1 to 1:0 Hz. With the eld tests it has been shown that it was possible to control the WTs to deliver a common WPP response that was consistent in both frequency and phase. This was achieved for both active and reactive power modulation.