Sensitivity Analysis of Load-Damping Characteristic in Power System Frequency Regulation

The smart grid initiative leads to growing interests in demand responses and the load models, especially the frequency-sensitive loads such as motors. The reason is that high-penetration controllable load may have substantial impact on system frequency response (SFR). However, the effect of the frequency-related load-damping coefficient is still not completely understood. This paper investigates the effect of frequency-sensitive load on system frequency using typical SFR model. Theoretic analyses based on transfer functions show that the frequency deviation under a different load-damping coefficient is relatively small and bounded when the power system is essentially stable; while the frequency deviation can be accelerated when a power system is unstable after disturbance. For the stable case, the largest frequency dip under a perturbation and the corresponding critical time can be derived by inverse Laplace transformation using a full model considering load-damping coefficient. Further, the error in evaluating the load-frequency coefficient gives the largest impact to frequency deviation right at the time when the largest frequency dip occurs. Multiple-machine cases and automatic generation control (AGC) are also included in the analyses with verifications by simulation studies. The conclusion can be useful for system operators for decision-making of load control or interruption.