UFLS Design by Using f and Integrating df/dt

Under frequency load shedding (UFLS), which has been worldwidely adopted in modern power systems, is an effective method to stop rapid frequency decay and to restore power system stability following heavy loss of generation. The traditional UFLS scheme is proposed for determining the amount of load to be shed based on the observed frequency deviation (Deltaf) following the system disturbances, but it has some drawbacks of itself. Although it is attractive to use the variation rate of frequency (df/dt) as an additional signal for load shedding, but there is no practical scheme available today. The reason lies in the fact that the instant df/dt changes so violently that it cannot indicate the information of the severity of generation deficiency in power system directly. In this paper, the authors proposed a method to try to use the df/dt as auxiliary information for the UFLS scheme design. The integrating of dynamic frequency from one UFLS frequency step to the next step is assigned as the df/dt in the UFLS design, which is called integrating df/dt in this paper. The study results show that this new UFLS scheme has much more adaptability than the traditional ones