Load modulation for damping of electro-mechanical oscillations

Today it is feasible for utilities to control selected customer loads in a nondisturbing fashion. This is comparable to load shedding, but has a wider area of application. This paper focuses on direct load control or modulation for power system damping and is based on a field test of on-off control and modal analysis of differential-algebraic equation models of three test systems. Real power load controlled by bus frequency is found to be robust to changes in network topology. It is shown that on-off modulation is more effective than sinusoidal modulation for damping of large oscillations, but not for small oscillations. It proves difficult to give a general measure of the required amount of controlled load, since modulation of real power loads has an additive rather than multiplicative effect on power flows. Different structures of load control systems are listed. If the system is centralized, it is suggested that the distribution company owns and operates the system and that damping is sold as ancillary service