The principle of absolute rotor angle control and its effect on suppressing inter-area low frequency oscillations

Abstract

How to suppress low frequency oscillations effectively in inter-connected power systems has been a challenging problem for many years. The problem may be solved by accurate control of absolute rotor angles. The structure of a rotor angle controller is shown in this paper. The input of the controller is the absolute rotor angle measured by local phasor measurement unit (PMU). The controller ensures that this rotor angle remains unchanged in rotating coordinate system determined by pulse per second (PPS). This way, zero steady state error control of angle and frequency can be achieved at the same time. Since the rotor angle and speed remain constant under normal conditions, it is possible to get information of all kinds of oscillations through local measurement after disturbance. Analysis in this paper also shows that the stability margin and the characteristic of the damping torque provided by the angle controller can be improved significantly after a compensation block is added. When used together with power system stabilizer (PSS), the angle controller can suppress inter-area oscillations effectively without help of any remote measurement.