Time Delay Damping Control Of Low Frequency Oscillation In Power Systems Based On WAMS

With interconnection of power grids, power system size becomes larger, and operation condition becomes more variable. In operation of interconnected power systems, there are low/ultra-low frequency oscillations, which drastically endanger system stability. The emerging of wide-area measurement systems (WAMS) provides new opportunities for the analysis and control of wide area power systems. Since there is an unavoidable time delay in wide-area measurements, it is necessary to take delay into consideration when wide-area measurements are adopted as output feedback signals of damping controller for inter-area low frequency oscillations.At present, design of inter-area low frequency oscillation damping control, which considers time delay effect introduced by wide-area output feedback signals, is on the elementary stage, and there are still many problems to be explored thoroughly. Therefore, exploring the new theory, new technology and new method, researching on delayed output feedback robust damping control to inhibit inter-area low frequency oscillations in large power systems, have enormous theoretic and project significance. The dissertation consists of three main parts as follows:In the first part, by adopting large number of real-time accurate wide-area measurements from WAMS, a general Prony algorithm for transfer function identification is brought forward, in order to obtain the reduced model of power systems with no need to model/remodel every device in power system in detail. This algorithm permits the appearance of non-zero initial states and any type of pumping signals in the system to be identified, and could deal with multiple time-intervals situation. Simulation and analysis results show that this algorithm identifies initial states and transfer function accurately; moreover computation-time for identification is short and almost identical when system size changes. The general Prony identification algorithm is promising for online applications.In the second part, for inter-area low-frequency oscillation in power systems, two novel strategies for robust damping controller design using time delayed wide-area measurements are proposed. One of them is applicable to single-input single-output control. Time delay model of power system is established by employing general Prony identification of transfer function and Pade approximation of dead time delay. The damping controller is designed based on the mixed-sensitivity Hoo control theory and pole placement approach. Another one of them is applicable to multi-input multi-output control. Combining theories of delay-dependent state-feedback robust control and state observer, time-delay output feedback robust control is realized for wide-area power system. Small signal analyses and time-domain simulations demonstrate that these two controllers can inhibit inter-area low frequency oscillations evidently; meanwhile they are insensitive to time delay and robust to operating conditions.In the third part, based on the centre of inertia (COI) data provided by WAMS in power systems, completely decoupled generator model is constructed within COI-reference coordinate frame. According to Lyapunov theory and back-stepping concept, a simple and practical method is brought forward for decentralized nonlinear excitation control design. Simulation results show that this nonlinear excitation controller is robust to generator parameters, operating conditions and load types; meanwhile it allows the existence of relatively large time delays in COI signals. Based on this discovery, a novel strategy for time delay wide-area measurements selection is proposed in order to depress delay effects on control performance and simplify control design.