Power System Wide Area Damping Control

With the application of nation-wide power grid inter-connection and China's power transmission from the West to the East, a national hybrid AC/DC power grid will be formed in the future. Low-frequency oscillation has become an important factor that affecting the inter-connected power grids' stability and limiting the power transmission ability of the inter-area power system. Conventional power system stabilizer (CPSS) can damp local mode low-frequency oscillation effectively, but not the inter-area mode oscillations due to local information alone.At present, the development of synchronous phasor measurements technology and wide-area measurement system can provide nearly every real time signals of the power system under the same time frame, those real time signals including power angles and rotor speeds of generators, voltage vectors of the bus and the active power of the tie lines in the whole power system. With the progress of the wide area measurement system (WAMS) technology, we get new opportunity to damping low-frequency oscillation. The impact of time delays introduced by synchronous phasor measurement unit signal transmission and processing in wide-area measurement system should be considered. Because the time delay involved could deteriorate the power system's stability, so the effective devices to alleviate the effect of the time delay must be considered in the power system studies.In this paper, the design of WADC is considered. Firstly, the current status of low-frequency oscillation study and damping control of power system is recognized. Secondly, the model of inter-connection power system is introduced, and the design method of WADC is recommended lastly.A method for designing a wide area damping controller (WADC) of excitation system for damping inter-area power oscillations considering signals transmission delay and closed-loop power systems is presented. WADC using wide-area measurements signal of remote generations as input, then PSS using the output of WADC as its input can effectively damp inter-area oscillation. The effectiveness of lag compensation of a wide area damping controller (WADC) for offsetting the long time delay of wide area signals is analyzed. Firstly, the lead or lag compensation and time constants are selected according to the lag-angle of wide area signal caused by time delay. Secondly, Transform the selection of the gain of WADC and time constant of into the optimization of objective function using BCC (bacterial colony chemotaxis) and PSO(Particle Swarm Optimization) methods. Thirdly, an integral of the time-weighted squared error (ITSE) is used as performance index. And performance index would be got by solving the nonlinear differential-algebraic equations of multiple power systemsThe paper transform the selection of the gain of WADC into the optimization of objective function using PSO method, migration strategy is proposed by the simulation of nomadic migration, and the local extremum problem of particle swarm optimization has been solved by merging migration strategy. At the same time, the particle swarm optimization algorithm with ensemble technique has enhanced the global search capability of the algorithm badly. Finally, the novel algorithm has been used to deal with Multi-modal Function Problem, which is a complex problem in Function Optimization and the experiments show that the advanced particle swarm optimization is effective.The method of setting the gain of WADC using BCC is also introduced, Both BCC and PSO has been compared due to their different characters.The simulation results of a four-machine, two-area system with large disturbance show that WADC can damp the low frequency oscillations and improve power system stability for multiple time delays with a wide operating range according to the proposed method. And numerical results still demonstrate that the controller derived from the above method can damp low-frequency oscillations in the system for the feedback signals with multiple time delays.