The Sdudy On Propagation And Control Of Electromechanical Wave In Power Systems

It is meaningful for ensuring the safe and stable operation of power systems to study the propagation rules of electromechanical disturbances further and find its control methods. Electromechanical wave theory of power systems is a new method which uses the continuum modeling to study electromechanical disturbances. There are many issues which need to be in-depth studied in applying the electromechanical wave theory into the analysis and control of actual power systems. For the issues of electromechanical disturbances’propagation and control, the three aspects, electromechanical disturbances propagation of actual power systems, the effect of internal reactance on its propagation, and its control based on superconducting magnetic energy storage(SMES) are studied tentatively in the paper.Existing research results of electromechanical wave theory are briefly introduced in the paper. The continuum electromechanical wave propagation equations of one-dimensional and two-dimensional space, and electromechanical propagation of one-dimensional chain discrete power system are showed. The velocity, characteristic impedance and the control principle of zero-reflection and zero-transmission are given according to those.The frequency sensitivity was studied on a practical power grid simulation system. The amplitude variation of all500kV buses frequency and generators angular frequency reach the given threshold value0.005Hz within2seconds after the grid suffers a0.43pu-active-power disturbance by PSASP. The value accounts for0.0616%of the total generation of the grid. The generator density and the tightness of the grid connection can be evaluated roughly by measuring the electromechanical wave propagation velocity of CDM grid and CN grid.On the one-dimensional chain power system, the fourth order nonlinear dispersion wave equation of bus voltage phase angle is given considering the internal reactance. The difference of wave with different wavelength propagation velocity may lead to waveform distortion because of dispersion. Through Laplace transform and residue method, the analytic solutions of bus voltage phase angle increment and active power increment after a step-power disturbance was solved. The simulations prove that the solutions are correct. It can be find that P.M. Anderson et al. proposed the analytic solutions of generator’s initial and inertia power assignment, while this paper’s analytic solutions could describe the whole process of power change by comparing the paper’s power propagation theory with the power assignment formula of P.M. Anderson et al. after a disturbance. Meanwhile, the effects of each of the bus voltage phase angle’s analytic solution on disturbance propagation were studied considering the typical parameters. It is concluded that in an actual power system a part of the disturbance power of every generator is assigned instantaneously, while the other part of the disturbance power is assigned at a certain speed by propagation in the electromechanical-coupled power system.The electromechanical characteristic impedance is got by the method based on measuring. The electromechanical disturbance propagation controller of power systems is designed based on SMES. On the WECC127-bus system using PSS/E, the zero-transmission-coefficient and0.6-transmission-coefficient controller are tested. The simulations show that the reflection and transmission of disturbance is in according with the theory and the controllers’effectiveness is verified. The design of disturbance controller based electromechanical wave is nothing with the disturbance itself, while it only concerns the network structure and parameters, which shows its superiority.