The Location Of Out-of-step Oscillation Center Based On Wide Area Measurements

During the operation of power system, no matter how stringent we treat the stability,steady damage accidents even out of step condition may always happen, which is causedby unpredictable factors. Practice shows that splitting the section of oscillation center canquell oscillation and make the system stable, so positioning out-of-step oscillation centeraccurately is necessary. With the gradual application of WAMS in power systems, it haspractical significance that we apply WAMS to locate the oscillation center andcompensate for the lack of existing methods.Traditional method of positioning out-of-step oscillation center is proposed underthe premise of the equivalent two-machine system, and it is based on the single-endedlocal electrical quantities, which is difficult to deal with the complex grid. Taking intoaccount that Ucos criterion is single-ended judgment, and it can only provide possiblerange of oscillation center, this article proposes a comprehensive method of positioningout-of-step oscillation center, which use variations of current, voltage and double-endedelectrical quantities of reactive power. All of these constitute a comprehensive approach,which includes starting criterion, out-of-step criterion and auxiliary criterion. In the end,verify the feasibility and accuracy of the method by the simulation examples.During the synchronous operation of power system, all the state variables have thesame frequency. Once it occurs out of step oscillation, the system frequency is no longerconstant, but shows some variation. Taking into account that existing methods rarelyused frequency and frequency can be directly measured by PMU, this paper proposes amethod of positioning out-of-step oscillation center, according to the monotonic andamplitude of the voltage frequency difference between the two ends of the line, we candetermine whether the system is out of step or not and distinguish the line where theoscillation center is located from other lines, then when the maximum frequencydifference occurs, use the voltage amplitude across the contact line to choose the rightsplitting point. Finally it verifies the feasibility and accuracy of the method by thesimulation examples, and conducts a comparative analysis with the previous methodfrom the aspects of sensitivity, accuracy and implementation.Under the premise that WAMS is widely used in the interconnected power system,this paper proposed two methods to locate the out-of-step oscillation center. By using thedouble-end electrical quantities, this paper makes full use of the wide-area measurementinformation, and improves the traditional positioning method, and it has practicalsignificance.