Transient Stability Analysis And Control For Power System Based On SGEAC Method

With the development of the national economy, the ever-increasing demand ofelectric energy has made it an essential part in modern society. Any fault in themodern power system may be a threat to the social stability and economic growth.Therefore, the steady and safe operation of the power system is gurantee of people’sdaily life as well as the element of the grid operation. The main reason causing blackout is that the transient state of the power system works on unstable condition duringthe large disturbance. In view of the steady and safe of the power system, it proposesthe control method by estimating the transient stability margin based on the transientstability, preventive and emergency control algorithm in this paper.The one machine infinite bus (OMIB) method, which have defined transientstability margin of dynamic OMIB, is shown that mechanical power adjustment basedon OMIB equivalent affects the transient stability. In this paper, in accordance of thebasic theory of OMIB equivalent and Single Generator Equal Area Criterion (SGEAC),the analysis of stability margin, the preventive and the emergent control of OMIBequivalent are studied and compared by using the equal area criterion based on OMIBand single equivalent. It is discovered that single equivalent based on the stabilitymargin, emergent and preventive mechanical power adjustment is exactly identicalwith the stability margin, emergent and preventive mechanical power adjustmentbased on OMIB equivalent. The understandings on the consistency based on differentequivalents and the influence between the mechanical power adjustment of eachequivalent and the transient stability are easier.We choose the data of the OMIB equivalent or the single equivalent generators inshort time as the Time-domain simulate data. And fit the rotor angle’s polynomialfunction of electromagnetic torque. Then get the arithmetic expression of stabilitymargin, preventive and emergent mechanical power adjustment in each equivalentgenerator during the fist swing on unstable condition. On the basis of those arithmeticexpressions, a calculation method for the amount of critical control during eachequivalent generator on unstable condition after first swing is proposed in this paper.System transient stability analysis results by simulations verify the theoretical results.In views of features of SGEAC method, it proposes an automatic calculationprogram to get the emergent mechanical power adjustment for the transient stability. This program in detail can verdicts the transient stability, distinguishes criticalgenerators, chooses the emergent control plan, and so on. The IEEE17test system andlarge-scale practical power system are checked out for evaluating the performance.Not only the high computational accuracy but also the fast counting rates are verifiedby the results of the tests. It is useful to the engineering application.As modern power system and new energy developed dramatically along, powersystem including several sections with tiny time constant, such as double feedinduction generator (DFIG), is popular recently. According to the DFIG model inMatlab/Simulink, it builds a wind power generation model for transient simulateprogram in power system, and calculated the initial value of the DFIG by Newtoniterative method. The results by simulating on one machine infinite system verify theprecision of the theoretical model and computing method.Because of the power system contained several sections with tiny time constant,the primary “nonrigid” power system is changed into “rigid” system. And it can not beanalyzed by the Euler method and the implicit trapezoid method. For this reason weproposed a new improved numerical method involved into the Euler method and theimplicit trapezoid method. This numerical method suits for the features of powersystem, can solve “rigid” system with high accuracy rate and is the multi-stepnumerical integration method with the analysis of the numerical stability and stabilitydomain. The consistency between the results calculated by that numerical method andtheoretical values are shown in the “rigid” system.A fast transient simulation method linked with the multi-step fast numericalintegration method for rigid power system also is proposed in this paper. Underconstant system integration step size, the integration step size of sections with tinytime constant can be changed by the variable parameter. Thus the numericalcalculation method of the model with tiny time constant can be obtained by thechanged step size regardless of the solution of network equations in power system. Itis note that the model with tiny time constant should be taken exact numericalcalculation with other elements in power system when the integration time of themodel with tiny time constant synchronizes with the system’s integration time. Theresults from the simulation about the DFIG show that the proposed method with fastcalculation speed and high precision is effective and practical.For transient features of DFIG affected by the protection of the crowbar, faultride-though capability of DFIG with crowbar are verified by the simulation results.The power system including the wind farm as object is analyzed and controlled by the SGEAC methods. According to the results obtained by the simulations, the SGEACmethod is feasible and its application range is obviously expanded.