The Calculation Of Thevenin Equivalent Parameters Based On Wide Area Measurement System With Application On Voltage Stability Analysis

The modern power system is one of the largest and most complicated structure ofartificial system. Its stability problem is the import issue and was made more attentionto electric power scientific research personnel. Through the study we found that thestability of the entire system has close relation with a point or a certain degree ofregional stability. So how to find the weak nodes of voltage become the key to thevoltage stability analysis.Because the voltage collapse with concealment and sudden, so the weak nodes ofvoltage monitor becomes crucial. Looking for the weak nodes of voltage often adopt themethod that it is tracking thevenin equivalent parameters of nodes.So the accuracy ofthe thevenin equivalent parameters will be the key point to look for the voltage weaknodes. Only find the weak nodes and weak area of system voltage quickly and adjust itthat we can ensure the stable operation of the whole system. From this perspective, thispaper takes the measurement results of vector measurement unit of wide-areameasurement technology used for calculating the thevenin equivalent parameters of thenode which proposed in this paper. Using the full admittance matrix to solve thethevenin equivalent parameters,this theory is rigorous and does not exist anyassumptions. At the same time, solves the thevenin equivalent parameters of a certainmoment only need the parameter vector in this moment. This method can avoid theproblems of zero drift when use the parameter values on different moment. Through theproving of numerical examples and theoretical analysis this paper gets the importantrelation with self-impedance, thevenin equivalent impedance and load impedance. Therelation is self-impedance equal to thevenin equivalent impedance and load impedancein parallel. The process of solving the thevenin equivalent impedance in this paper relieson the node admittance matrix, which in the network voltage equation. From theformula solution we can see the matrix A, B, C and D are symmetric matrix. So, thispaper gives the new calculation method. First, the symmetric matrix is decomposed intothe form of LDLT, then the triangle matrix can be inversed respectively. In order toguarantee the method correctness, the paper gives the proving of simple three-nodenetworking. From the results we can see that the method of the thevenin equivalentparameters which proposed in this paper its theoretical error is zero.This method shall be applied in the arbitrary load nodes in power system, and it is suitable for solution the thevenin equivalent parameters of static and dynamic. Theresults can be used in real-time tracking to ensure that the system is stability. With theIEEE14nodes system as an example for the simulation calculation, and making thispaper’s calculation method comparison with the different solution methods of theveninequivalent parameters in nodes, you can see this article’s method has high calculationaccuracy and method is simple, at same time it has practical application value. Inaddition, on the basis of the thevenin equivalent parameters of system we can used it tocalculate the margin of the node impedance and analysis voltage stability of theparticular nodes.