Power System Harmonic State Estimation Algorithm Based On Phasor Measurements

With the tendency that the harmonic sources are changing from small scale and partlydistribution to large scale and widespread distribution, harmonic power flow analysis isbecoming more and more inapplicable, and harmonic state estimation is appreciated.Harmonic state estimation is such a technology that forms measurement-state equationaccording to partly distributed measurement equipment, with the help of certain estimationprinciple, gets all nodes’ voltage vectors. On this basis, we can get current message and powerflow message of the whole power system according to the topology and parameter of thesystem. Then locate the harmonic sources.Firstly, in this paper, some analysis and contrasts are done on three concepts in powersystem: power system state estimation, harmonic power flow analysis and harmonic stateestimation. We do this in the purpose of getting clearly knowledge and distinction of the threeconcepts, and getting a better grasp of the difference between the harmonic state estimationand traditional methods.Secondly, in this paper, bus voltages are chosen as state variables, part of bus injectedcurrents, part of branch currents and part of bus voltages are chosen as measurement variables.On this basis, measurement-state equation is formed. Then the measurement-state equation issimplified with the help of some known conditions, and is solved according to the least squareestimation principle. Later, the theory to locate the harmonic sources is discussed in detail.The above processes are programmed by Visual Studio. In this program, input the topologyand parameter of the system, then we can get node voltages of the whole system. The validityof the method and the program is proved through Modified IEEE14buses system.Thirdly, four aspects about the observability of the power system are studied in thispaper:①This paper combines mathematics with the analysis of power systems, together withPseudo-measurements to decrease the number of the measurement equipment. And we can getthe smallest number of the measurement when the power system is observable. TheHeze-Fangshan distribution system is presented to illustrate the benefits of methods. ②Find and compute the unobservable states when the power system is not fullyobservable. The Singular Value Decomposition (SVD) is applied to accomplish the purpose.③Combined with condition number, a practical Linear Independent Ranking Method isproposed. The complexity of method is simplified when combining the Pseudo-measurements,Linear Independent Ranking Method, and the arrangement of measurement-state equation inadvance. The method proposed in the paper can work together with the solvation ofmeasurement-state equation directly. By using the condition number, the computed results canbe optimized and results are more reliable the same time when the measurement placementsare optimized.④The method proposed in this paper is applied to the Heze-Fangshan distribution system,and a reasonable configuration is given.