Research On Single-port And Multi-port External Network Static Equivalent Method Based On The Internal Imformaion

In the actual power system, in the case of the external network imformationcompletely unknown, the simple equivalent machine method is commonly used by thedomestic Energy Management System. This method replace the adjacent power gridwith equivalent power injection hanging in the boundary node, which is too simple andwill causes big error for static security analysis to the independent subnetwork.Moreover, the research of estimating external network’s equivalent parameters based oninterner network information mainly concentrated in the single-port,and it have somelimitations, as for the multi-port external network equivalent, there are fewstudies.Therefore, this paper presents single-port and multi-port external network staticequivalent method based on the internal imformaion, it can estimate the externalnetwork’s equivalent parameters effectively on the basis of the internal network’stopology and state imformation. According to the scope of its application, this methodcan be divided into the following two parts:①This paper presents a single-port external network static equivalent method onthe basis of internal imformaion: this paper analyzes the limitations of the traditionalThevenin equivalent, Basd on it, obtaining two improved equivalent circuits by addingthe important element of the power system respectively, That is the extended Theveninequivalent with equivalent load and the extended Thevenin equivalent with the branchover the ground, on this account it can reflects the external network non-generator’snode power injection, and the line’s capacitance over the ground and the staticcompensator of substations. Then, based on the internal network’s topology and themulti-period state imformation, establishing the two improved external networkequivalent circuit parameters’s measurement equations, and establish the least squaremodel after taking into account of some components’ physical constraint, at last, it cancalculate the paremeters of the two improved external network equivalent circuits byusing interior point method.②This paper presents a multi-port external network equivalent method on the basisof internal imformaion: on the basis of general Ward equivalent circuit, it can obtainmulti-port simple Ward equivalent circuit and multi-port extended voltage-source Wardequivalent circuit by simplifying and expanding equivalent network circuit elementrespectively. Corresponding to the two equivalent circuit, there are two steps to calculate the multi-port external network equivalent parameters. First of all, on the basisof multi-period internal imformation, establish the multi-port simple Ward equivalentnetwork circuit parameters’s measurement equations and its least square model, thencalculate the equivalent parameters using interior point method; after that, on the basisof constraint relationship between the multi-port extended voltage-source Wardequivalent network circuit and the multi-port simple Ward equivalent network circuit,establish the former’s measurement equations and its least square model, to calculatingits parameters and take it as the final external network equivalent circuit. Finally,according to the measurement equations and estimation models of the two multi-portequivalent circuit’s parameters, this paper analyzes the relationship between the internalnetwork information’s number of period and the number of border nodes, and deducethe relation expression between them.This paper presents the single-port and multi-port external network staticequivalent method, solve the parameter estimation problem under the condition of theexternal network information is completely unknown in the interconnected power grid,laid the deep foundation for improving static security steady analysis’s accuracy ofindependent subnetwork. The simulation results of the IEEE-39bus system andGuangdong power grid verify the correctness of this paper’s method.