Translated Abstract
Power flow is the most important and fundamental tool for the analysis of any power system. With the development of distribution systems, the research of power flow in distribution systems draws much attention. A lot of effective algorithms have been proposed to solve power flow problem in distribution systems. In addition, some factors bringing asymmetry to the operation of three-phase power system arise with the development of power system. It is necessary to do three-phase power flow calculation under the imbalanced state in the programming, design and operation of power systems. Based on the existing power flow algorithms, a novel method for distribution systems is presented. The power flow equations in this new method are solved using extra-matrix technique. The novel method also is applied to the three-phase power flow in distribution networks. Based on Newton method, the novel power flow equations could be derived from nodal injected power equations by linearizing the complex power equations. According to the definition of self-admittance, the diagonal elements of Jacobian Matrix could be simplified. The Jacobian matrix of PQ buses becomes constant. The traditional real power equations and voltage equations are applied to PV buses. Some of the Jacobian elements of PV buses need update. Most of the Jacobian elements are constant because of few PV buses in distribution systems. The variable elements in Jacobian matrix are put behind the constant ones. The extra-matrix technique is used to solve the equations. Hence, not only the PV buses are properly handled, but also the constant trait of Jacobian matrix is applied to attaining the high computation speed. Numerical tests on several typical distribution systems show that the high resistance/reactance ratio does not influence its convergence, and it can also be used in the distribution networks with PV nodes and the meshed ones. Father compares with traditional Newton method and fast-decoupled method show that the proposed algorithm has excellent convergence characteristics and is very robust. The proposed method is extended to calculating three-phase power flow. The Jacobian matrix for PQ buses and slack bus keep constant in three phase distribution networks. The internal buses are introduced to PV and slack buses. Each PV buses have eight iterative equations. Only two of them have variable Jacobian coefficients. So most of Jacobian elements are constant. The eatra-matrix technique also is applied to solving the power flow equations. The proposed method has been tested in several distribution networks. Results are compared with Newton method and show that the proposed method is more efficient. The applications of proposed method to high r/x networks and meshed ones have also been demonstrated.
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