A three-phase power flow algorithm for ungrounded network based on constraints of zero-sequence components. (February 2023)

• Record Type: Journal Article
• Authors: Zhang, Yi; Lin, Jinrong; Li, Chuandong
• Is Part Of: International journal of electrical power & energy systems. Volume 145(2023)
• Publication Date: 2023-02
• Subjects: Three-phase power flow -- Ungrounded network -- Zero-sequence -- Power quality; Electrical engineering -- Periodicals; Electric power systems -- Periodicals; Électrotechnique -- Périodiques; Réseaux électriques (Énergie) -- Périodiques; Electric power systems; Electrical engineering; Periodicals; 621.3
• DOI: 10.1016/j.ijepes.2022.108676
• Languages: English
• ISSNs: 0142-0615

Abstract

Highlights: The paper constrains the zero-sequence currents of the ungrounded winding nodes to zero, and combines with the power equations and the Newton Raphon method to propose a three-phase power flow algorithm for ungrounded distribution networks. The paper analyzes (a) the convergence problem of the method that constrains squares of zero-sequence voltages and currents to zero based on mathematical derivation and (b) the inapplicability problem of the method that constrains zero-sequence voltages to zero of the ungrounded winding nodes based on both a theoretical analysis and verification by examples. The algorithm proposed in the paper is universally applicable, and has a low computation time, high efficiency and good convergence performance. It has the potential to be widely applicable to engineering practice. Abstract: The existing research on three-phase power flow in ungrounded distribution networks primarily adopts the methods of presetting zero-sequence reference voltages and neutral point reference voltages. This makes it impossible to calculate the power flow in ungrounded network with non-zero neutral point voltages or zero-sequence voltages. Furthermore, a unified zero-sequence components constraint method of ungrounded distribution network does not exist. In this paper, a three-phase power flow algorithm is proposed to calculate three-phase power flow in an ungrounded distribution network. First, power flow equation variables, transformer admittance matrices and zero-sequence components are used to analyze the characteristic of three-phase power flow in an ungrounded distribution network. Second, a three-phase power flow algorithm for ungrounded distribution network is designed by constraining the zero-sequence currents of the ungrounded winding nodes to zero. Third, theoretical analyses and mathematical derivations are used to prove the applicability of the two methods, one of which constrains zero-sequence voltages of ungrounded winding nodes to zero and the other constrains squares of zero-sequence voltages and currents to zero. Last, a five-nodes network, modified IEEE123 network and practical network are used to demonstrate that the proposed method has a high accuracy and good applicability in calculating the three-phase power flow of ungrounded distribution networks.