Volt-VAR Interaction Evaluation in Bulk Power Systems - IEEE Xplore

Volt-VAR Interaction Evaluation in Bulk Power Systems Tao Jiang, Linquan Bai, Xue Li, Hongjie Jia, Fangxing Li, and Yao Xu

Abstract-This paper presents a novel method to evaluate the Volt-VAR interactions among the buses using relative gain (RG). Following the viewpoint of a multi-input-multi-output system, the Volt-VAR coupling RG is calculated based on the QV matrix which is extracted from power flow Jacobian matrix to evaluate the Volt-VAR interactions among the buses. The voltage stability weak buses are identified through a modified loading margin, and considered as voltage stability critical buses. The proposed evaluation method has great significance for partitioning Volt-VAR control areas in power systems. New England 39-bus system and Polish power system are used to test the performance of the proposed approach. The simulation results verify the effectiveness of the proposed approach in evaluating the Volt-VAR interactions. Index Terms-Bulk power system, cross-relative gain (eRG), loading margin, QV matrix, voltage coupling, voltage stability.

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I. INTRODUCTION

n the past several decades, electricity demand has been growing faster than the upgrading and expansion of electricity network. This fact leads to a high load level operating point for bulk power systems, which brings enormous challenges to maintain the system voltage stability [1]-[2]. The voltage control strategies adopted by system operators are usually on the basis of the layering and zoning regulation principle, which relies on the voltage control areas partitioning. The voltage control areas partitioning strategy relies on evaluating VoltiV AR coupling among the buses in the system. Therefore, it is of great significance to explore the methods for VolN AR coupling evaluation. At present, voltage interactions among buses are evaluated by using electrical distance, cluster analysis, and a combination of the both methods based on power flow Jacobian matrix. In [3], the degree of voltage coupling among nodes was defined based on P-Q decoupled power flow Jacobian matrix. Then, the concept of electrical distance was proposed, and according to the critical electrical distance, voltage control areas were partitioned. In [4], a hierarchical classification algorithm was employed to determine the voltage control areas based on the concept of electrical distance proposed in [3]. In [5], to eliminate the disadvantages of the reduced order matrix which

T. Jiang and X. Li are with Department of Electrical Engineering, Northeast Dianli University, Jilin, JL, 132012. P. R. China (e-mail: [email protected]). L. Bai and F. Li are with Deparlment of Electrical Engineering and Computer Engineering, The University of Tennessee, Knoxville, TN, 37996, USA (e-mail: [email protected]; [email protected]). H. Jia is with with Key Laboratory of Smart Grid of Ministry of Education, Tianjin University, Tianjin, 300072. P. R. China (e-mail: [email protected]). Y. Xu is with the Deparlment of Electrical Engineering, Lamar University, Beaumont, TX 77710 USA

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cannot reflect the coupling relationships between active power, reactive power, and angles, the voltage control areas were partitioned based on the senSItIvIty of full rank Newton-Raphoson power flow Jacobian matrix. Based on electrical distances and clustering analysis, a multi-attribute hybrid method for partitioning a power system into voltage control areas and zones was presented in [6] using graph partitioning algorithm in combination with an evolutionary computational algorithm. In [7], the load nodes were mapped into a space formed by generator nodes according to the sensitivity in quasi steady state. In the space, the electrical distance was defined, base on which, the voltage/reactive power areas were partitioned using clustering algorithm. An automatic voltage control software for online adaptive weak voltage stability areas partitioning was further developed and applied in the State Grid and China Southern Grid. The fundamental idea of voltage control strategies is to inject reactive power to the buses that contribute the most to the voltage stability of the studied area. To measure the voltage couplings, a novel relative gain (RG) based approach was proposed in [8] for identifying the voltage stability critical injection region (VSCIR). However, the proposed RG-based approach was based on the power system impedance matrix which only represents the influence of the system topology on voltage coupling. To address the aforementioned issues, this paper develops the RG in power systems based on QV matrix derived from power flow Jacobian matrix to evaluate the Volt-VAR interaction among the buses. In the proposed approach, the coupled single-port model is introduced, based on which, voltage stability index (VSI) is calculated to identify the voltage stability critical buses. Then, the RGs between critical buses and other buses are calculated to identify the buses that are tightly Volt-VAR coupled with critical buses. The effectiveness of the proposed approach is verified on the New England 39-bus system and Polish power grid. The rest of paper is organized as follows: In Section II, the RG calculation based on QV matrix is presented, and the Vol/V AR interaction evaluation method is proposed based on RG. In Section III, the effectiveness of the proposed approach is demonstrated by the case studies on the New England 39-bus system and Polish power grid. Section IV concludes this paper. II. VOLTAGE CONTROL AREAS PARTITIONING BASED ON RG

A. Relative gain array RG is a powerful tool for evaluating the interactions among decentralized controllers in multi-input multi-output (MIMO) systems to determine tight-coupled input-output pairs for

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eliminating the effects of interactions among multiple controllers [9]. In [10]-[11], RG was applied to detect dominant oscillation modes in power systems and place power system stabilizers (PSSs). In this work, RG is employed to assess the Vol/V AR interactions among buses in power systems. Definition of RC: a typical multi variable MIMO system is described in Fig. 1, where the system has m inputs and n outputs. The relative gain rij between input Uj and output Yi is defined as ",.

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