Distributed Voltage Control with Electric Springs: Comparison with STATCOMIEEE Trans. Smart Grid

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Authors
Xiao Luo, Zohaib Akhtar, Chi Kwan Lee, Balarko Chaudhuri, Siew-Chong Tan, Shu Yuen Ron Hui
Year
2015
DOI
10.1109/TSG.2014.2345072
Subject
Computer Science (all)

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IEEE TRANSACTIONS ON SMART GRID 1

Distributed Voltage Control with Electric

Springs: Comparison with STATCOM

Xiao Luo, Zohaib Akhtar, Student Member, IEEE, Chi Kwan Lee, Member, IEEE,

Balarko Chaudhuri, Senior Member, IEEE, Siew-Chong Tan, Senior Member, IEEE, and Shu Yuen Ron Hui, Fellow, IEEE

Abstract—The concept of electric spring (ES) has been proposed recently as an effective means of distributed voltage control. The idea is to regulate the voltage across the critical (C) loads while allowing the noncritical (NC) impedance-type loads (e.g., water heaters) to vary their power consumption and thus contribute to demand-side response. In this paper, a comparison is made between distributed voltage control using ES against the traditional single point control with STATic COMpensator (STATCOM). For a given range of supply voltage variation, the total reactive capacity required for each option to produce the desired voltage regulation at the point of connection is compared.

A simple case study with a single ES and STATCOM is presented first to show that the ES and STATCOM require comparable reactive power to achieve similar voltage regulation. Comparison between a STATCOM and ES is further substantiated through similar case studies on the IEEE 13-bus test feeder system and also on a part of the distribution network in Sha Lo Wan Bay,

Hong Kong. In both cases, it turns out that a group of ESs achieves better total voltage regulation than STATCOM with less overall reactive power capacity. Dependence of the ES capability on proportion of critical and NC load is also shown.

Index Terms—Demand response, electric springs (ES), STATic

COMpensator (STATCOM), voltage control, voltage regulation.

I. INTRODUCTION

VOLTAGE control in medium voltage (MV) or low voltage(LV) distribution networks is typically exercised through transformer tap-changers and/or switched capacitors/reactors.

Sometimes a STATic COMpensator (STATCOM) is used for fast and precise voltage regulation, especially for the sensitive/critical loads [1].

Manuscript received December 19, 2013; revised May 21, 2014; accepted July 14, 2014. This work was supported in part by the

Commonwealth Fellowship, the Hong Kong Research Grant Council under

Grant HKU10/CRG/10; in part by the University of Hong Kong Seed

Funds under Project 201111159239 and Project 201203159010, and in part by the Engineering and Physical Sciences Research Council under Grant

EP/K006274/1. Paper no. TSG-00927-2013.

X. Luo, C. K. Lee, and S. C. Tan are with the Department of Electrical and Electronic Engineering, University of Hong Kong, Hong Kong (e-mail: luoxiao@eee.hku.hk; cklee@eee.hku.hk; sctan@eee.hku.hk).

Z. Akhtar and B. Chaudhuri are with the Department of Electrical and

Electronic Engineering, Imperial College London, London SW7 2AZ, U.K. (e-mail: z.akhtar13@imperial.ac.uk; b.chaudhuri@imperial.ac.uk).

S. Y. R. Hui is with the Department of Electrical and Electronic

Engineering, University of Hong Kong, Hong Kong; and also with Imperial

College London, London SW7 2AZ, U.K. (e-mail: ronhui@eee.hku.hk).

Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/TSG.2014.2345072

The novel concept of electric spring (ES) has been proposed as an effective means of distributed voltage control [2].

The idea is to regulate the voltage across the critical loads while allowing the noncritical (NC) impedance-type loads (e.g., water heaters) to vary their power consumption and thus contribute to demand-side response [3], [4] as well. This would allow and facilitate large penetration of intermittent renewable energy sources without requiring huge amounts of energy storage to act as a buffer between supply and demand [5]. The basic proof of concept of ES has already been demonstrated through hardware experimentation with the developed prototypes [2], [6]. Distributed voltage regulation through collective action of a cluster of ESs, each employing droop control has also been illustrated [7].

In this paper, the focus is to compare the effectiveness of single point voltage control using STATCOM against distributed voltage control using a group of ESs. The basis for comparison is total voltage regulation [root mean square of the deviation of the actual voltages from the rated (1.0 p.u) values] achieved and the overall reactive capability required for each option in order to achieve that [8], [9].

A number of papers [2], [5]–[7] have been published recently on the ES concept and its control. However, none of those papers have focused on the collective performance of multiple of ESs considering realistic distribution networks.

This paper demonstrates the effectiveness of multiple ESs working in unison through case studies on an IEEE test feeder network and also a part of a real distribution system in Hong Kong. The voltage regulation performance and total reactive power requirement of a group of ESs in case of distributed voltage control is compared against the single-point control using a STATCOM. In both cases, it turns out that a group of ESs achieves better total voltage regulation than

STATCOM with less overall reactive power capacity.

II. ELECTRIC SPRING (ES) CONCEPT

Voltage control in LV and MV distribution networks and demand-side management (DSM) have traditionally been treated and tackled separately. Voltage control is usually achieved by control devices discussed in the previous section. DSM, on the other hand, is employed in a more distributed fashion (often at the appliance level) and is predicated on intelligence or communication facility in the appliance [10]–[12]. 1949-3053 c© 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.

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