3584 IEEE TRANSACTIONS ON POWER SYSTEMS, VOL. 32, NO. 5, SEPTEMBER 2017 Critical Bus Voltage Support in Distribution Systems With Electric Springs and Responsibility Sharing Yu Zheng, Member, IEEE, David John Hill, Life Fellow, IEEE, Ke Meng, Member, IEEE, and S. Y. Hui, Fellow, IEEE Abstract—With the development of a new smart load device, the electric spring (ES), the operation of distribution systems with high renewable penetration becomes more flexible. The ESs can be installed at noncritical loads for grid support. This paper proposes a two-level voltage management scheme to optimize the voltage profiles of the network, especially at chosen critical buses. In the upper level, the tap positions of load tap changer and capacitor banks switching are optimized to prevent the voltages along the feeder from being out of limits. The model predictive control tech- nique is applied to handle the uncertainties in renewable energy and demand. In the lower level, the responsibility of maintaining the voltages of the critical buses is shared among the ES in a dis- tributed way via consensus control which is suitable for systems with limited communication and calculation capabilities. The pro- posed management scheme is verified on a modified IEEE 15-bus distribution network. The results show that different voltage regu- lation devices can work together to maintain the voltage of critical buses by sharing the responsibility in the proposed scheme. Index Terms—Consensus control, distribution system, electric spring, model predictive control, voltage regulation. NOMENCLATURE AL Set of buses and lines B ij G ij Susceptance and conductance and of the line ij θ ij Phase difference between bus i and bus j Err t i Voltage violation of bus i at time t k p k i Proportional and integral parameters of the PI controller i, j Bus number I t i Current magnitude of bus i at time t m Modulation index of the Electric Spring N s The number of prediction error scenarios Manuscript received March 3, 2016; revised October 1, 2016 and November 25, 2016; accepted December 24, 2016. Date of publication December 29, 2016; date of current version August 17, 2017. This work was suported in part by the Hong Kong RGC Theme Based Research Scheme under Grants T23-407/13N and T23-701/14N, in part by the General Research Fund through Project 17202414, and in part by the National and Natural Science Foundation of China under Grants 51277016 and 71401017. Paper no. TPWRS-00342-2016. Y. Zheng and S. Y. Hui are with the Department of Electrical and Elec- tronic Engineering, The University of Hong Kong, Hong Kong (e-mail: zhy9639@hotmail.com; ronhui@eee.hku.hk). D. J. Hill is with the Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong, and also with the School of Elec- trical and Information Engineering, University of Sydney, Sydney, NSW 2006, Australia (e-mail: dhill@eee.hku.hk). K. Meng is with the School of Electrical and Information Engineering, University of Sydney, Sydney, NSW 2006, Australia (e-mail: ke.meng@ sydney.edu.au). 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/TPWRS.2016.2645940 P t i Q t i Net active power and reactive power at bus i at time t P L i ,Q L i Active power and reactive power consumption at of the load at bus i P L,N i Q L,N i Active power and reactive power consumption of the load at bus i at nominal voltage t Time step t s Start time of the operation horizon V upper V lower Upper and lower voltage magnitude limit V t i Bus voltage of bus i at time t V N Nominal voltage V es V max es Voltage output and maximum voltage output of the Electric Spring V t es,i V t o,i Voltage of the Electric Spring and load located at bus i at time t V t C ,V tar Voltage of the critical at time t and target voltage magnitude ΔV t C Voltage deviation of the critical bus at time t I. INTRODUCTION I N the past, distribution systems have been designed for a one- way flow of energy from substations to customers. However, in recent years, increasing numbers of distributed generators have being connected at the customer side, such as wind or solar, due to environmental and economic concerns [1]. These renewables, besides offering sustainability solutions to energy crisis, can defer network reinforcement, reduce energy transac- tion, and save power losses. However, due to the high penetra- tion level, energy now can flow in reverse directions during peak generation time, which is not allowed in the traditional systems, causing the voltage rise issue. Additionally, the voltage fluctu- ation along feeder caused by the intermittent nature of renew- able energy is unacceptable for some critical energy consumers, who require more reliable energy supply with higher power quality. In a conventional distribution system without renewable en- ergy penetration, voltage regulation is achieved through com- pensating voltage drop along feeder by typical means, such as load tap changer (LTC) and capacitor banks (CB). Such voltage regulation devices can respond to the voltage deviations accord- ing to different control strategies. Classic control algorithms and device models were proposed to keep the system voltages within constraints in [2]. However, in future distribution systems with the emerging voltage issues, LTC and CB are not flexible enough, especially for the voltage fluctuation mitigation [3]. The 0885-8950 © 2017 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications standards/publications/rights/index.html for more information.