TPEL 1 Abstract—Electric spring (ES) was originally proposed as a distributed demand-side management (DSM) technology for stabilizing power distribution network in the presence of intermittent power generation without using communication. This paper explores the practical use of consensus control for a cluster of electric springs (ESs) through a WiFi communication layer for new functions not previously realized in practice. This approach can be considered as a form of DSM for smart grid technology. A novel consensus control is introduced to enable distributed ES circuits to provide local voltage and system frequency regulations in a microgrid with shared responsibility of active and reactive power compensation. The practical implementation details of consensus control for a cluster of ESs are addressed. New plug-and-play functions of ESs are practically demonstrated for the first time under consensus control. Practical results indicate that droop control (without communication) and consensus control (with communication) are complementary. Under normal condition when the communication network is available, distributed ESs can perform with shared power compensation efforts based on consensus control. If the communication network fails, ESs can revert to perform under droop control. Index Terms—Consensus control, droop control, demand-side management, distributed control, electric spring, microgrid. I. INTRODUCTION NSTANTANEOUS balance of electric “power generation” and “power demand” is a fundamental requirement for power system stability. If the percentage of renewable power generation is negligible, utility companies can adopt the traditional control paradigm of “power generation following power demand”. Controlling power generation/supply is a type of “supply-side management” (SSM) with which the utility companies generate electric power to meet the load demand. In the emerging power grids with increasing penetration of Manuscript received November 23, 2017; revised February 19, April 16 and August 14, 2018; accepted September 20, 2018. This work was supported in part by the Hong Kong Research Grant Council under the theme-based project T23-701/14-N. J. Chen, S. Yan, T. Yang and S.C. Tan are with the Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong (e-mail: distributed renewable energy generation of intermittent nature (known or unknown to the utility companies), the total power generation/supply becomes difficult to predict and control in real time. This situation will be worsen when the penetration of intermittent renewable energy becomes substantial. Under such situation, the power generation on the supply side is changing dynamically with the wind and solar power profiles. Any mismatch of power generation and demand could lead to fluctuations in the mains voltage and frequency. Generally, mismatch of active power leads to frequency variations while mismatch of reactive power results in voltage variations. Therefore, utility companies would have difficulty in ensuring that the local ac mains voltage can meet the typically +/-5% tolerance, because tap changing of local transformers is too slow to cope with fast transients. For a weak power grid or a microgrid using small generators with low inertia, the frequency fluctuation could become a serious issue and a threat of power system collapse. An alternative control paradigm of “power demand following power generation” has been suggested for future power grid with a high percentage of intermittent renewable energy generation [1]. If power consumption of some loads can vary adaptively to follow the fluctuating renewable power generation profile, the power demand and power generation can be balanced in real time [2]. Modulating the load consumption adaptively to achieve power balance in a power grid is a type of “Demand-Side Management” (DSM). In practice, SSM and DSM are two approaches that can play a part in achieving power balance. They are not mutually exclusive and can be complementary. For example, consensus control of distributed generators has been proposed to maintain voltage stability [13]. Fig.1 (a) shows a simplified schematic of using distributed generators for providing regulated mains voltage at the point of common coupling (PCC). Curtailment of wind and solar power is one example of SSM [3]. However, using SSM itself is insufficient in maintaining local voltage stability particularly when the load is remotely connected to the local transformer through a long distribution line (e.g. in rural areas) as shown in Fig.1 (b). If DSM can be applied on the remote load in Fig.1(b), the local load voltage can also be regulated. This important jiechen@eee.hku.hk; yanshuo@connect.hku.hk; yang2014@connect.hku.hk; sctan@eee.hku.hk). S. Y. R. Hui is with the Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong, and also with the Department of Electrical and Electronic Engineering, Imperial College London, London SW7 2AZ, U.K. (e-mail: ronhui@eee.hku.hk; r.hui@imperial.ac.uk). Practical Evaluation of Droop and Consensus Control of Distributed Electric Springs for Both Voltage and Frequency Regulation in Microgrid Jie Chen, Student Member, IEEE, Shuo Yan, Member, IEEE, Tianbo Yang, Student Member, IEEE, S.C. Tan, Senior Member, IEEE, S.Y. (Ron) Hui, Fellow, IEEE I