sustainability Article Decentralized Control of DC Microgrid Based on Droop and Voltage Controls with Electricity Price Consideration Al Faris Habibullah , Faris Adnan Padhilah and Kyeong-Hwa Kim *   Citation: Habibullah, A.F.; Padhilah, F.A.; Kim, K.-H. Decentralized Control of DC Microgrid Based on Droop and Voltage Controls with Electricity Price Consideration. Sustainability 2021, 13, 11398. https://doi.org/10.3390/ su132011398 Academic Editors: Luis Carlos Herrero de Lucas, Dionisio Ramírez Prieto and Nestor Francisco Guerrero Rodriguez Received: 1 September 2021 Accepted: 12 October 2021 Published: 15 October 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Research Center for Electrical and Information Technology, Department of Electrical and Information Engineering, Seoul National University of Science and Technology, 232 Gongneung-ro, Nowon-gu, Seoul 01811, Korea; al.faris.habibullah@gmail.com (A.F.H.); farisap.fa@gmail.com (F.A.P.) * Correspondence: k2h1@seoultech.ac.kr; Tel.: +82-2-970-6406 Abstract: In this paper, a power flow control strategy (PFCS) for the decentralized control of DC microgrids (DCMGs) is proposed to enhance the flexibility and scalability of the microgrid power system. The proposed scheme is achieved by combining the droop control and DC-link voltage control with the consideration of the electricity price condition. Generally, the droop control method can be used effectively in decentralized DCMGs to achieve power-sharing without additional com- munication links. However, the deviation of the DC-link voltage caused by the droop control affects the amount of power delivered to the load. As an alternative, the DC-link voltage control can be used to prevent such a deviation. To combine both control schemes in this study, the utility grid (UG) unit uses the DC-link voltage control to exchange the power between the DC-link and a UG in the grid-connected mode, while a distributed generator (DG) and energy storage system (ESS) units use the droop control method in the islanded mode. The operating modes of the UG, DG, ESS, and load units are determined by the deviation values of the DC-link voltage to maintain DCMG power balance. The overall PFCS is also developed for a decentralized DCMG system by taking into consideration several uncertainties such as DG power variation, battery state of charge (SOC) level, load demand, and grid availability. The proposed PFCS also considers electricity price conditions to adaptively change the DC-link voltage level for the purpose of minimizing the utility cost. When the DC-link voltage level is reduced due to the high electricity price condition, the proposed droop controller is designed such that the ESS unit operates with a discharging mode, which leads to the required minimum power support from the UG. The effectiveness of the proposed PFCS is demon- strated by comprehensive simulation and experimental results under various conditions. Those test results clearly confirm the control flexibility and overall performance of the proposed PFCS for a decentralized DCMG system. Keywords: DC microgrid; DC-link voltage control; decentralized control architecture; droop control; electricity price consideration; power flow control 1. Introduction The increase of electronic devices has triggered the growth of research in electrical power systems, especially in renewable energy sources (RESs) like wind and solar resources. Several RES units are connected into electrical power systems as distributed generators (DGs) [1]. RES-based DGs are commonly interconnected with an energy storage system (ESS) to enhance the power system flexibility by storing the surplus power from DG and using it when necessary. On the other hand, the direct interconnection of ESSs and DGs in a utility grid (UG) supply leads to several control-related issues associated with different frequencies and voltages [2]. As a result, the microgrid concept has been introduced to develop an effective integration of power units such as the AC grid, DGs, and ESSs, and loads through a power converter interface in an electrical power system [3]. A microgrid uses a bus bar as the point of common coupling (PCC) which is used to connect power units and to share the power among electrical power sources [4]. According Sustainability 2021, 13, 11398. https://doi.org/10.3390/su132011398 https://www.mdpi.com/journal/sustainability