17-E-AAA-0000 Droop based Fuzzy Control of a Low-Voltage Islanded DC Microgrid Mehrdad Beykverdi Department of Electrical Engineering Science and Research branch, Islamic Azad University Tehran, Iran Abolfazl Jalilvand Department of Electrical Engineering University of Zanjan Zanjan, Iran Mehdi Ehsan Department of Electrical Engineering Sharif University of Technology Tehran, Iran Abstract— This paper presented a new intelligent control strategy for DC microgrid in islanded operation mode based on droop control method. The DC microgrid under study included a Wind Turbine Generator (WTG), photovoltaic (PV), battery energy storage system (BESS) and a linear resistive load. According to the proposed method, each of distributed generation (DG) sources and BESS can be deployed independently within any controlled microgrid through the fuzzy control strategy. Proposed fuzzy control regulated virtual resistance of DGs and BESS unit locally and real-time based on the available power of DGs and the battery state of charge (SOC), to coordinate the module performances independently and establish the power balance and regulating DC bus voltage. Proposed control strategy for BESS enables the microgrid to supply independently the power required for the load demand when the DGs are not capable of supplying the required power to the load. The proposed fuzzy control strategy was applied locally and without dependency on the telecommunication links or any centralized energy management system. In order to validate the proposed method, the control system was implemented on a DC microgrid within MATLAB/SIMULINK, where the simulation results were analyzed and validated. Keywords— DC microgrid, fuzzy inference system (FIS), droop method, decentralized control, islanded operation. I. INTRODUCTION Microgrid refers to an integration of loads and distributed generation sources in low or medium voltage levels functioning as a power system for power generation and, if possible, as combined heat and power (CHP) [1–4]. A microgrid is utilized through two modes of connected or independently of the network. Electrical energy generation sources used in microgrids can be micro-turbines, fuel cells, Photovoltaic (PV) solar cells, Wind Turbine Generator (WTG) or other forms of distributed generation along with any storage devices such as super-capacitors and batteries [5,6]. With the progress made in distributed generation technology, there have been many advantages together with numerous problems in terms of network operation and protection. For example, one of the problems arising due to the growth and development of power systems is the aggravated level of fault current and short circuit because of the presence of Distributed Generations (DG). In addition, it is crucial to coordinate DG and Battery Energy Storage System (BESS) units in order to avoid that the power generated by DG may collapse the system when BESS are full of the charge and there is a power unbalance in the microgrid. So, DGs may change their control strategies from MPPT to a control strategy for regulating the voltage on the DC bus [7,8]. A good stored energy balance has been achieved, by adaptively adjusting the virtual resistance in droop controllers [9]. This method was useful for restoring the DC bus voltage, while the effect of the enhancement of current sharing accuracy was not obvious enough. The main purpose of analyzing the microgrid for power management is to maintain power balance between DGs and BESS, DC bus voltage regulation and minimizing power losses in the system concurrently [10]-[11]. Although the mentioned targets can be achieved by centralized controllers, implementation of the above method requires high-speed communication links, which reduce the reliability of the system [12]. It is noteworthy that functional status of the microgrid is identified and analyzed by DC voltage and transition between different microgrid operating points. In [13], four-terminal DC microgrid with a voltage source converter connected to the main network involves a WTG, a BESS and a linear DC load. In independent and local decentralized microgrid control, the virtual resistance value is determined by trial and error, or artificial intelligence techniques, where the former is extremely time-consuming and rarely yields an optimal solution [14]. When microgrid operates in island mode, DG converter operates as voltage source playing the role of slack bus in the conventional power system [15, 16]. Given the optimal allocation of power between DG units, the controlling effect on the circulating currents among resources is necessary to reduce power losses. In addition, coordination of DG and BESS units are necessary to control of battery charge and discharge process. In this case, the DG may change their control strategy from MPPT to a control strategy for