J Electr Eng Technol.2018; 13(6): 2254-2261 http://doi.org/10.5370/JEET.2018.13.6.2254 2254 Copyright ⓒ The Korean Institute of Electrical Engineers This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/ licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Stability Improvement of Battery Energy Storage System considering Synchronous Inductance Effect of Diesel Generator Jongmin Jo*, Hyunsung An* and Kwan-Ho Chun † Abstract – This paper analyzes stability of current control in respect of four cases of battery energy storage system (BESS) in a stand-alone microgrid. The stand-alone microgrid is composed of BESS, diesel generator and controllable loads, where all of them have a rated power of 50kW. The four cases are considered as following: 1) BESS with a stiff grid 2) BESS with the diesel generator 3) BESS with passive damping + diesel generator 4) BESS with active damping + diesel generator, and their stabilities are analyzed in the frequency domain and discrete time domain. The comparative analysis for four cases are verified through simulation and experiments through demonstration site of the stand- alone microgrid, where the DC link is connected to a 115kW battery bank composed of 48 lead-acid batteries (400AH/12V). Experimental results show a good agreement with the analysis. Keywords: Battery energy storage system, Microgrid, Stability analysis, Diesel generator. 1. Introduction Although demands for electrical energy have been consistently increased worldwide, many of the population such as developing countries are not receiving the benefits of electricity. In order for these people to use electrical energy, it is possible to expand existing electric networks or to introduce renewable energy systems based on wind turbine (WT), photovoltaic (PV) power generation. In general, it might be preferred to expand the existing electric networks, however, economic feasibility should be always considered since most of them in developing countries are resided in remote areas [1]. Furthermore, the concept of these remote areas is not limited to developing countries. In this case, a stand-alone microgrid can be recommended as an alternative, and it is considered as a small-scale distributed generation system [2, 3]. A study of microgrid has been already investigated from many researchers. The stand-alone microgrid is generally based on battery energy storage system (BESS), diesel generator (DG) and renewable energy, and BESS is the main unit among them. The primary role of BESS is to supply sinusoidal line voltage as the main source [4]. However, this can be impossible when the BESS does not generate enough output voltage because of an insufficient state of charge (SOC) of battery bank. BESS is equipped with ability to charge energy from other sources. When BESS is charged from diesel generator, a large synchronous inductance of that can cause resonance problem due to interference with LCL filter contained to BESS. Therefore, the techniques for stability improvement should be required to attenuate the resonance, and many literatures have been studied to perform that such as passive damping [5-7] and active damping [8-10]. This process needs stability analysis in order to determine damping resistor and/or damping gain as well as guarantee stable operating condition. This paper proposes control and operation of BESS in a stand-alone microgrid. BESS operates as a main source in the stand-alone microgrid and supplies power to loads, also PV and DG operate by an auxiliary power supply of BESS in parallel. In addition, current control for ensuring the stable BESS operation in the stand-alone microgrid is analyzed. An effect of relatively large synchronous inductance on LCL filter and current control with several operating conditions are comparatively analyzed through bode plot in continuous time domain and root locus in discrete time domain. Stability and performance for current control of BESS in terms of four cases are verified through simulation and experiments based on 50kW demonstration site. 2. Configuration of Stand-Alone Microgrid Fig. 1 shows configuration of the stand-alone microgrid which is composed of BESS, PV, diesel generator (DG) and controllable loads. BESS consists of Lead-Acid battery bank, DC-AC inverter. BESS operates as a main source in the stand-alone microgrid for supplying power to load. PV system consists of DC-AC inverter and PV array, and the load includes balanced, unbalanced and non-linear loads. Fig. 2 shows configuration of BESS which consists of DC link, three-phase DC-AC inverter and LC (or LCL) filter, and three-phase PWM inverter is applied to transmit high quality power from battery bank and renewable energy sources. † Corresponding Author: Dept. of Electrical and Electronic Engineering, Chungnam National University, Korea. (khchun@cnu.ac.kr) * Dept. of Electrical and Electronic Engineering, Chungnam National University, Korea. (jmjo@cnu.ac.kr; hsan@cnu.ac.kr) Received: April 5, 2018; Accepted: May 14, 2018 ISSN(Print) 1975-0102 ISSN(Online) 2093-7423