**Coordinated Frequency and State-of-Charge Control Multi-Battery Energy Storage Systems and GeneratorsinIsolatedMicrogrid**

### **Jae-Won Chang 1, Gyu-Sub Lee 1,\*, Hyeon-Jin Moon 1, Mark B. Glick 2 and Seung-Il Moon 1**


Received: 4 April 2019; Accepted: 23 April 2019; Published: 28 April 2019

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**Abstract:** Recently, isolated microgrids have been operated using renewable energy sources (RESs), diesel generators, and battery energy storage systems (BESSs) for an economical and reliable power supply to loads. The concept of the complementary control, in which power imbalances are managed by diesel generators in the long time scale and BESSs in the short time scale, is widely adopted in isolated microgrids for efficient and stable operation. This paper proposes a new complementary control strategy for regulating the frequency and state of charge (SOC) when the system has multiple diesel generators and BESSs. In contrast to conventional complementary control, the proposed control strategy enables the parallel operation of diesel generators and BESSs, as well as SOC management. Furthermore, diesel generators regulate the equivalent SOC of BESSs with hierarchical control. Additionally, BESSs regulate the frequency of the system with hierarchical control and manage their individual SOCs. We conducted a case study by using Simulink/MATLAB to verify the effectiveness of the proposed control strategy in comparison with conventional complementary control.

**Keywords:** isolated microgrid; renewable energy source; diesel generator; battery energy storage system; hierarchical control
