Energy management of smart grid connected hybrid energy storage system

Abstract

With the rapidly increasing demand of energy, renewable energy generation becomes increasingly popular due to its clean and sustainable features. Therefore, microgrids are gaining more attention with increased penetration of Renewable Energy Sources (RES). Among all the RESs, the Photovoltaic (PV) technology brings a huge advantage in the power industry. Due to its wide availability, microgrids can be used as independent power source for critical loads; hospitals and military bases during emergency situations such as earthquakes or bad weather, where there is no access to the main grid. Highly improved storage facility can be an option for these critical issues in the energy industry. Although Battery Energy Storage System (BESS) would be an option, its limited cycle life makes it cost ineffective to use only batteries for smoothing out the PV power fluctuations caused by renewable intermittency. In view of this, the combination of battery and Supercapacitor (SC) is one of the popular Hybrid Energy Storage System (HESS) configurations. The SC absorbs all transients and that will increase the life span of the battery. However, an effective Energy Management System (EMS) is required for these HESSs to achieve cost-effective system with high efficiency along with system stability. In this research thesis, among different types of control systems, the fuzzy logic system is considered. First of all, Mamdani type fuzzy inference system is implemented to track the maximum power point of the PV as this is very important in isolated microgrids where there is no backup power from the smart grid. The DC bus power balance can be achieved through the proposed Sugeno type fuzzy controller due to its high efficiency. With the variation of the load demand can be addressed successfully through another Mamdani type Fuzzy Inference System (FIS) to keep the State of Charge (SOC) of the battery and SC within safe range. Furthermore, in grid-connected mode, the new fuzzy logic based PQ controlled Voltage Source Converter (VSC) is implemented with the results. The simulation results are obtained using the MATLAB/Simulink R2017b integrated development environment. At the end of the simulation, these fuzzy logic results are compared with the conventional PI controlled system’s results to prove the proposed system’s efficiency. A new adaptive fuzzy controller is introduced in the later of this research to achieve more cost-effective operation for PQ controlled VSC. This controller will be generated different gains due to the electricity market price variations and current SOC of the HESS. Therefore, active power reference which will be used to exchange power from the grid will be changed due to the system output gain variations. Finally, hardware experiments are carried out for microgrid DC bus voltage regulation to further verify the efficiency of the proposed method. The dSPACE MicroLabBox is used to perform real-time simulation. The dSPACE is capable of communicating with the hardware using the Ethernet protocol. A universal dSPACE experiment software (ControlDesk 6.3) is used as the supervisory controlled and data acquisition platform for the MicroLabBox hardware. SEMIKRON Insulated Gate Bipolar Transistors(IGBTs) and their drivers are used to implement the DC-DC converters. However, hardware results show the proposed system has better characteristics than traditional PI controller based system. Keywords: Hybrid Energy Storage System (HESS), State of Charge (SOC), Energy Management, Fuzzy Logic Controller (FLC), Fuzzy Inference System (FIS).