Abstract
Direct current (dc) microgrids have gained significant interest in research due to dc generation/storage technologies—such as photovoltaics (PV) and batteries—increasing performance and reducing in cost. However, proper protection and control systems are critical in order to make dc microgrids feasible. This paper aims to propose a novel integrated control and protection scheme by using the state-dependent Riccati equation (SDRE) method for PV-battery based islanded dc microgrids. The dc microgrid under study consists of photovoltaic (PV) generation, a battery energy storage system (BESS), a capacitor bank and a dc load. The aims of this study are fast fault detection and voltage control of the dc load bus. To do so, the SDRE observer-controller—a nonlinear mathematical model—is employed to model the operation of the dc microgrid. Simulation results show that the proposed SDRE method is effective for fault detection and robust against external disturbances, resulting in it being capable of controlling the dc load bus voltage during disturbances. Finally, the dc microgrid and its proposed protection scheme are implemented in an experimental testbed prototype to verify the fault detection algorithm feasibility. The experimental results indicate that the SDRE scheme can effectively detect faults in a few milliseconds.
Highlights
In recent years, the microgrid has become more attractive, because of its ability to meet increasing energy demands in a greener way
The first part gives the results of the control of the output voltage of the PV system, battery, capacitor bank and dc bus in the presence of parameter uncertainty using an state-dependent Riccati equation (SDRE) controller
The second part is dedicated to analyzing the results of the SDRE observer for fast fault detection
Summary
The microgrid has become more attractive, because of its ability to meet increasing energy demands in a greener way. The energy storage device plays a key role in the demand–supply balance, which helps during islanding and re-synchronizing between the utility grid and microgrid [3]. It can tackle the energy crisis, and improve grid efficiency. The dc microgrid can lead to low power quality problems in the utility grid. For such a system, there are absences of harmonics, reactive power, and frequency regulation, but when dealing with an ac system such issues might arise [4].
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