In recent decades, attention to renewable energy sources and distributed generation has increased significantly. The need for optimal deployment of these sources at the distribution level and dealing with the challenges of traditional distribution systems has led to the emergence of the concept of microgrids. As controllable and flexible systems, microgrids can work in grid-connected and off-grid modes and provide efficient power supply to consumers. These systems also help to increase the reserve capacity of the power grid and reduce transmission line losses. In recent years, DC microgrids have attracted a lot of attention due to their high efficiency, fewer power conversion steps, elimination of imbalance effects, and inherent compatibility with distributed generation units and energy storage systems. Despite many advantages of DC microgrids, these systems have great challenges such as low inertia and a variety of faults and failures including temporary and permanent electrical faults, sensor and actuator faults, and communication faults and failures that threaten their efficiency and stability. Therefore, to guarantee the continuity of operation and reliability of a DC microgrid, it is necessary to use fault-tolerant methods in these systems. Like severe electrical faults such as short-circuit and open-circuit, fault-tolerance of communication, sensor, and actuator faults is also of supreme importance. To compensate for the adverse impacts of these faults, fault-tolerant control methods are generally used in DC microgrids. In this thesis, fault-tolerant methods in DC microgrids are introduced and the advantages and disadvantages of each are stated. Then, to deal with the effects of the actuator fault, a new fault-tolerant control method is proposed. First, the dynamic system of the DC microgrid has been derived based on the state space equations in the presence of actuator faults in the control input of the DG unit converter. Then, using the H∞ method, a state observer is introduced to estimate system states and actuator faults. Based on the Lyapunov stability theory and with the help of linear matrix inequalities, the asymptotic stability of the observer’s estimation tracking is justified. Then by introducing some limitations, the proposed observer has been transformed to a local and independent observer. In the following, a fault-tolerant control method based on the proposed observer estimation is presented for a DC microgrid with actuator faults. The control method includes proportional-integral controllers for the primary control level and distributed control based on a consensus algorithm to achieve appropriate power sharing among DG units. To eva‎luate the performance of the proposed method, it is implemented in a typical DC microgrid and the simulation results indicate the validity of the proposed method.

محمد سعيد مهدوي

احمدرضا تابش , حميدرضا كارشناس