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Due to the interconnected scheme of multiple components, such as distributed generators, storage systems, and loads through converters to a common bus in DC microgrids, the possibility of fault occurrence is increasing significantly. Meanwhile, due to the huge and rapid increase of short-circuit currents, the development of a small- and large-scale DC system requires a reliable and fast protection system to ensure fault clearance and maintain safety for the rest of the system. Thus, fault protection has been focused on as one of the most critical issues in a direct current network. The application of traditional circuit-breakers for DC fault protection has the drawback of slow operation, which requires a high rating power equipment. Recently, the high speed and excellent performance capabilities of semiconductor breakers have attracted a lot of attention and been considered as an optimal solution for fast DC fault interruption. In this study, a bidirectional Insulated-Gate Bipolar Transistor (IGBT) semiconductor breaker, suitable for the fault protection of low-voltage DC networks, is proposed. The operating characteristics of this breaker are based on changes in the circuit current and terminal voltage of IGBTs. It detects the abrupt change of the terminal voltage as an abnormal condition and isolates the faulted branch in a short time to prevent the operation disturbance in the healthy part of the network. Therefore, for the entire protection of a typical 400V DC-microgrid cluster, breakers need to be integrated and examined in each branch and the interconnected lines. The proposed protection method in this study is examined in a Simulink®/MATLAB environment to analyze and assess its operation. [ABSTRACT FROM AUTHOR]

Featured Application: The incentive method with flexible contribution functions can be applied to demand response by the reactive power market and distribution company, which has the possibility to reduce the additional installation of distribution control equipment and battery capacity. It also leads to the reduction of total electricity purchase cost of consumers, and the power system can achieve high mixing of renewable energy in the grid with the reactive power incentive demand response and the IoT development. Furthermore, reliability assessment of cooperative control with the participation rate will give an important contribution to the robust design of the system. In order to solve urgent energy and environmental problems, it is essential to carry out high installation of distributed generation using renewable energy sources (RESs) and environmentally-friendly storage technologies. However, a high penetration of RESs usually leads to a conventional power system unreliability, instability and low power quality. Therefore, this paper proposes a reactive power control method based on the demand response (DR) program to achieve a safe, reliable and stable power system. This program does not enforce a change in the active power usage of the customer, but provides a reactive power incentive to customers who participate in the cooperative control of the distribution company (DisCo). Customers can achieve a reduction in their total energy purchase by gaining a reactive power incentive, whilst the DisCo can achieve a reduction of its total procurement of equipment and distribution losses. An optimal control schedule is calculated using the particle swarm optimization (PSO) method, and also in order to avoid over-control, a modified scheduling method that is a dual scheduling method has been adopted in this paper. The effectiveness of the proposed method was verified by numerical simulation. Then, simulation results have been analyzed by case studies. [ABSTRACT FROM AUTHOR]

In consideration of the natural environment and depletion of energy resources, the widespread use of electric power system is expected in which the power is generated from sources of renewables such as wind and solar. When these plants are introduced in large scale, the use of broad land is required. Due to low transmission losses and small stability problems, multi-terminal high voltage direct current (MTDC) transmission becomes advantageous as long-distance power transmission system. Since DC current does not incorporate a zero cross point, therefore it's blocking is difficult. This paper proposes a DC resonant semiconductor breaker which enables rapid fault clearance for self-excited HVDC transmission. This circuit breaker is connected as a semiconductor switch, in parallel with a group of capacitors, and resistors in the DC transmission line. The capacitor is charged to a higher voltage from the DC transmission line. For generating reverse current to allow the zero cross point in the transmission line, the semiconductor switch turns on to open the circuit breaker. After blocking, the inductance of the line is demagnetized by the resistor and fault clearing is achieved. The system except fault point can continue its normal operation. [ABSTRACT FROM AUTHOR]