Currently, the Direct-Current (DC) microgrid has been gaining popularity because most electronics devices require a DC power input. A DC microgrid can significantly reduce the AC to DC energy conversion loss. However, a power grid may experience a line fault situation that may damage important household devices and cause a blackout in the power system. This work proposes a new line fault protection scheme for a DC microgrid system by using a battery energy storage system (BESS). Nowadays, the BESS is one of the most cost effective energy storage technologies for power system applications. The proposed system is designed from a distributed wind farm smart grid. A total of three off-shore wind farms provide power to the grid through a high voltage DC (HVDC) transmission line. The DC microgrid was modeled by a BESS with a bi-directional DC–DC converter, various DC-loads with step down DC–DC converters, a voltage source converter, and a voltage source inverter. Details of the control strategies of the DC microgrid are described. During the line fault situation, a transient voltage was controlled by a BESS. From the simulation analyses, it is confirmed that the proposed method can supply stable power to the DC grid, which can also ensure protection of several loads of the DC microgrid. The effectiveness of the proposed system is verified by in a MATLAB/SIMULINK^® environment.

This paper proposes an uninterruptible all-electric smart house equipped with photovoltaic system and storage battery. There is a control delay in the conventional control system, because the system uses root mean square or average values for the control method. Therefore, it causes transient currents when load variation and system faults occur. The transient current adversely affects the in-house loads (e.g., precision equipment). In this paper, the control delay is reduced by using a control system with single-phase dq-transformation information. Therefore, the smart house achieves a reduction of the transient current caused by load variation and system faults through the use of instantaneous inverter control. The effectiveness of the proposed method is verified by simulation results given by the Matlab/SimPowerSystems® environment.

In recent years, the introduction of renewable energy generation facilities has been increasing all over the world. However, renewable energy generation often requires long-distance power transmission. Because it is widely distribution in all around. When the electric power is transmitted over a long distance, high voltage direct current (HVDC) power transmission is suitable. The HVDC transmission lines can reduce the transmission losses and equipment costs as compared to the AC system for a long distance power transmission. If the renewable energy generates a DC power, the HVDC transmission lines will improve the power system efficiency. However, it is not easy to boost a DC systems. This research proposes a DC power converter with a high step-up performance. The DC-DC converter modules are cascaded to achieve high voltage and large capacity. The LLC resonance type DC-DC converter is used for the DC-DC converter module. Soft switching can be achieved with a simple circuit configuration, and switching loss can be reduced. In addition, high frequency transformers in the converter ensures insulation from the transmission system. The operation of the proposed converter is verified by the simulation using MATLAB / Simulink. From the simulation results, the proposed method can reduce the cost and losses for a grid connected HVDC system.