Hidehito Matayoshi

This study proposes Higher Rotational Speed Maintaining (HRSM) control as a novel control algorithm that is suitable for large wind speed fluctuations. One of the challenges for wind generators is operating with significant wind speed oscillations. A wind generator with a large moment of inertia increases the time constant in rotational speed control and delays the tracking of the optimal operating point. It could reduce generated power by up to 40% or more. There are numerous regions in Japan’s inland areas where average wind speeds exceed 6.5 m/s. However, frequent fluctuations in wind speeds make wind power generation challenging. Therefore, this paper proposes a control algorithm suitable for wind turbines under unstable wind conditions. Higher rotational speeds are required to convert sudden high wind speeds into higher power when wind speed oscillations are large. Hence, the proposed algorithm focuses on maintaining the rotational speed throughout periods of unstable wind conditions for improving generation efficiency. The effectiveness of the proposed control method for wind turbines is verified via numerical simulation results. The novel control algorithm promotes the spread of wind turbines in unstable wind conditions area by overcoming the disadvantages.

Recently, the number of generation facilities using renewable energy is increasing, and HVDC attracts attention. With the proliferation of HVDC, it is expected that MTDC will be formed with complicated transmission system. Although HVDC is a promising system, there is a problem with system protection. For DC systems, faults must be detected and removed at high speed. Therefore, this paper proposes a fast fault detection method by measuring current slope using current differential information. With this proposed method, faults can be detected at high speed, and faulty areas and types can be distinguished.

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.

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.

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.