Large-scale integration of renewable energy sources (RESs) such as wind power can impact on the existing power system's stability. For example, there is a possibility that the wind farm (WF) cannot be maintained stable and then it is disconnected from the grid when the instantaneous voltage sag caused by a grid disturbance occurs. Moreover, the increasing integration of RESs in the power system can reduce the number of conventional synchronous generators (SGs) connected to the grid, and lead to a reduction of system inertia in the grid. The system inertia reduction can cause larger and faster frequency fluctuations during the transient period. Hence, this paper proposes a new control strategy composed of the voltage control for suppressing the voltage sag and the virtual synchronous generator (VSG) control based on the proportional-integral-differential (PID) fuzzy logic control (FLC) for maintaining the frequency stability which is performed by high voltage direct current (HVDC) interconnection line. The aim of the new control strategy is to improve the stability of the entire power system with large-scale integration of RESs. The effectiveness of the proposed strategy is confirmed through the simulation analyses by PSCAD/EMTDC.

To supply a stable and efficient electricity, small-scaled wind turbine's brake system plays an immense role in various wind speeds. Small-wind power generation systems are difficult to operate in strong wind region since the turbine could be over-rotated and damaged if the brake system is not robust enough to maintain a stable angular velocity. Most of the smallscaled wind turbines use friction brakes to control the turbine speed for a stable electricity output. Since the friction brake are run out of time and needs frequent maintenance and eventually replacement, we introduce an eddy current based wind turbine brake system which is contactless with the rotor as an alternative to the friction brake system. The advantage of the proposed brake system is that the energy loss due to the friction will be reduced and will be more durable than the friction brake. The flow of this study is at first we did the analogical experiment of blade destruction to set to the maximum allowed angular velocity. Later, in order to verify the performance and stability requirement the mathematical implementation of eddy current brake system have done in DC-Green house for various wind penetration. Eventually the feasibility of eddy current brake system is confirmed in simulation results.

The aim of this research is to evaluate the behavior of small scaled wind turbine system against strong wind input using electromagnetic stall control system. In general, the wind turbine system is generating energy from the revolution of blades. The revolution of blade is varying through the environmental wind that is swept to blade. Therefore, if there is strong wind then the revolution of blade is increased and consequently more energy will be generated. Essentially the wind turbine systems are located in the gale area in order to generate energy efficiently. However, there is a boundary of revolution of blade, especially in small-scaled turbine due to small inertia momentum. If the angular velocity exceeds the boundary of revolution then wind turbine system may breakdown. Thus in this paper, in order to avoid the malfunction of small-scaled wind turbine system, electromagnetic stall control (ESC) is suggested. ESC can control the angular velocity without having any connection with shaft. Thus, we would control angular velocity much efficiently than the conventional stall control method such as friction stall control. For stability determination and performance evaluation phase plane method is applied in order for certain determination of stability. As a consequence, we could verify the reliability of ESC system by phase plane method.

Renewable energy generation systems are promising energy sources; however, they have a problem that they do not have, in general, inertia and synchronous power. A system with low inertial and synchronization forces has low stabilizing capability, and such systems are vulnerable to network fault and can cause large frequency fluctuations. This paper focuses on a large storage battery and a permanent magnet synchronous generator (PMSG) based variable‐speed wind power generator, and a new cooperative virtual inertia and reactive power control system between them which is based on Fuzzy Logic controller (FLC) and asymmetric hysteresis deadband is proposed and designed. Its effectiveness on the system stability enhancement during a grid fault is confirmed by simulation analyses on PSCAD/EMTDC.

This research aims to enhance the generated power of the small-scaled wind turbine using the eddy current brake system and Maximum Power Point Tracking (MPPT) control method. We analyzed the behavior of the generated power and power factor, with and without the MPPT control which implemented by eddy current brake system. Also, the feasibility of the system investigated using different wind conditions such as strong and calm wind conditions. The load data has different voltage respond to the system since its conditions depend on the day/night loads pattern, weather conditions, soil moisture. Moreover, the analogical experiment for small-scaled wind turbine blade destruction is analyzed to determine the maximum penetration value of mechanical power in order to retrieve an optimal angular velocity which resulting in provides a possible maximum power to loads. At the same time, emergency break is operated when angular velocity reaches to critical speed to avoid destruction. In the simulation, we collected the real load data from a mango farm in Okinawa prefecture in Japan. The results were analyzed through simulations for the different wind conditions. In the end of simulation, we could verify that either Maximum Power Point and emergency control are activated correspondingly.

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