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In recent years, there have been problems such as exhaustion of fossil fuels, e.g., coal and oil, and environmental pollution resulting from consumption. Effective utilization of renewable energies such as wind energy is expected instead of the fossil fuel. Wind energy is not constant and windmill output is proportional to the cube of wind speed, which cause the generated power of wind turbine generators (WTGs) to fluctuate. In order to reduce fluctuating components, there is a method to control pitch angle of blades of the windmill. In this paper, output power leveling of wind turbine generator by pitch angle control using an adaptive control is proposed. A self-tuning regulator is used in adaptive control. The control input is determined by the minimum variance control. It is possible to compensate control input to alleviate generating power fluctuation with using proposed controller. The simulation results with using actual detailed model for wind power system show effectiveness of the proposed controller.

SUMMARYEffective utilization of renewable energies such as wind energy as a replacement for fossil fuels is highly desirable. Wind energy is not constant and wind generator output is proportional to the cube of the wind speed, which causes the power output of wind turbine generators (WTGs) to fluctuate. In order to reduce output power fluctuations of wind farms, this paper presents an output power leveling control strategy for wind farms based on both the mean and the standard deviation of wind farm output power, a cooperative control strategy for WTGs, and a pitch angle control method using a generalized predictive controller (GPC) intended for all operating regions of WTGs. Simulation results using an actual detailed model for wind farm systems show the effectiveness of the proposed method.

In order to improve the response speed of a very low level dc current amplifier, we propose a novel method in which a photocoupler, instead of a high resistor (1010 Ω), is employed for the negative feedback circuit. In this paper, it is shown experimentally that with the proper use of positive feedback, the rise time t r of 10 µs is obtained for this circuit at the current sensitivity of 10 pA. In comparison, the t r with the use of the high resistor with the shielding plate is 120 µs. (Here, the current sensitivity is the minimum measurable input signal current that produces an output signal voltage of a very low level dc current amplifier equal to its output noise voltage, or that leads to a signal-to-noise ratio of unity.)

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