Output power leveling of wind turbine generators using pitch angle control for all operating regions in wind farm

Effective utilization of renewable energies such as wind energy instead of fossil fuels is desirable. Wind energy is not constant and windmill output is proportional to the cube of the wind speed, which causes the generated power of wind turbine generators (WTGs) to fluctuate. In order to reduce the output power fluctuation of wind farms, this paper presents an output power leveling control strategy for a wind farm based on both the average wind farm output power and the standard deviation of the wind farm output power, a cooperative control strategy for WTGs, and pitch angle control using a generalized predictive controller (GPC) in all WTG operating regions. Simulation results using an actual detailed model for wind farm systems show the effectiveness of the proposed method. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 158(4): 31– 41, 2007; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.20448     

A dual doubly curved reflector antenna having good circular polarization characteristics

A new type of shaped-beam radar antenna having good polarization characteristics is described. This antenna is composed of a dual doubly curved reflector system and a feed horn with good axial ratio, such as a dual-mode horn. The rotationally symmetrical beam of the feed horn can be converted into a shaped beam by the reflector system without degradation of the axial ratio. The design of this type antenna is discussed and the experimental results of a model antenna with a cosecant squared beam are shown. Integrated cancellation ratio of the model was 22 dB.     

Output power dispatch control for a wind farm in a small power system

Nowadays, a wind turbine generator (WTG) is required to provide control capabilities as the output power of WTG fluctuates. Under this scenario, this paper proposes an output power control method of a wind farm (WF) connected to a small power system using pitch angle control. In this control approach, the WF output power control is achieved by two control levels: central and local. In the central control, the WF output power command is determined by considering the frequency deviations and wind speeds using a fuzzy function. Then, the local output power commands for each of the WTGs are based on the proposed dispatch control. In the proposed dispatch control, the output commands of each WTG are determined by considering wind conditions for each of the WTGs. The simulation results by using an actual detailed model for the wind power system show the effectiveness of the proposed method. Copyright © 2010 John Wiley & Sons, Ltd.     

Control strategy for a distributed DC power system with renewable energy

This paper deals with a DC-micro-grid with renewable energy. The proposed method is composed of a gearless wind power generation system, a battery, and DC loads in a DC distribution system. The battery helps to avoid the DC over-voltages by absorbing the power of the permanent magnet synchronous generator (PMSG) during line-fault. In addition, the control schemes presented in this paper including the maximum power point tracking (MPPT) control and a pitch angle control for the gearless wind turbine generator. By means of the proposed method, high-reliable power can be supplied to the DC distribution system during the line-fault and stable power supply from the PMSG can be achieved after line-fault clearing. The effectiveness of the proposed method is examined in a MATLAB/Simulink^® environment.     

An integrated control method for a wind farm to reduce frequency deviations in a small power system

Output power of wind turbine generator (WTG) is not constant and fluctuates due to wind speed changes. To reduce the adverse effects of the power system introducing WTGs, there are several published reports on output power control of WTGs detailing various researches based on pitch angle control, variable speed wind turbines, energy storage systems, and so on. In this context, this paper presents an integrated control method for a WF to reduce frequency deviations in a small power system. In this study, the WF achieves the frequency control with two control schemes: load estimation and short-term ahead wind speed prediction. For load estimation in the small power system, a minimal-order observer is used as disturbance observer. The estimated load is utilized to determine the output power command of the WF. To regulate the output power command of the WF according to wind speed changing, short-term ahead wind speed is predicted by using least-squares method. The predicted wind speed adjusts the output power command of the WF as a multiplying factor with fuzzy reasoning. By means of the proposed method, the WF can operate according to the wind and load conditions. In the WF system, each output power of the WTGs is controlled by regulating each pitch angle. For increasing acquisition power of the WF, a dispatch control method also is proposed. In the pitch angle control system of each WTG, generalized predictive control (GPC) is applied to enhance the control performance. Effectiveness of the proposed method is verified by the numerical simulations.     

Effect of Support Materials on the Selective Methanation of CO over Ru Catalysts

Selective methanation of CO in the reformate gas (CO/CO₂/H₂/H₂O = 0.175/17.9/70.9/11.1) proceeded over Ru catalysts supported on metal oxides and zeolites. CO was selectively methanated at wide temperature ranges (200–275 °C) over Ru/γ-Al₂O₃, Ru/TiO₂ Ru/H-Y and Ru/H-beta catalysts. Higher Ru contents in Ru/γ-Al₂O₃ improved the selective CO methanation rate.     

Surface Structure of Converter Slag Stabilized by Heating

Converter slag contains free lime (CaO) and unstable iron oxides (FeO, FeOOH) that may lead to expansive self-destruction. A typical industry practice for converter slag has been stabilization by steam curing and autoclaving; however, the stabilization can only reach the surface, and not the inside, of slag particles. A new method is proposed in this study to stabilize the converter slag by heating at a low temperature. After magnetic separation, specimens of converter slag were subjected to heating for 2 h at a temperature of 500°C, resulting in a decrease of free lime content irrespective of the particle size. This effect was attributed to the formation of Ca₂Fe₉O₁₃ and complicated apatite groups owing to the heating. The iron oxides in the converter slag were analyzed by X-ray photoelectron spectra. It was found that after heating, the unstable FeO (wustite) content decreased and an oxidized α-Fe₂O₃ (hematite) increased. This led to the prevention of the iron-induced expansion. The rate of heat liberation by the free lime in converter slag was smaller than that of the reagent CaO. This suggests that the presumed free lime is in a different form based on the Ca bond energy in the surface of slag particles.     

Gain scheduling control of variable speed WTG under widely varying turbulence loading

Probabilistic paradigms for wind turbine controller design have been gaining attention. Motivation derives from the need to replace outdated empirical-based designs with more physically relevant models. This paper proposes an adaptive controller in the form of a linear quadratic Gaussian (LQG) for control of a stall-regulated, variable speed wind turbine generator (WTG). In the control scheme, the strategy is twofold: maximization of energy captured from the wind and minimization of the damage caused by mechanical fatigue due to variation of torque peaks generated by wind gusts. Estimated aerodynamic torque and rotational speed are used to determine the most favorable control strategy to stabilize the plant at all operating points (OPs). The performance of the proposed controller is compared with the classical proportional-integral-derivative (PID) controller. The LQG is seen to be significantly more efficient especially in the alleviation of high aerodynamic torque variations and hence mechanical stresses on the plant drive train. Simulation results validate the effectiveness of the proposed method.     

Effect of Silicate Anion Structure on Fixation of Chloride Ions by Calcium Silicate Hydrates

Calcium silicate hydrates, CaO–SiO₂-H₂O (C-S-H), were studied as a chloride fixation material. C-S-H of two different CaO/SiO₂ ratios were synthesized and burned with calcium chloride in a temperature range from 600° to 1000°C. Minerals with a chemical composition of CaO·SiO₂·CaCl₂ and 9CaO·6SiO₂·CaCl₂ were identified by X-ray diffraction analysis. Comparing the diffraction intensity, it was found that the most efficient chloride fixation was attained when burned at 800°C. Changes in the morphology of silicate anion associated with burning and fixation of the chloride were studied in terms of chloride fixation capability using the trimethylsililation technique. It was confirmed that some silicate anions formed a glassy infinite chain where the chloride ions were fixed as a solid solution.     

Effects of the GABA mimetic drug, sodium valproate, on event-related potentials and its relation to the law of initial value

The effects of gamma-aminobutyric acid (GABA) mimetic drug sodium valproate (VPA) on event-related potentials (ERPs) were investigated in 18 healthy volunteers during an auditory odd ball task. VPA (200 or 400 mg) or an inactive placebo was administered according to a completely randomized double-blind, cross-over design. ERPs were recorded one hour after medication was given. VPA did not affect the latencies of N100, P200, N200 and P300. Although on the whole VPA had no effect on the amplitudes of the ERP components in the subjects, it increased the P300 amplitude in the low P300 amplitude subjects and decreased it in the high P300 amplitude subjects. This tendency toward a bidirectional response was also seen in the P200 and N200 amplitudes. It was concluded that the response which takes place being dependent on the difference in the initial values was recognized on the effect of a single administration of 200 or 400 mg VPA to ERPs. The results of this study are discussed, especially in relation to the law of initial value.