Reverse matrix converter control method for PMSM drives using DPC

This paper proposes a control method for a reverse matrix converter (RMC) that drives a three-phase permanent magnet synchronous motor (PMSM). In this proposed method, direct power control (DPC) is used to control the voltage source rectifier of the RMC. The RMC is an indirect matrix converter operating in the boost mode, in which the power-flow directions of the input and output are switched. It has a minimum voltage transfer ratio of 1/0.866 in a linear-modulation region. In this paper, a control method that uses DPC as an additional control method is proposed in order to control the RMC driving a PMSM in the output stage. Simulations and experimental results verify the effectiveness of the proposed control method.     

森林物语 阿根廷Cher住宅

驱车来到阿根廷玛阿祖森林度假,你不仅会为海边森林优美的风景和宜人的气候所折服,不经意间,也许你还会看到一座与周边风景浑然一体别具风格的别墅,它就是BAK建筑事务所在阿根廷的玛阿祖森林里设     

Aerodynamic optimization of wind turbine rotors using a blade element momentum method with corrections for wake rotation and expansion

The blade element momentum (BEM) method is widely used for calculating the quasi‐steady aerodynamics of horizontal axis wind turbines. Recently, the BEM method has been expanded to include corrections for wake expansion and the pressure due to wake rotation (), and more accurate solutions can now be obtained in the blade root and tip sections. It is expected that this will lead to small changes in optimum blade designs. In this work, has been implemented, and the spanwise load distribution has been optimized to find the highest possible power production. For comparison, optimizations have been carried out using BEM as well. Validation of shows good agreement with the flow calculated using an advanced actuator disk method. The maximum power was found at a tip speed ratio of 7 using , and this is lower than the optimum tip speed ratio of 8 found for BEM. The difference is primarily caused by the positive effect of wake rotation, which locally causes the efficiency to exceed the Betz limit. Wake expansion has a negative effect, which is most important at high tip speed ratios. It was further found that by using , it is possible to obtain a 5% reduction in flap bending moment when compared with BEM. In short, allows fast aerodynamic calculations and optimizations with a much higher degree of accuracy than the traditional BEM model. Copyright © 2011 John Wiley & Sons, Ltd.     

Secluded maternity areas for parturient dairy cows offer protection from herd members

Use of individual maternity pens for dairy cows is recommended to ensure undisturbed calving and postpartum transfer of colostrum to calves, but management of these pens is a challenge due to difficulty predicting the time of calving. If group-housed cows, however, have the opportunity to calve in a secluded area of a group pen, this may limit disturbance of the dam and her newborn, especially if this area is fitted with a gate preventing other cows from entering. The aims of this study were to assess effects of cows calving inside a secluded area versus cows calving in the group area on maternal behavior and social interaction between dam and herd members during the first postpartum hour, calf's latency to stand, number of calves suckling an alien cow, and the dam's acute response to separation from the calf. This was investigated in pens consisting of a central group area with access to 6 secluded areas with or without a mechanical push gate allowing only 1 cow access at a time. At least 2 wk before expected calving, 60 Danish Holstein multiparous cows were assigned alternately, in groups of 6, to a group pen with 6 gated secluded areas or a group pen with 6 ungated secluded areas. The effects of treatment (gated, ungated) and calving place chosen within treatment (secluded area, group area) on maternal behavior, interactions with herd members, maternal response to separation, and calf latency to stand were investigated. Irrespective of whether cows calved in a secluded area or not and whether the secluded area was gated or not, cows spent, on average, 39 (±7.9) min of the first hour after calving licking their calves. When calving in a gated secluded area, the cows interacted less with herd members than when calving in the group area (0.5, 28, 18, and 33 min/h for gated/secluded, gated/group, ungated/secluded, and ungated/group areas, respectively), and no calves suckled an alien cow within the first hour after birth. In addition, the longer the calf stayed with the dam, the longer the dam stood with her head out of the pen after removal of the calf. Calf's latency to stand after calving was unaffected by treatment and calving place (mean = 39 min; range = 8–243 min). The results show that dam and calf can be protected from disturbances when cows calve in a secluded maternity area, especially if the secluded maternity area is fitted with a gate preventing other cows form entering.     

Successive laser-induced breakdowns in atmospheric pressure air and premixed ethane–air mixtures

Two successive focused laser pulses are employed to experimentally simulate laser-induced breakdown plasmas at high repetition rates. We find that energy absorption of the second laser pulse by the plasma produced by the first laser pulse is enhanced slightly when the time interval between the pulses is shorter than several tens of nanoseconds but falls to almost zero when the time interval is between a few hundreds of nanoseconds and several tens of microseconds. This behavior is attributed to gas heating by the first breakdown event. In premixed ethane–air mixtures, we identify another strong reduction in the second laser pulse absorption when this pulse coincides with the heat released by combustion, typically milliseconds after the first laser pulse. The fuel–air equivalence ratio (?) and base flow speed are also varied in this study. The results show that the window of reduced absorption coinciding with heat release due to combustion is narrowed when the base flow speed is increased, and also under fuel lean and fuel rich conditions. These results suggest that the use of pulsed high frequency laser breakdowns for premixed combustion stabilization is optimized when laser pulse repetition rates below a certain frequency (e.g., 500 Hz at the conditions that ? is 1 and the base flow speed is 4.9 m/s) to maximize laser energy coupling and for improved anchoring of the flame base.     

Increase in the annual energy production due to a retrofit of vortex generators on blades

The aim of the current work was to analyze the effect of retrofitting vortex generators (VGs) on the blades of a constant RPM, pitch‐regulated, megawatt‐sized turbine suffering from surface roughness. Engineering modelling and experimental work were utilized, indicating that the degradation of energy production may be mitigated by the VGs. The modelling results indicated that the optimal configuration of VGs to maximize the annual energy production (AEP) depends on the degree of severity of surface roughness. Depending on blade surface condition and turbine characteristics, installation of VGs on an incorrect blade span or installation of too large VGs too far out on the blade may cause loss in the AEP. Therefore, engineering modelling is necessary before VGs may be retrofitted on a specific turbine. The modelling results indicated that the worse blade surface, the more gain may be obtained from the VGs. The work included a full‐scale experimental validation of the present engineering model, lasting 27 months and comprising six turbines where VGs were mounted on three, each with a neighboring turbine as a reference. The turbines were analyzed in pairs, and the influence of the VGs was judged upon the relative difference in energy production before and after the installation. The reason was to limit measurement uncertainty. The results showed that all three turbines increased their energy production after the installation. Results from the three pairs showed an average increase in the energy production of 3.3%, being satisfactorily close to the average 2.8% predicted by the present engineering tool.     

Active fault tolerant control of piecewise affine systems with reference tracking and input constraints

An active fault tolerant control (AFTC) method is proposed for discrete‐time piecewise affine (PWA) systems. Only actuator faults are considered. The AFTC framework contains a supervisory scheme, which selects a suitable controller in a set of controllers such that the stability and an acceptable performance of the faulty system are held. The design of the supervisory scheme is not considered here. The set of controllers is composed of a normal controller for the fault‐free case, an active fault detection and isolation controller for isolation and identification of the faults, and a set of passive fault tolerant controllers (PFTCs) modules designed to be robust against a set of actuator faults. In this research, the piecewise nonlinear model is approximated by a PWA system. The PFTCs are state feedback laws. Each one is robust against a fixed set of actuator faults and is able to track the reference signal while the control inputs are bounded. The PFTC problem is transformed into a feasibility problem of a set of LMIs. The method is applied on a large‐scale live‐stock ventilation model. Copyright © 2013 John Wiley & Sons, Ltd.     

Color change of white spot lesions after resin infiltration

This study evaluates color change of the enamel lesion before and after resin infiltration and after thermocycling (TC) in order to assess clinical usefulness of resin infiltrant in restoring esthetics of incipient enamel caries lesions. Twenty‐five healthy premolars were prepared and crown portions were vertically cut. Specimens were emerged in acryl blocks with relatively flat proximal surface facing outside. Specimens were put in decalcification solution (50 mM acetic acid solution, 3 mM CaCl₂·H₂O, 3 mM KH₂PO₄, 6 µM methylhydroxydiphosphonate, pH 4.95, 37°C), and were kept for 160 h, in order to make white spot lesions on the exposed enamel. Degree of decalcification was observed with microscope and nine specimens were excluded because of inadequate decalcification (n = 41). L^*, a^*, and b^* were measured with colorimeter at the baseline (T₁), after production of white spot lesions (T₂), after infiltration of resin infiltrants (ICON^®, DMG, Hamburg, Germany) (T₃), after 3000 (T₄), 6000 (T₅), and 10,000 cycles (T₆) of TC. L^* was highest at T₂, but significantly decreased until T₆ which was the closest value to T₁ (P < 0.05). a^* was highest at T₂ and decreased gradually until T₆, whereas b^* was lowest at T₂ and was highest at T₃ and decreased gradually until T₆. Δ less than 3.7 showed between T₁ and T₄, between T₁ and T₅, and between T₁ and T₆, which suggested that it was hard to differentiate one from the other clinically. Resin infiltrated lesions showed recovery of CIE value close to that of healthy enamel over time. © 2013 Wiley Periodicals, Inc. Col Res Appl, 39, 506–510, 2014     

New High-Performance Pb-Based Nanocomposite Anode Enabled by Wide-Range Pb Redox and Zintl Phase Transition

This paper describes a new, high-performance, Pb-based nanocomposite anode material for lithium-ion batteries. A unique nanocomposite structure of Pb@PbO core-shell nanoparticles in a carbon matrix is obtained by using a simple high-energy ball milling method using the low-cost starting materials PbO and carbon black. Electrochemical performance tests show its excellent reversible capacity (≈600 mAh g⁻¹) and cycle stability (92% retention at 100th cycle), which are one of the best values reported for Pb-based anodes in the literature. Synchrotron X-ray diffraction and absorption techniques revealed the detailed lithium storage mechanism that can be highlighted with the unexpectedly wide reversible Pb redox range (between Pb²⁺ and Pb⁴⁻) and the evolution of Zintl-type Li_yPb structures during the electrochemical lithium reaction. The results provide new insights into the lithium storage mechanism of these Pb-based materials and their potential as low-cost, high-performance anodes.