Analysis of the dynamic performance of a variable-frequency induction motor drive using various control structures and algorithms

A comparative analysis of the dynamic characteristics of field-oriented induction motor drive control systems relying on the main magnetic flux linkage vector reference, space-vector pulse width modulation (SVPWM) of the voltage inverter output, and direct torque control (DTC) is carried out using the Matlab/Simulink program package, with the parameters of the induction motor model used being the same. A changeover from stepless vector control systems to systems using microprocessors and modern controllable frequency converters operating on the principle of relay control entails possible changes in the properties of the electric drives being controlled. In this connection, there is a need to compare the dynamic performance characteristics of an electric drive with a slave vector control system (with an idealized frequency converter), referred to as electric drive 1 (ED1), an electric drive with a DTC system (ED2), and an electric drive using direct torque control and SVPWM (ED3). Modeling has shown that the response time of the torque control loop in all the control systems considered is the same, the time delay being no more than 0.01 s. On the whole, speed control transients in all of the above systems take their course in one and the same way. The differences in flux linkage control transients between ED2 and ED3, on the one hand, and ED1, on the other hand, are due to the differences between the methods used to form the electromagnetic torque. No provision is made in the above control systems for the stabilization of the magnitude of the flux linkage vector. At low loads, the flux linkage automatically follows the load. In an ED3 with direct torque control, the calculation of the necessary instant magnitudes of the voltage vector projections and the SVPWM based formation of the voltages applied to the motor allows implementation of a fast-response control system with minimal harmonic distortions and torque pulsations. The control system coefficients are calculated beforehand. The speed controller is adjusted to the technical optimum. In the main flux linkage oriented control system, it is also desirable to use an SVPWM-based formation of the motor voltage.     

Effects of blended vegetable‐based cutting fluids with extreme pressure on tool wear and force components in turning of Al 7075‐T6

In this study, performances of four different types of vegetable‐based cutting fluids (VBCFs) over a commercial mineral cutting fluid were evaluated for machinability of Al 7075‐T6. Lubrication properties of VBCFs were improved with additive of extreme pressure. Cutting force and tool wear data were obtained for performance analyses of cutting fluids during longitudinal turning of Al 7075‐T6. Cutting, feed and radial forces indicated 1.70–38.25% improvements for VBCFs over the commercial mineral cutting fluid. The lowest average values of flank and nose wears obtained with blended cutting fluid containing 12% of extreme pressure were 0.09 and 0.10 mm, respectively, whereas these values for the commercial mineral cutting fluid were 0.18 and 0.15 mm. The scanning electron microscope results showed adherence of workpiece material occurred on rake and flank faces, and flank and nose wears were the dominant wear modes. It was found that performances of VBCFs during turning of Al 7075‐T6 were better than that of the commercial mineral cutting fluid. Copyright © 2012 John Wiley & Sons, Ltd.     

The effect of transglutaminase on some physicochemical and sensory properties of the Turkish drinking yoghurt Ayran

This article presents research on the effect of microbial transglutaminase on the properties of Turkish drinking yoghurt Ayran. Transglutaminase (TGase) enzyme was added to Ayran milk at different production steps, after pasteurisation and together with starter culture addition, and two different incubation times (10 min and 1 h) were used. Three TGase‐treated Ayran samples and control sample were analysed on 1st, 10th and 20th days of storage. TGase addition did not cause significant changes on chemical properties of Ayran (P > 0.05). However, physical properties of Ayran were improved by TGase throughout the storage period. Compared to the untreated control sample, pretreatment of milk with enzyme increased the viscosity dramatically (P < 0.05) and prevented serum separation. Scanning electron microscopic studies revealed that transglutaminase treatment of milk led to more regular distribution of proteins in Ayran gel and decreased gel permeability. TGase treatment did not show any unfavourable effect on the sensory properties of the final product.     

Experimental diagnostics of ball bearings using statistical and spectral methods

Vibration measurements and signal analysis is widely used for condition monitoring of ball bearings as their vibration signature reveals important information about the defect development within them. Time domain analysis of vibration signature such as peak-to-peak amplitude, root mean square, Crest factor and kurtosis indicates defects in ball bearings. However, these measures do not specify the position and/or nature of the defects. Each defect produces characteristic vibrations in ball bearings. Hence, examining the vibration spectrum may deliver information on the type of defects. In this paper a test rig is designed and a pair of brand new commercial ball bearings is installed. The bearings run throughout their lifespan under constant speed and loading conditions. Vibration signatures produced are recorded and statistical measures are calculated during the test. When anomalies are detected in the statistical measures, vibration spectra are obtained and examined to determine where the defect is on the running surfaces. At the end of the test, the ball bearings are disassembled in order to take microscopic photos of the defects.     

Formation of a detonation wave in the process of chemical condensation of carbon nanoparticles

A new physical phenomenon — the formation of a detonation wave as a result of the condensation of substances — was investigated in detail. A detonation wave was formed under the action of the energy released in a process of chemical condensation of carbon nanoparticles behind a shock wave in the mixture initially containing 10–30% of the carbon suboxide C₃O₂ or acetylene C₂H₂ in argon. The propagation of the shock wave in this mixture led to the rapid thermal disintegration of its initial molecules and the subsequent formation of a condensed carbon with a significant energy release. The increase in the temperature and in the pressure of the reacting mixture leads to a strengthening of the shock wave and to its transformation into a detonation wave. The main kinetic characteristics of the reaction of thermal disintegration of the indicated molecules and their subsequent chemical condensation as well as the interrelation of these characteristics with the heat-release processes forming the detonation wave were determined.     

Simulation of dynamics of the neural ensemble in an active wireless network

The problem of emulation of the Hopfield networks in active wireless networks is considered. A network with six elements communicating via radio channels is studied experimentally.