Reduction of Cogging Force in Linear Permanent-Magnet Generators

Although linear permanent-magnet generators (LPMGs) are widely used for converting wave energy into electrical energy, they suffer from large cogging force. The cogging force causes oscillatory output power, which shortens lifetime and increases the maintenance costs of the generators. To reduce this force in the generator, we have designed and simulated a three-phase LPMG for direct wave energy conversion and predicted its performance using the finite-element method. We studied the influence of different design parameters on the cogging force and minimized this force by varying the proposed parameters. The results obtained confirm a large reduction in the cogging force and an enhancement in the generator performance.     

Artificial neural networks for automotive air-conditioning systems performance prediction

In this study, ANN model for a standard air-conditioning system for a passenger car was developed to predict the cooling capacity, compressor power input and the coefficient of performance (COP) of the automotive air-conditioning (AAC) system. This paper describes the development of an experimental rig for generating the required data. The experimental rig was operated at steady-state conditions while varying the compressor speed, air temperature at evaporator inlet, air temperature at condenser inlet and air velocity at evaporator inlet. Using these data, the network using Lavenberg–Marquardt (LM) variant was optimized for 4–3–3 (neurons in input–hidden–output layers) configuration. The developed ANN model for the AAC system shows good performance with an error index in the range of 0.65–1.65%, mean square error (MSE) between 1.09 × 10^?5 and 9.05 × 10^?5 and the root mean square error (RMSE) in the range of 0.33–0.95%. Moreover, the correlation which relates the predicted outputs of the ANN model to the experimental results has a high coefficient in predicting the AAC system performance.     

Performance analysis of fast reclosing transients in inductionmotors

Induction motors are used extensively in heavy industry. For these loads, this often requires reclosing on the motor before it reaches zero speed. However, if the supply voltage is applied before the motor reaches zero speed, the motor can be damaged due to excessive current and torque transients. This paper presents a performance analysis of fast reclosing transients in induction motors. It is shown that the optimum time instant for reclosing depends upon the supply voltage and load parameters. The results indicate that the maximum absolute value of instantaneous torque occurs in the first cycle and for every time cycle of supply voltage. In fact, there are at least one positive peak and one negative peak for the torque     

Performance of Object Classification Using Zernike Moment

Moments have been used in all sorts of object classification systems based on image. There are lots of moments studied by many researchers in the area of object classification and one of the most preference moments is the Zernike moment. In this paper, the performance of object classification using the Zernike moment has been explored. The classifier based on neural networks has been used in this study. The results indicate the best performance in identifying the aggregate is at 91.4% with a ten orders of the Zernike moment. This encouraging result has shown that the Zernike moment is a suitable moment to be used as a feature of object classification systems.     

Sensorless direct torque control of induction motors used in electric vehicle

A three-phase squirrel-cage induction motor is used as a propulsion system of an electric vehicle (EV). The motor is controlled at different operating conditions using a direct torque control (DTC) technique combined with a new switching pattern producing low harmonics. The operating flux of the motor is chosen optimally for losses minimization and good dynamic response. Since speed estimation is sensitive to rotor resistance variations, the rotor resistance value is calculated and modified in real time continuously. Simulation and experimental results show that the proposed DTC is able to follow the reference speed (which may be only input reference of the system) with a reasonable dynamic and relatively low error.     

Preparation,FTIR spectroscopic characterization and isothermal stability of differently doped fibrous conducting polymers based on polyaniline and nylon-6,6

The fibrous conducting polymers based on polyaniline and nylon-6,6 are obtained by stirring with magnetic bar. The increase in the ratio of conducting polymer volume in case of such fibers make them attractive materials for potential applications. As it is difficult directly to form fibers of conducting polymers, stirring process is attempted to form fibers of conducting polyaniline and nylon-6,6. In the present paper, the fibrous polyaniline:nylon-6,6 (PANI:Ny-6,6) with different weight percentages (5–20%, w/w) are prepared by stirring process. The fibers obtained are characterized using Fourier-transform infrared spectra (FTIR) and scanning electron microscopy (SEM), the variation of electrical conductivity with different type doping agents 0.1 M (HCl, H₂SO₄ and HClO₄) and the stability in terms of DC electrical conductivity retention was studied in an oxidative environment by isothermal characteristics.     

A novel technique for estimation and control of stator flux of a salient-pole PMSM in DTC method based on MTPF

A permanent-magnet synchronous machine (PMSM) can be controlled using the direct torque control (DTC) technique in three different ways, i.e., by controlling flux, reactive torque and rotor d-axis current. Frequently, the DTC technique controls the speed of the motor by controlling stator flux with the aim of obtaining an optimal torque. A varying flux, proportional to the torque, may be used instead of a fixed flux, resulting in a maximum torque per ampere or maximum torque per flux (MTPF). In this paper, a reference-flux-generating method is followed to achieve the MTPF. An approximate equation is then derived using numerical techniques in order to obtain the reference flux from the torque. This equation is then applied to the DTC control system in order to obtain the reference flux. The control scheme has been verified by simulation and tests on a salient-pole permanent-magnet synchronous motor.     

Design of a high power brushless linear variable transformer

High power variable transformers are required for use in advanced high voltage-high power laboratories. However, their design is always confronted with various difficulties caused by different physical and electromagnetic design constraints. This paper presents a new design for a high power brushless linear variable transformer. The proposed design has desirable features such as low short circuit impedance which may be useful for different tests particularly high current tests, over a wide range of power requirement. An analytical design procedure is followed, after which a finite element analysis is used to confirm the analytical design results.     

A complete lumped equivalent circuit of three-phase squirrel-cage induction motors using two-dimensional finite-elements technique

The paper presents the use of the finite element technique for determining the parameters of a three-phase squirrel-cage induction motor. The common parameters in addition to the core losses and ratio of number of turns are obtained from the finite-element field solutions. The magnetizing characteristic and core losses curve are used to determine the flux distribution within the motor structure. The linear time harmonic vector potential field solution is used for the inductances computation. The accuracy of the finite-element application is verified using the available precise results.     

α-Fe2O3 as an anode material with capacity rise and high rate capability for lithium-ion batteries

We report a simple molten salt method to prepare nanosize α-Fe₂O₃, as well as its electrochemical performance as anode material for lithium ion batteries. The structure and morphology were confirmed by Raman spectroscopy, X-ray diffraction, and transmission electron microscopy. The as-prepared α-Fe₂O₃ is a rhombohedral phase of hematite with crystal size in the range of 20-40 nm. The electrochemical measurements were performed using the as-prepared powders as the active material for a lithium-ion cell. The nanosized α-Fe₂O₃ shows excellent cycling performance and rate capability. It also exhibits the feature of capacity increase upon cycling. The outstanding electrochemical performance of the α-Fe₂O₃ can be related to several factors, namely, the short Li⁺ diffusion length along the porous rhombohedral structures and the nanosized nature of the materials, which decreases the traverse time for electrons and Li⁺ ions, and reduces the volume expansion to some extent during charge/discharge reactions.