Search results

Models of power semiconductor devices for use in circuit simulators need to take account of effects which can be neglected in low power device models; they then become very complex and difficult to parameterise. The power PIN diode model described in this paper demonstrates how the use of empirically derived look‐up tables can simplify the characterisation problem and how non quasi‐static effects can be incorporated

This paper aims to investigate the performance of two novel direct torque control (DTC) schemes dedicated to three-switch three-phase inverter (B3-VSI), also called delta inverter, fed induction motor (IM) drives.

The principle of operation of the B3-VSI-fed IM drive is recalled in a first step. Then, the basis of both proposed DTC strategies is presented. The first DTC scheme considers a subdivision of the stationary plane into three sectors and the application of the intrinsic as well as virtual voltage vectors to achieve the control combinations. While, the second DTC scheme considers a subdivision of the stationary plane into six sectors and a limitation of the voltage vectors incorporated in the look-up table to the three intrinsic ones.

Simulation and experimental results have revealed that, under steady-state operation and transient conditions, the harmonic content of the IM stator phase currents is lower in the case of the DTC2 strategy, resulting in a lower ripple of electromagnetic torque. Furthermore, it has led to a quasi-circular shape of the locus described by the stator flux vector in the stationary plane.

This work should be extended to the synthesis and performance analysis of a new DTC strategy for B3-VSI-fed IM drive, which emulates the operation of the conventional six-switch three-phase inverter-fed IM drive.

The limitation associated with the reduced number of the intrinsic voltage vectors generated by the B3-VSI has been eradicated, thanks to the suitable synthesis of the look-up table incorporated in the DTC scheme.

This study aimed to developed a defect detection system for a segment-type display module panel.

The system included a data acquisition card, a video camera, a computer and a display module on a testing table. The video camera captured the display pattern of the display module and transferred it to the computer through the data acquisition card. The dynamic multi-thresholding method and analysis as well as back propagation neural network classification was used to classify the detected defects.

The threshold values for the brightness at different positions in the display module image were obtained using the neural network and then stored in the look-up table, using two to six matrixes.

The recognition speed was faster and the system was more flexible in comparison to the previous system. The proposed method, using unsophisticated and economical equipment, was also verified as providing highly accurate results with a low error rate.

Although spreadsheets are now widely used in libraries, there is little evidence that their application to practical problems of library stock management has been recognised. This paper describes a project undertaken at Aston University Library and Information Services to use the spreadsheet package Excel to assist in planning the respacing of the periodical stock. After briefly outlining the background to the project, the paper describes in detail the construction of the spreadsheet and its implementation. Use of the Excel model demonstrated how the capacity of spreadsheets to perform complex calculations can be successfully applied to practical library problems.

In this paper, a new application of the Selected Harmonic Elimination Pulse Width Modulation (SHEPWM) technique used in the cascade multilevel inverter topology which is formed by series connections of one‐phase bridge type inverters (H‐bridge) is introduced. The advantage of the SHEPWM technique is its ability to operate in low switching frequency that makes it suitable for high power applications.

First, the switching angles are calculated using constrained optimization technique. By using these switching angles, the fundamental harmonic can be controlled and the selected harmonics can be eliminated. Then, using these calculated switching angles, a set of equation is formed which calculate the switching angles with respect to the modulation index. The switching angles at any modulation index can be easily obtained by solving the equation set. In this study, this equation set has been solved online using dSPACE DS1103 controller board. Using this technique, three‐phase voltages have been obtained from a five‐level cascade inverter. These voltages are applied to an induction motor.

The simulation results are verified by the experimental results. The results show that selected harmonics can be eliminated and an ac voltage with variable amplitude and frequency can be obtained using the proposed technique.

This paper presents a new application of the (SHEPWM) technique for multilevel inverters.

It is acknowledged that certain contradictions, or at least incongruities, are implicit in the idea of artificial intelligence. It is fairly certain that these were appreciated by the originators of the field and that the bold introduction of the new term was seen as a lifemanship ploy. This is not to deny the value of work under the heading.

An improved simulation model of switched reluctance motor (SRM) for steady-state operation that considers the core losses in the stator and rotor is established to obtain the steady performance of the high-speed SRM during the design, analysis and control of SRM driving system more accurately.

The transient core loss model for the material and SRM is presented. Then a new method for calculating the flux density of the motor in real time is introduced, and a steady-state simulation model of the SRM including real-time transient core losses calculation model is established according to the transient flux density. Because the transient core losses calculated by above method are the total core losses of the motor, a core losses distribution method is proposed and the steady-state simulation model of the SRM including the distributed core losses’ effect on the phase winding is established.

The comparison results show that the proposed model has higher accuracy than the traditional model, excluding core losses, especially at the moments when phase voltage is turn-on and turn-off. The proportion of the core losses to the motor losses increases with the increase in speed. So, the core losses’ effect on the steady-state performance of the high-speed SRM cannot be ignored.

The method to obtain flux density in the real time is presented and the improved steady-state simulation model of SRM that considering transient core losses is proposed.

The paper outlines a new approach for positioning a patient on the treatment table for radiation therapy sessions. The vision approach utilizes lasers and cameras for positioning and has several advantages over the conventional methods.

The positioning is accomplished by comparison of a set of computed tomography (CT) contours (acquired from the patient) with a set of corresponding contours acquired by a 3D vision system from the same region of the patient's body. The overall positioning error calculated by the iterative closest point algorithm is used to reorient the treatment table. Various issues related to the acquisition and generation of the 3D spatial data are discussed.

Positioning is accurate and can detect small movement in the patient's position.

Testing was done on a cast of a human torso and additional testing is required on in a hospital environment to fully test the efficiency of the approach.

The method merges data readily available from standard CT imaging systems and 3D imaging systems. Therefore, the additional hardware requirements are minimal. The system integrates well with existing hardware, software and treatment practices.

The method introduces a new approach to patient positioning employing a combination of sensor technologies. The approach is accurate, reliable, consumes less time and most importantly prevents the use of X‐rays for patient positioning.

This paper aims to imitate a cownose ray to develop a fish robot with paired flexible multi-fin-ray oscillating pectoral fins (OPFs) and control it to accomplish vivid stable 3-D motions using central pattern generators (CPGs) and fuzzy algorithm.

The cownose ray’s asymmetric sine-like oscillations were analyzed. Then a cownose-ray-like fish robot named Robo-ray was developed, which has paired flexible multi-fin-ray OPFs to actively control the fin shape and two tail fins to control the depth. To solve the problem of coordinated control for multi-degree-of-freedom Robo-ray, CPGs were adopted. An improved phase oscillator as a CPG unit with controlled amplitude, phase lag, smooth frequency transition and asymmetric oscillation characteristic was established. Furthermore, the CPG-fuzzy algorithm was developed for vivid stable 3-D motions. The open-loop speed control, the closed-loop control of depth and yaw were established.

The kinematic comparisons indicate that Robo-ray imitates the cownose ray realistically. The experimental results of closed-loop are obtained that the depth error of Robo-ray is less than ±100 mm and the course error is less than ±3°. Furthermore, the comprehensive experiments demonstrate that Robo-ray has high mobility, stability and robustness.

This research makes the fish robot with OPF propulsion closer to practical applications in complex underwater environment, for instance, ocean explorations, water quality monitoring and stealth military reconnaissance. In addition, Robo-ray can be taken as a scientific tool for better understanding of the hydrodynamics of OPF batoid.

Describes the Okapi projects and Okapi′s development as an experimental online catalogue system over ten years. The first Okapi project in 1984 introduced “best match” retrieval and focused on the user interface design. The second investigated word stemming, spelling correction and cross‐reference tables as retrieval aids. A comparative study of two library catalogues was undertaken in 1987, while in 1988 query expansion and relevance feedback were introduced and evaluated by laboratory tests. Live evaluation of automatic query expansion in an online catalogue and an online database was carried out in 1990. In 1993, subject enhancement of bibliographic records was investigated. The latest project has examined the design of a graphical user interface to support interactive query expansion. Discusses the research and evaluation of each project.