Evaluation of two prototype three phase photovoltaic water pumping systems

Bibliography: p. 221-223.Two prototype three phase AC photovoltaic pump systems (Solvo, ML T) and a DC PV pump (Miltek) were tested on a farm borehole in Namibia (latitude 21°6', longitude 17°6'). The PV array consisted of twelve modules (636Wpeak) mounted on a single-axis passive tracker. The depth of the water was 75m and a progressive cavity pump with a self-compensating stator was used in all the tests. Customised data acquisition was designed to measure performance characteristics through a range of operating conditions (mainly steady state); a secondary data acquisition system was used to capture samples of high frequency signals. The data allowed detailed analysis of system, subsystem and component performance, as well as performance evaluation over Standard Solar Days. The focus of the investigation was evaluation of the AC prototypes, in terms of performance, other technical factors, reliability and economic criteria. The analog-based DC system served as a basis for comparison. Both AC systems employed microprocessor control and PWM variable-frequency variable-voltage inversion. Efficiencies, optimality, stability, start-up behaviour, non-productive operating modes and protection were examined. A number of recommendations were proposed for improvements in the basic control algorithms, monitoring and managing non-productive modes, improved protection, layout and user diagnostic features

Signal processing techniques for analysis of heart sounds and electrocardiograms

Audible heart sounds represent less than 5% of the vibrational energy associated with the cardiac cycle. In this study, experiments have been conducted to explore the feasibility of examining cardiac vibration by means of a single display encompassing the entire bandwidth of the oscillations and relating components at different frequencies. Zero-phase-shift digital filtering is shown to be required in producing such displays, which extend from a recognizable phonocardiogram at one frequency extreme to a recognizable apexcardiogram at the other. Certain features in mid-systole and early diastole, observed by means of this technique, appear not to have been previously described. Frequency modulation of an audio-frequency sinusoid by a complex signal is shown to be effective in generating sounds analogous to that signal and containing the same information, but occupying a bandwidth suitable to optimum human auditory perception. The generation of such sounds using an exponential-response voltage- controlled oscillator is found to be most appropriate for converting amplitude as well as frequency changes in the original signal into pitch changes in the new sounds, utilizing the human auditory system\u27s more acute discrimination of pitch changes than amplitude changes. Pseudologarithmic compression of the input signal is shown to facilitate emphasis in the converted sounds upon changes at high or low amplitudes in the original signal. A noise-control circuit has been implemented for amplitude modulation of the converted signal to de- emphasize sounds arising from portions of the input signal below a chosen amplitude threshold. This method is shown to facilitate the transmission of analogs of audible and normally inaudible sounds over standard telephone channels, and to permit the slowing down of the converted sounds with no loss of information due to decreased frequencies. The approximation of an arbitrary waveform by a piecewise-linear (PL) function is shown to permit economical digital storage in parametric form. Fourier series and Fourier transforms may be readily calculated directly from the PL breakpoint parameters without further approximation, and the number of breakpoints needed to define the PL approximation is significantly lower than the number of uniformly-spaced samples required to satisfy the Nyquist sampling criterion; aliasing problems are shown not to arise. Thus data compression is feasible by this means without recourse to a parametric model defined for the signal (e.g., speech) being processed. Methods of automatic adaptive PL sampling and waveform reconstruction are discussed, and microcomputer algorithms implemented for this purpose are described in detail. Examples are given of the application of PL techniques to electrocardiography, phonocardiography, and the digitization of speech

A multi-channel system for use in cardiac electrophysiologic studies

The location of accessory pathways in Wolff-Parkinson-White syndrome patients is performed manually during open heart surgery at Groote Schuur Hospital, using a hand-held roving electrode. This manual procedure is slow and tedious, prolonging the operation and the time for which the patient remains on cardiac bypass. A multichannel electrogram acquisition and display system with a storage facility would significantly reduce the time taken and improve the reliability of locating the accessory pathways. Having considered a number of currently available cardiac mapping systems it was decided that a new system be developed for specific application within Groote Schuur Hospital. The main design goals of this system are to improve accuracy, increase reliability and enhance the speed of the entire mapping procedure with direct benefit to staff and patients. The system is based on an IBM compatible computer and allows for the acquisition of a maximum of thirty-two electrogram inputs. A typical configuration would acquire twenty epicardial, two references (one each from atrium and ventricle), one roving electrode and two surface lead signals. The epicardial signals are obtained from a custom-built electrode belt which is placed around the heart over the atrioventricular groove. The project includes the development of front-end hardware and software for processing, display and storage of electrogram signals. The relative activation times of the signals are displayed under software control in order to facilitate the location of any accessory pathway(s)

Computer control of an HF chirp radar

This thesis describes the interfacing of an IBM compatible microcomputer to a BR Communications chirp sounder. The need for this is twofold: Firstly for control of the sounder including automatic scheduling of operations, and secondly for data capture. A signal processing card inside the computer performs a Fast Fourier Transform on the sampled data from two phase matched receivers. The transformed data is then transferred to the host computer for further processing, display and storage on hard disk or magnetic tape, all in real time. Critical timing functions are provided by another card in the microcomputer, the timing controller. Built by the author, the design and operation of this sub-system is discussed in detail. Additional circuitry is required to perform antenna and filter switching, and a possible design thereof is also presented by the author. The completed system, comprising the chirp sounder, the PC environment, and the signal switching circuitry, has a dual purpose. It can operate as either a meteor radar, using a fixed frequency (currently 27,99 MHz), or as an advanced chirp ionosonde allowing frequency sweeps from 1,6 to 30 MHz. In the latter case fixed frequency doppler soundings are also possible. Examples of data recorded in the various modes are given

Training platform for the design of a windows multimedia device

There are many Windows Multimedia plug-in cards available for a Personal Computer (PC), but they are not suitable for a laboratory teaching platform for several reasons. Firstly, their hardware and software details are not available because of the market driven need to keep all hardware and software details from competitors. Secondly, the cards are not designed to allow faults to be introduced. Thirdly there is the inherent requirement that Windows applications be uniform to the point where application software sees the same interface, irrespective o f which Windows compatible card is being used. These latter points are highly desirable from the user's point of view but not from a teaching viewpoint, where the goal is to enlighten the student in the hardware and software design techniques used to perform the stated objective. The Multimedia Teaching Platform consists of a sound card, Windows 3.1 application and a Windows standard mode device driver. The sound card can continuously play or record audio files to the PC's hard disc in an analogue or a digital format. The digital format conforms to the consumer digital formats, IEC-958 Consumer, S/PDIF and CP-340 Type 2. Programmable logic was used on the sound card to allow hardware faults to be easily introduced. Hardware faults can be introduced by replacing the memory device which programs the logic array. Software design faults can be introduced by providing faulty source code for the device drivers and for the user interface. By introducing both hardware and software design faults, students can gain valuable experience in software and hardware debugging techniques and in the Windows environment

REAL TIME MICROPROCESSOR TECHNIQUES FOR A DIGITAL MULTITRACK TAPE RECORDER

Transport properties of a standard compact - cassette tape system are measured and software techniques devised to configure a low - cost,direct digital recording system. Tape - velocity variation is typically ± 10% of standard speed over tape lengths of 5 µm.with occasional variations of ±40%. Static tape - skew can result due to axial movement of the tape reel when it spools.Dynamic tape skew occurs and is primarily caused by tape - edge curvature with a constant contribution due to the transport mechanism.Spectral skew components range from 0.32 Hz to 8 Hz with magnitude normally within one 10 kbit/ sec- bit cell.The pinch roller works against the friction of the tape guides to cause tape deformation.Average values of tape deformation are 0.67 µm,0.85 µm and 1.08 µm for C60,C90 and C120 tape respectively. Parallel,software encoding / decoding algorithms have been developed for several channel codes.Adaptive software methods permit track data rates up to 3.33 k bits/sec in a rnultitrack system using a simple microcomputer.For a 4 - track system,raw error rates vary from 10ˉ⁷ at 500 bits/sec/track to 10ˉ⁵ at 3.33 kbits/sec/track.Adaptive software reduces skew - induced errors by 50%.A skew - correction technique has been developed and implemented on an 8 - track system at a track data rate of 10 k bits/sec. Real - time error correction gives a theoretical corrected error rate of 10ˉ¹¹for a raw error rate of 10ˉ⁷. Multiple track errors can cause mis - correction and interleaving is advised. Software algorithms have been devised for Reed - Solomon code. With a more powerful microprocessor this code m ay be combined with the above techniques in a layered error-correction scheme. The software techniques developed may be applied to N tracks with an N - bit computer.Recording density may be increased by using thin - film,multitrack heads and a faster computer.British Broadcasting Corporatio

Digital control of contactless battery charging system

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1995.Includes bibliographical references (leaves 230-234).by Aaron M. Schultz.Ph.D