Browsing by Author "Gunda, Lovemore"

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    Brush-DC Equivalent control based delta modulation for a PWM inverter-fed nine-phase induction machine drive
    (Stellenbosch : Stellenbosch University, 2015-12) Gunda, Lovemore; Gule, Nkosinathi; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
    ENGLISH ABSTRACT: A considerable amount of research has been done on the control of induction machines since the introduction of the power electronic inverter. The use of power electronic inverters has also opened the way for the design of multiphase induction machines. The current rating of the power electronic components used in multiphase inverters is lower than those used in three-phase inverters. On the machine side, the multiphase machines have higher power and torque density than their three-phase counterparts. The control of these multiphase induction machines poses a challenge for the designer of the drive system. Scalar control, direct torque control and vector control methods work well in three-phase machines. However, the analysis of vector based techniques becomes complex as the number of phases increases and new methods are being proposed to reduce the complexity of implementing machine control. The Brush-DC Equivalent (BDCE) control method was proposed to simplify the design of controllers. This method does not include complex coordinate transformations like are used in vectorbased techniques. The BDCE control method is derived from the control of separately excited brushDC machines utilising compensating windings. The induction machine controlled using the BDCE method is designed such that the phases of the machine act alternately in rime as torque-producing or field-producing phases. This is achieved by supplying the induction machine windings with specially designed trapezoidal stator current waveforms. The BDCE control method enables decoupled control of flux and torque without complex coordinate transformations. The method can be implemented for high phase-number multiphase induction machines without added complexity. In this thesis, the BDCE control method implementing a delta modulated current controller which generates pulse width modulated signals for the power electronic inverter is presented. The delta modulation technique is proposed because it gives good inverter performance characteristics and reduces torque and current ripples. It also reduces total current harmonic distortions through the use of a fixed switching frequency. The BDCE controlled drive is simulated using Matlab/Simulink. The simulation results suggest that delta modulation gives lower current and torque ripples with attenuated low order voltage harmonics. Practical evaluation of the drive is done using the delta modulated current controller to validate the simulation results. An alternative delta modulation scheme in which the reference current signal is integrated before being fed to the forward comparator is proposed, designed and tested. The alternative delta modulation scheme produces the required trapezoidal stator currents and allows decoupled control of the field and torque currents. The results of the practical evaluation compare well with the simulation results and show that a delta modulated current controller can be used in the drive. Better results are expected if stator voltages are fed back to the modulator to estimate the reference signal.
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    RFID Based Automatic Tollgate System (RATS)
    (South African Institute for Industrial Engineering, 2012) Gunda, Lovemore; Masuka, Lee; Gonye, Reginald; Mhlanga, Samson; Nyanga, Lungile
    Radio Frequency Identification (RFID) is an auto identification technology which uses Radio Frequencies (between 30 kHz and 2.5GHz) to identify objects remotely. The paper describes a system which does the job of detecting, billing and accounting for vehicles as they pass through a tollgate using RFID as the identification technology. In the design, a frequency of 928MHz is used as it is in the Industrial Scientific and Medical (ISM) band. The system is a great investment in the transport industry. It reduces the common hustles in accounting for the movement of goods from point to point. The design can be further developed to aid the satellite surveillance systems once all toll gates are networked. An RFID tag is programmed with information in the form of an Electronic Product Code (EPC), which can be read over a considerable distance so that its contents identify the vehicle and enhance a transaction to be undertaken with respect to the specific tag identity taking advantage of radio frequencies’ ability to travel longer ranges with better data capacities and high speed attained with maximum accuracy. The design has been implemented as a miniaturized prototype.