Browsing by Author "Van der Merwe, Carel"
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- ItemCulprit and victim management RFI environment for a radio astronomy site(Stellenbosch : Stellenbosch University, 2012-03) Van der Merwe, Carel; Reader, H. C.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: A methodology is developed to manage the large number of RFI Culprits on a new Radio Telescope location such as the South African site being developed in the Karoo, both during construction and ongoing operations. The requirement for RFI control is presented, with brief reference to the more traditional methods used by other Radio Telescope observatories. The new approach is then presented, based on methods used in the engineering field of Logistic Engineering. Three case studies are used to illustrate how the approach can be applied. Finally, recommendations are made on how the approach can be implemented for new Radio Telescope projects.
- ItemDigitally controlled class-D audio amplifier(2017-03) Van der Merwe, Carel; Mouton, H. du T.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: Class-D audio ampli ers have become increasingly popular due to the fact that they use transistors as switches to amplify audio and do not operate them in their linear region, as is the case with other classes of ampli ers. This ensures that class-D ampli ers have very high e ciencies, making them a lot smaller than their counterparts. Traditionally, class-D ampli ers have been controlled using analogue circuits. This thesis will discuss the digital control of a class-D ampli er. The goal is to implement the ampli er using only a switching output stage, demodulation lter, simple analogue-todigital converter and an FPGA with peripheral components. This will make it possible for further work to reduce the ampli er to a single integrated circuit and output stage, making it even more compact than its analogue-controlled counterpart while maintaining equivalent performance. The controller design is done in the z-domain with the PWM modelled as a sampling operation. A mathematical expression is obtained to determine the PWM input signal from which the comparator small-signal gain is calculated. Ripple compensation is implemented to ensure that the comparator small-signal gain remains constant. The main challenge in the controller design is adequately attenuating the quantization noise, which is induced into the system by the digital PWM and the analogue-to-digital converter. This is done by ensuring that the system has a high gain across the audio band (20 Hz to 20 kHz). Simulations are done in an environment emulating that of the FPGA. VHDL is used to practically implement the controller. A system setup is constructed using pre-designed hardware and experimental results are presented.
- ItemThe space vector analysis of a squirrel-cage induction motor allowing for all MMF and permeance harmonics(Stellenbosch : Stellenbosch University, 1993) Van der Merwe, Carel; Stellenbosch University. Faculty of . Dept. of .