Design of a dedicated IFT microcontroller
- Authors: Himunzowa, Grayson
- Date: 2018
- Subjects: Feedback control systems , Automatic control , Engineering design -- Data processing
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/30017 , vital:30809
- Description: The design of a Dedicated IFT Microcontroller originated from the successful implementation of the Iterative Feedback Tuning (IFT) technique into the Digital Signal Processor microcontroller (DSP56F807C) at the University of Cape Town in 2006. However, implementation of the IFT technique on a general-purpose microcontroller is neither optimal, nor a cost-effective exercise, as most of the microcontroller peripherals remain unused, and drain energy for doing nothing. In addition, microcontrollers and DSPs are software-driven devices whose nature is sequential in executing algorithms, and hence have a significant effect on the bandwidth of the closed-loop control. To mitigate the said problem, the design of a Dedicated IFT Microcontroller is proposed in this thesis. To accomplish this goal, the preliminary task was to explore the IFT theory and its applications, followed by a review of the literature on FPGA design methodology for industrial control systems, Microcontroller design principles, and FPGA theory and trends. Furthermore, a survey of electronic design automation (EDA) tools and other application software was also conducted. After the literature review, the IFT was investigated exhaustively by applying it to three types of plants, namely: a DC motor, an oscillatory plant, and an unstable plant. Each of these plants were tested using three types of initial controllers, namely heavilydamped, critically damped and under-damped initial controllers. The plants were also tested by varying the amplitude of the reference signal, followed by using a single-step signal of constant amplitude of one volt. The intention of exploring all of these possibilities was meant to firmly expose the IFT boundaries of applicability, so that the final product would not be vulnerable to unnecessary post-production discoveries. The design methodology adopted in this research was a popular hierarchical and modular top-down procedure, which is an array of abstraction levels that are detailed as: system level, behavioural level, Register-Transfer Level (RTL) and Gate level. At system level, the Dedicated IFT Microcontroller was defined. Thereafter, at behavioural level, the design was simulated using VHDL, created by porting the LabView IFT code to the Xilinx EDA tool. At the RTL, the synthesisable VHDL code utilising fixed-point number representation was written. The compiled bit file was downloaded onto National Instruments (NI) Digital Electronics FPGA Board featuring iii the Spartan 3 series FPGA. This was tested, using a method known as simulation in the hardware. The key contribution of this thesis is the experimental validation of the IFT technique on FPGA hardware as it has never been published before, the work described in chapter four and five. The other contribution is the analysis of 1DOF IFT technique in terms of limitations of applicability for correct implementation, which is the main work of chapter three. This work could be used to explore other computational methods, like the use of floating-point number representation for high resolution and accuracy in numerical computations. Another avenue that could be exploited is Xilinx's recent Vivado methodology, which has the capacity for traditional programming languages like C or C++, as these have in-built floating-point number capability. Finally, out of this work, two papers have already been published by Springer and IEEE Xplore Publishers, and a journal paper has also been written for publication in the Control Systems Technology journal.
- Full Text:
- Date Issued: 2018
- Authors: Himunzowa, Grayson
- Date: 2018
- Subjects: Feedback control systems , Automatic control , Engineering design -- Data processing
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/30017 , vital:30809
- Description: The design of a Dedicated IFT Microcontroller originated from the successful implementation of the Iterative Feedback Tuning (IFT) technique into the Digital Signal Processor microcontroller (DSP56F807C) at the University of Cape Town in 2006. However, implementation of the IFT technique on a general-purpose microcontroller is neither optimal, nor a cost-effective exercise, as most of the microcontroller peripherals remain unused, and drain energy for doing nothing. In addition, microcontrollers and DSPs are software-driven devices whose nature is sequential in executing algorithms, and hence have a significant effect on the bandwidth of the closed-loop control. To mitigate the said problem, the design of a Dedicated IFT Microcontroller is proposed in this thesis. To accomplish this goal, the preliminary task was to explore the IFT theory and its applications, followed by a review of the literature on FPGA design methodology for industrial control systems, Microcontroller design principles, and FPGA theory and trends. Furthermore, a survey of electronic design automation (EDA) tools and other application software was also conducted. After the literature review, the IFT was investigated exhaustively by applying it to three types of plants, namely: a DC motor, an oscillatory plant, and an unstable plant. Each of these plants were tested using three types of initial controllers, namely heavilydamped, critically damped and under-damped initial controllers. The plants were also tested by varying the amplitude of the reference signal, followed by using a single-step signal of constant amplitude of one volt. The intention of exploring all of these possibilities was meant to firmly expose the IFT boundaries of applicability, so that the final product would not be vulnerable to unnecessary post-production discoveries. The design methodology adopted in this research was a popular hierarchical and modular top-down procedure, which is an array of abstraction levels that are detailed as: system level, behavioural level, Register-Transfer Level (RTL) and Gate level. At system level, the Dedicated IFT Microcontroller was defined. Thereafter, at behavioural level, the design was simulated using VHDL, created by porting the LabView IFT code to the Xilinx EDA tool. At the RTL, the synthesisable VHDL code utilising fixed-point number representation was written. The compiled bit file was downloaded onto National Instruments (NI) Digital Electronics FPGA Board featuring iii the Spartan 3 series FPGA. This was tested, using a method known as simulation in the hardware. The key contribution of this thesis is the experimental validation of the IFT technique on FPGA hardware as it has never been published before, the work described in chapter four and five. The other contribution is the analysis of 1DOF IFT technique in terms of limitations of applicability for correct implementation, which is the main work of chapter three. This work could be used to explore other computational methods, like the use of floating-point number representation for high resolution and accuracy in numerical computations. Another avenue that could be exploited is Xilinx's recent Vivado methodology, which has the capacity for traditional programming languages like C or C++, as these have in-built floating-point number capability. Finally, out of this work, two papers have already been published by Springer and IEEE Xplore Publishers, and a journal paper has also been written for publication in the Control Systems Technology journal.
- Full Text:
- Date Issued: 2018
The effect of English as a medium of instruction on the academic performance of students in life orientation at Dower Campus of the Port Elizabeth College
- Authors: Magxaki, Akhona
- Date: 2016
- Subjects: English language -- Study and teaching (Higher) -- South Africa -- Port Elizabeth English language -- Ability testing -- South Africa -- Port Elizabeth
- Language: English
- Type: Thesis , Masters , MA
- Identifier: http://hdl.handle.net/10948/14697 , vital:27825
- Description: South Africa is a country with 11 official languages including English. English, however, dominates the educational sector, as medium of instruction. This is despite a plethora of research that shows the cognitive advantages of mother tongue instruction and language policies that promote additive bilingual approaches. As subtractive language approaches characterise poor schooling contexts, the outcomes for students are poor. This is because they do not develop proficiency in any language. The abolition of apartheid in South Africa and the advent of democracy in 1994 resulted in dramatic changes in the education system. Nevertheless, the medium of instruction from Grade four has remained English. Consequently, for the majority of the population the education is in their second language. This study takes place in the higher education setting of a TVET college, namely the Dower Campus in Port Elizabeth. It focuses specifically on Level 2 (first year) Life Orientation students to consider the effect English has, as medium of instruction, on the academic performance of students. There is concern about the status of TVET colleges. Even though the higher education sector has transformed, these skills based colleges are still given inferior status in the eyes of the general public and students themselves. These students may be particularly at risk of success given that they have lower entry requirements than other students in the higher education sector. The subject Life Orientation was used to examine the effect of English on student performance. Life Orientation has come under scrutiny for its usefulness and it cognitive value. This study argues that it is a valuable subject for students at colleges, equipping them with knowledge to succeed at studies and in society at large. However, the pass rates for Life Orientation have been consistently low. The study wanted to probe the role of English in this performance. To address the aims and objectives of this study, relevant literature and various multilingual approaches were reviewed to determine which strategies might be most effective in helping students cope with English as medium of instruction. The study also presents a case for the development of indigenous languages as medium of instruction. The study used a mixed methods approach, that is both qualitative and quantitative methods, to explore the use, attitude and perceptions of English among lecturers and students. The research used an interpretive approach and the study took the form of a case study. The researcher took the stance of being a non-participant observer. Qualitative data was obtained through the use of interviews while quantitative data was obtained through the use of questionnaires. The interviews were recorded and transcribed by a transcriber. Data was analysed using a thematic approach. The results showed that majority of the students did not speak English frequently nor had it as a home language yet they all had a positive regard for the language. Many factors were responsible for student performance in Life Orientation such as attitude to subject, theoretical versus practical components of the subject and student background. However, the medium of instruction played a large role in this performance. Though lecturers foregrounded the importance of English as medium of instruction, they recognise that it was a barrier to understanding and affected student performance. Analysis of the lecturer interviews and the questionnaires with students revealed that students were experiencing difficulty speaking, reading and writing in English. Lecturers adapted their teaching strategies when teaching by including translanguaging strategies of code-switching to facilitate understanding. The data also indicated that code switching was considered by the lecturers to be the most suitable method in teaching to student. Code-meshing and written translations of material were not strategies employed by lecturers. Students indicated that they would prefer to write assignments drafts initially in mother tongue. The findings also suggested that it was necessary for the lecturer to use a variety of multilingual strategies to ensure that students enjoy success in Life Orientation. Based on the findings, this study makes recommendations regarding the teaching and learning of English to students which includes the use of multilingual classroom strategies, collaboration with language lecturers and development of a multilingual language policy to aid in the understanding and acquisition of English terminology used in LO content. Such a language policy should also seek to develop indigenous languages as mediums of instructions at the college.
- Full Text:
- Date Issued: 2016
- Authors: Magxaki, Akhona
- Date: 2016
- Subjects: English language -- Study and teaching (Higher) -- South Africa -- Port Elizabeth English language -- Ability testing -- South Africa -- Port Elizabeth
- Language: English
- Type: Thesis , Masters , MA
- Identifier: http://hdl.handle.net/10948/14697 , vital:27825
- Description: South Africa is a country with 11 official languages including English. English, however, dominates the educational sector, as medium of instruction. This is despite a plethora of research that shows the cognitive advantages of mother tongue instruction and language policies that promote additive bilingual approaches. As subtractive language approaches characterise poor schooling contexts, the outcomes for students are poor. This is because they do not develop proficiency in any language. The abolition of apartheid in South Africa and the advent of democracy in 1994 resulted in dramatic changes in the education system. Nevertheless, the medium of instruction from Grade four has remained English. Consequently, for the majority of the population the education is in their second language. This study takes place in the higher education setting of a TVET college, namely the Dower Campus in Port Elizabeth. It focuses specifically on Level 2 (first year) Life Orientation students to consider the effect English has, as medium of instruction, on the academic performance of students. There is concern about the status of TVET colleges. Even though the higher education sector has transformed, these skills based colleges are still given inferior status in the eyes of the general public and students themselves. These students may be particularly at risk of success given that they have lower entry requirements than other students in the higher education sector. The subject Life Orientation was used to examine the effect of English on student performance. Life Orientation has come under scrutiny for its usefulness and it cognitive value. This study argues that it is a valuable subject for students at colleges, equipping them with knowledge to succeed at studies and in society at large. However, the pass rates for Life Orientation have been consistently low. The study wanted to probe the role of English in this performance. To address the aims and objectives of this study, relevant literature and various multilingual approaches were reviewed to determine which strategies might be most effective in helping students cope with English as medium of instruction. The study also presents a case for the development of indigenous languages as medium of instruction. The study used a mixed methods approach, that is both qualitative and quantitative methods, to explore the use, attitude and perceptions of English among lecturers and students. The research used an interpretive approach and the study took the form of a case study. The researcher took the stance of being a non-participant observer. Qualitative data was obtained through the use of interviews while quantitative data was obtained through the use of questionnaires. The interviews were recorded and transcribed by a transcriber. Data was analysed using a thematic approach. The results showed that majority of the students did not speak English frequently nor had it as a home language yet they all had a positive regard for the language. Many factors were responsible for student performance in Life Orientation such as attitude to subject, theoretical versus practical components of the subject and student background. However, the medium of instruction played a large role in this performance. Though lecturers foregrounded the importance of English as medium of instruction, they recognise that it was a barrier to understanding and affected student performance. Analysis of the lecturer interviews and the questionnaires with students revealed that students were experiencing difficulty speaking, reading and writing in English. Lecturers adapted their teaching strategies when teaching by including translanguaging strategies of code-switching to facilitate understanding. The data also indicated that code switching was considered by the lecturers to be the most suitable method in teaching to student. Code-meshing and written translations of material were not strategies employed by lecturers. Students indicated that they would prefer to write assignments drafts initially in mother tongue. The findings also suggested that it was necessary for the lecturer to use a variety of multilingual strategies to ensure that students enjoy success in Life Orientation. Based on the findings, this study makes recommendations regarding the teaching and learning of English to students which includes the use of multilingual classroom strategies, collaboration with language lecturers and development of a multilingual language policy to aid in the understanding and acquisition of English terminology used in LO content. Such a language policy should also seek to develop indigenous languages as mediums of instructions at the college.
- Full Text:
- Date Issued: 2016
On the characterisation of solar cells using light beam induced current measurements
- Authors: Kwarikunda, Nicholas
- Date: 2015
- Subjects: Solor cells Spectrum, Solar
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/11147 , vital:26889
- Description: The presence of inhomogeneities in semiconductor materials used to fabricate solar cell devices may result in spatial non uniformities in the device properties which may affect current generation in these devices. Besides, current reducing defects such as inclusions, local shunts and optical blockages may be introduced during the various device manufacturing processes which may adversely affect the performance and overall efficiency of solar cells. Diagnostic techniques are therefore needed to identify these defects so as to improve the production technology. This thesis presents the Light Beam Induced Current (LBIC) technique for mapping spatial non uniformities in solar cell devices. The LBIC is a non destructive characterisation technique that uses a focused light beam to raster scan a solar cell surface as the photo-generated current is recorded as a function of position to generate a photo-response map. The technique was used to obtain photoresponse maps for a mc-Si, Back contact Back junction (BC-BJ) silicon solar cell and the InGaP/InGaAs/Ge concentrating triple junction (CTJ) solar cell from which various local current reducing defects were mapped. A reflection signal detector was incorporated into the LBIC measurement system to enable us distinguish between optical blockages on the cell surface and current reducing defects within the solar cell devices. By dynamically biasing the solar cell devices, the electrical activity of the identified defects was investigated and also point-by-point current-voltage (I-V) characteristics were obtained. An interval division algorithm was applied to the measured point-by-point I-V characteristics to extract device and performance parameters from which device and performance parameter uniformity of the devices were mapped. Dark and full cell solar illumination I-V characteristics were also measured to extract device parameters. Analysis of extracted parameters revealed differences between extracted dark and illuminated device parameters which was attributed to departure from the superposition principle due to non-linearity of the semiconductor device equations with respect to carrier concentration. An investigation into the effect of illumination intensity on the I-V parameters of a spot illuminated BC-BJ Si solar cell showed a linear increase and a logarithmic increase of the short circuit current and open circuit voltage respectively with intensity while the series resistance decreased with intensity, which was attributed to increase in conductivity of the active layer. The ideality factor and saturation current were observed to increase while the shunt resistance initially increased before decreasing at higher intensity levels. Under monochromatic illumination, the photo-response of the BC-BJ Si cell was higher at 785nm than at 445nm due to low absorption coefficient of Si for longer wavelength radiations, resulting in carrier generation within the bulk, where there is a higher probability of carriers being collected at the p-n junction before they recombine. Under solar illumination, as the spectral content was altered using long pass colour filters with cut off wavelengths of 610nm and 1000nm, the performance parameters were observed to decrease and this was mainly due to decrease in intensity. For the CTJ solar cell, however, blocking of radiations below 610nm resulted in current mismatch that severely degraded the short circuit current (Isc). The current mismatch affected the extracted device and performance parameters. With a 1000nm long pass filter, a dark I-V was obtained since only the bottom Ge subcell was activated.
- Full Text:
- Date Issued: 2015
- Authors: Kwarikunda, Nicholas
- Date: 2015
- Subjects: Solor cells Spectrum, Solar
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/11147 , vital:26889
- Description: The presence of inhomogeneities in semiconductor materials used to fabricate solar cell devices may result in spatial non uniformities in the device properties which may affect current generation in these devices. Besides, current reducing defects such as inclusions, local shunts and optical blockages may be introduced during the various device manufacturing processes which may adversely affect the performance and overall efficiency of solar cells. Diagnostic techniques are therefore needed to identify these defects so as to improve the production technology. This thesis presents the Light Beam Induced Current (LBIC) technique for mapping spatial non uniformities in solar cell devices. The LBIC is a non destructive characterisation technique that uses a focused light beam to raster scan a solar cell surface as the photo-generated current is recorded as a function of position to generate a photo-response map. The technique was used to obtain photoresponse maps for a mc-Si, Back contact Back junction (BC-BJ) silicon solar cell and the InGaP/InGaAs/Ge concentrating triple junction (CTJ) solar cell from which various local current reducing defects were mapped. A reflection signal detector was incorporated into the LBIC measurement system to enable us distinguish between optical blockages on the cell surface and current reducing defects within the solar cell devices. By dynamically biasing the solar cell devices, the electrical activity of the identified defects was investigated and also point-by-point current-voltage (I-V) characteristics were obtained. An interval division algorithm was applied to the measured point-by-point I-V characteristics to extract device and performance parameters from which device and performance parameter uniformity of the devices were mapped. Dark and full cell solar illumination I-V characteristics were also measured to extract device parameters. Analysis of extracted parameters revealed differences between extracted dark and illuminated device parameters which was attributed to departure from the superposition principle due to non-linearity of the semiconductor device equations with respect to carrier concentration. An investigation into the effect of illumination intensity on the I-V parameters of a spot illuminated BC-BJ Si solar cell showed a linear increase and a logarithmic increase of the short circuit current and open circuit voltage respectively with intensity while the series resistance decreased with intensity, which was attributed to increase in conductivity of the active layer. The ideality factor and saturation current were observed to increase while the shunt resistance initially increased before decreasing at higher intensity levels. Under monochromatic illumination, the photo-response of the BC-BJ Si cell was higher at 785nm than at 445nm due to low absorption coefficient of Si for longer wavelength radiations, resulting in carrier generation within the bulk, where there is a higher probability of carriers being collected at the p-n junction before they recombine. Under solar illumination, as the spectral content was altered using long pass colour filters with cut off wavelengths of 610nm and 1000nm, the performance parameters were observed to decrease and this was mainly due to decrease in intensity. For the CTJ solar cell, however, blocking of radiations below 610nm resulted in current mismatch that severely degraded the short circuit current (Isc). The current mismatch affected the extracted device and performance parameters. With a 1000nm long pass filter, a dark I-V was obtained since only the bottom Ge subcell was activated.
- Full Text:
- Date Issued: 2015
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