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This thesis deals with the problem of control system design for power electronic controllers when high performance is desired despite unaccounted for internal and external conditions. Factors such as parameter variations, operating condition changes, and filtering and measurements delays, may adversely impact the performance of a circuit whose controller design is not immune to external and internal disturbances. The thesis explores the method of internal model design as a viable approach for designing controllers with superior performance despite system variations. Following a presentation of the theoretical background of the internal model design, the thesis considers two examples of state variable models, improving the stability of a voltage source converter and speed control of an induction motor. Conclusions show the new control system is more stable and offers better controllability despite unexpected system variations, compared to classical control system.

No description available.

No description available.

Thesis (PhD)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: This dissertation presents a circuit-based design technique that leads to benefits in terms of the physical size, manufacturability, and exibility in the design of N-way conical line power combiners. An equivalent circuit model for the peripheral input ports of conical line power combiners is extracted, as well as empirical equations that allow the circuit element values to be calculated directly from the physical dimensions of the combiner, and vice versa. This allows for rapid optimization of various dimensions of the combiner at a significantly reduced computational cost compared to full-wave simulations. A design procedure is presented and a conical combiner designed with a measured reflection coefficient of better than -18 dB over a 46 % bandwidth around 10 GHz. The designed prototype is much smaller compared to previous designs while exhibiting similar performance. Design procedures for single-section and multi-section impedance tapered conical to coaxial line transitions are also presented, which can be used to simplify the design of conical combiners and reduce the manufacturing effort. Two combiners are designed, one with a single-section and one with a multi-section transition, and output port reflection coefficients of -23 dB and -17 dB over bandwidths of 20 % and 43 % around 10 GHz are measured, respectively. This dissertation additionally presents a method that can be used in general to improve the input port isolation of N-way power combiners without affecting their reciprocity. A simple S-parameter proof is presented, followed by a derivation of equations that can be used to estimate the worst-case performance. Some design examples are presented, showing that terminations can be used for isolation loads. A prototype based on microstrip transmission lines is manufactured and a much improved input port reflection and isolation performance of -15 dB and 20 dB is measured, respectively, compared to a simulated input port reflection coefficient of -2:5 dB and isolation of 2:5 dB before the method was applied. ii / AFRIKAANSE OPSOMMING: Hierdie proefskrif stel 'n stroombaangebaseerde ontwerpsmetode voor wat lei tot voordele in terme van die fisiese grootte, vervaardigbaarheid, en vryheid in die ontwerp van koniese lyn kombineerders. 'n Ekwivalente stroombaanmodel vir die voerpoorte word onttrek, asook empiriese vergelykings wat gebruik kan word om die stroombaanelement waardes vanaf die afmetings van die kombineerder te bepaal. Dit laat die ontwerper toe om verskeie afmetings van die kombineerder te optimeer teen 'n beduidende laer koste in vergelyking met volgolf simulasies. 'n Ontwerpsprosedure word voorgestel en gebruik om 'n koniese kombineerder te ontwerp en 'n weerkaatskoëffisient van beter as -18 dB met 'n bandwydte van 46 % om 10 GHz word gemeet. Die prototipe is aansienlik kleiner as vorige ontwerpe, maar toon soortgelyke werkverrigting. Ontwerpsprosedures vir enkel en veelvoudige deel koniese na koaksiale lyn oorgange word ook voorgestel, wat gebruik kan word om die ontwerp en vervaardiging van koniese kombineerders te vereenvoudig. Twee kombineerders word ontwerp, een met 'n enkel deel oorgang en een met veelvoudige dele, en onderskeidelike uittree weerkaatskoëffisiente van -23 dB en -17 dB oor bandwydtes van 20 % en 43 % word gemeet. Hierdie proefskrif stel ook 'n metode voor wat gebruik kan word om die intree poort isolasie van N-rigting kombineerders in die algemeen te verbeter, sonder om die wederkerigheid daarvan te beïnvloed. 'n Bewys van die metode word gelewer, gevolg deur 'n afleiding van vergelykings wat gebruik kan word om die slegste-geval werkverrigting af te skat. Verskillende voorbeelde van kombineerders word getoon waarop die metode toegepas is, en wys dat terminasies gebruik kan word vir die isolasie laste. 'n Prototipe gebaseer op mikrostrook transmissielyne word vervaardig en 'n verbeterde intreepoort weerkaatskoëffisient en isolasie van onderskeidelik -15 dB en 20 dB word gemeet, in vergelyking met 'n weerkaatskoëffisient van -2:5 dB en isolasie van 2:5 dB voordat die metode toegepas is.

The Marnoch heat engine (MHE) is a new type of heat engine currently under development at the University of Ontario Institute of Technology. The MHE can use waste or collected heat at temperatures that are currently unusable or not eco- nomically viable to use by conventional technologies. The MHE operates by using a heat source to heat the air in one heat exchanger and cool the air in another. This creates a pressure di erence. This pressure di erence drives a two-way piston connected to a ywheel. A generator connected to the ywheel converts the me- chanical energy of the ywheel into electricity. This thesis presents a simulation of the current MHE prototype. The simulation is designed to be easily customized to allow it to model the performance of future possible MHE installations and predict their performance. The simulation is shown to accurately model the performance of the MHE prototype by running under conditions similar to those found in the lab, and comparing its results to collected data from the prototype. Simulations were also run to show the model's ability to model possible applications with di erent operating conditions and physical components. / UOIT

This study focuses on the development of a validated and confirmed employee engagement measuring model for use by managers and academia. Data was collected from an array of South African managers by employing a structured 5-point Likert scale questionnaire. A total of 260 usable questionnaires could be analysed, signifying a high response rate of 80%. The Statistical Package for Social Sciences software (Version 18, Version 22.0 and AMOS for Windows) was used as the quantitative analytical software. The following statistical techniques were employed to analyse the data, namely the Kaiser-Meyer-Olkin measure of sampling adequacy, Bartlett‟s test of sphericity, Cronbach Alpha reliability coefficients, Exploratory factor analysis, Confirmatory factor analysis and the Pearson correlation coefficient. The development of the Measure Employee Engagement model wielded theoretical and empirical research. The format was structured into four logical stages, hence the presentation of the study in the approved article format. The study covers the following four steps (as per articles): Article one departed by performing a literature study of employee engagement constructs and its measuring criteria. It examined the application of a myriad of models in various application settings to identify the relevant constructs and measuring criteria. From these constructs and criteria, a draft questionnaire was constructed to collect the data on 11 employee engagement constructs. Validation of measuring criteria was performed to ensure that the criteria accurately measure the specific employee engagement construct. The data was also tested for acceptable reliability levels. The second article departs on the validation of the constructs and its measuring criteria, this time as a unified model and not, as performed in Article 1, the construct validation individually. The objective of this article was to simplify the complex model without deterioration of the measuring contribution thereof. This was achieved by employing factor analysis, and after four rounds of eliminating low-loading and dual-loading criteria, the questionnaire was reduced by 25 measuring criteria and seven factors were extracted explaining a favourable 69.75% of the variance. The simplified model was scrutinised to ascertain statistical validity thereof, an objective achieved with flying colours. The inter-correlations between the seven factors were satisfactory, underpinning the validity of the model. The third article focuses on confirming the employee engagement constructs statistically by means of Confirmatory Factor Analysis as well as to determine the goodness of the model fit. The results confirmed that all seven constructs were significant (p<0.05) and important according to the standardised regression weights. Surprisingly, the most important respondent construct Behavioural engagement had the lowest regression weight, while the lower rated Career growth opportunities showed a much higher regression weight – signifying a higher importance and influence on employee engagement. Regarding goodness of model fit, the CFI, RMSEA and Hoelter‟s indices‟ were used. These indices showed that the model as stated above to measure employee engagement is a good fit and that it can be operationalised to be employed in managerial application settings. Article four operationalised the model validated in Articles 2 and 3. The article thus reports on the actual measurement of the different employee engagement constructs as perceived by the respondents. The results showed that the respondents regarded all seven the constructs as important, with Behavioural employment being regarded as the most important one. Career growth opportunities, surprisingly, was rated the least important construct of employee engagement. Correlational analysis indicated that no significant correlation coefficients exist between the demographic variables and the constructs of employee engagement. The study consisted of both a literature study as well as an empirical study. The university libraries of the North-West University and Management College of South Africa‟s Business School were used to source reference materials with the aid of a specialised research librarian at the North-West University to assist in the location of the most appropriate sources. Apart from the conclusions based on the results obtained in model development, generalised conclusions include the development of a successful model development methodology and guidance in the use of a number of the statistical techniques. This could greatly assist future researchers in the design of their studies, even outside the discipline of employee engagement. / PhD (Business Administration), North-West University, Potchefstroom Campus, 2015

This study focuses on the development of a validated and confirmed employee engagement measuring model for use by managers and academia. Data was collected from an array of South African managers by employing a structured 5-point Likert scale questionnaire. A total of 260 usable questionnaires could be analysed, signifying a high response rate of 80%. The Statistical Package for Social Sciences software (Version 18, Version 22.0 and AMOS for Windows) was used as the quantitative analytical software. The following statistical techniques were employed to analyse the data, namely the Kaiser-Meyer-Olkin measure of sampling adequacy, Bartlett‟s test of sphericity, Cronbach Alpha reliability coefficients, Exploratory factor analysis, Confirmatory factor analysis and the Pearson correlation coefficient. The development of the Measure Employee Engagement model wielded theoretical and empirical research. The format was structured into four logical stages, hence the presentation of the study in the approved article format. The study covers the following four steps (as per articles): Article one departed by performing a literature study of employee engagement constructs and its measuring criteria. It examined the application of a myriad of models in various application settings to identify the relevant constructs and measuring criteria. From these constructs and criteria, a draft questionnaire was constructed to collect the data on 11 employee engagement constructs. Validation of measuring criteria was performed to ensure that the criteria accurately measure the specific employee engagement construct. The data was also tested for acceptable reliability levels. The second article departs on the validation of the constructs and its measuring criteria, this time as a unified model and not, as performed in Article 1, the construct validation individually. The objective of this article was to simplify the complex model without deterioration of the measuring contribution thereof. This was achieved by employing factor analysis, and after four rounds of eliminating low-loading and dual-loading criteria, the questionnaire was reduced by 25 measuring criteria and seven factors were extracted explaining a favourable 69.75% of the variance. The simplified model was scrutinised to ascertain statistical validity thereof, an objective achieved with flying colours. The inter-correlations between the seven factors were satisfactory, underpinning the validity of the model. The third article focuses on confirming the employee engagement constructs statistically by means of Confirmatory Factor Analysis as well as to determine the goodness of the model fit. The results confirmed that all seven constructs were significant (p<0.05) and important according to the standardised regression weights. Surprisingly, the most important respondent construct Behavioural engagement had the lowest regression weight, while the lower rated Career growth opportunities showed a much higher regression weight – signifying a higher importance and influence on employee engagement. Regarding goodness of model fit, the CFI, RMSEA and Hoelter‟s indices‟ were used. These indices showed that the model as stated above to measure employee engagement is a good fit and that it can be operationalised to be employed in managerial application settings. Article four operationalised the model validated in Articles 2 and 3. The article thus reports on the actual measurement of the different employee engagement constructs as perceived by the respondents. The results showed that the respondents regarded all seven the constructs as important, with Behavioural employment being regarded as the most important one. Career growth opportunities, surprisingly, was rated the least important construct of employee engagement. Correlational analysis indicated that no significant correlation coefficients exist between the demographic variables and the constructs of employee engagement. The study consisted of both a literature study as well as an empirical study. The university libraries of the North-West University and Management College of South Africa‟s Business School were used to source reference materials with the aid of a specialised research librarian at the North-West University to assist in the location of the most appropriate sources. Apart from the conclusions based on the results obtained in model development, generalised conclusions include the development of a successful model development methodology and guidance in the use of a number of the statistical techniques. This could greatly assist future researchers in the design of their studies, even outside the discipline of employee engagement. / PhD (Business Administration), North-West University, Potchefstroom Campus, 2015

BACKGROUND. The relaxation of the global conditions, mainly but not reduced to the introduction of the Internet, and the demanding competitive pressures have triggered the expansionary phenomenon of startups that seek to compete internationally right after its birth. This urge for a mechanism to facilitate the internationalisation process, namely the business model. In this regard, there is a need to elaborate on the field of the business model in combination to the internationalization literature, which has tended to develop in isolation. PURPOSE. The purpose of this master thesis is to expand the knowledge about the process of designing the business model of a new international venture and how the drivers of internationalisation affect this process. METHODOLOGY. The research problem was identified by exploring two major streams of theory, the business model and the internationalisation, which were developed jointly in a visual representation. In the next step, from two Sweden-based international new ventures, named Againity AB and MIMSI Materials AB, empirical information was collected from diverse stakeholders. The technique was qualitative research method, which was scrutinized following a process model approach. Finally, a model proposition was constructed by analysing the realities of the practical and theoretical phenomenon to serve the purpose of enhancing knowledge. RESULT. The BMD process is composed by three stages, namely initiating, generating and refining, of iterative and interdependent nature. Each driver of internationalization, when scrutinized using the empirical realities of the INVs, tends to have different influential roles at different stages of the business model. This is integrated into a conceptual model of the key internationalization drivers and BMD stages, which reflects the strategic fit from which new ventures benefit.

Nowadays about 1.2 billion people in world lack modern access to electricity, with the majority of them living in rural areas in low-income and developing contexts. This research addresses the issue of energy access by investigating the design of sustainable business models, and in particular by exploring the combination of Product-Service Systems (PSS) with Distributed Renewable Energy systems (DRE). The combination of PSS and DRE represents a new design approach to explore promising business models for energy access and to deliver clean and affordable solutions in low-income contexts. The overall aim of this research is to explore the applications of PSS and DRE in low-income and developing contexts, thus defining characteristics of these models, their variables and critical factors. Additionally, this research aims at developing a support for companies, practitioners and other stakeholders for designing sustainable PSS applied to DRE, with a specific focus on the idea generation phase of new solutions. The first part of this PhD resulted in the development of a classification system for PSS applied to DRE, in the identification of 15 Archetypal Models and in the collection of critical factors to successfully implement these models. Then, these findings have been translated into three tools for designing PSSs applied to DRE: the Innovation Map, the Design Framework and Cards, the Energy System Map. These tools have been tested, refined and evaluated through a series of iterative applications in South Africa, Botswana, Kenya and the UK. Through the testing activities, which involved a wide range of companies, NGOs, practitioners and experts, the usefulness, usability and completeness of the tools were demonstrated. This research concludes with reflections on the design process for different scenarios of applications and by highlighting further research activities for the field of PSS applied to DRE in low-income and developing contexts.