Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2009 / This project was started as a result of strict environmental and health regulations together with a demand tor cost effective operation of wastewater treatment plants (VVWTPs). The main aim of this project is how to keep effluent concentration below a prescribed limit at the lowest possible cost. Due to large fluctuations in the quality and quantity of the influent concentrations, traditional control methods are not adequate to achieve this aim The major drawback with these methods is that the disturbances affect the process before the controller has time to correct the error (Olsson and Newell, 1999: 454). This problem is addressed through the use of modern control systems. Modern control systems are model based predictive algorithms arranged as feed-forward controllers (Olsson and Newell. 1999: 454). Normally a controller is equipped with a constant set point; the goal In this project is to calculate an optimal DO trajectory that may be sampled to provide a varying optimal set-point for the Activated Sludge Process, In this project an optimal control problem Is formulated using DO concentration as a control variable. This requires a model of the process to be controlled a mathematical expressions of the limitations on the process input and output variables and finally the objective functional. which consists of the objectives of the control. The structures of the Benchmark plant (developed within the COST 682 working group) and the Athlone WWTPs are used to implement this opt.mat control strategy in MATLAB. The plant's full models are developed based on the mass balance principle incorporating the activated sludge biological models: ,ASM1, ASM2, ASM2d and ASM3 (developed by the IWA working groups). To be able to develop a method that may later on be used for online control, the full models are reduced based on the technique In Lukasse (1996). To ensure that the reduced models keep the same prediction capabilities as the full models, parameters of the reduced models are calculated based on the Least Squares principle, The formulated optimal control problem is solved based on the decompostion-coorcdination method that involves time decomposition in a two layer structure. MATLAB software [5 developed to solve the problems for parameter estimation. fun and reduced mode! simulation. and optimal control calculation for the considered different cases of plant structures and biological models. The obtained optimal 00 trajectories produced the effluent state trajectories within prescribed requirements. These DO trajectories may be implemented in different SCADA systems to be tracked as set points or desired trajectories by different types of controllers.

Thesis (MTech (Information Technology))--Cape Peninsula University of Technology, 2007 / The increasingly sedentary lifestyle of the past 30 years has contributed to declining health. Consequently, exercise is vital for good health maintenance. The global Health and Fitness Industry repeatedly indicates the need for optimally managed exercise with accurate information feedback. Compared to other industries, the fitness industry is lagging behind in incorporating Information Technology into its operations. On the other hand, the most current exercise equipment impose fixed-trajectory exercise on users with the dominance of static equipment designs. These exercise equipment are normally deadweight-based equipment. In deadweight-based exercise equipment, the weights generally can be changed only when the equipment is inactive. Therefore, a more novel exercise environment is required for current exercisers in the fitness industry. This thesis explores to develop a computer-controlled pneumatic dynamic resistance exercise equipment with onboard data management. This new technology optimises exercise effectiveness for users. Exercisers will have advanced diagnostic capacity, and will capture user data which can be manipulated into meaningful information for use by Health and Fitness Industry stakeholders. This thesis will explore all the key concepts about computer-controlled equipment. The key concepts to be investigated will include FX (force-displacement) control technology, pneumatic system control, fail-safe mechanics, and Graphical User Interface design. The primary aim of the project is to replicate and enhance the functionality, performance, and sensation of deadweight-based equipment. A further aim of the project is to investigate the feasibility of designing a compact retrofit-able pneumatic unit to replace the deadweights of existing standard exercise equipment. The computer control will be implemented on a "National Instruments PXI" computer featuring Data Acquisition and Control (DAQAC) capacity, and the software will be implemented using "LabVIEW 7.0', which is a graphic object-oriented computer language developed to facilitate hardware I software communications.

This Thesis is concerned with model-based control, where models of linear nonminimal state-space (NMSS) and nonlinear state-dependent parameter (SDP) form are considered. In particular, the focus is on model-based predictive control (MPC) in conjunction with the linear NMSS model and on proportional-integralplus (PIP) pole-assignment control in conjunction with the SDP model. The SDP-PIP pole-assignment controller is based on a nonlinear SDP model, however, the approach uses a linear pole-assignment controller design technique. This ‘potential paradox’ is addressed in this Thesis. A conceptual approach to realising the SDP-PIP pole-assignment control is proposed, where an additional conceptual time-shift operator is introduced. This allows the SDPPIP, at each sampling time instance, to be considered as an equivalent linear controller, while operating, in fact, in a nonlinear overall context. Additionally, an attempt to realise SDP-PIP control, where the SDP model exhibits equivalent linear system numerator zeros, is proposed. Regarding the NMSS MPC, emphasis is on square, i.e. equal number of inputs and outputs, multi-input multi-output (MIMO) modelled systems, which exhibit system output cross-coupling effects. Moreover, the NMSS MPC in incremental input form and making use of an integral-of-errors state variable, is considered. A strategy is proposed, that allows decoupling of the system outputs by diagonalising the closed-loop system model via an input transformation. A modification to the NMSS MPC in incremental input form is proposed such that the transformed system input - system output pairs can be considered individually, which allows the control and prediction horizons to be assigned to the individual pairs separately. This modification allows imposed constraints to be accommodated such that the cross-coupling effects do not re-emerge. A practical example is presented, namely, a DC-DC boost converter operating in discontinuous conduction mode (DCM), for which a SDP model is developed. This model is based on measured input-output data rather than on physical relationships. The model incorporates the output current so that the requirements for the load, driven by the converter, is constrained to remain within a predefined output current range. The proposed SDP model is compared to an alternative nonlinear Hammerstein-bilinear structured (HBS) model. The HBS model is, in a similar manner to the SDP model, also based on measured input-output data. Moreover, the differences as well as the similarities of the SDP and HBS model are elaborated. Furthermore, SDP-PIP pole-assignment control, based on the developed SDP model, is applied to the converter and the performance is compared to baseline linear PIP control schemes.

Proportional, Integral and Derivative feedback control (PID) is a mature technology responsible for the majority of automated decision making in the process industry. Despite the high reliance on this technology, low levels of maintenance and performance measurement are the norm in the process industry. Several analysis techniques exist for identifying oscillation, and then highlighting the root cause of the problem. Several time and frequency domain statistical techniques, as well as wavelet analysis are used to diagnose loop performance. In this study, 127 different control loops are analysed, and in depth troubleshooting is performed on a selection of 18 different control loops. The performance of flow loop F1035 is tracked through a number of different analysis techniques, highlighting the pitfalls of using only a single analysis technique. Lower order statistics and minimum variance performance analysis show that the loop is performing well. Plotting the PV-OP relationship suggests non-linear tendencies on F1035, and this is corroborated using high order statistical analysis (bicoherence). Non-linear loop behaviour is often as a result of a slip stick cycle, a sign that valve maintenance may be required. Frequency (power spectrum) analysis shows a 43 minute dominant oscillation, suggesting a low frequency disturbance affecting loop performance. Process units are typically exposed to cyclic behaviour occurring at several different frequencies, each having a different effect on the control of the process. By using a frequency based approach based on sinusoidal basis functions (ie Fourier analysis), these different frequencies get aggregated. This smudging of specific frequency information makes it difficult to pin-point the root cause, and makes the grouping of common oscillations difficult. In order to address the above issue, F1035 is analysed using othornormal wavelet basis functions. The results show that the period of oscillation is affected between day and night, with roughly a 2 minute oscillation prevalent at mid night, compared to a 100 minute oscillation at mid day. Obviously the 12 hour day-night swing is also prevalent. This information is unique to this approach. Ways of visualising changes in oscillatory behaviour using the wavelet analysis are also presented. Technical analysis of controller performance is only a small subsection of the issues that need to be considered when implementing a loop monitoring and maintenance solution. Issues such as connectivity, configuration, analysis, reporting and auditing are key in designing a workable maintenance environment for PID loop maintenance. Several packages are available commercially to assist industry in performing loop maintenance. When evaluating which package is best suited to a specific requirement, it is important to consider several different issues. The different audiences with a vested interest in loop performance require special attention in terms of reporting requirements. Visualisation of results is often more important than the physical measure of performance. Finally, the ability of a company to benchmark itself against current best practices and performance is often perceived as a major advantage. The results presented and discussed were generated using real industrial data. Information regarding suggested best practice when evaluating commercially available products is based largely on the author’s personal experience in the large scale industrial installation of such a monitoring solution. / Dissertation (MEng (Process Control))--University of Pretoria, 2007. / Chemical Engineering / unrestricted

We start by discussing fuzzy sets and the algebra of fuzzy sets. We consider some properties of fuzzy modeling tools. This is followed by considering the Mamdani and Sugeno models for designing fuzzy controllers. Various methods for using sets of data for desining controllers are discussed. This is followed by a chapter illustrating the use of genetic algorithms in designing and optimizing fuzzy controllers.Finally we look at some previous applications of fuzzy control in telecommunication networks, and illustrate a simple application that was developed as part of the present work.

In the last few years carbon dioxide received increasing attention as a possible replacement for fluorocarbon-based refrigerants used within present automotive A/C system technology. R-134a is harmless to the ozone layer but the greenhouse effect is more than 1300 times higher than that of an equivalent amount of CO2. Alternative refrigerants are natural gasses such as propane and butane, however these gasses are considered explosive. With many objections raised it appears if CO2 will be the future refrigrant for automotive use. One concern with R-744 is its high operating pressure and suction/discharge pressure difference when compared to common refrigeration processes. A major problem with the CO2 cycle is the loss of effciency at high ambient temperatures. With a COP optimized control system for the expansion value based on pressure, temperature and mass flow of the refrigerant, an effective A/C system for CO2 could be deleloped. This resrach offers basic knowledge of refrigerant cycles and gives an overall view of the refrigerant change-over problem. With the results obtained from the experimental work a better understanding of the CO2 cycle and a better understanding towards effective A/C systems have been realized.

The practical implementation of optimal control systems in large industrial process applications has been limited by the high costs of the required computing facilities. With the recent advances in component fabrication and the resultant decrease in hardware costs, special purpose computers, utilizing virtually no software at all, can be constructed as economical alternatives to presently available general purpose computers for use in optimal process controllers. A design for one such special purpose machine, an automatic optimizer, is presented in this thesis. Tests conducted on a working optimizer constructed on the basis of the given design, demonstrate that it is suitably fast and powerful for use in process controllers. In addition, the optimizer is inexpensive enough to be used as part of an economical process controller. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

Indices which quantitatively predict the ability of a particular MIMO control system design to meet certain performance objectives are discussed in this dissertation. These performance objectives include: * Input and output rejection of noise and disturbances. * Input and output insensitivity to changes in the process. * Good output regulation and minimal control effort. A counter-current heat exchanger process (simulating the carbon-in-pulp gold extraction process) has been designed and constructed. The quality of control systems synthesized for this process is gauged using these performance indices. The control of this large-scale process has been decentralized to reduce the design complexity. The strategy adopted is to regulate the process flows and levels using a cascade compensator, and then to use these setpoints as inputs to control the temperatures at various points on the heat exchange cascade standard PI-type controllers were designed for the regulation of the flow and level outputs. The outputs were regulated accurately in the presence of process disturbances, and the relatively slow level dynamics were improved considerably. Performance index analysis of control systems is achieved by observing frequency-dependent plots of the singular values of certain characteristic matrices describing the system. These matrices are obtained as ratios of the plant and controller matrices. A CAD software package has been developed to enable this type of analysis on state-space control systems with state observers. The package enables the synthesis of LQG optimal control systems and the quantitative assessment of the ability of such systems to meet their design objectives. A package has been developed to run the heat exchanger and to implement control systems for the process. Two LQG control systems were synthesized for the process in which the two flow inputs (setpoints) were used to regulate the two outlet temperature outputs. The performance of the systems were predicted quantitatively using performance indices. The systems were tested by digital simulation. Good correlation between the predicted and simulated performance was observed. One of the systems was successfully implemented on the heat exchanger process, and the controlled system revealed that the predictions made by the indices were indeed accurate. This analysis technique is a powerful indicator of the general performance of a MIMO control system. It also provides a means of analysing the frequency-dependent performance of state-space control systems. Bibliography: pages 219-223.

Master of Engineering

The primary aims of this thesis, is to provide a body of knowledge on variable structure system theory and to apply the developed design concepts to control practical systems. It introduces the concept of a structure. The main aim in designing variable structure controllers, is to synthesize a variable structure system from two or more single structure systems, in such a way that the ensuing system out-performs its component structures. When a sliding mode is defined, the ensuing closed loop behaviour of the system is invariant to plant parameter changes and external disturbances. A variable structure controller was designed for a servo motor and successfully applied to the system. In practice, the phase plane representative point does not slide at infinite frequency with infinitesimal amplitude along the switching surface(s). Thus, the concept of a quasi-sliding regime was introduced. For high performance system specifications, the phase plane representative point could cycle about the origin. In some instances, sliding could be lost. For high speed applications, a novel design modification ensured that the system did not lose sliding. In addition, the controller could track a rapidly changing set point. Successful results support the developed theory.