O número crescente de cargas baseadas em conversores eletrônicos criou a preocupação com a distorção harmônica em sistemas de energia elétrica. Qualidade de energia é um assunto importante tanto para as companhias distribuidoras e geradoras de energia elétrica como para os consumidores. A utilização de equipamentos para a eliminação de harmônicos tornou-se necessária e são diversas as soluções possíveis. Em sistemas trifásicos com quatro fios, os filtros ativos de potência e os sistemas de energia ininterrupta são equipamentos empregados para a melhoria da qualidade de energia elétrica. Tais equipamentos apresentam em sua estrutura um conversor trifásico com quatro fios podendo ser do tipo fonte de tensão ou fonte de corrente. Este estudo propõe uma estratégia para a minimização da ondulação das correntes de linha e de neutro em um conversor do tipo fonte de tensão trifásico com quatro fios. A estratégia consiste em injetar uma tensão de seqüência zero nas referências dos blocos PWM\'s que não altere o valor médio da corrente, mas somente a sua ondulação. Propõe-se uma metodologia que possibilita a escolha de um valor ótimo para a tensão de seqüência zero. São também apresentados a região dos vetores sintetizáveis, a análise da tensão de saída e o modelamento do conversor. Propõe-se uma estratégia de controle de corrente com reguladores PI para um sistema trifásico com quatro fios usando conversor com quatro fios. O comportamento do conversor é verificado por simulações numéricas e resultados experimentais, confirmando o desempenho da estratégia de PWM proposta. / The growing number of power electronics-based loads has created concern about harmonic distortion in electric systems. Power quality is an important issue both for utilities and consumers. The use of harmonic filtering equipment has become necessary and many solutions have been studied. In three phase systems, active power filters and uninterruptible power supply are used for improving power quality. These equipments present in their topologies a three-phase four-wire voltage source converter or three-phase four-wire current source converter. This study proposes a strategy for the minimization of the line and neutral ripple current of a three-phase four-wire Voltage Source Converter. The strategy consists of injecting an instantaneous zero sequence to the references of a triangular carrier PWM that does not affects the local average of the converter output voltages, but only the ripple currents. A methodology to evaluate the instantaneous optimal value of the injected zero sequence voltage is presented. The locus of the synthesizable voltage vectors and the modeling of the converter are also shown. It presents a strategy of current control for three-phase four-wire systems using three-phase four-wire converter. The behavior of the converter is verified by numerical simulation and experimental results, confirming the performance of the proposed PWM strategy.

Thesis (MTech (Electrical Engineering)))--Cape Peninsula University of Technology, 2011. / This thesis presents an investigation into the generic tools, hardware and firmware, involved in power electronic converter control and feedback. The aim was to determine the optimal controller architecture through research of existing controllers. As soon as the architecture was established, design of the controller commenced. Explanations for the various components selected were provided. The design considerations when designing a printed circuit board (PCB) with mixed signals was also presented. The theory behind the control of a multicell converter as well the practical implementation of the control scheme in firmware was presented.

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The following report presents the development of a computer-based system designed to examine the response of a physical process is a process trainer, PT326, from Feedback Corporation. There are two main categories of control available to the user: (1) analog control and (2) digital control. Within each of these categories the following types of control systems are available: (1) Proportional control, (2) Proportional-Integral control, (3) Proportional-Integral-Derivative control and (4) On-Off control. The user can examine both regulator and servo response for any of the given control systems. All parameters associated with the selected control system are variable and user-input. The software is designed to be user-friendly. The user examines the response of the process to different control systems through the use of full-screen, high-resolution, color graphs. These graphs are linear and labeled. There are two main categories of graphs available to the user: (1) real-time monitoring and (2) graphs with labeled time base. Within each category there are four different graphs available. These graphs are available under any given control system. The user may also obtain hardcopy of these graphs.

The LLC resonant converter has been widely used as a DC-DC converter due to its high efficiency, high power density and hold-up capability in power supplies for communication systems, computers and consumer electronics. Use of the high-frequency LLC converter has also been increasing in recent years due to its high power density and integrated magnetics, which reduce the total cost. With the fast development of wideband gap devices and novel magnetic materials, the trend of pushing switching frequency higher continues. However, the control characteristics of the LLC resonant converter are much more complex than that of the PWM converter due to the dynamics of the resonant tank. This paper employs state-trajectory analysis to describe and analyze the behavior of the resonant tank. Control methods based on state-trajectory analysis were used to solve the challenges in the control of the LLC resonant converter, including unpredictable dynamics, burst mode for light-load efficiency, soft start-up and short circuit protection. Additionally, digital controllers are gradually taking the place of analog controllers in the control of the LLC resonant converter due to the advantages of the digital controllers over the analog controllers, such as their ability to be flexible and re-configurable, capable of non-linear control, and able to communicate with other controllers. Among the digital controllers, cost-effective microcontrollers (MCU) are preferred for industrial applications. Because of the advantages of the state-trajectory control and the industrial preference in the cost-effective digital controllers, it would be of great benefit to apply state-trajectory control to high-frequency LLC converters with cost-effective digital controllers. This thesis investigates the impact of digital delay on state-trajectory control. Simplified Optimal Trajectory Control (SOTC) for LLC converters is further simplified so that SOTC can be achieved with cost-effective digital controllers. Furthermore, the limitations caused by digital controller are explained in detail, and methods are proposed to apply the SOTC to high frequency LLC converter is proposed. A detailed analysis of fast load transient response, soft start-up, burst mode for light-load efficiency and synchronous rectification (SR) driving is provided. Multi-step SOTC for fast load transient response is proposed to apply cost-effective digital controllers to high-frequency LLC converters; SOTC for soft start-up with only sensing Vo is proposed to minimized the impact of digital delay on state-trajectory control; SOTC for burst mode with multi-step is proposed to eliminate the limitation of minimum off-time caused by digital controllers in constant burst-on time control; a generalized adaptive SR driving method using the ripple counter concept is proposed to significantly reduce controller resource utilization for the SR control of high-frequency LLC converters. The whole control system is demonstrated on a 500kHz 1kW 400V/12V LLC converter with a 60MHz MCU, which integrates all the proposed control methods. / Master of Science

An estimator for Nonlinear system estimation using Jump Matrix Technique is developed. The idea of the Jump Matrix Technique is to break up the nonlinear system into linear and nonlinear subsystems. The linear subsystem projection, during the sampling interval, is on the basis of the transition matrix of the linear subsystem. At each sampling instant, the system variables are updated using an instantaneous "jump" in the values. The estimator for the nonlinear case is developed on the lines of Kalman filter for the linear case. The Jump Matrix technique is used for system simulation for three different nonlinear systems and then estimation of the system state is carried out using the above mentioned estimator. The system response and the estimated states are considered and the effect of change in system noise parameters is observed. Feedback control of nonlinear system response using the estimated state variables is investigated. Two different systems are considered and their responses are changed using feedback of linear combination of the system state variables. / Master of Science

Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2014. / The application of digital control techniques has become dominant in power electronics owing to several advantages they present, when compared to analogue solutions. Their development is based on the use of microprocessors and microcontrollers, such as Application Specific Integrated Circuit (ASIC), Digital signal processors (DSP), Field Programmable Gate Arrays (FPGA), or a combination of these devices. This thesis presents an investigation of a soft-core based FPGA control system as a solution for power electronic applications. The aim was the development and implementation of a conversion controller, which purpose is to supply control inputs in the form of digital Pulse Width Modulation (PWM) signals, to a number of power electronic applications, such as single half and full bridge DC-DC converters, three phase and multicell inverters. The PWM control technique is achieved via their power semiconductor switching devices. These PWM control signals are necessary for the high frequency conversion of an analog input voltage (AC, DC or unregulated) to an analog output voltage of another level (AC or DC). This was intended to be achieved by exploiting and combining the advantages that FPGA and embedded processors provide such as high reconfigurability and multipurpose ability. This controller’s digital outputs, namely PWM switching signals, can be directly delivered to an analog signal amplification circuit to create an adequate voltage level before being processed by the converters’ switches.

The paper presents design solution and physical implementation of a system for examination of electro hydraulic steering based on OSPE 200 components. The implementation is based on synthesis of required hydraulic and structure parameters, presented in a previous paper. Now we present the interconnection of the digital control system and the closed-loop flow diagram. A formal description of embedded software is presented too, which supports operation of PI control algorithm in real-time. Identification is performed based on experimentally reported the transitional process by developing mathematical models. Presents the structure and capabilities of the models for identification, as well as procedures for their validation.

Thesis (MScIng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: In the field of power electronic engineering, there is a need for a reconfigurable power electronic controller. Such a controller will enable engineers to stay focussed on their main field of study, not being side-tracked by the process of designing a high-speed digital controller to implement their ideas with. The design, construction and implementation of such a controller is presented in this paper. The design process involved defining the specifications of the controller and finding electronic components to satisfy them. After suitable components had been identified, a schematic design of the system was done. The netlist of the schematic was exported to a printed circuit board (PCB) design program, where the final layout was done and the connections between the devices routed. Before the PCB was manufactured, the firmware for the programmable logic devices (PLDs) was written to ensure that it fits in the selected PLDs of the system. After the PCB was manufactured and all its components fitted, it was tested and eventually used to implement the control of a shunt active power filter. / AFRIKAANSE OPSOMMING: Wanneer navorsing gedoen word in die drywings-elektronika gebied, word ’n behoefte vir ’n heropstelbare drywings-elektroniese beheerder ondervind. So ’n beheerder sal ingenieurs in staat stel om gefokus te bly op hulle hoof studieveld, sonder dat hulle aandag hoef te skenk daaraan om ’n ho¨e spoed digitale beheerder te ontwerp om hulle idees mee te implementeer. Die ontwerp, konstruksie en implementering van so ’n beheerder word in hierdie tesis voorgelˆe. Die ontwerp behels die bepaling van die spesifikasies van die beheerder en die opsporing van elektroniese komponente wat hierdie spesifikasies sal bevredig. Nadat geskikte komponente gevind is, is ’n skematiese ontwerp van die hele beheerder gedoen. Die lys van die verbindings tussen die komponente (Eng. netlist) is na die stroombaanbord ontwerp program gestuur, waar die finale uitleg van die bord gedoen is. Voordat die bord gemaak kon word, is die programmatuur vir die programmeerbare logikatoestelle geskryf om te verseker dat dit in die toestelle wat in die sisteem gebruik word, sal pas. Nadat die stroombaanborde vervaardig is en al die komponente daarop gemonteer is, is die bord getoets en uiteindelik gebruik om die beheer van ’n aktiewe drywingsfilter te implementeer.

published_or_final_version / Electrical Engineering / Master / Master of Philosophy