OpenUCT :: Browsing by Author "Malengret, Michel"

Browsing by Author "Malengret, Michel"

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Open Access
Active filter current compensation for transmission optimisation
(2015) Carpenter, Paul Andrew; Gaunt, C Trevor; Malengret, Michel
This dissertation is based on the fact that any m-wire electrical system can be modelled as m-equivalent Thevenin voltages and impedances when viewed from any node. The dissertation describes how to calculate the optimal distribution of currents, so a specific amount of power can flow through and reach the network equivalent Thevenin voltages with minimal losses. The optimal current distribution method uses a recently patented method which calculates the optimal currents for each of the wires which are shown to be obtained from the Thevenin parameters and power flow at any instant in time at any node. Once the ideal currents are found, these can be obtained by active and passive devices to inject a specific amount of power (positive and negative) as to compensate existing currents. The focus is particularly on the proof of concept by simulations and physical experiments with work not specifically described in the patent with more emphasis on the optimisation to active compensation. It is explained and shown how this can be implemented using the Malengret and Gaunt method. This method reduces the cost in application where not all the currents need to be processed through a converter (e.g. inverter) but only the difference between the existing and desired optimal currents. A smaller shunt parallel converter can result with ideal current flow without the need for interrupting the currents as described in the present patent. The methodology is explained and demonstrated by simulation.
Open Access
Adaptive single to three-phase converter using variable passive elements
(2004) Ashrafi-Monfared, ShI; Malengret, Michel
The main objective of this thesis is to investigate the possible methods of converting a single-phase supply to a three-phase balanced voltage, using passive elements. Three distinct methodologies have been developed, each with its own merits and constructed prototypes. The seven chapters of this thesis contain large amound of non-real and real-time simulated results. These results were then compared with the experimental results.
Open Access
Definition of apparent power in 3-phase 4-wire non-sinusoidal power systems
(2008) Malengret, Michel; Gaunt, C Trevor
The thesis starts by collating and comparing most power theories in the instantaneous and average power domain. The instantaneous theories are reformulated and classified into three groups, which can be linked with one equation. Introducing a new instantaneous theory based on vector space allows the fundamental properties of the groups to be examined and provides the means to extend instantaneous power into the rms domain and calculate the compensating currents required. The approach results in power components that can be attributed a real physical interpretation. The new approach to three phase power theory has significant potential for education, the practical design of active compensators, and the revision of international standard definitions of power.
Open Access
Design and implementation of a 500 kVAr hybrid power factor
(2007) Goldschmidt, Christopher; Malengret, Michel
The goal of this thesis project was to design, build and test a 500 kVA-hybrid power factor/current unbalance correction unit. The unit will be used to reduce the maximum demand and reactive power consumption through power factor correction of large electricity users as well as minimize power disruption and improve power quality through unbalance correction. Through literature research, it was discovered that a particular combination of delta and wye connected capacitors exist for a particular unbalanced load that result in a reduction of unbalance (given enough load inductiance). Simulation of the proposed compensator topology allowed for the verification of this and and appropriate control strategy could be developed. Simulations also revealed the average portion of available capacitors that would be required for each of the delta and wye connected filters.
Open Access
Design and implementation of a 6 kW wind powered water heater controller with PI control
(2005) Lutchman, Ritesh; Malengret, Michel
In our quest to use more renewable energy to reduce our dependence on non-renewable fuels man has been harnessing wind, solar and hydro energy for many years. While hydo and solar energy are well established, it is only during the last decade that serious progress in wind energy has been made. Solar energy is widely used for water or space heating while wind is used for pumping water for remote areas. This project looks into the design and development of a 6kW wind powered water heating unit.
Open Access
Design and implementation of a single phase active power filter
(2011) Mkhize, Michael; Malengret, Michel
Various active filter solutions have been proposed in recent years {I], {2], and are still being widely investigated today. This thesis discusses the design and implementation of the shunt AP F topology.
Open Access
The design and optimization of a system using an induction motor driven pump, powered by solar panels
(1992) Davies, J L; Malengret, Michel
This thesis describes the design and evaluation of an induction motor driven water pumping system which is powered by solar panels. The system consists of a positive displacement pump, solar panels and an induction motor with a microprocessor controlled inverter. The reason that an induction motor has been chosen for the project is that these motors are cheaper and more robust than the more conventional DC motors. It is expected that by using an induction motor, the system performance will improve significantly for the same investment. The motor has a power rating of 0.75kW and it has been specially designed for a solar application. The system has been designed to operate from between five and seven solar panels, which yields a system capacity of 350W. The capacity could be extended to operate up to the full rating of the motor. A variable frequency drive has been designed to control the motor speed. The drive consists of a power MOSFET inverter bridge which is controlled by an 8031 microcontroller. Software has been written for the controller to generate the required pulse-width modulated signals to the inverter. Also included in the system design is an array tracker which optimizes the power output of the solar panels. The efficiency of the motor has been optimized for the torque requirements of the pump. This has been achieved by implementing an optimized voltage frequency curve and by providing for operation above the rated frequency of the motor. The motor has been operated in the frequency range of 5 - 80Hz. The inverter efficiency was high at 87% and this is expected to increase at higher power ratings. The combined motor and inverter efficiency was found to be 67% over a frequency range of 45 - 80Hz. This is only marginally less than the efficiency found in DC systems where a DC-DC converter is required to drive the motor. The control method for the system incorporated a method of maximizing the water delivery. This was achieved by optimizing the motor speed while monitoring the panel voltage. The voltage was monitored because of the high inertia of the pump, which made pure speed control difficult to implement. A field test was conducted to compare the developed AC system with a Mono DC system. The gearing of the DC system was not optimal and hence a higher flow rate was achieved with the AC system. However, the efficiency of the DC motor and converter combination proved to be slightly higher than that of the AC system. This comparison neglected the effect of poor maximum power point tracking of the DC system. In conclusion, the implementation of an AC induction motor system offers significant advantages over a DC system in terms of cost and reliability, while similar efficiencies are expected from the two systems. The cost reduction with a seven panel system will more than cover the cost of another panel, which represents a 15% increase in the system input power. The speed control of the system ensures that the water delivery is maximized at all operating irradiance levels and hence the panel output is fully utilized. The system performance is further enhanced with the use of an array tracker, which will improve the panel output by approximately 20%.
Open Access
DSP controlled three phase to single phase uninterruptible power supply
(2001) Beber, DG; Malengret, Michel
With the increase in use of electronic equipment such as personal computers, network stations and AC drive conrollers, an increased "polution" of the AC mains has resulted in the form of unwanted harmonics generated by the switching currents associated with these devices. Combined with the problem of mains "pollution" is the problem of balancing a large number of single phase loads onto a three phase supply, such as in a large computer network. This has resulted in more frequent supply voltage failure, causing substantial data and financial loss and in the extreme case death due to hospital equipment not being powered. Thus the need for an uninterruptible power supply (UPS) which is capable of resolving these problems. Taking these considerations into account, a three to single phase converter topology was developed and tested, using a Texas Instruments TMS320F243 Digital Signal Processor (DSP) for control of the system. The topology is based on a technique that utilises minimal semiconductor devices whilst still allowing for sinusoidal current to be drawn from the mains supply.
Open Access
DSP phase angle controlled three phase to single phase uninterruptible power supply
(2003) Magozore, Caxton; Malengret, Michel
Includes bibliographical references.
Open Access
Evaluation and mitigation of the undesired effect of DC bias on inverter power transformer
(2009) Isumbingabo, Emma Francoise; Malengret, Michel
Inverters have traditionally been used mostly in standalone systems (non-grid connected), Uninterruptible Power Supplies (UPS) and, more recently, in distributed generated systems (DGs). DG systems are based on grid connected inverters and are increasingly being connected to utility grids to convert renewable energy sources to the utility grids. Such sources are likely to have a significant impact in the future in meeting the electricity demands of industry and domestic consumption. Common DGs utilize DC power sources such as fuel cells, batteries, photovoltaic (solar) power, and wind power. Most of power supplies in domestic and industries are AC power consumers and, for this reason, the DC power has to be converted to meet the requirement. Two main causes of DC current in inverter power transformer are: 1) Non-linearity and asymmetry in its switching mechanism which may result in undesired DC current at its input. This DC current introduced into an inverter transformer results in the transformer's magnetic flux distortion and in some cases magnetic saturation. This, in turn, results in asymmetrical primary currents in the transformer (inverter side). This is due to the non linear characteristics of the transformer magnetic flux. 2) The same effects can be produced by the connection of asymmetrical loads (e.g. asymmetrical rectifier) to the inverter output. The result in both cases is an asymmetrical magnetic flux in the transformer. This is manifested as even and odd current harmonics as well as an increase in the reactive power requirement from the inverter. vi To remedy this situation, it is, therefore, necessary to incorporate into the inverter's control system a mechanism of cancelling the DC magnetic motive force (mmf) that causes the magnetic flux distortion. This Thesis presents a method of introducing a DC voltage component in the inverter's voltage output so as to inject the necessary DC current into the primary side of the inverter's transformer so as to cancel the total DC mmf that the transformer is subjected to ( supply and load side). This project consists of three main parts namely: Modeling, Simulation and Laboratory Experiment. Activities undertaken under Modeling and Simulation were as follows: Determining the effects of DC current on a power transformer. Investigating the likely occurrence of saturation of the power transformer incorporated in inverter systems. Mitigating the effects that can be caused by the presence of a DC component in the windings of a power transformer. After understanding the literature on the subject of interest, MATLAB SIMULINK and MATLAB m-files were used to simulate the behavior of the power transformer under three situations : The transformer under linear load. The transformer subjected to asymmetrical loading. The inverter system that has a power transformer on its output were designed in MATLAB and used to simulate the situation for each case. To validate the theory and simulation results, experimental work was carried out as follows: vii Investigation of the effects that DC (current) injection can have on a 6 kVA power transformer. Investigation of the performance of a 6 kVA power transformer under linear loading. Investigation of the performance of a 6 kVA power transformer under non-linear loads. Investigation of the likely occurrence of DC offset in inverter system. Mitigation of the effect of DC bias on power transformer using extra windings. Mitigation of the effects of DC offset in power inverter transformer by using the second harmonic content of the primary current as a feedback signal. Results obtained showed a successful implementation of the proposed method. However limitations of the controller performances were experienced and will require future work. It was concluded that a total removal of the undesired effects of DC bias is achievable and that total removal of DC offset in power inverter transformer is possible if the limitations of the controller are overcome.
Open Access
A frequency converter to power a soudronic VAA20 welding machine
(1991) Jacques, R; Malengret, Michel; Van Nierop, Johan H
This thesis covers the design, manufacture and testing of a frequency converter, that transforms three phase AC 380V, into one phase AC 50 to 120Hz, 100 to 650V. The inverter output is intended to power a Soudronic VAA2 O welding machine. The input to the converter was stepped down and rectified to generate an unregulated DC bus of 250V. A full bridge transistorised inverter was controlled by a 6809 microprocessor that generated pulse width modulated waveforms to derive a desired inverter output current and frequency. A base drive was developed to control the power transistor in the inverter. It facilitates the rapid switching of the transistors and provides them with overcurrent protection. The inverter was originally constructed in push-pull configuration. At 20KVA this type of inverter was found to be undesirable, so a full bridge configuration was used in the final design. The converter has been installed and is operating successfully. Many recommendations are made for the improvement of future converters. The changes will improve the operation of the converter and can also reduce the size, cost and weight of it.
Open Access
Induction motor drive for battery vehicle
(1978) Malengret, Michel; Enslin, NC de V
A 9 phase transistor inverter fed induction motor for a battery vehicle with direct wheel drive is discussed. A new method of motor voltage control by pulse, width modulation, where the phases are interlaced in a manner to conserve continuity of the supply current, is described. In addition to this, a novel construction, where the motor and the inverter are built into one compact and economical unit, is presented.
Open Access
Load compensation : design of a real time analysis and control device
(2001) Sebitosi, A B; Malengret, Michel
The aim of this thesis is to produce a load compensator for a three-phase system. It should be simple, accurate and affordable. The three-phase load compensator design is based on a more recent definition of power factor. Attempts to establish a universally acceptable definition can be traced as early as 1920 at the 36th Annual convention of the American Institution of Electrical Engineers. Subsequently, a number of definitions have been adopted by different scholars. Each definition can lead to a different compensator solution. This problem, for example, is illustrated by Eammanuel [25].
Open Access
A prototype energy management system for a solar powered cycle
(2002) Webber, Gordon Andrew; Malengret, Michel
Bibliography: leaves 92-93.
Open Access
Remote control and monitoring of a hybrid power system
(2008) Phillips, Tristan; Malengret, Michel
Increasingly, South Africa is developing a need for grid-independent power systems. Many options exist already in the form of diesel generators, solar panels and wind generators. This project is to do with marrying the various sources of power with efficient and intelligent control. Specifically, the terms of reference describe an existing solution that has been developed. The focus of this thesis is to design a replacement system for the existing system which incorporates many communication technologies and additional features. The design centres on a central digital signal processor board. The redesign of this hardware and software will form the bulk of the content of this document. The scope of the design encompasses all the communications and new features including remote programming, control and monitoring software and robustness. The new system is to form the infrastructure or base hardware and software for many different power-related applications. A specific example of such an application, the hybrid power system, is discussed in detail to demonstrate the success of the design.
Open Access
Remote control and monitoring of power systems
(2008) Parry, Richard A J; Malengret, Michel
Power systems are typically complex and can be affected by their environment in ways that cannot be completely predicted by their designers. It is thus imperative that monitoring is considered as part of the design of new power systems. Due to the associated costs of maintenance, repair, and downtime, monitoring these systems is particularly important when the installations are remote. Remote locations benefit greatly from renewable energy sources. As a result, this work focuses on a novel Hybrid Inverter system developed by Optimal Power Solutions Pty. Ltd. (OPS). This system uses renewable energy sources, grid power, and diesel generators together with a bi-directional inverter to supply a remote location with grid-quality power.
Open Access
A series-connected VSC for voltage regulation, balancing and harmonics mitigation
(2006) Bathfield, Gregory; Malengret, Michel
Voltage sensitive electronic equipment, such as computers, process controllers, programmable logic controllers, adjustable speed drives and robotic devices is increasingly used in modern industrial processes. Industrial loads thus require a supply free of voltage disturbances such as voltage dips, swells, unbalances and harmonics. The effect of these disturbances may be as bad as a complete shut down of a production line, hence giving rise to the growing interest and need, for mitigation of such power quality problems. The objective of this thesis is to design and build a mitigation device to shield loads from these problems.
Open Access
A single three phase variable speed drive with unity power factor
(2000) Douglas, Hugh; Malengret, Michel
The new proposed topology for a single three-phase variable speed drive was developed after considering the advantages and disadvantages of previous topologies. The new topology employs only six switches that form and active front-end rectifier and a four-switch inverter. The active front-end rectifier is the first leg of the three-phase bridge. It not only rectifies the voltage source but it also regulates one of the phases for the motor. The four-switch inverter produces the variable frequency. Excessive distortion currents drawn by a converter can cause voltage distortions. For this reason the converter should draw a high quality sinusoidal current from the supply. Excessive currents drawn from the supply are also the result of poor power factors. The converter should therefore operate at close to unit power factor. N Mohan, T Underland, W.P Robins [3].
Open Access
Supply-friendly single phase uninteruptible power supply
(1998) Mills, Carlo Juan; Malengret, Michel
Uninterruptible power supplies (UPS) maintain a constant supply of power to a critical load. The distinguishing features are a fixed voltage and frequency, low harmonic content and the ability to supply the load for a period of time after the incoming supply has failed. The document begins by identifying the typical power-line disturbances and their effect on various types of equipment. Together with the power conditioners used to suppress these disturbances, various UPS standby, line-interactive and on-line configurations are introduced. Next, the possibility of modifying a locally manufactured UPS to meet the design specifications is investigated. The performance of the system under load is evaluated, and forms the basis for the following decision. Due to the large number of modifications required and the inflexibility of local UPS topology, an alternative topology is adopted. In the new topology a power factor corrector, constructed around a DC to DC boost converter, interfaces with the incoming AC line. It delivers a half sinusoidal current into the DC bus. An IGBT inverter using sinusoidal unipolar pulse-width modulation regenerates the AC load voltage after filtering through a LC-filter. The DC bus voltage ripple is reduced by synchronising the inverter load and power factor corrector current while the battery pack maintains the DC bus during a power failure. The power factor corrector employs a dedicated analogue controller chip while a MCS-51 microcontroller generates the inverter PWM, provides the remote monitoring facilities, battery charging and performs general support tasks. The total harmonic distortion of the input current is measured at less than 4% while the power factor remained above 0.99 over the entire load range. The ripple regulator reduced the DC bus voltage ripple without any noticeable effect on the load. Under maximum load, the steady state output voltage is maintained during the -20%, +10% variation in the incoming line voltage. However, the transient response fails to meet the 5% design specification. A 0-100% load step results in a 7% drop in the output voltage while the loss of the load results 10% jump in voltage. System efficiency is measured at 85%. It is the lack of processing power, precluding the use of floating point or an optimal control algorithm, which ultimately compromises the performance of the system. It is recommended that the microcontroller be replaced with a 16-bit processor or digital signal processor to provide the extra computational power needed to optimise the UPS response. To improve the voltage regulation, it is recommended that the control include an inner current loop while the switching frequency should be increased to reduce the energy storage in the output filter. Further adjustments and refinements to the topology are suggested in the final chapter.
Open Access
Viability study to implement peak load shaving at UCT Medical School
(2007) Cornelio, Antonio M M; Malengret, Michel
This Master thesis investigates the application of Peak Load Shaving (PLS) at University of Cape Town Medical School (UCTMS). The purpose was to decrease the monthly maximum demand (MMD) in kVA such that UCTMS monthly electricity bill is decreased. It was purposed that implementing a three-phase inverter in conjunction with a lead-acid battery at UCTMS for PLS is technical and financial viable. Five-year UCTMS MMD data history was gathered from UCT maintenance office as well as eight-month UCTMS load profile, which was gathered using the available electrical meter at Electrical Department Substation for Medical School at FalmouthRoad. Control strategies studies from previous works enabled the quickly synchronization of the three-phase inverter to a three-phase grid. It gave a good quality balanced control of the three-phase currents through the filter inductors, consequently gave a good quality control of the real and reactive power. Secondly a PLS algorithm (PLSA) was developed, which had the aim of setting a threshold point (TP) to prevent the MMD supplied to UCTMS to surpass the TP. In addition, the PLSA in conjunction with designed controllers would charge the battery at unity power factor (PF), whenever the MD is below the set TP and discharge at the same PF conversely, hence limiting the MMD at the TP. To test the purposed PLS topology, simplorer simulator was used, where two daily UCTMS load profile were simulated. The controls design and PLSA were implemented and the result showed that implementing PLS at UCTMS is technical viable. In practice, a prototype was built to show the synchronization of the three-phase inverter with three-phase grid by using a digital phase locked loop PI-based controller implemented in a DSP chip.