'n Elektroniese wisselrigter met nie-lineêre resonante fase-arms
- Authors: Theron, Philippus Coenraad
- Date: 2015-03-02
- Subjects: Power electronics
- Type: Thesis
- Identifier: uj:13393 , http://hdl.handle.net/10210/13402
- Description: M.Ing. , Inverters are daily used in industry, and to a large extent, as induction motor drives. Power levels of inverters vary from a few watt to several megawatt. The most common part of inverters is a phase arm or a pole, consisting of two power electronic switches and two freewheeling diodes. The hard switched phase arm is the standard in industry due to simplicity and cost. Regenerative snubbing is often used at larger power levels to reduce losses in the inverter. Some aspects of the non-linear resonant pole inverter, such as regenerative snubbing and zero voltage switching, are investigated. It is obtained by utilising a non-linear resonant tank. Low current stresses permit the optimal use of the power electronic switches. The non-linear resonant pole inverter can replace the hard switched inverter, with no restriction with respect to power levels. Experimental and analytical modelling was employed to investigate some aspects, such as controllability, losses and feasibility.
- Full Text:
- Authors: Theron, Philippus Coenraad
- Date: 2015-03-02
- Subjects: Power electronics
- Type: Thesis
- Identifier: uj:13393 , http://hdl.handle.net/10210/13402
- Description: M.Ing. , Inverters are daily used in industry, and to a large extent, as induction motor drives. Power levels of inverters vary from a few watt to several megawatt. The most common part of inverters is a phase arm or a pole, consisting of two power electronic switches and two freewheeling diodes. The hard switched phase arm is the standard in industry due to simplicity and cost. Regenerative snubbing is often used at larger power levels to reduce losses in the inverter. Some aspects of the non-linear resonant pole inverter, such as regenerative snubbing and zero voltage switching, are investigated. It is obtained by utilising a non-linear resonant tank. Low current stresses permit the optimal use of the power electronic switches. The non-linear resonant pole inverter can replace the hard switched inverter, with no restriction with respect to power levels. Experimental and analytical modelling was employed to investigate some aspects, such as controllability, losses and feasibility.
- Full Text:
'n Hibriede vervormingskompensator, beheer deur 'n kunsmatige neurale netwerk
- Authors: Pretorius, Robert W.
- Date: 2014-03-10
- Subjects: Power electronics , Electric power systems , Neural networks (Computer science)
- Type: Thesis
- Identifier: uj:4245 , http://hdl.handle.net/10210/9603
- Description: M.Ing. (Electrical and Electronics) , The increased use of power electronic equipment in power networks prompted the development of various topologies to compensate for the distortion in the power networks. The various compensator topologies employ a vast range of converters for the compensation of the different non-active power components. The compensators are either designed to eliminate a specific non-active power component, or a combination of converters is used to simultaneously compensate for several non-active components. The choice of compensator depends largely on the type of load, the distortion levels in the power network, the effectiveness of the compensator and very importantly, the cost implications for the user. Under constant load conditions a particular compensator would suffice. It is however not the case when the load and the accompanied distortion varies with time, which is the case with present non-linear, dynamic high power loads on the network. In these cases,. a need for another compensator or compensation strategy, that is more effective in compensating the changing load condition, exists. It would therefore be advantageous to construct a single compensator from various converters -the hybrid compensator -, so as to enable the user to compensate effectively at all times the distortion caused by his load. In order to be able to operate such a hybrid compensator cost-effectively an intelligent control system capable of constantly monitoring the load and updating the compensation strategy, is needed. Keeping in mind that, with the technology available today, compensators can effectively operate for periods in excess of twenty years, it makes sound economical sense to operate the compensator as cost-optimally as possible. This dissertation investigates the development of an artificial neural network based controller for the cost-optimal control of a hybrid compensator. The hybrid compensator considered consists of the following: A 21 kVAR three phase FF-TCR compensator with LC-fiIters tuned at the 5th, 7th,11th and 13th harmonic frequencies and a 6 kVA three-phase dynamic power filter. The hybrid compensator is to be applied for the compensation of a 25 KVA non-linear load (Inductively loaded controlled rectifier). The above mentioned compensators have been modelled to agree with experimental pilot plants. The complete system with low-level controllers was simulated with EMTP (The Electromagnetic Transients Program). This simulation was used to verify the intelligent controller operation. The neural network based controller that is investigated, consists of a Backpropagation-trained neural network, that continuously analyses the load conditions, considers the operational characteristics and losses of the hybrid compensator and proposes a cost-optimal compensation strategy for the hybrid compensator. The modelling of the hybrid compensator's operational losses and characteristics to enable the cost-effective operation thereof is discussed. Special attention is given to the modelling of the cost-effective control strategy, in the training data used for the training of the neural network controller. The training of the neural network controller, and an evaluation of its behaviour when applied to two different hybrid compensator structures, is also given.
- Full Text:
- Authors: Pretorius, Robert W.
- Date: 2014-03-10
- Subjects: Power electronics , Electric power systems , Neural networks (Computer science)
- Type: Thesis
- Identifier: uj:4245 , http://hdl.handle.net/10210/9603
- Description: M.Ing. (Electrical and Electronics) , The increased use of power electronic equipment in power networks prompted the development of various topologies to compensate for the distortion in the power networks. The various compensator topologies employ a vast range of converters for the compensation of the different non-active power components. The compensators are either designed to eliminate a specific non-active power component, or a combination of converters is used to simultaneously compensate for several non-active components. The choice of compensator depends largely on the type of load, the distortion levels in the power network, the effectiveness of the compensator and very importantly, the cost implications for the user. Under constant load conditions a particular compensator would suffice. It is however not the case when the load and the accompanied distortion varies with time, which is the case with present non-linear, dynamic high power loads on the network. In these cases,. a need for another compensator or compensation strategy, that is more effective in compensating the changing load condition, exists. It would therefore be advantageous to construct a single compensator from various converters -the hybrid compensator -, so as to enable the user to compensate effectively at all times the distortion caused by his load. In order to be able to operate such a hybrid compensator cost-effectively an intelligent control system capable of constantly monitoring the load and updating the compensation strategy, is needed. Keeping in mind that, with the technology available today, compensators can effectively operate for periods in excess of twenty years, it makes sound economical sense to operate the compensator as cost-optimally as possible. This dissertation investigates the development of an artificial neural network based controller for the cost-optimal control of a hybrid compensator. The hybrid compensator considered consists of the following: A 21 kVAR three phase FF-TCR compensator with LC-fiIters tuned at the 5th, 7th,11th and 13th harmonic frequencies and a 6 kVA three-phase dynamic power filter. The hybrid compensator is to be applied for the compensation of a 25 KVA non-linear load (Inductively loaded controlled rectifier). The above mentioned compensators have been modelled to agree with experimental pilot plants. The complete system with low-level controllers was simulated with EMTP (The Electromagnetic Transients Program). This simulation was used to verify the intelligent controller operation. The neural network based controller that is investigated, consists of a Backpropagation-trained neural network, that continuously analyses the load conditions, considers the operational characteristics and losses of the hybrid compensator and proposes a cost-optimal compensation strategy for the hybrid compensator. The modelling of the hybrid compensator's operational losses and characteristics to enable the cost-effective operation thereof is discussed. Special attention is given to the modelling of the cost-effective control strategy, in the training data used for the training of the neural network controller. The training of the neural network controller, and an evaluation of its behaviour when applied to two different hybrid compensator structures, is also given.
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'n Nuwe tegnologie vir geintegreerde elektromagnetiese komponente vir resonante drywingselektroniese mutators
- Authors: Smit, Marthinus Christoffel
- Date: 2015-03-02
- Subjects: Power electronics
- Type: Thesis
- Identifier: uj:13372 , http://hdl.handle.net/10210/13384
- Description: M.Ing. , A constant demand exists for ever decreasing size in switch mode supplies. The first step has been the introduction of resonant mode converters. Such converters typically consist of a resonant tank, a transformer and an input or output filter. The soft-switching characteristics of these converters allow an order of magnitude higher frequency, thus reducing the size of the reactive components. The next logical step towards a smaller package is introduced, namely the electromagnetic integration of the resonant tank and, if possible, the transformer into a single component, which; not only saves mass and volume, but can also reduce manufacturing costs. The particular converter investigated is the well known series resonant converter. It is shown that the necessary capacitance can be achieved by using a bifilar primary and the leakage inductance of the transformer replaces the physical inductor. Simulation of a suitable distributed circuit network indicates the same frequency domain characteristics and time domain waveforms for both the integrated component, and the discrete inductor, capacitor an transformer in series. Possible configurations for the integrated LCT-component are proposed, and theoretical analysis predicts an operating frequency in the MHZ region. Notwithstanding the complicated manufacturing, results show An integrated LCT-component, applied in a prototype 1 MHz power supply, with an efficiency of approximately 90 %. If manufacturing of the LCT-component allows an acceptable dimension and an acceptable resonant frequency, this can be a very competitive technology.
- Full Text:
- Authors: Smit, Marthinus Christoffel
- Date: 2015-03-02
- Subjects: Power electronics
- Type: Thesis
- Identifier: uj:13372 , http://hdl.handle.net/10210/13384
- Description: M.Ing. , A constant demand exists for ever decreasing size in switch mode supplies. The first step has been the introduction of resonant mode converters. Such converters typically consist of a resonant tank, a transformer and an input or output filter. The soft-switching characteristics of these converters allow an order of magnitude higher frequency, thus reducing the size of the reactive components. The next logical step towards a smaller package is introduced, namely the electromagnetic integration of the resonant tank and, if possible, the transformer into a single component, which; not only saves mass and volume, but can also reduce manufacturing costs. The particular converter investigated is the well known series resonant converter. It is shown that the necessary capacitance can be achieved by using a bifilar primary and the leakage inductance of the transformer replaces the physical inductor. Simulation of a suitable distributed circuit network indicates the same frequency domain characteristics and time domain waveforms for both the integrated component, and the discrete inductor, capacitor an transformer in series. Possible configurations for the integrated LCT-component are proposed, and theoretical analysis predicts an operating frequency in the MHZ region. Notwithstanding the complicated manufacturing, results show An integrated LCT-component, applied in a prototype 1 MHz power supply, with an efficiency of approximately 90 %. If manufacturing of the LCT-component allows an acceptable dimension and an acceptable resonant frequency, this can be a very competitive technology.
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'n Saamgestelde drywingselektroniese tussenkringmutator as deurloopspanningsbron
- Authors: Badenhorst, Maré
- Date: 2014-05-08
- Subjects: Power electronics , Modulation (Electronics)
- Type: Thesis
- Identifier: uj:10935 , http://hdl.handle.net/10210/10508
- Description: M.Ing. (Electrical and Electronic Engineering) , The South African Railways covers a total distance of some 24 000 km, making use of a signalling network of 1000 interlocking systems. This comprises of the order of 1000 signalling houses each with its own unlnterruptible power supply system of which a DC·AC converter Is one of the components. Due to the requirements by Spoomet, high frequency (ultrasonic) chopper technology had to be used. This treatise describes the design and development of a 3 kVA composite DC·AC converter with an ultrasonic AC link for this application. In the primary converter (centre tapped topology) ZVS Is achieved by good circuit layout and controlled transformer capacitance. As a result the performance of the converter was improved with regard to efficiency and switching transients compared to the conventional hard switched converter. The four pulse topology with an output LC·filter was used for the secondary converter. Due to the modulation technique being used, the load perceived the switching frequency as 20kHz while the actual switching frequency was only 10kHz. In this way switching losses were kept within reasonable limns as well as satisfying the low audible noise requirement. The stability of the LC·filter was achieved with a current feedback loop. The literature describes the capacitor current being used in the feedback loop. In this case the Inductor current was used with the advantage of output short circuit protection without an additional current measurement. Apart from the advantages of small weight and volume from a maintenance point of view, the composite DC·AC converter also achieved high efficiency (> 85%) over a wide load range (10%-100% of full load).
- Full Text:
- Authors: Badenhorst, Maré
- Date: 2014-05-08
- Subjects: Power electronics , Modulation (Electronics)
- Type: Thesis
- Identifier: uj:10935 , http://hdl.handle.net/10210/10508
- Description: M.Ing. (Electrical and Electronic Engineering) , The South African Railways covers a total distance of some 24 000 km, making use of a signalling network of 1000 interlocking systems. This comprises of the order of 1000 signalling houses each with its own unlnterruptible power supply system of which a DC·AC converter Is one of the components. Due to the requirements by Spoomet, high frequency (ultrasonic) chopper technology had to be used. This treatise describes the design and development of a 3 kVA composite DC·AC converter with an ultrasonic AC link for this application. In the primary converter (centre tapped topology) ZVS Is achieved by good circuit layout and controlled transformer capacitance. As a result the performance of the converter was improved with regard to efficiency and switching transients compared to the conventional hard switched converter. The four pulse topology with an output LC·filter was used for the secondary converter. Due to the modulation technique being used, the load perceived the switching frequency as 20kHz while the actual switching frequency was only 10kHz. In this way switching losses were kept within reasonable limns as well as satisfying the low audible noise requirement. The stability of the LC·filter was achieved with a current feedback loop. The literature describes the capacitor current being used in the feedback loop. In this case the Inductor current was used with the advantage of output short circuit protection without an additional current measurement. Apart from the advantages of small weight and volume from a maintenance point of view, the composite DC·AC converter also achieved high efficiency (> 85%) over a wide load range (10%-100% of full load).
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'n Saamgestelde skakelmoduskragbron vir Tig-sweis
- Authors: Roux, Johannes Adam
- Date: 2014-02-17
- Subjects: Power electronics , Semiconductors , Electric welding , Aluminum
- Type: Thesis
- Identifier: uj:4054 , http://hdl.handle.net/10210/9405
- Description: M.Ing. (Electrical and Electronic Engineering) , The product of switching frequency and output power of solid state converters has increased dramatically during the past few years. This progress can mainly be attributed to the recent developments in power electronic switching devices. These developments are mainly responsible for a reduction in the physical size of the converter, especially that of the reactive components, and an increase in the dynamic response of the converter. The aim of this work is to use these characteristics of the power electronics converter in the development of an aluminum welding machine. This welding machine is developed for excisting welding processes namely: shield metal arc welding (STICK), and tungsten inert gas welding (TIG). More than one converter is necessary in order to shape the required output current and output voltage of the machine. Several different converters which can be used for the applications are compared. Each application has different conditions under which the converter must be able to work. The most convenient converter for each application is then fully described.
- Full Text:
- Authors: Roux, Johannes Adam
- Date: 2014-02-17
- Subjects: Power electronics , Semiconductors , Electric welding , Aluminum
- Type: Thesis
- Identifier: uj:4054 , http://hdl.handle.net/10210/9405
- Description: M.Ing. (Electrical and Electronic Engineering) , The product of switching frequency and output power of solid state converters has increased dramatically during the past few years. This progress can mainly be attributed to the recent developments in power electronic switching devices. These developments are mainly responsible for a reduction in the physical size of the converter, especially that of the reactive components, and an increase in the dynamic response of the converter. The aim of this work is to use these characteristics of the power electronics converter in the development of an aluminum welding machine. This welding machine is developed for excisting welding processes namely: shield metal arc welding (STICK), and tungsten inert gas welding (TIG). More than one converter is necessary in order to shape the required output current and output voltage of the machine. Several different converters which can be used for the applications are compared. Each application has different conditions under which the converter must be able to work. The most convenient converter for each application is then fully described.
- Full Text:
'n Saamgestelde skakelmoduskragbron vir Tig-sweis
- Authors: Roux, Johannes Adam
- Date: 2015-09-10
- Subjects: Power electronics , Semiconductors , Aluminum , Electric welding
- Type: Thesis
- Identifier: uj:14090 , http://hdl.handle.net/10210/14522
- Description: M.Ing. , The product of switching frequency and output power of solid state converters has increased dramatically during the past few years. This progress can mainly be attributed to the recent developments in power electronic switching devices. These developments are mainly responsible for a reduction in the physical size of the converter, especially that of the reactive components, and an increase in the dynamic response of the converter ...
- Full Text:
- Authors: Roux, Johannes Adam
- Date: 2015-09-10
- Subjects: Power electronics , Semiconductors , Aluminum , Electric welding
- Type: Thesis
- Identifier: uj:14090 , http://hdl.handle.net/10210/14522
- Description: M.Ing. , The product of switching frequency and output power of solid state converters has increased dramatically during the past few years. This progress can mainly be attributed to the recent developments in power electronic switching devices. These developments are mainly responsible for a reduction in the physical size of the converter, especially that of the reactive components, and an increase in the dynamic response of the converter ...
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'n Studie van die elektroniese kompensasie van vervormings in kragnetwerke
- Authors: Marshall, Dirk Adriaan
- Date: 2015-03-02
- Subjects: Electric distortion , Power electronics , Reactive power (Electrical engineering) , Power electronics - Equipment and supplies
- Type: Thesis
- Identifier: uj:13400 , http://hdl.handle.net/10210/13409
- Description: M.Ing. , Please refer to full text to view abstract
- Full Text:
- Authors: Marshall, Dirk Adriaan
- Date: 2015-03-02
- Subjects: Electric distortion , Power electronics , Reactive power (Electrical engineering) , Power electronics - Equipment and supplies
- Type: Thesis
- Identifier: uj:13400 , http://hdl.handle.net/10210/13409
- Description: M.Ing. , Please refer to full text to view abstract
- Full Text:
'n Studie van drywingselektroniese tegnologie vir verspreide hoogstroomuitsette
- Authors: Relihan, Willem Anton
- Date: 2014-02-17
- Subjects: Power electronics , Electric circuits
- Type: Thesis
- Identifier: uj:4027 , http://hdl.handle.net/10210/9380
- Description: M.Ing. (Electrical and Electronic Engineering) , Many applications need a high power (> 500W) at a relatively low voltage. The known technology of this class of converters is primitive and such converters are big as a result thereof. An investigation is made into the suitability of matrix transformer technology in the supply of large currents at low voltages. A layout for this topology which make optimal use of its characteristics is proposed . This includes modularity, possible application in distributed power supplies and equal current sharing. A system is designed and models are created to optimize the design. The models are extended to accommodate the effects of unavoidable parasitics which was observed in the practical system. A system consisting of sixteen modular units with a total output current capability of 320A at a voltage of between 0 and 5V is developed. The output capability and thus the number of modules needed is dependent on the application. Provision is thus made for a large power range. Power is transformed at a frequency of 100kHz to keep the physical dimensions of the system small.
- Full Text:
- Authors: Relihan, Willem Anton
- Date: 2014-02-17
- Subjects: Power electronics , Electric circuits
- Type: Thesis
- Identifier: uj:4027 , http://hdl.handle.net/10210/9380
- Description: M.Ing. (Electrical and Electronic Engineering) , Many applications need a high power (> 500W) at a relatively low voltage. The known technology of this class of converters is primitive and such converters are big as a result thereof. An investigation is made into the suitability of matrix transformer technology in the supply of large currents at low voltages. A layout for this topology which make optimal use of its characteristics is proposed . This includes modularity, possible application in distributed power supplies and equal current sharing. A system is designed and models are created to optimize the design. The models are extended to accommodate the effects of unavoidable parasitics which was observed in the practical system. A system consisting of sixteen modular units with a total output current capability of 320A at a voltage of between 0 and 5V is developed. The output capability and thus the number of modules needed is dependent on the application. Provision is thus made for a large power range. Power is transformed at a frequency of 100kHz to keep the physical dimensions of the system small.
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A cascaded NPC/H-bridge inverter with simplifiied control strategy and minimum component count
- Wanjekeche, T., Nicolae, Dan-Valentin, Jimoh, A. A.
- Authors: Wanjekeche, T. , Nicolae, Dan-Valentin , Jimoh, A. A.
- Date: 2009
- Subjects: Electric inverters , Harmonics (Electric waves) , Power electronics
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/22319 , uj:16188 , ISBN: 978-1-4244-3919-5 , Citation: Wanjekeche, T., Nicolae, D.V. & Jimoh, A.A. 2009. A cascaded NPC/H-bridge inverter with simplifiied control strategy and minimum component count. Proceedings of IEEE-Africon, 23-25 September, 2009, Kenya. DOI: 10.1109/AFRCON.2009.5308551
- Description: Abstract: Please refer to full text to view abstract Please refer to full text to view abstract
- Full Text:
- Authors: Wanjekeche, T. , Nicolae, Dan-Valentin , Jimoh, A. A.
- Date: 2009
- Subjects: Electric inverters , Harmonics (Electric waves) , Power electronics
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/22319 , uj:16188 , ISBN: 978-1-4244-3919-5 , Citation: Wanjekeche, T., Nicolae, D.V. & Jimoh, A.A. 2009. A cascaded NPC/H-bridge inverter with simplifiied control strategy and minimum component count. Proceedings of IEEE-Africon, 23-25 September, 2009, Kenya. DOI: 10.1109/AFRCON.2009.5308551
- Description: Abstract: Please refer to full text to view abstract Please refer to full text to view abstract
- Full Text:
Accurate modelling and experimental measurement of losses in planar inductors
- Authors: Imre, Tarik Gurhan
- Date: 2012-01-24
- Subjects: Electric inductors , Electric transformers , Electric circuits , Power electronics
- Type: Thesis
- Identifier: uj:1928 , http://hdl.handle.net/10210/4289
- Description: M.Ing. , Low profile power electronics components are currently in great demand. The rapid advances in semiconductor and micro-electronics technology during the last ten years have played a major role in the creation of this demand. These advances are in turn driven by the need for compact design in computing, communication, consumer electronic goods and control systems with direct consequences in power supply design and manufacture. The study covered by this thesis involves the design, manufacture and thermal analysis of a planar inductor, which is a typical planar power electronics component. First, a throughout literature survey of planar magnetics revealed that satisfactory experimental procedures for the thermal analysis of passive power electronic components under operating conditions representative of modern applications are seldomly applied. Secondly, a computer based field-solver program and analytical methods are used to design and analyse a planar inductor. The applicability of different methods for determination of low power loss in passive components is discussed next. Finally, an experimental method suitable for low power loss determination is proposed and investigated. This method can be used in the analysis of inductors or capacitors of different sizes. It has a wide spectrum of application due to the advantages of frequency independence and different possible power levels.
- Full Text:
- Authors: Imre, Tarik Gurhan
- Date: 2012-01-24
- Subjects: Electric inductors , Electric transformers , Electric circuits , Power electronics
- Type: Thesis
- Identifier: uj:1928 , http://hdl.handle.net/10210/4289
- Description: M.Ing. , Low profile power electronics components are currently in great demand. The rapid advances in semiconductor and micro-electronics technology during the last ten years have played a major role in the creation of this demand. These advances are in turn driven by the need for compact design in computing, communication, consumer electronic goods and control systems with direct consequences in power supply design and manufacture. The study covered by this thesis involves the design, manufacture and thermal analysis of a planar inductor, which is a typical planar power electronics component. First, a throughout literature survey of planar magnetics revealed that satisfactory experimental procedures for the thermal analysis of passive power electronic components under operating conditions representative of modern applications are seldomly applied. Secondly, a computer based field-solver program and analytical methods are used to design and analyse a planar inductor. The applicability of different methods for determination of low power loss in passive components is discussed next. Finally, an experimental method suitable for low power loss determination is proposed and investigated. This method can be used in the analysis of inductors or capacitors of different sizes. It has a wide spectrum of application due to the advantages of frequency independence and different possible power levels.
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Advances in integrated injection logic technology, a bipolar low power logic family
- Authors: Crooke, Michael
- Date: 2015-03-02
- Subjects: Power electronics
- Type: Thesis
- Identifier: uj:13380 , http://hdl.handle.net/10210/13391
- Description: M.Sc. , Please refer to full text to view abstract
- Full Text:
- Authors: Crooke, Michael
- Date: 2015-03-02
- Subjects: Power electronics
- Type: Thesis
- Identifier: uj:13380 , http://hdl.handle.net/10210/13391
- Description: M.Sc. , Please refer to full text to view abstract
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An investigation of primary tap changing transformers in high frequency isolated converters
- Authors: Joannou, Andrew John Lucas
- Date: 2012-08-01
- Subjects: Electric current converters , Power electronics , Voltage regulators
- Type: Thesis
- Identifier: uj:8891 , http://hdl.handle.net/10210/5363
- Description: M.Ing. , In this thesis, a new isolated DC-DC converter topology is designed which implements a high frequency primary tap changing transformer. This converter is designed to be implemented into renewable energy applications. Renewable or alternative energy resources are becoming more popular by necessity. The voltage generated by renewable energy resources is dependent on the weather conditions, thus the voltage may vary. This novel topology can maintain a regulated DC output voltage for a wide input voltage range by implementing a high frequency primary tap changing transformer. This converter is thus designed to accommodate the voltage changing conditions of renewable energy resources. This converter only requires output bus capacitance for DC bus stiffening. The overall required bus capacitance is therefore effectively reduced compared to other converter topologies. This isolated topology also improves the fundamental power quality. Other power quality components of this new converter are also analysed.
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- Authors: Joannou, Andrew John Lucas
- Date: 2012-08-01
- Subjects: Electric current converters , Power electronics , Voltage regulators
- Type: Thesis
- Identifier: uj:8891 , http://hdl.handle.net/10210/5363
- Description: M.Ing. , In this thesis, a new isolated DC-DC converter topology is designed which implements a high frequency primary tap changing transformer. This converter is designed to be implemented into renewable energy applications. Renewable or alternative energy resources are becoming more popular by necessity. The voltage generated by renewable energy resources is dependent on the weather conditions, thus the voltage may vary. This novel topology can maintain a regulated DC output voltage for a wide input voltage range by implementing a high frequency primary tap changing transformer. This converter is thus designed to accommodate the voltage changing conditions of renewable energy resources. This converter only requires output bus capacitance for DC bus stiffening. The overall required bus capacitance is therefore effectively reduced compared to other converter topologies. This isolated topology also improves the fundamental power quality. Other power quality components of this new converter are also analysed.
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An investigation on optimal current mode control for boost-type PWM rectifiers
- Richards, C. G., Ehlers, P. J., Nicolae, Dan-Valentin
- Authors: Richards, C. G. , Ehlers, P. J. , Nicolae, Dan-Valentin
- Date: 2009
- Subjects: Harmonics , Power electronics , Reactive power (Electrical enginnering)
- Language: English
- Type: Abstract: Static power converters produce harmonics due to the nature of the conversion process. This paper will investigate the effect on the power factor of a sinusoidal and Fryze current reference on a PWM boost type rectifier. It has been shown in previous papers that a Fryze current ref is best. This paper will develop a mathematical model, based on the single sided Fourier expansion. Using this mathematical model it will be shown that even though a high harmonic content could be present in a Fryze controlled PWM boost type rectifier, the power factor has been optimally improved.
- Identifier: http://hdl.handle.net/10210/21241 , uj:16131 , ISBN: 978-1-4244-2235-7 , Citation: Richards, C.G., Ehlers, P.J. & Nicolae, D.V. 2009. An investigation on optimal current mode control for boost-type PWM rectifiers. Proceedings of the IEEE PowerTech Conference, 26 June-02 July 2009, Bucharest, Rumania. DOI: 10.1109/PTC.2009.5282229
- Full Text:
- Authors: Richards, C. G. , Ehlers, P. J. , Nicolae, Dan-Valentin
- Date: 2009
- Subjects: Harmonics , Power electronics , Reactive power (Electrical enginnering)
- Language: English
- Type: Abstract: Static power converters produce harmonics due to the nature of the conversion process. This paper will investigate the effect on the power factor of a sinusoidal and Fryze current reference on a PWM boost type rectifier. It has been shown in previous papers that a Fryze current ref is best. This paper will develop a mathematical model, based on the single sided Fourier expansion. Using this mathematical model it will be shown that even though a high harmonic content could be present in a Fryze controlled PWM boost type rectifier, the power factor has been optimally improved.
- Identifier: http://hdl.handle.net/10210/21241 , uj:16131 , ISBN: 978-1-4244-2235-7 , Citation: Richards, C.G., Ehlers, P.J. & Nicolae, D.V. 2009. An investigation on optimal current mode control for boost-type PWM rectifiers. Proceedings of the IEEE PowerTech Conference, 26 June-02 July 2009, Bucharest, Rumania. DOI: 10.1109/PTC.2009.5282229
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Automating consumer's connections to the distribution network for enhanced performance
- Popoola, O. M., Jimoh, A. A., Nicolae, Dan-Valentin
- Authors: Popoola, O. M. , Jimoh, A. A. , Nicolae, Dan-Valentin
- Date: 2010
- Subjects: Power electronics , Electric circuit breakers , Voltage detectors
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/18674 , uj:16029 , ISSN:1827-6660 , Citation: Popoola, O.M., Jimoh, A. & Nicolae, D.V. 2010. Automating consumer's connections to the distribution network for enhanced performance. International Review of Electrical Engineering, 5(5), October 2010.
- Description: Abstract:Trial and error approach which involves service interruption is usually carried out to resolve unbalance on phases in power distribution system. This approach might improve the phase voltage and current but the resultant effect (change) does not last for too long; thereby reduces the market value in terms of quality and reliability of supply. To enhance the performance of the secondary distribution system there is a need for an automating technology. The aim of this paper is to introduce a method and technology developed for resolving imbalances in a secondary distribution system as a result of the uneven distribution of single phase load across a three phase power system. The technology developed is able to monitor, acquire/display collected data and perform self changing switching actions electronically. This action is in form of rearrangement or transfer of consumer loads for optimal performance of the distribution feeder. The proposed switching technology is based on open- transition switch that enables transfer or rearrangement of consumer loads in a three-phase system within milliseconds with supervisory control system. The following methodologies: System Simulator - Matlab (Simulink), Virtual Instrumentation-Lab VIEW and Hardware implementation were applied for the validation of the proposed technique
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- Authors: Popoola, O. M. , Jimoh, A. A. , Nicolae, Dan-Valentin
- Date: 2010
- Subjects: Power electronics , Electric circuit breakers , Voltage detectors
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/18674 , uj:16029 , ISSN:1827-6660 , Citation: Popoola, O.M., Jimoh, A. & Nicolae, D.V. 2010. Automating consumer's connections to the distribution network for enhanced performance. International Review of Electrical Engineering, 5(5), October 2010.
- Description: Abstract:Trial and error approach which involves service interruption is usually carried out to resolve unbalance on phases in power distribution system. This approach might improve the phase voltage and current but the resultant effect (change) does not last for too long; thereby reduces the market value in terms of quality and reliability of supply. To enhance the performance of the secondary distribution system there is a need for an automating technology. The aim of this paper is to introduce a method and technology developed for resolving imbalances in a secondary distribution system as a result of the uneven distribution of single phase load across a three phase power system. The technology developed is able to monitor, acquire/display collected data and perform self changing switching actions electronically. This action is in form of rearrangement or transfer of consumer loads for optimal performance of the distribution feeder. The proposed switching technology is based on open- transition switch that enables transfer or rearrangement of consumer loads in a three-phase system within milliseconds with supervisory control system. The following methodologies: System Simulator - Matlab (Simulink), Virtual Instrumentation-Lab VIEW and Hardware implementation were applied for the validation of the proposed technique
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Computer aided electromagnetic design of power electronic networks
- Authors: Cronje, Willem Abraham
- Date: 2014-02-11
- Subjects: Computer-aided design , Power electronics
- Type: Thesis
- Identifier: uj:3889 , http://hdl.handle.net/10210/9255
- Description: D.Ing. (Electrical and Electronics Engineering) , This thesis treats aspects of the modelling techniques required for Computer Aided Design (CAD) of electromagnetically integrated structures for use in power electronic networks. The concept of structural impedance is introduced and developed, building on transmission line theory. Computer based methods for calculating the distributed parameters of a given structure are investigated. These methods are the Finite Element Method and the Incremental Method. Based on the structural impedance lumped element equivalent circuit models for interconnections are developed for modelling of the distributed energy storage effects associated with a physical circuit as part of a lumped element network that can be submitted to circuit simulation programs like SPICE. The models are used in SPICE circuit simulations of power circuits and the simulated results are verified experimentally. Circuit level simulation models for switches are investigated in order to determine the complexity and detail of models suitable for CAD of complete converter topologies. A classification scheme for circuit models of switches is developed as an aid in selection of suitable models for particular simulation purposes. A DC circuit model for power BJT's is developed as a theoretical exercise to determine the requirements, with regard to development time and computational resources, for application of a particular switch model. It is based on new ideas in an attempt to model the effects of power BJT operation of interest to power electronic circuit designers while decreasing the calculation requirements in comparison with sophisticated device physics based models normally used or over simplified models. Finally suggestions are made with regard to a new way of approaching the optimization of power conditioning circuits by using power flow as the basis. This includes the novel use of specially manufactured high permittivity dielectric materials to adjust the characteristic impedance of connections to obtain optimal operation under particular operating conditions.
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- Authors: Cronje, Willem Abraham
- Date: 2014-02-11
- Subjects: Computer-aided design , Power electronics
- Type: Thesis
- Identifier: uj:3889 , http://hdl.handle.net/10210/9255
- Description: D.Ing. (Electrical and Electronics Engineering) , This thesis treats aspects of the modelling techniques required for Computer Aided Design (CAD) of electromagnetically integrated structures for use in power electronic networks. The concept of structural impedance is introduced and developed, building on transmission line theory. Computer based methods for calculating the distributed parameters of a given structure are investigated. These methods are the Finite Element Method and the Incremental Method. Based on the structural impedance lumped element equivalent circuit models for interconnections are developed for modelling of the distributed energy storage effects associated with a physical circuit as part of a lumped element network that can be submitted to circuit simulation programs like SPICE. The models are used in SPICE circuit simulations of power circuits and the simulated results are verified experimentally. Circuit level simulation models for switches are investigated in order to determine the complexity and detail of models suitable for CAD of complete converter topologies. A classification scheme for circuit models of switches is developed as an aid in selection of suitable models for particular simulation purposes. A DC circuit model for power BJT's is developed as a theoretical exercise to determine the requirements, with regard to development time and computational resources, for application of a particular switch model. It is based on new ideas in an attempt to model the effects of power BJT operation of interest to power electronic circuit designers while decreasing the calculation requirements in comparison with sophisticated device physics based models normally used or over simplified models. Finally suggestions are made with regard to a new way of approaching the optimization of power conditioning circuits by using power flow as the basis. This includes the novel use of specially manufactured high permittivity dielectric materials to adjust the characteristic impedance of connections to obtain optimal operation under particular operating conditions.
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Control strategy for a grid-connected inverter under unbalanced network conditions—a disturbance observer-based decoupled current approach
- Ozsoy, Emre, Padmanaban, Sanjeevikumar, Mihet-Popa, Lucian, Fedák, Viliam, Ahmad, Fiaz, Akhtar, Rasool, Sabanovic, Asif
- Authors: Ozsoy, Emre , Padmanaban, Sanjeevikumar , Mihet-Popa, Lucian , Fedák, Viliam , Ahmad, Fiaz , Akhtar, Rasool , Sabanovic, Asif
- Date: 2017
- Subjects: Power control , Power electronics , Pulse width modulation inverters
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/239290 , uj:24581 , Citation: Ozsoy, E. et al. 2017. Control strategy for a grid-connected inverter under unbalanced network conditions—a disturbance observer-based decoupled current approach. Energies 2017, 10, 1067; doi:10.3390/en10071067
- Description: Abstract: This paper proposes a new approach on the novel current control strategy for grid-tied voltage-source inverters (VSIs) with circumstances of asymmetrical voltage conditions. A standard grid-connected inverter (GCI) allows the degree of freedom to integrate the renewable energy system to enhance the penetration of total utility power. However, restrictive grid codes require that renewable sources connected to the grid must support stability of the grid under grid faults. Conventional synchronously rotating frame dq current controllers are insufficient under grid faults due to the low bandwidth of proportional-integral (PI) controllers. Hence, this work proposes a proportional current controller with a first-order low-pass filter disturbance observer (DOb). The proposed controller establishes independent control on positive, as well as negative, sequence current components under asymmetrical grid voltage conditions. The approach is independent of parametric component values, as it estimates nonlinear feed-forward terms with the low-pass filter DOb. A numerical simulation model of the overall power system was implemented in aMATLAB/Simulink (2014B, MathWorks, Natick, MA, USA). Further, particular results show that double-frequency active power oscillations are suppressed by injecting appropriate negative-sequence currents. Moreover, a set of simulation results provided in the article matches the developed theoretical background for its feasibility.
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- Authors: Ozsoy, Emre , Padmanaban, Sanjeevikumar , Mihet-Popa, Lucian , Fedák, Viliam , Ahmad, Fiaz , Akhtar, Rasool , Sabanovic, Asif
- Date: 2017
- Subjects: Power control , Power electronics , Pulse width modulation inverters
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/239290 , uj:24581 , Citation: Ozsoy, E. et al. 2017. Control strategy for a grid-connected inverter under unbalanced network conditions—a disturbance observer-based decoupled current approach. Energies 2017, 10, 1067; doi:10.3390/en10071067
- Description: Abstract: This paper proposes a new approach on the novel current control strategy for grid-tied voltage-source inverters (VSIs) with circumstances of asymmetrical voltage conditions. A standard grid-connected inverter (GCI) allows the degree of freedom to integrate the renewable energy system to enhance the penetration of total utility power. However, restrictive grid codes require that renewable sources connected to the grid must support stability of the grid under grid faults. Conventional synchronously rotating frame dq current controllers are insufficient under grid faults due to the low bandwidth of proportional-integral (PI) controllers. Hence, this work proposes a proportional current controller with a first-order low-pass filter disturbance observer (DOb). The proposed controller establishes independent control on positive, as well as negative, sequence current components under asymmetrical grid voltage conditions. The approach is independent of parametric component values, as it estimates nonlinear feed-forward terms with the low-pass filter DOb. A numerical simulation model of the overall power system was implemented in aMATLAB/Simulink (2014B, MathWorks, Natick, MA, USA). Further, particular results show that double-frequency active power oscillations are suppressed by injecting appropriate negative-sequence currents. Moreover, a set of simulation results provided in the article matches the developed theoretical background for its feasibility.
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DC Optimal Power Flow : a comparative study of a classical optimization method and metaheuristic solution algorithms
- Authors: Ajayi, Oluwafemi Peace
- Date: 2019
- Subjects: Power electronics , Electric power systems , Mathematical optimization
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/297299 , uj:32408
- Description: Abstract: Please refer to full text to view abstract. , M.Ing. (Electrical Engineering)
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- Authors: Ajayi, Oluwafemi Peace
- Date: 2019
- Subjects: Power electronics , Electric power systems , Mathematical optimization
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/297299 , uj:32408
- Description: Abstract: Please refer to full text to view abstract. , M.Ing. (Electrical Engineering)
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Determination and dynamic compensation of fictitious power in electric power systems
- Enslin, Johan Heinrich Richter
- Authors: Enslin, Johan Heinrich Richter
- Date: 2014-09-23
- Subjects: Power electronics , Electric power systems
- Type: Thesis
- Identifier: uj:12357 , http://hdl.handle.net/10210/12142
- Description: D.Ing. (Electrical & Electronic Engineering) , Please refer to full text to view abstract
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- Authors: Enslin, Johan Heinrich Richter
- Date: 2014-09-23
- Subjects: Power electronics , Electric power systems
- Type: Thesis
- Identifier: uj:12357 , http://hdl.handle.net/10210/12142
- Description: D.Ing. (Electrical & Electronic Engineering) , Please refer to full text to view abstract
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Determination of power components in nonlinear electrical networks
- Authors: De Beer, Arnold Stephanus
- Date: 1990
- Subjects: Power electronics , Electric networks, Nonlinear
- Language: English
- Type: Masters Thesis
- Identifier: http://hdl.handle.net/10210/22306 , uj:16186
- Description: Abstract: This thesis describes a study into the field of electrical power theory and specifically deals with the description and determination of power components in nonlinear electrical networks. A general description of fundamental power theory is given and the basic philosophy of fictitious power compensation ( according to Frryze ) is dealt with. The contributions of Budeanu, Nowomiejski, Enslin and others are described. The description of Czarnecki was found to be a good model for determining energy flow and power components in general power systems. It is shown how the Czarnecki power components can be calculated from practical noise infected data. A computer program was written for this purpose and is given in conjunction with two case studies. Relationships between power theories, power factor correction and general compensation are stated in principle. Certain power calculation errors as well as negative effects that can impair effective energy transfer and compenation are also discussed. , M.Ing. (Electrical and Electronic Engineering)
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- Authors: De Beer, Arnold Stephanus
- Date: 1990
- Subjects: Power electronics , Electric networks, Nonlinear
- Language: English
- Type: Masters Thesis
- Identifier: http://hdl.handle.net/10210/22306 , uj:16186
- Description: Abstract: This thesis describes a study into the field of electrical power theory and specifically deals with the description and determination of power components in nonlinear electrical networks. A general description of fundamental power theory is given and the basic philosophy of fictitious power compensation ( according to Frryze ) is dealt with. The contributions of Budeanu, Nowomiejski, Enslin and others are described. The description of Czarnecki was found to be a good model for determining energy flow and power components in general power systems. It is shown how the Czarnecki power components can be calculated from practical noise infected data. A computer program was written for this purpose and is given in conjunction with two case studies. Relationships between power theories, power factor correction and general compensation are stated in principle. Certain power calculation errors as well as negative effects that can impair effective energy transfer and compenation are also discussed. , M.Ing. (Electrical and Electronic Engineering)
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Die invloed van mutatorstruktuur op geleide elektromagnetiese steurings
- Authors: Sinclair, Andrew John
- Date: 2014-04-24
- Subjects: Power electronics , Electromagnetic interference
- Type: Thesis
- Identifier: http://ujcontent.uj.ac.za8080/10210/371979 , uj:10885 , http://hdl.handle.net/10210/10392
- Description: M.Ing. (Electrical and Electronic Engineering) , Recent world events such as the fall of Communism. attempts at the unification of Europe and the reaching of the most extensive international trade agreement yet (GATT ::: General Agreement on Trade and Tariffs). have all contributed to the expansion of world markets as well as a marked intensification in the competition in those markets. Rivalry in the market for power electronic equipment is as relentless as in any other. Strict regulations with regard to Electromagnetic Interference (EMf) and Electromagnetic Compatibility (EMC) apply in Europe and compliance with these standards is legally enforced. In South Africa, compliance with such standards is merely recommended, hence local manufacturers have not yet considered these phenomena seriously enough to pose a threat to their European opposition. The two main causes of EMI are switching action, which is such an integral part of power electronics, and the excitation of parasitic circuit elements. This thesis describes the investigation carried out to determine the effect of certain layout and construction parameters on the generation of EMf. Parasitic loop inductances, self-capacitances of coils and the ground connection of heat sinks were examined in the process. A test convener containing a full-bridge converter perfonning DC·DC conversion, was built. These converters are important building blocks for equipment such as uninterruptible power supplies. One configuration of this converter was designated as the reference configuration. For every modification of a layout or construction parameter its effect on the interference spectrum was determined through a comparison with the measured interference spectrum of the reference configuration. The use of snubbers and the minimisation of the self-capacitances of inductors in an output filter effected a marked decrease in the measured interference spectrum (approximately 10 dB or a third less). Certain loop inductances have to be minimised in the design stages through proper layout of conveners, and heat sinks should preferably be grounded through high resistances. Paying due attention to these aspects in the design of power electronic converters can aid in decreasing the size and cost of bulky, expensive EMf filters required to meet the standards. It could give local manufacturers a considerable advantage over their overseas competitors.
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- Authors: Sinclair, Andrew John
- Date: 2014-04-24
- Subjects: Power electronics , Electromagnetic interference
- Type: Thesis
- Identifier: http://ujcontent.uj.ac.za8080/10210/371979 , uj:10885 , http://hdl.handle.net/10210/10392
- Description: M.Ing. (Electrical and Electronic Engineering) , Recent world events such as the fall of Communism. attempts at the unification of Europe and the reaching of the most extensive international trade agreement yet (GATT ::: General Agreement on Trade and Tariffs). have all contributed to the expansion of world markets as well as a marked intensification in the competition in those markets. Rivalry in the market for power electronic equipment is as relentless as in any other. Strict regulations with regard to Electromagnetic Interference (EMf) and Electromagnetic Compatibility (EMC) apply in Europe and compliance with these standards is legally enforced. In South Africa, compliance with such standards is merely recommended, hence local manufacturers have not yet considered these phenomena seriously enough to pose a threat to their European opposition. The two main causes of EMI are switching action, which is such an integral part of power electronics, and the excitation of parasitic circuit elements. This thesis describes the investigation carried out to determine the effect of certain layout and construction parameters on the generation of EMf. Parasitic loop inductances, self-capacitances of coils and the ground connection of heat sinks were examined in the process. A test convener containing a full-bridge converter perfonning DC·DC conversion, was built. These converters are important building blocks for equipment such as uninterruptible power supplies. One configuration of this converter was designated as the reference configuration. For every modification of a layout or construction parameter its effect on the interference spectrum was determined through a comparison with the measured interference spectrum of the reference configuration. The use of snubbers and the minimisation of the self-capacitances of inductors in an output filter effected a marked decrease in the measured interference spectrum (approximately 10 dB or a third less). Certain loop inductances have to be minimised in the design stages through proper layout of conveners, and heat sinks should preferably be grounded through high resistances. Paying due attention to these aspects in the design of power electronic converters can aid in decreasing the size and cost of bulky, expensive EMf filters required to meet the standards. It could give local manufacturers a considerable advantage over their overseas competitors.
- Full Text: