A cascaded hybrid inverter with improved dc-link voltage control for grid connected systems
- Wanjekeche, T., Jimoh, A. A., Nicolae, Dan-Valentin
- Authors: Wanjekeche, T. , Jimoh, A. A. , Nicolae, Dan-Valentin
- Date: 2012
- Subjects: Voltage-frequency converters , Converters , Electronic circuits
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/17312 , uj:15870 , ISBN: 9781467301589 , Ciatation: Wanjekeche, T.,Jimoh, A.A. & Nicolae, D.V. 2012. A cascaded hybrid inventer with improved dc-link voltage control for grid connected systems IEEE – ISIE 2012, 28–31 May, Hangzhou, China:1950-1956. DOI:10:1109/ISIE.2012.6237391
- Description: Abstract: This paper presents investigation of a new Phase shifted PWM technique with improved harmonic suppression. A novel balance circuit for DC – link voltage balance of two three level legs connected back – to back is designed and tested. Combined with the individual voltage control, a complete voltage controller is developed for a cascaded nine level hybrid model with two cells. Robustness of the proposed algorithm under varying operating conditions and modulation indices is verified by simulation.
- Full Text:
- Authors: Wanjekeche, T. , Jimoh, A. A. , Nicolae, Dan-Valentin
- Date: 2012
- Subjects: Voltage-frequency converters , Converters , Electronic circuits
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/17312 , uj:15870 , ISBN: 9781467301589 , Ciatation: Wanjekeche, T.,Jimoh, A.A. & Nicolae, D.V. 2012. A cascaded hybrid inventer with improved dc-link voltage control for grid connected systems IEEE – ISIE 2012, 28–31 May, Hangzhou, China:1950-1956. DOI:10:1109/ISIE.2012.6237391
- Description: Abstract: This paper presents investigation of a new Phase shifted PWM technique with improved harmonic suppression. A novel balance circuit for DC – link voltage balance of two three level legs connected back – to back is designed and tested. Combined with the individual voltage control, a complete voltage controller is developed for a cascaded nine level hybrid model with two cells. Robustness of the proposed algorithm under varying operating conditions and modulation indices is verified by simulation.
- Full Text:
A critique on previous work in vision aided navigation
- Murcott, Charles, Du Plessis, Francois, Meyer, Johan
- Authors: Murcott, Charles , Du Plessis, Francois , Meyer, Johan
- Date: 2011-09
- Subjects: Robotic applications , Global Positioning System (GPS) , Vision aided navigation
- Type: Article
- Identifier: uj:6259 , ISBN 978-1-61284-993-5 , http://hdl.handle.net/10210/8240
- Description: This paper presents a critique on previous work in the field of vision aided navigation, particularly in the fusion of visual and inertial sensors for navigation. Several improvements and updates are proposed for the existent systems. GPS receivers have allowed for accurate navigation for many vehicles and robotic platforms. GPS based navigation can, however, prove to be impractical in applications where there is no GPS reception such as underground, indoors or in some urban areas. This pertains, in particular, to many robotic applications where position must be known in global coordinates or relative to a reference point. An inertial navigation system (INS) can be used to calculate one’s relative navigation state via dead-reckoning calculations. The downfall of a low-cost INS is the errors associated with the system. While these errors are initially small, integration causes large drift errors over time. To combat this problem, cameras can be used to estimate the errors present in the INS readings. These results can then be used to correct the navigation state output from the INS. While the motion estimations from the cameras are not error-free, this method is made highly effective because of the complementary nature of the errors from the cameras and INS. Several improvements are proposed for this method; algorithmically, in updates to its hardware, and with the introduction of graphics processors to improve computational performance. The overall system performance, individual steps, algorithms, and results are compared to results from similar works to those of the proposed improvements. It is shown that the accuracy, responsiveness and overall performance of the system can potentially be greatly improved.
- Full Text:
- Authors: Murcott, Charles , Du Plessis, Francois , Meyer, Johan
- Date: 2011-09
- Subjects: Robotic applications , Global Positioning System (GPS) , Vision aided navigation
- Type: Article
- Identifier: uj:6259 , ISBN 978-1-61284-993-5 , http://hdl.handle.net/10210/8240
- Description: This paper presents a critique on previous work in the field of vision aided navigation, particularly in the fusion of visual and inertial sensors for navigation. Several improvements and updates are proposed for the existent systems. GPS receivers have allowed for accurate navigation for many vehicles and robotic platforms. GPS based navigation can, however, prove to be impractical in applications where there is no GPS reception such as underground, indoors or in some urban areas. This pertains, in particular, to many robotic applications where position must be known in global coordinates or relative to a reference point. An inertial navigation system (INS) can be used to calculate one’s relative navigation state via dead-reckoning calculations. The downfall of a low-cost INS is the errors associated with the system. While these errors are initially small, integration causes large drift errors over time. To combat this problem, cameras can be used to estimate the errors present in the INS readings. These results can then be used to correct the navigation state output from the INS. While the motion estimations from the cameras are not error-free, this method is made highly effective because of the complementary nature of the errors from the cameras and INS. Several improvements are proposed for this method; algorithmically, in updates to its hardware, and with the introduction of graphics processors to improve computational performance. The overall system performance, individual steps, algorithms, and results are compared to results from similar works to those of the proposed improvements. It is shown that the accuracy, responsiveness and overall performance of the system can potentially be greatly improved.
- Full Text:
A group genetic algorithm for the fleet size and mix vehicle routing problem
- Mutingi, M., Mbohwa, Charles
- Authors: Mutingi, M. , Mbohwa, Charles
- Date: 2012
- Subjects: Logistics , Vehicle routing , Genetic algorithms , Vehicle fleets - Management
- Type: Article
- Identifier: uj:5181 , http://hdl.handle.net/10210/14423
- Description: In logistics management, the use of vehicles to distribute products from suppliers to customers is a major operational activity. Optimizing the routing of vehicles is crucial for providing cost-effective services to customers. This research addresses the fleet size and mix vehicle routing problem (FSMVRP), where the heterogeneous fleet and its size are to be determined. A group genetic algorithm (GGA) approach, with unique genetic operators, is designed and implemented on a number of existing benchmark problems. GGA demonstrates competitive performance in terms of cost and computation time when compared to other heuristics.
- Full Text:
- Authors: Mutingi, M. , Mbohwa, Charles
- Date: 2012
- Subjects: Logistics , Vehicle routing , Genetic algorithms , Vehicle fleets - Management
- Type: Article
- Identifier: uj:5181 , http://hdl.handle.net/10210/14423
- Description: In logistics management, the use of vehicles to distribute products from suppliers to customers is a major operational activity. Optimizing the routing of vehicles is crucial for providing cost-effective services to customers. This research addresses the fleet size and mix vehicle routing problem (FSMVRP), where the heterogeneous fleet and its size are to be determined. A group genetic algorithm (GGA) approach, with unique genetic operators, is designed and implemented on a number of existing benchmark problems. GGA demonstrates competitive performance in terms of cost and computation time when compared to other heuristics.
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A multilevel construction for mappings from binary sequences to permutation sequences
- Swart, Theo G., Ferreira, Hendrik C.
- Authors: Swart, Theo G. , Ferreira, Hendrik C.
- Date: 2006
- Subjects: Mappings , Binary sequences , Permutation sequences
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/18365 , uj:15991 , Citation: Swart, T.G. & Ferreira, H.C. 2006. A multilevel construction for mappings from binary sequences to permutation sequences. Proceedings of the IEEE International Symposium on Information Theory, 9-14 July, 2006, Seattle, USA.
- Description: Abstract: A multilevel construction is introduced to create distance-preserving mappings from binary sequences to permutation sequences. It is also shown that for certain values, the new mappings attain the upper bound on the sum of Hamming distances obtainable for such mappings, and in the other cases improve on those of previous mappings.
- Full Text:
- Authors: Swart, Theo G. , Ferreira, Hendrik C.
- Date: 2006
- Subjects: Mappings , Binary sequences , Permutation sequences
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/18365 , uj:15991 , Citation: Swart, T.G. & Ferreira, H.C. 2006. A multilevel construction for mappings from binary sequences to permutation sequences. Proceedings of the IEEE International Symposium on Information Theory, 9-14 July, 2006, Seattle, USA.
- Description: Abstract: A multilevel construction is introduced to create distance-preserving mappings from binary sequences to permutation sequences. It is also shown that for certain values, the new mappings attain the upper bound on the sum of Hamming distances obtainable for such mappings, and in the other cases improve on those of previous mappings.
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A new golden ratio local search based particle swarm optimization
- Sun, Yanxia, Van Wyk, Barend Jacobus, Wang, Zenghui
- Authors: Sun, Yanxia , Van Wyk, Barend Jacobus , Wang, Zenghui
- Date: 2012
- Subjects: Particle swarm optimization , Golden ratio , Local search
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/21329 , uj:16141 , Citation: Sun, Y., Van Wyk, B.J. & Wang, Z. 2012. A new golden ratio local search based particle swarm optimization. 2012 International Conference on Systems and Informatics (ICSAI 2012), Yantai, China 19-20 May, 2012. p. 754-757. ISBN: 978-1-4673-0198-5
- Description: Abstract: At beginning of the search process of particle swarm optimization, one of the disadvantages is that PSO focuses on the global search while the local search is weaken. However, at the end of the search procedure, the PSO focuses on the local search as all most all the particles converge to small areas which may make the particle swarm trapped in the local minima if no particle find position near the minima at the beginning of search procedure. To improve the optimization performance, the local search is necessary for particle swarm optimization. In this paper, golden ratio is used to determine the size of the search area. Only two positions need to be checked to find whether there are local positions with lower fitness value around a certain particle position. This method is easy to use. It is also tested using several famous benchmarks with high dimensions and big search space to the efficiency of the proposed method.
- Full Text:
- Authors: Sun, Yanxia , Van Wyk, Barend Jacobus , Wang, Zenghui
- Date: 2012
- Subjects: Particle swarm optimization , Golden ratio , Local search
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/21329 , uj:16141 , Citation: Sun, Y., Van Wyk, B.J. & Wang, Z. 2012. A new golden ratio local search based particle swarm optimization. 2012 International Conference on Systems and Informatics (ICSAI 2012), Yantai, China 19-20 May, 2012. p. 754-757. ISBN: 978-1-4673-0198-5
- Description: Abstract: At beginning of the search process of particle swarm optimization, one of the disadvantages is that PSO focuses on the global search while the local search is weaken. However, at the end of the search procedure, the PSO focuses on the local search as all most all the particles converge to small areas which may make the particle swarm trapped in the local minima if no particle find position near the minima at the beginning of search procedure. To improve the optimization performance, the local search is necessary for particle swarm optimization. In this paper, golden ratio is used to determine the size of the search area. Only two positions need to be checked to find whether there are local positions with lower fitness value around a certain particle position. This method is easy to use. It is also tested using several famous benchmarks with high dimensions and big search space to the efficiency of the proposed method.
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A note on non-binary multiple insertion/deletion correcting codes
- Paluncic, Filip, Swart, Theo G., Weber, Jos H., Ferreira, Hendrik C., Clarke, Willem A.
- Authors: Paluncic, Filip , Swart, Theo G. , Weber, Jos H. , Ferreira, Hendrik C. , Clarke, Willem A.
- Date: 2011
- Subjects: Insertion/deletion , Correcting codes
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/20202 , uj:16077 , ISBN: 978-1-4577-0437-6 , Citation: Paluncic, F. et al. 2011. A note on non-binary multiple insertion/deletion correcting codes. Proceedings of the IEEE Information Theory Workshop, 16-20 October, 2011, Paraty, Brazil.
- Description: Abstract: We propose the construction of a non-binary multiple insertion/deletion correcting code based on a binary multiple insertion/deletion correcting code. In essence, it is a generalisation of Tenengol’ts’ non-binary single insertion/deletion correcting code. We evaluate the cardinality of the proposed construction based on the asymptotic upper bound on the cardinality of a maximal binary multiple insertion/deletion correcting code derived by Levenshtein.
- Full Text:
- Authors: Paluncic, Filip , Swart, Theo G. , Weber, Jos H. , Ferreira, Hendrik C. , Clarke, Willem A.
- Date: 2011
- Subjects: Insertion/deletion , Correcting codes
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/20202 , uj:16077 , ISBN: 978-1-4577-0437-6 , Citation: Paluncic, F. et al. 2011. A note on non-binary multiple insertion/deletion correcting codes. Proceedings of the IEEE Information Theory Workshop, 16-20 October, 2011, Paraty, Brazil.
- Description: Abstract: We propose the construction of a non-binary multiple insertion/deletion correcting code based on a binary multiple insertion/deletion correcting code. In essence, it is a generalisation of Tenengol’ts’ non-binary single insertion/deletion correcting code. We evaluate the cardinality of the proposed construction based on the asymptotic upper bound on the cardinality of a maximal binary multiple insertion/deletion correcting code derived by Levenshtein.
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A preliminary investigation of the UHF properties of LV cable for WiFi over power line communications
- Jordaan, Sean, Janse van Rensburg, Petrus A., De Beer, Arnold S., Ferreira, Hendrik C., Han Vinck, A. J.
- Authors: Jordaan, Sean , Janse van Rensburg, Petrus A. , De Beer, Arnold S. , Ferreira, Hendrik C. , Han Vinck, A. J.
- Date: 2015-03-29
- Subjects: Power line communications , Wireless protocol , Wireless communication systems
- Type: Article
- Identifier: uj:5244 , http://hdl.handle.net/10210/14844
- Description: In pursuit of a wireless (contactless) power line communications (W-PLC) system for low voltage (LV) power distribution networks, a commonly utilized bundled low voltage electrical cable called Cabtyre, was energized with a range of frequencies up to 3 GHz. The intention was to characterize the cable from a radio frequency radiation perspective for the utilization of standard low voltage distribution cables as antennas in ultra high frequency (UHF) PLC systems. The range of test frequencies extends 550 MHz beyond the present IEEE 802.11g protocol which has a centre frequency of 2.45 GHz and a 80 MHz total bandwidth. The applied tests therefore allow adequately for the maximum bandwidth required with 40 MHz modulation on either side of the 2.45 GHz centre frequency.
- Full Text:
- Authors: Jordaan, Sean , Janse van Rensburg, Petrus A. , De Beer, Arnold S. , Ferreira, Hendrik C. , Han Vinck, A. J.
- Date: 2015-03-29
- Subjects: Power line communications , Wireless protocol , Wireless communication systems
- Type: Article
- Identifier: uj:5244 , http://hdl.handle.net/10210/14844
- Description: In pursuit of a wireless (contactless) power line communications (W-PLC) system for low voltage (LV) power distribution networks, a commonly utilized bundled low voltage electrical cable called Cabtyre, was energized with a range of frequencies up to 3 GHz. The intention was to characterize the cable from a radio frequency radiation perspective for the utilization of standard low voltage distribution cables as antennas in ultra high frequency (UHF) PLC systems. The range of test frequencies extends 550 MHz beyond the present IEEE 802.11g protocol which has a centre frequency of 2.45 GHz and a 80 MHz total bandwidth. The applied tests therefore allow adequately for the maximum bandwidth required with 40 MHz modulation on either side of the 2.45 GHz centre frequency.
- Full Text:
A statistical analysis of metal oxide varistor current under distorted supply voltage conditions
- Bokoro, Pitshou, Hove, Miidzo, Jandrell, Ian
- Authors: Bokoro, Pitshou , Hove, Miidzo , Jandrell, Ian
- Date: 2014
- Subjects: Metal oxide varistor , Third harmonic current , Large-sample statistical test of hypothesis
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/20201 , uj:16079 , Citation: Bokoro, P., Jandrell, I. & Hove, M. 2014. A statistical analysis of metal oxide varistor current under distorted supply voltage conditions. Proceedings of the 2014 IEEE Electrical Insulation Conference, Philadelphia, Pennsylvania, USA, 8 to 11 June 2014. p. 493-496. ISBN: 978-1-4799-2789-0
- Description: Abstract: Leakage current monitoring is still relied upon when on-site condition assessment or stability analysis of metal oxide varistors is to be conducted. The non-availability of adequate testing equipment, capable of directly measuring resistive component of varistor current, has paved the way to indirect diagnostic techniques which makes use of third harmonic component of varistor-arrester leakage current. The major shortcoming related to this method consists of high probability of measurement errors and subsequent misinterpretation of actual condition of varistor units should third harmonic-frequencies not be compensated in the supply voltage, prior to measurement. In this study, 90 identical low voltage varistor samples acquired from three leading manufacturers are subjected to distorted and non-distorted ac supply voltage. The magnitude of third harmonic currents observed in both measurement conditions, is deduced from the decomposition of time-domain leakage current waveforms into the frequency-domain using the flattop window algorithm of the Fast Fourier Transform. The large-sample statistical test of Hypothesis methodology is invoked to analyse the difference between the mean third harmonic currents of the varistor samples before and after harmonic injection in the supply. The average percentage of third harmonic injected in the supply voltage is 5%. However, the results obtained suggest over 95 % confidence that the measurement deviation in the third harmonic current-based assessment of varistor-arresters upon 5% third harmonic distortion in the supply voltage lies between 32%and 67%.
- Full Text:
- Authors: Bokoro, Pitshou , Hove, Miidzo , Jandrell, Ian
- Date: 2014
- Subjects: Metal oxide varistor , Third harmonic current , Large-sample statistical test of hypothesis
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/20201 , uj:16079 , Citation: Bokoro, P., Jandrell, I. & Hove, M. 2014. A statistical analysis of metal oxide varistor current under distorted supply voltage conditions. Proceedings of the 2014 IEEE Electrical Insulation Conference, Philadelphia, Pennsylvania, USA, 8 to 11 June 2014. p. 493-496. ISBN: 978-1-4799-2789-0
- Description: Abstract: Leakage current monitoring is still relied upon when on-site condition assessment or stability analysis of metal oxide varistors is to be conducted. The non-availability of adequate testing equipment, capable of directly measuring resistive component of varistor current, has paved the way to indirect diagnostic techniques which makes use of third harmonic component of varistor-arrester leakage current. The major shortcoming related to this method consists of high probability of measurement errors and subsequent misinterpretation of actual condition of varistor units should third harmonic-frequencies not be compensated in the supply voltage, prior to measurement. In this study, 90 identical low voltage varistor samples acquired from three leading manufacturers are subjected to distorted and non-distorted ac supply voltage. The magnitude of third harmonic currents observed in both measurement conditions, is deduced from the decomposition of time-domain leakage current waveforms into the frequency-domain using the flattop window algorithm of the Fast Fourier Transform. The large-sample statistical test of Hypothesis methodology is invoked to analyse the difference between the mean third harmonic currents of the varistor samples before and after harmonic injection in the supply. The average percentage of third harmonic injected in the supply voltage is 5%. However, the results obtained suggest over 95 % confidence that the measurement deviation in the third harmonic current-based assessment of varistor-arresters upon 5% third harmonic distortion in the supply voltage lies between 32%and 67%.
- Full Text:
A study of improving the power factor of a three-phase induction motor using a static switched capacitor
- Jimoh, Adisa A., Nicolae, Dan-Valentin
- Authors: Jimoh, Adisa A. , Nicolae, Dan-Valentin
- Date: 2006
- Subjects: Three-phase machines , Induction motors , Reactive compensation , Power factor correction
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/22367 , uj:16193 , ISSN: 1-4244-0121-6 , Citation: Jimoh, A.A. & Nicolae, D.V. 2006. A study of improving the power factor of a three-phase induction motor using a static switched capacitor. EPE-PEMC, 12th International Power Electronics and Motion Control, September, 2006, Portorož, Slovenia.
- Description: Abstract: In this paper a static switched capacitor with an auxiliary three-phase stator winding, which is only magnetically coupled to the stator main winding, is explored for improving the starting and operating power factor of a three-phase induction motor. The scheme improves the power factor of the motor without compromising significantly on other performances. Important advantages of the scheme include preventing harmonics in the line current, and eliminating regeneration possibility as well as preventing high inrush currents at starting.
- Full Text:
- Authors: Jimoh, Adisa A. , Nicolae, Dan-Valentin
- Date: 2006
- Subjects: Three-phase machines , Induction motors , Reactive compensation , Power factor correction
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/22367 , uj:16193 , ISSN: 1-4244-0121-6 , Citation: Jimoh, A.A. & Nicolae, D.V. 2006. A study of improving the power factor of a three-phase induction motor using a static switched capacitor. EPE-PEMC, 12th International Power Electronics and Motion Control, September, 2006, Portorož, Slovenia.
- Description: Abstract: In this paper a static switched capacitor with an auxiliary three-phase stator winding, which is only magnetically coupled to the stator main winding, is explored for improving the starting and operating power factor of a three-phase induction motor. The scheme improves the power factor of the motor without compromising significantly on other performances. Important advantages of the scheme include preventing harmonics in the line current, and eliminating regeneration possibility as well as preventing high inrush currents at starting.
- Full Text:
A study of insulation failure in a high voltage current transformer
- Jimoh, A. A., Mahlasela, V. S., Nicolae, Dan-Valentin
- Authors: Jimoh, A. A. , Mahlasela, V. S. , Nicolae, Dan-Valentin
- Date: 2005
- Subjects: Electric power transmission
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/22348 , uj:16190 , ISBN: 9075815085 , Citation: Jimoh, A.A., Mahlasela, V.S. & Nicolae, D.V. 2005. A study of insulation failure in a high voltage current transformer. EPE 2005 Conference, Dresden, Germany, 11-14 September 2005. DOI:10.1109/EPE.2005.219752
- Description: Abstract: The ageing and deterioration of insulation in high voltage (HV) plants have been a source of concerns to utilities. Breakdown of insulation leads to failures of HV equipment. The ageing and eventual failure of insulation in a high voltage curTent transformer (JHVCT) is the subject of investigation in this paper. A lumiiped parameter model ofHVCT is developed. This model is used to study the influlence of deteriorating and failed iinsulation on the state variables of the HVCT. Somie possible scenarios that could lead to a CT failure are investigated in this paper. For all the scelarios considered, steady alid transient equations relating the state variables of the mlodel have been developed and analyzed. The objectives of these analyses are to establish the behavioural claracteristics of the state variables, establish the interactions between these variables, and investigate the possible generations of harmonics under the various scenarios of deteriorating and outright failure of insulation in the CT. The paper concludes with a discussion of the results obtained
- Full Text:
- Authors: Jimoh, A. A. , Mahlasela, V. S. , Nicolae, Dan-Valentin
- Date: 2005
- Subjects: Electric power transmission
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/22348 , uj:16190 , ISBN: 9075815085 , Citation: Jimoh, A.A., Mahlasela, V.S. & Nicolae, D.V. 2005. A study of insulation failure in a high voltage current transformer. EPE 2005 Conference, Dresden, Germany, 11-14 September 2005. DOI:10.1109/EPE.2005.219752
- Description: Abstract: The ageing and deterioration of insulation in high voltage (HV) plants have been a source of concerns to utilities. Breakdown of insulation leads to failures of HV equipment. The ageing and eventual failure of insulation in a high voltage curTent transformer (JHVCT) is the subject of investigation in this paper. A lumiiped parameter model ofHVCT is developed. This model is used to study the influlence of deteriorating and failed iinsulation on the state variables of the HVCT. Somie possible scenarios that could lead to a CT failure are investigated in this paper. For all the scelarios considered, steady alid transient equations relating the state variables of the mlodel have been developed and analyzed. The objectives of these analyses are to establish the behavioural claracteristics of the state variables, establish the interactions between these variables, and investigate the possible generations of harmonics under the various scenarios of deteriorating and outright failure of insulation in the CT. The paper concludes with a discussion of the results obtained
- Full Text:
Active power control for capacitive divider tapping method
- Nicolae, Dan-Valentin, Jimoh, Adisa A., Britten, Anton C.
- Authors: Nicolae, Dan-Valentin , Jimoh, Adisa A. , Britten, Anton C.
- Date: 2006
- Subjects: Power systems , Captive divider systems , Tapping electric power
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/22404 , uj:16197 , ISSN: 1-4244-0121-6 , Citation: Nicolae, D.V., Jimoh, A.A. & Britten, A.C. 2006. Active power control for capacitive divider tapping method. EPE-PEMC, 12th International Power Electronics and Motion Control, 30 August-1 September, 2006, Portorož, Slovenia.
- Description: Abstract: Capacitive divider systems for tapping electric power from high voltage transmission lines are known to exhibit certain detrimental problems of stability, sub-resonance harmonic oscillations, and ferroresonance when coupled with non-linear loads. On the other hand, they can improve reactive power flow, power factor and contribute to improved harmonic filtration of the larger power system. This paper, therefore, proposes a controlled power flow conditioner as an essential integral component of a capacitive divider system to control power transfer between the high voltage transmission line, capacitive divider system, and the load. The ultimate objective of this conditioner is to mitigate or minimize the attendant problems associated with coupling the system to the load, and optimize the derivable benefits to the larger network.
- Full Text:
- Authors: Nicolae, Dan-Valentin , Jimoh, Adisa A. , Britten, Anton C.
- Date: 2006
- Subjects: Power systems , Captive divider systems , Tapping electric power
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/22404 , uj:16197 , ISSN: 1-4244-0121-6 , Citation: Nicolae, D.V., Jimoh, A.A. & Britten, A.C. 2006. Active power control for capacitive divider tapping method. EPE-PEMC, 12th International Power Electronics and Motion Control, 30 August-1 September, 2006, Portorož, Slovenia.
- Description: Abstract: Capacitive divider systems for tapping electric power from high voltage transmission lines are known to exhibit certain detrimental problems of stability, sub-resonance harmonic oscillations, and ferroresonance when coupled with non-linear loads. On the other hand, they can improve reactive power flow, power factor and contribute to improved harmonic filtration of the larger power system. This paper, therefore, proposes a controlled power flow conditioner as an essential integral component of a capacitive divider system to control power transfer between the high voltage transmission line, capacitive divider system, and the load. The ultimate objective of this conditioner is to mitigate or minimize the attendant problems associated with coupling the system to the load, and optimize the derivable benefits to the larger network.
- Full Text:
Alternating current source to voltage source converter
- Case, M. J., Van Rensburg, J. F. J., Nicolae, Dan-Valentin
- Authors: Case, M. J. , Van Rensburg, J. F. J. , Nicolae, Dan-Valentin
- Date: 2005
- Subjects: Voltage-frequency converters , Direct-current transmission
- Language: English
- Type: Conference proceedings
- Identifier: http://ujcontent.uj.ac.za8080/10210/388929 , http://hdl.handle.net/10210/21562 , uj:16150 , Citation: Nicolae, D.V., Van Rensburg, J.F.J. & Case, M.J. 2005. Alternating current source to voltage source converter. IPST’05 Conference, Montreal, Canada, June 2005, Paper# 05IPST081-22c
- Description: Abstract: A direct alternating current source to voltage source converter, which does not employ energy storage components, is presented. Conversion is done by a current steering mechanism in the form of a current transformer with two secondary windings. The direct conversion concept, basic circuit, simulation and experimental results of a reduced scale model are presented.
- Full Text:
- Authors: Case, M. J. , Van Rensburg, J. F. J. , Nicolae, Dan-Valentin
- Date: 2005
- Subjects: Voltage-frequency converters , Direct-current transmission
- Language: English
- Type: Conference proceedings
- Identifier: http://ujcontent.uj.ac.za8080/10210/388929 , http://hdl.handle.net/10210/21562 , uj:16150 , Citation: Nicolae, D.V., Van Rensburg, J.F.J. & Case, M.J. 2005. Alternating current source to voltage source converter. IPST’05 Conference, Montreal, Canada, June 2005, Paper# 05IPST081-22c
- Description: Abstract: A direct alternating current source to voltage source converter, which does not employ energy storage components, is presented. Conversion is done by a current steering mechanism in the form of a current transformer with two secondary windings. The direct conversion concept, basic circuit, simulation and experimental results of a reduced scale model are presented.
- Full Text:
An analysis into the impact of globalization on the clothing industry in conjunction with the clothing industry in South Africa
- Authors: Ramdass, Kem , Kruger, David
- Date: 2011
- Subjects: Clothing industry - South Africa
- Type: Article
- Identifier: uj:6070 , ISSN 978-1-4577-1552-5 , http://hdl.handle.net/10210/10672
- Description: The clothing industry in South Africa is seen as a conventional industry with characteristics such as: labour intensive with low levels of qualification; low salaries; low potential for investment in research and development and innovation; flexible labour legislation and powerful labour unions. However, it continues to be an important sector in terms of the South African labour market with regards to job creation. The strong impact of globalisation and delocalization in the organization of work is pressurizing the industry in terms of its competitiveness. Global competitiveness in terms of quality, price and supply chain management are reducing the viability of the industry. Few organisations are able to keep their positions in the marketplace without changes in the organisation of work and workers. Organisations that respond to the challenges have positioned themselves for economic stability. Organisations have found different methodologies in dealing with the reality of the situation. Two distinctive paths can be identified: outsourcing production with dismissal of workers and relocation of facilities; and skilling the workforce through continual improvement. The aim of the paper is to highlight the predicament faced by the clothing industry and what could be done to change the levels of productivity in the industry. This paper presents results through qualitative research analysis from the case study conducted in Kwa-Zulu Natal on several clothing organisations in comparison to international experiences.
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- Authors: Ramdass, Kem , Kruger, David
- Date: 2011
- Subjects: Clothing industry - South Africa
- Type: Article
- Identifier: uj:6070 , ISSN 978-1-4577-1552-5 , http://hdl.handle.net/10210/10672
- Description: The clothing industry in South Africa is seen as a conventional industry with characteristics such as: labour intensive with low levels of qualification; low salaries; low potential for investment in research and development and innovation; flexible labour legislation and powerful labour unions. However, it continues to be an important sector in terms of the South African labour market with regards to job creation. The strong impact of globalisation and delocalization in the organization of work is pressurizing the industry in terms of its competitiveness. Global competitiveness in terms of quality, price and supply chain management are reducing the viability of the industry. Few organisations are able to keep their positions in the marketplace without changes in the organisation of work and workers. Organisations that respond to the challenges have positioned themselves for economic stability. Organisations have found different methodologies in dealing with the reality of the situation. Two distinctive paths can be identified: outsourcing production with dismissal of workers and relocation of facilities; and skilling the workforce through continual improvement. The aim of the paper is to highlight the predicament faced by the clothing industry and what could be done to change the levels of productivity in the industry. This paper presents results through qualitative research analysis from the case study conducted in Kwa-Zulu Natal on several clothing organisations in comparison to international experiences.
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An analysis of power quality of matrix converters when using a Fryze reference
- Richards, C. G., Nicolae, Dan-Valentin
- Authors: Richards, C. G. , Nicolae, Dan-Valentin
- Date: 2014
- Subjects: Electric current power converters , Electric power systems
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/17680 , uj:15913 , ISBN: 978-1-4673-6487-4 , Citation: Richards, C.G. & Nicolae, D.V. 2014. An analysis of power quality of matrix converters when using a Fryze reference, ICHQP 2014, 16th International Conference on Harmonics and Quality of Power, 25-28 May Bucharest, Romania. DOI: 10.1109/ICHQP.2014.6842839
- Description: 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 Matrix Converters. 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 Matrix Converter; the power factor will have been improved
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- Authors: Richards, C. G. , Nicolae, Dan-Valentin
- Date: 2014
- Subjects: Electric current power converters , Electric power systems
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/17680 , uj:15913 , ISBN: 978-1-4673-6487-4 , Citation: Richards, C.G. & Nicolae, D.V. 2014. An analysis of power quality of matrix converters when using a Fryze reference, ICHQP 2014, 16th International Conference on Harmonics and Quality of Power, 25-28 May Bucharest, Romania. DOI: 10.1109/ICHQP.2014.6842839
- Description: 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 Matrix Converters. 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 Matrix Converter; the power factor will have been improved
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An EPICS-in-IEEE initiative: learners of St Alban’s college and students of the University of Pretoria seek earth observation solutions through air-quality microsensing
- Sinha, Saurabh, Bebwele, Phumudzo R., Mouton, Chris
- Authors: Sinha, Saurabh , Bebwele, Phumudzo R. , Mouton, Chris
- Date: 2013
- Subjects: Wireless sensor nodes , Sensor sink , Data terminal , Google cloud
- Type: Article
- Identifier: uj:4719 , ISSN 978-1-4799-2402-8 , http://hdl.handle.net/10210/11370
- Description: This paper describes the design and implementation of a microsensor-based air-quality monitoring system intended for earth observations. Traditionally, air-quality monitoring systems are limited to centralized or static sites and thus obtain a limited amount of data for estimation of hazardous air pollutants. The system in this paper was designed to improve the shortcomings experienced by traditional air-quality monitoring systems. The system uses the wireless sensor network (WSNs) nodes to sense and transmit selected ambient air-quality parameters to a sensor sink, which relays these parameters to a data terminal where final data processing is completed and the user interface is situated. The project development team that was involved in the design comprised a senior undergraduate student at the University of Pretoria and a group of eight grade-11 secondary-school learners from St Alban's College, a boys’ high school situated in Pretoria, South Africa. While the undergraduate final-year student designed an analogous system by first principles, the secondary-school learners used educational air-quality microsensor off-the-shelf components. The learners used an Android-based input/output sensor node to communicate to a mobile phone, which managed the upload to a Google drive folder. As a secondary outcome, the educational air-quality microsensor systems developed through this undertaking would serve as an educational tool for improving the public understanding of air-quality, including a new national airquality act in South Africa. This project was completed as an endeavor of Engineering Projects In Community Service (EPICS) in IEEE.
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- Authors: Sinha, Saurabh , Bebwele, Phumudzo R. , Mouton, Chris
- Date: 2013
- Subjects: Wireless sensor nodes , Sensor sink , Data terminal , Google cloud
- Type: Article
- Identifier: uj:4719 , ISSN 978-1-4799-2402-8 , http://hdl.handle.net/10210/11370
- Description: This paper describes the design and implementation of a microsensor-based air-quality monitoring system intended for earth observations. Traditionally, air-quality monitoring systems are limited to centralized or static sites and thus obtain a limited amount of data for estimation of hazardous air pollutants. The system in this paper was designed to improve the shortcomings experienced by traditional air-quality monitoring systems. The system uses the wireless sensor network (WSNs) nodes to sense and transmit selected ambient air-quality parameters to a sensor sink, which relays these parameters to a data terminal where final data processing is completed and the user interface is situated. The project development team that was involved in the design comprised a senior undergraduate student at the University of Pretoria and a group of eight grade-11 secondary-school learners from St Alban's College, a boys’ high school situated in Pretoria, South Africa. While the undergraduate final-year student designed an analogous system by first principles, the secondary-school learners used educational air-quality microsensor off-the-shelf components. The learners used an Android-based input/output sensor node to communicate to a mobile phone, which managed the upload to a Google drive folder. As a secondary outcome, the educational air-quality microsensor systems developed through this undertaking would serve as an educational tool for improving the public understanding of air-quality, including a new national airquality act in South Africa. This project was completed as an endeavor of Engineering Projects In Community Service (EPICS) in IEEE.
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An experimental study of switching GaN FETs in a coaxial transmission line
- Joannou, A. J. L.,Pentz, D. C., van Wyk, J. D. and de Beer, A. S.
- Authors: Joannou, A. J. L.,Pentz, D. C., van Wyk, J. D. and de Beer, A. S.
- Date: 2014
- Subjects: Component for measurements , Device application , Measurement
- Language: English
- Type: Conference
- Identifier: http://hdl.handle.net/10210/16684 , uj:15799 , Citation: Joannou, A. J. L.,Pentz, D. C., van Wyk, J. D. and de Beer, A. S. 2014. An experimental study of switching GaN FETs in a coaxial transmission line. Power Electronics and Applications, 16th European Conference, 26-28 Aug, 2014. Europe. 1-9. DOI:10.1109/EPE.2014.6910756. , DOI:10.1109/EPE.2014.6910756 , DOI: 10.1109/EPE.2014.6910756
- Description: Abstract: The switching characteristics of GaN FETs have not yet been measured accurately because of their small electromagnetic size in relation to the circuit and the electromagnetic environment the measurements are exposed to. Switching GaN FETs in a transmission line will allow for measurements to be taken in an electromagnetically defined environment. The transmission line is adapted to take optimum measurements. This is proven by the waveforms presented.
- Full Text:
- Authors: Joannou, A. J. L.,Pentz, D. C., van Wyk, J. D. and de Beer, A. S.
- Date: 2014
- Subjects: Component for measurements , Device application , Measurement
- Language: English
- Type: Conference
- Identifier: http://hdl.handle.net/10210/16684 , uj:15799 , Citation: Joannou, A. J. L.,Pentz, D. C., van Wyk, J. D. and de Beer, A. S. 2014. An experimental study of switching GaN FETs in a coaxial transmission line. Power Electronics and Applications, 16th European Conference, 26-28 Aug, 2014. Europe. 1-9. DOI:10.1109/EPE.2014.6910756. , DOI:10.1109/EPE.2014.6910756 , DOI: 10.1109/EPE.2014.6910756
- Description: Abstract: The switching characteristics of GaN FETs have not yet been measured accurately because of their small electromagnetic size in relation to the circuit and the electromagnetic environment the measurements are exposed to. Switching GaN FETs in a transmission line will allow for measurements to be taken in an electromagnetically defined environment. The transmission line is adapted to take optimum measurements. This is proven by the waveforms presented.
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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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Analysis of synchronous reluctance machine with magnetically coupled three-phase windings and reactive power compensation
- Ogunjuyigbe, A. S. O., Jimoh, A. A., Nicolae, Dan-Valentin, Obe, E. S.
- Authors: Ogunjuyigbe, A. S. O. , Jimoh, A. A. , Nicolae, Dan-Valentin , Obe, E. S.
- Date: 2010
- Subjects: Synchronous machinery
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/18578 , uj:16017 , ISSN :17518660 , Citation: Ogunjuyigbe, A.S.O. et al. 2010. Analysis of syhnchronous reluctance machine with magnetically coupled three phase windings and reactive power compensation. IET Electric Power Applications, 4(4):291-303. , DOI:10.1049/iet-epa.2009.0134
- Description: Abstract: Synchronous reluctance machine with simple salient rotor is known to have poor power factor because of its poor reactance ratio. This study presents the use of an auxiliary winding attached to a balanced capacitor to improve the effective reactance ratio as well as the performance characteristics of synchronous reluctance machine. A unique feature of this configuration is that although the machine runs at synchronous speed, the effective reactance ratio of the machine can be improved by appropriate sizing of the capacitor attached to the auxiliary winding, with the constraint of the ampere turn rating of the auxiliary winding. The operational characteristics of a simple salient rotor synchronous reluctance machine equipped with this configuration were investigated and shown to have a desirable performance. How the effective reactance ratio, power factor and airgap flux distribution depend on the size of capacitor attached to the auxiliary winding is determined using a simplified mathematical model of the system. Analytical results and experimental measurements are in good agreement, and demonstrate the effectiveness and benefits of the configuration
- Full Text:
- Authors: Ogunjuyigbe, A. S. O. , Jimoh, A. A. , Nicolae, Dan-Valentin , Obe, E. S.
- Date: 2010
- Subjects: Synchronous machinery
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/18578 , uj:16017 , ISSN :17518660 , Citation: Ogunjuyigbe, A.S.O. et al. 2010. Analysis of syhnchronous reluctance machine with magnetically coupled three phase windings and reactive power compensation. IET Electric Power Applications, 4(4):291-303. , DOI:10.1049/iet-epa.2009.0134
- Description: Abstract: Synchronous reluctance machine with simple salient rotor is known to have poor power factor because of its poor reactance ratio. This study presents the use of an auxiliary winding attached to a balanced capacitor to improve the effective reactance ratio as well as the performance characteristics of synchronous reluctance machine. A unique feature of this configuration is that although the machine runs at synchronous speed, the effective reactance ratio of the machine can be improved by appropriate sizing of the capacitor attached to the auxiliary winding, with the constraint of the ampere turn rating of the auxiliary winding. The operational characteristics of a simple salient rotor synchronous reluctance machine equipped with this configuration were investigated and shown to have a desirable performance. How the effective reactance ratio, power factor and airgap flux distribution depend on the size of capacitor attached to the auxiliary winding is determined using a simplified mathematical model of the system. Analytical results and experimental measurements are in good agreement, and demonstrate the effectiveness and benefits of the configuration
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Analysis of the devolo’s 500 kHz G3-PLC access technology based on smart grid field trials
- Papilaya, V. N., Han Vinck, A. J., Ouahada, K., Mengi, A., Weinand, M., Koch, M., devolo, AG
- Authors: Papilaya, V. N. , Han Vinck, A. J. , Ouahada, K. , Mengi, A. , Weinand, M. , Koch, M. , devolo, AG
- Date: 2014
- Subjects: Smart grid field trials , G3-PLC access technology
- Type: Article
- Identifier: uj:4799 , http://hdl.handle.net/10210/12053
- Description: In the smart grid, the G3-PLC solution is in direct competition with other IP-based communications technologies such as GPRS or DSL. In this paper, we present the devolo’s 500 kHz G3-PLC access technology and it’s analysis based on smart grid field trials in Germany. The focus of the analysis in this paper is concentrated on the following parameters: The influencing factor of near and far transmission throughput, the influence of a repeater on the throughput, and the influence of different UDP packet size on the throughput.
- Full Text: false
- Authors: Papilaya, V. N. , Han Vinck, A. J. , Ouahada, K. , Mengi, A. , Weinand, M. , Koch, M. , devolo, AG
- Date: 2014
- Subjects: Smart grid field trials , G3-PLC access technology
- Type: Article
- Identifier: uj:4799 , http://hdl.handle.net/10210/12053
- Description: In the smart grid, the G3-PLC solution is in direct competition with other IP-based communications technologies such as GPRS or DSL. In this paper, we present the devolo’s 500 kHz G3-PLC access technology and it’s analysis based on smart grid field trials in Germany. The focus of the analysis in this paper is concentrated on the following parameters: The influencing factor of near and far transmission throughput, the influence of a repeater on the throughput, and the influence of different UDP packet size on the throughput.
- Full Text: false
Another case of discrepancies when evaluating power theories using real data
- Cornelius, Jurgens J. J., Janse van Rensburg, J. F., Nicolae, Dan-Valentin
- Authors: Cornelius, Jurgens J. J. , Janse van Rensburg, J. F. , Nicolae, Dan-Valentin
- Date: 2014
- Subjects: Electric power systems , Electric power transmission
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/17548 , uj:15899 , ISBN: 978-1-4673-6487-4 , Citation: Cornelius, J.J.J., Janse van Rensburg, J.F. & Nicolae, D.V. 2014. Another case of Discrepancies when evaluating power theories using real data. International Conference on Harmonics and quality of power, 25-28 May 2014, Bucharest, Romania. DOI:10.1109/ICHQP.2014.6842839 /9781497394874
- Description: Abstract: Most non-sinusoidal power theories have been developed from theoretical techniques, as well as relying on hypothetical and experimental networks to highlight the advantages of each. The drawback of the power theories is that no single one has been universally accepted as a benchmark for other developments. This paper will however show this weakness by means of evaluating two power theories in the time domain, using real recorded data.
- Full Text:
- Authors: Cornelius, Jurgens J. J. , Janse van Rensburg, J. F. , Nicolae, Dan-Valentin
- Date: 2014
- Subjects: Electric power systems , Electric power transmission
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/17548 , uj:15899 , ISBN: 978-1-4673-6487-4 , Citation: Cornelius, J.J.J., Janse van Rensburg, J.F. & Nicolae, D.V. 2014. Another case of Discrepancies when evaluating power theories using real data. International Conference on Harmonics and quality of power, 25-28 May 2014, Bucharest, Romania. DOI:10.1109/ICHQP.2014.6842839 /9781497394874
- Description: Abstract: Most non-sinusoidal power theories have been developed from theoretical techniques, as well as relying on hypothetical and experimental networks to highlight the advantages of each. The drawback of the power theories is that no single one has been universally accepted as a benchmark for other developments. This paper will however show this weakness by means of evaluating two power theories in the time domain, using real recorded data.
- Full Text: