A cascaded hybrid inverter with improved dc-link voltage control for grid connected systems
- 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.
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A cascaded NPC/H-bridge inverter with simplifiied control strategy and minimum component count
- 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
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A novel 9-level multilevel inverter based on 3-level NPC/H-bridge topology for photovoltaic applications
- Authors: Wanjekeche, T. , Jimoh, A. A. , Nicolae, Dan-Valentin
- Date: 2009
- Subjects: Harmonics , Photovoltaic power generation , Electric power generation
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/21278 , uj:16136 , Citation: Wanjekeche, T, Jimoh, A.A. & Nicolae, D.V. 2009. A novel 9-level multilevel inverter based on 3-level NPC/H-bridge topology for photovoltaic applications. International Review of Electrical Engineering, 4(5):769-777. , ISSN: 1827-6660
- Description: Abstract: Please refer to full text to view abstract Please refer to full text to view abstract
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A study of insulation failure in a high voltage current transformer
- 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
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A study of the impact of broken neutral in a distribution system
- Authors: Xivambu, M. , Jimoh, A. A. , Nicolae, Dan-Valentin
- Date: 2006
- Subjects: Electric wiring , Neutral density filters
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/22058 , uj:16153 , Citation: Xivambu, M., Jimoh, A.A. & Nicolae, D.V. 2006. A study of the impact of broken neutral in a distribution system. IASTED, September, 2006, Gaborone, Botswana.
- Description: Abstract: In this paper a study of the impact of the neutral conductor in a distribution system is presented. The causes which determine faults of the neutral conductor together with its effects are presented. The paper proposes a solution which will minimize the impact of the neutral failure.
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Analysis of synchronous reluctance machine with magnetically coupled three-phase windings and reactive power compensation
- 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, modeling and control of cascaded NPC/H bridge inverter for high power quality grid connection
- Authors: Wanjekeche, T. , Nicolae, Dan-Valentin , Jimoh, A. A.
- Date: 2010
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/18314 , uj:15983 , Citation: Wanjekeche, T., Nicolae, D.V. & Jimoh, A.A. 2010. Analysis, modelling and control of cascaded NPC/HNPC/H bridge inverter for high power quality grid connection. In: Proceedings of the IASTED AsiaPes 2010, Thailand, Nov. 2010:74-79
- Description: Abstract: The cascaded NPC/H- bridge inverter is first analyzed by establishing a new switching model based on a derived control law. From the developed switching model, a general model is obtained using state space technique. A new and accurate average model is developed using abc to dqo transformation technique. Finally small signal model is obtained by linearizing all the state variables around their quiescent operating points. The small signal model is used to study the effects of various control feedback variables on the dynamic performance of the Grid connected system. Feedback control scheme is designed to improve the dynamic response of the system. The system with the proposed control technique also achieves sinusoidal grid voltage and current output with low THD which is a preferred characteristic for any power injected to the grid. Simulation results are provided to validate the analytical models
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Automating consumer's connections to the distribution network for enhanced performance
- 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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Comparative analysis of third harmonic injection PWM and SPWM control techniques for UPS inverter
- Authors: Wanjekeche, T. , Nicolae, Dan-Valentin , Jimoh, A. A.
- Date: 2008
- Subjects: Uninterruptible power supply , Pulse width modulation
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/20338 , uj:16086 , Citation: Wanjekeche, T., Nicolae, D. V. & Jimoh, A. A. 2008. Comparative analysis of third harmonic injection PWM and SPWM control techniques for UPS inverter. Proceedings of The IASTED International Conference on Power and Energy Systems, 8-10 September 2008, Gaborone, Botswana.
- Description: Abstract Pulse Width Modulation (PWM) techniques has been researched for three decades but there are no explicit guidelines on how one can choose the desired technique for particular application especially in power processing devices. Thus choosing a particular PWM technique for UPS application remains a challenging task since UPS operate under varying load conditions. All the techniques appear to give superior performance as well as short-comings when it comes to control of UPS inverter. This paper presents analytical and simulated results that demonstrate the equivalence between the two types of PWM control techniques and the superior performance when considering high conversion factor (C.F.) and Total Harmonic Distortion (THD) for UPS application.
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Complete analysis of a multilevel inverter based on 3 level NPC/H- bridge topology for photovoltaic application
- Authors: Wanjekeche, T. , Nicolae, Dan-Valentin , Jimoh, A. A.
- Subjects: Bridge circuits , Capacitance meters , Electric power measurement
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/18262 , uj:15978 , Citation: Wanjekeche, T., Nicolae, D.V. & Jimoh, A.A. 2010 Complete analysis of a multilevel inverter based on 3 level NPC/H- bridge topology for photovoltaic application. IEEE
- Description: Abstract: The cascaded NPC/H- bridge inverter is first analyzed by establishing a new switching model based on a derived control law, then using the model a general model using state space technique is obtained. A new and accurate average model is developed using abc to dqo transformation technique. A small signal model is developed by linearizing all the state variables around their quiescent operating points. The small signal model is used to study the effects of various control feedback variables on the dynamic performance of the PV- Grid system. Based on the transfer function developed feedback control loop is developed to improve the dynamic response of the system as well as voltage balancing of the DC link. Simulation results are provided to validate the analytical models.
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Controlled capacitance injection into a three-phase induction motor through a single-phase auxiliary stator winding
- Authors: Jimoh, A. A. , Nicolae, Dan-Valentin
- Date: 2007
- Subjects: Fusion power plants , Electromagnetic induction , Reactor fuel reprocessing
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/18755 , uj:16039 , Citation: Jimoh, A.A. & Nicolae, D.V. 2007. Controlled capacitance injection into a three-phase induction motor through a single-phase auxiliary stator winding.IEEE International Electric Machines and Drives Conference, Antalya, Turkey, May 03-05, 2007:1183-1188. DOI:10.1109/IEMDC.2007.383598
- Description: Abstact: In this paper a controlled static switched capacitor three-phase auxiliary winding fed by a three-phase PWM with single-phase auxiliary winding, which is only magnetically inverter is proposed with some positive results. This solution coupled to the stator main winding, is explored for improving the is, however, complex and there are some doubts about the starting and operating power factor of a three-phase induction controller presented. Other solution presented in [7, 8] is motor. The scheme improves the power factor of the motor applicable only to a wound rotor machine, as the rotor is without compromising significantly on other performances. Important advantages of the scheme include preventing required to be connected to an external circuit. harmonics in the line current, and eliminating regeneration In this paper a single-phase stator auxiliary winding that is possibility as well as preventing high inrush currents at starting
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Controlled power flow capacitive divider for electric power tapping
- Authors: Jimoh, A. A. , Munda, J. , Britten, A. C. , Nicolae, Dan-Valentin
- Date: 2006
- Subjects: Electric power systems , Capacitance meters
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/15982 , uj:15724 , ISBN: 1-4244-0121-6 , Citation: Jimoh, A.A. et al. 2006. Controlled power flow capacitive divider for eletric power tapping. In: Proceedings of the 12th International Power Electronics and Motion Control Conference, 30 August-1st September, 2006, Portoroz. DOI: 10.1109/EPEPEMC.2006.4778611-1477
- 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.
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DC current source to voltage source CT-based converter
- Authors: Nicolae, Dan-Valentin , Jimoh, A. A. , Van Rensburg, J. F. J.
- Date: 2007
- Subjects: Energy storage , Transformer substations
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/20504 , uj:16106 , Citation: Nicolae, D.V., Jimoh, A.A. & Van Rensburg, J.F.J. 2007. DC current source to voltage source CT-Based converter,International Aegean Conference on Electric Machines and Power Electronics & Electromotion Joint Conferences, Bodrum, Turkey, September 10-12, 2007:665-670. DOI10.1109/ACEMP.2007.4510587
- Description: Abstract: As generally known there is no energy transfer between a dc current and a current transformer. After a brief overview of other methods for tapping energy from the high voltage direct current transmission line, this paper presents the concept of a new dc to ac current source converter utilizing a current transformer. The advantage of this converter is that it is connected in series to the dc line and that at any moment in time the current flow is kept continuous. This paper presents the concept of the converter and simulation results.
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Dynamic model and control of power converters for grid connected renewable energy systems
- Authors: Nnachi, A. F. , Nicolae, Dan-Valentin , Jimoh, A. A.
- Date: 2008
- Subjects: Electric current converters , Renewable energy sources
- Language: English
- Type: Conference procedings
- Identifier: http://hdl.handle.net/10210/20449 , uj:16099 , Citation: Nnachi, A.F., Nicolae, D.V. & Jimoh, A.A. 2008. Dynamic model and control of power converters for grid connected renewable energy systems. Proceedings of the Second IASTED Africa Conference Power and Energy Sysyems (Africa PES 2008), 8-10 September, 2008, Gaborone, Botswana.
- Description: Abstract: In order to investigate certain dynamic events of a grid connected renewable energy system (RES), a systematic model and control is developed. The RES with its converter is taken as a controlled dc current source and the grid side converter model is based on approximate power balance of the dc-link and the ac-side. Here an AC-side decoupled current controller in dq reference frame and simplified net dc-bus voltage controllers are implied. Among different dynamic events that is studied, the response of the system during three-phase to ground fault, step change in reference DC voltage, active and reactive power change are studied and presented.
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Improving synchronous reluctance machine performance by direct capacitance injection through an auxiliary winding
- Authors: Ogunjuyigbe, A. S. O. , Jimoh, A. A. , Nicolae, Dan-Valentin
- Date: 2007
- Subjects: Synchronous generators , Capacitors , Power-factor meters
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/20415 , uj:16094 , Citation: Ogunjuyigbe, A.S.O., Jimoh, A.A. & Nicolae, D.V. 2007. Improving synchronous reluctance machine performance by direct capacitance injection through an auxiliary winding. ICEMS’07 International Conference on Electrical Machines and Systems 2007, October 8-11, Seoul Olympic Parktel, Seoul, Korea:1055-1060
- Description: Abstract: Synchronous reluctance machine with a conventional rotor structure and a 3-phase auxiliary winding attached to a balanced capacitance for power factor improvement will find application in high speed , high power drives. This paper presents an understanding of its operation using the electromagnetic as well as the electric circuit concepts. Analytical and simulation results of this machine configuration show that the torque as well as the power factor performance is better compared to conventional reluctance machine.
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LV self balancing distribution network configuration for minimum losses
- Authors: Nicolae, Dan-Valentin , Siti, M. W. , Jimoh, A. A.
- Date: 2009
- Subjects: Distribution systems , Electric networks , Low voltage systems
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/21377 , uj:16144 , ISBN: 978-1-4244-2235-7 , Citation: Nicolae, D.V., Siti, M.W. & Jimoh, A.A. 2009. LV self balancing distribution network configuration for minimum losses. Proceedings of the IEEE PowerTech Conference, 26-02 July, 2009, Bucharest, Romania. DOI: 10.1109/PTC.2009.5282233
- Description: Abstract: please refe to full text to view abstract Please refer to full text to view abstract
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Multilevel high power converters for reversible power flow between utilities and power pool transmission corridor
- Authors: Nnachi, A. F. , Jimoh, A. A. , Nicolae, Dan-Valentin
- Date: 2007
- Subjects: Circuit breakers , Wind-powered generation , Power transmission
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/20003 , uj:16066 , ISBN 078038606x , Citation: Nnachi, A.F., Jimoh,A.A. & Nicolae, D.V. 2007. Multilevel high power converters for reversible power flow between utilities and power pool transmission corridor. IEEE AFRICON'07, Windhoek, Namibia, 26-28 September 2007:1-8. DOI:10.1109/AFRCON.2007.4401473
- Description: Abstract: Multilevel converters have emerged as the state of the art high power conversion for applications in reversible power flow. Electric power could be tapped from or injected to the grid regardless of the discrepancies in voltage levels, frequency, phase number and different modes of operation of the grid and the system. This paper presents an overview of different topologies of multilevel converters and modulation strategies with a verification of back-to-back neutral point converter for bidirectional power flow application
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Novel heuristic and SVM based optimization algorithm for improving distribution feeder performance
- Authors: Jordaan, J. A. , Nicolae, Dan-Valentin , Jimoh, A. A.
- Date: 2012
- Subjects: Transmission , Electric transformer
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/17526 , uj:15895 , Citation: Jordaan, J.A., Nicolae, D.V. & Jimoh, A.A. 2012. Novel heuristic and SVM based optimization algorithm for improving distribution feeder performance. In: The 2012 International Joint Conference on Neural Networks. DOI;10.1109/IJCNN.2012.6252616-5. , DOI;10.1109/IJCNN.2012.6252616
- Description: Abstract: Secondary distribution networks generally perform as well as its LV feeders are performing. The main problem that a feeder is experiencing would be the load unbalancing due to the stochastic nature of its individual single-phase loads: larger losses in certain phases accompanied by bad voltage regulation and voltage unbalance. In order to address this problem, it may be economical to install apparatus to automatically balance or partially balance the loads progressing from the end of the feeder towards the front using smart devices based on a three-ways switch selector and an artificial intelligence algorithm to minimize the neutral current. The main idea behind this paper is therefore to keep the three phases progressively balanced along the whole length of the line. A Support Vector Machines (SVM) implementation and a heuristic method are presented as the numerical algorithms
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On-line automatic switching of consumers' connections for improved performance os a distribution feeder
- Authors: Popoola, O. , Jimoh, A. A. , Nicolae, Dan-Valentin
- Date: 2009
- Subjects: Electric power distribution , Electric networks
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/21132 , uj:16116 , ISBN: 978-1-4244-3811-2 , Citation: Popoola, O., Jimoh, A.A. & Nicolae, D.V. 2009. On-line automatic switching of consumers' connections for improved performance os a distribution feeder. Proceedings of the IEEE Power Systems Conference & Exposition, 15-18 March, 2009, Seattle, USA. DOI: 10.1109/PSCE.2009.4840160
- Description: Abstract: Resolving imbalances on phases is performed using conventional trial and error approach which involves service interruption. Phase current and voltage may improve however the resultant effect does not last for too long. To improve the performance of the secondary distribution system there is a need for an on-line and automating technology. The aim of this paper is to pioneer a method and technology 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 involves monitoring, acquisition/display of collected data and self changing switching actions electronically for rearrangement or transfer of consumer loads. The proposed switching technology is based on opentransition switch that enables transfer or rearrangement of consumer loads in a three-phase system within milliseconds with supervisory control system. Validation of the proposed technology was carried out using these methodologies: Matlab (Simulink), Virtual Instrumentation-Lab VIEW and Hardware implementation.
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On-line remote and automatic switching of consumers' connection for optimal performance of a distribution feeder
- Authors: Popoola, O. , Jimoh, A. A. , Nicolae, Dan-Valentin
- Date: 2007
- Subjects: Phase transformations , Voltage-frequency converters
- Language: English
- Identifier: http://hdl.handle.net/10210/20144 , uj:16073 , ISBN:078038606x , Citation: Popoola, O., Jimoh, A.A. & Nicolae, D. 2007. On-line remote and automatic switching of consumers' connection for optimal performance of a distribution feeder, IEEE AFRICON’07, Windhoek, Namibia, 26-28 September, 2007:1-6. DOI:10.1109/AFRCON.2007.4401536
- Description: Abstract: Load balancing on phases is performed using a conventional trial and error approach. With this approach, service interruption is unavoidable; hence rearrangement of consumers load distribution points on phases cannot be performed frequently. Also phase voltage and current imbalances might improve using this approach but the change does last for too long. To get the secondary distribution to operate at its optimal performance, a technique in the form of remote and automated technology is needed. This paper contributes such a technology at the low voltage side of the distribution network. The proposed static transfer switching technology is based on the open-transition switch that enables transfer or arrangement of consumer loads in a three-phase system within milliseconds and supervisory control system for effective co-ordination, computational and control of other intelligent units
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