OpenUCT :: Browsing by Author "Barendse, Paul Stanley"

Browsing by Author "Barendse, Paul Stanley"

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Open Access
The application of advanced signal processing techniques to the condition monitoring of electrical machine drive systems
(2007) Barendse, Paul Stanley; Pillay, Pragasen
The thesis examines the use of two time-frequency domain signal processing tools in its application to condition monitoring of electrical machine drive systems. The mathematical and signal processing tools which are explored are wavelet analysis and a non-stationary adaptive signal processing algorithm. Four specific applications are identified for the research. These applications were specifically chosen to encapsulate important issues in condition monitoring of variable speed drive systems. The main aim of the project is to highlight the need for fault detection during machine transients and to illustrate the effectiveness of incorporating and adapting these new class of algorithms to detect faults in electrical machine drive systems during non-stationary conditions.
Open Access
Condition monitoring of induction motors in the nuclear power station environment
(2018) Rylands, Naasef; Barendse, Paul Stanley
The induction motor is a highly utilised electrical machine in industry, with the nuclear industry being no exception. A typical nuclear power station usually contains more than 1000 motors, where they are used in safety and non-safety application. The efficient and fault-free operation of this machine is critical to the safe and economical operation of any plant, including nuclear power stations. A comprehensive literature review was conducted that covered the functioning of the induction machine, its common faults and methods of detecting these faults. The Condition Based Maintenance framework was introduced in which condition monitoring of induction machines is an essential component. The main condition monitoring methods were explained with the main focus being on Motor Current Signature Analysis (MCSA) and the various methods associated with it. Three analysis methods were selected for further study, namely, Current Signature Analysis, Instantaneous Power Signature Analysis (IPSA) and Motor Square Current Signature Analysis (MSCSA). Essentially, the methodology used in this dissertation was to study the three common motor faults (bearings, stator and rotor cage) in isolation and compare the results to that of the healthy motor of the same type. The test loads as well as fault severity were varied where possible to investigate its effect on the fault detection scheme. The data was processed using an FFT based algorithm programed in MATLAB. The results of the study of the three spectral analysis techniques showed that no single technique is able to detect motor faults under all tested circumstances. The MCSA technique proved the most capable of the three techniques as it was able to detect faults under most conditions, but generally suffered poor results in inverter driven motor applications. The IPSA and MSCSA techniques performed selectively when compared to MCSA and were relatively successful when detecting the mechanical faults. The fact that the former techniques produce results at unique points in the spectrum would suggest that they are more suitable for verifying results. As part of a comprehensive condition monitoring scheme, as required by a large population of the motors on a nuclear power station, the three techniques presented in this study could readily be incorporated into the Condition Based Maintenance framework where the strengths of each could be exploited.
Open Access
Condition monitoring of lithium-ion batteries using broadband multisine excitation and electrochemical impedance spectroscopy
(2018) Waligo, Alfred; Barendse, Paul Stanley
Electrochemical Impedance Spectroscopy (EIS) is a well-known technique that has been employed on various electrochemical cells to obtain their impedance spectra. Lithium-ion(Li-ion) cells are some of the cells to which it has been applied. The impedance spectra obtained from EIS can be used to estimate various batteries State of Health (SOH) and State of Charge (SOC) characteristics. The lengthy acquisition time associated with standard EIS makes it unsuitable for rapid on-line impedance measurements. Alternative methods that take a shorter time have therefore been proposed. This study compares the spectra obtained by the Harmonic Compensated Synchronous Detection (HCSD) broadband signal technique with the EIS and a custom Broadband Impedance Spectroscopy (BIS) technique, at different states of charge, which mimic a real-time load. The test cells are industry standard Nickel-Cobalt and Manganese Oxide (NCM) Li-ion cells. The BIS technique is like HCSD in the selection of frequencies; however, the amplitude of the excitation broadband signal is varied to match the impedance magnitude response of the cell. Also, parameter extraction is performed on both EIS and BIS techniques for fault detection purposes.
Open Access
Condition monitoring of polymer electrolyte membrane fuel cells
(2014) De Beer, Chris; Barendse, Paul Stanley; Pillay, Pragasen
As the global demand for energy continues to grow new technologies and systems must be developed to supply the market. This includes renewable energy generation, storage and conversion systems. The primary storage technology in use today in the portable electronics, the automotive sector and to a lesser extent power networks is battery based systems. To overcome some of the limitations inherent in batteries, fuel cell based power generators and converters have been developed. Fuel cells act as electrochemical energy converters that convert a fuel source such as natural gas directly into electrical power without any secondary phases. For systems running on Hydrogen generated via renewable or natural sources, the input/output cycle becomes completely sustainable. Out of the different fuel cell types available and under development, the Proton Exchange Membrane or Polymer Electrolyte Membrane (PEM) fuel cell has emerged as the technology of choice, and currently owns more than 80% of the commercial fuel cell market. This has spurred further research in the field to increase performance and life expectancy of the cell materials. A promising development in the form of High Temperature PEM (HT-PEM) fuel cells has recently emerged and addresses some of the shortcomings of the low temperature counterparts. A critical field of research is the condition monitoring strategies and technologies for the electrochemical device that ties in with the power conditioning sub-systems. This thesis presents the development of condition monitoring systems by conducting detailed studies on the fault/degradation mechanisms prevalent in the cell materials for the purpose of detection, classification and implementation of possible mitigation strategies. Specific consideration is given to the detailed analysis of the fault mechanisms in HT-PEM fuel cells that are not yet fully understood and commercialized. In particular, electrochemical equivalent circuit models and reduced order semi- empirical models are developed to facilitate fault detection. Based on these models, mitigation strategies for specific faults are proposed and experimentally verified. New systems and methods are developed for rapid online impedance signature mapping that provide a basis for early fault prediction that can increase system performance and life expectancy. The findings in this research provide valuable insight into the effect that most prevalent faults have on the internal electrochemistry and the impact on electrical performance. From the experimental results, a semi-empirical electrochemical model is developed to assist with life time estimation and system optimization. The model is integrated with a real time emulator platform that can reproduce single cell voltage levels at the high output currents and transient characteristics. A detailed analysis is conducted on CO poisoning and the resulting effects on key equivalent circuit parameters that enable quantification of the fault condition. It is shown that the catalyst at the higher operating temperature is still susceptible to a certain degree of semi-permanent degradation. To mitigate these effects, a new active current control strategy is proposed to enforce electro-oxidation of the CO to recover the lost active area that delivered superior results compared to current pulsing strategies. New rapid online detection strategies are proposed by using small voltage transients in an operational HT-PEM fuel cell. The method makes use of the discrete S-transform that overcomes some of the limits in other signal processing methods used in fuel cell diagnostics. To enable detailed parameter calculation, a population based incremental learning algorithm is implemented in the developed method. A new condition monitoring system is developed that makes use of Optimized Broadband Impedance Spectroscopy. The hardware is designed to accommodate both single cell and stack level implementation. It is shown that the proposed system is able to deliver measurements under extreme non-linear conditions that can occur in PEM fuel cells in a fraction of the time associated with normal EIS based systems.
Open Access
Design and implementation of variable speed wind energy induction generator systems for fault studies
(2004) Barendse, Paul Stanley; Pillay, Pragasen
Due to the economical and environmental benefits, Wind Energy Conversion Systems (WECS) have received tremendous growth in the past decade. The increased interest in wind energy has made it necessary to model and experimentally evaluate entire WECS, so as to attain a better understanding and to assess the performance of various systems. As a direct consequence of the increase in wind generation systems, comes the need for the reduction of operational and maintenance costs of these wind generators. The most efficient way of reducing these costs is by the early detection of the degeneration of these generators health, thus facilitating a proactive response, minimizing downtime, and maximizing productivity. The more common induction machine failures are caused by the deterioration of the stator insulation and by the breaking of rotor bars. The thesis describes the design, modeling and implementation of two different variable speed induction generator systems for studying faults in wind energy applications. This project served as a platform for further research into the development and evaluation of a non-stationary fault detection technique suitable for wind energy induction generator purposes. Some common faults are implemented on the wind generators in an attempt to identify them from measurements and by using a steady state fault analysis technique (Motor Current Signature Analysis). For variable speed wind generation, there are two systems using induction generators. The first consist of a squirrel cage induction generator, which uses back-to-back converters in the stator circuit, as shown in Fig. 0.1. The second consists of a wound rotor induction generator, whereby the stator is directly connected to the grid and the rotor circuit consists of back-to-back converters, as shown in Fig. 0.2. When both the rotor and stator are capable of delivering power as with the wound rotor induction generator, they are known as doubly-fed induction generators (DFIG).
Open Access
Design of a permanent magnet generator for a sustainable wind energy capture and storage system
(2011) Jagau, Hartmut; Khan, Mohamed Azeem; Barendse, Paul Stanley
The main objective of this dissertation is the detailed design, sizing, analysis and experimental validation of the sustainable wind generator. The proposed machine topology for the generator uses permanent magnets (PMs) from discarded hard disk drives (HDDs). The PM configuration inherently produces a non-uniform air gap flux-density distribution and the pole pitches of the PMs are relatively small. This would result to an unbalanced generator output and a number of stator inter-connecting leads, if conventional tooth-concentrated non-overlapping winding configurations are used. Hence, a concentrated full-pitch overlapping wave winding configuration is developed, which overcomes the aforementioned challenges. The proposed sustainable coreless axial flux generator is then analyzed with classical machine theory and verified by finite element analysis (FEA) software. It is shown that the traditional sizing approach for axial flux machines needs modification to accommodate the design of the proposed machine topology. For the numerical analysis, 3D-FEA is used to verify the 2Dmodel which is subsequently employed in the numerical analyses.
Open Access
Development of a grid emulator for network integration studies
(2014) Khan, Akrama; Khan, Mohamed Azeem; Barendse, Paul Stanley
The economic and environmental side effects of fossil fuels have forced governments and authorities to investigate sustainable solutions. Main interest is focused on environment friendly benefits, provided by renewable energy sources. The growth rate of these energy sources has increased remarkably in the past few years. Correspondingly the research and development in the field of power electronics has also increased, especially in medium voltage and high power grid connected systems. The grid behaviour of the renewable energy systems is heavily influenced by the control techniques of these systems. For further development of these control methods the most basic and conventional way is to simulate, test and prove the system performance on a down-scaled lab test bench. The objective of this thesis is to develop a laboratory test bench grid emulator for network integration studies. Design and performance are investigated by introducing several kinds of unbalanced voltage conditions to test the behavior of connected systems. Voltage dips and swells are implemented to test the system’s performance.
Open Access
Development of a scaled doubly-fed induction generator for assessment of wind power integration issues
(2016) Dehnavifard, Hossein; Khan, Mohamed Azeem; Barendse, Paul Stanley
Years of experience have been dedicated to the advancement of thermal power plant technology, and in the last decade the investigation has focused on the wind energy conversion system (WECS). Wind energy will play an important role in the future of the energy market, due to the changing climate and the fossil fuel crisis. Initially, wind energy was intended to cover a small portion of the energy market, but in the long term it should compete with conventional fossil fuel power generation. The movement of the power system towards this new phenomena has to be investigated before the wind energy share increases in the network. Therefore, the wind energy integration issues serve as an interesting topic for authors to improve the perception of integration, distribution, variability and power flow issues. Several simulation models have been introduced in order to resolve this issue, however, the variety in types of wind turbines and the network policies result in these models having limited accuracy or being developed for specific issues. The micro-machine is introduced in order to overcome the challenges of simulation models and the costs involved in field tests. In the past, the grid integration issue of large turbo-alternators was solved by the micro-machines. A variety of tests are possible with the micro-machines and they also increase the flexibility of the system. The increased accuracy as well as the ability to carry out real-time analysis and compare actual field test data are strengths worth utilizing. This project involves the designing and the prototyping of a scaled doubly-fed induction generator (micro-DFIG). The machine is also analysed and tested. The scaling of the micro-machine is achieved by means of a dimensional analysis, which is a mathematical method that allows machines and systems to be downscaled by establishing laws of similitude between the reference model and its scaled model. MATLAB/SIMULINK, Maxwell and Solid Work are employed to achieve the objectives of this project.
Open Access
Development of a system for testing grid-connected permanent magnet wind generators
(2011) De la Bat, Jaques Gerard; Khan, Mohamed Azeem; Barendse, Paul Stanley
Renewable energy will be included in the South African Energy Mix over the next two decades. The introduction of renewable energy will reduce South Africa's carbon emissions and also stimulate the economy through job creation as well as creating a local manufacturing sector. South Africa has a large coastal region which is ideal for wind energy deployment. The integration of wind power into the grid needs to be understood as well as the possible problems associated with it. The objective this thesis is to develop a laboratory-based system which can serve as a tool for studying non-ideal conditions associated with the integration of grid-connected Permanent Magnet (PM) wind generators.
Open Access
Development of an induction motor condition monitoring test rig And fault detection strategies
(2014) Dlamini, Mpendulo; Barendse, Paul Stanley
This thesis sets out to develop an induction motor condition monitoring test rig to experimentally simulate the common faults associated with induction motors and to develop strategies for detecting these faults that employ signal processing techniques. Literature on basic concepts of induction motors and inverter drives, the phenomena of common faults associated with induction motors, the condition monitoring systems were intensively reviewed.
Open Access
Dynamic modelling and emulation of a high temperature proton exchange membrane fuel cell (HT PEMFC)
(2011) De Beer, Chris; Barendse, Paul Stanley; Khan, Mohamed Azeem
Fuel cells (FC) are power sources that convert chemical energy into electrical and thermal energy in a clean and efficient manner. In the 21st century, fuel cells appear poised to meet the power demands of a variety of applications, ranging from portable electronics to utility power plants. Compared to systems utilizing fossil fuels, fuel cells offer greater efficiency and superior reliability. In particular, proton exchange membrane FCs (PEMFCs) presents a good alternative energy source for distributed generation (DG) systems. FCs however, have had limited commercial success despite their performance, durability and low environmental impact in comparison to other energy conversion and power generation devices. This lack of success has led to low commercial production levels resulting in high costs. Therefore, an increase in research and development is being conducted with the aim of producing cost effective, more efficient and reliable fuel cells for portable transportation and stationary applications. This dissertation aims to produce an emulator design for a HT PEM FC system. A model is developed that takes into account the steady state and the dynamic characteristics of the fuel cell. The emulator hardware is developed from first principles and tested to evaluate performance under dynamic operating conditions. Phenomena such as polarization curve hysteresis and fuel starvation is investigated, simulated and reproduced with the emulator system. The experimental results are compared with that of an actual HT PEM FC stack and evaluated. It was shown that the final system is able to deliver accurate steady state and transient state outputs when compared with the fuel cell stack. The final design can be used for hardware in the loop applications, specifically for fuel cell power conditioning system development.
Open Access
Effects of voltage unbalanced supplies on energy-efficient motors
(2010) Van Wyk, Ashwill Louis; Khan, Mohamed Azeem; Barendse, Paul Stanley
Eskom DSM has recently introduced an Energy Efficiency (EE) Motor program, which provides incentives to industrial customers to retrofit standard motors with EE motors. The main objective of the program is to realize energy savings through the replacement of standard (STD) induction motors with higher efficiency EE motors. Although the principle of the program is correct, there are several significant power quality and performance issues with EE motors.These issues need to be thoroughly investigated in order to achieve the overall energy saving objectives of program.
Open Access
High Speed flywheel and test rig design for rural energy storage
(2010) Okou, Richard; Pillay, Pragesen; Khan, Mohamed Azeem; Barendse, Paul Stanley
There is considerable growth in the renewable energy sector to contribute to sustainable development, environmental conservation and most importantly to provide affordable energy to isolated rural communities of sub-Saharan Africa. Renewable energy sources such as solar and wind require energy storage since the source of energy is intermittent. Electrochemical batteries especially from lead acid are commonly used to store energy in Solar Home Systems (SHS) for rural electrification in sub-Saharan Africa. Disadvantages such as low efficiencies, low life cycle costs, high maintenance, comparatively short life and serious environmental and human toxicity effects exist. Since recycling is not widespread, replacement costs are high, as are the resultant environmental damage and health hazards from lead and sulphuric acid. In this thesis, an electromechanical flywheel energy storage device is proposed as an alternative to a lead acid battery in order to increase efficiency, life expectancy, increased high depth of discharge, low life cycle cost and elimination of adverse environmental effects. Due to income and service skill constraints in rural areas, the proposed, high speed flywheel systems (for long time energy storage) will require the use of low cost configurations and topologies, special considerations on the flywheel rotor profile design, robust electrical machines, simple power electronics and a low cost bearing set. Low loss magnetic bearings are also possible but were limited by time while also making their maintenance complex especially in rural areas. Conventional high strength composite materials used in flywheel rotor manufacture for high speed operation are expensive. Therefore there is a need to develop techniques to profile the rotor shape so as to improve on material usage and exhibit lower mechanical stresses. A robust electrical machine topology for high speed operation and a simple drive system are investigated to ensure simple assembly, low cost and low maintenance. vii The various flywheel components were designed using analytical and numerical methods. Two techniques were used to develop two optimal profiles for the flywheel rotor structure. Partial differential equations and analytical solutions were employed to develop the profiles. Analytical equations were used to design the electrical machine, drive, bearing system and other accessories. The final electromechanical battery prototype consisted of a composite flywheel rotor made from E-glass fibre materials, double rotor Axial Flux Permanent Magnet (AFPM) machine and a drive system using Brushless DC (BLDC) mode of operation. The system was designed for 300Wh of energy storage for the delivery of 100W and 500W of power and an operating speed range of 8,000 rpm-25,000 rpm. The design and development of the flywheel energy storage system and test rig using locally available materials was investigated. Experiments were conducted for speeds up to 6,000 rpm. The electromechanical battery was able to store a maximum of 77Wh of energy. The shortfall of the system to meet its design specifications was investigated and found to have been caused by vibrations resulting from prototyping issues. A thermal model was developed to predict the temperature rise in the system which showed a good correlation with the experimental results.
Open Access
Impact of armature rewinding on induction motor efficiency in South Africa
(2009) Mzungu, Heskin Mkando; Khan, Azeem; Barendse, Paul Stanley
The aim of this thesis is to evaluate the impact of armature rewinding on the efficiency of Low Voltage (LV) industrial squirrel cage induction motors in South Africa. The efficiency of an electric motor is a measure of the effectiveness of the motor to convert electrical power at its terminals to mechanical power at its shaft. Although the definition is seemingly simple and straightforward, the determination of the efficiency of an induction motor is a much-debated topic. Motor manufacturers provide efficiency data obtained through measurement and calculation according to a variety of international standards. Several international standards exist, with each outlining different methods and procedures for the determination of induction motor efficiency. Most notable among the disparities is the treatment of stray losses. For example, the Japanese standard JEC-37 assumes stray losses to be negligible, others such as SANS 34-2 and ASINZ 1359.5 use a fixed value, while IEEE 112, CSA 390 and lEC 34-2 prefer to make actual measurements. A number of these standards were initially considered. However, after preliminary laboratory-tests were performed, it was observed that the IEEE 112 method B (2004) and IEC 60034-2 segregation method (2007) appeared to be the most consistent and repeatable. The two standards were therefore preferred and subsequently chosen for this project. The South African standard, SANS 34-2, is available but its methods of determining efficiency have been found to be unsupported due to its reference to the IEC 60034-2 (1984) which has been abandoned and replaced. The SANS 34-2 was therefore not used in the testing.
Open Access
Micro combined heat and power management for a residential system
(2013) Tichagwa, Anesu; Barendse, Paul Stanley; Khan, Azeem
Fuel cell technology has reached commercialisation of fuel cells in application areas such as residential power systems, automobile engines and driving of industrial manufacturing processes. This thesis gives an overview of the current state of fuel cell-based technology research and development, introduces a μCHP system sizing strategy and proposes methods of improving on the implementation of residential fuel cell-based μCHP technology. The three methods of controlling residential μCHP systems discussed in this thesis project are heat-led, electricity-led and cost-minimizing control. Simulations of a typical HT PEMFC -based residential μCHP unit are conducted using these control strategies. A model of a residential μCHP system is formulated upon which these simulated tests are conducted. From these simulations, equations to model the costs of running a fuel-cell based μCHP system are proposed. Having developed equations to quantify the running costs of the proposed μCHP system a method for determining the ideal size of a μCHP system is developed. A sizing technique based on industrial CHP sizing practices is developed in which the running costs and capital costs of the residential μCHP system are utilised to determine the optimal size of the system. Residential thermal and electrical load profile data of a typical Danish household are used. Having simulated the system a practical implementation of the power electronics interface between the fuel cell and household grid is done. Two topologies are proposed for the power electronics interface a three-stage topology and a two-stage topology. The efficiencies of the overall systems of both topologies are determined. The system is connected to the grid so the output of each system is phase-shifted and DC injection, harmonic distortion, voltage range and frequency range are determined for both systems to determine compliance with grid standards. Deviations between simulated results and experimental results are recorded and discussed and relevant conclusions are drawn from these.
Open Access
Modelling and detection of faults in axial-flux permanent magnet machines
(2016) Ogidi, Oladapo Omotade; Barendse, Paul Stanley; Khan, Mohamed Azeem
The development of various topologies and configurations of axial-flux permanent magnet machine has spurred its use for electromechanical energy conversion in several applications. As it becomes increasingly deployed, effective condition monitoring built on reliable and accurate fault detection techniques is needed to ensure its engineering integrity. Unlike induction machine which has been rigorously investigated for faults, axial-flux permanent magnet machine has not. Thus in this thesis, axial-flux permanent magnet machine is investigated under faulty conditions. Common faults associated with it namely; static eccentricity and interturn short circuit are modelled, and detection techniques are established. The modelling forms a basis for; developing a platform for precise fault replication on a developed experimental test-rig, predicting and analysing fault signatures using both finite element analysis and experimental analysis. In the detection, the motor current signature analysis, vibration analysis and electrical impedance spectroscopy are applied. Attention is paid to fault-feature extraction and fault discrimination. Using both frequency and time-frequency techniques, features are tracked in the line current under steady-state and transient conditions respectively. Results obtained provide rich information on the pattern of fault harmonics. Parametric spectral estimation is also explored as an alternative to the Fourier transform in the steady-state analysis of faulty conditions. It is found to be as effective as the Fourier transform and more amenable to short signal-measurement duration. Vibration analysis is applied in the detection of eccentricities; its efficacy in fault detection is hinged on proper determination of vibratory frequencies and quantification of corresponding tones. This is achieved using analytical formulations and signal processing techniques. Furthermore, the developed fault model is used to assess the influence of cogging torque minimization techniques and rotor topologies in axial-flux permanent magnet machine on current signal in the presence of static eccentricity. The double-sided topology is found to be tolerant to the presence of static eccentricity unlike the single-sided topology due to the opposing effect of the resulting asymmetrical properties of the airgap. The cogging torque minimization techniques do not impair on the established fault detection technique in the single-sided topology. By applying electrical broadband impedance spectroscopy, interturn faults are diagnosed; a high frequency winding model is developed to analyse the impedance-frequency response obtained.
Open Access
Non-intrusive efficiency estimation of induction machines under various power supplies
(2013) Gajjar, Chetan Sudhir; Khan, Azeem; Barendse, Paul Stanley
Considering that 45% of the world's generated electricity is consumed by induction machines, determining an induction motors efficiency non-intrusively is of great importance in that it enables the machine to operate productively whilst ensuring that the energy consumed by the machine is utilized efficiently. International efficiency testing methods such as the IEEE 112-B can determine a motors efficiency accurately at the cost of hindering the machines productivity. Alternatively, various methods used to determine a machines efficiency in-situ do so at the cost of accuracy. This research proposes a method that determines an induction machines efficiency over a range of load conditions from tests conducted and centered around one thermally stable load point in the least intrusive manner possible. Coupled with vibration sensors used to determine a motor's speed, measured input voltages and currents are used to deduce a machine efficiency-load profile through the use of a modified evolutionary algorithm, the Non-Intrusive Efficiency Estimation using Population-Based Incremental Learning(NIEE-PBIL) algorithm. Five temporal load measurements are taken, centered around one thermally stable load point, to determine the machines efficiency profile from two equivalent circuit implementations; the Standard Circuit NIEE-PBIL and the Iron-Loss NIEE-PBIL.
Open Access
Non-intrusive efficiency estimation of induction machines
(2010) Herndler, Barbara Linda; Barendse, Paul Stanley; Khan, Mohamed Azeem
Determining the efficiency of an in-service motor requires the motor to be decoupled from its load or the use of highly specialised equipment which is often unavailable on site. In order to assess the efficiency of an induction machine, it is subjected to numerous testing procedures established by recognised international testing standards. These procedures are considered to be time consuming, manually intensive and disruptive to the machine’s operation. Also, the efficiency of the machine quoted after these laboratory tests often does not reflect the motor’s efficiency under operating conditions. This thesis aims to address the aforementioned concerns by implementing a non-intrusive efficiency estimation technique that is applicable to induction motors in industry.
Open Access
Power management of a 1kW HTPEMFC based CHP system
(2011) Reddy, Direshni; Barendse, Paul Stanley
There is a growing interest in fuel cell technology for portable, stationary and transportation applications. This is driven by the need for a greener and more fuel efficient energy generation source. Fuel cells are electrochemical energy generating devices, which require natural gas for the production of electrical and thermal power, simultaneously.
Open Access
Single stage boost inverter for standalone fuel cell applications
(2015) Moraka, Otshepeng Johny; Barendse, Paul Stanley; Khan, Mohamed Azeem
The proton exchange membrane fuel cell (PEMFC) is a promising technology that can be manufactured in South Africa because of the platinum catalyst required. South Africa is rich in platinum and, therefore, the PEMFC system can be cost-effectively produced. In residential stationary applications of the PEMFC a power conditioning system is required to convert the de voltage output of the PEMFC to ac voltage. Therefore, the focus of this thesis is to analyse, simulate and design a power electronic dc-ac converter. The power electronic dc-ac converter is based on a transformerless single stage power conversion scheme, which has better weight, volume and efficiency than the commonly used two stage power conversion schemes. The selected topology is the boost inverter that consists of two identical boost converters for boosting and inversion of the PEMFC de voltage. Moreover, it achieves reliable operation under nonlinear loads, sudden load changes and inrush current, using a double loop control strategy. Initially, the double loop control strategy was introduced with proportional integral (Pl) controllers. Recently, with the widespread use of proportional resonant PR controllers, the PI controllers were replaced with PR controllers to achieve zero steady state error for the ac components of the reference. However, during the implementation of the PR controllers on the boost inverter, a significant de offset in the output voltage of the boost inverter was observed, which was due to the mismatch of the boost converters' parameters. The de voltage affects pulsating torque AC machines, accuracy in domestic watt-meter and safety of residual current protection. Furthermore, the output voltages of the boost converters showed a clipping effect, which was caused by the dead time of the switching devices used in the boost converters. An integral term was added to the PR controller to form the controller here called the proportional integral resonant (PIR) controller. This controller achieved satisfactory results of de and ac voltage reference following capability and maintains the same advantages of the PI controllers. However, the efficiency was not high due to the high resistance of the inductor used in the boost inverter system.