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1 – 10 of 217Grzegorz Iwanski, Piotr Pura, Tomasz Łuszczyk and Mateusz Szypulski
Doubly fed induction generator (DFIG) is widely used in wind energy conversion systems and it can operate with other primary movers. The purpose of this paper is to focus on the…
Abstract
Purpose
Doubly fed induction generator (DFIG) is widely used in wind energy conversion systems and it can operate with other primary movers. The purpose of this paper is to focus on the standalone operation of DFIG which may expand the area of possible applications and increase capabilities of the generation system in terms of power quality.
Design/methodology/approach
Synthesis of the control method was preceded by analysis of mathematical model of the machine. The control method based on the negative sequence and high harmonics extraction has been developed and verified in the laboratory unit. Control of the fundamental frequency component uses neither rotor speed nor position sensors.
Findings
The original method allows to compensate negative sequence and high harmonics of the generated voltage. At the same time, due to the active filtering capability of the grid side converter, the stator phase current shape is close to sine wave. Thus, it is seen by the machine as a linear load, what eliminates the electromagnetic torque ripples.
Practical implications
The system and control method can be applied in variable speed generation systems, e.g. wind turbines or diesel engines operating in the standalone mode.
Originality/value
Although the selective compensation of negative sequence and harmonics are known in the literature, until now the methods have been verified for the system with a rotor position sensor. Moreover, the stator current feed-forward improving the transient properties, as well as results of transient states caused by the load step change, have not been proposed in publications.
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Khurshid Hafiz, Gaurav Nanda and Narayan C. Kar
In order to assess the performance of an induction generator in standalone wind power application, it is imperative that mathematical models are developed that accurately…
Abstract
Purpose
In order to assess the performance of an induction generator in standalone wind power application, it is imperative that mathematical models are developed that accurately represent the system and take into account various electromagnetic influences such as skin effect. The purpose of this paper is to utilize mathematical models to study the transient and steady‐state behaviour of the self‐excited induction generator (SEIG), in one case with an aluminum rotor, in another case, with a copper rotor, under various load conditions while taking the above factor into account.
Design/methodology/approach
Mathematical models of a SEIG in the d‐q axis frame have been developed based on the generalized machine theory. A relationship between the mutual inductance and the magnetizing current of the machine has been presented. The rotor impedances have been customized to include skin effect. Using these relations, the model has been extended to include the saturation and skin effects. In order to verify the accuracy of the models, numerical and experimental investigations have been carried out on two 7.5 hp aluminum‐rotor and copper‐rotor SEIGs.
Findings
It was found that the model that takes into account the saturation and skin effects produces numerical results that closely match experimental values for both the machines.
Originality/value
This paper describes how a model of an SEIG considering saturation and skin effect has been developed and applied to aluminum‐ and copper‐rotor machines of similar power ratings to analyze their performance.
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Olubayo Moses Babatunde, Damilola Elizabeth Babatunde, Iheanacho Henry Denwigwe, Toyosi Beatrice Adedoja, Oluwaseye Samson Adedoja and Taiwo Emmanuel Okharedia
This study aims to analyze the effects of variations in annual real interest rates in the assessment of the techno-economic feasibility of a hybrid renewable energy system (HRES…
Abstract
Purpose
This study aims to analyze the effects of variations in annual real interest rates in the assessment of the techno-economic feasibility of a hybrid renewable energy system (HRES) for an off-grid community.
Design/methodology/approach
Hybrid Optimization of Multiple Energy Resources (HOMER) software is used to propose an HRES for Abadam community in northern Nigeria. The HRES was designed to meet the basic needs of the community over a 25-year project lifespan. Based on the available energy resources in the community, photovoltaic (PV), wind turbine, diesel generator and battery were suggested for integration to serve the load requirements.
Findings
When the annual real interest rates were taken as 10 and 8 per cent, the total amount of total energy fraction from PV, wind turbine and the diesel generator is 28, 57 and 15 per cent, respectively. At these interest rates, wind turbines contributed more energy across all months than other energy resources. The energy resource distribution for 0, 2,4 and 6 per cent annual real interest rates have a similar pattern, but PV contributed a majority of the energy.
Practical implications
This study has used annual real interest and inflation rates dynamic behavior to determine optimal HRES for remote communities. Hence, its analysis will equip decision-makers with the necessary information for accurate planning.
Originality/value
The results of this study can be used to plan and design HRES infrastructure for off-grid communities around the world.
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Roberto Eduardo Quintal-Palomo, Maciej Gwozdziewicz and Mateusz Dybkowski
The purpose of this paper is to obtain an accurate methodology for modelling and analysis of the permanent magnet synchronous generator connected to power electronic components.
Abstract
Purpose
The purpose of this paper is to obtain an accurate methodology for modelling and analysis of the permanent magnet synchronous generator connected to power electronic components.
Design/methodology/approach
This paper presents the methodology of the co-simulation of a permanent magnet synchronous generator. It combines Simulink, Maxwell and Simplorer software to demonstrate the electrical machine behaviour connected with the power electronics’ circuit. The finite element analysis performed on the designed machine exhibit a more accurate behaviour over simplified Simulink models. Results between both simulation and co-simulation are compared to measurements.
Findings
The co-simulation approach offers a more accurate depiction of the machine behaviour and its interaction with the non-linear circuits.
Research limitations/implications
This paper focuses on the interior permanent magnet type of PMSG and its interaction with a passive rectifier (nonlinear circuit).
Practical implications
The advanced capabilities of the co-simulation method allow to analyse more variations (geometry, materials, etc.), and its interaction with non-linear circuits, than previous simulation techniques.
Originality/value
The co-simulation as a tool for analysis and design of systems interconnected with unconventional and conventional electrical machines and prototypes, and the comparison of the obtained results with classical analysis and design methods, against measurements obtained from the prototype.
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Edson Mbedzi and Forget Mingiri Kapingura
Infrastructure deficiency and supply disruption challenges are quite common among developing economies. While Sub-Saharan Africa is not unique to these challenges, it is the…
Abstract
Purpose
Infrastructure deficiency and supply disruption challenges are quite common among developing economies. While Sub-Saharan Africa is not unique to these challenges, it is the extent of levels of infrastructure deficiency and disruptions that affect the level of performance of small businesses. Literature on the performance of small businesses suggests both infrastructure availability and disruptions affect the performance of small businesses, but the effects on informal enterprises that operate from locations where the supply of infrastructure is weak are less documented. The paper, therefore, investigates the effects of four types of infrastructure supply in two dimensions of availability and disruption levels on the performance of informal enterprises in 12 Sub-Saharan African countries.
Design/methodology/approach
The study uses data from World Bank informal enterprises surveys based on a sample of 3 735 informal enterprises. The study uses the multiple analysis of variance method based on the World Bank's Informal Enterprise Surveys (IFS) country-level cross-sectional data collected between 2009 and 2019.
Findings
Results show infrastructure supply is quite low irrespective of the form of infrastructure. Infrastructure availability is associated with high supply disruptions. Infrastructure supply deficiency and disruption intensities are negatively associated with informal enterprises' performance. Finally, the effects of both infrastructure availability and supply disruptions are positively associated with informal enterprises' business activity levels.
Research limitations/implications
Due to data limitations, only four types of infrastructure are captured in the analysis. A wider variety of types of infrastructure could improve the analysis.
Originality/value
Given the deficiency level of infrastructure and its implications on informal enterprise development, therefore, policy interventions aiming at addressing informal enterprises' challenges should focus on improving infrastructure supply deficiencies and disruption challenges. This paper provides the link between infrastructure levels, infrastructure supply disruptions and performance of the informal enterprises which is an essential starting point for policy intervention in informal enterprise development.
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The paper aims to present an application of teaching learning-based optimization (TLBO) algorithm and static Var compensator (SVC) to improve the steady state and dynamic…
Abstract
Purpose
The paper aims to present an application of teaching learning-based optimization (TLBO) algorithm and static Var compensator (SVC) to improve the steady state and dynamic performance of self-excited induction generators (SEIG).
Design/methodology/approach
The TLBO algorithm is applied to generate the optimal capacitance to maintain rated voltage with different types of prime mover. For a constant speed prime mover, the TLBO algorithm attains the optimal capacitance to have rated load voltage at different loading conditions. In the case of variable speed prime mover, the TLBO methodology is used to obtain the optimal capacitance and prime mover speed to have rated load voltage and frequency. The SVC of fixed capacitor and controlled reactor is used to have a fine tune in capacitance value and control the reactive power. The parameters of SVC are obtained using the TLBO algorithm.
Findings
The whole system of three-phase induction generator and SVC are established under MatLab/Simulink environment. The performance of the SEIG is demonstrated on two different ratings (i.e. 7.5 kW and 1.5 kW) using the TLBO algorithm and SVC. An experimental setup is built-up using a 1.5 kW three-phase induction machine to confirm the theoretical analysis. The TLBO results are matched with other meta heuristic optimization techniques.
Originality/value
The paper presents an application of the meta-heuristic algorithms and SVC to analysis the steady state and dynamic performance of SEIG with optimal performance.
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Roland Ryndzionek, Michal Michna, Filip Kutt, Grzegorz Kostro and Krzysztof Blecharz
The purpose of this paper is to provide an analysis of the performance of a new five-phase doubly fed induction generator (DFIG).
Abstract
Purpose
The purpose of this paper is to provide an analysis of the performance of a new five-phase doubly fed induction generator (DFIG).
Design/methodology/approach
This paper presents the results of a research work related to five-phase DFIG framing, including the development of an analytical model, FEM analysis as well as the results of laboratory tests of the prototype. The proposed behavioral level analytical model is based on the winding function approach. The developed DFIG model was used at the design stage to simulate the generator’s no-load and load state. Then, the results of the FEM analysis were shown and compared with the results of laboratory tests of selected DFIG operating states.
Findings
The paper provides the results of analytical and FEM simulation and measurement tests of the new five-phase dual-feed induction generator. The use of the MATLAB Simscape modeling language allows for easy and quick implementation of the model. Design assumptions and analytical model-based analysis have been verified using FEM analysis and measurements performed on the prototype. The results of the presented research validate the design process as well as show the five-phase winding design advantage over the three-phase solution regarding the control winding power quality.
Research limitations/implications
The main disadvantage of the winding function approach-based model development is the simplification regarding omitting the tangential airgap flux density component. However, this fault only applies to large airgap machines and is insignificant in induction machines. The results of the DFIG analyses were limited to the basic operating states of the generator, i.e. the no-load state, the inductive and resistive load.
Practical implications
The novel DFIG with five phase rotor control winding can operate as a regular three-phase machine in an electric power generation system and allows for improved control winding power quality of the proposed electrical energy generation system. This increase in power quality is due to the rotor control windings inverter-based PWM supply voltage, which operates with a wider per-phase supply voltage range than a three-phase system. This phenomenon was quantified using control winding current harmonic analysis.
Originality/value
The paper provides the results of analytical and FEM simulation and measurement tests of the new five-phase dual-feed induction generator.
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As the number of citation management tools including Refworks and EndNote increased in recent years, academic libraries struggle to remain on top of new developments and support…
Abstract
Purpose
As the number of citation management tools including Refworks and EndNote increased in recent years, academic libraries struggle to remain on top of new developments and support all of the tools used by their users. This paper seeks to address these issues.
Design/methodology/approach
A librarian at the University of Illinois surveyed graduate students and faculty about which tools they use, reasons for tool adoption, features that influence adoption, and support they expect from their library.
Findings
The results highlight that many users still use older tools including EndNote and RefWorks, but do have interests for and reasons to use new tools including Zotero and Mendeley and may not need as much library support as librarians believe.
Originality/value
This is the first research paper on citation management use and can influence what products libraries use and the support they offer.
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Guoda Wang, Ping Li, Yumei Wen and Zhichun Luo
Existing control circuits for piezoelectric energy harvesting (PEH) suffers from long startup time or high power consumption. This paper aims to design an ultra-low power control…
Abstract
Purpose
Existing control circuits for piezoelectric energy harvesting (PEH) suffers from long startup time or high power consumption. This paper aims to design an ultra-low power control circuit that can harvest weak ambient vibrational energy on the order of several microwatts to power heavy loads such as wireless sensors.
Design/methodology/approach
A self-powered control circuit is proposed, functioning for very brief periods at the maximum power point, resulting in a low duty cycle. The circuit can start to function at low input power thresholds and can promptly achieve optimal operating conditions when cold-starting. The circuit is designed to be able to operate without stable DC power supply and powered by the piezoelectric transducers.
Findings
When using the series-synchronized switch harvesting on inductor circuit with a large 1 mF energy storage capacitor, the proposed circuit can perform 322% better than the standard energy harvesting circuit in terms of energy harvested. This control circuit can also achieve an ultra-low consumption of 0.3 µW, as well as capable of cold-starting with input power as low as 5.78 µW.
Originality/value
The intermittent control strategy proposed in this paper can drastically reduce power consumption of the control circuit. Without dedicated cold-start modules and DC auxiliary supply, the circuit can achieve optimal efficiency within one input cycle, if the input signal is larger than voltage threshold. The proposed control strategy is especially favorable for harvesting energy from natural vibrations and can be a promising solution for other PEH circuits as well.
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