Online ISSN
1752-1424
Print ISSN
1752-1416
IET Renewable Power Generation
Volume 5, Issue 1, January 2011
Volumes & issues:
Volume 5, Issue 1
January 2011
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- Author(s): L. Ran ; M.A. Mueller ; C. Ng ; P.J. Tavner ; H. Zhao ; N.J. Baker ; S. McDonald ; P. McKeever
- Source: IET Renewable Power Generation, Volume 5, Issue 1, p. 1 –9
- DOI: 10.1049/iet-rpg.2009.0125
- Type: Article
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This study describes the power conversion and control solution used in the electrical power take-off of a 35 kW test rig developed to investigate a linear, direct drive, air-cored, tubular, permanent magnet generator for an offshore wave energy device. The solution proposed is to collect the power extracted directly from individual coils of the generator, which have different induced voltages and cannot easily be connected into a small number of phases. Local energy storage is integrated into the system to smooth the electrical output power and reduce the rating of the downstream inverter for grid interfacing. The solution is demonstrated by analysis, backed up by simulation and test results. This shows the potential and limitations of the proposed conversion technology solution. - Author(s): P. Igic ; Z. Zhou ; W. Knapp ; J. MacEnri ; H.C. Sørensen ; E. Friis-Madsen
- Source: IET Renewable Power Generation, Volume 5, Issue 1, p. 10 –17
- DOI: 10.1049/iet-rpg.2009.0090
- Type: Article
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Considerations of the electrical system configuration and the control strategy for the wave dragon (WD) multi-megawatt (MW) offshore wave energy converter (WEC) are presented in this study. The electrical system consists of 16–20 turbine–generator–AC/DC/AC converter units. The characteristics of the low-head water-turbine and generator control strategy enabling maximum energy capture and the best performance for the MW offshore wave energy power take-off system are described in detail. Simulation results from a single turbine–generator–frequency converter unit at different turbine heads are presented at the end of the study. - Author(s): S.Z. Chen ; N.C. Cheung ; K.C. Wong ; J. Wu
- Source: IET Renewable Power Generation, Volume 5, Issue 1, p. 18 –25
- DOI: 10.1049/iet-rpg.2009.0021
- Type: Article
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This study proposes a novel integral variable structure direct torque control (IVS-DTC) scheme for a doubly fed induction generator (DFIG). The proposed scheme directly controls the torque and reactive power of the DFIG with rotor winding voltage, and hence no extra current control loops are required. Uncertainties in the parameters are included in the design procedure, which guarantees the robustness of the system. Compared to conventional direct torque control (DTC) scheme, the constant switching frequency in the proposed scheme does not introduce low-frequency sub-harmonics. Both computer simulation and hardware implementation results show that proposed scheme has satisfactory parametric robustness and generated power quality. - Author(s): M.H. Albadi and E.F. El-Saadany
- Source: IET Renewable Power Generation, Volume 5, Issue 1, p. 26 –35
- DOI: 10.1049/iet-rpg.2009.0101
- Type: Article
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Although wind power is a sustainable, environmentally friendly and a viable option for renewable energy in many places, the effects of its intermittent nature on power systems need to be carefully examined. This study investigates the effects of different wind profiles on the scheduling costs of thermal generation units. Two profiles are considered: synoptic-dominated and diurnal-dominated variations of aggregated wind power. To simulate the wind profile impacts, a linear mixed integer unit commitment problem is formulated in a general algebraic modelling system (GAMS) environment. The uncertainty associated with wind power is represented using a chance constrained formulation. The simulation results illustrate the significant impacts of different wind profiles on fuel saving benefits, startup costs and wind power curtailments. In addition, the results demonstrate the importance of the wide geographical dispersion of wind power production facilities to minimise the impacts of network constraints on the value of the harvested wind energy and the amount of curtailed energy. - Author(s): H. Zhou ; G. Yang ; J. Wang ; H. Geng
- Source: IET Renewable Power Generation, Volume 5, Issue 1, p. 36 –47
- DOI: 10.1049/iet-rpg.2009.0171
- Type: Article
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This study presents the control method for a new hybrid high-voltage dc (HVDC) connection for large wind farms with doubly fed induction generators (DFIGs). The hybrid HVDC system consists of a line-commutated converter plus a static synchronous compensator (STATCOM) on the rectifier side and a pulse-width modulation (PWM) current source inverter (CSI) on the inverter side. The overall control strategy is divided into three parts, where the STATCOM subsystem supports the island bus voltage; the rectifier subsystem delivers the active power generated by the wind farm; and the CSI subsystem injects the active power – as well as reactive power, if necessary – to the grid. Taking into account the non-linear and coupling characteristics of each subsystem, a series of control schemes is proposed: for the STATCOM subsystem, a state feedback linearisation and decoupling method is employed; for the rectifier subsystem, a double-loop controller is designed and its inner loop is based on the inverse-system control techniques; for the CSI subsystem, independent active and reactive power control scheme is proposed. Through Simulink/SimPowerSystems simulations on a representative hybrid HVDC system, the startup process is demonstrated and system performances under both normal and fault conditions are investigated. - Author(s): V. Peesapati ; I. Cotton ; T. Sorensen ; T. Krogh ; N. Kokkinos
- Source: IET Renewable Power Generation, Volume 5, Issue 1, p. 48 –57
- DOI: 10.1049/iet-rpg.2008.0107
- Type: Article
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Latest wind turbine lightning protection systems have been refined to the point where lightning damage is now relatively rare. This is increasingly important as wind turbines move offshore where access for maintenance is more difficult than for most land-based wind farms. Manufacturers have been trying to make sure that the lightning protection systems they install comply with the highest protection levels stipulated in the relevant IEC standards. In this study, data from the Nysted Offshore Wind farm in Denmark and that from a large number of other wind turbines worldwide is reviewed to show the range of lightning currents that have been measured on wind turbines currently in operation. These current values are compared with the required protection levels within the standards. - Author(s): J. Zhu ; R. Bründlinger ; T. Mühlberger ; T.R. Betts ; R. Gottschalg
- Source: IET Renewable Power Generation, Volume 5, Issue 1, p. 58 –66
- DOI: 10.1049/iet-rpg.2009.0162
- Type: Article
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Inverters are typically sized based on guidelines. These do not consider the specifics of a maritime climate as seen in the UK, i.e. a high percentage of diffuse irradiance, fast moving weather fronts and a smaller variation in inter-seasonal module operating temperatures compared to continental climates. The existing UK-guidelines are shown to be sub-optimal. A more appropriate sizing methodology is presented. The first influence considered is the sampling rate. It is shown that high irradiances are underestimated in hourly models, resulting in a significant skewing in the inverter sizing. The use of datasets with time resolutions higher than 10 minutes is recommended to avoid this effect in the future. Variations of module operating temperature influence the DC voltages achieved by systems. It is shown that neglecting this in the sizing might result in several percent reduced annual output. The presented model considers the voltage dependence of the inverter efficiency which is affected by the temperature induced variation of the DC voltage. Different inverters are assessed and it is shown that no general rule of thumb can be given as the sizing depends strongly on the detailed inverter characteristics. - Author(s): A. Abedini and H. Nikkhajoei
- Source: IET Renewable Power Generation, Volume 5, Issue 1, p. 67 –78
- DOI: 10.1049/iet-rpg.2009.0123
- Type: Article
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This study presents a wind conversion system with integrated energy storage and dispatchable output power. The energy storage acts as an auxiliary source to mitigate the wind power fluctuations and to follow the load demand changes. A control strategy is developed which manages the flow of power among the wind-turbine generator, the energy storage and the grid. A dynamic model for the overall wind conversion system is developed. A controller is designed systematically for the wind conversion system based on the developed dynamic model. Performance of the system in various modes of operation is evaluated based on digital time-domain simulations in the power simulink (PSIM) software environment. - Author(s): Y.M. Atwa and E.F. El-Saadany
- Source: IET Renewable Power Generation, Volume 5, Issue 1, p. 79 –88
- DOI: 10.1049/iet-rpg.2009.0011
- Type: Article
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Recent development in small renewable/clean generation technologies such as wind turbines, photovoltaic, fuel cells, microturbines and so on has drawn distribution utilities' attention to possible changes in the distribution system infrastructure and policy by deploying distributed generation (DG) in distribution systems. In this study, a methodology has been proposed for optimally allocating wind-based DG units in the distribution system so as to minimise annual energy loss. The methodology is based on generating a probabilistic generation–load model that combines all possible operating conditions of the wind-based DG units and load levels with their probabilities, hence accommodating this model in a deterministic planning problem. The planning problem is formulated as mixed integer non-linear programming (MINLP), with an objective function for the system's annual energy losses minimise. The constraints include voltage limits at different buses (slack and load buses) of the system, feeder capacity, discrete size of the DG units, maximum investment on each bus, and maximum penetration limit of DG units. This proposed technique is applied to a typical rural distribution system and compared to the traditional planning technique (constant output power of DG units and constant peak load profile). - Author(s): A. Salehi-Dobakhshari and M. Fotuhi-Firuzabad
- Source: IET Renewable Power Generation, Volume 5, Issue 1, p. 89 –98
- DOI: 10.1049/iet-rpg.2008.0110
- Type: Article
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This study intends to develop a comprehensive procedure for evaluating locational value of a wind farm project incorporating reduction in transmission system losses, load delivery point interruption cost and operating cost of generating units. The energy extracted from the wind farm in normal operation condition is considered to replace the energy from fossil-fueled conventional units. In addition, composite system reliability analysis in the presence of wind power is carried out to evaluate total costs associated with curtailed energy at different load points as well as generation of generating units in contingency conditions. System reliability analysis related to large-scale wind farms, along with operating cost and transmission losses analysis, can assist policy makers to prioritise wind farm projects based on the total benefits of wind power including reliability benefits and savings in fossil-fueled energy sources. - Author(s): H.-B. Zhang ; J. Fletcher ; N. Greeves ; S.J. Finney ; B.W. Williams
- Source: IET Renewable Power Generation, Volume 5, Issue 1, p. 99 –108
- DOI: 10.1049/iet-rpg.2009.0207
- Type: Article
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This study presents a new operating scheme for variable speed wind/tidal stream turbines employing synchronous generators. Current maximum power tracking schemes for variable speed wind energy conversion systems rely on periodic comparison of the output power for guiding the direction of maximum power tracking or an online algorithm which continuously provides a generator torque/speed reference corresponding to the maximum power status at different wind speed conditions. The proposed scheme utilises only one-power-point on the maximum power curve. Once the information for the maximum power status of a local wind speed is known, then the wind energy conversion system implements maximum power tracking and constant power control for different wind speed conditions using simple control. The operation strategy is applicable to tidal stream turbines. Simulation results demonstrate the concept.
Power conversion and control for a linear direct drive permanent magnet generator for wave energy
Multi-megawatt offshore wave energy converters – electrical system configuration and generator control strategy
Integral variable structure direct torque control of doubly fed induction generator
Comparative study on impacts of wind profiles on thermal units scheduling costs
Control of a hybrid high-voltage DC connection for large doubly fed induction generator-based wind farms
Lightning protection of wind turbines – a comparison of measured data with required protection levels
Optimised inverter sizing for photovoltaic systems in high-latitude maritime climates
Dynamic model and control of a wind-turbine generator with energy storage
Probabilistic approach for optimal allocation of wind-based distributed generation in distribution systems
Integration of large-scale wind farm projects including system reliability analysis
One-power-point operation for variable speed wind/tidal stream turbines with synchronous generators
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