Online ISSN
1752-1424
Print ISSN
1752-1416
IET Renewable Power Generation
Volume 3, Issue 2, June 2009
Volumes & issues:
Volume 3, Issue 2
June 2009
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- Author(s): R. Majumder ; A. Ghosh ; G. Ledwich ; F. Zare
- Source: IET Renewable Power Generation, Volume 3, Issue 2, p. 109 –119
- DOI: 10.1049/iet-rpg:20080001
- Type: Article
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p.
109
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(11)
Control methods for proper load sharing between parallel converters connected in a microgrid and supplied by distributed generators (DGs) are described. It is assumed that the microgrid spans a large area and it supplies loads in both in grid-connected and islanded modes. A control strategy is proposed to improve power quality and proper load sharing in both islanded and grid-connected modes. It is assumed that each of the DGs has a local load connected to it which can be unbalanced and/or non-linear. The DGs compensate the effects of unbalance and non-linearity of the local loads. Common loads are also connected to the microgrid, which are supplied by the utility grid under normal conditions. However, during islanding, each of the DGs supplies its local load and shares the common load through droop characteristics. Both impedance and motor loads are considered to verify the system response. The efficacy of the controller has been validated through simulation for various operating conditions using PSCAD. It has been found through simulation that the total harmonic distortion (THD) of the microgrid voltage is ∼10% and the negative and zero sequence components are ∼20% of the positive sequence component before compensation. After compensation, the THD remains <0.5%, whereas negative and zero sequence components of the voltages remain <0.02% of the positive sequence component. - Author(s): M. Zhao ; Z. Chen ; F. Blaabjerg
- Source: IET Renewable Power Generation, Volume 3, Issue 2, p. 120 –132
- DOI: 10.1049/iet-rpg:20070094
- Type: Article
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p.
120
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A serial AC–DC integrated load flow algorithm for variable speed offshore wind farms is proposed. It divides the electrical system of a wind farm into several local networks, and different load flow methods are used for these local networks sequentially. This method is fast, more accurate, and many factors such as the different wind farm configurations, the control of wind turbines and the power losses of pulse width modulation converters are considered. The DC/DC converter model is proposed and integrated into load flow algorithm by modifying the Jacobian matrix. Two iterative methods are proposed and integrated into the load flow algorithm: one takes into account the control strategy of converters and the other considers the power losses of converters. In addition, different types of variable speed wind turbine systems with different control methods are investigated. Finally, the method is demonstrated using an 80-MW offshore wind farm. - Author(s): N.G. Jayanti ; M. Basu ; M.F. Conlon ; K. Gaughan
- Source: IET Renewable Power Generation, Volume 3, Issue 2, p. 133 –143
- DOI: 10.1049/iet-rpg:20080009
- Type: Article
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p.
133
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The ability of wind generation to remain connected to the grid in the event of system faults and dynamic reactive power compensation are two aspects of grid integration, which have received particular attention. The wind driven, fixed-speed induction generator (FSIG) on its own fails to fulfil these requirements of grid integration. The application of a unified power quality conditioner (UPQC) to overcome the grid integration problems of the FSIG is investigated. The role of the UPQC in enhancing the fault ride-through capability of the generator is also investigated under both full and partial terminal voltage restoration. A realistic estimation of the rating requirements of UPQC for this type of application is carried out. A general principle is presented to choose the most practical and economical rating of the UPQC. The performance comparison of a UPQC and a static synchronous compensator to aid fault ride-through capability of a 2 MW FSIG under Irish grid code requirements has been carried out and the UPQC is found to be more economical in relation to device rating. - Author(s): J.-C. Wu
- Source: IET Renewable Power Generation, Volume 3, Issue 2, p. 144 –151
- DOI: 10.1049/iet-rpg:20070100
- Type: Article
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p.
144
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A new AC/DC power conversion interface for the self-excited induction generator (SEIG) is proposed here. The proposed AC/DC conversion interface includes an excitation system and a diode rectifier connected in parallel. The variable frequency AC power generated by the SEIG is converted into DC power by the diode rectifier. The DC power of the diode rectifier can charge a battery set and supply DC loads or be further converted into fixed-frequency AC power by an inverter for AC loads. The DC voltage is expected to be regulated in the above applications. The excitation system supplies an exciting reactive current to maintain the amplitude of the SEIG output voltage to be a constant value. Moreover, it can also serve as an active power filter to suppress the harmonic current generated by the diode rectifier. The excitation system is composed of an AC power capacitor and a power converter connected in series. The AC power capacitor is adapted to provide a basic reactive power, and it can also reduce the voltage rating and the capacity of the power converter. The salient point of the proposed AC/DC power conversion interface is that the capacity of the power converter in the AC/DC power conversion interface can be minimised, and the power loss of the AC/DC power conversion interface can also be reduced. A prototype is developed and tested to verify the performance of the proposed AC/DC power conversion interface. - Author(s): T.-Y. Lee and C.-L. Chen
- Source: IET Renewable Power Generation, Volume 3, Issue 2, p. 152 –167
- DOI: 10.1049/iet-rpg:20070068
- Type: Article
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152
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As the capacity of wind and photovoltaic (PV) generation systems increases, wind-PV capacity coordination for a time-of-use (TOU) rate industrial user may become an important problem. This coordination can maximise the economic benefits of investing in a wind generation system and a PV generation system. An evolutionary particle swarm optimisation approach to solve the wind-PV capacity coordination for a TOU rate industrial user is proposed. A benefit-cost ratio (BCR) is used to evaluate the economic benefit of investing in wind and PV generation systems for a TOU rate industrial user. The optimal contract capacities and the optimal installed capacities of the wind and PV generation systems for a TOU rate industrial user are obtained. The BCR of investing in wind and PV generation systems are maximised. Test results illustrate the merits of the proposed approach and help determine the impact of changes in electricity cost and capital cost on wind-PV capacity coordination for a TOU rate industrial user. - Author(s): H. Geng and G. Yang
- Source: IET Renewable Power Generation, Volume 3, Issue 2, p. 168 –179
- DOI: 10.1049/iet-rpg:20070043
- Type: Article
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p.
168
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A robust pitch (RP) controller for variable-speed variable-pitch wind turbine generator systems (VSVP-WTGS) is presented. The controller can not only level the wind energy conversion but also be applicable in a wide wind speed region even subject to large parametric or non-parametric disturbances. VSVP-WTGS consists of multi-subsystems with different time scales. The dominant ‘slow’ dynamics are non-affine and high nonlinear. By considering ‘fast’ subsystems as perturbations to the ‘slow’ one, the dynamics of VSVP-WTGS can be represented by a nominal model and an error one. The RP controller is composed of a nominal inverse-system controller and a robust compensator. With the nominal inverse-system controller, the nominal closed-loop system can track its reference dynamics. With the robust compensator, turbine parameter uncertainties and non-parametric perturbations are tolerated. The performance of the RP controller is confirmed through theoretical analyses and computer simulations. Results show that RP controller can operate in a wider wind speed region robustly compared with a proportional-integral-derivative controller. Compared with other nonlinear controllers, the RP controller is simpler and can be more easily extended to other kinds of WTGS. - Author(s): P. Li ; P.-K. Keung ; B.-T. Ooi
- Source: IET Renewable Power Generation, Volume 3, Issue 2, p. 180 –189
- DOI: 10.1049/iet-rpg:20070093
- Type: Article
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p.
180
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The authors show that: (a) with reliable prediction of low variance in the wind velocity, modern wind farms have the wherewithal to produce regulated power in the next hour; (b) when the conditions for producing regulated power are not predicted, the wind farms may opt to use the tracking mode which tracks the slowly time-varying, non-turbulent component of wind power and (c) the proposed control system has the capability to divert some of the wind farm power to implement dynamic performance enhancement strategies, for system damping. The capabilities are demonstrated by simulations of a wind farm made up of 24 wind-turbine generators using one-hour-long wind velocity data. - Author(s): B.V. Mathiesen and H. Lund
- Source: IET Renewable Power Generation, Volume 3, Issue 2, p. 190 –204
- DOI: 10.1049/iet-rpg:20080049
- Type: Article
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p.
190
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An analysis of seven different technologies is presented. The technologies integrate fluctuating renewable energy sources (RES) such as wind power production into the electricity supply, and the Danish energy system is used as a case. Comprehensive hour-by-hour energy system analyses are conducted of a complete system meeting electricity, heat and transport demands, and including RES, power plants, and combined heat and power production (CHP) for district heating and transport technologies. In conclusion, the most fuel-efficient and least-cost technologies are identified through energy system and feasibility analyses. Large-scale heat pumps prove to be especially promising as they efficiently reduce the production of excess electricity. Flexible electricity demand and electric boilers are low-cost solutions, but their improvement of fuel efficiency is rather limited. Battery electric vehicles constitute the most promising transport integration technology compared with hydrogen fuel cell vehicles (HFCVs). The costs of integrating RES with electrolysers for HFCVs, CHP and micro fuel cell CHP are reduced significantly with more than 50% of RES. - Author(s): M. Zhao ; Z. Chen ; F. Blaabjerg
- Source: IET Renewable Power Generation, Volume 3, Issue 2, p. 205 –216
- DOI: 10.1049/iet-rpg:20070112
- Type: Article
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p.
205
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An optimisation platform based on genetic algorithm (GA) is presented, where the main components of a wind farm and key technical specifications are used as input parameters and the electrical system design of the wind farm is optimised in terms of both production cost and system reliability. The power losses, wind power production, initial investment and maintenance costs are considered in the production cost. The availability of components and network redundancy are included in the reliability evaluation. The method of coding an electrical system to a binary string, which is processed by GA, is developed. Different GA techniques are investigated based on a real example offshore wind farm. This optimisation platform has been demonstrated as a powerful tool for offshore wind farm design and evaluation. - Author(s): Y. Gao and R. Billinton
- Source: IET Renewable Power Generation, Volume 3, Issue 2, p. 217 –226
- DOI: 10.1049/iet-rpg:20080036
- Type: Article
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p.
217
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(10)
Wind power is an important renewable energy resource. Electrical power generation from wind energy behaves quite differently from that of conventional sources, and maintaining a reliable power supply is an important issue in power systems containing wind energy. In these systems, the wind speeds at different wind sites are correlated to some degree if the distances between the sites are not very large. Genetic algorithm methods are applied here to adjust autoregressive moving-average time series models in order to simulate correlated hourly wind speeds with specified wind speed cross-correlation coefficients of two wind sites. Multi-state wind energy conversion system models are used to incorporate the correlated wind farms in reliability studies of generating systems. A method to generate random numbers with specified correlation coefficients for application in a state-sampling Monte Carlo simulation technique is introduced. It is shown that the proposed method can be used in the adequacy assessment of a generating system incorporating partially dependent wind farms. - Author(s): A. Alarcon-Rodriguez ; E. Haesen ; G. Ault ; J. Driesen ; R. Belmans
- Source: IET Renewable Power Generation, Volume 3, Issue 2, p. 227 –238
- DOI: 10.1049/iet-rpg:20080045
- Type: Article
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p.
227
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The amount of distributed energy resources (DER) in the grid is continually increasing, and the potential benefits and drawbacks are becoming clearer. However, there is still a lack of clarity in how these multiple effects interact and which trade-offs should be made in the integration of new DER. There is a clear need for appropriate DER planning tools in the current market environment, in which both DER operators and distribution system operators (DSOs) may have multiple, often conflicting objectives and where uncertainty remains present as to which targets can be reached with a high amount of DER in the grid. A novel multi-objective planning framework is presented for the integration of stochastic and controllable DER in the distribution grid. A case study that illustrates the proposed framework is presented. Active DER management in terms of curtailment as well as dispatch of units is studied using the proposed multi-objective approach. Additionally, the extent to which active DER can be used as an alternative for grid reinforcements is analysed. The results show that the proposed multi-objective approach permits a better evaluation of the potential of active DER to support system operation. - Author(s): Syafaruddin ; E. Karatepe ; T. Hiyama
- Source: IET Renewable Power Generation, Volume 3, Issue 2, p. 239 –253
- DOI: 10.1049/iet-rpg:20080065
- Type: Article
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p.
239
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The one of main causes of reducing energy yield of photovoltaic systems is partially shaded conditions. Although the conventional maximum power point tracking (MPPT) control algorithms operate well under uniform insolation, they do not operate well in non-uniform insolation. The non-uniform conditions cause multiple local maximum power points on the power–voltage curve. The conventional MPPT methods cannot distinguish between the global and local peaks. Since the global maximum power point (MPP) may change within a large voltage window and also its position depends on shading patterns, it is very difficult to recognise the global operating point under partially shaded conditions. In this paper, a novel MPPT system is proposed for partially shaded PV array using artificial neural network (ANN) and fuzzy logic with polar information controller. The ANN with three layer feed-forward is trained once for several partially shaded conditions to determine the global MPP voltage. The fuzzy logic with polar information controller uses the global MPP voltage as a reference voltage to generate the required control signal for the power converter. Another objective of this study is to determine the estimated maximum power and energy generation of PV system through the same ANN structure. The effectiveness of the proposed method is demonstrated under the experimental real-time simulation technique based dSPACE real-time interface system for different interconnected PV arrays such as series-parallel, bridge link and total cross tied configurations. - Author(s): J. Fletcher ; T. Judendorfer ; M. Mueller ; N. Hassanain ; M. Muhr
- Source: IET Renewable Power Generation, Volume 3, Issue 2, p. 254 –264
- DOI: 10.1049/iet-rpg:20080083
- Type: Article
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p.
254
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For the majority of proposed wave- and tidal current-driven power generation applications, the electrical generators are submerged in sea water, frequently at many metres of depth. The environment places significant stress on the rotating or translating seals between the driven shaft and the electrical generator leading to reduced reliability and lifetime. A potential solution is to eliminate the seal, thereby flooding the generator and allowing sea water to circulate around the shaft, windings and rotor of the machine. The impact of immersing the windings of the machine in sea water is assessed here. Specifically, the impact that the insulation has on the leakage capacitance as well as the consequent impact the leakage capacitance has on current and voltage oscillations in the switching converter used to excite the winding is assessed. Thermal tests are conducted to assess the impact of the insulation on the thermal conductance of the coil–insulation system. Experimental evidence is provided.
Load sharing and power quality enhanced operation of a distributed microgrid
Load flow analysis for variable speed offshore wind farms
Rating requirements of the unified power quality conditioner to integrate the fixed-speed induction generator-type wind generation to the grid
AC/DC power conversion interface for self-excited induction generator
Wind-photovoltaic capacity coordination for a time-of-use rate industrial user
Robust pitch controller for output power levelling of variable-speed variable-pitch wind turbine generator systems
Development and simulation of dynamic control strategies for wind farms
Comparative analyses of seven technologies to facilitate the integration of fluctuating renewable energy sources
Optimisation of electrical system for offshore wind farms via genetic algorithm
Adequacy assessment of generating systems containing wind power considering wind speed correlation
Multi-objective planning framework for stochastic and controllable distributed energy resources
Artificial neural network-polar coordinated fuzzy controller based maximum power point tracking control under partially shaded conditions
Electrical issues associated with sea-water immersed windings in electrical generators for wave- and tidal current-driven power generation
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