Online ISSN
1752-1424
Print ISSN
1752-1416
IET Renewable Power Generation
Volume 5, Issue 5, September 2011
Volumes & issues:
Volume 5, Issue 5
September 2011
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- Author(s): H. Nian and R. Zeng
- Source: IET Renewable Power Generation, Volume 5, Issue 5, p. 323 –331
- DOI: 10.1049/iet-rpg.2010.0216
- Type: Article
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p.
323
–331
(9)
This study presents an improved control strategy for a distributed generation system under stand-alone mode. Since there is no grid supply in a stand-alone system, the output voltage has to be controlled in the constant amplitude and frequency by the load-side inverter under the unbalanced and non-linear loads. The mathematic model of the load-side inverter is described. The dual-loop control method based on the stationary αβ reference coordinate is used for the load-side inverter so that the coordinate transformation is not needed. The outer-loop voltage controller consists of a proportional controller and a resonant regulator tuned at low-order harmonic frequency to compensate for the low-order harmonic components of the output voltage. A predictive current control scheme based on space vector modulation is adopted in the inner-loop current controller to improve the transient performance under the sudden load disturbances. Finally, experiment studies are carried out on a 5 kW stand-alone generation system. The experiment results show the excellent output voltage performance under both the steady-state and dynamic process with the load-adaptive ability. - Author(s): Y. Cheng ; M. Sahni ; J. Conto ; S.-H. Huang ; J. Schmall
- Source: IET Renewable Power Generation, Volume 5, Issue 5, p. 332 –346
- DOI: 10.1049/iet-rpg.2010.0112
- Type: Article
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p.
332
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(15)
This paper presents a novel voltage-profile-based approach to develop collection system aggregated models for various WGR facilities to accurately represent their detailed counterparts from a steady state and dynamic voltage response standpoint. A customised automated module developed by the authors is utilised to develop detailed collector system models for WGR facilities accurately representing various aspects of the facility. Short-circuit analysis at the point of common coupling is utilised to obtain the fault-voltage profile at each turbine terminal within the WGR facility. The resulting voltage profile is utilised in conjunction with the under-voltage relay settings associated with the turbine type or types being employed at the facility to identify the number and nature of the groups comprising the aggregated model. Additional short-circuit analysis is performed at breakpoint buses to selectively identify the subnetwork equivalent impedance to represent the aggregated WGR models. The resulting collector system aggregated models are validated from a steady state and dynamic voltage response standpoint by comparison with their detailed counterparts. The paper also demonstrates the robustness of the proposed approach by means of application on different types of WGR facilities currently operational in the ERCOT system. Finally, the effectiveness of the approach is demonstrated performing dynamic simulations utilising the detailed and the aggregated collector system models on the ERCOT dynamic data set and performing comparative analysis on the response with and without the voltage relay models incorporated. - Author(s): M. Nick ; G.H. Riahy ; S.H. Hosseinian ; F. Fallahi
- Source: IET Renewable Power Generation, Volume 5, Issue 5, p. 347 –355
- DOI: 10.1049/iet-rpg.2010.0196
- Type: Article
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p.
347
–355
(9)
Wind power is site dependent and is by nature partially dispatchable. Furthermore, good wind sites are far from grid. Owing to these problems, and along with the existing limitations in the transmission networks, a comprehensive analysis over an extended time is needed to properly explore all potential wind sites for wind capacity allocation. This problem is computationally expensive and decomposition methods are required to break down this problem. Here Benders decomposition approach is used, which is a popular technique for solving large-scale problems, to decompose the original problem into a master and a subproblem. The master problem is a linear problem, which allocates wind capacity to each site and determines the transmission line capacity for connection to the grid. The subproblem is a mixed-integer problem and performs a year-long unit commitment accompanied with DC optimal load flow. The subproblem uses the solution of the master problem to form the appropriate cut, representing operation cost, for the next iteration of the master problem. This procedure is iterated until the optimal solution is found. The IEEE 24-bus test system is used to demonstrate the proposed method. Simulation results show that the maximum profit is gained when there is a trade-off between transmission cost and wind curtailment. It is shown that by using a proper wind capacity allocation, wind penetration into the system will be maximised. - Author(s): T. Niknam ; H.Z. Meymand ; H.D. Mojarrad ; J. Aghaei
- Source: IET Renewable Power Generation, Volume 5, Issue 5, p. 356 –367
- DOI: 10.1049/iet-rpg.2010.0190
- Type: Article
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p.
356
–367
(12)
Fuel cells are environmentally clean, have low emission of oxides of nitrogen and sulfur and, at the same time, they can operate with a very low level of noise. In addition, they can provide energy in a controlled way with higher efficiency compared to conventional power plants. This study presents an efficient multi-objective new fuzzy self adaptive particle swarm optimisation evolutionary algorithm to solve the multi-objective optimal operation management considering fuel cell power plants in the distribution network. The objective functions of the problem are to decrease the total electrical energy losses, the total electrical energy cost, the total pollutant emission and deviation of bus voltages. The proposed algorithm is tested on a real distribution test feeder and the results demonstrate the capabilities of the proposed approach to generate true and well-distributed Pareto-optimal non-dominated solutions. - Author(s): M. Mohseni ; S. Islam ; M.A.S. Masoum
- Source: IET Renewable Power Generation, Volume 5, Issue 5, p. 368 –376
- DOI: 10.1049/iet-rpg.2010.0154
- Type: Article
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p.
368
–376
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Recent fault ride-through (FRT) requirements have proven problematic for variable-speed wind generation systems. A particular problem regarding to doubly-fed induction generators (DFIGs) is that standard proportional integral (PI) current controllers, designed with very limited control bandwidth, cannot eliminate rotor current oscillations that occur during a grid fault. As a consequence, the current in the rotor-side converter can exceed the safety limits of semiconductor switches, which potentially leads to converter failure. This study introduces a hybrid current controller to enhance the FRT capability of DFIGs through keeping the rotor current below the safety limits. The proposed current controller includes two switching strategies: the standard PI current controller for normal operating conditions and a vector-based hysteresis current controller (with very fast transient response) for overcurrent protection during grid faults. Simulation studies are carried out to demonstrate the effectiveness of the proposed hybrid current controller under various symmetrical and asymmetrical voltage sag conditions. - Author(s): Y.Y. Xia ; J.E. Fletcher ; S.J. Finney ; K.H. Ahmed ; B.W. Williams
- Source: IET Renewable Power Generation, Volume 5, Issue 5, p. 377 –386
- DOI: 10.1049/iet-rpg.2010.0108
- Type: Article
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p.
377
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(10)
A conventional topology for a small-scale wind energy conversion system consists of a permanent magnet synchronous generator, a diode bridge rectifier, a boost converter and a grid-side inverter. Since generator phase currents contain low-order harmonics and cannot be controlled independently using a diode bridge rectifier, electromagnetic torque ripple is relatively large and may have a detrimental effect on the life of the turbine through fatigue induced by shaft torque ripple. This study investigates methods to reduce this electromagnetic torque ripple, from both the viewpoints of the circuit topology and the control strategy. The effect of the DC-side capacitor on torque ripple is investigated and different control strategies and their effect on torque ripple are compared and analysed. This shows that the torque ripple can be reduced by removing the DC-side capacitor and can be further reduced by controlling DC-side current to a constant value. These methods have been investigated theoretically and the validity of the results confirmed by both simulation and experiment. - Author(s): L. Wang ; J.-Y. Yu ; Y.-T. Chen
- Source: IET Renewable Power Generation, Volume 5, Issue 5, p. 387 –396
- DOI: 10.1049/iet-rpg.2010.0194
- Type: Article
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p.
387
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This study presents a control scheme using a flywheel energy-storage system (FESS) to simultaneously achieve power-fluctuation mitigation and dynamic-stability enhancement of an offshore wind farm (OWF) and marine-current farm (MCF) connected to a power grid. The performance of the studied OWF is simulated by an equivalent aggregated 80-MW doubly-fed induction generator (DFIG), while the characteristics of the studied MCF are simulated by an equivalent aggregated 40-MW squirrel-cage induction generator. A proportional–integral–derivative (PID) damping controller of the proposed FESS which is connected to the common AC bus of the OWF and MCF is designed by using modal control theory to contribute effective damping characteristics to the studied OWF and MCF under different operating conditions. A frequency-domain approach based on a linearised system model using eigenvalue analysis is performed. A time-domain scheme based on a non-linear system model subject to disturbance conditions is also carried out. It can be concluded from the simulation results that the proposed FESS combined with the designed PID damping controller can effectively stabilise the studied OWF and MCF under various disturbance conditions. The inherent power fluctuations injected to the power grid can also be effectively mitigated by the proposed control scheme. - Author(s): S. Hazra and P. Sensarma
- Source: IET Renewable Power Generation, Volume 5, Issue 5, p. 397 –405
- DOI: 10.1049/iet-rpg.2010.0168
- Type: Article
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p.
397
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This study presents a detailed investigation on self-excitation of a squirrel-cage induction generator (SCIG) used in a wind energy conversion system. Air-gap flux of the SCIG is gradually built up through controlled current injection from a voltage source converter (VSC), connected directly across its stator terminals. Dc voltage of the VSC is ramped from a small initial value, which is the rectified output of the small terminal voltage developed because of remanent magnetism. Increase in air-gap flux increases generator terminal voltage and output power which further increases the dc bus voltage. The field-oriented control method is appropriately applied both for control of voltage build-up as well as dynamic transients. The critical factors deciding this collaborative excitation are analysed and sufficient conditions are derived analytically. System modelling and analytical results are validated through numerical simulation and verified on a 2.2 kW laboratory prototype.
Improved control strategy for stand-alone distributed generation system under unbalanced and non-linear loads
Voltage-profile-based approach for developing collection system aggregated models for wind generation resources for grid voltage ride-through studies
Wind power optimal capacity allocation to remote areas taking into account transmission connection requirements
Multi-objective daily operation management of distribution network considering fuel cell power plants
Fault ride-through capability enhancement of doubly-fed induction wind generators
Torque ripple analysis and reduction for wind energy conversion systems using uncontrolled rectifier and boost converter
Dynamic stability improvement of an integrated offshore wind and marine-current farm using a flywheel energy-storage system
Vector approach for self-excitation and control of induction machine in stand-alone wind power generation
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