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Online ISSN 1752-1424 Print ISSN 1752-1416

IET Renewable Power Generation

Volume 5, Issue 4, July 2011

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Volume 5, Issue 4

July 2011

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    • Fault ride through capability enhancement for self-excited induction generator-based wind parks by installing fault current limiters
      • Author(s): M.S. El-Moursi
      • Source: IET Renewable Power Generation, Volume 5, Issue 4, p. 269 –280
      • DOI:  10.1049/iet-rpg.2010.0123
      • Type: Article
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      • p. 269 –280 (12)
        This study presents a new technique for improving the fault ride through (FRT) capability of self-excited induction generator (SEIG)-based wind parks by implementing fault current limiters (FCLs) using the electromagnetic transient program simulation program (PSCAD/EMTDC). A non-inductive high-temperature superconducting coil of an FCL is developed comprising its major components, operation control algorithm, sequence of events and fault detection techniques. The test system is adopted with an integrated 80 MW SEIG-based wind park that comprises a static synchronous compensator (STATCOM) at each wind turbine. A novel damping voltage control algorithm for the STATCOM is presented for improving the FRT and damping the power system oscillation. FCLs are installed in series with the high voltage (HV) side of the substation transformers of the wind park. The operation of the FCLs is tested in the proposed system to demonstrate its superior performance for reducing the high fault currents and improving the FRT capability. The system performance is tested in steady-state operation and in response to system contingencies, taking into account the impact of the short circuit ratios on the transient stability margin with and without FCLs. Thereafter, the simulation results are presented to demonstrate the effectiveness of installing the FCLs for improving the FRT and transient stability margin of the wind park.
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      Comparison of direct maximum power point tracking algorithms using EN 50530 dynamic test procedure
      • Author(s): T. Andrejašič ; M. Jankovec ; M. Topič
      • Source: IET Renewable Power Generation, Volume 5, Issue 4, p. 281 –286
      • DOI:  10.1049/iet-rpg.2010.0175
      • Type: Article
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      • p. 281 –286 (6)
        Three direct maximum power point tracking (MPPT) algorithms with non-adaptive voltage step are evaluated in the light of their performance for photovoltaic systems under dynamic conditions for a resistive load. A microcontroller-based buck–boost DC–DC converter platform is used to implement and compare the algorithms. Dynamic test procedures from a new standard for inverter efficiency determination EN 50530 were implemented to evaluate dynamic MPPT algorithms’ efficiency and their dependence.Experimental results show that MPPT algorithms’ regulating frequency and regulating voltage step play a crucial role in the dynamic performance of direct algorithms. A range of regulating frequencies and voltage steps were examined. If proper parameter values are chosen, all algorithms perform well and close to each other. Detailed evaluation was performed with determining partial MPPT efficiency under different irradiance slopes. Results show that at least 10 Hz should be used to satisfy the 99% tracking efficiency over all slopes in the range from 0.5 to 100 W/m2/s as specified by EN 50530 standard. Further increase of regulating frequency would result in higher slope efficiency only at dynamic conditions.
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      Foundation-based flow acceleration structures for marine current energy converters
      • Author(s): J. Giles ; L. Myers ; A. Bahaj ; J. O'Nians ; B. Shelmerdine
      • Source: IET Renewable Power Generation, Volume 5, Issue 4, p. 287 –298
      • DOI:  10.1049/iet-rpg.2009.0181
      • Type: Article
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      • p. 287 –298 (12)
        This study presents a preliminary experimental study investigating the potential benefits of foundation-based flow acceleration structures for marine current energy converters (MCECs). Such structures would provide multiple benefits, including; increased device power output, increased foundation footprint and scour protection. Two phases of experimental testing have been conducted. The first series of tests investigated the flow acceleration caused by a ramp foundation without the presence of a MCEC. They were scaled from a shallow tidal flow site and provide evidence that these structures could give power benefits of 12–25% depending on ramp size and flow depth. An optimum ramp size was established based on the suitability of the vertical velocity profiles for energy extraction. The second phase of testing modelled a commercial marine current energy convertor with a gravity-based ramp foundation. The device was modelled using actuator plates to represent the interaction between the device and the surrounding flow field. A proposed single-operation installation method using a concrete ramp foundation is proposed and preliminary stability calculations are presented.
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      Unsteady wake modelling for tidal current turbines
      • Author(s): T. McCombes ; C. Johnstone ; A. Grant
      • Source: IET Renewable Power Generation, Volume 5, Issue 4, p. 299 –310
      • DOI:  10.1049/iet-rpg.2009.0203
      • Type: Article
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      • p. 299 –310 (12)
        The authors present a numerical model for three-dimensional unsteady wake calculations for tidal turbines. Since wakes are characterised by the shedding of a vortex sheet from the rotor blades, the model is based on the vorticity transport equations. A vortex sheet may be considered a jump contact discontinuity in tangential velocity with, in inviscid hydrodynamic terms, certain kinematic and dynamic conditions across the sheet. The kinematic condition is that the sheet is a stream surface with zero normal fluid velocity; the dynamic condition is that the pressure is equal on either side of the sheet. The dynamic condition is explicitly satisfied at the trailing edge only, via an approximation of the Kutta condition. The shed vorticity is the span-wise derivative of bound circulation, and the trailed vorticity is the time derivative of bound circulation, and is convected downstream from the rotors using a finite-volume solution of vorticity transport equations thus satisfying the kinematic conditions. Owing to an absence in the literature of pressure data for marine turbines, results from the code are presented for the NREL-UAE Phase IV turbine. Axial flow cases show a close match in pressure coefficients at various spanwise stations; however, yawed flow cases demonstrate the shortcomings of a modelling strategy lacking viscosity.
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      Dispersed generation units providing system ancillary services in distribution networks by a centralised control
      • Author(s): A. Bracale ; R. Angelino ; G. Carpinelli ; M. Mangoni ; D. Proto
      • Source: IET Renewable Power Generation, Volume 5, Issue 4, p. 311 –321
      • DOI:  10.1049/iet-rpg.2009.0189
      • Type: Article
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      • p. 311 –321 (11)
        This study considers a distribution system with a number of dispersed generation (DG) units interconnected to the AC grid through power electronic interfaces. Some selected DG units were able to provide energy service and system ancillary services (in particular, voltage regulation and partial compensation or elimination of some power quality disturbances, such as waveform distortions and voltage unbalances) through a proper centralised control system that provides the reference signals to the converters of the DG units in real time. In addition, the problem of time delays owing to data acquisition and digital signal processing for reference signal calculations and the effects of these delays on compensation actions were studied. Several time-domain simulations of an actual distribution system are reported, taking into account different DG units and time-delay scenarios.
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