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Online ISSN 1751-8679 Print ISSN 1751-8660

IET Electric Power Applications

Volume 6, Issue 4, April 2012

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Volume 6, Issue 4

April 2012

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    • Output voltage control of synchronous generator using diode and thyristor excitation structures combined with multivariable H∞ controllers
      • Author(s): A. Barakat ; S. Tnani ; G. Champenois ; E. Mouni
      • Source: IET Electric Power Applications, Volume 6, Issue 4, p. 203 –213
      • DOI:  10.1049/iet-epa.2011.0013
      • Type: Article
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      • p. 203 –213 (11)
        In this study, the authors present a comparison between two excitation structures. The first one consists of a diode bridge rectifier connected to a wound field synchronous machine. In the second structure, the diode bridge is replaced by a thyristor one. A multi-input single-output (MISO) H∞ voltage controller is designed for each structure. The proposed controllers take into account the modeling of each structure and permit to guarantee the system stability during the sudden variation of the load connected to the terminal of the main synchronous machine. The performance of each structure is evaluated by experimental tests in the presence of unknown variations of the power system operating conditions. The results show the great efficiency of the thyristor excitation structure combined with the MISO H∞ controller as regards the response time, the voltage drop and the voltage overshoot.
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      Automatic procedure for induction motor parameter estimation at standstill
      • Author(s): L. Peretti  and  M. Zigliotto
      • Source: IET Electric Power Applications, Volume 6, Issue 4, p. 214 –224
      • DOI:  10.1049/iet-epa.2010.0262
      • Type: Article
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      • p. 214 –224 (11)
        The study presents a self-commissioning procedure for the automatic parameter estimation of three-phase induction motor drives. The procedure consists of a step-by-step approach with different test signals to obtain the parameter values while maintaining the motor at standstill. The actual implementation is capable of mapping both inverter and motor parameters non-linearities, providing accurate data for the tuning of common current regulators and for advanced sensorless drives as well. Theoretical and experimental results are provided, proving the effectiveness of the procedure.
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      Characterisation of internal incipient faults in transformers during impulse test using index based on S matrix energy and standard deviation
      • Author(s): A. Ashrafian ; M.S. Naderi ; G.B. Gharehpetian
      • Source: IET Electric Power Applications, Volume 6, Issue 4, p. 225 –232
      • DOI:  10.1049/iet-epa.2011.0257
      • Type: Article
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      • p. 225 –232 (8)
        In this study, the application of S-transform with a frequency-dependent window is proposed for distinguishing internal incipient faults in transformers. The S-transform is applied to the recorded input current waveforms during the impulse test. Then, time–frequency contours of the S matrix are plotted and a suggested index is computed, accordingly. Faulty and healthy windings can be discriminated using time–frequency contours and proposed decision index. A 66-kV/25-MVA interleaved transformer winding is modelled in a MATLAB environment, also an arc discharge model is used and the effectiveness of the proposed method is studied. Laboratory tests are performed on this transformer winding and the performance of the method in noisy environments is investigated. According to the laboratory test and simulation results, it can be said that the suggested S-transform-based method is capable of detecting incipient faults conveniently.
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      Model reduction of transformer detailed R-C-L-M model using the imperialist competitive algorithm
      • Author(s): V. Rashtchi ; E. Rahimpour ; H. Shahrouzi
      • Source: IET Electric Power Applications, Volume 6, Issue 4, p. 233 –242
      • DOI:  10.1049/iet-epa.2011.0331
      • Type: Article
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      • p. 233 –242 (10)
        Detailed R-C-L-M model of power transformers is based on lumped parameters. This model is used extensively not only for transient analysis inside transformers but also for transient study in power systems. Simulating transformers by means of the detailed R-C-L-M is very time-consuming because of the large number of model parameters. Consequently, models with fewer parameters are more practical for system studies. This study aims at introducing a model reduction technique for detailed R-C-L-M model and parameter identification of reduced models based on the imperialist competitive algorithm. The accuracy of the resulting models is verified by comparing the measured transfer function of high-voltage transformer with those obtained from the imperialist competitive algorithm and common analytical formulae.
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      Implicit position and speed estimation algorithm without the flux computation for the rotor side control of doubly fed induction motor drive
      • Author(s): A. Karthikeyan ; C. Nagamani ; A.B. Ray Chaudhury ; G.S. Ilango
      • Source: IET Electric Power Applications, Volume 6, Issue 4, p. 243 –252
      • DOI:  10.1049/iet-epa.2010.0286
      • Type: Article
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      • p. 243 –252 (10)
        A simple and implicit sensorless algorithm for estimating the rotor position and speed of the doubly fed induction machine is proposed in this study. Instead of computing the stator magnetic flux directly or indirectly, the stator flux vector components in the stationary reference frame are substituted with analytical equivalents in terms of measurable stator and rotor quantities. Thus, it is an implicit estimation process devoid of computing any flux terms and requires only the measured stator voltage and currents in stator and rotor windings apart from knowledge of the machine parameters. It is an open-loop scheme. However, it does not involve integration, recursive techniques, re-computations or programmable low-pass filters etc. Starting on the fly, accurate estimation near synchronous speed, immunity against variation in stator and rotor resistances or in the magnetising inductance are the principal advantages of the algorithm. Reduced complexity and the computational burden facilitate the easy implementation of the algorithm on a low-cost fixed point processor. Excellent agreement between the simulation and test results on a laboratory doubly fed induction motor validates the proposed estimation algorithm implemented for the vector control of a doubly fed induction motor. On the whole, the estimation algorithm is a new insight that holds promise in the area of sensorless control of the DFIM, whether used as a motor or as a generator.
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