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Electric Power Applications, IEE Proceedings B

Issue 3 • Date May 1990

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Displaying Results 1 - 6 of 6
  • GTO thyristor and bipolar transistor cascode switches

    Publication Year: 1990 , Page(s): 141 - 153
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1000 KB)  

    The switching performance of both the bipolar transistor and gate turn-off thyristor is improved when used in a cascode switch configuration. `Snubberless' turn-off occurs without second breakdown and the technique results in shorter saturation delay times, faster current fall and higher operational sustaining voltages than obtained with conventional switching techniques. Improved switching performance is traded for increased drive circuit complexity and an increased on-state power loss associated with two series connected power semiconductor switches. The circuit techniques features and performance of two 720 V DC, 320 A cascode switches are presented. The bipolar transistor cascode switch is tested up to 100 kHz, whereas tail current power loss limits the GTO thyristor cascode switch to 16 kHz View full abstract»

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  • Capacitance requirement for isolated self-excited induction generator

    Publication Year: 1990 , Page(s): 154 - 159
    Cited by:  Papers (16)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (380 KB)  

    Advanced knowledge of the minimum capacitor value required for self-excitation of an induction generator is of practical interest. To find this capacitor value two nonlinear equations have to be solved. Different numerical methods for solving these equations are known from previous literature. However, these solutions involve some guessing in a trial-and-error procedure. A new simple and direct method is developed to find the capacitance requirement under RL load. Exact values are derived for the minimum capacitance required for self-excitation and the output frequencies under no-load, inductive and resistive loads. These calculated values can be used to predict theoretically the minimum value of the terminal capacitance required for self-excitation. For stable operation C must be chosen to be slightly greater than Cmin. Furthermore, it is found that there is a speed threshold, below which no excitation is possible no matter what the capacitor value. This threshold is called the cut-off speed. Expressions for this speed under no-load and inductive load are also given View full abstract»

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  • Comments on `Power components in a system with sinusoidal and nonsinusoidal voltages and/or currents' [and reply]

    Publication Year: 1990 , Page(s): 194 - 196
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (264 KB)  

    Two separate comments are made on the resistive load paradox in the paper by M.A. Slonim and J.D. Van Wyk (see ibid., vol.135, no.2, p.76-84 (1988)). The authors of the paper reply to these comments View full abstract»

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  • Transient currents and torques in wound-rotor induction motors using the finite-element method

    Publication Year: 1990 , Page(s): 160 - 173
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (972 KB)  

    The authors describe a time-stepping finite-element technique for modelling transient torques and currents in a slip-ring induction motor. The method is based on a coupled fields and circuit equation approach that allows the winding inductances to be modified to account for certain three-dimensional effects. The numerical solution incorporates a moving rotor so that slotting and saturation effects can be modelled accurately. The method is verified by direct comparison with experimental results obtained from a motor subjected to a supply reconnection at speed. It is shown that the general method can be extended in a straightforward manner to accommodate cage induction motors View full abstract»

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  • Performance and design of an electromagnetic sensor for brushless DC motors

    Publication Year: 1990 , Page(s): 174 - 183
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (916 KB)  

    The electromagnetic position sensing device described operates both at standstill and running speeds by detecting the phase change of the second harmonic component of induced voltage in pick-up coils around a stator of magnetically nonlinear material. The magnetic circuit associated with each pick-up coil is excited by a high frequency sinusoidal current and has a magnetic bias that is switched by the position of a simple magnet attached to the rotor of the machine. Results are presented from a prototype device and signal processing is considered to the point where three logic position signals are available, as in Hall effect units. An analytical treatment of the device is given such that geometrical optimisation is possible View full abstract»

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  • Analysis of variable-voltage thyristor controlled induction motors

    Publication Year: 1990 , Page(s): 184 - 193
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (720 KB)  

    A full analysis is presented of the steady-state performance of a variable-voltage thyristor controlled induction motor system, based on the representation of the rotor as a sinusoidal EMF in series with a resistance-inductance circuit. In the development of this circuit, magnetising current and stator resistance are included and the amplitude and phase of the EMF are determined as functions of motor torque and speed. This enables the full performance of the system to be evaluated for any of three specified conditions: current hold-off angle and speed, thyristor firing angle and speed, torque and speed. Good agreement is shown between computed and measured performance of an industrial drive system. The analysis reveals the influence of motor EMF, which is shown to improve system performance, particularly at small slips View full abstract»

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