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Electric Power Applications, IEE Proceedings -

Issue 5 • Date Sep 1994

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Displaying Results 1 - 7 of 7
  • Negative-phase-sequence reduction with adjacent static reactive-power compensators

    Page(s): 259 - 263
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (320 KB)  

    Static reactive power (VAr) compensators (SVCs) can be used to reduce negative phase sequence (NPS) voltages by balancing, for example, phase-to-phase-connected loads. In such cases, they are effective until their controlled elements, usually thyristor-controlled reactors, reach their operating limits. Once this happens, NPS currents flow in the system and produce NPS voltages. If several load balancing SVCs are located in close electrical proximity, adjacent load balancing SVCs are able to absorb some of this uncompensated NPS current, reducing the overall NPS voltage profile. The mutual support thus provided should be considered when designing the ranges of such load balancing SVCs. The paper describes how to quantify the mutual support in a system with multiple load balancing SVCs View full abstract»

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  • Damper windings in synchronous machines fed by a current-source inverter

    Page(s): 229 - 234
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (316 KB)  

    The mathematical model of an inverter-fed synchronous machine which permits detailed analysis of the behaviour of the damper winding is described. The effects of the damper winding on the steady-state characteristics of the inverter-fed synchronous-machine, especially on the torque ripple and commutation behaviour, are examined. It is shown that the damper winding has relatively little effect on the torque and overload capability View full abstract»

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  • Static VAr compensator with fully controlled reactors

    Page(s): 264 - 268
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (264 KB)  

    A novel configuration for a static VAr compensator (of fundamental harmonic reactive power) is proposed. The compensator operates by controlling coupled reactors through force-commutated switches. The compensator is compared with traditional systems and its specific advantages, including cost factors, are discussed View full abstract»

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  • Optimal-current control of convertor-fed DC motors. I. Special case for continuous current with negligible resistance

    Page(s): 240 - 248
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (552 KB)  

    The paper describes a new method of firing control for a three-phase thyristor bridge supplying a DC motor in both motoring and regenerating modes. The method uses the firing points as the sampling instants and the `cusp current' at these instances as the controlled variable. For continuous-current operation, the method enables the current to be changed from one steady-state level to another in two thyristor firings (6.6 ms). The paper provides the theoretical analysis on which the method is based and, assuming the resistance to be negligible, derives an algorithm for control implementation. The paper gives examples of current waveforms for transient changes in current obtained from computer simulations, an equivalent zero-resistance practical circuit and a DC motor. The results verify the theoretical predictions View full abstract»

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  • Losses in PWM inverters using IGBTs

    Page(s): 235 - 239
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (264 KB)  

    The aim of this paper is to calculate the forward and switching losses of a PWM inverter employing IGBTs using a relatively simple method from manufacturers' catalogue parameters, that is, finding a reasonable compromise between accuracy and complexity. The system will be able to calculate losses for different modulation methods, provided the current output is sinusoidal. Part of the results can be used for other devices, such as bipolar transistors or MOSFETs View full abstract»

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  • Highly stable power supply using digitally controlled phase-controlled rectifier and active filter

    Page(s): 221 - 228
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (492 KB)  

    A design of a highly stable current-controlled power supply combining a phase controlled rectifier (PCR), passive filter and active filter is investigated. A digital phase-locked voltage control (PLVC) with a capability of compensating the thyristor firing angles under an unbalanced power source is proposed; otherwise the PCR output voltage has low-order subharmonics whose suppression requires a bulky passive filter. The digital PLVC has a fast dynamic characteristic as an inner control loop of the PCR. To suppress further the output ripple, an active filter using a transformer is introduced and its design is described through a frequency-domain analysis. An optimal, proportional and measurable-variable feedback (IPM) controller is designed using a time-weighted performance index based on a time-domain analysis. The design method based on the time-weighted performance index gives a better response characteristic than that based on the conventional performance index. It is shown via experimental results that the proposed scheme gives good dynamic and static performance View full abstract»

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  • Optimal-current control of convertor-fed DC motors. II. General case

    Page(s): 249 - 258
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (616 KB)  

    For pt. I see ibid., vol.141, no.5, p. 240-8. (1994). In this paper a new method of firing control for a three-phase thyristor bridge supplying a DC motor in both monitoring and regenerating modes is described. The method uses the firing points as the sampling instants and the `cusp current' at these instances as the controlled variable. For continuous-current operation, the method enables the current to be changed from one steady-state level to another in two thyristor firings (6.6 ms). The method developed in Part I is extended to apply to normal systems with motor or DC-link resistance present and shows that basically the same continuous-current-control algorithm may be used. It also presents an improved method for current control with discontinuous currents which permits rapid changes and reversals of current to be achieved. Examples of waveforms of step-current changes and reversals are provided for a 3.5 kW practical system operating under microprocessor control. Frequency-response tests up to 90 Hz showed that the current-control dynamic response is equivalent to a finite time delay of 5.2 ms with constant unity gain View full abstract»

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