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    5 - L-26 (SSG) (Pe) ( (Ee) Nptel)

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    5_L-26(SSG)(PE) ((EE)NPTEL)

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    5 - L-26 (SSG) (Pe) ( (Ee) Nptel)

    Uploaded by

    Chark
    14 views1 page
    5_L-26(SSG)(PE) ((EE)NPTEL)

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    5_L-26(SSG)(PE) ((EE)NPTEL)

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    © © All Rights Reserved

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    5_L-26(SSG)(PE) ((EE)NPTEL)

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    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    14 views1 page

    5 - L-26 (SSG) (Pe) ( (Ee) Nptel)

    Uploaded by

    Chark
    5_L-26(SSG)(PE) ((EE)NPTEL)

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    of 1

    Fig. 26.

    3 The rms output voltage and the most important harmonics versus triggering
    angle α.

    As is evident from the current waveforms, the PAC introduces significant harmonics both into
    the load and the supply. This is one of the main reasons why such controllers are today not
    acceptable. The ideal waveform as shown in Fig 26.2 is half wave symmetric. However it is to be
    achieved by the trigger circuits. The controller in Fig. 26.4 ensures this for the TRIAC based
    circuit. While the TRIAC has a differing characteristic for the two polarities of biasing with the
    32V DIAC - a two terminal device- triggering is effected when the capacitor voltage reaches 32
    V. This ensures elimination of DC and even components in the output voltage.

    Fig. 26.4 DIAC based trigger circuit for a TRIAC to ensure symmetrical triggering
    in the two halves of the supply.
    For the SCR based controllers, identical comparators for the two halves of the AC supply, which
    generates pulses for the two SCRs ensures DC and even harmonic free operation.
    The PAC operates with a resistive load for all values of α ranging from 0o

    The fundamental current, if can be represented as

    2V ⎡ α sin 2α 1 cos 2α
    if = ⎢ ( π− + ) sin ωt − ( − ) cos ωt ⎤⎥ 26.1
    Rπ ⎣ 2 2 2 2 ⎦

    In machine drives it is only the fundamental component, which is useful. However, in


    resistance heating type of application all harmonics are of no consequence. The corrupted supply
    current nevertheless is undesirable.

    Version 2 EE IIT, Kharagpur 5

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