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    Ch4 3-Phase Full-Wave AC Voltage Controllers

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    smithprajapati.el21
    1) The document discusses three-phase full-wave AC voltage controllers with resistive loads. It describes the firing sequence of thyristors and operating modes based on the firing delay angle. 2) The controller can operate in three modes depending on the firing delay angle: two or three thyristors conducting (0° ≤ α < 60°), two thyristors in each phase conducting (60° ≤ α < 90°), and one or two thyristors conducting (90° ≤ α < 150°). 3) Expressions are derived for the output voltage, current, power, and input power factor in terms of the firing delay angle, line voltage, and

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    Ch4 3-Phase Full-Wave AC Voltage Controllers

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    smithprajapati.el21
    32 views28 pages
    1) The document discusses three-phase full-wave AC voltage controllers with resistive loads. It describes the firing sequence of thyristors and operating modes based on the firing delay angle. 2) The controller can operate in three modes depending on the firing delay angle: two or three thyristors conducting (0° ≤ α < 60°), two thyristors in each phase conducting (60° ≤ α < 90°), and one or two thyristors conducting (90° ≤ α < 150°). 3) Expressions are derived for the output voltage, current, power, and input power factor in terms of the firing delay angle, line voltage, and

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    1) The document discusses three-phase full-wave AC voltage controllers with resistive loads. It describes the firing sequence of thyristors and operating modes based on the firing delay angle. 2) The controller can operate in three modes depending on the firing delay angle: two or three thyristors conducting (0° ≤ α < 60°), two thyristors in each phase conducting (60° ≤ α < 90°), and one or two thyristors conducting (90° ≤ α < 150°). 3) Expressions are derived for the output voltage, current, power, and input power factor in terms of the firing delay angle, line voltage, and

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    32 views28 pages

    Ch4 3-Phase Full-Wave AC Voltage Controllers

    Uploaded by

    smithprajapati.el21
    1) The document discusses three-phase full-wave AC voltage controllers with resistive loads. It describes the firing sequence of thyristors and operating modes based on the firing delay angle. 2) The controller can operate in three modes depending on the firing delay angle: two or three thyristors conducting (0° ≤ α < 60°), two thyristors in each phase conducting (60° ≤ α < 90°), and one or two thyristors conducting (90° ≤ α < 150°). 3) Expressions are derived for the output voltage, current, power, and input power factor in terms of the firing delay angle, line voltage, and

    Copyright:

    © All Rights Reserved
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    of 28

    Chapter 4

    Three-phase full-wave
    AC voltage controllers
    By
    Dr. Ayman Yousef
    Three-phase full-wave
    AC voltage controllers
    with resistive load
    Three-Phase
    Full-Wave AC Voltage Controller
    (Three-Wire, Star-Connected Load)

    l The neutral of the supply is not


    connected to the neutral of the load.
    l The firing sequance of thyristors is T1 ,
    T2 , T 3 , T 4 , T 5 , T 6 .
    l The gate-control circuit must be capable
    of triggering at the same instant two
    thyristor, one in each of two phases.
    l These pulses are applied at intervals of
    60° to various thyristors in a sequence
    the same as that of the supply voltage.

    l The current flow to the load is controlled by the thyristors T1, T3 and T5 and the
    thyristors T2, T4 and T6 provide the return current path.

    Power Electronics II
    Dr. Ayman Yousef
    Three-Phase
    Full-Wave AC Voltage Controller

    Power Electronics II
    Dr. Ayman Yousef
    Three-Phase
    Full-Wave AC Voltage
    Controller

    l At any interval, either three SCRs or two SCRs, or no SCRs may be ON (conduct)

    l If three SCRs conduct, a normal three-phase operation occurs and the output (load)
    phase voltage (van) is the same as the input (supply) phase voltage (v AN)

    l If two SCRs conduct, the current flows only through two lines and the third line is
    open-circuited, and the output phase voltage (v an)

    l If no SCRs conduct, the output phase voltage becomes zero.


    Three-Phase
    full-Wave AC Voltage Controller

    l Mode (0° ≤ α < 60° ) in this mode of operation, either two or three thyristors can
    conduct at the same time.
    l
    l Mode (60° ≤ α < 90° ) in this mode of operation, at any time two thyristors, one in
    each phase, always conduct.

    l For (90° ≤ α < 150° ) in this mode of operation, at any time one or two thyristors
    conduct at the same time.

    Power Electronics II
    Dr. Ayman Yousef
    3-Phase full-Wave
    AC Voltage Controller
    Mode (0° ≤ α < 60° )

    Power Electronics II
    Dr. Ayman Yousef
    Switching Pattern of 3-Phase half-Wave
    AC Voltage Controller

    l For (0° ≤ α < 60° )


    In this mode of operation, either two or three thyristors can conduct
    at the same time.

    Power Electronics II
    Dr. Ayman Yousef
    Switching Pattern
    of 3-Phase full-
    Wave AC Voltage
    Controller at
    (α = 30˚ )

    5 5 6 6 1 1 2 2 3 3 4 4
    6 6 1 1 2 2 3 3 4 4 5 5
    1 2 3 4 5 6

    Power Electronics II
    Dr. Ayman Yousef
    Output voltage waveform
    for three-phase, star-
    connected, three-wire full-
    wave AC voltage controller
    (α =30˚).
    3-Phase full-Wave
    AC Voltage Controller
    Mode (60° ≤ α < 90° )

    Power Electronics II
    Dr. Ayman Yousef
    Switching Pattern of 3-Phase Half-Wave
    AC Voltage Controller

    l Mode (60° ≤ α < 90° )


    In this mode of operation, at any time two thyristors, one in each
    phase, always conduct.

    Power Electronics II
    Dr. Ayman Yousef
    Switching Pattern
    of 3-Phase Full-
    Wave AC Voltage
    Controller at
    (α = 75˚ ).

    5 5 6 6 6 1 1 1 2 2 2 3 3 3 44 4
    6 1 1 2 2 3 3 4 4 5 5

    Power Electronics II
    Dr. Ayman Yousef
    Output voltage waveform
    for three-phase, star-
    connected, three-wire full-
    wave AC voltage controller
    (α =75˚).
    3-Phase full-Wave
    AC Voltage Controller
    Mode (90° ≤ α < 150° )

    Power Electronics II
    Dr. Ayman Yousef
    Switching Pattern of 3-Phase Half-Wave
    AC Voltage Controller

    l Mode (90° ≤ α < 150° )


    In this mode of operation, at any time one or two thyristors conduct
    at the same time.

    Power Electronics II
    Dr. Ayman Yousef
    Switching Pattern
    of 3-Phase Full-
    Wave AC Voltage
    Controller at
    (α = 120˚ ).

    4 5 5 6 6 1 1 2 2 3 3 4
    5 6 1 2 3 4

    Power Electronics II
    Dr. Ayman Yousef
    Output voltage waveform
    for three-phase, star-
    connected, three-wire full-
    wave AC voltage controller
    (α =120˚).
    Analysis of three-phase
    Full-wave AC voltage controller
    with resistive load
    RMS value of the output voltage
    l The expressions of the rms value
    of the output voltage per phase
    for balanced star-connected
    resistive load are as follows:
    RMS output voltage at:
    RMS output voltage at:
    RMS output voltage at:
    Analysis of three-phase Full-wave AC voltage
    controller with resistive load
    Mode I ( also known as Mode 2/3): (0° ≤ α < 60° )

    Mode II ( also known as Mode 2/2): (60° ≤ α < 90° )

    Mode III ( also known as Mode 0/2): (90° ≤ α < 150° )


    Analysis of three-phase
    Full-wave AC voltage controller
    with resistive load
    RMS Output current

    Where: Io = Ia is the Output


    (load) current in phase (a)

    Output power

    Input VA rating

    Supply power factor


    Ex .1: The three-phase bidirectional controller supplies a wye-
    connected resistive load of 10 Ω /phase and the line-to-line input voltage
    is 380-V, 50 Hz. The firing delay angle is 30° .
    (a) Draw the output phase voltage waveform.
    (b) Drive the output phase voltage expression.
    (b) Determine the rms output phase voltage and current.
    (b) Determine the input power factor.
    Solution
    VL= 380v fs = 50 Hz R = 10 ohm α = 30o

    Mode (1)
    Firing angle range
    (0° ≤ α < 60° )

    Power Electronics II
    Dr. Ayman Yousef
    The expression for the instantaneous output phase
    voltage, van, the positive half-cycle is:

    The rms value of the output phase voltage


    (Vo) can be derived as follows:
    RMS Output current

    Output power
    Input VA rating

    Supply power factor

    Exercise:
    (a) Repeat the previous example for α = 75° and 120°.
    (b) Derive two general expressions for the rms output phase voltage for mode
    (Π ) and mode (III).

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