DC Choppers and Converters
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Questions and Answers

What type of switches are GTO, BJT, MOSFET, MCT, IGBT, and IGCT?

  • Partially-controlled switches
  • Uncontrolled switches
  • Semi-controlled switches
  • Fully controlled switches (correct)

    • Which of the following is a First Quadrant converter?

  • Three-phase controlled rectifier
  • Step-down choppers
  • Diode rectifier (correct)
  • AC controller

    • What is the range of the average output voltage Vo,dc in a step-down chopper?

  • 0 to Vi
  • -Vi to +Vi (correct)
  • Vi to 2Vi
  • -Vi to 0

    • What are the two parameters of the control function in fully controlled switches?

    <p>Tsw and d</p> Signup and view all the answers

    What is the quadrant of operation when vo is positive and io is negative?

    <p>Second Quadrant</p> Signup and view all the answers

    What are the most common fully controlled switches used presently?

    <p>MOSFET and IGBT</p> Signup and view all the answers

    What is the range of the magnitude control ratio M?

    <p>0 ≤ M ≤ 1</p> Signup and view all the answers

    What is the expression for the output current Io,dc in terms of the input voltage Vi, magnitude control ratio M, and resistance R?

    <p>(MVi - E)/R</p> Signup and view all the answers

    What is the condition for the inductor current to be approximated to a constant?

    <p>The inductor current is approximated to a constant</p> Signup and view all the answers

    What is the expression for the current ripple ΔIo in terms of the input voltage Vi, magnitude control ratio M, switching frequency Ts, and inductance L?

    <p>M(1-M)TsVi/L</p> Signup and view all the answers

    What is the quadrant of operation of the chopper in Example 1?

    <p>Quadrant I</p> Signup and view all the answers

    What is the value of the average output voltage of the chopper in Example 1?

    <p>80 V</p> Signup and view all the answers

    What is the value of the AC component of the armature current in Example 1?

    <p>0.5 A</p> Signup and view all the answers

    What is the ripple factor of the output voltage in Example 1?

    <p>0.2</p> Signup and view all the answers

    What is the magnitude control ratio, M, defined as?

    <p>Vo,d/Vi</p> Signup and view all the answers

    What is the differential equation of the load in terms of the output current?

    <p>L(di_o/dt) + Ri_o + E = Vo</p> Signup and view all the answers

    What is the general form of the solution to the differential equation of the load?

    <p>i_o(t) = (Vo-E)/R + i_o(to) e^(-(R/L)(t-to))</p> Signup and view all the answers

    What is the expression for the output voltage of the chopper in terms of the periodic binary switching variable x1?

    <p>Vo = x1 Vi</p> Signup and view all the answers

    What is the duty ratio of switch S1, denoted by?

    <p>d1</p> Signup and view all the answers

    What is the expression for the average output voltage, Vo,dc, in terms of the duty ratio d1?

    <p>Vo,dc = d1 Vi</p> Signup and view all the answers

    What is the range of the magnitude control ratio, M, for a 1st Quadrant Chopper?

    <p>0 &lt; M &lt;= 1</p> Signup and view all the answers

    What is the physical significance of the duty ratio, d1, in the context of the chopper circuit?

    <p>It represents the fraction of time for which the switch S1 is ON</p> Signup and view all the answers

    Study Notes

    DC Choppers

    • Fully controlled switches include: GTO, BJT, MOSFET, MCT, IGBT, IGCT, and others
    • The most common ones are MOSFET and IGBTs

    Control Function

    • The control function has two parameters: Tsw (switching period) and d (duty ratio)
    • d = Ton / Tsw, where Ton is the on-time of the switch

    Quadrant of Operation

    • Converter quadrant is identified by the polarity of output voltage and current
    • Four quadrants:
      • First Quadrant: vo and io are positive
      • Second Quadrant: vo is positive and io is negative
      • Third Quadrant: vo and io are negative
      • Fourth Quadrant: vo is negative and io is positive

    Step-Down Choppers

    • The average output voltage, Vo,dc, depends linearly on the duty ratio of the chopper switches
    • The magnitude control ratio, M, is defined as Vo,dc / Vi
    • Vo,dc can be adjusted in the range of -Vi to +Vi

    Output Current

    • The differential equation of the load is: L(di/dt) + Ri + E = vo
    • The output current has a general solution of the form: io(t) = (vo - E) / R + (E - vo) / R * e^(-R(t-to) / L)

    First Quadrant Chopper

    • The output voltage can be expressed as: vo = x1 * Vi
    • The duty ratio, d1, is defined as: d1 = Ton / Tsw

    Output Voltage and M Range

    • The average output voltage, Vo,dc, is: Vo,dc = d1 * Vi
    • The range of M is: E / Vi <= M <= 1, which implies d1,min = E / Vi

    Output Current Approximation

    • The output current can be approximated as: Io,dc = M * Vi / R
    • The current ripple, ΔIo, is: ΔIo = M(1 - M) * Tsw * Vi / L

    Example Problem

    • A step-down chopper with a magnitude control ratio of 0.4 operates a dc motor with an armature EMF of 70 V and armature resistance of 0.5 Ω
    • The average output voltage and current can be calculated using the formulas above
    • The AC component of the armature current and ripple factor of the current can be calculated using the approximate analysis formulas

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    Related Documents

    DC to DC Chopper PDF

    Description

    Learn about the different types of fully controlled switches and their applications in DC choppers, as well as the control function and quadrants of operation.

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