Power Electronics Switching
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Questions and Answers

What is the primary reason for turning off a switch shortly before the turn-on of the other switch in the same leg?

  • To reduce the load current
  • To decrease the voltage across the load
  • To increase the frequency of the output
  • To avoid a short circuit (correct)

    • What is the assumption made in the subsequent discussion about the dead time?

  • It is assumed to be infinite
  • It is assumed to be dependent on the load current
  • It is assumed to be zero (correct)
  • It is assumed to be a constant value

    • What is the characteristic of semiconductor switches in practice?

  • They have nonzero on-off time (correct)
  • They can operate at any frequency
  • They can handle any amount of load current
  • They have zero on-off time

    • What is the purpose of introducing a dead time in inverter circuits?

    <p>To avoid a short circuit</p> Signup and view all the answers

    What is the consequence of not introducing a dead time in inverter circuits?

    <p>A short circuit will occur</p> Signup and view all the answers

    What is the relationship between the switches SA and SB in an inverter circuit?

    <p>They are turned on and off alternately</p> Signup and view all the answers

    What is the switching state designated as?

    <p>ab2</p> Signup and view all the answers

    What is the role of SA and SB in the inverter circuit?

    <p>They are switching devices</p> Signup and view all the answers

    What is the condition when a = 1?

    <p>SA is turned on and SB is turned off</p> Signup and view all the answers

    What is the significance of 'a' and 'b' in the inverter circuit?

    <p>They are switching variables</p> Signup and view all the answers

    What is the load connected to in the inverter circuit?

    <p>Node A and Node B</p> Signup and view all the answers

    What is the purpose of the inverter circuit?

    <p>To convert DC to AC</p> Signup and view all the answers

    What is the relationship between 'a' and 'b' in the switching state 'ab2'?

    <p>a = 1 and b = 0</p> Signup and view all the answers

    What is the input voltage source in the inverter circuit?

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

    What is the term used to describe the process of a diode taking over conduction of current from another diode?

    <p>Natural commutation</p> Signup and view all the answers

    In a full-bridge 3-phase diode rectifier, what is the expression for the output current?

    <p>io = vo/R</p> Signup and view all the answers

    What is the condition for a line current to be equal to the DC side current?

    <p>The line upper diode is ON</p> Signup and view all the answers

    What is the expression for the power factor for a highly inductive load?

    <p>PF = cos(θ)</p> Signup and view all the answers

    What is the purpose of a diode in a full-bridge 3-phase diode rectifier?

    <p>To convert AC voltage to DC voltage</p> Signup and view all the answers

    What is the state of a line current when both line upper and lower diodes are OFF?

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

    What is the expression for the output voltage in a full-bridge 3-phase diode rectifier?

    <p>vo = vp - vn</p> Signup and view all the answers

    What is the condition for a line current to be equal to the negative of the DC side current?

    <p>The line lower diode is ON</p> Signup and view all the answers

    What is the purpose of a 3-phase diode rectifier?

    <p>To convert AC voltage to DC voltage</p> Signup and view all the answers

    What is the expression for the line current in a full-bridge 3-phase diode rectifier?

    <p>iA = Io when DA is ON and -Io when DA' is ON</p> Signup and view all the answers

    Study Notes

    Semiconductor Switches

    • Practically, semiconductor switches have nonzero on-off time to avoid short circuits.
    • To avoid short circuits, a switch is turned off shortly before the turn-on of the other switch in the same leg, introducing a dead time.

    Switching Variables

    • Two switching variables, a and b, are assigned as control variables to the inverter legs.
    • The switching variables are defined as follows:
      • a = 1 when SA is ON and DA is OFF
      • a = 0 when SA is OFF and DA is ON
      • b = 1 when SB is ON and DB is OFF
      • b = 0 when SB is OFF and DB is ON

    Inverter States

    • An inverter state is designated as ab, where a and b are the switching variables.
    • The process of a diode taking over conduction of current from another diode is called natural commutation.

    Line Current

    • The line current iA is equal to Io when DA is ON and to -Io when DA' is ON and to 0 when both DA and DA' are OFF.
    • Similar relationships exist for iB and iC.

    Power Factor for Highly Inductive Load

    • The expression of the power factor for a highly inductive load needs to be derived.

    Full-Bridge 3-Phase Diode Rectifier with R-Load

    • The output voltage vo = vp - vn.
    • The output current io = vo/R.
    • The line currents iA, iB, and iC are equal to the DC side current when their line upper diode is ON and to the negative of the DC side current when their line lower diode is ON and zero otherwise.

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    Description

    This quiz covers the basics of semiconductor switches in power electronics, including their on-off time and dead time to avoid short circuits. It also introduces switching variables and their definitions.

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