DC Chopper vs AC Link Chopper
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Questions and Answers

What distinguishes a DC chopper from an AC link chopper?

  • AC link choppers do not use transformers, while DC choppers do.
  • DC choppers are designed to decrease voltage only, while AC link choppers can increase voltage.
  • DC choppers convert AC to AC while AC link choppers convert DC to DC.
  • DC choppers execute single-stage conversion while AC link choppers follow a two-stage conversion. (correct)

    • In which scenario are chopper circuits particularly necessary?

  • When the input voltage is already variable DC.
  • When devices require variable DC input from a fixed AC supply. (correct)
  • When AC voltage must be directly stepped down to another AC voltage.
  • When the output should be a fixed DC voltage regardless of input.

    • What is a primary characteristic of the two types of DC to DC conversion techniques?

  • Both types are equally efficient in all applications.
  • AC link choppers involve higher costs and inefficiency due to two conversion stages. (correct)
  • AC link choppers can only step down voltage, while DC choppers can only step up.
  • DC choppers utilize transformers while AC link choppers do not.

    • What type of control strategies can be used in DC choppers?

    <p>Current limit control and time ratio control</p> Signup and view all the answers

    Why can chopper circuits be compared to AC transformers?

    <p>Both can step up or step down a voltage level.</p> Signup and view all the answers

    What does the term 'static power electronics device' imply in the context of DC choppers?

    <p>It indicates that the device operates without any mechanical parts.</p> Signup and view all the answers

    What might be a disadvantage of using an AC link chopper compared to a DC chopper?

    <p>Higher cost and reduced efficiency.</p> Signup and view all the answers

    How does the output voltage behavior in DC choppers change?

    <p>The average value of the output voltage can be altered under control strategies.</p> Signup and view all the answers

    What is the primary function of a transformer in an AC link chopper circuit?

    <p>To step up or step down the AC signal voltage.</p> Signup and view all the answers

    What is the duty cycle in the context of time ratio control?

    <p>The ratio of ON time to total time.</p> Signup and view all the answers

    Which control strategy keeps the frequency constant while varying ON time?

    <p>Pulse Width Modulation (PWM)</p> Signup and view all the answers

    What is a significant disadvantage of frequency modulation (FM) in control systems?

    <p>Load current may become irregular due to high OFF times.</p> Signup and view all the answers

    How does current limit control function in a DC to DC converter?

    <p>It turns the converter ON and OFF to keep current between limits.</p> Signup and view all the answers

    What occurs when the auxiliary thyristor TA is triggered after the capacitor has charged?

    <p>The main thyristor TM becomes reverse biased.</p> Signup and view all the answers

    What characterizes voltage-commutated chopper circuits?

    <p>They apply a large reverse voltage to commutate the thyristor.</p> Signup and view all the answers

    During which time period does the commutation current ic reach its maximum value?

    <p>At t1/2 of the time period.</p> Signup and view all the answers

    What is forced commutation in the context of thyristors?

    <p>It uses external components to turn off the thyristor.</p> Signup and view all the answers

    What happens to a thyristor during load commutation?

    <p>Conduction stops when load current reaches zero.</p> Signup and view all the answers

    What is the load voltage V0 at instant t2 after both the load voltage and the capacitor voltage are accounted for?

    <p>2 Vdc</p> Signup and view all the answers

    What is the relationship between the capacitor voltage Vc and the voltage across the auxiliary thyristor TA at the point when the load voltage is Vdc?

    <p>Vc equals 0.</p> Signup and view all the answers

    Which of the following describes pulse width modulation (PWM) correctly?

    <p>It requires varying the ON time while keeping frequency constant.</p> Signup and view all the answers

    What critical component is used in the voltage-commutated chopper circuit for protection against inductive loads?

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

    Which component maintains the voltage –Vs constant during the operation of the chopper?

    <p>Diode D</p> Signup and view all the answers

    Which of the following statements about time ratio control is true?

    <p>The ON time is varied in relation to total time.</p> Signup and view all the answers

    What is a defining characteristic of a step-down chopper compared to a step-up chopper?

    <p>It decreases the output voltage.</p> Signup and view all the answers

    What happens to the load voltage V0 as the capacitor begins to discharge through the load?

    <p>It decreases from 2 Vdc to Vdc.</p> Signup and view all the answers

    What is the primary function of an AC chopper in a circuit?

    <p>To control the power flow in an AC circuit.</p> Signup and view all the answers

    What defines the operation of a voltage commutated chopper?

    <p>The capacitor voltage turns off the main thyristor.</p> Signup and view all the answers

    What is not considered a standard chopper type in power electronics?

    <p>Jones chopper</p> Signup and view all the answers

    What distinguishes the efficiency of a DC chopper from that of an AC link chopper?

    <p>DC choppers provide single-stage conversion.</p> Signup and view all the answers

    What is the primary role of the diode rectification unit in an AC link chopper?

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

    Which of the following statements about time ratio control in DC choppers is correct?

    <p>The output voltage is varied by adjusting the time the switch is ON.</p> Signup and view all the answers

    In what way do chopper circuits provide adjustable DC power according to requirements?

    <p>By modifying the duty cycle of the switching element.</p> Signup and view all the answers

    Why is the AC link chopper considered less efficient compared to the DC chopper?

    <p>It involves multiple conversion stages requiring more components.</p> Signup and view all the answers

    How do applications requiring power from DC voltage sources relate to chopper circuits?

    <p>They depend on variable DC voltage outputs for operation.</p> Signup and view all the answers

    What might be a consequence of using a transformer in an AC link chopper?

    <p>Loss of energy due to heat during operation.</p> Signup and view all the answers

    What is a significant feature of a static power electronics device like a DC chopper?

    <p>It can function without any moving parts.</p> Signup and view all the answers

    Which characteristic defines the average output voltage in both control strategies of DC choppers?

    <p>It can be modified according to load requirements.</p> Signup and view all the answers

    What defines the operation of current limit control in a DC to DC converter?

    <p>The current is regulated between specified upper and lower limits.</p> Signup and view all the answers

    Which of the following statements accurately describes load commutation?

    <p>It occurs when load current reduces to zero or shifts to another device.</p> Signup and view all the answers

    In the context of voltage-commutated choppers, which statement is correct?

    <p>Large reverse voltage is applied to turn off the conducting thyristor.</p> Signup and view all the answers

    What is a disadvantage associated with variable frequency operation in DC choppers?

    <p>Designing filters for wide frequency ranges is complex.</p> Signup and view all the answers

    What is the primary advantage of using pulse width modulation (PWM) over frequency modulation in DC-DC converters?

    <p>PWM simplifies the design of output filters.</p> Signup and view all the answers

    What role does the capacitor play in the operation of a voltage-commutated chopper?

    <p>It must be charged to the supply input with matching polarity.</p> Signup and view all the answers

    During frequency modulation, which of the following occurrences is expected?

    <p>The frequency change may interfere with other systems.</p> Signup and view all the answers

    What happens to the load current when the DC-DC converter turns OFF during current limit control?

    <p>It begins to freewheel through the diode and decreases exponentially.</p> Signup and view all the answers

    Which component is crucial for the functioning of voltage-commutated chopper circuits to avoid inductive load issues?

    <p>A freewheeling diode</p> Signup and view all the answers

    What primarily differentiates forced commutation from load commutation?

    <p>Forced commutation utilizes external components for thyristor turn-off.</p> Signup and view all the answers

    What occurs to the main thyristor TM when the auxiliary thyristor TA is triggered?

    <p>TM becomes reverse biased and enters a non-conducting state.</p> Signup and view all the answers

    During which time period does the commutation current ic reach its maximum value?

    <p>From when the capacitor voltage equals the supply voltage to when it becomes zero.</p> Signup and view all the answers

    How does the operation of a step-up chopper differ from that of a step-down chopper?

    <p>Step-up choppers regulate the output voltage higher than input by controlling duty cycle.</p> Signup and view all the answers

    What defines the behavior of the load voltage V0 during the discharge of the capacitor through the load?

    <p>V0 changes from a maximum of 2Vdc to Vdc as the capacitor discharges.</p> Signup and view all the answers

    In a voltage-commutated chopper, what maintains the load current's flow after TM is turned off?

    <p>The discharging capacitor now configured in series with TA.</p> Signup and view all the answers

    What is the significance of the voltage across the capacitor in the context of voltage-commutated choppers?

    <p>It is responsible for turning off the main thyristor TM.</p> Signup and view all the answers

    How is the auxiliary thyristor TA affected after the capacitor becomes fully charged?

    <p>TA is reverse biased and stops conducting.</p> Signup and view all the answers

    What role does the diode D play in the circuit described for the voltage-commutated chopper?

    <p>It maintains the voltage –Vs constant during operation.</p> Signup and view all the answers

    What is the principal difference in functionality between an AC chopper and a step-up chopper?

    <p>AC choppers manage power in AC circuits whereas step-up choppers are designed for increasing DC voltage.</p> Signup and view all the answers

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