# 250+ TOP MCQs on Chopper Control Strategies and Answers

Power Electronics Multiple Choice Questions on “Chopper Control Strategies”.

1. In case of TRC (Time Ratio Control), _________ is varied
A. duty cycle
B. firing angle
C. supply frequency
D. supply voltage magnitude
Clarification: In case of TRC, α (Duty cycle) is varied to change the average value of output voltage.

2. In constant frequency TRC or pulse width modulation scheme, ________ is varied.
A. Vs
B. Ton
C. T
D. f
Clarification: In pulse width modulation scheme also known as constant frequency time ratio control, the on-time Ton is varied keeping total time T constant. Toff also varies automatically with Ton to keep Ton constant.

3. In case of variable frequency system __________ is varied
A. T
B. Ton
C. Toff
D. supply frequency
Clarification: In frequency modulation scheme, the frequency (f) hence T (1/f) is varied by either keeping Ton constant or keeping Toff constant.

4. In pulse width modulation scheme, _________ is kept constant.
A. Vs
B. Ton
C. T
D. Toff
Clarification: In pulse width modulation scheme also known as constant frequency time ratio control, the on-time Ton is varied keeping total time T constant. Toff also varies automatically with Ton to keep Ton constant.

5. In case of a constant frequency system, Ton = (1/4)T. If the chopping frequency 2 kHz, find the value of Toff.
A. (1/8) ms
B. (3/8) ms
C. (1/8) μs
D. (3/8) μs
Clarification: Ton = (1/4) T
T = 1/2kHz = 0.5 ms
Ton = T/4
Therefore, Toff = T – Ton = T – T/4 = 3T/4 = 3/8 msec.

6. In case of frequency modulation system, ________ is kept constant.
A. T
B. Ton
C. Toff
D. Either Ton or Toff
Clarification: In frequency modulation scheme, the frequency (f) hence T (1/f) is varied by either keeping Ton constant or keeping Toff constant.

7. The control strategy in which on and off time is guided by the pervious set of values of a certain parameter is called as
A. time ratio control
B. pulse width modulation
C. current limit control
D. constant frequency scheme
Clarification: In current ratio control, the on and off time is guided by the pervious set of value of load current.

8. In the current limit control method, the chopper is switched off when
A. load current reaches the lower limit
B. load current reaches the upper limit
C. load current falls to zero
D. none of the mentioned
Clarification: In CLC, when the current reaches the upper limit the chopper is switched off and current starts to decay. When current reaches a predefined lower limit, the chopper is again switched on and current starts to rise, the process is thus again repeated.

9. Which of the following mentioned control strategy/strategies would require a feedback loop?
A. pwm
B. constant frequency system
C. current limit control
D. none of the mentioned