Power Electronics Test Questions - Set 4

1)   Regulator sampling PWM is usually used in

a. High power inverters
b. Rectifiers
c. Low power inverters
d. Only (a) and (b)
Answer  Explanation 

ANSWER: Only (a) and (b)

Explanation:
No explanation is available for this question!


2)   In a 3 phase VSI SPWM to use a single carrier signal and preserve the features of PWM technique, the normalized carrier frequency should be

a. Multiple of two
b. Odd multiple of three
c. Odd multiple of five
d. Odd multiple of seven
Answer  Explanation 

ANSWER: Odd multiple of three

Explanation:
No explanation is available for this question!


3)   In square wave operation mode of 3 phase VSI, the VSI

a. Can control the load voltage
b. Cannot control the load voltage
c. Cannot control the load voltage except by means of dc link voltage
d. Cannot control the load voltage except by means of dc link current
Answer  Explanation 

ANSWER: Cannot control the load voltage except by means of dc link voltage

Explanation:
No explanation is available for this question!


4)   If all the SCR’s of 3 phase PAC is replaced by diodes, they would be triggered

a. 120 degree after the zero crossing of the corresponding line voltages
b. 60 degree after the zero crossing of the corresponding line voltages
c. 120 degree before the zero crossing of the corresponding line voltages
d. 60 degree before the zero crossing of the corresponding line voltages
Answer  Explanation 

ANSWER: 60 degree after the zero crossing of the corresponding line voltages

Explanation:
No explanation is available for this question!


5)   The ability of an electronic system to function properly in its intended electromagnetic environment and should not be a source of pollution to that electromagnetic environment is known as

a. Susceptibility
b. Emission
c. Interference
d. Electromagnetic compatibility
Answer  Explanation 

ANSWER: Electromagnetic compatibility

Explanation:
No explanation is available for this question!


6)   The opposite of susceptibility is

a. Immunity
b. Emission
c. Interference
d. Electromagnetic compatibility
Answer  Explanation 

ANSWER: Immunity

Explanation:
No explanation is available for this question!


7)   The output current in PWM DC - DC converters is equal to

a. Average value of the output inductor current
b. Product of an average inductor current and a function of duty ratio
c. Either (a) or (b)
d. None of these
Answer  Explanation 

ANSWER: Either (a) or (b)

Explanation:
No explanation is available for this question!


8)   A step - down choppers can be used in

a. Electric traction
b. Electric vehicles
c. Machine tools
d. All of these
Answer  Explanation 

ANSWER: All of these

Explanation:
No explanation is available for this question!


9)   In a lossless inverter, the average power absorbed in one period by the load must be

a. Equal to the average power supplied by the dc source
b. Greater than the average power supplied by the dc source
c. Lesser than the average power supplied by the dc source
d. Equal to the average power supplied by the ac source
Answer  Explanation 

ANSWER: Equal to the average power supplied by the dc source

Explanation:
No explanation is available for this question!


10)   In a full bridge VSI, in order to avoid the short circuit across the DC bus and the undefined AC output voltage condition, the modulating technique should ensure that

a. Top switch of each leg is on at any instant
b. Bottom switch of each leg is on at any instant
c. Either (a) or (b)
d. None of these
Answer  Explanation 

ANSWER: Either (a) or (b)

Explanation:
No explanation is available for this question!


11)   In the SPWM, the modulating signal is

a. Square
b. Sinusoidal
c. Triangular
d. Saw - tooth
Answer  Explanation 

ANSWER: Sinusoidal

Explanation:
No explanation is available for this question!


12)   The transfer function of PWM is generally developed in

a. Time domain
b. Frequency domain
c. Either (a) or (b)
d. None of these
Answer  Explanation 

ANSWER: Either (a) or (b)

Explanation:
No explanation is available for this question!


13)   In constant frequency PWM, at perturbation the amplitude of the sinusoidal component is a

a. Linear function
b. Non linear function
c. Constant function
d. None of these
Answer  Explanation 

ANSWER: None of these

Explanation:
No explanation is available for this question!


14)   In variable frequency, PWM gain

a. Phase lead helps to increase the phase margin of the control loop
b. Phase lag helps to increase the phase margin of the control loop
c. Phase lead helps to decrease the phase margin of the control loop
d. Phase lag helps to decrease the phase margin of the control loop
Answer  Explanation 

ANSWER: Phase lead helps to increase the phase margin of the control loop

Explanation:
No explanation is available for this question!


15)   A carrier based PWM technique in CSI is composed of

a. A switching pulse generator and a shorting pulse generator
b. A shorting pulse distributor
c. A switching and shorting pulse combination
d. All of these
Answer  Explanation 

ANSWER: All of these

Explanation:
No explanation is available for this question!


16)   In a square - wave operation of 3 phase CSIs, the power values are on for

a. 60 degree
b. 90 degree
c. 120 degree
d. 150 degree
Answer  Explanation 

ANSWER: 120 degree

Explanation:
No explanation is available for this question!


17)   Silicon controlled rectifier can be turned on

a. By applying a gate pulse and turned off only when current becomes zero
b. And turned off by applying gate pulse
c. By applying a gate pulse and turned off by removing the gate pulse
d. By making current non zero and turned off by making current zero
Answer  Explanation 

ANSWER: By applying a gate pulse and turned off only when current becomes zero

Explanation:
No explanation is available for this question!


18)   TRIAC is a semiconductor power electronic device which contains

a. Two SCR’s connected in reverse parallel
b. Two SCR’s connected in parallel
c. Two SCR’s connected in series
d. Two BJT’s connected in series
Answer  Explanation 

ANSWER: Two SCR’s connected in reverse parallel

Explanation:
No explanation is available for this question!


19)   An SCR can be used

a. as static conductor
b. for power control
c. for speed control of dc shunt motor
d. all of these
Answer  Explanation 

ANSWER: all of these

Explanation:
No explanation is available for this question!


20)   A crowbar is a circuit which is used to protect a

a. voltage sensitive load from excessive dc power supply output voltages
b. current sensitive load from excessive dc power supply output voltages
c. voltage sensitive load from excessive ac power supply output voltages
d. current sensitive load from excessive ac power supply output voltages
Answer  Explanation 

ANSWER: voltage sensitive load from excessive dc power supply output voltages

Explanation:
No explanation is available for this question!