51. Due to low inertia, BLDC motors have __________
A. Faster acceleration
B. Slower acceleration
C. High-cost
D. Low cost
Answer: A
Due to low inertia, BLDC motors have faster acceleration. BLDC motors have less weight. They can run at high speed than a conventional DC motor.
52. Calculate the electrical angle for the 6 pole machine. (θm represents mechanical angle)
A. 4×θm
B. 5×θm
C. 2×θm
D. 3×θm
Answer: D
The electrical angle for 6 pole machine is 3×θm.
One electrical angle is equal to a 180° mechanical angle.
θe=(P÷2)×θm.
53. Which of the following are the types of BLDC motor?
A. Unipolar, Bipolar
B. Unipolar, PWM
C. Bipolar, PWM
D. Synchronous, Induction
Answer: A
Unipolar and Bipolar are the types of BLDC motor. They use the Hall effect rotor position sensor and optical rotor position sensor.
54. Calculate peak-peak voltage if Vmax=45 V and Vmin=45 V.
A. 60 V
B. 30 V
C. 50 V
D. 0 V
Answer: D
Peak-Peak voltage is equal to the difference between the maximum and minimum voltage. It is mathematically represented as
Vp-p=Vmax-Vmin=45-45=0 V.
It signifies the signal is a DC signal.
55. Calculate the value of the Crest factor if Vpeak=141 V and Vr.m.s=100 V for sinusoidal voltage.
A. 1.41
B. 2.38
C. 4.42
D. 5.58
Answer: A
The value of the crest factor is Vpeak÷Vr.m.s=141÷100=1.41. It signifies the peak value is 1.41 times the r.m.s value.
56. In the biomedical instruments like artificial heart pumps, the motor used is ____________
A. DC shunt motor
B. DC series motor
C. Induction motor
D. BLDC motor
Answer: D
BLDC motors are widely used in various applications in the medical industry. Sensorless BLDC motors and sensor BLDC motors are used because of their easy operation and high reliability compared to conventional motors.
57. Calculate the output power of the Buck converter if the supply voltage is 4 V and the duty cycle value is .1 for a 4 Ω load.
A. 40 mW
B. 20 mW
C. 50 mW
D. 60 mW
Answer: A
The output voltage of the buck converter is Vo = Vin×(D.=.4).
The value of the duty cycle is less than one which makes the Vo < Vin. The buck converter is used to step down the voltage. The output power is
Vo2÷R=40 mW.
58. Calculate the compensator rating required for cos(Φ)=.1.
A. 0.91 P.U
B. 0.99 P.U
C. 0.97 P.U
D. 0.92 P.U
Answer: B
The compensator rating can be calculated using the relation
QP.U=√1-cos2(∅)
=√1-.01=.99.
This per unit value VAR compensator is required to improve the power factor of the system.
59. Calculate the average inductor current of the Boost converter if the load current is 7 A and the duty cycle value is .8.
A. 36 A
B. 35 A
C. 34 A
D. 31 A
Answer: B
The average inductor current of the Boost converter is
Io÷(1-D.=7÷.2=35 A.
The average value of the inductor current can be calculated using the ampere-sec balance method.
60. Calculate the output voltage of the Buck-Boost converter if the supply voltage is 14 V and the duty cycle value is .85.
A. 79.3 V
B. 45.5 V
C. 86.5 V
D. 54.7 V
Answer: A
The output voltage of the buck-boost converter is
Vo = D×Vin ÷ (1-D)
=.85(14)÷.15=79.3 V.
It can step up and step down the voltage depending upon the value of the duty cycle. If the value of the duty cycle is less than .5 it will work as a buck converter and for a duty cycle greater than .5 it will work as a boost converter.
