Q-In a half wave circuit, forced commutation is essential when the
a) load is inductive
b) load is resistive
c) source voltage is below 150 V
d) none of the mentioned
……………
Answer: b
Explanation: When the load is resistive (R load) , the diodes do not conduct, hence they cannot help stop the conduction of the SCRs. Hence, forced commutation in such cases becomes essential
Q-The harmonic factor of nth harmonic is given by
a) Vn
b) V1/Vn
c) Vn/V1
d) None of the mentioned
…………….
Answer: c
Explanation: It is the ratio of rms value of the nth harmonic voltage component to the rms value of the fundamental voltage component (V1).
Q-In voltage fed thyristor inverters __________ commutation is required.
a) load
b) forced
c) self
d) any commutation technique can be used
…………..
Answer: b
Explanation: In VSI, the input voltage source Vs keeps the SCRs always forward biased. Hence, forced commutation becomes essential.
Q-Forced commutation requires
a) a precharged inductor
b) a precharged capacitor
c) an overdamped RLC load
d) a very high frequency ac source
………….
Answer: b
Explanation: Forced commutation requires a pre charged capacitor of correct polarity to turn-off the earlier conducting SCR.
Q-The number of diodes, SCRs and other components in full-bridge inverter McMurray inverter is ____________ of those in half-bridge McMurray inverter.
a) same
b) double
c) three times
d) none of the mentioned
…………..
Answer: b
Explanation: The modified McMurray full-bridge requires twice the components that required in the half-wave type.
Q-In inverters, to make the supply voltage constant
a) an inductor is placed in series with the load
b) capacitor is connected in parallel to the load side
c) capacitor is connected in parallel to the supply side
d) none of the mentioned
…………..
Answer: c
Explanation: A large C connected across the input terminal keep the supply voltage from altering.
Q-The series-inverter control method is a/an
a) internal voltage control method
b) external frequency control method
c) external voltage control method
d) none of the mentioned
………………
Answer: c
Explanation: It is a external voltage control method where the outputs of the two inverters are connected to the transformers where the secondary of the transformer sums up the two input voltages.
Q- In the series-inverter control method
a) two inverters are connected back-to-back
b) the output from the inverter is taken serially
c) output voltages of two inverters are summed up with the help of a transformer
d) output voltages of two inverters are summed up with the help of a third inverter
………..
Answer: c
Explanation: It is a external voltage control method where the outputs of the two inverters are connected to the transformers where the secondary of the transformer sums up the two input voltages.
Q-In the PWM method
a) external commutating capacitors are required
b) more average output voltage can be obtained
c) lower order harmonics are minimized
d) higher order harmonics are minimized
…………….
Answer: c
Explanation: In all the PWM methods, only odd harmonics are present. The lower order harmonics are eliminated along with its output voltage control.
Q-Which of the following is not a PWM technique?
a) Single-pulse width modulation
b) Multiple-pulse width modulation
c) Triangular-pulse width modulation
d) Sinusoidal-pulse width modulation
……………
Answer: c
Explanation: There is no such “Triangular” PWM.
Q-In pulse width modulation
a) the output voltage is modulated
b) the input voltage is modulated
c) the gating pulses are modulated
d) none of the mentioned
…………
Answer: c
Explanation: In PWM, the gating pluses are modulated, i.e. the gating pulses or firing pulses are made to go on of rapidly which changes the output voltage values accordingly.
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