151. The primary control parameter in PWM inverters is
A) Pulse width
B) Frequency
C) Voltage amplitude
D) Phase angle
Answer: A) Pulse width
152. The frequency of output voltage in a single-phase inverter depends on
A) DC input
B) Switching frequency
C) Transformer ratio
D) Load resistance
Answer: B) Switching frequency
153. The forced commutation technique is used in
A) AC circuits only
B) DC circuits
C) Both AC and DC circuits
D) None
Answer: B) DC circuits
154. A dual converter consists of
A) Two full converters connected back-to-back
B) Two half converters in parallel
C) One converter and one inverter
D) One chopper and one inverter
Answer: A) Two full converters connected back-to-back
155. In regenerative braking of DC motor, the energy is
A) Lost in resistor
B) Fed back to supply
C) Stored in battery
D) Converted to heat
Answer: B) Fed back to supply
156. The effect of increasing firing angle in single-phase converter is
A) Decrease in output voltage
B) Increase in output voltage
C) No change
D) Decrease in current only
Answer: A) Decrease in output voltage
157. The input power factor of single-phase converter decreases with
A) Increase in firing angle
B) Decrease in firing angle
C) Constant angle
D) None
Answer: A) Increase in firing angle
158. A step-up chopper can produce output voltage
A) Higher than input
B) Equal to input
C) Lower than input
D) Negative
Answer: A) Higher than input
159. The step-up ratio of boost converter depends on
A) Duty cycle
B) Load resistance
C) Inductance
D) Switching frequency
Answer: A) Duty cycle
160. The regenerative capability of converter is achieved by
A) Reversing voltage polarity
B) Using dual converter
C) Using freewheeling diode
D) Using snubber
Answer: B) Using dual converter
161. The output voltage of AC voltage controller is controlled by
A) Varying firing angle
B) Changing frequency
C) Changing input voltage
D) Changing duty cycle
Answer: A) Varying firing angle
162. In a three-phase full converter, the ripple frequency is
A) 3f
B) 6f
C) f
D) 2f
Answer: B) 6f
163. The delay angle in controlled rectifiers is measured from
A) Zero crossing of supply voltage
B) Peak of supply voltage
C) Zero crossing of current
D) Midpoint of conduction
Answer: A) Zero crossing of supply voltage
164. The average output voltage of full converter is maximum at
A) α = 0°
B) α = 90°
C) α = 180°
D) α = 45°
Answer: A) α = 0°
165. The primary function of commutation circuit is
A) Turn off SCR
B) Turn on SCR
C) Trigger gate
D) Reduce voltage
Answer: A) Turn off SCR
166. Class C commutation is also known as
A) Complementary commutation
B) Resonant commutation
C) Load commutation
D) Line commutation
Answer: A) Complementary commutation
167. Cycloconverters are suitable for
A) High frequency conversion
B) Low frequency conversion
C) DC conversion
D) None
Answer: B) Low frequency conversion
168. The transistor used in chopper operation acts as
A) Amplifier
B) Switch
C) Regulator
D) Modulator
Answer: B) Switch
169. The main purpose of isolation transformer in inverter is
A) Voltage transformation and isolation
B) Current regulation
C) Harmonic reduction
D) None
Answer: A) Voltage transformation and isolation
170. The harmonic order in single-phase full converter is
A) n = 2k ± 1
B) n = k
C) n = 3k
D) n = even only
Answer: A) n = 2k ± 1
171. The efficiency of SMPS is generally
A) 40–50%
B) 60–70%
C) 80–95%
D) 100%
Answer: C) 80–95%
172. In a step-down chopper, the output voltage increases with
A) Duty ratio
B) Inductance
C) Resistance
D) Capacitance
Answer: A) Duty ratio
173. The converter used in DC motor drive is usually
A) Fully controlled converter
B) Half-controlled converter
C) Diode bridge
D) Inverter
Answer: A) Fully controlled converter
174. The major disadvantage of line commutation is
A) Requires AC supply
B) Poor power factor
C) Complex circuit
D) High cost
Answer: B) Poor power factor
175. The speed of a DC motor in converter-fed drive can be controlled by
A) Firing angle
B) Duty cycle
C) Supply voltage
D) Both A and C
Answer: D) Both A and C
176. In current source inverter, the output current is
A) Constant
B) Variable
C) Zero
D) Pulsating
Answer: A) Constant
177. The main advantage of VSI over CSI is
A) Simple control
B) Constant current output
C) Low harmonic
D) None
Answer: A) Simple control
178. The commutation failure occurs in
A) Line-commutated converter
B) Force-commutated converter
C) Chopper circuit
D) Inverter circuit
Answer: A) Line-commutated converter
179. A PWM inverter improves
A) Voltage control
B) Harmonic performance
C) Both A and B
D) None
Answer: C) Both A and B
180. The harmonic components of order n in converter output are eliminated by
A) Proper choice of α
B) Filtering
C) Snubbering
D) Load variation
Answer: B) Filtering
181. The inductor in chopper circuit is used to
A) Store energy
B) Filter harmonics
C) Limit current
D) All
Answer: D) All
182. The turn-on process of SCR is affected by
A) Gate drive amplitude
B) dv/dt
C) Junction temperature
D) All of these
Answer: D) All of these
183. The SCR conducts only when
A) Forward biased and gate triggered
B) Reverse biased
C) Gate off
D) None
Answer: A) Forward biased and gate triggered
184. The reverse recovery current in a diode flows
A) During transition from ON to OFF
B) During steady conduction
C) During OFF state
D) None
Answer: A) During transition from ON to OFF
185. The DC link capacitor in inverter is used to
A) Reduce ripple
B) Store energy
C) Maintain voltage
D) All
Answer: D) All
186. The switching frequency in PWM inverter is
A) High
B) Low
C) Same as output
D) Constant
Answer: A) High
187. The snubber circuit is made of
A) R and C
B) L and C
C) L and R
D) All
Answer: A) R and C
188. The conduction angle of SCR depends on
A) Firing angle
B) Load current
C) Load type
D) All
Answer: D) All
189. The freewheeling diode conducts when
A) SCR turns off
B) SCR turns on
C) Supply reverses
D) None
Answer: A) SCR turns off
190. The inverter fed induction motor operates with
A) Variable frequency supply
B) Fixed frequency
C) Variable voltage
D) Constant current
Answer: A) Variable frequency supply
191. The converter power factor improves with
A) Low firing angle
B) High firing angle
C) Constant current
D) None
Answer: A) Low firing angle
192. The type of commutation used in inverter is
A) Forced
B) Load
C) Natural
D) All
Answer: A) Forced
193. The most suitable device for low-voltage, high-frequency chopper is
A) MOSFET
B) IGBT
C) SCR
D) GTO
Answer: A) MOSFET
194. The ripple in converter output decreases with
A) Inductance
B) Capacitance
C) Both A and B
D) None
Answer: C) Both A and B
195. The conduction losses in SCR occur due to
A) Forward voltage drop
B) Gate current
C) Leakage current
D) dv/dt
Answer: A) Forward voltage drop
196. The device which can be turned off by a control signal is
A) GTO
B) SCR
C) Diode
D) TRIAC
Answer: A) GTO
197. The phase control method of converters results in
A) Harmonic generation
B) Power factor reduction
C) Both A and B
D) None
Answer: C) Both A and B
198. The output of inverter is ideally
A) Square wave
B) Sinusoidal
C) Triangular
D) DC
Answer: A) Square wave
199. The duty cycle of chopper is the ratio of
A) ON time to total time
B) OFF time to total time
C) OFF time to ON time
D) ON time to OFF time
Answer: A) ON time to total time
200. The maximum efficiency of inverter is achieved when
A) Switching losses are minimum
B) Frequency is high
C) Voltage is high
D) Load is resistive
Answer: A) Switching losses are minimum
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