201. For a single-phase full converter, the average output voltage is given by
A) (Vm/π)(1+cosα)
B) (2Vm/π)cosα
C) (Vm/2)cosα
D) (Vm/π)sinα
Answer: B)
202. The input power factor of a fully controlled converter is
A) Unity
B) Lagging
C) Leading
D) Zero
Answer: B)
203. The output voltage of a single-phase half converter for α = 90° is
A) 0
B) Vm/π
C) Vm/2π
D) Vm
Answer: A)
204. The RMS output voltage of a single-phase half-wave rectifier is
A) Vm/2
B) Vm/√2
C) Vm/π
D) Vm/√3
Answer: A)
205. The form factor of a single-phase half-wave rectifier is approximately
A) 1.11
B) 1.57
C) 1.21
D) 1.8
Answer: B)
206. For α = 60° in a single-phase full converter, output voltage is
A) (2Vm/π)cos60°
B) Vm/π
C) (Vm/2)cos60°
D) 0
Answer: A)
207. In a 3-phase full converter, the average DC output voltage is
A) (3Vm/π)cosα
B) (3√2Vm/π)cosα
C) (1.35Vm)cosα
D) (2Vm/π)cosα
Answer: C)
208. The maximum DC voltage of a 3-phase full converter is
A) 1.35Vm
B) 1.17Vm
C) 2Vm
D) 0.9Vm
Answer: A)
209. The ripple frequency of a 3-phase full converter is
A) 3f
B) 6f
C) f
D) 12f
Answer: B)
210. The lowest order harmonic in 6-pulse converter is
A) 3rd
B) 5th
C) 7th
D) 11th
Answer: B)
211. The commutation overlap angle μ depends on
A) Load current and source inductance
B) Voltage only
C) Resistance only
D) Frequency only
Answer: A)
212. In a converter, overlap causes
A) Decrease in output voltage
B) Increase in current
C) Increase in power factor
D) No effect
Answer: A)
213. The commutation failure occurs when
A) Supply voltage decreases
B) Overlap increases
C) Both A and B
D) Supply frequency increases
Answer: C)
214. The displacement factor of a fully controlled converter is equal to
A) cosα
B) sinα
C) tanα
D) unity
Answer: A)
215. The power factor of a converter is
A) cosα
B) cos(α + μ/2)
C) cos(μ/2)
D) 1
Answer: B)
216. The freewheeling diode improves
A) Power factor
B) Efficiency
C) Load current continuity
D) Voltage regulation
Answer: C)
217. The firing angle of a converter is measured from
A) Zero crossing of supply voltage
B) Peak of supply
C) Current zero
D) Load voltage zero
Answer: A)
218. The back emf of a motor in a converter drive opposes
A) Source voltage
B) Current
C) Both
D) None
Answer: A)
219. The regeneration occurs in converter drive when
A) α > 90°
B) α < 90°
C) α = 0°
D) α = 60°
Answer: A)
220. The converter works as inverter when
A) Output voltage negative, current positive
B) Output voltage positive, current positive
C) Both negative
D) None
Answer: A)
221. In dual converter, circulating current mode uses
A) Inductor between converters
B) Transformer isolation
C) Capacitor
D) None
Answer: A)
222. Non-circulating mode of dual converter avoids
A) Power loss
B) Reactive power
C) Both A and B
D) None
Answer: C)
223. The average output current of full converter feeding RL load is
A) Depends on load and α
B) Independent of α
C) Constant
D) Zero
Answer: A)
224. In a chopper, duty cycle D = 0.6 means
A) ON time is 60% of total
B) OFF time is 60%
C) Output is 40%
D) None
Answer: A)
225. The average output voltage of step-down chopper is
A) Vdc × D
B) Vdc / D
C) D / Vdc
D) D²Vdc
Answer: A)
226. The average output voltage of step-up chopper is
A) Vdc/(1-D)
B) Vdc×D
C) (1-D)Vdc
D) D²Vdc
Answer: A)
227. The step-down chopper is also known as
A) Buck converter
B) Boost converter
C) Flyback converter
D) Forward converter
Answer: A)
228. In current commutated chopper, commutation achieved by
A) Reverse current pulse
B) Reverse voltage
C) Forward bias
D) Supply drop
Answer: A)
229. Class E chopper is also known as
A) Two-quadrant chopper
B) Four-quadrant chopper
C) Single-quadrant chopper
D) Regenerative chopper
Answer: B)
230. The typical switching frequency of choppers is
A) 100 Hz
B) 1 kHz–100 kHz
C) 1 MHz
D) 50 Hz
Answer: B)
231. In motor control, dynamic braking means
A) Motor acts as generator, energy dissipated in resistor
B) Power fed back to supply
C) Motor speed increases
D) None
Answer: A)
232. Regenerative braking occurs when
A) Motor back emf > supply
B) Motor back emf < supply
C) Motor current zero
D) None
Answer: A)
233. Plugging is a method of
A) Braking
B) Acceleration
C) Commutation
D) Filtering
Answer: A)
234. Plugging causes
A) High current
B) Smooth stop
C) Low losses
D) None
Answer: A)
235. The VSI-fed induction motor operates at
A) Variable frequency and voltage
B) Constant frequency
C) Constant torque only
D) Constant power
Answer: A)
236. The torque-speed characteristics of V/f control are
A) Constant torque below base speed
B) Constant power above base speed
C) Both A and B
D) None
Answer: C)
237. The slip of an induction motor at rated torque is
A) 1–3%
B) 10–20%
C) 5–10%
D) 0%
Answer: A)
238. The main function of DC link capacitor in VFD is
A) Energy storage and filtering
B) Voltage division
C) Current limiting
D) Commutation
Answer: A)
239. The filter in SMPS reduces
A) Ripple
B) Power factor
C) Voltage
D) Current
Answer: A)
240. In a PWM inverter, the carrier frequency is
A) Much higher than reference
B) Equal to reference
C) Lower than reference
D) None
Answer: A)
241. In sinusoidal PWM, modulation index controls
A) Output voltage
B) Frequency
C) Power factor
D) Losses
Answer: A)
242. The inverter which can handle reactive loads effectively is
A) Current source inverter
B) Voltage source inverter
C) Cycloconverter
D) Chopper
Answer: A)
243. The single-phase bridge inverter output fundamental RMS voltage =
A) (Vm/√2)
B) (Vm/√2π)
C) (Vm/2)
D) (Vm/π)
Answer: C)
244. The square-wave inverter has
A) More harmonics
B) Less harmonics
C) No harmonics
D) Ideal waveform
Answer: A)
245. The harmonic elimination method uses
A) Selective switching angles
B) Random switching
C) Frequency variation
D) Voltage control
Answer: A)
246. In multi-level inverter, number of levels =
A) (m-1)/2
B) (m+1)/2
C) (2m-1)
D) m
Answer: D)
247. The advantage of multilevel inverter is
A) Low THD
B) High dv/dt stress
C) More losses
D) Complex triggering
Answer: A)
248. The neutral point clamped inverter is
A) Diode clamped
B) Flying capacitor
C) Cascaded H-bridge
D) PWM inverter
Answer: A)
249. In a three-level NPC inverter, number of switches per phase
A) 2
B) 4
C) 6
D) 8
Answer: B)
250. The main advantage of soft switching is
A) Reduced switching loss
B) Increased frequency
C) Better cooling
D) All
Answer: A)
251. The ZVS technique means
A) Zero voltage switching
B) Zero current switching
C) Zero loss switching
D) None
Answer: A)
252. In ZCS technique
A) Current reduced to zero before switching
B) Voltage reduced
C) Frequency zero
D) None
Answer: A)
253. The resonant converter uses
A) LC network
B) RC network
C) RL network
D) None
Answer: A)
254. The quasi-resonant converter operates at
A) Variable frequency
B) Constant frequency
C) Fixed DC
D) Constant voltage
Answer: A)
255. In SMPS, isolation is provided by
A) Transformer
B) Inductor
C) Capacitor
D) Resistor
Answer: A)
256. The output of a UPS is generally
A) Pure sine wave
B) Square wave
C) PWM controlled sine wave
D) DC
Answer: C)
257. The inverter section of UPS uses
A) IGBT
B) SCR
C) MOSFET
D) Any of the above
Answer: A)
258. The transfer time from mains to inverter in online UPS is
A) Zero
B) Few ms
C) 100 ms
D) 1 s
Answer: A)
259. The transfer time in offline UPS is
A) Few ms
B) Zero
C) 1 s
D) 100 ms
Answer: A)
260. Inverter efficiency in UPS is around
A) 50–60%
B) 90–95%
C) 70–80%
D) 100%
Answer: B)
261. The battery voltage of 12 V system is
A) 12.6 V fully charged
B) 10 V
C) 14 V
D) 9 V
Answer: A)
262. The float charging voltage per cell is
A) 2.2–2.3 V
B) 2.5 V
C) 1.8 V
D) 2.0 V
Answer: A)
263. The battery used in UPS is
A) Lead acid
B) Ni-Cd
C) Li-ion
D) Any of above
Answer: A)
264. In battery charging circuit, constant voltage charging maintains
A) Fixed terminal voltage
B) Fixed current
C) Fixed resistance
D) Fixed power
Answer: A)
265. The SMPS operates at
A) High frequency
B) Low frequency
C) 50 Hz
D) DC
Answer: A)
266. The advantage of SMPS over linear supply is
A) High efficiency
B) Light weight
C) Compact
D) All of the above
Answer: D)
267. The disadvantage of SMPS is
A) EMI noise
B) Low efficiency
C) Heavy
D) Slow response
Answer: A)
268. The EMI in SMPS can be reduced by
A) Shielding and filters
B) Increasing duty
C) Increasing voltage
D) Reducing current
Answer: A)
269. The control IC in SMPS performs
A) PWM generation
B) Feedback control
C) Protection
D) All
Answer: D)
270. The efficiency of SMPS is around
A) 50%
B) 70%
C) 80–95%
D) 100%
Answer: C)
271. In a push-pull converter, core saturation avoided by
A) Using center-tap
B) Proper reset winding
C) Symmetrical drive
D) All
Answer: D)
272. The flyback converter operates with
A) Transformer energy storage
B) Transformer direct transfer
C) No transformer
D) Constant current
Answer: A)
273. The forward converter transfers energy
A) During switch ON
B) During switch OFF
C) Both
D) None
Answer: A)
274. The ripple current in output capacitor of SMPS depends on
A) Inductance and duty
B) Load
C) Frequency
D) All
Answer: D)
275. The output regulation in SMPS is achieved by
A) PWM feedback
B) Series resistor
C) Linear amplifier
D) Transformer tap
Answer: A)
276. The line regulation in SMPS is
A) Variation due to input voltage change
B) Due to load
C) Due to frequency
D) None
Answer: A)
277. Load regulation in SMPS refers to
A) Output variation with load
B) Input variation
C) Frequency variation
D) Temperature
Answer: A)
278. The EMI filter in SMPS is located
A) At input side
B) Output side
C) DC link
D) None
Answer: A)
279. The gate driver circuit provides
A) Isolation and required gate voltage
B) Power amplification
C) Current limiting
D) Filtering
Answer: A)
280. The gate resistor controls
A) Switching speed
B) Conduction voltage
C) Output voltage
D) None
Answer: A)
281. The dead time in inverter avoids
A) Short circuit through switches
B) Harmonics
C) Voltage drop
D) Ripple
Answer: A)
282. The snubber circuit provides
A) dv/dt limitation
B) Protection
C) Absorption of transients
D) All
Answer: D)
283. The soft-start circuit in converter prevents
A) Inrush current
B) High ripple
C) Low voltage
D) Oscillation
Answer: A)
284. The efficiency of converter reduces mainly due to
A) Switching losses
B) Conduction losses
C) Control losses
D) All
Answer: D)
285. Power loss in MOSFET =
A) I²R(on)
B) V×I
C) f×C×V²
D) None
Answer: A)
286. The turn-on loss of IGBT increases with
A) Current
B) Voltage
C) Both A and B
D) None
Answer: C)
287. The heat sink in converter removes
A) Power device heat
B) Switching noise
C) EMI
D) Voltage spikes
Answer: A)
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