121. The main purpose of phase control in converters is
A) To regulate output voltage
B) To change frequency
C) To improve power factor
D) To reduce harmonics
Answer: A)
122. The single-phase dual converter allows
A) Unidirectional current and voltage
B) Bidirectional current and voltage
C) Only current reversal
D) Only voltage reversal
Answer: B)
123. The inverter-fed induction motor can operate at
A) Fixed frequency
B) Variable frequency
C) Constant voltage only
D) Constant speed
Answer: B)
124. The speed of an induction motor drive using a VSI is controlled by
A) Changing DC link voltage
B) Changing supply voltage
C) Changing switching frequency
D) Both A and C
Answer: D)
125. The most commonly used modulation technique in modern inverters is
A) Sinusoidal PWM
B) Square wave
C) Single pulse
D) Multiple pulse
Answer: A)
126. The main advantage of Sinusoidal PWM is
A) Reduced harmonic distortion
B) Increased current
C) Higher losses
D) Increased voltage
Answer: A)
127. In a boost converter, if duty cycle increases, the output voltage
A) Decreases
B) Increases
C) Remains constant
D) Becomes zero
Answer: B)
128. The current in an inductor of a buck converter is
A) Continuous
B) Discontinuous
C) Both depending on load
D) Zero
Answer: C)
129. The ripple in output current of a buck converter depends on
A) Inductance
B) Frequency
C) Duty ratio
D) All of the above
Answer: D)
130. A buck converter steps
A) Voltage up
B) Voltage down
C) Current up
D) Power up
Answer: B)
131. A boost converter steps
A) Voltage up
B) Voltage down
C) Power down
D) Frequency up
Answer: A)
132. In a buck-boost converter, the output voltage is
A) Always higher than input
B) Always lower than input
C) Can be higher or lower
D) Equal to input
Answer: C)
133. The ripple voltage in SMPS can be reduced by
A) Increasing filter capacitance
B) Reducing frequency
C) Increasing load
D) Decreasing inductance
Answer: A)
134. The duty cycle in a DC-DC converter is the ratio of
A) ON time to total period
B) OFF time to total period
C) Output voltage to input voltage
D) Input current to output current
Answer: A)
135. The output voltage of a boost converter is related to input by
A) Vo = Vin / (1 - D)
B) Vo = Vin × (1 - D)
C) Vo = Vin × D
D) Vo = Vin / D
Answer: A)
136. The SMPS operating in discontinuous mode means
A) Inductor current falls to zero
B) Inductor current continuous
C) Output current constant
D) Switching frequency low
Answer: A)
137. The flyback converter provides
A) DC isolation
B) No isolation
C) Direct connection
D) No output regulation
Answer: A)
138. The output voltage polarity of a buck-boost converter is
A) Same as input
B) Opposite to input
C) Zero
D) Undefined
Answer: B)
139. A full-bridge converter has
A) 2 switches
B) 4 switches
C) 6 switches
D) 8 switches
Answer: B)
140. The most important characteristic of IGBT is
A) High input impedance and high current capability
B) Low voltage drop
C) Fast switching
D) Low frequency
Answer: A)
141. The typical voltage drop across IGBT in conduction is
A) 0.7 V
B) 1–3 V
C) 5–10 V
D) 0 V
Answer: B)
142. The safe operating area (SOA) of IGBT is limited by
A) Voltage, current, and temperature
B) Voltage only
C) Current only
D) Frequency only
Answer: A)
143. In SMPS, increasing switching frequency
A) Reduces size of filter
B) Increases losses
C) Increases efficiency slightly
D) Both A and B
Answer: D)
144. A forward converter uses
A) Transformer with demagnetizing winding
B) Inductor only
C) Transformer without reset
D) No isolation
Answer: A)
145. The input current in buck converter is
A) Continuous
B) Discontinuous
C) Pulsating
D) Constant
Answer: C)
146. The output voltage control in PWM inverter is achieved by
A) Varying pulse width
B) Varying frequency
C) Varying duty cycle
D) Both A and C
Answer: D)
147. The main reason for harmonic distortion in PWM inverter is
A) High switching frequency
B) Non-linear load
C) Device delay
D) All of the above
Answer: D)
148. The total harmonic distortion (THD) of PWM inverter is
A) Less than square wave inverter
B) Greater than square wave inverter
C) Same as square wave inverter
D) Infinite
Answer: A)
149. The typical PWM frequency in industrial inverters is
A) 50 Hz
B) 100 Hz
C) 2–20 kHz
D) 1 MHz
Answer: C)
150. The harmonic order of lowest significant harmonic in a 6-pulse converter is
A) 3
B) 5
C) 7
D) 6n±1 (n=1)
Answer: D)
151. The lowest order harmonics in a 6-pulse converter are
A) 5th and 7th
B) 3rd and 9th
C) 11th and 13th
D) 17th and 19th
Answer: A)
152. The 12-pulse converter eliminates
A) 3rd and 5th harmonics
B) 5th and 7th harmonics
C) 11th and 13th harmonics
D) 17th and 19th harmonics
Answer: B)
153. The total harmonic distortion (THD) of a 12-pulse converter is
A) Higher than 6-pulse
B) Lower than 6-pulse
C) Same as 6-pulse
D) Independent of pulse number
Answer: B)
154. The GTO has
A) Turn-off capability
B) No turn-off capability
C) Unidirectional control
D) Bidirectional current control
Answer: A)
155. The main limitation of GTO is
A) High gate drive current required
B) High cost
C) Low voltage rating
D) High on-state drop
Answer: A)
156. The switching loss of MOSFET is mainly due to
A) Drain capacitance
B) Gate charge
C) On resistance
D) Leakage
Answer: B)
157. The dv/dt turn-on can cause
A) False triggering
B) Gate failure
C) Overvoltage
D) Reverse current
Answer: A)
158. The most suitable snubber for dv/dt protection is
A) RC circuit
B) RL circuit
C) LC circuit
D) RC series with diode
Answer: A)
159. The di/dt protection for SCR is given by
A) Inductor in series
B) Capacitor in parallel
C) Resistor in series
D) RC across SCR
Answer: A)
160. The forced commutation circuit using LC resonant network belongs to
A) Class B
B) Class C
C) Class D
D) Class E
Answer: B)
161. A converter operating in inversion mode has
A) Positive current, negative voltage
B) Negative current, positive voltage
C) Both reversed
D) Both positive
Answer: A)
162. The line-commutated inverter requires
A) Inductive load
B) AC supply for commutation
C) DC source only
D) Freewheeling diode
Answer: B)
163. The main disadvantage of line-commutated inverter is
A) Requires AC source
B) High frequency operation not possible
C) Limited power factor
D) All of the above
Answer: D)
164. The output voltage waveform of single-phase inverter without filter is
A) Sinusoidal
B) Square
C) Triangular
D) Constant DC
Answer: B)
165. The efficiency of a power electronic converter is typically
A) 40–60%
B) 60–80%
C) 90–98%
D) 30–50%
Answer: C)
166. The converter circuit that converts AC of one frequency to AC of another frequency directly is
A) Inverter
B) Cycloconverter
C) Chopper
D) Rectifier
Answer: B)
167. The main advantage of cycloconverter is
A) Direct AC–AC conversion
B) Compact design
C) High frequency output
D) Low cost
Answer: A)
168. The frequency of output of a cycloconverter is
A) Higher than input
B) Lower than input
C) Equal to input
D) Twice input
Answer: B)
169. The control circuit of SCR must supply
A) Trigger pulse with sufficient gate current
B) Constant voltage
C) DC only
D) Pulse of low duration only
Answer: A)
170. The MOSFET gate is insulated from channel by
A) Silicon dioxide layer
B) Silicon nitride
C) Air gap
D) Metal contact
Answer: A)
171. The conduction in n-channel MOSFET occurs due to
A) Electrons
B) Holes
C) Both
D) None
Answer: A)
172. The on-resistance of MOSFET increases with
A) Temperature rise
B) Temperature fall
C) Frequency rise
D) Gate voltage increase
Answer: A)
173. The main advantage of using PWM inverter is
A) Low harmonics
B) Low cost
C) Easy triggering
D) High noise
Answer: A)
174. In single-phase half-bridge inverter, neutral point is obtained by
A) Split DC supply
B) Transformer
C) Center tap
D) None
Answer: A)
175. The total output power of a three-phase inverter is
A) Three times that of single phase
B) Half
C) Equal
D) Double
Answer: A)
176. The modulation index in PWM is the ratio of
A) Amplitude of control to carrier signal
B) Frequency of control to carrier
C) Output to input voltage
D) Load to supply
Answer: A)
177. If modulation index < 1, the PWM inverter operates in
A) Linear mode
B) Overmodulation
C) Clipping mode
D) Harmonic mode
Answer: A)
178. The overmodulation in PWM leads to
A) Distorted waveform
B) Smooth waveform
C) Lower voltage
D) None
Answer: A)
179. The synchronous speed in induction motor is proportional to
A) Supply frequency
B) Voltage
C) Torque
D) Load
Answer: A)
180. Variable frequency drives (VFDs) control
A) Supply voltage
B) Supply frequency
C) Supply current
D) Load impedance
Answer: B)
181. The “V/f” control of induction motor maintains
A) Constant torque
B) Constant flux
C) Constant current
D) Both A and B
Answer: D)
182. The typical efficiency of IGBT inverter is around
A) 40%
B) 70%
C) 90–98%
D) 100%
Answer: C)
183. A regenerative converter allows
A) Power flow from load to source
B) Source to load
C) No power flow
D) AC to AC
Answer: A)
184. In a 3-phase fully controlled converter, maximum output voltage occurs at
A) α = 0°
B) α = 90°
C) α = 120°
D) α = 180°
Answer: A)
185. The power factor of converter decreases as
A) α increases
B) α decreases
C) Frequency increases
D) None
Answer: A)
186. The load current of a converter becomes continuous with
A) Inductive load
B) Resistive load
C) Capacitive load
D) None
Answer: A)
187. The firing circuit of SCR must provide
A) Isolated triggering pulses
B) Continuous current
C) Voltage feedback
D) AC input
Answer: A)
188. The isolation in gate drive circuit is obtained by
A) Pulse transformer or optocoupler
B) Diode
C) Inductor
D) Resistor
Answer: A)
189. The reverse recovery time of diode affects
A) Switching losses
B) On-state loss
C) Power factor
D) Efficiency only
Answer: A)
190. A Schottky diode is preferred in SMPS because
A) Low forward voltage drop
B) Fast recovery
C) Both A and B
D) Low cost
Answer: C)
191. The freewheeling diode is used to
A) Reduce voltage spikes
B) Provide current path during off state
C) Prevent commutation failure
D) Reduce losses
Answer: B)
192. The commutation failure in converter is due to
A) High overlap angle
B) Low supply voltage
C) Inductive load
D) All of the above
Answer: D)
193. The overlap angle increases with
A) Load inductance
B) Supply voltage
C) Frequency
D) Resistance
Answer: A)
194. The device used for overvoltage protection in converters is
A) MOV
B) Snubber
C) Fuse
D) Thermistor
Answer: A)
195. The commutation method used in inverters is
A) Forced commutation
B) Natural commutation
C) Load commutation
D) Resonant commutation
Answer: A)
196. A current source inverter requires
A) Large inductor in input
B) Large capacitor in input
C) Transformer
D) Filter only
Answer: A)
197. The input to a voltage source inverter is
A) Constant voltage
B) Constant current
C) Variable voltage
D) Variable current
Answer: A)
198. In a VSI, the output voltage is controlled by
A) PWM
B) Firing angle
C) Supply current
D) Inductor
Answer: A)
199. In a CSI, the output current is controlled by
A) Inductor
B) PWM
C) Load resistance
D) Supply voltage
Answer: A)
200. In a PWM inverter, increasing modulation index
A) Increases output voltage
B) Decreases output voltage
C) Increases harmonics
D) Reduces DC
Answer: A)
No comments:
Post a Comment