Free Power Electronics MCQs with Answers

• A. electromagnetic induction
• B. varying the resistance
• C. varying the reactance
• D. variable transformer

Explanation: A magnetic amplifier controls output voltage by saturating its magnetic core, thereby changing the effective reactance of its windings.

• A. Cmin = V / ( Vr L f2 )
• B. Cmin= ( 1 - D ) V / ( Vr L f2 )
• C. Cmin= ( 1 - 2 D ) V / 32 ( Vr L f2 )
• D. Cmin= ( 1 - 2 D ) V / 42 ( Vr L f2 )

Explanation: In a push-pull converter, the effective ripple frequency is doubled, and the capacitor ripple relation introduces the triangular-current…

• A. Flyback capacitor
• B. Flyback resistor
• C. Flyback transformer
• D. Flyback transistor

Explanation: A flyback converter stores energy in the magnetizing inductance of a coupled inductor and transfers it to the output when the switch turns…

• A. Large number of reactive component
• B. Low stress on switch
• C. Low stress on capacitor
• D. None of these

Explanation: The Ćuk converter requires several reactive components and its energy-transfer capacitor can experience substantial voltage stress, so…

• A. Divert the collector current during turn - off
• B. Improves the reverse bias safe operating area
• C. Dissipates a fair amount of switching power
• D. All of these

Explanation: An RC snubber temporarily absorbs or diverts switching current, limits the collector-voltage rise, improves the BJT's reverse-bias safe…

• A. High dv / dt, low di / dt
• B. Low dv / dt, low di / dt
• C. Low dv / dt, high di / dt
• D. High dv / dt, high di / dt

Explanation: A VSI produces a switched voltage with steep voltage transitions, giving high dv/dt, while a CSI produces a switched current with steep…

• A. Motoring mode operation
• B. Braking mode operation
• C. Regenerative mode operation
• D. None of these

Explanation: When power flows from the AC side back to the DC source, the inverter is operating regeneratively.

• A. Boost single - phase power factor converter
• B. A buck dc - dc converter to reduce ripple in the intermediate dc bus capacitor
• C. Both A. and B.
• D. None f these

Explanation: Synchronized leading-edge and trailing-edge modulation can be applied to a boost single-phase power-factor converter and to a buck…

• A. High power inverters
• B. Rectifiers
• C. Low power inverters
• D. Only A. and B.

Explanation: Regular-sampling PWM is commonly used in high-power inverters and PWM rectifiers because its fixed sampling process is convenient for…

• A. Multiple of two
• B. Odd multiple of three
• C. Odd multiple of five
• D. Odd multiple of seven

Explanation: For three-phase SPWM with one carrier, the carrier ratio is selected as an odd multiple of three, such as 3, 9, or 15, to preserve…

• A. Can control the load voltage
• B. Cannot control the load voltage
• C. Cannot control the load voltage except by means of dc link voltage
• D. Cannot control the load voltage except by means of dc link current

Explanation: In square-wave operation the switches have fixed conduction intervals, so the VSI cannot vary its output magnitude through modulation.

• A. Three inductances
• B. Three capacitances
• C. Three resistance
• D. Three transistors

Explanation: The three AC source phases are connected through source inductances, which limit current rise and provide the overlap needed during…

• A. 120 degree after the zero crossing of the corresponding line voltages
• B. 60 degree after the zero crossing of the corresponding line voltages
• C. 120 degree before the zero crossing of the corresponding line voltages
• D. 60 degree before the zero crossing of the corresponding line voltages

Explanation: With diodes replacing the SCRs, conduction begins automatically when the corresponding line-voltage conditions forward-bias them…

• A. Average value of the output inductor current
• B. Product of an average inductor current and a function of duty ratio
• C. Either A. or B.
• D. None of these

Explanation: In a buck converter, output current equals the average inductor current, while in other PWM converters it may be a duty-ratio-weighted…

• A. Electric traction
• B. Electric vehicles
• C. Machine tools
• D. All of these

Explanation: A step-down chopper provides controlled lower DC voltage and is therefore used in traction drives, electric vehicles, and variable-speed…

• A. Equal to the average power supplied by the dc source
• B. Greater than the average power supplied by the dc source
• C. Lesser than the average power supplied by the dc source
• D. Equal to the average power supplied by the ac source

Explanation: A lossless inverter has no power dissipation, so conservation of energy requires the load's average absorbed power to equal the average…

• A. Lighting and heating control
• B. On - line transformer tap changing
• C. Soft starting
• D. All of these

Explanation: AC voltage controllers regulate the RMS load voltage and are used for lamp and heater control, transformer tap-changing applications, and…

• A. Top switch of each leg is on at any instant
• B. Bottom switch of each leg is on at any instant
• C. Either A. or B.
• D. None of these

Explanation: Each inverter leg must always have exactly one device conducting, with the upper and lower switches operated complementarily, including…

• A. A capacitor
• B. A variable resistor
• C. An inductor
• D. Only (a) and (b)

Explanation: A TRIAC firing circuit commonly uses an RC network, where the capacitor charging time and variable resistance determine the gate-pulse…

• A. Square
• B. Sinusoidal
• C. Triangular
• D. Saw - tooth

Explanation: Sinusoidal PWM compares a sinusoidal modulating reference with a high-frequency triangular carrier.