WorksheetsPower Electronic Drives Quiz - Basic to Intermediate
Total questions: 40
Worksheet time: 20mins
A buck converter is used to step down 24V to 12V. What is the expected duty cycle (ideal case)?
0.25
0.5
0.75
1
A chopper is used to control the speed of a DC motor. If the duty cycle increases, what happens to average motor voltage?
Decreases
Remains the same
Increases
Zero
What is the function of a freewheeling diode in a power drive?
Provides continuous path for armature current during OFF time
Blocks DC
Filters voltage
Increases speed
Which of the following is a unidirectional chopper?
Type-B
Type-C
Type-A
Type-D
What does a flyback converter store energy in?
Capacitor
Diode
Transformer
Inductor
Why is heat sinking required in power devices like IGBTs?
Reduce voltage
Improve current
Avoid thermal runaway
Improve signal response
Which power semiconductor device is best suited for high-frequency operation?
SCR
TRIAC
MOSFET
GTO
In a three-phase inverter, what is the maximum line-to-line output voltage for 400V DC input (ideal)?
400V
692V
400√3 V
400/√3 V
In an H-bridge used for motor control, what happens when both upper and lower switches in one leg are ON simultaneously?
Boost
PWM
Short circuit (shoot-through)
Regeneration
What is the main function of a snubber circuit in power drives?
Reduce torque
Boost frequency
Protect switches from voltage spikes
Increase current
A single-phase full converter uses four thyristors. What is the conduction angle for continuous load current?
90°
120°
180°
360°
What is the nature of the output of a step-down (buck) chopper?
Pulsating DC
Pure AC
Pure DC
Sinusoidal
A full-controlled bridge rectifier is used for speed control. What is varied?
Frequency
Trigger angle (firing delay)
Back EMF
Temperature
A dual converter is used for:
AC-to-AC conversion
DC motor bidirectional control
Frequency multiplication
Chopper control
What is ripple factor in rectifier output?
Ratio of DC to RMS
Ratio of AC to DC components
Ratio of RMS to peak
Ratio of AC to peak
A PWM inverter improves output waveform by:
Increasing harmonics
Reducing switching
Approximating sinusoidal waveforms
Shorting load
In a basic SMPS, the feedback loop maintains:
Load impedance
Input power
Output voltage regulation
Ripple frequency
Why is synchronous rectification preferred in modern converters?
Less noise
More losses
Reduced conduction losses
Adds delay
Which device naturally commutates?
SCR
MOSFET
TRIAC
GTO
In a VFD drive, increasing the carrier frequency leads to:
Higher ripple
Lower switching loss
Smoother output waveform
Increased dead-time
In a boost converter, the input is 12V, output is 24V. Assuming ideal components, what should be the duty cycle?
0.33
0.5
0.67
0.75
In regenerative braking of a DC motor, the motor acts as:
Inductor
Load
Generator feeding energy back
Open circuit
What limits the minimum ON time in high-frequency converters?
Transformer leakage
MOSFET RDS(ON)
Control loop bandwidth
Gate driver rise time and switching delay
A chopper-fed DC motor shows oscillations in current waveform. What is the likely cause?
Long cables
Poor controller tuning or inadequate filter
High voltage
High torque
An IGBT fails in short circuit. What is the immediate consequence in an inverter leg?
Reduced ripple
Overcurrent and possible shoot-through
Low speed
Soft start
In soft starting of an induction motor using an AC drive, what parameter is gradually increased?
Slip
Frequency and voltage together (maintaining V/f)
Torque
DC injection
An H-bridge inverter with dead time leads to:
Excessive speed
Zero output
Output voltage distortion and torque ripple
Filter failure
If snubber capacitance is too large in a power converter, what issue arises?
Slow switch turn-off
High EMI
Overcurrent
Dead short
A multilevel inverter reduces:
Device cost
THD (Total Harmonic Distortion)
Power factor
Regeneration
A four-quadrant chopper is used for:
Single speed
Two-direction speed and torque control
Forward only
Braking only
In a buck converter, increasing load current causes output voltage to:
Drop unless compensated
Increase
Remain fixed
Oscillate
Which converter topology is best suited for high step-down ratio?
Boost
Buck-boost
Flyback
Interleaved buck
In DC drives, current ripple causes:
Higher speed
Torque pulsation and vibration
Better control
Reduced inductance
A DC motor drive using a dual converter needs interlocking. Why?
Reduce speed
Prevent shorting both converter outputs
Increase efficiency
Switch modes
An inverter-fed motor gets overheated. What is a probable cause?
High-frequency harmonics and low-quality modulation
High input voltage
PWM disabled
Soft starter
A DC chopper reduces motor noise by:
Lowering switching frequency
Using higher switching frequency
Boost control
Using a freewheeling diode
For high-power IGBT modules, what is used for isolation and protection?
Snubber and gate driver with desaturation detection
MOSFET driver
Thermal relay
Zener diode
In a DC-DC converter, ESR of output capacitor affects:
Switching frequency
Output voltage ripple
Switching loss
Input current
What is an effect of long motor cables in VFD-driven systems?
Faster speed
Reflection-induced overvoltage at motor terminals
Increased PWM resolution
Reduced torque
Why is synchronous rectification preferred in buck converters for high current?
Less heat dissipation and higher efficiency than diode
No EMI
Boosts voltage
No feedback required
