Power Electronics 4

Which PWM technique is most commonly used in PFC circuits?

• Single-pulse modulation

• Sinusoidal PWM

• Hysteresis control

• Space vector modulation

A step- down chopper has Vs = 230 V and R = 10 Ω. For a duty cycle of 0.4, the

power taken by the chopper is 2097 Watts. Find the chopper efficiency. Take the

voltage drop across the chopper switch as 2 V.

• 98 %

• 89.96 %

• 99.14 %

• 96.54

A step-up chopper has input voltage of 220 V and output voltage of 660 V. If the

conducting time of the IGBT based chopper is 100 μs, compute Toff width of the

output voltage pulse.

• 100 μs

• 150 μs

• 50 μs

• Insufficient data

The buck regulator has an input voltage of Vs = 12V. The required average output

voltage is Va = 5V at R = 500 Ω and the peak-to-peak output ripple voltage is 20 mV.

The switching frequency is 25 kHz. If the peak-to-peak ripple current of inductor is

limited to 0.8 A, determine the filter inductance L (in µH)

• 145.83

• 160.70

• 200.40

• 250.10

Which of the following techniques are used to improve the power factor?

• extinction angle control

• symmetrical angle control

• Both

• None

What is the purpose of using a phase-locked loop (PLL) in a PWM rectifier control

system?

• To synchronise the switching frequency with the grid frequency

• To regulate the output voltage

• To minimise the harmonic distortion

• To adjust the power factor

In case of a constant frequency system, Ton = (1/4)T. If the chopping frequency 2

kHz, find the value of Toff.

• (1/8) ms

• (3/8) ms

• (1/8) μs

• (3/8) μs

What does the term "Continuous Conduction Mode (CCM)" mean in the context of a

buck-boost converter?

• The switch is always on

• The diode is always conducting

• The inductor current never drops to zero

• The output voltage is always constant

What is the main disadvantage of a buck-boost converter?

• Low efficiency at all operating points

• Inverted output voltage polarity relative to the input

• Complex control strategy

• High component count

In a boost converter, what is the effect of operating in Discontinuous Conduction

Mode (DCM)?

• The output voltage ripple decreases

• The inductor current falls to zero during each cycle

• The efficiency increases significantly

• The output voltage becomes unregulated