POWER ELECTRONICS - B.Tech 6th Semester Exam., 2019

Draw the symbols of BJT, MOSFET and SITH.

The reverse recovery time of a diode is \( t_{rr} = 3~\mu s \) and the rate of fall of the diode current is \( di/dt = 30 \text{ A}/\mu s \). Determine the stored charge \( Q_{RR} \) in reverse recovery zone.

What is the softness factor of diodes?

Explain forward-biased safe operating area (FBSOA) of BJT.

Define distortion factor (DF).

A step-up d.c.-d.c. converter has input voltage \( V_s = 10 \text{ V} \), inductance \( L = 1 \text{ mH} \), duty ratio \( d = 0.5 \) and time period \( T = 1 \text{ ms} \). Find the peak-to-peak ripple current in inductor.

The H-bridge inverter has an R-L-C load with \( R = 10~\Omega \), \( L = 31.5 \text{ mH} \) and \( C = 112~\mu F \). The inverter frequency is \( f_0 = 60 \text{ Hz} \) and d.c. input voltage is \( V_s = 220 \text{ V} \). Find the output fundamental r.m.s. voltage.

Find the line-to-line r.m.s. voltage of three-phase inverter operating in \( 180^{\circ} \) conduction mode if d.c. input voltage \( V_s = 220 \text{ V} \).

Explain dynamic current sharing in parallel operation of thyristors.

The full converter is connected to a 120 V, 60 Hz supply. The load current \( I_a = 8 \text{ A} \) is continuous and its ripple content is negligible. If the delay angle is \( \alpha = \pi/3 \), calculate power factor.

The three-phase bidirectional delta-connected controller has a resistive load of \( R = 10~\Omega \). The line-to-line voltage is \( V_s = 208 \text{ V} \) (r.m.s.), 60 Hz and the delay angle is \( \alpha = 2\pi/3 \). Determine the r.m.s. output voltage \( V_0 \), the input PF and the r.m.s. current of a thyristor \( I_R \).

Explain three-phase full-wave delta-connected controller with various waveforms.

A single-phase half-wave converter is operated from a 120 V, 60 Hz supply and the resistive load is \( R = 10~\Omega \). If the average output voltage is 50% of the maximum possible output voltage, calculate the delay angle, the r.m.s. and average output currents.

Explain three-phase full converter with R-L load with various waveforms.

Explain two-transistor model of a thyristor.

A single-phase half-bridge inverter has resistive load of \( R = 5~\Omega \) and the d.c. input voltage is \( V_s = 100 \text{ V} \). Determine the r.m.s. output voltage at the fundamental frequency \( V_{01} \) and the output power \( P_0 \).

A single-phase full-bridge inverter is operated at 1 kHz and uses a uniform PWM with four pulses per half-cycle for voltage control. Plot the fundamental component, distortion factor and THD against the modulation index M.

The bridge inverter has an R-L-C load with \( R = 10~\Omega \), \( L = 31.5 \text{ mH} \) and \( C = 112~\mu F \). The inverter frequency is \( f_o = 60 \text{ Hz} \) and d.c. input voltage is \( V_s = 220 \text{ V} \). Calculate the r.m.s. load current at the fundamental frequency \( I_{o1} \) and the THD of the load current.

The buck converter has d.c. input voltage \( V_s = 110 \text{ V} \), average load voltage \( V_a = 80 \text{ V} \) and average load current \( I_a = 15 \text{ A} \). The chopping frequency is \( f = 10 \text{ kHz} \). The peak-to-peak ripples are 5% for load voltage, 2.5% for load current and 10% for filter \( L_e \) current. Determine the values of \( L_e \), \( L \), \( C_e \).

Write on the steady state analysis of buck converter.

Explain briefly about Cuk-converter.

The buck-boost regulator has an input voltage of \( V_s = 12 \text{ V} \). The duty cycle \( k = 0.25 \) and the switching frequency is 25 kHz. The inductance \( L = 150~\mu\text{H} \) and filter capacitance \( C = 220~\mu\text{F} \). The average load current \( I_a = 1.25 \text{ A} \). Determine the peak-to-peak output voltage ripple \( \Delta V_c \) and the peak-to-peak ripple current of inductor \( \Delta I_L \).