Page 65 – Power Electronics Mega Question Bank (With Detailed Solutions)
Level: GATE / PSU Comprehensive Practice
🔹 Section 1 – Power Semiconductor Devices
Q1. Why is IGBT preferred over MOSFET at high voltage?
Answer:
IGBT has lower conduction loss at high voltage due to bipolar conduction. MOSFET has higher Rds(on) at high voltage ratings.
---Q2. SCR Turn-off condition?
Answer:
Anode current must fall below holding current (Ih).
---🔹 Section 2 – Controlled Rectifiers
Q3. Single-phase fully controlled rectifier average output voltage?
Solution:
Vo = (2Vm/π) cosα
---Q4. If α = 60°, find output for Vm = 200 V.
Vo = (2×200/Ï€) cos60 = (400/3.14)(0.5) ≈ 63.7 V
---🔹 Section 3 – Choppers
Q5. Buck converter output voltage?
Vo = D × Vin
---Q6. Vin = 50V, D=0.4 → Vo?
Vo = 0.4 × 50 = 20 V
---Q7. Boost converter voltage gain?
Vo/Vin = 1/(1−D)
---🔹 Section 4 – DC-DC Converters
Q8. Buck-Boost gain (CCM)?
Vo/Vin = −D/(1−D)
---Q9. DCM gain depends on?
Duty cycle, Load resistance, Inductance, Switching frequency.
---🔹 Section 5 – Inverters
Q10. Output RMS of square wave inverter?
Vrms = Vdc
---Q11. Fundamental RMS value?
V1(rms) = (4Vdc)/(Ï€√2)
---🔹 Section 6 – PWM
Q12. What happens when modulation index m > 1?
Overmodulation occurs. Waveform becomes non-sinusoidal.
---🔹 Section 7 – Numerical Advanced
Q13. Buck converter:
Vin = 24V D = 0.5 R = 12Ω Find Io.Vo = 0.5×24 = 12V Io = 12/12 = 1A
---Q14. Boost converter:
Vin = 20V D = 0.6 Find Vo.Vo = 20/(1−0.6) = 20/0.4 = 50V
---Q15. Inductor ripple in buck:
Vin=30V, D=0.4, L=100µH, fs=50kHzΔIL = VinD/(Lfs) = 30×0.4/(100×10⁻⁶×50000) = 12/5 = 2.4A
---🔹 Section 8 – Stability & Control
Q16. Buck converter order?
Second order system (LC filter).
---Q17. Natural frequency?
ω₀ = 1/√(LC)
---Q18. ESR effect?
Introduces zero → improves phase margin.
---Final Power Electronics Master Summary
✔ SCR → Line commutation ✔ Buck → Vo = DVin ✔ Boost → Gain = 1/(1−D) ✔ Buck-Boost → Inverting ✔ DCM gain depends on R, L, fs ✔ Inverter fundamental important ✔ Control ensures stability
Power Electronics Mega Revision – Shaktimatha Learning
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