Page 57 – Ultra Hard Mixed Test (Multilevel + PWM)
Subject: Power Electronics
Level: GATE / PSU Ultra Advanced
🔹 Q1.
A CHB inverter has 4 H-bridges per phase. Find number of output levels.Levels = 2n + 1 = 2(4) + 1 = 9
Answer: 9 Levels🔹 Q2.
For a 5-level NPC inverter, find number of clamping diodes per phase.Diodes = (m−1)(m−2) = (5−1)(5−2) = 4×3 = 12
Answer: 12 diodes🔹 Q3.
For a 7-level FC inverter, find number of flying capacitors per phase.Capacitors = (m−1)(m−2)/2 = (7−1)(7−2)/2 = (6×5)/2 = 15
Answer: 15 capacitors🔹 Q4.
A 3-level NPC inverter operates with Vdc = 900 V. Find switch voltage stress.Stress = Vdc/(m−1) = 900/(3−1) = 450 V
Answer: 450 V🔹 Q5.
In Phase-Shifted PWM for 7-level CHB, find carrier phase shift.Number of carriers = m−1 = 6 Phase shift = 360°/6 = 60°
Answer: 60°ðŸ”¹ Q6.
Increasing number of levels mainly reduces: A) Switching loss B) Voltage rating C) THD D) DC sourceAnswer: C
🔹 Q7.
Which inverter requires multiple isolated DC sources? A) NPC B) CHB C) FC D) 2-LevelAnswer: B (CHB)
🔹 Q8.
Which PWM technique is best for CHB inverter? A) Level-shifted B) Phase-shifted C) Sinusoidal only D) Random PWMAnswer: B
🔹 Q9.
For 9-level NPC inverter, find switch stress if Vdc = 1200 V.Stress = 1200/(9−1) = 1200/8 = 150 V
Answer: 150 V🔹 Q10.
More flying capacitors lead to: A) Easier balancing B) Complex control C) Lower switching frequency D) Lower voltage stressAnswer: B
Ultra Memory Capsule
✔ CHB → Multiple DC sources ✔ NPC → Many diodes ✔ FC → Many capacitors ✔ Stress = Vdc/(m−1) ✔ Levels = 2n + 1 ✔ PS-PWM shift = 360°/(m−1)
Ultra Advanced Mixed Test – Shaktimatha Learning
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