Govt. Exams
Entrance Exams
For a boost converter, Vo/Vin = 1/(1-D), where D is duty cycle. 48/24 = 1/(1-D) → 2 = 1/(1-D) → 1-D = 0.5 → D = 0.5 or 50%
Active front-end rectifiers use closed-loop current control with PWM modulation to inject harmonics that cancel grid distortion.
Matrix converter requires m×n switches where m=output phases and n=input phases. For 3×3: 9 bi-directional switches.
Cycloconverters use back-to-back (antiparallel) thyristor pairs to enable bidirectional power flow for frequency conversion.
With THD=3%, the fundamental current component is significant. Displacement PF ≈ 0.98 for low THD with controlled rectification.
Combined MOV and RC snubber provides both transient suppression (MOV) and dV/dt protection (RC), offering comprehensive protection.
Dead time should be 2-3 times the device switching time (~0.5-1μs for modern IGBTs), typically 1-3μs to ensure safe commutation.
Modulation index m = Vm/Vc = 0.8/1 = 0.8, where Vm is peak modulating signal and Vc is peak carrier signal.
Theoretical efficiency = 95% (ideal boost), minus 5% losses = 90% actual efficiency.
Gate current = Gate sensitivity × Gate voltage. With 800V forward breakover and 40mA/V sensitivity, minimum gate current ≈ 20mA for reliable triggering.
