Page 32 – Fully Controlled Rectifier with RL Load (GATE Focus)
Subject: Power Electronics
Topic: Single Phase Fully Controlled Bridge – RL Load
Level: GATE / PSU Advanced
🔹 Why RL Load is Important?
- Current becomes continuous
- Conduction extends beyond π
- Extinction angle (β) appears
- Inverter mode possible
🔹 Circuit Behaviour
Due to inductance, current does not fall to zero instantly.
Thyristors continue conducting even after supply becomes negative.
🔹 Average Output Voltage
Vavg = (Vm/Ï€) (cos α − cos β)
Where:
α = Firing Angle
β = Extinction Angle
🔹 Continuous Conduction Mode (CCM)
If load inductance is large → Current continuous
β ≈ α + Ï€
Then formula simplifies to:
Vavg = (2Vm/π) cos α
(Same as R load case in CCM condition)🔹 Important GATE Points
- Ripple frequency = 2f
- Inverter mode when α > 90°
- Overlap occurs if source inductance present
- Power factor decreases as α increases
🔹 Numerical Example
Given: 230V rms, α = 45°, Continuous current
Vm = √2 × 230 = 325 V
Vavg = (2 × 325 / Ï€) cos 45°
= (650 / 3.14) × 0.707
= 207 × 0.707
= 146.3 V
Quick Revision
RL Load → Current continuous → β appears
Vavg = (Vm/Ï€)(cos α − cos β)
Practice Daily – Shaktimatha Learning
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