POWER ELECTRONICS – PAGE 17
Single Phase Fully Controlled Bridge Rectifier
1️⃣ What is Fully Controlled Bridge?
A converter using 4 SCRs arranged in bridge configuration.
- All switches are controllable
- Output voltage controlled using firing angle α
- Can operate in rectifier & inverter mode
2️⃣ Circuit Operation
Positive Half Cycle:
- SCR1 & SCR2 conduct
- Triggered at firing angle α
Negative Half Cycle:
- SCR3 & SCR4 conduct
- Triggered at π + α
Each pair conducts for 180°
3️⃣ Output Voltage Equation (R Load)
Vavg = (2Vm / π) cos α
- α = 0° → Maximum output
- α = 90° → Vavg = 0
- α > 90° → Inverter mode
4️⃣ Important Features
- Better control than half wave
- Higher average output
- Bidirectional power flow possible
- Lower ripple compared to half wave
5️⃣ Waveform Behaviour
- Output starts at firing angle α
- Symmetrical waveform
- Negative region possible if α > 90°
🎯 GATE / PSU Important Points
- Derivation of average voltage
- Rectifier vs Inverter mode
- Waveform identification
- Effect of firing angle
Very Important: Fully controlled bridge gives maximum control over output voltage.
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