Page 35 – Three Phase Half Controlled Rectifier (Semi Converter)
Subject: Power Electronics
Topic: 3-Phase Semi Converter
Level: GATE / PSU Core
🔹 What is Half Controlled Converter?
- Uses 3 SCRs + 3 Diodes
- Also called Semi Converter
- Freewheeling path exists
- Better power factor than fully controlled
🔹 Average Output Voltage
Vavg = (3√2 VLL / Ï€) (1 + cos α)/2
Where:VLL = Line-to-Line RMS Voltage
α = Firing Angle
🔹 Important Characteristics
- Cannot operate in inverter mode
- Output voltage always positive
- Ripple frequency = 6f
- Freewheeling reduces ripple
🔹 Comparison with Fully Controlled
| Feature | Fully Controlled | Half Controlled |
|---|---|---|
| Devices | 6 SCRs | 3 SCRs + 3 Diodes |
| Inverter Mode | Possible | Not Possible |
| Power Factor | Lower | Better |
🔹 Numerical Example
Given:
VLL = 400 V
α = 60°
Vavg = (3√2 × 400 / Ï€) × (1 + cos 60°)/2
= 540.4 × (1 + 0.5)/2
= 540.4 × 0.75
= 405 V (approx)
Quick Revision
Semi Converter → 3 SCR + 3 Diodes
Vavg = (3√2 VLL / Ï€) (1 + cos α)/2
Power Electronics Series – Shaktimatha Learning
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