Page 20 – Dual Converter (Fully Controlled Bridge)
1️⃣ What is a Dual Converter?
A Dual Converter consists of two fully controlled bridge converters connected back-to-back.
- ✔ Allows Bidirectional Power Flow
- ✔ Used for Reversible DC Drives
- ✔ Enables Four-Quadrant Operation
2️⃣ Basic Configuration
- Converter 1 → Rectifier Mode
- Converter 2 → Inverter Mode
- Both connected to same DC load
(A) Non-Circulating Current Mode
- Only one converter operates at a time
- No circulating current
- Simpler control
(B) Circulating Current Mode
- Both converters operate simultaneously
- Reactor required to limit circulating current
- Smooth transition between modes
3️⃣ Average Output Voltage
Vavg = (2Vm / π) cos α
For dual converter:
α₁ + α₂ = 180°
This ensures:
Vd1 = −Vd2
Necessary to avoid large circulating currents.
4️⃣ Applications
- ✔ Reversible Speed Control
- ✔ Regenerative Braking
- ✔ High Power DC Motor Drives
- ✔ Rolling Mills
- ✔ Elevators
5️⃣ Four Quadrant Operation
| Quadrant | Voltage | Current | Operation |
|---|---|---|---|
| I | + | + | Forward Motoring |
| II | + | − | Forward Braking |
| III | − | − | Reverse Motoring |
| IV | − | + | Reverse Braking |
⚠ GATE Important Points
- Firing angle relationship (α₁ + α₂ = 180°)
- Circulating current control
- Reactor sizing concept
- Power reversal understanding
- Four quadrant interpretation
Very Important: Dual converter enables complete reversible control of DC motor.
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