Single and Three phase dual converters

SINGLE PHASE DUAL CONVERTERS

Dual converter: The back to back connection of two fully controlled converters across the load circuit is named as Dual converter.

The single phase full converters allow only two quadrant operation with inductive loads to extent the operation to four quadrant the dual converters are used.

--> Dual converters are suitable for high power applications but not for low power applications.

*The below circuit explains 1-φ dual converters with circulating current.

*Why circulating current mode operation is efficient?

In circulating current mode

1. load current is continuous and it is fast process

2. Two converters are simultaneously operated

3. The circuit will protect with current limiting reactors

4. Average output load will be more than the load.

*The dual converters consists of two full converters one with positive and another with negative output voltages.

*for highly inductive load the dual converters will operate in four quadrant with continuous current mode.

*The delay angle varies from 0 to +2Em/π, -2Em/π

Wave forms:

The below figure shows wave forms related to single phase dual converters

-->When the circuit is fed with the supply the thyristor T1 and T3 conducts positive half cycle at converter 1 and T5, T6 conducts positive half cycle at converter 2

-->For negative half cycle the thyristors T3,T4,T7,T8 are takes the active position at converter 1 and converter 2.

*For positive half cycle the current direction is given by

For converter 1: P – T1 – Lr1/2 – LOAD – T2 – N

For converter 2: N – T6 – Lr2/2 – LOAD – T5 – P

*For negative half cycle the current direction is given by

Converter 1: N – T3 – Lr1/2 – LOAD – T4 – P

Converter 2: P – T8 – Lr2/2 – LOAD – T7 – N

THREE PHASE DUAL CONVERTERS

For high voltage applications three phase dual converters are used. The two three phase full converter connected back to back to form the dual converters as shown in below figure: