What is the purpose of double pulsing a thyristor?

Double pulsing a thyristor is a technique used primarily in fully controlled thyristor bridge circuits, particularly during the starting process and in intermittent operation. The main purpose of double pulsing is to ensure reliable and consistent firing of the thyristors, especially during commutation.

1. Reliable Commutation: In a three-phase thyristor bridge, each thyristor needs to be triggered at the right moment to ensure proper commutation. Double pulsing helps ensure that the thyristors are conductive at the time of commutation by providing a subsequent pulse 60 degrees after the initial firing pulse. This is crucial for maintaining the flow of current and preventing misfires, which could disrupt the operation of the circuit2.

2. Handling Rotating Field Directions: Double pulsing is also important when dealing with different directions of the rotating field in three-phase AC systems. It allows the circuit to adapt to both clockwise and counterclockwise rotating fields without requiring external adjustments, ensuring consistent operation regardless of the field direction2.

3. Enhanced Control: In some configurations, double pulsing can enhance the control over the thyristor bridge by providing additional timing flexibility. This can be particularly useful in complex power conversion systems where precise timing of thyristor firing is critical12.

In summary, double pulsing thyristors is essential for ensuring reliable operation, especially during startup and in systems where precise timing and adaptation to different operating conditions are necessary.