Thyristor Convertors

The convertors in dc drive systems are designed to control and supply separately-excited dc machines in applications that demand rapid response, high accuracy and great reliability.

The convertors are available with single-convertor arrangement and in double-convertor arrangement.

Operation. The armature supply unit has a closed-loop current control system which ensures that the armature current follows the set current, reference. The system is based on a current controller, the output signal of which can influence the armature current via the control pulse circuits and the thyristor unit.

The current measurine circuits continuallv supply the current controller with information on the actual value of the armature current, and when this is compared with the reference an error signal is obtained which corrects the output voltage of the controller if necessary.

The controller current includes circuits for adaptive control. This means that the pain of the controller increases if the current is discontinuous. This maintains the response time of the current control system. A typical response time for the current control is 10—15 min.

The current control system includes a buffer amplifier for the actual current value. This makes it possible to connect a meter to displav the armature current, for example. By applying a control signal, the output of the buffer amplifier can be converted, so that the output signal changes sign when the direction of current flow changes in a double convertor.