Torque and speed control of asynchronous machines - involves using three phase thyristor bridge network which can return power to supply when appropriate

摘要

The circuit consists of two full wave three phase rectifying bridges (5) each comprising six thyristors, which are driven by a timed gating circuit. These two circuits are connected effectively in series with intervening chokes between the three phase mains supply and the asynchronous machine. A phase shifted parallel full wave three phase bridge (6) completes the motor operation, whilst a similar pair of bridges (7, 12) is capable of feeding power in the opposite direction via a transformer back to the supply. This achieves a voltage limitation at the machine under changing load conditions, and within certain limits allows smoother control of speed and torque using sequenced firing circuits.