| 摘要 |
<p>For protection against commutation failures in a motor control circuit, there is provided a method and apparatus by which the charge on a commutating capacitor is made to track the armature current of a separately excited motor regardless of the operating mode of the motor. In preferred form, a commutating network is provided having a commutating capacitor, a charge reversal thyristor, and a commutating thyristor configured to cause commutation of a main, control thyristor upon sequentially gating the charge reversal thyristor and the commutating thyristor with charge of sufficient magnitude stored on the capacitor. The thyristors of the commutating network are gated according to the operating mode of the motor; thus, there is included a means, or step, for sensing the motor operating mode. In the braking mode, the main thyristor is inhibited while the charge reversal and commutating thyristors are alternately, sequentially gated such that commutating capacitor charge is at all times proportional to the braking current. Upon resuming operation in the motoring mode, there is assurance that capacitor charge is sufficient to prevent commutation failures.</p> |
