Based on investigating the theory of the model of the synchronous motor and vector control, this thesis designed the measuring device for detecting current crossing zero, the commutating logic circuit without circumfluence, the digital pulse flip-flop circuit.

The wire control circuit is composed by pulse trigger circuit,voltage of armature feedback circuit and chopped wave circuit.

The detail analyses are given of the electric circuit principle in respects such as magnetic control sputter, trigger pulse, self adaptive regulator and the current cut off accompanied with negative feedback.

In accordance with the change of voltage phase on the positive pole of thyristor, this method, which the accurate trigger pulse outputs at the appropriate moment,is called the synchronous or locating phase.

This paper supplied a practical analysis method for us on judging the open-close situation of a thyristor(SCR)under a trigger pulse after analysing a practical pulse,measuring,calculating some important parameters and completing a commision to a control system successfully.