A microprocessor-based self-adaptive trigger for thyristor converters

A digital trigger with lock-phase synchro power makes it possible to trace, automatically the change of a power network´s frequency and to ensure symmetrical phases trigger pulses. It is used for thyristor power convertors to restrain the harmful effect of harmonics on power networks. In this paper, a scheme of implementing digital lock-phase by a microprocessor is presented: the principle of digital lock-phase is discussed and a self-adaptive trigger adopting a single chip microprocessor as its core is introduced. The design of a hardware circuit and software system are also given. Finally, this paper analyzes pulse stability and the pulse loss problem, poses an effective solution measure. Because phase-locked loop synchro power is used, the symmetrical error between trigger pulses can be minimized to 0.054°. Practical application shows that this type of trigger not only saves hardware, but also has excellent properties, and the powerful ability of anti-disturbance