Design Of Digital Trigger For A Soft Starter

The controller of soft-starting for new type three-phase asynchronous motor mostly adopts circuits which change the stator voltage of asynchronous motor, which has simple structure, reliable performance, low cost and facile with transducer. Accordingly, the maintenance in application on comparison high-power asynchronous motor of the controller becomes wider and wider. But existing systems mostly have some shortages, for example, too big, imprecise control, simple man-machine interface and low intelligence.This introduces the development of the SCR trigger, On discussing the analog trigger , the integrated trigger ,the computer-controlled trigger and the digital trigger ,we adopt the CPLD+MCU controller. The CPLD is used to produce the trigger pulse signal and MCU complete control and generating algorithm .This method makes the system have a wide triggering angle, high controlling, precision and better symmetry output pulses.This discusses the theory of impendence conversion of the soft starter on motor firstly, including the trigger principle, it refers to the designed programme, besides, it introduces the hardware and the software system that are centered by CPLD and MCU of the digital trigger. This paper uses the intelligent algorism, it compares the practical current of the motor staring and the expected current in order to make sure of the control angle of the SCR and delivers the control signal to CPLD, the CPLD will get the trigger impulse in respond to the signal. So in this course, the motor will start softly.In view of the importance of sync signal and trigger pulse in the digital trigger system ,the generating of sync signal and trigger pulse are simulated and the various parts of the simulation waveform are given...