Fault Diagnosis Of Full-control SCR Bridge Rectifier And Reliability Design Of Trigger System

The thyristor trigger control system of full bridge rectification is used for generating the trigger pulse signal to realize AC-DC conversion, which is a key control device for rectification. Its quality is directly related to whether the system running smoothly. The research subject comes from cooperative enterprise, there are the following problems in existing systems. One is voltage zero crossing detection is not accurate enough, another is there are false triggering and missing pulses under intense interference, the last one is that it cannot provide phase-absent protection in time and it is difficult to find the cause of fault and so on. To solve the above problems, the following research work has been implemented.Firstly, it could realize the identification of voltage zero crossing. According to the interference in the industrial field, the voltage zero-crossing detection circuit of constant current diode was designed, the shortages of the traditional RC filter were analyzed, and combining the characteristic of zero crossing signal, a filtering algorithm which could identify the precise moment of the zero crossing according to the moment and the width of the interference was proposed.Secondly, it gave the fault diagnosis method and trigger strategy under fault. Aimed at the absence of phase, it proposed the correction strategy after analyzing the zero crossing signal change at different time of failure. According to the fault of cycle and phase, the influence of the fault on the rectifier output voltage was analyzed, and the limit parameters related to the fault were determined. Furthermore, the trigger strategy under fault was proposed to realize protection.Thirdly, it could make the reliable triggering control. It analyzed the reason of missing pulse of the phase shifting method based on zero crossing signal of single-phase, and proposed a phase shifting method based on zero crossing signals of three-phase. According to the SCR trigger sequence relation and inter turn off interlock, the interlock control logic of trigger pulse was designed.Finally, a platform for debug rectifying control system was constructed. It made the experiment and observed zero crossing signal, voltage waveforms of thyristor gate, system output voltage and phase-shifted pulse. The experimental results show that the trigger is stable and able to realize the rectification control logic smoothly.