A novel line synchronization scheme for static power converters

The conduction intervals of power semiconductors in static converters connected to the AC mains are dictated by the AC line voltages. Accurate and reliable synchronization signals must therefore be generated despite the significant distortion that can be present in the AC voltage. The authors propose a novel method for obtaining accurate zero-crossing signals, based on the use of switched-capacitor filters. The characteristic frequency of such filters depends on the frequency of an external control signal. Therefore, this frequency can be accurately set and made to track the input frequency variations. The scheme is presented and analyzed, and design criteria are derived. Experimental results demonstrate the superiority of the method over conventional filtering techniques. The scheme has been used successfully for phase-controlled thyristor converters and transistorized four-quadrant PWM (pulse-width modulated) AC/DC converters