NEW SYNCHRONIZATION METHOD FOR THYRISTOR POWER CONVERTERS TO WEAK AC-SYSTEMS

This paper presents an improved approach to obtaining good zero voltag e crossing signals. These signals are subsequently used as synchroniza tion signals for a phase controlled thyristor power converter. Detecti on of accurate zero crossings are possible even under the following co nditions: large frequency changes, sudden load changes, and large comm utation overlap angles. The improved accuracy in the integrity of the zero crossing is obtained by reconstructing a voltage representing the ac source voltage . This voltage is determined from the distorted thy ristor converter input voltage, the converter input current, and an on line identification of the source impedance using a microcontroller-ba sed adaptive algorithm. The improvement provided by the new zero cross ing detection scheme is verified experimentally.