New synchronization method for thyristor power converters to weak AC-systems

An improved approach to obtaining good zero-voltage-crossing signals is presented. These signals are subsequently used as synchronization signals for a phase-controlled thyristor power converter. Detection of accurate zero crossings is possible even when there are large frequency changes, sudden load changes, or large commutation 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 thyristor converter input voltage, the converter input current, and an online identification of the source impedance using a microcontroller-based adaptive algorithm. The improvement provided by the new zero crossing detection scheme is verified experimentally.<
>