Inverter thyristors control unit - is connected to three-phase mains for supply of a current to DC motors and uses saw-tooth voltage

摘要

When a control voltage coincides with a saw-tooth voltage, an ignition command is delivered to the corresponding thyristors. The starting point of the saw- tooth voltage depends on a smoothed test voltage which is derived in a series of integrators from zero crossings of a phase voltage. The zero crossing of a test voltage is derived from a phase voltage and this zero crossing is shifted by a phase shifter and a smoothing circuit into the area of another zero crossing of a phase voltage; it serves as a reference point for the beginning of the saw- tooth voltage integration for a next half-wave.