Patent ID: 7368891

Claim:
A charge control method of a capacitor in a thyristor converter equipped with a thyristor for rectifying an AC voltage, a CPU for outputting an on/off control signal to a thyristor driver for driving the thyristor, a voltage detection sensor for measuring the AC voltage and a capacitor charging voltage, and a capacitor connected to a DC circuit, said method comprising the steps of: measuring the AC voltage and the capacitor charging voltage with the voltage detection sensor, and determining a differential voltage between the thyristor firing phase voltage and the capacitor charging voltage, and firing the thyristor only when the firing phase voltage of the thyristor becomes lower than a specified voltage determined from the differential voltage, wherein, if a firing start interval of the thyristor is not shorter than a time calculated by subtracting a predetermined time from the previous firing start interval, the thyristor is fired at one control cycle earlier than the previous firing start timing by subtracting 1 from the previous firing start counter value.