PURPOSE: To enable operating an apparatus up to a high frequency by controlling the overlapping ratio of bias voltage of a cycloconverter in the manner of decreasing said bias voltage according to the increase of an output frequency.
CONSTITUTION: When an AC power of voltage Vi and frequency fi is supplied to a cycloconverter 3 from a power source 1 via an input transformer 2, a cycloconverter controller outputs an AC power of voltage V0 and frequency f0 and supplies it to an AC motor 4 to drive said motor 4 at a variable speed. According to the bias control system of said cycloconverter, the rate of change of a voltage increases by overlapping of bias voltages. Therefore, when the overlapping ratio of a bias voltage is so controlled as to drop with the increase of an output frequency, it is possible to control the increase of the rate of change of an output voltage. As a result, said controller can continue to operate up to a high frequency.
ETO TETSUO
YAMASHINA MITSUNORI
MATSUTAKE MITSUGI
TAKAHASHI JUNICHI
