An automatic voltage regulator (45) and comparator (43) cooperate for calculating the reactive component of converter input voltage applied to the power converter via a reactive element on the basis of deviation between DC voltage across a capacitive element and a DC reference voltage. The real component of converter input voltage is calculated on the basis of the deviation of the phase difference between alternating current and voltage of the power source relative to a reference phase angle difference. A co-ordinate transforms (63) calculates the absolute value of converter input voltage and phase of the voltage, relative to the source voltage, using the calculated values of real and reactive components of converter input voltage. A gate pulse generator (65) modulates a carrier wave using the absolute value and phase angle calculated in the transformer to produce gate pulses for the semiconductor switching elements of the converter based on the existing modulation factor.
