PURPOSE: To perform steady operation without increasing current capacity, by a method wherein after making gate signal of a second cycloconverter, lagging reactive power at input side taken by this is gradually increased, and voltage of a phase advancing capacitor is made high.

CONSTITUTION: A high-frequency link converter is constituted by three-phase AC power source SUP, AC reactor Ls, first∼second circulation current type cycloconverters CC-1∼2, a high-frequency phase advancing capacitor CAP, and three-phase AC motor M. Control circuits include a starting control circuit START, a voltage control circuit AVR, a speed control circuit SPC, a reactive power control circuit AQR and the like as shown in the figure. In this constitution, at the starting state, since voltage peak value of the phase advancing capacitor CAP is lowered, the leading reactive power taken by this is decreased and therefore the circulation current of the first cycloconverter CC-1 is decreased. Also the reactive power of the second converter CC-2 is gradually increased and voltage of the CAP is raised.