PURPOSE: To prevent a resonance by a system impedance and a load-side capacitor and thereby prevent the appearance of a higher harmonic current component which is caused by a higher harmonic voltage component of the bus bar voltage by considering an active filter as an equivalent resistance at a specified frequency by a connection voltage detection method.

CONSTITUTION: This is a combination of two methods; a load current IL detection method wherein a higher harmonic current component ILh of a load 3 current IL is detected and a first compensating current Ian which is opposite phase to the higher harmonic current component ILh is generated and an active filter (AF) 13 connection voltage detection method wherein a higher harmonic voltage component of a bus bar 2 voltage Vs is detected at a power reception point B and a second compensating current Iav which is in phase with the higher harmonic voltage component and which has an amplitude proportional to that of the higher harmonic voltage component. The higher harmonic current component ILh which appears on the load 3 side is cancelled and compensated for by the load current IL detection method. And, by the AF 13 connection voltage detection method, the AF 13 is apparently considered as an equivalent resistance at a specified frequency and thereby a resonance is prevented from occurring.