HIGHER HARMONICS COMPENSATING DEVICE

PURPOSE:To prevent occurrence of the switching loss by selecting a compensating mode in response to the level of the higher harmonic current to be compensated. CONSTITUTION:A compensating capacity arithmetic circuit 6 calculates the compensating capacity KVA from an AC component - p of the instantaneous real electric power and an AC component - q of the instantaneous imaginary electric power. A comparator 7 produces an actuating command R* for a compensating device from the capacity KVA, the prescribed compensating device designated capacity KVA* and a constant T which decides the lower limit capacity. A command power arithmetic circuit 8 multiplies both the instantaneous real electric power (p) and the instantaneous imaginary electric power (q) calculated by an electric power arithmetic circuit 1 by the command R* for calculation of the commanded real electric power p' and the commanded imaginary electric power q' respectively. Both powers p' and q' are supplied to an HPF 2' for deletion of DC component and an AC component - p' of the commanded real electric power and an AC component - q' of the commanded imaginary electric power are obtained. A current control circuit 5 is controlled by the command R* received from the comparator 7.