Patent ID: 7974113

Claim:
An electric power unit for induction heating for providing high frequency alternate pulse current to an induction coil ( 3 ) for induction heating of an object to be heated, the electric power unit comprising: a DC power supply ( 5 ), a smoothing coil ( 4 ) for smoothing DC power from the DC power supply, a bridge circuit ( 1 ) having four reverse-conductive type semiconductor switches connected in a bridge structure, each reverse-conductive type semiconductor switch comprising an anti-parallel circuit with a self arc-extinguishing type element and a diode, a capacitor ( 2 ) connected between the DC terminals of the bridge circuit ( 1 ) for storing the magnetic energy recovered from the circuit when the switches of the bridge circuit ( 1 ) are turned OFF, and control unit ( 6 ) for controlling ON/OFF of the reverse-conductive type semiconductor switches, wherein the control unit ( 6 ) controls, in the cycle of the alternate pulse current to be provided to the induction coil ( 3 ) so as to simultaneously turn ON/OFF a pair of the reverse-conductive type semiconductor switches located diagonally and yet to prevent the two pairs from being turned ON simultaneously; and wherein the control unit ( 6 ) controls the operation so that the frequency of the generated alternate pulse current is lower than the resonance frequency determined by the inductance of the induction coil ( 3 ) and the capacitance of the capacitor ( 2 ) to thereby maintain the resonance conditions without depending on the pulse frequency, to reuse the magnetic energy of the circuit by recovering such energy, and to continuously provide the alternate pulse current to the induction coil ( 3 ) by charging the capacitor ( 2 ) from the DC power supply ( 5 ) through the smoothing coil ( 4 ).