PURPOSE:To reduce the size and to decrease a cost by providing two converters connected in anti-parallel, and stopping the operation of one converter during energizing period of a current attenuating resistor. CONSTITUTION:A power source for a nuclear fusion reactors has two thyristor converters 3, 4 connected in anti-parallel for converting AC power transformed by transformers 1, 2 to the prescribed amplitude into DC to supply forward and reverse currents to a load coil 11, and a DC breaker 6. Further, a diode 15 is connected in series to attenuate a current by a resistor 9 for attenuating a current, an inverting capacitor 12 and a load coil 11, and an inverting switch 13 closed near zero point in series circuit, and a bypass diode 14 connected in parallel. In this case, the current flowing period of the resistor 9 stops operating of the forward thyristor converter 3 to eliminate the circulating current. Thus, the current direction of the load coil 11 can be readily inverted without generating a current zero zone at current inverting time.
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