STARTING HIGH FREQUENCY INVERTER OF PARALLEL RESONANCE TYPE

摘要

PURPOSE:To make a starting stably operable regardless of light load and heavy load, by processing an operation of the attenuation factor of output voltage obtaimed by discharging a condenser in the starting circuit, and by adjusting a starting current for the inverter in accordance with the attenuation factor. CONSTITUTION:When operated an induction furnace 4 and the like by an inverter 3, firstly with a starting thristor 6 turned on before going into operation, an attenuation waveform of the voltage produced by the above is detected and inputted to a controller 9, and a value of the starting current is set in accordance with a ratio of e3/e2 of the attenuation waveform. Thereafter with the load side of a DC reactance 2 short-circuited to flow a DC current Id, in a comparison with the starting current set value, for the level of Id when becoming the set value, the thyristor 6 is again turned on to make a starting operation. Consequently, the starting current is adjusted in accordance with the condition of a load of the furnace 4, thus capable of stably making a starting operation without causing an excessiveness of output voltage and failure of commutation.