The full bridge zero voltage zero current switching(FB-ZVZCS),which could adjust the output power by keeping the duty ratio of lagging leg constant and changing the duty ratio of leading leg,was a common circuit of soft switching arc welding inverter power source.However,when the duty ratio of leading leg was reduced to zero,the output power stayed the constant value instead of becoming zero.The working status and waveforms of some major parameters were studied in this paper while the duty ratio of leading leg was zero.It was concluded that the minimum output power of soft switching inverter was related to the charging voltage of parallel capacitors,and the output power also could be reduced by reducing the duty ratio of lagging leg.A novel two-stage continuous PWM control method that could switch working-mode between full bridge and half bridge was put forward in this paper.This kind of control method could further reduce the output power of soft switching inverter in order to meet the requirement of low heat input of sheet metal welding.
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