Inverter type resistance welding control unit

摘要

PURPOSE:To ensure safety of an inverter element by controlling current variation to exceed a set value by a limiter function to allow a limiter level to correspond to a set value of a secondary current instead of the vicinity of a maximum allowable current value of the inverter element. CONSTITUTION:The limiter level is allowed to correspond to the set value of the secondary current (welding current) and ordinary current control is carried out by pulse width modulation(PWM) of a feedback system. When contact conditions of materials to be welded, etc., are varied and the welding current decreases rapidly, the pulse width of a primary current pulse extends so as to compensate it and its peak value also rises. When the peak value attains the limiter level, a limiter means is actuated and the pulse width of a primary current is limited. By this method, even if the contact conditions are improved and the secondary current is going to increase immediately after that, the limiter function at the primary side works and the secondary current is maintained at the set value. In addition, the abnormal rise of the primary current pulse which is caused by magnetic saturation of a transformer is suppressed and the safety of the inverter element is secured.