Capacitor-type welding device and capacitor-type welding method

A welding method using a capacitor type welding device, the capacitor type welding device including:

• a charging circuit configured to receive an AC electric power and convert the AC electric power to a DC electric power, and including a hybrid bridge full wave rectifier circuit, which has thyristors and rectifier diodes connected in a bridge structure, or a thyristor full wave rectifier circuit, which has thyristors connected in a bridge structure;
• a welding transformer having a primary winding and a secondary winding;
• a welding capacitor configured to be charged by a charging current of the DC electric power which flows in a charging path from the charging circuit, the charging path including at least the primary winding or an inductor connected in series to the primary winding and provided between the charging circuit and the primary winding;
• a discharge switching element configured to discharge the welding capacitor charged by the charging circuit for transforming electric charge from the welding capacitor to the welding transformer to perform welding when the discharge switching element is in a conduction state, the discharge switching element configured to stop discharging the welding capacitor when the discharge switching element is in a non-conduction state;
• and
• a bypass switching element connectable in parallel to the charging circuit and connectable across output terminals of the charging circuit, the bypass switching element having a forward-blocking function not to allow current to flow through the bypass switching element when the bypass switching element is in a non-conduction state, the bypass switching element configured to cause a backflow current, which flows due to a magnetic energy stored in an inductance of the primary winding or the inductor of the charging path, to bypass the charging circuit when the bypass switching element is in a conduction state;
• and
• a control circuit including:
• a sequencer configured to generate a charge signal having a time width and generate a discharge signal after the charge signal terminates;
• a control signal generating circuit configured to send a control signal to the thyristors of the charging circuit to cause the charging circuit to perform a charging process while the charge signal is being generated;
• and
• a drive circuit configured to send a first drive signal to the bypass switching element in synchronization with the charge signal to bring the bypass switching element into the conduction state for causing the backflow current to bypass the charging circuit when the backflow current flows, and send a second drive signal to the discharge switching element in synchronization with the discharge signal to bring the discharge switching element into the conduction state for transferring the electric charge from the welding capacitor to the welding transformer after the bypass switching element enters the non-conduction state when the DC electric power is not supplied to the welding capacitor from the charging circuit;
• the welding method comprising:
• preparing the bypass switching element to be connected in parallel across output terminals of the charging circuit;
• bringing the bypass switching element into the conduction state to cause the backflow current to bypass the charging circuit, the backflow current being caused to flow by the magnetic energy stored in the inductance of the primary winding or the inductor of the charging path;
• and
• bringing the discharge switching element into the conduction state after the bypass switching element enters the non-conduction state and recovers the forward-blocking function.