Frequency-Controlled Inverter Power Supply for Spot Welding based on Transformer Leakage Inductance

In the frequency-controlled inverter power supplies, the reactance component of the transformer connected to the inverter is proportional to the power supply frequency. Transformer leakage inductance as seen from the primary winding of the transformer is known to decrease as the power supply frequency increases. This signifies that merely controlling the power supply frequency may not be sufficient to control transformer secondary current over a wide range. This paper discusses the possibility of a frequency-controlled inverter power supply. Experimental results indicate that it is possible. Control of an actual welding current with a frequency-controlled inverter power supply was found to require a non-inductive current sensor Thus, a current sensor consisting of two copper pipes is introduced. PWM inverter power supplies that utilize IGBTs capable of driving induction motors at variable speeds are well known. In recent years, research into reducing IGBT switching losses has intensified due to increased interest in issues concerning energy conservation and the global environment. The frequency-controlled inverter power supply, unlike the PWM design, does not require high-frequency switching, and therefore contributes to reduced switching losses.