Purpose. Development of a three-phase power supply for a single-phase resistance welding machine (RWM). The presented power supply utilizes active power factor correction and draws balanced grid currents. Usage of such power supplies allows ensuring electromagnetic compatibility of the RWM with the power grid. Methodology. A mathematical model of the three-phase power supply for single phase RWM based on the frequency converter with direct coupling is developed. The model accounts for welding circuit parameters. Converter input and output currents, converter output voltage are shown. The following power quality parameters of the developed RWM power supply are calculated: power factor, harmonic distortion of input currents, negative sequence current ratio. Findings. To ensure minimum power losses in the power grid, RWM power supply should present a symmetrical active load to the supply network. In case of symmetrical mains voltages, the consumed instantaneous active power is constant. On this basis, the RWM power supply converter operates in a rectifier mode providing constant power to the load. To avoid RWM transformer biasing and to prevent saturation of its magnetic core, the polarity of the converter output voltage is periodically changed. Thus, the primary voltage of the transformer has a form close to rectangular. Formation of the inverter output voltage with a predetermined amplitude and frequency is done by six bidirectional switches with pulse width modulation control. The developed control method allows controlling converter input currents to be proportional to the corresponding phase voltages. Originality. The theoretical basis for the creation of new RWM power supplies with high energy efficiency and electromagnetic compatibility with the power grid is proposed. Practical value. The use of the direct matrix type converter with developed control algorithm for RWM supply makes it possible to ensure the power supply electromagnetic compatibility with the power grid and to improve its energy efficiency by forming symmetrical input currents and eliminating reactive component of the input currents.

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