Soft Charge Circuit for Diode Front-End Variable Frequency Drives Evaluation

This paper evaluates and proposes a new topology for soft charging DC bus capacitors in Variable Frequency Drives (VFDs) to replace traditional mechanical contactor-resistor arrangements, addressing issues like contact fatigue and brown-out transients. The proposed circuit uses a DC link inductor with a resistor-assist circuit and two thyristors to achieve autonomous, logic-free operation, and is compared against other techniques such as magneto-resistive elements and semi-converter topologies.