This paper investigates the starting current of an AC/DC/DC converter, consisting of a three-phase diode bridge rectifier and a synchronous buck converter. The use of microprocessors in such converters increases the total cost and also reduces reliability due to EMI phenomena. For this reason, by removing the microprocessor, a start-up plan including a limiting starting resistor and then soft starting the switching module is proposed in this paper. By modeling the system under different operating modes, a solution is presented to minimize the circuit startup period, which includes minimizing the bypass time of the startup resistor and reducing the switching soft startup period as possible. The proposed method has been implemented on a 15-kW converter feeding from a three-phase 380 V power grid and provides up to 300 Vdc/50 Adc to supply an electroplating pool. The results show that the sequential startup procedure, including using a 50 ohm/1500 w resistor for 3 seconds, and then bypassing it, then soft start switching after half a second and during 1.5 s, can move this circuit to a steady state in 5 seconds, keeping current in all parts below half rated current.
