A development of novel DC 48 V power supply system utilizing 18-pulse rectified active DCL and resonant converter

This paper proposes a 48 V DC power supply system utilizing a new 18-pulse rectified active DCL and a resonant DC/DC converter. This system consists of rectifier and DC/DC converter units. The rectifier unit includes an 18-pulse rectifier and an active DCL, and realizes high efficient rectification and mitigation of harmonics. The 18-pulse rectifier consists of a main diode rectifier, two sub diode rectifiers and an 18-pulse transformer. The outputs of the main rectifier and two sub ones are connected with each other at DC side terminal in parallel. The capacity of the 18-pulse transformer is decreased to one-third to a conventional 12-pulse rectification. The efficiency of the rectifier unit is increased by means of the passive circuit against the conventional PVM converters. The main circuit of the active DCL includes the voltage source single bridge circuit, RC filter and small capacity of reactance. The voltage source single bridge circuit includes capacitors and MOSFET switching devices. The active DCL realizes the mitigation of harmonics by generating of a compensating ripple voltage by PWM switching of power devices. The resonant DC/DC converter consists of a voltage source half-bridge circuit, high frequency transformers, diodes for rectification and LC filter. The switching frequency of the IGBTs is controlled so as to maintain the DC voltage 48 V. The DC link capacitor and the leak reactance of the high frequency transformers determine the frequency of the resonance. The power losses are decreased by soft switching scheme. The efficiency of the rectifier unit is measured at 98 % with a load of 4.8 kW. The efficiency of the DC/DC converter is 95 %. Consequently the total efficiency of the system is 93 %. By utilizing the 18-pulse rectified active DCL, the total harmonic distortion (THD) of current is improved to 8.6 % by mitigating harmonics.