Design of a 200 amp telecom rectifier family using 50 amp DC-DC converters

Abstract

Design of three phase 208/240 Vac, 380/415 Vac, and a 480 Vac input, 54 V dc/200 Adc output telecom rectifiers using the same DC-DC converters is described. The 208/240 Vac rectifier has four 50 Amp DC-DC converters connected in parallel at the inputs and outputs. The DC-DC converters utilize current mode control to insure equal load sharing between DC-DC converters. To allow the use of the same DC-DC converters in a 380 or 480 Vac input design, a split input capacitor bank is utilized. The 480 Vac rectifier has the same four 50 Amp DC-DC converters connected in parallel at the output; at the input, a split capacitor bank is used with two converters across each input capacitor. With a split input capacitor bank, to maintain voltage balance on the input capacitors and equal load sharing between DC-DC converters, current mode control alone is inadequate. A capacitor bank balance control loop was developed to insure that the input capacitor's voltage and the DC-DC converter's output currents remain balanced. The mechanism causing the split input capacitor bank to unbalance is discussed and the bank balance circuit is presented. Finally, results obtained from a 480 Vac input, 54 V dc/200 A dc output telecom rectifier are used to verify the operation of the bank balance circuit. Also, the advantages and disadvantages of using multiple DC-DC converters in different series/parallel combinations are discussed.