Analytical Calculation of the Difference in Parallel Output Current Between the 12-pulse Rectifier Bridges Based on Transformer Leakage Inductance and DC inter-phase Reactor

Electric propulsion is a future trend in terms of ship propulsion. The high-power multi-pulse rectifier will be widely applied to the electric propulsion system due to its simple structure, high efficiency, high reliability and low cost. Considering the non-ideal characteristics of the 12-pulse rectifier transformer system(RTS) used for 2MW-level propulsion and such factors as transformer leakage inductance, DC inter-phase reactor and rectifier commutation overlap, this paper has presented an equivalent circuit of the two paralleled rectifiers with an inter-phase reactor, formulated the equations of their DC steady-state voltage and AC small signal voltage and derived an analytical expression for the output current difference between the two rectifiers, according to each of four sections. On this basis, the output current difference is calculated and simulated according to different output voltage, AC side leakage inductance and inter-phase reactor value of the transformer. The results show that the derived analytical expression for the output current difference is correct and feasible which will provide the theoretical basis for the optimal design of a 2MW-level 12-pulse RTS involving the transformer leakage inductance and DC inter-phase reactor.