Power Decoupled Three-Port Isolated DC-DC Converter Based on MMC and Optimization Design of Submodule Capacitance and Arm Inductance

A three-port isolated resonant dc-dc converter based on the modular multilevel converter (MMC) is proposed. The essential reason for power coupling between the low-voltage ports is analyzed for the first time. The topology-level power decoupling approach by setting the switching frequency equal to the resonant frequency of the equivalent resonant link on the high-voltage side (HVS) is proposed. A unified multishift-phase angle optimization modulation strategy is proposed based on the quasi-two-level modulation to minimize the root mean square of resonant current. Furthermore, the transient characteristics of submodule (SM) capacitor voltages and arm inductor currents of the proposed converter are analyzed in detail. Based on this, the precise design rule of the SM capacitance and arm inductance is proposed to significantly reduce their size and cost. The correctness and feasibility of the proposed converter, corresponding modulation strategy, and the parameter design rule are verified by the detailed experimental results.