Inductor Current Ripple Modeling and Mitigation Method of Cascaded Half-Bridge DC/DC Converter Under Unbalanced Conditions

For cascaded half-bridge DC/DC converter based on phase-shifted carrier modulation, if input voltages and references of each module are different, the current ripple on inductor will increase, which could cause more power loss and larger size of the filter. In this paper, the problems of traditional fixed-angles phase-shifting technology are revealed through analyzing the model of current ripple in different conditions. In order to express the ripple characteristics under unbalanced conditions, a frequency domain model is established, which explain the relation among the harmonics in ripple, input and output voltages and phase-shifted angles. Based on the model, a current ripple mitigation strategy by varying the angles is proposed to remove the selective harmonic in ripple. Simulation results on a three-cell modular multilevel DC/DC converter is presented to verify the feasibility and effectivity of proposed models and modulation method.