Second-Carrier Harmonic Cancellation for a DC Bus Fed by Multiple Dual Active Bridges in More Electric Aircraft Applications

This paper develops a mechanism to suppress second-carrier harmonics on a common DC bus fed by multiple dual-active bridge (DAB) converters. A mathematical model of dc-link current harmonic components of a DAB is derived. Using this model, it is found that the magnitude and the phase angle of the second-carrier harmonic are mainly determined by the phase shift ratio of the DAB converter. Based on this conclusion, a harmonic suppression control scheme has been developed to manage the phase shifts in carrier waves of the two converters. To mitigate the impacts of differences in leakage inductances, voltage source types and levels, an enhanced harmonic cancellation scheme has been developed using an extra control loop to coordinate the duty cycles between DABs to achieve entire harmonic cancellation in general cases. The proposed method demonstrates a significant reduction of second-carrier harmonics and has been validated in both simulation and experiment results.