Accurate frequency-domain analysis and hybrid control method for isolated dual active bridge series resonant DC/DC converters

This study proposes an accurate frequency model of dual active bridge series resonant DC/DC converters (DABSRC). Differing from the conventional first harmonic approximation method, the proposed steady-state model considers all the harmonic components, which gives an accurate expression of transferred power and resonant current. Based on the proposed model, a precise soft switching criterion was derived, and the soft switching region was extended. On top of that, a hybrid control strategy combining phase shift modulation and frequency modulation was proposed, to achieve soft switching under wide voltage gain and load variations. Thanks to the extended soft switching region, DABSRC can achieve zero-voltage-switching turn-on at light loads, only with a slight increase in switching frequency, hence improving the efficiency a lot. The accurate frequency model and the hybrid control were validated using a 500 W laboratory prototype. The experiment results showed accurate predictions of the proposed model and significant improvements in light load efficiency over a wide range of input voltages.