Two novel control methods expanding input-output operating range for a bi-directional isolated DC-DC converter with active clamp circuit

A bi-directional isolated DC-DC converter is described that uses an active clamp circuit and two novel control methods. The proposed circuit can turn on all switching devices under zero-voltage switching conditions in both buck and boost modes. A “commutation overlap period reduction” method is used to expand the maximum actual duty cycle so that the output power is maintained even if the input voltage decreases in buck mode. An “active commutation and acceleration” method is used to increase the output power by temporarily reversing the power flow from the output side so that the voltage applied to the low-voltage side MOSFETs is kept down in boost mode. Testing under minimum input voltage conditions demonstrated that the proposed methods increased the output power 1.5 times in buck mode and 3.6 times in boost mode. A 2 kW class prototype showed good efficiency (over 90 %) over a wide operating range especially for a high step-up/step-down voltage ratio (more than 20) at high frequency (~100 kHz).