Kimiaki Taniguchi

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).

A novel scheme for a bi-directional isolated DC-DC converter with a DC-link diode using reverse recovery current

A bi-directional isolated DC-DC converter using a novel circuit topology and its control method are described. The proposed circuit is based on a voltage-fed full-bridge circuit on the high-voltage side and a current-fed full-bridge circuit with an active clamp circuit on the low-voltage side. In order to make use of only MOSFETs with slow body diodes in the high-voltage full-bridge circuit to reduce the switching loss, the high-voltage side has a newly added DC-link fast recovery diode. The proposed control method, reverse recovery commutation and acceleration, recovers the reverse recovery current of the DC-link diode and stores the current in Lr, and accelerates the current for smooth boost operation so that the voltage applied to the low-voltage side MOSFETs is kept down. All nine MOSFETs can be turned on under zero-voltage switching conditions in both buck and boost modes. The results of testing under minimum input voltage conditions demonstrated that the proposed method increases the maximum output power without increasing the voltage applied to the low-voltage side MOSFETs. A 1.5-kW prototype exhibited efficiency of 94 % at maximum output power at a switching frequency of 100 kHz.

Small boost circuit topology for expanding input voltage range for a bi-directional isolated dc-dc converter

A circuit topology for a bi-directional isolated DC-DC converter and its operation are proposed and evaluation results are discussed. This converter is based on a voltage-source primary circuit and a current-source secondary circuit with an active clamp circuit. To decrease the lower limit of the input voltage for a large voltage range, the proposed topology uses a “small boost circuit” consisting of only a boosting capacitor and a switch on the secondary side. Only when the input voltage is decreased, the switch is kept in the on-state and the secondary voltage is boosted by using transformer series inductance. A 2-kW prototype converter, which has a previously proposed control and the new small boost circuit of the proposed topology, decreased the input voltage lower limit from 289 to 267 V under maximum output conditions.