Charging system including AC/DC converter and DC/DC converter in which inrush current is suppressed
A charging system includes an AC/DC converter a DC/DC converter, and a control circuit. The AC/DC converter is connected between first/second input nodes and first/second intermediate nodes and is connected to an AC power supply via the first/second input nodes. The DC/DC converter is connected between the first/second intermediate nodes and first/second output nodes and is connectable to a battery via the first/second output nodes. The DC/DC converter includes an isolation transformer, a primary circuit, and a secondary circuit. The primary circuit includes switching elements. The control circuit causes the switching elements to start operation at a first frequency when the AC/DC converter and the DC/DC converter are activated, and causes the switching elements to operate at a second frequency when the AC/DC converter and the DC/DC converter are in steady operation. The first frequency is higher than the second frequency.
1 . A charging system comprising:
an alternating current/direct current (AC/DC) converter connected between: a first input node and a second input node, and a first intermediate node and a second intermediate node, the AC/DC converter being connected to an AC power supply via the first input node and the second input node;
a direct current/direct current (DC/DC) converter connected between: the first intermediate node and the second intermediate node, and a first output node and a second output node, the DC/DC converter being connectable to a battery via the first output node and the second output node, the DC/DC converter including an isolation transformer, a primary circuit, and a secondary circuit, the primary circuit being disposed on a primary side of the isolation transformer and including switching elements, the secondary circuit being disposed on a secondary side of the isolation transformer; and
a control circuit that, in operation:
causes the switching elements to start operation at a first frequency when the AC/DC converter and the DC/DC converter are activated,
causes the switching elements to operate at a second frequency when the AC/DC converter and the DC/DC converter are in steady operation, the first frequency being higher than the second frequency,
when the AC/DC converter and the DC/DC converter are activated:
sets a reference duty ratio of a gate signal of each of the switching elements to a predetermined duty ratio while maintaining an operation frequency of each of the switching elements at the first frequency, and
increases the reference duty ratio of the gate signal of each of the switching elements from zero to the predetermined duty ratio while maintaining an operation frequency of each of the switching elements at the first frequency.
2 . The charging system according to claim 1 , wherein the DC/DC converter is an inductor-inductor-capacitor (LLC) converter.
3 . The charging system according to claim 1 , wherein the first frequency is closer to a resonance frequency of the isolation transformer than the second frequency is.
4 . The charging system according to claim 1 , wherein the control circuit is further configured, when the AC/DC converter and the DC/DC converter are activated, to lower an operation frequency of each of the switching elements from the first frequency to the second frequency while maintaining a reference duty ratio of a gate signal of each of the switching elements at the predetermined duty ratio.
5 . The charging system according to claim 4 , wherein the control circuit lowers the operation frequency of each of the switching elements from the first frequency to the second frequency in a gradual manner or in a step-by-step manner.