US-12620814-B2 - Charging system including AC/DC converter and DC/DC converter in which inrush current is suppressed

Abstract

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.

Inventors

• Hiroyuki HOSOI
• Atsushi Seki

Assignees

• PANASONIC INTELLECTUAL PROPERTY MANAGEMENT CO., LTD.

Dates

Publication Date

20260505

Application Date

20230203

Priority Date

20220224

Claims (5)

1. 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. 2 . The charging system according to claim 1 , wherein the DC/DC converter is an inductor-inductor-capacitor (LLC) converter.
3. 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. 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. 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.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2022-026820, filed on Feb. 24, 2022, the entire contents of which are incorporated herein by reference. FIELD The present disclosure relates generally to a charging system. BACKGROUND A charging system connected between an alternating current (AC) power supply and a battery is configured to convert AC power received from the AC power supply into direct current (DC) power, convert the DC power into other DC power, and charge the battery with the other DC power (See, for example, JP P2013-516955 A). In such a charging system, an inrush current may be generated due to unstable DC power to be converted in a transition period at the time of activation when the supply of AC power by the AC power supply is started. In the charging system at this moment, it is desirable to suppress the inrush current. SUMMARY A charging system according to the present disclosure includes an AC/DC converter, a DC/DC converter, and a control circuit. The AC/DC converter is 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 is connected to an AC power supply via the first input node and the second input node. The DC/DC converter is 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 is connectable to a battery via the first output node and the second output node. The DC/DC converter includes an isolation transformer, a primary circuit, and a secondary circuit. The primary circuit is disposed on a primary side of the isolation transformer. The primary circuit includes switching elements. The secondary circuit is disposed on a secondary side of the isolation transformer. The control circuit is configured to cause the switching elements to start operation at a first frequency when the AC/DC converter and the DC/DC converter are activated. The control circuit is configured to cause 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. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram illustrating a configuration of a charging system according to an embodiment; FIGS. 2A to 2C are waveform diagrams illustrating pulse width modulation (PWM) control and pulse frequency modulation (PFM) control according to the embodiment; FIG. 3 is a flowchart illustrating operation of the charging system according to the embodiment; FIG. 4 is a diagram illustrating a relationship between operation frequencies of switching elements and voltage gains of the charging system in the embodiment; FIG. 5 is a waveform diagram illustrating operation of the charging system according to the embodiment; and FIG. 6 is a waveform diagram illustrating operation of the charging system according to the embodiment. DETAILED DESCRIPTION Hereinafter, an embodiment of a charging system according to the present disclosure will be described with reference to the drawings. Embodiment The charging system according to the embodiment is connected between an AC power supply and a battery. The charging system is able to charge the battery by converting AC power of the AC power supply into DC power, whereas the charging system is devised to suppress an inrush current at the time of activation when the supply of the AC power by the AC power supply is started. For example, a charging system 1 can be configured as illustrated in FIG. 1. FIG. 1 is a circuit diagram illustrating a configuration of the charging system 1. The charging system 1 is connected between an AC power supply PS and a battery BT. The charging system 1 includes an AC/DC converter 10, a DC/DC converter 20, and a control circuit 30. The DC/DC converter 20 is, for example, an LLC converter. Under the control of the control circuit 30, the charging system 1 converts an AC voltage Vin from the AC power supply PS into a DC voltage Vsub while stepping up the AC voltage Vin by the AC/DC converter 10, converts the converted DC voltage Vsub into a DC voltage Vout for charging while stepping down the DC voltage Vsub by the DC/DC converter 20, and charges the battery BT. The charging system 1 may be, for example, an in-vehicle charger mounted on an electric vehicle or a hybrid vehicle, or the AC power supply PS may be a power system at home or a charging stand, or the battery BT may be an in-vehicle battery. In the charging system 1, an input node Nin1 is connected to one end of the AC power supply PS, and an input node Nin2 is connected to another end of the AC power supply PS. In the charging system 1, an output node Nout1 is connected to the positive electrode of the battery BT, and an output node Nout2 is connected to the negative electrode of the battery BT