Charging system

Abstract

To provide a charging system capable of suppressing an inrush current.SOLUTION: An AC / DC converter is connected to an AC power supply PS via an input node Nin1 and an input node Nin2. A DC / DC converter is connected between an intermediate node Nmid1 and an intermediate node Nmid2 and an output node Nout1 and an output node Nout2. The DC / DC converter includes an isolation transformer TR, a primary circuit 21, and a secondary circuit 22. The primary circuit is disposed on a primary side of the isolation transformer. The primary circuit includes a plurality of switching elements SW11 to SW14. The secondary circuit is disposed on a secondary side of the isolation transformer. A control circuit causes the switching element to operate at a first frequency when the AC / DC converter and the DC / DC converter are activated, and causes the switching element 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.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a charging system. [Background technology]

[0002] A charging system connected between an AC power source and a battery converts AC power received from the AC power source into DC power, converts the DC power into another DC power, and charges the battery with the other DC power (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2013-516955 Summary of the Invention [Problem to be solved by the invention]

[0004] In a charging system, when the AC power supply starts supplying AC power, an inrush current may occur due to transient instability of the converted DC power, etc. In such cases, it is desirable for the charging system to suppress the inrush current.

[0005] The present disclosure provides a charging system capable of suppressing inrush current. [Means for solving the problem]

[0006] 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, a second input node, and a first intermediate node, a second intermediate node. The AC-DC converter is connected to an AC power source via the first input node, a second input node, and a first output node, a second output node. The DC-DC converter is connectable to a battery via the first output node, a second output node. The DC-DC converter includes an isolation transformer, a primary side circuit, and a secondary side circuit. The primary side circuit is arranged on the primary side of the isolation transformer. The primary side circuit includes multiple switching elements. The secondary side circuit is arranged on the secondary side of the isolation transformer. The control circuit operates the switching elements at a first frequency during startup of the AC-DC converter and the DC-DC converter. The control circuit operates the switching elements at a second frequency during steady operation of the AC-DC converter and the DC-DC converter. The first frequency is higher than the second frequency. When the AC-DC converter and the DC-DC converter are started up, the control circuit increases the reference duty ratio of the gate signal of the switching element from zero to a predetermined duty ratio while maintaining the operating frequency of the switching element at a first frequency. [Effects of the Invention]

[0007] According to the charging system according to the present disclosure, inrush current can be suppressed. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a circuit diagram showing a configuration of a charging system according to an embodiment; [Figure 2] 3A to 3C are waveform diagrams showing PWM (Pulse Width Modulation) control and PFM (Pulse Width Modulation) control in the embodiment. [Figure 3] 3 is a flowchart showing the operation of the charging system according to the embodiment. [Figure 4] FIG. 4 is a diagram showing the relationship between the operating frequency of a switching element and the voltage gain of a charging system according to the embodiment. [Figure 5] FIG. 3 is a waveform diagram showing the operation of the charging system according to the embodiment. [Figure 6]FIG. 3 is a waveform diagram showing the operation of the charging system according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of a charging system according to the present disclosure will be described with reference to the drawings.

[0010] (Embodiment) A charging system according to an embodiment is connected between an AC power supply and a battery, and is capable of converting AC power from the AC power supply into DC power to charge the battery. However, the charging system is designed to suppress inrush current at startup when the AC power supply starts to supply AC power. For example, the charging system 1 may be configured as shown in Fig. 1. Fig. 1 is a circuit diagram showing the configuration of the charging system 1.

[0011] The charging system 1 is connected between an AC power source 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 source PS into a DC voltage Vsub while boosting it using the AC-DC converter 10, and then converts the converted DC voltage Vsub into a DC voltage Vout while stepping it down using the DC-DC converter 20, thereby charging the battery BT. For example, the charging system 1 may be an on-board charger mounted on an electric vehicle or a hybrid vehicle, the AC power source PS may be a power system in a home or a charging station, and the battery BT may be an on-board battery.

[0012] In the charging system 1, an input node Nin1 is connected to one end of an AC power supply PS, and an input node Nin2 is connected to the other end of the AC power supply PS. In the charging system 1, an output node Nout1 is connected to the positive electrode of a battery BT, and an output node Nout2 is connected to the negative electrode of the battery BT.

[0013] In the charging system 1, the control circuit 30 controls the switching elements in the ACDC converter 10 and the DCDC converter 20 by PWM (Pulse Width Modulation) when the ACDC converter 10 and the DCDC converter 20 are started. When the ACDC converter 10 and the DCDC converter 20 are in steady operation, the charging system 1 controls the switching elements in the ACDC converter 10 by PWM and controls the switching elements in the DCDC converter 20 by PFM (Pulse Frequency Modulation).

[0014] PWM control is a control method in which the pulse width of a pulse signal is modulated according to the level of a control signal, as shown in Figures 2(a) and 2(b). Figure 2 is a waveform diagram illustrating PWM control and PFM control. The control circuit 30 varies the pulse width from a reference pulse width according to the amount of change in the level of the control signal from the reference level. In this case, the period can be any period, but the period may also be maintained constant.

[0015] When performing PWM control, the control circuit 30 generates a PWM-modulated wave as shown in Fig. 2(b) in response to the control signal as shown in Fig. 2(a). For example, the reference level of the control signal is set to maximum amplitude Amax, and the reference pulse width of the PWM control is set to maximum pulse width Wmax. In response to the maximum amplitude Amax of the control signal, the control circuit 30 sets the pulse width of the PWM-modulated wave to a maximum pulse width (reference pulse width) Wmax in response to the maximum amplitude Amax of the control signal. In response to the minimum amplitude Amin of the control signal, the control circuit 30 reduces the pulse width of the PWM control from the maximum pulse width (reference pulse width) Wmax to a minimum pulse width Wmin in response to the amount of change in the minimum amplitude Amin of the control signal from the maximum amplitude Amax.

[0016] At this time, if the period is maintained at a constant T, the control circuit 30 changes the duty ratio from the reference duty ratio in accordance with the amount of change in the level of the control signal from the reference level. For example, the reference level of the control signal is set to maximum amplitude Amax, and the reference duty ratio of the PWM modulated wave is set to maximum duty ratio Dmax. In response to maximum amplitude Amax of the control signal, the control circuit 30 sets the duty ratio of the PWM modulated wave to the maximum duty ratio (reference duty ratio) Dmax in accordance with the maximum amplitude Amax of the control signal. As a result, the control circuit 30 sets the pulse width of the PWM modulated wave to the maximum pulse width Wmax (=T×Dmax). In response to minimum amplitude Amin of the control signal, the control circuit 30 reduces the duty ratio of the PWM modulated wave to the minimum duty ratio Dmin in accordance with the amount of change in the minimum amplitude Amin of the control signal from the maximum amplitude Amax. As a result, the control circuit 30 sets the pulse width of the PWM control to the minimum pulse width Wmin (=T×Dmin).

[0017] As shown in Figures 2(a) and 2(c), PFM control is a control that modulates the frequency of a pulse signal according to the level of a control signal. The control circuit 30 changes the frequency from a reference frequency according to the amount of change in the level of the control signal from the reference level. In this case, the pulse width is arbitrary, but the pulse width may be maintained constant, or the duty ratio may be maintained constant. Figure 2(c) illustrates the case where the pulse width is maintained constant.

[0018] When performing PFM control, the control circuit 30 generates a PFM-modulated wave as shown in FIG. 2(c) in response to the control signal shown in FIG. 2(a). For example, the reference level of the control signal is set to a maximum amplitude Amax, and the reference frequency of the PFM control is set to a maximum frequency Fmax. Alternatively, the reference period of the PFM control is set to a minimum period Tmin. In response to the maximum amplitude Amax of the control signal, the control circuit 30 sets the frequency of the PFM-modulated wave to a maximum frequency (reference frequency) Fmax in response to the maximum amplitude Amax of the control signal. In response to the minimum amplitude Amin of the control signal, the control circuit 30 reduces the frequency of the PFM control from the maximum frequency (reference frequency) Fmax to the minimum frequency Fmin in response to the amount of change in the minimum amplitude Amin of the control signal from the maximum amplitude Amax. Alternatively, the control circuit 30 increases the period of the PFM control from the minimum period (reference period) Tmin to the maximum period Tmax in response to the amount of change in the minimum amplitude Amin of the control signal from the maximum amplitude Amax.

[0019] Returning to FIG. 1, the charging system 1 includes an AC / DC converter 10, a DC / DC converter 20, and a control circuit 30, as well as an AC filter 2, a capacitance element C1, a DC filter 3, voltage sensors VS1 to VS3, and current sensors CS1 and CS2.

[0020] The AC filter 2 is connected between the input nodes Nin1, Nin2 and the AC-CDC converter 10. One end of the AC filter 2 is connected between the input node Nin1 and the input node 10a of the AC-CDC converter 10, and the other end is connected between the input node Nin2 and the input node 10b of the AC-CDC converter 10. When noise components flow out from the AC-CDC converter 10 side, the AC filter 2 performs filtering on the noise components to attenuate them. This allows the AC filter 2 to prevent noise components from flowing out from the AC-CDC converter 10 side to the AC power supply PS.

[0021] The AC-CDC converter 10 is connected between input nodes Nin1, Nin2 and intermediate nodes Nmid1, Nmid2. The AC-CDC converter 10 can be connected to an AC power supply PS via the input nodes Nin1, Nin2. The AC-CDC converter 10 is connected between the AC filter 2 and intermediate nodes Nmid1, Nmid2. The AC-CDC converter 10 uses a PFC (Power Factor Correction) circuit to convert AC power into DC power while correcting the power factor of the AC power.

[0022] The AC-DC converter 10 includes, for example, a PFC circuit, including multiple rectifier elements D1-D6, multiple inductive elements L1 and L2, and multiple switching elements SW1 and SW2. The rectifier elements D1-D4 are bridge-connected to form a bridge circuit. In this configuration, the bridge circuit full-wave rectifies the AC voltage, and then the switching operations of the switching elements SW1 and SW2 repeatedly store and release energy in the inductive elements L1 and L2. Accordingly, the current flow to the capacitive element C1 via the rectifier elements D5 and D6 is repeatedly stopped and injected. This allows the AC-DC converter 10 to generate a DC voltage Vsub while approximating the phase of the AC current to the phase of the AC voltage, thereby improving the power factor.

[0023] Rectifying element D1 rectifies in the direction from input node 10a to output node 10c. Rectifying element D1 is, for example, a diode, and has an anode connected to input node 10a and a cathode connected to output node 10c via inductive element L1 and rectifying element D5.

[0024] Rectifying element D2 rectifies in the direction from input node 10b to output node 10c. Rectifying element D2 is, for example, a diode, and has an anode connected to input node 10b and a cathode connected to output node 10c via inductive element L1 and rectifying element D5.

[0025] Rectifying element D3 rectifies in the direction from input node 10a to output node 10d. Rectifying element D3 is, for example, a diode, with an anode connected to input node 10a and a cathode connected to output node 10d.

[0026] Rectifying element D4 rectifies in the direction from input node 10b to output node 10d. Rectifying element D4 is, for example, a diode, with an anode connected to input node 10b and a cathode connected to output node 10d.

[0027] A series connection of inductive element L1 and rectifying element D5 and a series connection of inductive element L2 and rectifying element D6 are connected in parallel between rectifying elements D1, D2 and output node 10c. A switching element SW1 is connected between a node 10e between inductive element L1 and rectifying element D5 and output node 10d. A switching element SW2 is connected between a node 10f between inductive element L2 and rectifying element D6 and output node 10d.

[0028] The inductive element L1 is connected between the rectifying elements D1 and D2 and the node 10e. The inductive element L1 is, for example, a coil, and has one end connected to the rectifying elements D1 and D2 and the other end connected to the node 10e. The inductive element L1 can contribute to improving the power factor of the AC / DC converter 10 by storing and releasing electromagnetic energy.

[0029] Rectifying element D5 rectifies in the direction from node 10e to output node 10c. Rectifying element D5 is, for example, a diode, with an anode connected to node 10e and a cathode connected to output node 10c.

[0030] The inductive element L2 is connected between the rectifying elements D1 and D2 and the node 10e. The inductive element L2 is, for example, a coil, and has one end connected to the rectifying elements D1 and D2 and the other end connected to the node 10f. The inductive element L2 can contribute to improving the power factor of the AC / DC converter 10 by storing and releasing electromagnetic energy.

[0031] Rectifying element D6 rectifies in the direction from node 10f to output node 10c. Rectifying element D6 is, for example, a diode, with an anode connected to node 10f and a cathode connected to output node 10c.

[0032] The switching element SW1 is connected between the node 10e and the rectifying elements D3 and D4. The switching element SW1 electrically connects or disconnects the node 10e and the rectifying elements D3 and D4 in response to a control signal from the control circuit 30. The switching element SW1 is, for example, an N-channel MOSFET transistor, and has a source connected to the rectifying elements D3 and D4, a drain connected to the node 10e, and a gate connected to the control circuit 30.

[0033] The switching element SW1 is turned on when it receives an active level control signal at its gate from the control circuit 30, thereby electrically connecting the node 10e to the rectifying elements D3 and D4. The switching element SW1 is turned off when it receives a non-active level control signal at its gate from the control circuit 30, thereby electrically disconnecting the node 10e from the rectifying elements D3 and D4.

[0034] The switching element SW2 is connected between the node 10f and the rectifying elements D3 and D4. The switching element SW2 electrically connects or disconnects the node 10f and the rectifying elements D3 and D4 in response to a control signal from the control circuit 30. The switching element SW2 is, for example, an N-channel MOSFET transistor, and has a source connected to the rectifying elements D3 and D4, a drain connected to the node 10f, and a gate connected to the control circuit 30.

[0035] The switching element SW2 is turned on when it receives an active-level control signal at its gate from the control circuit 30, thereby electrically connecting the node 10f with the rectifying elements D3 and D4. The switching element SW2 is turned off when it receives a non-active-level control signal at its gate from the control circuit 30, thereby electrically disconnecting the node 10f from the rectifying elements D3 and D4.

[0036] The capacitive element C1 is connected between the AC-DC converter 10 and the DC-DC converter 20. The capacitive element C1 is a smoothing capacitor such as an aluminum electrolytic capacitor, a film capacitor, or a ceramic capacitor, and has one end connected to the intermediate node Nmid1 and the other end connected to the intermediate node Nmid2. The capacitive element C1 can contribute to improving the power factor of the AC-DC converter 10 by charging and discharging an electric charge, and can generate a DC voltage Vsub.

[0037] The DC-DC converter 20 is, for example, an LLC converter. The DC-DC converter 20 is connected between intermediate nodes Nmid1, Nmid2 and output nodes Nout1, Nout2. The DC-DC converter 20 has input nodes 20a, 20b connected to the intermediate nodes Nmid1, Nmid2, and output nodes 20c, 20d connected to the output nodes Nout1, Nout2. The DC-DC converter 20 can be connected to a battery BT via the output nodes Nout1, Nout2. The DC-DC converter 20 is connected between the intermediate nodes Nmid1, Nmid2 and a DC filter 3. The DC-DC converter 20 uses an isolation transformer TR to convert DC power into DC power for charging while insulating and separating the input side (primary side) and the output side (secondary side).

[0038] The DC-DC converter 20 includes, for example, a primary circuit 21, an insulating transformer TR, and a secondary circuit 22. The primary circuit 21 includes a plurality of switching elements SW11 to SW14 and a capacitance element C11. The insulating transformer TR includes a primary winding L11, a secondary winding L12, and a core CR1. The secondary circuit 22 includes a plurality of rectifying elements D11 to D14.

[0039] The switching element SW11 is connected between the input node 20a and the node 20e. The switching element SW11 electrically connects or disconnects the input node 20a and the node 20e in response to a control signal from the control circuit 30. The switching element SW11 is, for example, an N-channel MOSFET transistor, and has a source connected to the node 20e, a drain connected to the input node 20a, and a gate connected to the control circuit 30.

[0040] The switching element SW11 is turned on when it receives an active level control signal at its gate from the control circuit 30, thereby electrically connecting the input node 20a and the node 20e. The switching element SW11 is turned off when it receives a non-active level control signal at its gate from the control circuit 30, thereby electrically disconnecting the input node 20a and the node 20e.

[0041] The switching element SW12 is connected between the input node 20a and a node 20f. The switching element SW12 electrically connects or disconnects the input node 20a and the node 20f in response to a control signal from the control circuit 30. The switching element SW12 is, for example, an N-channel MOSFET transistor, and has a source connected to the node 20f, a drain connected to the input node 20a, and a gate connected to the control circuit 30.

[0042] The switching element SW12 is turned on when it receives an active level control signal at its gate from the control circuit 30, thereby electrically connecting the input node 20a and the node 20f. The switching element SW12 is turned off when it receives a non-active level control signal at its gate from the control circuit 30, thereby electrically disconnecting the input node 20a and the node 20f.

[0043] The switching element SW13 is connected between the node 20e and the input node 20b. The switching element SW13 electrically connects or disconnects the node 20e and the input node 20b in response to a control signal from the control circuit 30. The switching element SW13 is, for example, an N-channel MOSFET transistor, and has a source connected to the input node 20b, a drain connected to the node 20e, and a gate connected to the control circuit 30.

[0044] The switching element SW13 is turned on when it receives an active level control signal at its gate from the control circuit 30, thereby electrically connecting the node 20e and the input node 20b. The switching element SW13 is turned off when it receives a non-active level control signal at its gate from the control circuit 30, thereby electrically disconnecting the node 20e and the input node 20b.

[0045] The switching element SW14 is connected between the node 20f and the input node 20b. The switching element SW14 electrically connects or disconnects the node 20f and the input node 20b in response to a control signal from the control circuit 30. The switching element SW14 is, for example, an N-channel MOSFET transistor, and has a source connected to the input node 20b, a drain connected to the node 20f, and a gate connected to the control circuit 30.

[0046] Switching element SW14 is turned on when it receives an active-level control signal at its gate from control circuit 30, thereby electrically connecting node 20f and input node 20b. Switching element SW14 is turned off when it receives a non-active-level control signal at its gate from control circuit 30, thereby electrically disconnecting node 20f and input node 20b.

[0047] Note that the transistor electrodes are described as drain, gate, and source on the assumption that each of the switching elements SW1, SW2, SW11 to SW14 is an N-channel MOSFET, but if each of the switching elements SW1, SW2, SW11 to SW14 is an IGBT (insulated gate bipolar transistor), the drain can be read as collector and the source as emitter.

[0048] The capacitance element C11 is connected between the node 20e and the primary winding L11. One end of the capacitance element C11 is connected to the node 20e, and the other end is connected to one end of the primary winding L11. The capacitance element C11 performs a resonant operation together with the primary winding L11, thereby reducing switching loss caused by the switching elements SW11 to SW14.

[0049] In the isolation transformer TR, the primary winding L11 is electrically isolated from the secondary winding L12 and is magnetically coupled to the secondary winding L12 via a core CR1. The primary winding L11 and the secondary winding L12 are each, for example, a coil. The isolation transformer TR may be configured as a flyback type. As shown by the black circles in FIG. 1, the primary winding L11 and the secondary winding L12 are wound in opposite directions relative to the path of the magnetic field lines in the core CR1. The isolation transformer TR may be configured without the core CR1, as long as the primary winding L11 and the secondary winding L12 are magnetically coupled to each other.

[0050] The primary winding L11 has one end connected to a node 20e via a capacitive element C11 and the other end connected to a node 20f. The secondary winding L12 has one end connected to a node 20g and the other end connected to a node 20h.

[0051] The rectifying element D11 rectifies in the direction from the node 20g toward the output node 20c. The rectifying element D11 is, for example, a diode, and has an anode connected to the node 20g and a cathode connected to the output node 20c.

[0052] The rectifying element D12 rectifies in the direction from the node 20f toward the output node 20c. The rectifying element D12 is, for example, a diode, and has an anode connected to the node 20f and a cathode connected to the output node 20c.

[0053] Rectifying element D13 rectifies in the direction from output node 20d to node 20g. Rectifying element D13 is, for example, a diode, with an anode connected to output node 10d and a cathode connected to node 20g.

[0054] Rectifying element D14 rectifies in the direction from output node 20d to node 20h. Rectifying element D14 is, for example, a diode, with an anode connected to output node 20d and a cathode connected to node 20h.

[0055] The DC filter 3 is connected between the DC-DC converter 20 and the output nodes Nout1 and Nout2. One end of the DC filter 3 is connected between the DC-DC converter 20 and the output node Nout1, and the other end is connected between the DC-DC converter 20 and the output node Nout2. The DC filter 32 filters the DC power supplied from the DC filter 3 and supplies it to the battery BT. This allows the DC filter 3 to reduce noise contained in the DC power before supplying it to the battery BT.

[0056] The voltage sensor VS1 detects the input voltage Vin of the charging system 1. The voltage sensor VS1 detects the voltage between the input node 10a and the input node 10b as the input voltage Vin. The voltage sensor VS1 supplies the detected input voltage Vin to the control circuit 30.

[0057] The voltage sensor VS2 detects the output voltage Vout of the charging system 1. The voltage sensor VS2 detects the voltage between the output node 20c and the output node 20d as the output voltage Vout. The voltage sensor VS2 supplies the detected output voltage Vout to the control circuit 30.

[0058] The voltage sensor VS3 detects the voltage Vsub of the charging system 1. The voltage sensor VS3 detects the voltage between the intermediate node Nmid1 and the intermediate node Nmid2 as the voltage Vsub. The voltage sensor VS3 supplies the detected voltage Vsub to the control circuit 30.

[0059] The current sensor CS1 detects the input current Iin of the charging system 1. The current sensor CS1 detects the current flowing between the input node Nin1 and the input node 10a as the input current Iin. The current sensor CS1 supplies the detected input current Iin to the control circuit 30.

[0060] The current sensor CS2 detects the output current Iout of the charging system 1. The current sensor CS2 detects the current flowing between the output node 20c and the output node Nout1 as the output current Iout. The current sensor CS2 supplies the detected output current Iout to the control circuit 30.

[0061] When the AC-DC converter 10 and the DC-DC converter 20 start up, the control circuit 30 PWM controls the switching elements in the AC-DC converter 10 and the DC-DC converter 20. At this time, the control circuit 30 controls the operating frequency of the switching elements in the DC-DC converter 20 to a frequency Fstart, which is higher than the frequency Fop during steady operation. The frequency Fstart is closer to the resonant frequency of the isolation transformer TR than the frequency Fop. Therefore, by controlling the operating frequency of the switching elements to the frequency Fstart, the control circuit 30 can control the output voltage of the isolation transformer TR to be lower than the output side of the DC-DC converter 20.

[0062] At startup, the control circuit 30 starts the operation of the switching elements at a frequency Fstart. The control circuit 30 increases the reference duty ratio of PWM control from an initial value (e.g., zero) to a predetermined duty ratio while maintaining the operating frequency of the switching elements in the DC-DC converter 20 at the frequency Fstart. Thereafter, the control circuit 30 decreases the operating frequency of the switching elements from the frequency Fstart to the frequency Fop while maintaining the reference duty ratio of PWM control at the predetermined duty ratio. The control circuit 30 gradually or stepwise decreases the operating frequency of the switching elements from the frequency Fstart to the frequency Fop. This allows the control circuit 30 to gradually or stepwise transition from a state in which the output voltage of the isolation transformer TR is lower than the output side of the DC-DC converter 20 to a state in which the output voltage of the isolation transformer TR is higher than the output side of the DC-DC converter 20. As a result, the gate signals of the switching elements can be appropriately adjusted, and inrush current at startup of the charging system 1 can be suppressed.

[0063] During steady-state operation of the AC-DC converter 10 and the DC-DC converter 20, the control circuit 30 PWM controls the switching elements in the AC-DC converter 10 and PFM controls the switching elements in the DC-DC converter 20. The control circuit 30 controls the switching elements in the DC-DC converter 20 by varying the frequency according to the level of the control signal, while using a predetermined frequency as the reference frequency for PFM control.

[0064] For example, at the time of startup, the control circuit 30 performs control as shown in Fig. 3. Fig. 3 is a flowchart showing the operation of the charging system 1.

[0065] In the charging system 1, the control circuit 30 waits until it receives a start-up command (No in S1), and upon receiving the start-up command (Yes in S1), it starts up the AC-DC converter 10 and starts PWM control (S2) on the DC-DC converter 20 at the operating frequency Fstart. Using previously acquired voltage gain-load-frequency correspondence information (see FIG. 4), the control circuit 30 starts up the DC-DC converter 20 at the frequency Fstart at which the output voltage of the isolation transformer TR in the DC-DC converter 20 becomes lower than the voltage of the battery BT. In other words, it starts the switching operations of the switching elements SW11 to SW14 at the operating frequency Fstart.

[0066] As shown in FIG. 4, the operating frequency Fstart is higher than the operating frequency Fop during steady operation. FIG. 4 is a diagram showing the relationship between the operating frequency of the switching elements SW11-SW14 and the voltage gain of the charging system 1. FIG. 4 illustrates the relationship between the operating frequency of the switching elements SW11-SW14 and the voltage gain of the charging system 1 for different load states of the batteries BT. As shown in FIG. 4, the operating frequency Fstart is closer to the resonant frequency F0 of the isolation transformer TR than the operating frequency Fop. Therefore, the voltage gain Gstart of the charging system 1 corresponding to the operating frequency Fstart is lower than the voltage gain Gop of the charging system 1 corresponding to the operating frequency Fop in any of the load states. In response to this, the control circuit 30 controls the operating frequency of the switching elements to the frequency Fstart, thereby enabling control so that the output voltage of the isolation transformer TR is lower than the output side of the DC-DC converter 20, regardless of the load state of the battery BT.

[0067] Returning to FIG. 3, when PWM control starts, the control circuit 30 adjusts the reference duty ratio of the PWM control (S21). The control circuit 30 increases the reference duty ratio of the PWM control from an initial value to a predetermined duty ratio while maintaining the operating frequency of the switching elements S11 to S14 at frequency Fstart (while maintaining the operating cycle of the switching elements S11 to S14 at cycle Tstart). The predetermined duty ratio is, for example, approximately 0.5, and can be set to 0.45 to 0.49 if a dead time is provided. The cycle Tstart is a cycle corresponding to frequency Fstart.

[0068] For example, as shown in FIG. 5(a), the control circuit 30 generates gate signals QA and QD for the switching elements SW11 and SW14 at a period T1 corresponding to the frequency Fstart. At this time, the control circuit 30 increases the reference duty ratio of the PWM control from the initial value (=0) to D1. The control circuit 30 generates the gate signals QA and QD for the switching elements SW11 and SW14 by PWM modulation with a reference pulse width T1×D1 corresponding to the reference duty ratio D1. Similarly, as shown in FIG. 5(b), the control circuit 30 generates gate signals QB and QC for the switching elements SW12 and SW13 by PWM modulation with a period T1 and a reference pulse width T1×D1. The gate signals QA and QD and the gate signals QB and QC are maintained at the H level in a complementary manner.

[0069] As shown in FIG. 5(c), the control circuit 30 increases the reference duty ratio of PWM control from D1 to D2 (>D1) while maintaining the frequency of the gate signals QA and QD of the switching elements SW11 and SW14 at Fstart (while maintaining the period at T1). The control circuit 30 generates the gate signals QA and QD of the switching elements SW11 and SW14 by PWM modulation with a reference pulse width T1×D2 corresponding to the reference duty ratio D2. Similarly, as shown in FIG. 5(d), the control circuit 30 generates the gate signals QB and QC of the switching elements SW12 and SW13 by PWM modulation with a period T1 and a reference pulse width T1×D2.

[0070] As shown in FIG. 5(e), the control circuit 30 increases the reference duty ratio of PWM control from D2 to D3 (>D2) while maintaining the frequency of the gate signals QA and QD of the switching elements SW11 and SW14 at Fstart (while maintaining the period at T1). The control circuit 30 generates the gate signals QA and QD of the switching elements SW11 and SW14 by PWM modulation with a reference pulse width T1×D3 corresponding to the reference duty ratio D3. Similarly, as shown in FIG. 5(f), the control circuit 30 generates the gate signals QB and QC of the switching elements SW12 and SW13 by PWM modulation with a period T1 and a reference pulse width T1×D3.

[0071] Returning to FIG. 3, when the adjustment of the reference duty ratio (S21) is completed, the control circuit 30 adjusts the frequency (S22). The control circuit 30 decreases the operating frequency of the switching elements SW11 to SW14 from the frequency Fstart to the frequency Fop while maintaining the reference duty ratio of the gate signals of the switching elements SW11 to SW14 at a predetermined duty ratio.

[0072] For example, as shown in FIG. 6(a), the control circuit 30 generates the gate signals QA and QD of the switching elements SW11 and SW14 by PWM modulation with a period T1 corresponding to the frequency Fstart and a reference pulse width T1×D3 corresponding to the reference duty ratio D3. Similarly, as shown in FIG. 6(b), the control circuit 30 generates the gate signals QB and QC of the switching elements SW12 and SW13 by PWM modulation with the period T1 and the reference pulse width T1×D3.

[0073] As shown in FIG. 6(c), the control circuit 30 decreases the frequency from Fstart to F2 (<Fstart) while maintaining the reference duty ratio of the PWM control of the gate signals QA and QD of the switching elements SW11 and SW14 at D3. The control circuit 30 generates the gate signals QA and QD of the switching elements SW11 and SW14 by PWM modulation with a period T2 (>T1) corresponding to the frequency F2 and a reference pulse width T2×D3 corresponding to the reference duty ratio D3. Similarly, as shown in FIG. 6(d), the control circuit 30 generates the gate signals QB and QC of the switching elements SW12 and SW13 by PWM modulation with the period T2 and the reference pulse width T2×D3.

[0074] As shown in FIG. 6(e), while maintaining the reference duty ratio of the PWM control of the gate signals QA and QD of the switching elements SW11 and SW14 at D3, the control circuit 30 decreases the frequency from F2 to Fop (<F2). The control circuit 30 PWM-modulates and generates the gate signals QA and QD of the switching elements SW11 and SW14 with a period T3 (>T2) corresponding to the frequency Fop and a reference pulse width T3×D3 corresponding to the reference duty ratio D3. Similarly, as shown in FIG. 6(f), the control circuit 30 PWM-modulates and generates the gate signals QB and QC of the switching elements SW12 and SW13 with the period T3 and the reference pulse width T3×D3.

[0075] Returning to FIG. 3, when the frequency adjustment (S22) is completed, the control circuit 30 performs PFM control with the frequency Fop as the reference frequency (S3).

[0076] As described above, in the charging system 1, at startup, the control circuit 30 starts the operation of the switching elements SW11 to SW14 at a frequency Fstart higher than that during steady operation. The control circuit 30 sets the reference duty ratio of the gate signals of the switching elements to a predetermined duty ratio while maintaining the frequency Fstart. The control circuit 30 decreases the operating frequency of the switching elements from the frequency Fstart to the frequency Fop for steady operation while maintaining the reference duty ratio of the gate signals of the switching elements at the predetermined duty ratio. The control circuit 30 gradually or stepwise decreases the operating frequency of the switching elements SW11 to SW14 from Fstart to Fop while maintaining the reference duty ratio of the PWM control at D3. Thereby, in the charging system 1, regardless of the battery load state, the inrush current can be suppressed at startup, and the gate signals of the switching elements SW11 to SW14 can be appropriately adjusted.

[0077] A voltage detection circuit may be added to detect the voltage across or one of the terminals of the secondary winding L12 of the isolation transformer TR (e.g., the voltage at node 20h or node 20d shown in FIG. 1), and the detected voltage may be supplied to the control circuit 30. In this case, the control circuit 30 monitors the voltage across or one of the terminals of the secondary winding L12 of the isolation transformer TR during startup and / or steady-state operation. The voltage across the secondary winding L12 is observed as a square wave of positive and negative voltages, and the voltage at one of the terminals is observed as a square wave of positive voltage. Based on the observation results, the control circuit 30 may determine the startup frequency Fstart so that it is lower than the output voltage Vout. This minimizes the difference between the output voltage of the isolation transformer TR and the voltage of the battery BT, allowing startup to be performed at a lower frequency. The closer the startup frequency is to the steady-state operation frequency, the shorter the startup time. Then, in order to maintain the voltage magnitude relationship, the reference duty ratio of the PWM control is increased to approximately 0.5 (for example, 0.45 to 0.49), and the frequency is gradually changed to the extent that no inrush current flows, thereby achieving the desired power transmission operation, as in the embodiment.

[0078] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention described in the claims and their equivalents. [Explanation of symbols]

[0079] 1 Charging System 10 AC / DC converter 20 DC-DC converter 30 Control circuit

Claims

1. an AC-DC converter connected between a first input node and a second input node and a first intermediate node and a second intermediate node, and connected to an AC power source via the first input node and the second input node; a DC-DC converter connected between the first intermediate node and the second intermediate node and a first output node and a second output node, and connectable to a battery via the first output node and the second output node, the DC-DC converter including an isolation transformer, a primary-side circuit arranged on a primary side of the isolation transformer and including a plurality of switching elements, and a secondary-side circuit arranged on a secondary side of the isolation transformer; a control circuit that starts operation of the switching elements at a first frequency when the AC-DC converter and the DC-DC converter are started up, and operates the switching elements at a second frequency during steady-state operation of the AC-DC converter and the DC-DC converter; Equipped with the first frequency is higher than the second frequency; The control circuit increases a reference duty ratio of a gate signal of the switching element from zero to a predetermined duty ratio while maintaining an operating frequency of the switching element at the first frequency when the AC-DC converter and the DC-DC converter are started up. Charging system.

2. The DC-DC converter is an LLC converter. The charging system of claim 1 .

3. The first frequency is closer to the resonant frequency of the isolation transformer than the second frequency. The charging system of claim 1 .

4. An AC-DC converter connected between a first input node, a second input node and a first intermediate node, and a second intermediate node, and connected to an AC power source via the first input node and the second input node; a DC-DC converter connected between the first intermediate node and the second intermediate node and a first output node and a second output node, and connectable to a battery via the first output node and the second output node, the DC-DC converter including an isolation transformer, a primary-side circuit arranged on a primary side of the isolation transformer and including a plurality of switching elements, and a secondary-side circuit arranged on a secondary side of the isolation transformer; a control circuit that starts operation of the switching elements at a first frequency when the AC-DC converter and the DC-DC converter are started up, and operates the switching elements at a second frequency during steady-state operation of the AC-DC converter and the DC-DC converter; Equipped with the first frequency is higher than the second frequency; The control circuit gradually or stepwise reduces the operating frequency of the switching element from the first frequency to the second frequency while maintaining a reference duty ratio of a gate signal of the switching element at a predetermined duty ratio when the AC-DC converter and the DC-DC converter are started up. Charging system.

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