Power supply unit and control method for power supply unit

Abstract

This suppresses stress on the switching element, enabling pre-charging in a short time. [Solution] A transformer including a first switching element with one end connected to a first terminal, a second switching element connected between the other end of the first switching element and a second terminal, a third switching element with one end connected to the first terminal, a fourth switching element connected between the other end of the third switching element and a second terminal, a first winding connected between the other end of the first switching element and the other end of the third switching element, and a second winding magnetically coupled to the first winding; an inductor section connected between the center tap of the second winding and a third terminal; a fifth switching element connected between one end of the second winding and a fourth terminal; a sixth switching element electrically connected between the other end of the second winding and a fourth terminal; a first switch connected between one end of the fifth switching element and a third terminal; and a second switch connected between one end of the sixth switching element and a third terminal.

Description

Technical Field

[0001] The present disclosure relates to a power supply device and a control method thereof.

Background Art

[0002] For example, in an electric vehicle, a DC-DC converter is used that steps down and outputs power from the primary side (high voltage side, e.g., a driving battery) to the secondary side (low voltage side, e.g., an accessory battery), and steps up and outputs power from the secondary side to the primary side. This DC-DC converter mainly uses a phase-shifted full-bridge circuit.

[0003] Patent Document 1 describes a DC-DC converter that does not cause a converter failure even if a switching element malfunctions.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When power is transmitted from the secondary side to the primary side using a phase-shifted full-bridge circuit, it becomes a choke input method. Also, if the turns ratio of the transformer is set as primary turns:secondary turns = N:1, when outputting a voltage higher than ((secondary battery voltage) × N) to the primary side, in addition to boosting by the transformer, it is necessary to boost also by the output inductor. As a result, a surge voltage occurs in the output inductor, and this surge voltage is applied to the switching element on the secondary side. Therefore, the switching element on the secondary side may be stressed.

[0006] When the voltage of the precharge target capacitor on the primary side is near 0V, there is a possibility that the stored energy of the output inductor cannot be reset and it may reach saturation.

[0007] On the other hand, if a simultaneous shutdown period is introduced for the secondary switching elements (transistors Q5 and Q6, described later) in order to reset the stored energy of the output inductor, a surge voltage will be generated. Furthermore, a reduction in pre-charging time was also desired.

[0008] This disclosure aims to enable power transmission to the primary side while suppressing stress on the secondary side switching elements, and to perform precharging in a short time. [Means for solving the problem]

[0009] A power supply device in one aspect of this disclosure is A power supply device that steps down a first voltage input between a first terminal and a second terminal and outputs it from between a third terminal and a fourth terminal, and steps up a second voltage input between the third terminal and the fourth terminal and outputs it from between the first terminal and the second terminal, A bridge circuit comprising: a first switching element with one end electrically connected to the first terminal; a second switching element with one end electrically connected to the other end of the first switching element and the other end electrically connected to the second terminal; a third switching element with one end electrically connected to the first terminal; and a fourth switching element with one end electrically connected to the other end of the third switching element and the other end electrically connected to the second terminal; A transformer comprising: a first winding, one end of which is electrically connected to the other end of the first switching element and one end of the second switching element, and the other end of which is electrically connected to the other end of the third switching element and one end of the fourth switching element; and a second winding that is magnetically coupled to the first winding; An inductor section having one end electrically connected to the center tap of the second winding and the other end electrically connected to the third terminal, A fifth switching element, one end of which is electrically connected to one end of the second winding and the other end of which is electrically connected to the fourth terminal, A sixth switching element, one end of which is electrically connected to the other end of the second winding and the other end of which is electrically connected to the fourth terminal, A first switch, one end of which is electrically connected to one end of the fifth switching element and one end of the second winding, and the other end of which is electrically connected to the other end of the inductor and the third terminal, A second switch, one end of which is electrically connected to one end of the sixth switching element and the other end of the second winding, and the other end of which is electrically connected to the other end of the inductor and the third terminal, This includes, The inductor section further includes a first inductor section, a second inductor section, and a switch section, wherein the first inductor section and the second inductor section are set to have different inductances. The switch unit is characterized by switching between the first inductor unit and the second inductor unit by turning it on and off.

[0010] In the aforementioned power supply device, The inductor section electrically connects the first inductor section and the second inductor section, One end of the first inductor is electrically connected to the center tap of the second winding. The other end of the first inductor is electrically connected to one end of the second inductor. The other end of the second inductor is electrically connected to the third terminal. The switch section comprises a first switch section and a second switch section. One end of the first switch section is electrically connected to the intermediate portion between one end of the first inductor section and the center tap of the second winding, The other end of the first switch section is electrically connected to the intermediate section between the first inductor section and the second inductor section. One end of the second switch section is electrically connected to the intermediate section between the first inductor section and the second inductor section, to which the other end of the first switch section is electrically connected. The other end of the second switch section is electrically connected to one end of the first inductor section.

[0011] In the aforementioned power supply device, Further includes a control unit that controls the first switching element to the sixth switching element, as well as the first switch and the second switch. The control unit is as follows. When boosting the second voltage and outputting it between the first terminal and the second terminal, In the first period, turn on the fifth switching element. In the second period following the first period, turn on the first switch. In the third period following the second period, turn on the sixth switching element. In the fourth period following the third period, turn on the second switch. It is characterized by this.

[0012] In the power supply device, The control unit is as follows. In the first period, turn on the second switching element or the third switching element. In the third period, turn on the fourth switching element or the first switching element. It is characterized by this.

[0013] In the power supply device, The control unit is as follows. In the first period, the second period, the third period, and the fourth period, turn on the switch unit. It is characterized by this.

[0014] In the power supply device, Further includes a control unit that controls the first switching element to the sixth switching element, as well as the first switch and the second switch. The control unit is as follows. When boosting the second voltage and outputting it between the first terminal and the second terminal, In the first period, turn on both the fifth switching element and the sixth switching element. In the second period following the first period, turn on the first switch. In the third period following the second period, both the fifth switching element and the sixth switching element are turned on. In the fourth period following the third period, the second switch is turned on. It is characterized by the following:

[0015] In the aforementioned power supply device, The control unit, During the first period, the second period, the third period, and the fourth period, the switch unit is turned on. It is characterized by the following:

[0016] In the aforementioned power supply device, The inductor section electrically connects the first inductor section and the second inductor section, One end of the first inductor is electrically connected to the center tap of the second winding. The other end of the first inductor is electrically connected to one end of the second inductor. The other end of the second inductor is electrically connected to the third terminal. The switch section comprises a first switch section and a second switch section. One end of the first switch section is electrically connected to the intermediate portion between one end of the first inductor section and the center tap of the second winding, The other end of the first switch section is electrically connected to the intermediate section between the first inductor section and the second inductor section. One end of the second switch section is electrically connected to the intermediate portion between one end of the first inductor section, to which one end of the first switch section is electrically connected, and the center tap of the second winding. The other end of the second switch section is electrically connected to one end of the first inductor section. The inductance of the first inductor is set to be greater than the inductance of the second inductor.

[0017] In the aforementioned power supply device, The system further includes the first to sixth switching elements, and a control unit that controls the first and second switches, The control unit, When the second voltage is boosted and output between the first terminal and the second terminal, During the first period, the fifth switching element is turned on, In the second period following the first period, the first switch is turned on. In the third period following the second period, the sixth switching element is turned on. In the fourth period following the third period, the second switch is turned on. It is characterized by the following:

[0018] In the aforementioned power supply device, The control unit, During the first period, the second switching element or the third switching element is turned on. During the third period, the fourth switching element or the first switching element is turned on. It is characterized by the following:

[0019] In the aforementioned power supply device, The control unit, During the first period, the second period, the third period, and the fourth period, the first switch unit is turned on and the second switch unit is turned off. It is characterized by the following:

[0020] In the aforementioned power supply device, The system further includes the first to sixth switching elements, and a control unit that controls the first and second switches, The control unit, When the second voltage is boosted and output between the first terminal and the second terminal, During the first period, both the fifth switching element and the sixth switching element are turned on. In the second period following the first period, the first switch is turned on. In the third period following the second period, both the fifth switching element and the sixth switching element are turned on. In the fourth period following the third period, the second switch is turned on. It is characterized by the following:

[0021] In the aforementioned power supply device, The control unit, During the first period, the second period, the third period, and the fourth period, the first switch unit is turned on and the second switch unit is turned off. It is characterized by the following:

[0022] In the aforementioned power supply device, The inductor section electrically connects the first inductor section and the second inductor section in parallel, One end of the first inductor is electrically connected to the center tap of the second winding. The other end of the first inductor is electrically connected to the third terminal. One end of the second inductor is electrically connected to the intermediate portion between one end of the first inductor and the center tap of the second winding. The other end of the second inductor is electrically connected to the intermediate portion between the other end of the first inductor and the third terminal. The switch section comprises a first switch section and a second switch section. One end of the first switch section is electrically connected to the intermediate portion between one end of the first inductor section and the center tap of the second winding. The other end of the first switch section is electrically connected to one end of the second inductor section. One end of the second switch section is electrically connected to the intermediate portion between one end of the first inductor section, to which one end of the first switch section is electrically connected, and the center tap of the second winding. The other end of the second switch section is electrically connected to one end of the first inductor section. The inductance of the first inductor is set to be greater than the inductance of the second inductor. It is characterized by the following.

[0023] In the aforementioned power supply device, The system further includes the first to sixth switching elements, and a control unit that controls the first and second switches, The control unit, When the second voltage is boosted and output between the first terminal and the second terminal, During the first period, the fifth switching element is turned on, In the second period following the first period, the first switch is turned on. In the third period following the second period, the sixth switching element is turned on. In the fourth period following the third period, the second switch is turned on. It is characterized by the following:

[0024] In the aforementioned power supply device, The control unit, During the first period, the second switching element or the third switching element is turned on. During the third period, the fourth switching element or the first switching element is turned on. It is characterized by the following:

[0025] In the aforementioned power supply device, The control unit, During the first period, the second period, the third period, and the fourth period, the first switch unit is turned on and the second switch is turned off. It is characterized by the following:

[0026] In the aforementioned power supply device, The system further includes the first to sixth switching elements, and a control unit that controls the first and second switches, The control unit, When the second voltage is boosted and output between the first terminal and the second terminal, During the first period, both the fifth switching element and the sixth switching element are turned on. In the second period following the first period, the first switch is turned on. In the third period following the second period, both the fifth switching element and the sixth switching element are turned on. In the fourth period following the third period, the second switch is turned on. It is characterized by the following:

[0027] In the aforementioned power supply device, The control unit, During the first period, the second period, the third period, and the fourth period, the first switch unit is turned on and the second switch is turned off. It is characterized by the following:

[0028] A control method for a power supply device according to one aspect of this disclosure is: A bridge circuit including a first switching element with one end electrically connected to a first terminal, a second switching element with one end electrically connected to the other end of the first switching element and the other end electrically connected to a second terminal, a third switching element with one end electrically connected to the first terminal, and a fourth switching element with one end electrically connected to the other end of the third switching element and the other end electrically connected to a second terminal; a transformer including a first winding with one end electrically connected to the other end of the first switching element and one end of the second switching element, and the other end electrically connected to the other end of the third switching element and one end of the fourth switching element, and a second winding that is magnetically coupled to the first winding; an inductor section with one end electrically connected to the center tap of the second winding and the other end electrically connected to the third terminal; and one end of the second The inductor includes a fifth switching element electrically connected to one end of the winding and the other end electrically connected to the fourth terminal, a sixth switching element electrically connected to the other end of the second winding and the other end electrically connected to the fourth terminal, a first switch electrically connected to one end of the fifth switching element and one end of the second winding and the other end electrically connected to the other end of the inductor and the third terminal, and a second switch electrically connected to one end of the sixth switching element and the other end of the second winding and the other end electrically connected to the other end of the inductor and the third terminal, wherein the inductor further includes a first inductor, a second inductor, and a switch, the first and second inductors being set to different inductances, and the switch being switched on and off. A control method for a power supply device that switches between the first inductor section and the second inductor section, When the second voltage input between the third terminal and the fourth terminal is boosted and output from between the first terminal and the second terminal, During the first period, the fifth switching element is turned on, In the second period following the first period, the first switch is turned on. In the third period following the second period, the sixth switching element is turned on. In the fourth period following the third period, the second switch is turned on. It is characterized by the following:

[0029] A control method for a power supply device according to one aspect of this disclosure is: A bridge circuit including a first switching element with one end electrically connected to a first terminal, a second switching element with one end electrically connected to the other end of the first switching element and the other end electrically connected to a second terminal, a third switching element with one end electrically connected to the first terminal, and a fourth switching element with one end electrically connected to the other end of the third switching element and the other end electrically connected to a second terminal; a transformer including a first winding with one end electrically connected to the other end of the first switching element and one end of the second switching element, and the other end electrically connected to the other end of the third switching element and one end of the fourth switching element, and a second winding that is magnetically coupled to the first winding; an inductor section with one end electrically connected to the center tap of the second winding and the other end electrically connected to the third terminal; and a component with one end electrically connected to one end of the second winding and the other end connected to the fourth terminal A power supply control method comprising: a fifth switching element electrically connected to; a sixth switching element having one end electrically connected to the other end of the second winding and the other end electrically connected to the fourth terminal; a first switch having one end electrically connected to one end of the fifth switching element and one end of the second winding and the other end electrically connected to the other end of the inductor section and the third terminal; and a second switch having one end electrically connected to one end of the sixth switching element and the other end of the second winding and the other end electrically connected to the other end of the inductor section and the third terminal, wherein the inductor section further comprises a first inductor section, a second inductor section, and a switch section, wherein the first inductor section and the second inductor section are set to have different inductances, and the switch section switches between the first inductor section and the second inductor section by turning it on and off. When the second voltage input between the third terminal and the fourth terminal is boosted and output from between the first terminal and the second terminal, During the first period, both the fifth switching element and the sixth switching element are turned on. In the second period following the first period, the first switch is turned on. In the third period following the second period, both the fifth switching element and the sixth switching element are turned on. In the fourth period following the third period, the second switch is turned on. It is characterized by the following:

[0030] A power supply device in one aspect of this disclosure is A power supply device that steps down a first voltage input between a first terminal and a second terminal and outputs it from between a third terminal and a fourth terminal, and steps up a second voltage input between the third terminal and the fourth terminal and outputs it from between the first terminal and the second terminal, A first bridge circuit comprising: a first switching element with one end electrically connected to the first terminal; a second switching element with one end electrically connected to the other end of the first switching element and the other end electrically connected to the second terminal; a third switching element with one end electrically connected to the first terminal; and a fourth switching element with one end electrically connected to the other end of the third switching element and the other end electrically connected to the second terminal; A transformer comprising: a first winding, one end of which is electrically connected to the other end of the first switching element and one end of the second switching element, and the other end of which is electrically connected to the other end of the third switching element and one end of the fourth switching element; and a second winding that is magnetically coupled to the first winding; A second bridge circuit comprising: an eleventh switching element with one end electrically connected to one end of the second winding; a twelfth switching element with one end electrically connected to one end of the second winding and the other end electrically connected to the fourth terminal; a thirteenth switching element with one end electrically connected to the other end of the second winding; and a fourteenth switching element with one end electrically connected to the other end of the second winding and the other end electrically connected to the fourth terminal; An inductor unit having one end electrically connected to the other end of the 11th switching element and the other end of the 13th switching element, and the other end electrically connected to the 3rd terminal, A first switch, one end of which is electrically connected to one end of the second winding, one end of the 11th switching element, and one end of the 12th switching element, and the other end of which is electrically connected to the other end of the inductor and the third terminal, A second switch, one end of which is electrically connected to the other end of the second winding, one end of the 13th switching element, and one end of the 14th switching element, and the other end of which is electrically connected to the other end of the inductor and the third terminal, This includes, The inductor section further includes a first inductor section, a second inductor section, and a switch section, wherein the first inductor section and the second inductor section are set to have different inductances. The switch unit switches between the first inductor unit and the second inductor unit by turning it on and off. It is characterized by the following: [Effects of the Invention]

[0031] According to this disclosure, it is possible to transmit power to the primary side while suppressing stress on the secondary side switching elements, and to perform precharging in a short time. [Brief explanation of the drawing]

[0032] [Figure 1] Figure 1 shows an example of the configuration of the power system of an electric vehicle. [Figure 2] Figure 2 shows the configuration of a conventional DC-DC converter. [Figure 3] Figure 3 is a first timing diagram of the boost operation of a conventional DC-DC converter. [Figure 4] Figure 4 is a second timing diagram of the boost operation of a conventional DC-DC converter. [Figure 5] Figure 5 shows the configuration of the DC-DC converter according to the first embodiment. [Figure 6] Figure 6 is a timing diagram of the first boost operation of the DC-DC converter according to the first embodiment. [Figure 7] Figure 7 shows the current path during the first boost operation of the DC-DC converter in the first embodiment. [Figure 8] Figure 8 shows the current path during the first boost operation of the DC-DC converter in the first embodiment. [Figure 9] Figure 9 shows the current path during the first boost operation of the DC-DC converter in the first embodiment. [Figure 10] Figure 10 shows the current path during the first boost operation of the DC-DC converter in the first embodiment. [Figure 11] Figure 11 shows the current path of a first modified example of the first boost operation of the DC-DC converter of the first embodiment. [Figure 12] Figure 12 shows the current path in a second modified example of the first boost operation of the DC-DC converter of the first embodiment. [Figure 13] Figure 13 is a timing diagram of the second boost operation of the DC-DC converter of the first embodiment. [Figure 14] Figure 14 shows the current path during the second boost operation of the DC-DC converter in the first embodiment. [Figure 15] Figure 15 shows the current path during the second boost operation of the DC-DC converter in the first embodiment. [Figure 16] Figure 16 shows the current path during the second boost operation of the DC-DC converter in the first embodiment. [Figure 17] Figure 17 shows the current path for the second boost operation of the DC-DC converter in the first embodiment. [Figure 18] Figure 18 is a timing diagram of the fourth boost operation of the DC-DC converter in the first embodiment. [Figure 19]Figure 19 shows the current path for the fourth boost operation of the DC-DC converter in the first embodiment. [Figure 20] Figure 20 shows the current path for the fourth boost operation of the DC-DC converter in the first embodiment. [Figure 21] Figure 21 shows the current path for the fourth boost operation of the DC-DC converter in the first embodiment. [Figure 22] Figure 22 shows the current path for the fourth boost operation of the DC-DC converter in the first embodiment. [Figure 23] Figure 23 shows the configuration of the DC-DC converter in the second embodiment. [Figure 24] Figure 24 shows the configuration of the inductor section in the first modified DC-DC converter. [Figure 25] Figure 25 is a timing diagram of the first boost operation of the DC-DC converter of the first modified example. [Figure 26] Figure 26 is a timing diagram of the second boost operation of the DC-DC converter of the first modified example. [Figure 27] Figure 27 shows the configuration of the inductor section in the second modified DC-DC converter. [Figure 28] Figure 28 is a timing diagram of the first boost operation of the DC-DC converter of the second modified example. [Figure 29] Figure 29 is a timing diagram of the second boost operation of the DC-DC converter of the second modified example. [Figure 30] Figure 30 shows the configuration of the inductor section in the DC-DC converter of the third modified example. [Figure 31] Figure 31 is a timing diagram of the first boost operation of the DC-DC converter of the third modified example. [Figure 32] Figure 32 is a timing diagram of the second boost operation of the DC-DC converter of the third modified example. [Modes for carrying out the invention]

[0033] Embodiments relating to this disclosure will be described in detail below with reference to the attached drawings. However, this embodiment does not limit this disclosure, and in the following embodiments, the same parts are denoted by the same reference numerals to avoid redundant explanations.

[0034] <First Embodiment> (Example of power system configuration for electric vehicles) Figure 1 shows an example of the configuration of the power system of an electric vehicle.

[0035] Power system 1 includes a high-voltage battery 2, a resistor 3, contactors 4, 5, and 6, an inverter 7, a motor 9, a DC-DC converter 10, and a low-voltage battery 11. The inverter 7 includes a smoothing capacitor 8 on the input side.

[0036] The DC-DC converter 10 corresponds to an example of a "power supply device" in this disclosure.

[0037] The high-voltage battery 2 is exemplified by a traction battery, but the disclosure is not limited thereto. The voltage of the high-voltage battery 2 is arbitrary. The low-voltage battery 11 is exemplified by an auxiliary battery, but the disclosure is not limited thereto. The voltage of the low-voltage battery 11 is arbitrary.

[0038] Initially (for example, when starting an electric vehicle), there may be no power (charge) stored in capacitor 8. In this case, contactors 5 and 6 are turned on, and capacitor 8 is pre-charged (pre-charged) from the high-voltage battery 2 via resistor 3. After pre-charging is complete, contactor 5 is turned off and contactor 4 is turned on.

[0039] When charging the low-voltage battery 11, the DC-DC converter 10 steps down the DC voltage across the capacitor 8 and outputs it to the low-voltage battery 11. The low-voltage battery 11 is charged by the DC voltage output from the DC-DC converter 10.

[0040] (Conventional configuration) Figure 2 shows the configuration of a conventional DC-DC converter. The DC-DC converter 100 is a phase-shifted full-bridge circuit. Currently, phase-shifted full-bridge circuits are the mainstream for power conversion from high-voltage battery 2 to low-voltage battery 11.

[0041] The DC-DC converter 100 has a first terminal 21, a second terminal 22, a third terminal 23, and a fourth terminal 24.

[0042] The first terminal 21 is electrically connected to one end (high potential side) of the capacitor 8. The second terminal 22 is electrically connected to the other end (low potential side) of the capacitor 8. The third terminal 23 is electrically connected to one end (high potential side) of the low-voltage battery 11. The fourth terminal 24 is electrically connected to the other end (low potential side) of the low-voltage battery 11.

[0043] The DC-DC converter 100 steps down the first voltage V1 input between the first terminal 21 and the second terminal 22 and outputs the second voltage V2 between the third terminal 23 and the fourth terminal 24.

[0044] The DC-DC converter 100 includes a bridge circuit 31, an inductor Lr, a transformer T, a choke Lo (the choke Lo functions as the inductor Lo, and the same applies to the choke Lo hereafter), a transistor Q5, a transistor Q6, a capacitor 51, and a control unit 61.

[0045] The bridge circuit 31 includes transistors Q1 through Q4.

[0046] Transistor Q1 corresponds to an example of the "first switching element" in this disclosure. Transistor Q2 corresponds to an example of the "second switching element" in this disclosure. Transistor Q3 corresponds to an example of the "third switching element" in this disclosure. Transistor Q4 corresponds to an example of the "fourth switching element" in this disclosure. Transistor Q5 corresponds to an example of the "fifth switching element" in this disclosure. Transistor Q6 corresponds to an example of the "sixth switching element" in this disclosure. In addition, bridge circuit 31 corresponds to an example of the "first bridge circuit" in this disclosure.

[0047] In the embodiments, each transistor is a MOSFET, but the disclosure is not limited to this. Each transistor may be a silicon power device, a GaN power device, a SiC power device (e.g., an IGBT (Insulated Gate Bipolar Transistor)), or the like.

[0048] Each transistor has a parasitic diode (body diode) that can actively conduct current, or a diode connected in antiparallel. A parasitic diode is the pn junction between the back gate and the source and drain of a MOSFET.

[0049] The source of transistor Q1 is electrically connected to the drain of transistor Q2. The drain of transistor Q1 is electrically connected to the drain of transistor Q3. The source of transistor Q3 is electrically connected to the drain of transistor Q4. The source of transistor Q2 is electrically connected to the source of transistor Q4.

[0050] The drains of transistor Q1 and Q3 are electrically connected to the first terminal 21. The sources of transistor Q2 and Q4 are electrically connected to the second terminal 22.

[0051] The transformer T includes a first winding 41, a second winding 42, and a core 43. The first winding 41 and the second winding 42 are wound around the core 43.

[0052] The source of transistor Q1 and the drain of transistor Q2 are electrically connected to one end of inductor Lr. The other end of inductor Lr is electrically connected to one end of the first winding 41. The other end of the first winding 41 is electrically connected to the source of transistor Q3 and the drain of transistor Q4.

[0053] The inductor Lr may be a wound component, or it may be the leakage inductance of the first winding 41.

[0054] The second winding 42 is divided into a first part 42a and a second part 42b at the intermediate tap 42c.

[0055] Let the turns ratio between the first winding 41 and the first part 42a of the second winding 42 be N:1. Similarly, let the turns ratio between the first winding 41 and the second part 42b of the second winding 42 be N:1. N can be any value.

[0056] The center tap 42c is electrically connected to one end of the choke Lo (inductor Lo). The other end of the choke Lo (inductor Lo) is electrically connected to one end (high potential side) of the capacitor 51 and the third terminal 23.

[0057] One end of the first section 42a is electrically connected to the center tap 42c. The other end of the first section 42a is electrically connected to the drain of transistor Q5.

[0058] One end of the second section 42b is electrically connected to the center tap 42c. The other end of the second section 42b is electrically connected to the drain of transistor Q6.

[0059] The sources of transistor Q5 and transistor Q6 are electrically connected to the other end (low-potential side) and fourth terminal 24 of capacitor 51.

[0060] The control unit 61 outputs a drive control signal P1 to the bridge circuit 31, a drive control signal P2 to the transistor Q5, and a drive control signal P3 to the transistor Q6.

[0061] When the DC-DC converter 100 outputs a step-down voltage from the first side (capacitor 8 side) to the second side (low-voltage battery 11 side) (when charging the low-voltage battery 11), the DC-DC converter 100 uses a capacitor input method because capacitor 8 is connected in parallel with the high-voltage battery 2.

[0062] When the DC-DC converter 100 outputs a boosted voltage from the second side (low-voltage battery 11 side) to the first side (capacitor 8 side) (pre-charging capacitor 8), the DC-DC converter 100 uses a choke input method because the choke Lo (inductor Lo) is connected in series with the low-voltage battery 11.

[0063] When the DC-DC converter 100 outputs a boosted voltage from the second side (low-voltage battery 11 side) to the first side (capacitor 8 side) (pre-charging capacitor 8), if the target first voltage V1 is less than or equal to N times the second voltage V2, the boost from the winding ratio of the transformer T is sufficient. However, if the target first voltage V1 is higher than N times the second voltage V2, a boost from the choke Lo (inductor Lo) is required in addition to the transformer T. In that case, when the choke Lo (inductor Lo) discharges energy, a surge voltage is generated by the choke Lo (inductor Lo), and a large surge voltage is applied to transistors Q5 and Q6, potentially stressing transistors Q5 and Q6.

[0064] (Conventional operation) Figure 3 is a first timing diagram of the boost operation of a conventional DC-DC converter.

[0065] As shown in Figure 3, one cycle of the boost operation includes a first period Mode 1, a second period Mode 2, a third period Mode 3, and a fourth period Mode 4. The first period Mode 1 is the charging period of the choke Lo (inductor Lo). The second period Mode 2 is the discharge period of the choke Lo (inductor Lo). The third period Mode 3 is the charging period of the choke Lo (inductor Lo). The fourth period Mode 4 is the discharge period of the choke Lo (inductor Lo).

[0066] The control unit 61 controls transistors Q1 through Q4 to be in the OFF state for the entire period from the first period Mode1 to the fourth period Mode4.

[0067] At timing t0, the first period Mode1 starts. The control unit 61 controls transistors Q5 and Q6 to the ON state.

[0068] The current on the second side flows through the path from the high-potential end of the low-voltage battery 11 → choke Lo (inductor part Lo) → center tap 42c. This current splits into two at the center tap 42c and flows into the first part 42a and the second part 42b of the second winding 42. One of the split currents flows through the path from the first part 42a of the second winding 42 to transistor Q5. The other split current flows through the path from the second part 42b of the second winding 42 to transistor Q6. The current that merges at the source of transistor Q5 and the source of transistor Q6 flows to the low-potential end of the low-voltage battery 11.

[0069] During the first period, Mode 1, the current ILo across the choke Lo (inductor Lo) increases linearly. Also, the voltage VLo across the choke Lo (inductor Lo) becomes V2.

[0070] At timing t1, the second period Mode2 starts. The control unit 61 controls transistor Q6 to the OFF state.

[0071] Referring to Figure 5, the current on the second side flows through the path shown by line 211: high-potential end of low-voltage battery 11 → choke Lo (inductor part Lo) → center tap 42c → first part 42a of second winding 42 → transistor Q5 → low-potential end of low-voltage battery 11.

[0072] At this time, transistor Q6 is in the off state, and the energy (current) that was flowing through the second part 42b of the second winding 42 has nowhere to go, so a surge voltage is generated. This surge voltage is applied to transistor Q6.

[0073] The current on the first side, caused by the induced voltage in the first winding 41, flows through the following path: one end of the first winding 41 → inductor Lr → parasitic diode of transistor Q1 → high-potential end of capacitor 8 → low-potential end of capacitor 8 → parasitic diode of transistor Q4 → other end of the first winding 41.

[0074] This current on the first side precharges capacitor 8.

[0075] In the second period, Mode 2, the current ILo across the choke Lo (inductor Lo) becomes approximately constant. Also, the voltage VLo across the choke Lo (inductor Lo) becomes (V2 - NV1).

[0076] At timing t2, the third period, Mode3, starts. The control unit 61 controls transistor Q6 to the ON state.

[0077] The current on the second side flows through the path from the high-potential end of the low-voltage battery 11 → choke Lo (inductor part Lo) → center tap 42c. This current splits into two at the center tap 42c and flows into the first part 42a and the second part 42b of the second winding 42. One of the split currents flows through the path from the first part 42a of the second winding 42 to transistor Q5. The other split current flows through the path from the second part 42b of the second winding 42 to transistor Q6. The current that merges at the source of transistor Q5 and the source of transistor Q6 flows to the low-potential end of the low-voltage battery 11.

[0078] In the third period, Mode 3, the current ILo across the choke Lo (inductor Lo) increases linearly. Also, the voltage VLo across the choke Lo (inductor Lo) becomes V2.

[0079] At timing t3, the fourth period, Mode 4, starts. The control unit 61 controls transistor Q5 to the off state.

[0080] The current on the second side flows through the following path: high-potential end of the low-voltage battery 11 → choke Lo (inductor part Lo) → center tap 42c → second part 42b of the second winding 42 → transistor Q6 → low-potential end of the low-voltage battery 11.

[0081] At this time, transistor Q5 is in the off state, and the energy (current) that was flowing through the first part 42a of the second winding 42 has nowhere to go, so a surge voltage is generated. This surge voltage is applied to transistor Q5.

[0082] The current on the first side, caused by the induced voltage in the first winding 41, flows through the following path: the other end of the first winding 41 → the parasitic diode of transistor Q3 → the high-potential end of capacitor 8 → the low-potential end of capacitor 8 → the parasitic diode of transistor Q2 → inductor Lr → and finally to one end of the first winding 41.

[0083] This current on the first side precharges capacitor 8.

[0084] In the fourth period, Mode 4, the current ILo across the choke Lo (inductor Lo) becomes almost constant. Also, the voltage VLo across the choke Lo (inductor Lo) becomes (V2 - NV1).

[0085] Thus, in the DC-DC converter 100, a surge voltage is generated when transistor Q5 or transistor Q6 is turned off and applied to transistor Q5 or transistor Q6. This can cause stress on transistor Q5 or transistor Q6.

[0086] Furthermore, at the start of precharging of capacitor 8, the voltage across capacitor 8 may be very low (for example, 0V). In this case, the choke Lo (inductor Lo) is not reset (energy cannot be fully released) during the discharge period (second period Mode 2 and fourth period Mode 4), so the current ILo in the choke Lo (inductor Lo) becomes large, and the choke Lo (inductor Lo) may saturate.

[0087] To suppress the saturation of the choke Lo (inductor Lo), it is conceivable to introduce a rest period between the second period (Mode 2) and the third period (Mode 3).

[0088] Figure 4 is a second timing diagram of the boost operation of a conventional DC-DC converter.

[0089] In Figure 4, a pause period is provided between the second period (Mode 2) and the third period (Mode 3) to reset the stored energy of the choke Lo (inductor Lo), compared to Figure 3.

[0090] The timings from t4 to t6 and from t7 onward in Figure 4 are the same as those from t0 to t2 and from t2 onward in Figure 3, so the explanation is omitted.

[0091] At timing t6, the pause period begins. The control unit 61 controls transistors Q5 and Q6 to the OFF state.

[0092] When transistors Q5 and Q6 are turned off, the path for current to flow through the choke Lo (inductor Lo) disappears, so the current ILo in the choke Lo (inductor Lo) becomes zero. However, at this time, a surge voltage VX (<0) is generated in the choke Lo (inductor Lo).

[0093] (Configuration of the first embodiment) Figure 5 shows the configuration of the DC-DC converter according to the first embodiment.

[0094] Compared to the conventional DC-DC converter 100 (see Figure 2), the DC-DC converter 10 further includes a first switch 71 and a second switch 72.

[0095] The first switch 71 includes a diode D7 and a transistor Q7. The anode of diode D7 is electrically connected to the other end of the first portion 42a of the second winding 42 and to the drain of transistor Q5. The cathode of diode D7 is electrically connected to the drain of transistor Q7. The source of transistor Q7 is electrically connected to the other end of the choke Lo (inductor Lo), one end of capacitor 51 and the third terminal 23. Diode D7 is a reverse current protection diode. The first switch 71 may also be a mechanical switch.

[0096] The second switch 72 includes a diode D8 and a transistor Q8. The anode of diode D8 is electrically connected to the other end of the second portion 42b of the second winding 42 and to the drain of transistor Q6. The cathode of diode D8 is electrically connected to the drain of transistor Q8. The source of transistor Q8 is electrically connected to the other end of the choke Lo (inductor Lo), one end of capacitor 51 and the third terminal 23. Diode D8 is a reverse current protection diode. The second switch 72 may also be a mechanical switch. Transistor Q7 corresponds to an example of the "seventh switching element" in this disclosure. Transistor Q8 corresponds to an example of the "eighth switching element" in this disclosure.

[0097] The control unit 61 outputs a drive control signal P4 to the gate of transistor Q7 and a drive control signal P5 to the gate of transistor Q8.

[0098] In this embodiment, diode D7 is placed on the second winding 42 side and transistor Q7 is placed on the capacitor 51 side, but this disclosure is not limited thereto. Transistor Q7 may be placed on the second winding 42 side and diode D7 may be placed on the capacitor 51 side. That is, the drain of transistor Q7 may be electrically connected to the other end of the first portion 42a of the second winding 42 and the drain of transistor Q5, the source of transistor Q7 may be electrically connected to the anode of diode D7, and the cathode of diode D7 may be electrically connected to the other end of the choke Lo (inductor Lo), one end of capacitor 51 and the third terminal. The same applies to diode D8 and transistor Q8.

[0099] When the DC-DC converter 10 steps down the voltage output from the first side (capacitor 8 side) to the second side (low-voltage battery 11 side) (to charge the low-voltage battery 11), the control unit 61 controls transistors Q7 and Q8 to the off state. In this case, the DC-DC converter 10 becomes the equivalent circuit of the DC-DC converter 100. In this case, since capacitor 8 is connected in parallel with the high-voltage battery 2, the DC-DC converter 10 becomes a capacitor input type.

[0100] When the DC-DC converter 10 outputs a boosted voltage from the second side (low-voltage battery 11 side) to the first side (capacitor 8 side) (pre-charging capacitor 8), the choke Lo (inductor Lo) is connected in series with the low-voltage battery 11, resulting in a choke input configuration. In this case, the DC-DC converter 10, like the DC-DC converter 100, may generate a surge voltage due to the choke Lo (inductor Lo). However, the control unit 61 controls transistor Q7 or transistor Q8 to be in the ON state. As a result, the DC-DC converter 10 regenerates the surge voltage to capacitor 51 via the first switch 71 or the second switch 72.

[0101] Therefore, the DC-DC converter 10 can suppress the application of surge voltage to transistor Q5 or transistor Q6, and can suppress stress on transistor Q5 or transistor Q6.

[0102] (Overview of the boost operation in the first embodiment) In the conventional DC-DC converter 100, the second voltage V2 is boosted to the first voltage V1 by a choke Lo (inductor Lo) and a transformer T. Similarly, in the DC-DC converter 10 of the embodiment, the second voltage V2 is boosted to the first voltage V1 by a choke Lo (inductor Lo) and a transformer T.

[0103] In Table 110, "buck-down type" refers to a type that outputs a voltage of (second voltage V2 × N) or less to capacitor 8. "Buck-up type" refers to a type that outputs a voltage of (second voltage V2 × N) or less and (second voltage V2 × N) or more to capacitor 8. "Boost type" refers to a type that outputs a voltage of (second voltage V2 × N) or more to capacitor 8. Which of these types the DC-DC converter 10 operates in is set at the design stage according to the specifications. Multiple types may be combined. For example, the DC-DC converter 10 may operate in "buck-down type" until the first voltage V1 reaches (second voltage V2 × N), and then switch to "buck-up type" or "boost type" once the first voltage V1 reaches (second voltage V2 × N).

[0104] (First boost operation of the first embodiment) The first boost operation (boost operation No. 1) of the DC-DC converter 10 of the first embodiment will be described below.

[0105] Figure 6 is a timing diagram of the first boost operation of the DC-DC converter in the first embodiment. Figures 7 to 10 are diagrams showing the current flow path during the first boost operation of the DC-DC converter in the first embodiment.

[0106] Referring to Figure 6, one cycle of the first boost operation includes a first period Mode1, a second period Mode2, a third period Mode3, and a fourth period Mode4.

[0107] At timing t10, the first period Mode1 starts. The control unit 61 controls transistors Q2, Q5, and Q7 to the ON state. As a result, as shown in the first column 111-1 of the first row 111 of Table 110 in Figure 8, transistor Q5 conducts on the second side and transistor Q2 conducts on the first side.

[0108] As a variation, the control unit 61 may control transistor Q3 to be ON instead of transistor Q2. This variation will be explained later.

[0109] During the first period, Mode 1, the choke Lo (inductor Lo) is charged.

[0110] Referring to Figure 7, the current on the second side flows through the path shown by line 301: high-potential end of the low-voltage battery 11 → choke Lo (inductor part Lo) → center tap 42c of the second winding 42 → first part 42a of the second winding → transistor Q5 → low-potential end of the low-voltage battery 11.

[0111] The current on the first side due to the induced voltage generated in the first winding 41 flows through the path shown by line 302: one end of the first winding 41 → inductor Lr → transistor Q2 → parasitic diode D4 of transistor Q4 → the other end of the first winding 41.

[0112] Referring to Figure 6, the voltage VLo applied to the choke Lo (inductor Lo) is constant (second voltage V2), and the current ILo flowing through the choke Lo (inductor Lo) increases linearly.

[0113] At timing t11, the second period, Mode 2, starts. The control unit 61 controls transistors Q2 and Q5 to the off state and keeps transistor Q7 in the on state. As a result, transistor Q7 conducts on the second side, and parasitic diodes D1 and D4 conduct on the first side.

[0114] In the second period, Mode 2, the choke Lo (inductor Lo) is discharged.

[0115] Referring to Figure 8, the current on the second side flows through the path shown by line 311: one end of the choke Lo (inductor part Lo) → the center tap 42c of the second winding 42 → the first part 42a of the second winding 42 → diode D7 → transistor Q7 → the other end of the choke Lo (inductor part Lo).

[0116] In this way, the DC-DC converter 10 can form a regenerative path for the choke Lo (inductor Lo), thereby suppressing the application of surge voltage to transistor Q5. Therefore, the DC-DC converter 10 can suppress stress on transistor Q5. Furthermore, the DC-DC converter 10 can reset the choke Lo (inductor Lo).

[0117] The current on the first side flows through the path shown by line 312: one end of the first winding 41 → inductor Lr → parasitic diode D1 of transistor Q1 → capacitor 8 → parasitic diode D4 of transistor Q4 → the other end of the first winding 41.

[0118] This current on the first side precharges capacitor 8.

[0119] Referring to Figure 6, in the second period, Mode 2, the voltage VLo applied to the choke Lo (inductor Lo) is constant (-N·V1), and the current ILo in the choke Lo (inductor Lo) decreases linearly.

[0120] At timing t12, the third period, Mode 3, starts. The control unit 61 controls transistor Q7 to the off state and transistors Q4, Q6, and Q8 to the on state. As a result, transistor Q6 conducts on the second side, and transistor Q4 conducts on the first side.

[0121] As a variation, the control unit 61 may control transistor Q1 to be ON instead of transistor Q4. This variation will be explained later.

[0122] In the third period, Mode 3, the choke Lo (inductor Lo) is charged.

[0123] Referring to Figure 9, the current on the second side flows through the path shown by line 321: high-potential end of the low-voltage battery 11 → choke Lo (inductor part Lo) → center tap 42c of the second winding 42 → second part 42b of the second winding → transistor Q6 → low-potential end of the low-voltage battery 11.

[0124] The current on the first side due to the induced voltage generated in the first winding 41 flows through the path shown by line 322: the other end of the first winding 41 → transistor Q4 → parasitic diode D2 of transistor Q2 → inductor Lr → one end of the first winding 41.

[0125] Referring to Figure 6, the voltage VLo applied to the choke Lo (inductor Lo) is constant (second voltage V2), and the current ILo flowing through the choke Lo (inductor Lo) increases linearly.

[0126] At timing t13, the fourth period, Mode 4, starts. The control unit 61 controls transistors Q4 and Q6 to the off state and keeps transistor Q8 in the on state. As a result, transistor Q8 conducts on the second side, and parasitic diodes D2 and D3 conduct on the first side.

[0127] In the fourth period, Mode 4, the choke Lo (inductor Lo) is discharged.

[0128] Referring to Figure 10, the current on the second side flows through the path shown by line 331: one end of the choke Lo (inductor part Lo) → the center tap 42c of the second winding 42 → the second part 42b of the second winding 42 → diode D8 → transistor Q8 → the other end of the choke Lo (inductor part Lo).

[0129] In this way, the DC-DC converter 10 can form a regenerative path for the choke Lo (inductor Lo), thereby suppressing the application of surge voltage to transistor Q6. Therefore, the DC-DC converter 10 can suppress damage to transistor Q6. In addition, the DC-DC converter 10 can reset the choke Lo (inductor Lo).

[0130] Furthermore, at this time, no magnetic field is generated in the first portion 42a of the second winding 42, and only in the second portion 42b of the second winding 42, so an induced voltage is generated in the first winding 41.

[0131] The current on the first side due to the induced voltage generated in the first winding 41 flows through the path shown by line 332: the other end of the first winding 41 → parasitic diode D3 of transistor Q3 → capacitor 8 → parasitic diode D2 of transistor Q2 → inductor Lr → one end of the first winding 41.

[0132] This current on the first side precharges capacitor 8.

[0133] Referring to Figure 6, in the fourth period, Mode 4, the voltage VLo applied to the choke Lo (inductor Lo) is constant (-N·V1), and the current ILo in the choke Lo (inductor Lo) decreases linearly.

[0134] (summary) As explained above, when the DC-DC converter 10 outputs a boosted voltage from the second side (low-voltage battery 11 side) to the first side (capacitor 8 side) (pre-charging capacitor 8), the control unit 61 controls transistor Q7 or transistor Q8 to be turned ON.

[0135] As a result, the DC-DC converter 10 can form a regenerative path for the choke Lo (inductor Lo), thereby suppressing the application of surge voltage to transistor Q5 or transistor Q6. Therefore, the DC-DC converter 10 can suppress stress on transistor Q5 or transistor Q6.

[0136] Furthermore, the DC-DC converter 10 allows for the resetting of the choke Lo (inductor section Lo). Furthermore, since the DC-DC converter 10 can precharge the capacitor 8, the resistor 3 and contactor 5 (see Figure 1) of the power system 1 become unnecessary.

[0137] (Modified example of the first embodiment) As mentioned above, the DC-DC converter 10 may also control transistor Q3 to be ON instead of transistor Q2 during the first period Mode 1, as shown in the first column 111-1 of the first row 111 of Table 110.

[0138] Figure 11 shows the current path of a first modified example of the first boost operation of the DC-DC converter of the first embodiment.

[0139] Referring to Figure 11, the current on the second side flows through the path shown by line 301: high-potential end of the low-voltage battery 11 → choke Lo (inductor part Lo) → center tap 42c of the second winding 42 → first part 42a of the second winding → transistor Q5 → low-potential end of the low-voltage battery 11.

[0140] The current on the first side flows through the path shown by line 303: one end of the first winding 41 → inductor Lr → parasitic diode D1 of transistor Q1 → transistor Q3 → the other end of the first winding 41.

[0141] (Second modified example of the first embodiment) As mentioned above, the DC-DC converter 10 may also control transistor Q1 to be ON instead of transistor Q4 during the third period Mode 3, as shown in the third column 111-3 of the first row 111 of Table 110.

[0142] Figure 12 shows the current path in a second modified example of the first boost operation of the DC-DC converter of the first embodiment.

[0143] Referring to Figure 12, the current on the second side flows through the path shown by line 321: high-potential end of the low-voltage battery 11 → choke Lo (inductor part Lo) → center tap 42c of the second winding 42 → second part 42b of the second winding → transistor Q6 → low-potential end of the low-voltage battery 11.

[0144] The current on the first side due to the induced voltage generated in the first winding 41 flows through the path shown by line 323: other end of the first winding 41 → parasitic diode D3 of transistor Q3 → transistor Q1 → inductor Lr → one end of the first winding 41.

[0145] (Combinations of variations) Since there are two possible Mode 1 scenarios for the first period and two possible Mode 3 scenarios for the third period, there are a total of four possible boost operations for the first boost operation (the boost operation numbered No. 1).

[0146] (Second boost operation of the first embodiment) The second boost operation (boost operation No. 2) of the DC-DC converter 10 of the first embodiment will now be described.

[0147] Figure 13 is a timing diagram of the second boost operation of the DC-DC converter of the first embodiment. Figures 14 to 17 are diagrams showing the current flow path of the second boost operation of the DC-DC converter of the first embodiment.

[0148] Referring to Figure 13, one cycle of the second boost operation includes a first period Mode1, a second period Mode2, a third period Mode3, and a fourth period Mode4.

[0149] At timing t20, the first period Mode1 starts. The control unit 61 controls transistors Q5 and Q7 to the ON state. As a result, transistor Q5 conducts on the second side, and parasitic diodes D1 and D4 conduct on the first side.

[0150] During the first period, Mode 1, the choke Lo (inductor Lo) is charged.

[0151] Referring to Figure 14, the current on the second side flows through the path shown by line 331: high-potential end of the low-voltage battery 11 → choke Lo (inductor part Lo) → center tap 42c of the second winding 42 → first part 42a of the second winding → transistor Q5 → low-potential end of the low-voltage battery 11.

[0152] The current on the first side flows through the following path, as shown by line 332: one end of the first winding 41 → inductor Lr → parasitic diode D1 of transistor Q1 → capacitor 8 → parasitic diode D4 of transistor Q4 → the other end of the first winding 41.

[0153] This current on the first side precharges capacitor 8.

[0154] Referring to Figure 13, the voltage VLo applied to the choke Lo (inductor Lo) is constant (V2 - N·V1), and the current ILo flowing through the choke Lo (inductor Lo) increases linearly.

[0155] At timing t21, the second period, Mode 2, starts. The control unit 61 controls transistor Q5 to the off state and keeps transistor Q7 in the on state. As a result, transistor Q7 conducts on the second side, and parasitic diodes D1 and D4 conduct on the first side.

[0156] In the second period, Mode 2, the choke Lo (inductor Lo) is discharged.

[0157] Referring to Figure 15, the current on the second side flows through the path shown by line 341: one end of the choke Lo (inductor part Lo) → the center tap 42c of the second winding 42 → the first part 42a of the second winding 42 → diode D7 → transistor Q7 → the other end of the choke Lo (inductor part Lo).

[0158] In this way, the DC-DC converter 10 can form a regenerative path for the choke Lo (inductor Lo), thereby suppressing the application of surge voltage to transistor Q5. Therefore, the DC-DC converter 10 can suppress stress on transistor Q5. Furthermore, the DC-DC converter 10 can reset the choke Lo (inductor Lo).

[0159] The current on the first side due to the induced voltage generated in the first winding 41 flows through the path shown by line 342: one end of the first winding 41 → inductor Lr → parasitic diode D1 of transistor Q1 → capacitor 8 → parasitic diode D4 of transistor Q4 → the other end of the first winding 41.

[0160] This current on the first side precharges capacitor 8.

[0161] Referring to Figure 13, in the second period, Mode 2, the voltage VLo applied to the choke Lo (inductor Lo) is constant (-N·V1), and the current ILo in the choke Lo (inductor Lo) decreases linearly.

[0162] At timing t22, the third period, Mode 3, starts. The control unit 61 controls transistor Q7 to the off state and transistors Q6 and Q8 to the on state. As a result, transistor Q6 conducts on the second side, and parasitic diodes D2 and D3 conduct on the first side.

[0163] In the third period, Mode 3, the choke Lo (inductor Lo) is charged.

[0164] Referring to Figure 16, the current on the second side flows through the path shown by line 351: high-potential end of the low-voltage battery 11 → choke Lo (inductor part Lo) → center tap 42c of the second winding 42 → second part 42b of the second winding → transistor Q6 → low-potential end of the low-voltage battery 11.

[0165] The current on the first side flows through the path shown by line 352: the other end of the first winding 41 → parasitic diode D3 of transistor Q3 → capacitor 8 → parasitic diode D2 of transistor Q2 → inductor Lr → one end of the first winding 41.

[0166] Referring to Figure 13, the voltage VLo applied to the choke Lo (inductor Lo) is constant (V2 - N·V1), and the current ILo flowing through the choke Lo (inductor Lo) increases linearly.

[0167] At timing t23, the fourth period, Mode 4, starts. The control unit 61 controls transistor Q6 to the off state and keeps transistor Q8 in the on state. As a result, transistor Q8 conducts on the second side, and parasitic diodes D2 and D3 conduct on the first side.

[0168] In the fourth period, Mode 4, the choke Lo (inductor Lo) is discharged.

[0169] Referring to Figure 17, the current on the second side flows through the path shown by line 361: one end of the choke Lo (inductor part Lo) → the center tap 42c of the second winding 42 → the second part 42b of the second winding 42 → diode D8 → transistor Q8 → the other end of the choke Lo (inductor part Lo).

[0170] In this way, the DC-DC converter 10 can form a regenerative path for the choke Lo (inductor Lo), thereby suppressing the application of surge voltage to transistor Q6. Therefore, the DC-DC converter 10 can suppress stress on transistor Q6. In addition, the DC-DC converter 10 can reset the choke Lo (inductor Lo).

[0171] The current on the first side due to the induced voltage generated in the first winding 41 flows through the path shown by line 362: the other end of the first winding 41 → parasitic diode D3 of transistor Q3 → capacitor 8 → parasitic diode D2 of transistor Q2 → inductor Lr → one end of the first winding 41.

[0172] This current on the first side precharges capacitor 8.

[0173] (summary) As explained above, when the DC-DC converter 10 outputs a boosted voltage from the second side (low-voltage battery 11 side) to the first side (capacitor 8 side) (pre-charging capacitor 8), the control unit 61 controls transistor Q7 or transistor Q8 to be turned ON.

[0174] As a result, the DC-DC converter 10 can form a regenerative path for the choke Lo (inductor Lo), thereby suppressing the application of surge voltage to transistor Q5 or transistor Q6. Therefore, the DC-DC converter 10 can suppress stress on transistor Q5 or transistor Q6.

[0175] Furthermore, the DC-DC converter 10 allows for the resetting of the choke Lo (inductor section Lo). Furthermore, since the DC-DC converter 10 can precharge the capacitor 8, the resistor 3 and contactor 5 (see Figure 1) of the power system 1 can be made unnecessary.

[0176] (Fourth boost operation in the first embodiment) The fourth boost operation (boost operation No. 4) of the DC-DC converter 10 of the first embodiment will now be described.

[0177] Figure 18 is a timing diagram of the fourth boost operation of the DC-DC converter in the first embodiment. Figures 19 to 22 are diagrams showing the current flow path of the fourth boost operation of the DC-DC converter in the first embodiment.

[0178] Referring to Figure 18, one cycle of the fourth boost operation consists of the first period Mode1 and the second period M It includes ode2, the third period Mode3, and the fourth period Mode4.

[0179] At timing t40, the first period Mode1 starts. The control unit 61 controls transistors Q2 and Q5 to the ON state. As a result, transistor Q5 conducts on the second side, and transistor Q2 conducts on the first side.

[0180] As a variation, the control unit 61 may control transistor Q3 to be ON instead of transistor Q2, similar to Mode 1 during the first boost operation.

[0181] During the first period, Mode 1, the choke Lo (inductor Lo) is charged.

[0182] Referring to Figure 19, the current on the second side flows through the path shown by line 411: high-potential end of the low-voltage battery 11 → choke Lo (inductor part Lo) → center tap 42c of the second winding 42 → first part 42a of the second winding → transistor Q5 → low-potential end of the low-voltage battery 11.

[0183] The current on the first side flows through the path shown by line 412: one end of the first winding 41 → inductor Lr → transistor Q2 → parasitic diode D4 of transistor Q4 → the other end of the first winding 41.

[0184] Referring to Figure 18, at timing t41, the second period Mode 2 starts. The control unit 61 controls transistor Q2 to the off state and keeps transistor Q5 in the on state. As a result, transistor Q5 conducts on the second side, and parasitic diodes D1 and D4 conduct on the first side.

[0185] In the second period, Mode 2, the choke Lo (inductor Lo) is discharged.

[0186] Referring to Figure 20, the current on the second side flows through the path shown by line 421: high-potential end of the low-voltage battery 11 → choke Lo (inductor part Lo) → center tap 42c of the second winding 42 → first part 42a of the second winding → transistor Q5 → low-potential end of the low-voltage battery 11.

[0187] The current on the first side due to the induced voltage generated in the first winding 41 flows through the path shown by line 422: one end of the first winding 41 → inductor Lr → parasitic diode D1 of transistor Q1 → capacitor 8 → parasitic diode D4 of transistor Q4 → the other end of the first winding 41.

[0188] This current on the first side precharges capacitor 8.

[0189] Referring to Figure 18, at timing t42, the third period Mode 3 starts. The control unit 61 controls transistor Q5 to the off state and transistors Q4 and Q6 to the on state. As a result, transistor Q6 conducts on the second side and transistor Q4 conducts on the first side.

[0190] As a variation, the control unit 61 may control transistor Q1 to be ON instead of transistor Q4, similar to Mode 3 during the third period of the first boost operation.

[0191] In the third period, Mode 3, the choke Lo (inductor Lo) is charged.

[0192] Referring to Figure 21, the current on the second side flows through the path shown by line 431: high-potential end of the low-voltage battery 11 → choke Lo (inductor part Lo) → center tap 42c of the second winding 42 → second part 42b of the second winding → transistor Q6 → low-potential end of the low-voltage battery 11.

[0193] The current on the first side flows through the path shown by line 432: the other end of the first winding 41 → transistor Q4 → parasitic diode D2 of transistor Q2 → inductor Lr → one end of the first winding 41.

[0194] Referring to Figure 18, at timing t43, the fourth period, Mode 4, starts. The control unit 61 controls transistor Q4 to the off state and keeps transistor Q6 in the on state. As a result, transistor Q6 conducts on the second side, and parasitic diodes D2 and D3 conduct on the first side.

[0195] In the fourth period, Mode 4, the choke Lo (inductor Lo) is discharged.

[0196] Referring to Figure 22, the current on the second side flows through the path shown by line 441: high-potential end of the low-voltage battery 11 → choke Lo (inductor part Lo) → center tap 42c of the second winding 42 → second part 42b of the second winding → transistor Q6 → low-potential end of the low-voltage battery 11.

[0197] The current on the first side flows through the path shown by line 442: the other end of the first winding 41 → parasitic diode D3 of transistor Q3 → capacitor 8 → parasitic diode D2 of transistor Q2 → inductor Lr → the other end of the first winding 41.

[0198] This current on the first side precharges capacitor 8.

[0199] (summary) As explained above, when the DC-DC converter 10 outputs a boosted voltage from the second side (low-voltage battery 11 side) to the first side (capacitor 8 side) (when pre-charging capacitor 8), there is no period during which a surge voltage is generated, so the application of a surge voltage to transistor Q5 or transistor Q6 can be suppressed. Therefore, the DC-DC converter 10 can suppress stress on transistor Q5 or transistor Q6.

[0200] Furthermore, since the DC-DC converter 10 can precharge the capacitor 8, the resistor 3 and contactor 5 (see Figure 1) of the power system 1 can be made unnecessary.

[0201] <Second Embodiment> (composition) Figure 23 shows the configuration of the DC-DC converter in the second embodiment. The DC-DC converter 10A is a full-wave rectifier type converter.

[0202] Compared to the DC-DC converter 10 of the first embodiment (see Figure 5), the DC-DC converter 10A includes a bridge circuit 81 in place of transistors Q5 and Q6.

[0203] The bridge circuit 81 includes transistors Q11 to Q14. Transistor Q11 corresponds to an example of the "eleventh switching element" in this disclosure. Transistor Q12 corresponds to an example of the "twelfth switching element" in this disclosure. Transistor Q13 corresponds to an example of the "thirteenth switching element" in this disclosure. Transistor Q14 corresponds to an example of the "fourteenth switching element" in this disclosure. The bridge circuit 81 also corresponds to an example of the "second bridge circuit" in this disclosure.

[0204] The source of transistor Q11 is electrically connected to the drain of transistor Q12. The drain of transistor Q11 is electrically connected to the drain of transistor Q13. The source of transistor Q13 is electrically connected to the drain of transistor Q14. The source of transistor Q12 is electrically connected to the source of transistor Q14.

[0205] The source (one end) of transistor Q11 and the drain (one end) of transistor Q12 are electrically connected to one end of the second winding 42 of transformer T. The source (one end) of transistor Q13 and the drain (one end) of transistor Q14 are electrically connected to the other end of the second winding 42 of transformer T. The drain (other end) of transistor Q11 and the drain (other end) of transistor Q13 are electrically connected to one end of choke Lo (inductor Lo). The source (other end) of transistor Q12 and the source (other end) of transistor Q14 are electrically connected to the low-potential side and fourth terminal 24 of capacitor 51. The first switch 71 has one end electrically connected to one end of the second winding 42, one end of transistor Q11 (11th switching element), and one end of transistor Q12 (12th switching element), and the other end electrically connected to the other end of the choke Lo (inductor Lo) and the third terminal 23. The second switch 72 has one end electrically connected to the other end of the second winding 42, one end of transistor Q13 (13th switching element), and one end of transistor Q14 (14th switching element), and the other end electrically connected to the other end of choke Lo (inductor Lo) and the third terminal 23.

[0206] The control unit 61 outputs a drive control signal P6 to the bridge circuit 81.

[0207] (operation) One cycle of the boost operation of the DC-DC converter 10A includes a first period Mode1, a second period Mode2, a third period Mode3, and a fourth period Mode4.

[0208] In the first period, Mode1, the control unit 61 controls transistors Q11 to Q14 to be in the on state and controls transistors Q7 and Q8 to be in the off state.

[0209] In the second period, Mode2, the control unit 61 maintains transistor Q11 in the on state and controls transistors Q12 to Q14 to be in the off state. Also, the control unit 61 maintains transistor Q7 in the off state and controls transistor Q8 to be in the on state.

[0210] In the third period, Mode3, the control unit 61 controls transistors Q11 to Q14 to be in the on state. Also, the control unit 61 controls transistors Q7 and Q8 to be in the off state.

[0211] In the fourth period, Mode4, the control unit 61 maintains transistor Q13 in the on state and controls transistors Q11, Q12, and Q14 to be in the off state. Also, the control unit 61 controls transistor Q7 to be in the on state and controls transistor Q8 to be in the off state.

[0212] (Summary) When the DC-DC converter 10A boosts and outputs from the second side (low-voltage battery 11 side) to the first side (capacitor 8 side) (when pre-charging the capacitor 8), the control unit 61 controls transistor Q7 or transistor Q8 to be in the on state.

[0213] Thereby, the DC-DC converter 10A can form a regeneration path of the choke Lo (inductor part Lo), so that it can suppress the application of a surge voltage to transistors Q11 to Q14. Therefore, the DC-DC converter 10A can suppress transistors Q11 to Q14 from being stressed.

[0214] Also, the DC-DC converter 10A can reset the choke Lo (inductor part Lo).

[0215] In addition, since the DC-DC converter 10A can pre-charge the capacitor 8, the resistor 3 and the contactor 5 (see FIG. 1) of the power system 1 can be made unnecessary.

[0216] As described above, the embodiments of the present disclosure have been described, but the present disclosure is not limited by the contents of these embodiments. Further, the above-described components include those that can be easily assumed by those skilled in the art, those that are substantially the same, and those within the so-called equivalent range. Furthermore, the above-described components can be combined as appropriate. Further, various omissions, substitutions, or changes of the components can be made without departing from the gist of the above-described embodiments. Hereinafter, modified examples of the present invention will be shown.

[0217] [First Modified Example] A first modified example in the above-described embodiment will be described based on FIGS. 24, 25, and 26. FIG. 24 is a diagram showing the configuration of the inductor section in the DC-DC converter of the first modified example, FIG. 25 is a timing diagram of the first boosting operation of the DC-DC converter of the first modified example, and FIG. 26 is a timing diagram of the second boosting operation of the DC-DC converter of the first modified example.

[0218] In other words, the inductor section Lo' in the first modified example has the inductor section Lo shown in Figures 5, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 19, 20, 21, 22, and 23, which show the configuration of the DC-DC converter in the above-described embodiment, as the first inductor section Lo1, and also has a second inductor section Lo2, and a switch section 90 consisting of a first switch section 91 and a second switch section 92. The configuration other than the inductor section Lo' is assumed to be the same as that shown in Figures 5, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 19, 20, 21, 22, and 23, and the explanation of the configuration other than the inductor section Lo' may be omitted. Furthermore, Figure 25 shows the operation related to Figure 6, and Figure 26 shows the operation related to Figure 13. These operations are assumed to be successors to the operations of the first switching element Q1 to the eighth switching element Q8 in Figures 6, 13, and 18, respectively, and their explanations may be omitted.

[0219] Although the switch section 90 uses a MOSFET transistor, it is not limited to this and may also use silicon power devices, GaN power devices, SiC power devices (for example, IGBTs (Insulated Gate Bipolar Transistors)), etc.

[0220] The transistor switch section 90 has a diode (body diode) 90di that can actively conduct current, or more specifically, a parasitic diode, or a diode connected in antiparallel. A parasitic diode is the pn junction between the back gate and the source and drain of the MOSFET.

[0221] In other words, the inductor section Lo' in the DC-DC converters 10, 10A, and 10B according to the first embodiment further includes a first inductor section Lo1, a second inductor section Lo2, and a switch section 90, wherein the first inductor section Lo1 and the second inductor section Lo2 are set to different inductances, and the switch section 90 can switch between the first inductor section and the second inductor section by turning it on and off.

[0222] More specifically, in DC-DC converters 10, 10A, and 10B, the inductor section Lo' is electrically connected in series with the first inductor section Lo1 and the second inductor section Lo2. One end Lo1' of the first inductor section Lo1 is electrically connected to the center tap 42c of the second winding 42. The other end Lo1'' of the first inductor section Lo1 is electrically connected to one end Lo2' of the second inductor section Lo2. The other end Lo2'' of the second inductor section Lo2 is electrically connected to the third terminal 23. More specifically, the source 90s of the switch section 90 is electrically connected to the intermediate section 42c' between one end Lo1' of the first inductor section Lo1 and the center tap 42c of the second winding 42, and more specifically, the drain 90d of the switch section 90 is electrically connected to the intermediate section 100 between the first inductor section Lo1 and the second inductor section Lo2, and the inductance of the first inductor section Lo1 is set to be greater than the inductance of the second inductor section Lo2.

[0223] Furthermore, the DC-DC converters 10, 10A, and 10B according to the first embodiment further include a control unit 61 that controls the first switching element Q1 to the sixth switching element Q6, as well as the first switch 71 and the second switch 72. When the control unit 61 boosts the second voltage V2 and outputs it from between the first terminal 21 and the second terminal 22, in the first period Mode 1, it turns on the fifth switching element Q5, in the second period Mode 2 following the first period Mode 1, it turns on the first switch 72, and in the third period following the second period Mode 2... In Mode 3, the sixth switching element Q6 is turned on, and in the fourth period Mode 4 following the third period Mode 3, the second switch 72 is turned on. Furthermore, in the first period Mode 1, the control unit 61 turns on either the second switching element Q2 or the third switching element Q3, and in the third period Mode 3, it turns on either the fourth switching element Q4 or the first switching element Q1. In addition, the control unit 61 turns on the switch unit 90 in the first period Mode 1, the second period Mode 2, the third period Mode 3, and the fourth period Mode 4.

[0224] Alternatively, the DC-DC converters 10, 10A, and 10B according to the first embodiment further include a control unit 61 that controls the first switching element Q1 to the sixth switching element Q6, as well as the first switch 71 and the second switch 72. When the control unit 61 boosts the second voltage V2 and outputs it from between the first terminal 21 and the second terminal 22, in the first period Mode 1, it turns on both the fifth switching element Q5 and the sixth switching element Q6; in the second period Mode 2 following the first period Mode 1, it turns on the first switch 71; in the third period Mode 3 following the second period Mode 2, it turns on both the fifth switching element Q5 and the sixth switching element Q6; in the fourth period Mode 4 following the third period Mode 3, it turns on the second switch 72. Furthermore, the control unit 61 turns on the switch unit 90 in the first period Mode 1, the second period Mode 2, the third period Mode 3, and the fourth period Mode 4.

[0225] In other words, the DC-DC converters 10, 10A, and 10B according to the first embodiment have this configuration and switch between power conversion from the high-voltage battery 2 to the low-voltage battery 11 and power conversion from the low-voltage battery 11 to the high-voltage battery 2.

[0226] In other words, by turning on the switch unit 90, more current can be supplied to the second inductor Lo2, which has a relatively small inductance. This suppresses stress on the secondary switching element and enables power transmission to the primary side, allowing for a quick pre-charge (preliminary charge) of the primary side, which converts power from the low-voltage battery 11 to the high-voltage battery 2.

[0227] Furthermore, during normal operation when converting power from the high-voltage battery 2 to the low-voltage battery 11, the switch unit 90 can be turned off to allow conduction to both the first inductor unit Lo1 and the second inductor unit Lo2, ensuring that the inductance required for normal operation is secured, thus enabling operation without disrupting normal operation.

[0228] [Second variation] A second modified example of the above-described embodiment will be explained with reference to Figures 27, 28, and 29. Figure 27 is a diagram showing the configuration of the inductor section in the DC-DC converter of the second modified example, Figure 28 is a timing diagram of the first boost operation of the DC-DC converter of the second modified example, and Figure 29 is a timing diagram of the second boost operation of the DC-DC converter of the second modified example.

[0229] In other words, the inductor section Lo' in the second modified example has the inductor section Lo shown in Figures 5, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 19, 20, 21, 22, and 23, which show the configuration of the DC-DC converter in the above-described embodiment, as the first inductor section Lo1, and also has a second inductor section Lo2, and a switch section 90 consisting of a first switch section 91 and a second switch section 92. The configuration other than the inductor section Lo' is assumed to be the same as that shown in Figures 5, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 19, 20, 21, 22, and 23, and the explanation of the configuration other than the inductor section Lo' may be omitted. Furthermore, Figure 27 represents the operation related to Figure 6, Figure 28 represents the operation related to Figure 13, and Figure 29 represents the operation related to Figure 17. These operations are assumed to be successors to the operations of the first switching element Q1 to the eighth switching element Q8 in Figures 6, 13, and 18, respectively, and their explanations may be omitted.

[0230] Although the switch section 90 uses a MOSFET transistor, it is not limited to this and may also use silicon power devices, GaN power devices, SiC power devices (for example, IGBTs (Insulated Gate Bipolar Transistors)), etc.

[0231] More specifically, the first switch section 91, which is a transistor, has a diode (parasitic diode) 90di that can actively conduct current, or a diode connected in antiparallel. A parasitic diode is the pn junction between the back gate and the source and drain of a MOSFET.

[0232] Furthermore, the second switch section 92 has a diode (parasitic diode) 92di connected in antiparallel, which can actively conduct current. A parasitic diode is a pn junction between the back gate and the source and drain of a MOSFET.

[0233] In other words, the inductor section Lo' in the DC-DC converters 10, 10A, and 10B according to the second embodiment further includes a first inductor section Lo1, a second inductor section Lo2, and a switch section 90, wherein the first inductor section Lo1 and the second inductor section Lo2 are set to different inductances, and the switch section 90 can switch between the first inductor section and the second inductor section by turning it on and off.

[0234] More specifically, in the DC-DC converters 10, 10A, and 10B according to the second embodiment, the inductor section Lo' connects the first inductor section Lo1 and the second inductor section Lo2 in series, one end Lo1' of the first inductor section Lo1 is electrically connected to the center tap 42c of the second winding 42, the other end Lo1'' of the first inductor section Lo1 is electrically connected to one end Lo2' of the second inductor section Lo2, and the other end Lo2'' of the second inductor section Lo2 is electrically connected to the third terminal 23, the switch section 90 has a first switch section 91 and a second switch section 92, and more specifically, the source 91s of the first switch section 91 is the intermediate between one end Lo1' of the first inductor section Lo1 and the center tap 42c of the second winding 42 The drain 91d of the first switch 91 is electrically connected to the part 42c, and more specifically to the other end of the first switch 91, it is electrically connected to the intermediate part 100 between the first inductor part Lo1 and the second inductor part Lo2. More specifically to the drain 92d of the second switch 92 is electrically connected to the intermediate part 42c' between the one end Lo1' of the first inductor part Lo1, to which the one end 91d of the first switch 91 is electrically connected, and the center tap 42c of the second winding 42. More specifically to the other end of the second switch 92, the source 92s of the second switch 92 is electrically connected to the one end Lo1' of the first inductor part Lo1, and the inductance of the first inductor part Lo1 is set to be greater than the inductance of the second inductor part Lo2.

[0235] And in the DC-DC converters 10, 10A, 10B according to the second embodiment, it further includes a control unit 61 that controls the first switching element Q1 to the sixth switching element Q6, as well as the first switch 71 and the second switch 72. When boosting the second voltage V2 and outputting it from between the first terminal 21 and the second terminal 22, in the first period Mode1, the control unit 61 turns on the fifth switching element Q5. In the second period Mode2 following the first period Mode1, the control unit 61 turns on the second switch 72. In the third period Mode3 following the second period Mode2, the control unit 61 turns on the sixth switching element Q6. In the fourth period Mode4 following the third period Mode3, the control unit 61 turns on the second switch 72. Further, in the first period Mode1, the control unit 61 turns on the second switching element Q2 or the third switching element Q3. In the third period Mode3, the control unit 61 turns on the fourth switching element Q4 or the first switching element Q1. Additionally, in the first period Mode1, the second period Mode2, the third period Mode3, and the fourth period Mode4, the control unit 61 turns on the first switch unit 91 and turns off the second switch unit 92.

[0236] Alternatively, in the DC-DC converters 10, 10A, 10B according to the first embodiment, it further includes a control unit 61 that controls the first switching element Q1 to the sixth switching element Q6, as well as the first switch 71 and the second switch 72. When boosting the second voltage V2 and outputting it from between the first terminal 21 and the second terminal 22, in the first period Mode1, the control unit 61 turns on both the fifth switching element Q5 and the sixth switching element Q6. In the second period Mode2 following the first period Mode1, the control unit 61 turns on the first switch 71. In the third period Mode3 following the second period Mode2, the control unit 61 turns on both the fifth switching element Q5 and the sixth switching element Q6. In the fourth period Mode4 following the third period Mode3, the control unit 61 turns on the second switch 72. Further, in the first period Mode1, the second period Mode2, the third period Mode3, and the fourth period Mode4, the control unit 61 turns on the first switch unit 91 and turns off the second switch unit 92.

[0237] In other words, the DC-DC converters 10, 10A, and 10B according to the second embodiment have this configuration and switch between power conversion from the high-voltage battery 2 to the low-voltage battery 11 and power conversion from the low-voltage battery 11 to the high-voltage battery 2.

[0238] In other words, by turning off the second switch unit 92 while turning on the first switch unit 91, it is possible to conduct only to the second inductor Lo2, which has a relatively small inductance, thereby suppressing stress on the secondary switching element and enabling power transmission to the primary side, and allowing primary side pre-charging (pre-charging) for power conversion from the low-voltage battery 11 to the high-voltage battery 2 to be performed in a short time.

[0239] Furthermore, during normal operation, when converting power from the high-voltage battery 2 to the low-voltage battery 11, the first switch unit 91 is turned off while the second switch unit 92 is turned on, allowing both the first inductor unit Lo1 and the second inductor unit Lo2 to conduct, thus ensuring the inductance required for normal operation, and enabling operation without disrupting normal operation.

[0240] [Third variation] A third modified example of the above-described embodiment will be explained with reference to Figures 30, 31, and 32. Figure 30 is a diagram showing the configuration of the inductor section in the DC-DC converter of the third modified example, Figure 31 is a timing diagram of the first boost operation of the DC-DC converter of the third modified example, and Figure 32 is a timing diagram of the second boost operation of the DC-DC converter of the third modified example.

[0241] In other words, the inductor section Lo' in the third modified example has the inductor section Lo shown in Figures 5, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 19, 20, 21, 22, and 23, which show the configuration of the DC-DC converter in the above-described embodiment, as the first inductor section Lo1, and also has a second inductor section Lo2, and a switch section 90 consisting of a first switch section 91 and a second switch section 92. The configuration other than the inductor section Lo' is assumed to be the same as that shown in Figures 5, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 19, 20, 21, 22, and 23, and the explanation of the configuration other than the inductor section Lo' may be omitted. Furthermore, Figure 31 shows the operation related to Figure 6, and Figure 32 shows the operation related to Figure 13. These operations are assumed to be successors to the operations of the first switching element Q1 to the eighth switching element Q8 in Figures 6, 13, and 18, respectively, and their explanations may be omitted.

[0242] Although the switch section 90 uses a MOSFET transistor, it is not limited to this and may also use silicon power devices, GaN power devices, SiC power devices (for example, IGBTs (Insulated Gate Bipolar Transistors)), etc.

[0243] The transistor switch section 90 has a parasitic diode (body diode) 90di that can actively conduct current, or a diode connected in antiparallel. A parasitic diode is the pn junction between the back gate and the source and drain of a MOSFET.

[0244] In other words, the inductor section Lo' in the DC-DC converters 10, 10A, and 10B according to the third embodiment further includes a first inductor section Lo1, a second inductor section Lo2, and a switch section 90, wherein the first inductor section Lo1 and the second inductor section Lo2 are set to different inductances, and the switch section 90 can switch between the first inductor section Lo1 and the second inductor section Lo2 by turning it on and off.

[0245] More specifically, in the DC-DC converters 10, 10A, and 10B according to the third embodiment, the inductor section Lo' is electrically connected in parallel with a first inductor section Lo1 and a second inductor section Lo2, one end Lo1' of the first inductor section Lo1 is electrically connected to the center tap 42c of the second winding 42, the other end Lo1'' of the first inductor section Lo1 is electrically connected to the third terminal 23, one end Lo2' of the second inductor section Lo2 is electrically connected to the intermediate section 42c' between one end Lo1' of the first inductor section Lo1 and the center tap 42c of the second winding 42, the other end Lo2'' of the second inductor section Lo2 is electrically connected to the intermediate section 200 between the other end Lo1'' of the first inductor section Lo1 and the third terminal 23, and the switch section 90 has a first switch section 91 and a second switch section 92, and more specifically the drain of the first switch section 91 91d is electrically connected to the intermediate portion 42c' between one end Lo1' of the first inductor section Lo1 and the center tap 42c of the second winding 42; more specifically, the source 91s of the first switch section 91 is electrically connected to one end Lo2' of the second inductor section Lo2; more specifically, the drain 92d of the second switch section 92 is electrically connected to the intermediate portion 42c' between one end Lo1' of the first inductor section Lo1 and the center tap 42c of the second winding 42, to which the drain 91d of the first switch section 91 is electrically connected; more specifically, the source 92s of the second switch section 92 is electrically connected to one end Lo1' of the first inductor section Lo1; and the inductance of the first inductor section Lo1 is set to be greater than the inductance of the second inductor section Lo2.

[0246] Furthermore, the DC-DC converters 10, 10A, and 10B according to the third embodiment further include a control unit 61 that controls the first switching element Q1 to the sixth switching element Q6, as well as the first switch 71 and the second switch 72, and when the control unit 61 boosts the second voltage V2 and outputs it from between the first terminal 21 and the second terminal 22, in the first period Mode 1, the fifth switching element Q5 is turned on, in the second period Mode 2 following the first period Mode 1, the first switch 72 is turned on, and in the third period Mode 3 following the second period Mode 2, The control unit 61 turns on the sixth switching element Q6, and in the fourth period Mode 4 following the third period Mode 3, it turns on the second switch 72. Furthermore, in the first period Mode 1, the control unit 61 turns on the second switching element Q2 or the third switching element Q3, and in the third period Mode 3, it turns on the fourth switching element Q4 or the first switching element Q1. Furthermore, in the first period Mode 1, the second period Mode 2, the third period Mode 3, and the fourth period Mode 4, the control unit 61 turns on the first switch unit 91 and turns off the second switch unit 92.

[0247] Alternatively, the DC-DC converters 10, 10A, and 10B according to the first embodiment further include a control unit 61 that controls the first switching element Q1 to the sixth switching element Q6, as well as the first switch 71 and the second switch 72. When the control unit 61 boosts the second voltage V2 and outputs it from between the first terminal 21 and the second terminal 22, in the first period Mode 1, it turns on both the fifth switching element Q5 and the sixth switching element Q6; in the second period Mode 2 following the first period Mode 1, it turns on the first switch 71; in the third period Mode 3 following the second period Mode 2, it turns on both the fifth switching element Q5 and the sixth switching element Q6; in the fourth period Mode 4 following the third period Mode 3, it turns on the second switch 72. Furthermore, in the first period Mode 1, the second period Mode 2, the third period Mode 3, and the fourth period Mode 4, the control unit 61 turns on the first switch unit 91 and turns off the second switch unit 92.

[0248] In other words, the DC-DC converters 10, 10A, and 10B according to the third embodiment have this configuration and switch between power conversion from the high-voltage battery 2 to the low-voltage battery 11 and power conversion from the low-voltage battery 11 to the high-voltage battery 2.

[0249] In other words, by turning off the second switch unit 92 while turning on the first switch unit 91, it is possible to conduct only to the second inductor Lo2, which has a relatively small inductance, thereby suppressing stress on the secondary switching element and enabling power transmission to the primary side, and allowing primary side pre-charging (pre-charging) for power conversion from the low-voltage battery 11 to the high-voltage battery 2 to be performed in a short time.

[0250] Furthermore, during normal operation, when converting voltage from the high-voltage battery 2 to the low-voltage battery 11, the first switch unit 91 is turned off while the second switch unit 92 is turned on, allowing conduction only to the first inductor unit Lo1, which has a relatively large inductance. This ensures that the inductance required for normal operation is secured, and the operation can be performed without hindering normal operation. [Explanation of Symbols]

[0251] 1 Power system 2 High-voltage battery 3 resistors 4, 5, 6 Contactors 7 Inverter 8 Capacitors 9 Motors 10, 10A, 10B, 100 DC-DC converters 11 Low-voltage battery 31, 81 Bridge Circuit 51 Capacitors 61 Control Unit 71. Switch 1 72 Second switch 90 Switch section 91 First Switch Section 92 Second Switch Section Lo choke (inductor section) Lo' Inductor section Lo1 First Inductor Section Lo2 Second Inductor Section Lr, L1, L2 Inductors Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, Q11, Q12, Q13, Q14 transistor T Transformer

Claims

1. A power supply device that steps down a first voltage input between a first terminal and a second terminal and outputs it from between a third terminal and a fourth terminal, and steps up a second voltage input between the third terminal and the fourth terminal and outputs it from between the first terminal and the second terminal, A bridge circuit comprising: a first switching element with one end electrically connected to the first terminal; a second switching element with one end electrically connected to the other end of the first switching element and the other end electrically connected to the second terminal; a third switching element with one end electrically connected to the first terminal; and a fourth switching element with one end electrically connected to the other end of the third switching element and the other end electrically connected to the second terminal; A transformer comprising: a first winding, one end of which is electrically connected to the other end of the first switching element and one end of the second switching element, and the other end of which is electrically connected to the other end of the third switching element and one end of the fourth switching element; and a second winding that is magnetically coupled to the first winding; An inductor section having one end electrically connected to the center tap of the second winding and the other end electrically connected to the third terminal, A fifth switching element, one end of which is electrically connected to one end of the second winding and the other end of which is electrically connected to the fourth terminal, A sixth switching element, one end of which is electrically connected to the other end of the second winding and the other end of which is electrically connected to the fourth terminal, A first switch, one end of which is electrically connected to one end of the fifth switching element and one end of the second winding, and the other end of which is electrically connected to the other end of the inductor and the third terminal, One end is electrically connected to one end of the sixth switching element and the other end of the second winding, A second switch whose other end is electrically connected to the other end of the inductor and the third terminal, This includes, The inductor section further includes a first inductor section, a second inductor section, and a switch section, wherein the first inductor section and the second inductor section are set to have different inductances. The power supply device is characterized in that the switch unit switches between the first inductor unit and the second inductor unit by turning it on and off.

2. The inductor section electrically connects the first inductor section and the second inductor section, One end of the first inductor is electrically connected to the center tap of the second winding. The other end of the first inductor is electrically connected to one end of the second inductor. The other end of the second inductor is electrically connected to the third terminal. One end of the switch section is electrically connected to the intermediate portion between one end of the first inductor section and the center tap of the second winding, The other end of the switch section is electrically connected to the intermediate section between the first inductor section and the second inductor section. The power supply device according to claim 1, characterized in that the inductance of the first inductor is set to be greater than the inductance of the second inductor.

3. The system further includes the first to sixth switching elements, and a control unit that controls the first and second switches, The control unit, When the second voltage is boosted and output between the first terminal and the second terminal, During the first period, the fifth switching element is turned on. In the second period following the first period, the first switch is turned on. In the third period following the second period, the sixth switching element is turned on. In the fourth period following the third period, the second switch is turned on. The power supply device according to claim 2, characterized in that...

4. The control unit, During the first period, the second switching element or the third switching element is turned on. During the third period, the fourth switching element or the first switching element is turned on. The power supply device according to claim 3, characterized in that...

5. The control unit, During the first period, the second period, the third period, and the fourth period, the switch unit is turned on. The power supply device according to claim 4, characterized in that...

6. The system further includes the first to sixth switching elements, and a control unit that controls the first and second switches, The control unit, When the second voltage is boosted and output between the first terminal and the second terminal, During the first period, both the fifth switching element and the sixth switching element are turned on. In the second period following the first period, the first switch is turned on. In the third period following the second period, both the fifth switching element and the sixth switching element are turned on. In the fourth period following the third period, the second switch is turned on. The power supply device according to claim 2, characterized in that...

7. The control unit, During the first period, the second period, the third period, and the fourth period, the switch unit is turned on. The power supply device according to claim 6, characterized in that...

8. The inductor section electrically connects the first inductor section and the second inductor section, One end of the first inductor is electrically connected to the center tap of the second winding. The other end of the first inductor is electrically connected to one end of the second inductor. The other end of the second inductor is electrically connected to the third terminal. The switch section comprises a first switch section and a second switch section. One end of the first switch section is electrically connected to the intermediate portion between one end of the first inductor section and the center tap of the second winding, The other end of the first switch section is electrically connected to the intermediate section between the first inductor section and the second inductor section. One end of the second switch section is electrically connected to the intermediate portion between one end of the first inductor section, to which one end of the first switch section is electrically connected, and the center tap of the second winding. The other end of the second switch section is electrically connected to one end of the first inductor section. The power supply device according to claim 1, characterized in that the inductance of the first inductor is set to be greater than the inductance of the second inductor.

9. The system further includes the first to sixth switching elements, and a control unit that controls the first and second switches, The control unit, When the second voltage is boosted and output between the first terminal and the second terminal, During the first period, the fifth switching element is turned on. In the second period following the first period, the first switch is turned on. In the third period following the second period, the sixth switching element is turned on. In the fourth period following the third period, the second switch is turned on. The power supply device according to claim 8, characterized in that...

10. The control unit, During the first period, the second switching element or the third switching element is turned on. During the third period, the fourth switching element or the first switching element is turned on. The power supply device according to claim 9, characterized in that...

11. The control unit, During the first period, the second period, the third period, and the fourth period, the first switch unit is turned on and the second switch unit is turned off. The power supply device according to claim 10, characterized in that...

12. The system further includes the first to sixth switching elements, and a control unit that controls the first and second switches, The control unit, When the second voltage is boosted and output between the first terminal and the second terminal, During the first period, both the fifth switching element and the sixth switching element are turned on. In the second period following the first period, the first switch is turned on. In the third period following the second period, both the fifth switching element and the sixth switching element are turned on. In the fourth period following the third period, the second switch is turned on. The power supply device according to claim 8, characterized in that...

13. The control unit, During the first period, the second period, the third period, and the fourth period, the first switch unit is turned on and the second switch unit is turned off. The power supply device according to claim 12, characterized in that...

14. The inductor section electrically connects the first inductor section and the second inductor section in parallel, One end of the first inductor is electrically connected to the center tap of the second winding. The other end of the first inductor is electrically connected to the third terminal. One end of the second inductor is electrically connected to the intermediate portion between one end of the first inductor and the center tap of the second winding. The other end of the second inductor is electrically connected to the intermediate portion between the other end of the first inductor and the third terminal. The switch section comprises a first switch section and a second switch section. One end of the first switch section is electrically connected to the intermediate portion between one end of the first inductor section and the center tap of the second winding. The other end of the first switch section is electrically connected to one end of the second inductor section. One end of the second switch section is electrically connected to the intermediate portion between one end of the first inductor section, to which one end of the first switch section is electrically connected, and the center tap of the second winding. The other end of the second switch section is electrically connected to one end of the first inductor section. The inductance of the first inductor is set to be greater than the inductance of the second inductor. The power supply device according to claim 1, characterized by the following:

15. The system further includes the first to sixth switching elements, and a control unit that controls the first and second switches, The control unit, When the second voltage is boosted and output between the first terminal and the second terminal, During the first period, the fifth switching element is turned on. In the second period following the first period, the first switch is turned on. In the third period following the second period, the sixth switching element is turned on. In the fourth period following the third period, the second switch is turned on. The power supply device according to claim 14, characterized in that

16. The control unit, During the first period, the second switching element or the third switching element is turned on. During the third period, the fourth switching element or the first switching element is turned on. The power supply device according to claim 15, characterized in that

17. The control unit, During the first period, the second period, the third period, and the fourth period, the first switch unit is turned on and the second switch unit is turned off. The power supply device according to claim 16, characterized in that...

18. The system further includes the first to sixth switching elements, and a control unit that controls the first and second switches, The control unit, When the second voltage is boosted and output between the first terminal and the second terminal, During the first period, both the fifth switching element and the sixth switching element are turned on. In the second period following the first period, the first switch is turned on. In the third period following the second period, both the fifth switching element and the sixth switching element are turned on. In the fourth period following the third period, the second switch is turned on. The power supply device according to claim 14, characterized in that

19. The control unit, During the first period, the second period, the third period, and the fourth period, the first switch unit is turned on and the second switch unit is turned off. The power supply device according to claim 18, characterized in that

20. A bridge circuit including a first switching element with one end electrically connected to a first terminal, a second switching element with one end electrically connected to the other end of the first switching element and the other end electrically connected to a second terminal, a third switching element with one end electrically connected to the first terminal, and a fourth switching element with one end electrically connected to the other end of the third switching element and the other end electrically connected to the second terminal; a transformer including a first winding with one end electrically connected to the other end of the first switching element and one end of the second switching element, and the other end electrically connected to the other end of the third switching element and one end of the fourth switching element, and a second winding that is magnetically coupled to the first winding; an inductor section with one end electrically connected to the center tap of the second winding and the other end electrically connected to the third terminal; and a component with one end electrically connected to one end of the second winding and the other end connected to the fourth terminal A control method for a power supply device comprising: a fifth switching element electrically connected to; a sixth switching element having one end electrically connected to the other end of the second winding and the other end electrically connected to the fourth terminal; a first switch having one end electrically connected to one end of the fifth switching element and one end of the second winding and the other end electrically connected to the other end of the inductor section and the third terminal; and a second switch having one end electrically connected to one end of the sixth switching element and the other end of the second winding and the other end electrically connected to the other end of the inductor section and the third terminal, wherein the inductor section further comprises a first inductor section, a second inductor section, and a switch section, the first inductor section and the second inductor section being set to different inductances from each other, and the switch section switching between the first inductor section and the second inductor section by turning it on and off, When the second voltage input between the third terminal and the fourth terminal is boosted and output from between the first terminal and the second terminal, During the first period, the fifth switching element is turned on. In the second period following the first period, the first switch is turned on. In the third period following the second period, the sixth switching element is turned on. In the fourth period following the third period, the second switch is turned on. A method for controlling a power supply device, characterized by the following features.

21. A bridge circuit including a first switching element with one end electrically connected to a first terminal, a second switching element with one end electrically connected to the other end of the first switching element and the other end electrically connected to a second terminal, a third switching element with one end electrically connected to the first terminal, and a fourth switching element with one end electrically connected to the other end of the third switching element and the other end electrically connected to the second terminal; a transformer including a first winding with one end electrically connected to the other end of the first switching element and one end of the second switching element, and the other end electrically connected to the other end of the third switching element and one end of the fourth switching element, and a second winding that is magnetically coupled to the first winding; an inductor section with one end electrically connected to the center tap of the second winding and the other end electrically connected to the third terminal; and a component with one end electrically connected to one end of the second winding and the other end connected to the fourth terminal A control method for a power supply device comprising: a fifth switching element electrically connected to; a sixth switching element having one end electrically connected to the other end of the second winding and the other end electrically connected to the fourth terminal; a first switch having one end electrically connected to one end of the fifth switching element and one end of the second winding and the other end electrically connected to the other end of the inductor section and the third terminal; and a second switch having one end electrically connected to one end of the sixth switching element and the other end of the second winding and the other end electrically connected to the other end of the inductor section and the third terminal, wherein the inductor section further comprises a first inductor section, a second inductor section, and a switch section, the first inductor section and the second inductor section being set to different inductances from each other, and the switch section switching between the first inductor section and the second inductor section by turning it on and off, When the second voltage input between the third terminal and the fourth terminal is boosted and output from between the first terminal and the second terminal, During the first period, both the fifth switching element and the sixth switching element are turned on. In the second period following the first period, the first switch is turned on. In the third period following the second period, both the fifth switching element and the sixth switching element are turned on. In the fourth period following the third period, the second switch is turned on. A method for controlling a power supply device, characterized by the following features.

22. A power supply device that steps down a first voltage input between a first terminal and a second terminal and outputs it from between a third terminal and a fourth terminal, and steps up a second voltage input between the third terminal and the fourth terminal and outputs it from between the first terminal and the second terminal, A first bridge circuit comprising: a first switching element with one end electrically connected to the first terminal; a second switching element with one end electrically connected to the other end of the first switching element and the other end electrically connected to the second terminal; a third switching element with one end electrically connected to the first terminal; and a fourth switching element with one end electrically connected to the other end of the third switching element and the other end electrically connected to the second terminal; A transformer comprising: a first winding, one end of which is electrically connected to the other end of the first switching element and one end of the second switching element, and the other end of which is electrically connected to the other end of the third switching element and one end of the fourth switching element; and a second winding that is magnetically coupled to the first winding; A second bridge circuit comprising: an eleventh switching element with one end electrically connected to one end of the second winding; a twelfth switching element with one end electrically connected to one end of the second winding and the other end electrically connected to the fourth terminal; a thirteenth switching element with one end electrically connected to the other end of the second winding; and a fourteenth switching element with one end electrically connected to the other end of the second winding and the other end electrically connected to the fourth terminal; An inductor unit having one end electrically connected to the other end of the 11th switching element and the other end of the 13th switching element, and the other end electrically connected to the 3rd terminal, A first switch, one end of which is electrically connected to one end of the second winding, one end of the 11th switching element, and one end of the 12th switching element, and the other end of which is electrically connected to the other end of the inductor and the third terminal, A second switch, one end of which is electrically connected to the other end of the second winding, one end of the 13th switching element, and one end of the 14th switching element, and the other end of which is electrically connected to the other end of the inductor and the third terminal, This includes, The inductor section further includes a first inductor section, a second inductor section, and a switch section, wherein the first inductor section and the second inductor section are set to have different inductances. The power supply device is characterized in that the switch unit switches between the first inductor unit and the second inductor unit by turning it on and off.

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