JP7503769B2 - DC/DC conversion device - Google Patents

Description

This disclosure relates to a DC/DC conversion device that converts DC power to DC power of a different voltage.

Power conditioners connected to storage batteries, solar cells, fuel cells, etc. use DC/DC converters and inverters. Highly efficient power conversion and compact design are desired for DC/DC converters and inverters. As a DC/DC converter to achieve this, a multilevel power conversion device has been proposed in which a flying capacitor circuit (including multiple switching elements connected in series and at least one flying capacitor) is connected to the rear stage of a reactor, and the voltage at the connection point between the reactor and the flying capacitor circuit is multileveled (see, for example, Patent Document 1).

A multilevel power conversion device can reduce the voltage applied to each switching element, thereby reducing switching losses and achieving highly efficient power conversion. For example, in a multilevel power conversion device in which four switching elements are connected in series and two flying capacitor circuits, each with flying capacitors connected to the two inner switching elements, are connected in series to a DC bus, the voltage applied to each switching element can be reduced to 1/4 of the DC bus voltage. Switching elements with low voltage resistance are cheaper than switching elements with high voltage resistance, and have less conduction loss and switching loss during power conversion.

In the multilevel power conversion device described above in which eight switching elements are connected in series to a DC bus, a configuration is possible in which eight resistors are connected in parallel to each of the eight switching elements. In this configuration, even when all eight switching elements are in the off state, the two flying capacitors and the output capacitor can be precharged via the eight resistors.

Because the input capacitor is at 0V before precharging, the voltage between the third and sixth switching elements of the eight switching elements is 0V. Furthermore, because the two flying capacitors are also at 0V, the voltage between the second and third switching elements, and the voltage between the sixth and seventh switching elements are also 0V. Therefore, when precharging begins, most of the voltage on the DC bus is applied to the first and eighth switching elements.

JP 2019-92242 A

Generally, in a multilevel power conversion device, the withstand voltage of each switching element is set on the assumption that the voltage of the DC bus is divided by half of the multiple switching elements connected in series to the DC bus. In the above example, the withstand voltage of each switching element is set on the assumption that the voltage of the DC bus is divided by four switching elements.

However, in the precharge situation described above, a state occurs in which the voltage of the DC bus is divided by two switching elements, the first switching element and the eighth switching element. In this case, there is a possibility that the first switching element and the eighth switching element may exceed their withstand voltage.

This disclosure has been made in consideration of these circumstances, and its purpose is to provide a DC/DC conversion device that can safely precharge a flying capacitor.

In order to solve the above problems, a DC/DC conversion device according to one aspect of the present disclosure includes a low-voltage side capacitor connected in parallel to a low-voltage side DC power supply, a high-voltage side capacitor connected in parallel to a high-voltage side DC power supply, a plurality of switching elements connected in series, and at least one flying capacitor, in which the high-voltage side DC power supply is connected to both ends of the plurality of switching elements connected in series, and the low-voltage side DC power supply is connected to both ends of a portion of the plurality of switching elements constituting the plurality of switching elements connected in series, a flying capacitor section, at least one reactor inserted in a path between both ends of the low-voltage side capacitor and both ends of the portion of the plurality of switching elements, and a switch circuit inserted in a path between the high-voltage side capacitor and the high-voltage side DC power supply.

This disclosure makes it possible to realize a DC/DC conversion device that can safely precharge a flying capacitor.

1 is a diagram for explaining a basic configuration of a DC/DC conversion device according to an embodiment; 2 is a diagram showing switching patterns of a first switching element to an eighth switching element of the DC/DC conversion device shown in FIG. 1. 3(a) to 3(d) are circuit diagrams showing current paths for each switching pattern during boost operation. 4(a) to 4(d) are circuit diagrams showing current paths for each switching pattern during step-down operation. 11 is a timing chart showing an example of a switching pattern of a first switching element-an eighth switching element when a boost ratio is two or more; 11 is a timing chart showing an example of a switching pattern of a first switching element-an eighth switching element when a boost ratio is less than two. 1 is a diagram for explaining a configuration of a DC/DC conversion device with a soft precharge function according to an embodiment; 8 is a diagram for explaining an operation at the time of start-up of the DC/DC conversion device shown in FIG. 7 . 9A to 9F are diagrams showing configuration examples of the switch circuit. 11 is a diagram for explaining another configuration of a DC/DC conversion device with a soft precharge function according to an embodiment. FIG. 11 is a diagram for explaining a configuration of a DC/DC conversion device with a soft precharge function according to a modified example. FIG. 12A to 12C are diagrams showing configuration examples of flying capacitor circuits. FIG. 1 is a diagram showing a flying capacitor circuit having N stages (N is a natural number).

Figure 1 is a diagram for explaining the basic configuration of a DC/DC conversion device 3 according to an embodiment. The DC/DC conversion device 3 according to an embodiment is a bidirectional step-up/step-down DC/DC converter. The DC/DC conversion device 3 can step up the DC power supplied from the low-voltage side DC power supply 1 and supply it to the high-voltage side DC power supply 2. The DC/DC conversion device 3 can also step down the DC power supplied from the high-voltage side DC power supply 2 and supply it to the low-voltage side DC power supply 1.

The low-voltage DC power source 1 may be, for example, a storage battery or an electric double-layer capacitor. The high-voltage DC power source 2 may be, for example, a DC bus to which a bidirectional DC/AC inverter is connected. In a power storage system application, the AC side of the bidirectional DC/AC inverter is connected to a commercial power system and an AC load. In an electric vehicle application, it is connected to a motor (with regenerative function). In a power storage system application, a DC/DC converter for a solar cell or a DC/DC converter for another storage battery may be further connected to the DC bus.

The DC/DC conversion device 3 includes a low-voltage side capacitor C3, a first reactor L1, a second reactor L2, a flying capacitor section 30, a high-voltage side capacitor C4, a voltage sensor 41, and a control section 40.

A low-voltage side capacitor C3 for input/output is connected in parallel to the low-voltage side DC power supply 1. A high-voltage side capacitor C4 for input/output is connected in parallel to the high-voltage side DC power supply 2. A flying capacitor section 30 is connected between a positive DC bus and a negative DC bus connected to both ends of the high-voltage side DC power supply 2. In the circuit configuration shown in FIG. 1, the flying capacitor section 30 is configured by connecting an upper first flying capacitor circuit and a lower second flying capacitor circuit in series. A first reactor L1 is connected between the positive terminal of the low-voltage side DC power supply 1 and the midpoint of the first flying capacitor circuit. A second reactor L2 is connected between the negative terminal of the low-voltage side DC power supply 1 and the midpoint of the second flying capacitor circuit.

The first reactor L1 and the second reactor L2 may be configured as a magnetically coupled reactor with a common core. In this case, when current is applied, the magnetic fluxes of the first reactor L1 and the second reactor L2 can be mutually strengthened. Note that the configuration may be such that only one of the first reactor L1 and the second reactor L2 is connected.

The first flying capacitor circuit on the upper side includes a first switching element S1, a second switching element S2, a third switching element S3, a fourth switching element S4, and a first flying capacitor C1. The second flying capacitor circuit on the lower side includes a fifth switching element S5, a sixth switching element S6, a seventh switching element S7, an eighth switching element S8, and a second flying capacitor C2. The first switching element S1 to the eighth switching element S8 are connected in series between the positive DC bus and the negative DC bus.

The first flying capacitor C1 is connected between the connection point between the first switching element S1 and the second switching element S2 and the connection point between the third switching element S3 and the fourth switching element S4, and is charged and discharged by the first switching element S1 and the fourth switching element S4. The second flying capacitor C2 is connected between the connection point between the fifth switching element S5 and the sixth switching element S6 and the connection point between the seventh switching element S7 and the eighth switching element S8, and is charged and discharged by the fifth switching element S5 and the eighth switching element S8.

The first resistor R1 to the eighth resistor R8 are connected in parallel with the first switching element S1 to the eighth switching element S8, respectively. Therefore, the voltage between the first flying capacitor circuit and the second flying capacitor circuit (the voltage between the fourth switching element S4 and the fifth switching element S5) is maintained at a voltage divided by the first resistor R1 to the eighth resistor R8 to 1/2 of the voltage E of the high-voltage side DC power supply 2.

At the midpoint of the first flying capacitor circuit, a potential is generated in the range between the voltage E [V] of the high-voltage DC power supply 2 applied to the upper terminal of the first switching element S1 and 1/2E [V] applied to the lower terminal of the fourth switching element S4. The first flying capacitor C1 is initially charged (precharged) to a voltage of 1/4E [V] by the first resistor R1 to the eighth resistor R8, and charging and discharging are repeated with the voltage at 1/4E [V] as the center. Therefore, three levels of potential, roughly E [V], 3/4E [V], and 1/2E [V], are generated at the midpoint of the first flying capacitor circuit.

At the midpoint of the second flying capacitor circuit, a potential is generated in the range between 1/2E [V] applied to the upper terminal of the fifth switching element S5 and 0 [V] applied to the lower terminal of the eighth switching element S8. The second flying capacitor C2 is initially charged (precharged) to a voltage of 1/4E [V] by the first resistor R1-eighth resistor R8, and charging and discharging are repeated with the voltage of 1/4E [V] at the center. Therefore, three levels of potential, roughly 1/2E [V], 1/4E [V], and 0 [V], are generated at the midpoint of the second flying capacitor circuit.

The first to eighth switching elements S1 to S8 are respectively formed/connected in anti-parallel with the first to eighth diodes D1 to D8. The first to eighth switching elements S1 to S8 use switching elements with a lower withstand voltage than the voltages of the low-voltage side DC power supply 1 and the high-voltage side DC power supply 2. In the following embodiment, an example is assumed in which the first to eighth switching elements S1 to S8 use N-channel MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) with a withstand voltage of 150V. In the N-channel MOSFET, a parasitic diode is formed from the source to the drain.

Note that IGBTs (Insulated Gate Bipolar Transistors) or bipolar transistors may be used for the first switching element S1 to the eighth switching element S8. In that case, no parasitic diodes are formed in the first switching element S1 to the eighth switching element S8, and external diodes are connected in inverse parallel to the first switching element S1 to the eighth switching element S8, respectively. Note that wide band gap semiconductors using silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga2O3), diamond (C), etc. may be used, in addition to general silicon (Si) semiconductors.

The voltage sensor 41 detects the voltage across the high-voltage side capacitor C4 and outputs the detected voltage value to the control unit 40. Although not shown in FIG. 1, a voltage sensor that detects the voltage across the low-voltage side capacitor C3, a voltage sensor that detects the voltage of the first flying capacitor C1, a voltage sensor that detects the voltage of the second flying capacitor C2, and a current sensor that detects the current flowing through the first reactor L1 are provided, and the measured values of each are output to the control unit 40. It is also possible to detect the current flowing through the second reactor L2 instead of the current flowing through the first reactor L1.

The control unit 40 controls the first flying capacitor circuit and the second flying capacitor circuit to transmit DC power from the low-voltage side DC power supply 1 to the high-voltage side DC power supply 2 by step-up operation. It can also transmit DC power from the high-voltage side DC power supply 2 to the low-voltage side DC power supply 1 by step-down operation. More specifically, the control unit 40 supplies a drive signal (PWM (Pulse Width Modulation) signal) to the gate terminals of the first switching element S1 to the eighth switching element S8 to control the on/off of the first switching element S1 to the eighth switching element S8, thereby transmitting power in both directions by step-up operation or step-down operation.

The configuration of the control unit 40 can be realized by a combination of hardware and software resources, or by hardware resources alone. Analog elements, microcomputers, DSPs, ROMs, RAMs, FPGAs, ASICs, and other LSIs can be used as hardware resources. Programs such as firmware can be used as software resources.

Figure 2 is a diagram summarizing the switching patterns of the first switching element S1 to the eighth switching element S8 of the DC/DC conversion device 3 shown in Figure 1. In the switching patterns shown in Figure 2, the pair of the first switching element S1 and the eighth switching element S8 is complementary to the pair of the fourth switching element S4 and the fifth switching element S5. Also, the pair of the second switching element S2 and the seventh switching element S7 is complementary to the pair of the third switching element S3 and the sixth switching element S6.

The control unit 40 executes the voltage step-up operation or the voltage step-down operation using four modes.
In mode a, the control unit 40 controls the second switching element S2, the fourth switching element S4, the fifth switching element S5, and the seventh switching element S7 to be in the on state, and the first switching element S1, the third switching element S3, the sixth switching element S6, and the eighth switching element S8 to be in the off state. In mode a, the voltage between the midpoint of the first flying capacitor circuit and the midpoint of the second flying capacitor circuit (i.e., the input/output voltage _VL of the low-voltage side of the flying capacitor unit 30) is 1/2E.

In mode b, the control unit 40 controls the first switching element S1, the third switching element S3, the sixth switching element S6, and the eighth switching element S8 to be in the ON state, and the second switching element S2, the fourth switching element S4, the fifth switching element S5, and the seventh switching element S7 to be in the OFF state. In mode b, the input/output voltage _VL on the low voltage side of the flying capacitor unit 30 becomes 1/2E.

In mode c, the control unit 40 controls the first switching element S1, the second switching element S2, the seventh switching element S7, and the eighth switching element S8 to be in the ON state, and the third switching element S3, the fourth switching element S4, the fifth switching element S5, and the sixth switching element S6 to be in the OFF state. In mode c, the input/output voltage _VL on the low voltage side of the flying capacitor unit 30 becomes E.

In mode d, the control unit 40 controls the third switching element S3, the fourth switching element S4, the fifth switching element S5, and the sixth switching element S6 to be in the ON state, and the first switching element S1, the second switching element S2, the seventh switching element S7, and the eighth switching element S8 to be in the OFF state. In mode d, the input/output voltage _VL on the low-voltage side of the flying capacitor unit 30 becomes 0.

Figures 3(a)-(d) are circuit diagrams showing the current paths of each switching pattern during boost operation. Figures 4(a)-(d) are circuit diagrams showing the current paths of each switching pattern during buck operation. Note that to simplify the drawings, MOSFETs are depicted with simple switch symbols.

Figure 3(a) shows the current path in mode a during boost operation, Figure 3(b) shows the current path in mode b during boost operation, Figure 3(c) shows the current path in mode c during boost operation, and Figure 3(d) shows the current path in mode d during boost operation. Similarly, Figure 4(a) shows the current path in mode a during buck operation, Figure 4(b) shows the current path in mode b during buck operation, Figure 4(c) shows the current path in mode c during buck operation, and Figure 4(d) shows the current path in mode d during buck operation.

The direction of the current is opposite during boost operation and step-down operation. In mode a, the first flying capacitor C1 and the second flying capacitor C2 are charging during boost operation as shown in FIG. 3(a), but the first flying capacitor C1 and the second flying capacitor C2 are discharging during step-down operation as shown in FIG. 4(a). In mode b, the first flying capacitor C1 and the second flying capacitor C2 are discharging during boost operation as shown in FIG. 3(b), but the first flying capacitor C1 and the second flying capacitor C2 are charging during step-down operation as shown in FIG. 4(b).

When power is transmitted from the low-voltage side DC power supply 1 to the high-voltage side DC power supply 2 by step-up operation, the control unit 40 sets a positive current command value and controls the duty ratio (on time) of the first switching element S1 to the eighth switching element S8 so that the measured value of the current flowing through the first reactor L1 or the second reactor L2 maintains the positive current command value. Conversely, when power is transmitted from the high-voltage side DC power supply 2 to the low-voltage side DC power supply 1 by step-down operation, the control unit 40 sets a negative current command value and controls the duty ratio (on time) of the first switching element S1 to the eighth switching element S8 so that the measured value of the current flowing through the first reactor L1 or the second reactor L2 maintains the negative current command value.

When the ratio between the voltage of the low-voltage side DC power supply 1 and the voltage of the high-voltage side DC power supply 2 is smaller than a set value, the control unit 40 transmits power using modes a, b, and c. When the ratio is larger than the set value, the control unit 40 transmits power using modes a, b, and d. When the ratio matches the set value, the control unit 40 transmits power using modes a and b.

The above set value is set according to the ratio of the total voltage 1/2E of the voltages of the first flying capacitor C1 and the second flying capacitor C2 to the voltage E of the high-voltage side DC power supply 2. In this embodiment, the above set value is set to 2.

The control unit 40 generates a duty ratio so that the current command value matches the measured value of the current flowing through the first reactor L1 or the second reactor L2, and the voltage of the first flying capacitor C1 and the second flying capacitor C2 is 1/4E, respectively. Specifically, the control unit 40 increases the duty ratio as the measured value of the current flowing through the first reactor L1 or the second reactor L2 is smaller than the current command value, and decreases the duty ratio as the measured value is larger.

Figure 5 is a timing chart showing an example of the switching pattern of the first switching element S1 to the eighth switching element S8 when the step-up ratio is 2 or more. Figure 6 is a timing chart showing an example of the switching pattern of the first switching element S1 to the eighth switching element S8 when the step-up ratio is less than 2. The control examples shown in Figures 5 and 6 show control examples using a double carrier drive method. In the double carrier drive method, two carrier signals (triangular waves in Figures 5 and 6) that are 180 degrees out of phase with each other are used. The duty ratio duty is a threshold value that is compared with the two carrier signals. When the step-up ratio is 2 or more, the duty ratio duty takes a value in the range of 0.5 to 1.0, and when the step-up ratio is less than 2, the duty ratio duty takes a value in the range of 0.0 to 0.5.

The first gate signal to be supplied to the first switching element S1 and the eighth switching element S8, and the fourth gate signal to be supplied to the fourth switching element S4 and the fifth switching element S5 are generated based on the result of comparing the thick carrier signal with the duty ratio (duty). Specifically, in the region where the thick carrier signal is higher than the duty ratio (duty), the first gate signal is on and the fourth gate signal is off. In the region where the thick carrier signal is lower than the duty ratio (duty), the first gate signal is off and the fourth gate signal is on. The first gate signal and the fourth gate signal are complementary. Note that when the first gate signal and the fourth gate signal switch on/off, a dead time period is set during which the first gate signal and the fourth gate signal are simultaneously off.

Based on the comparison result between the carrier signal of the thin line and the duty ratio (duty), a second gate signal to be supplied to the second switching element S2 and the seventh switching element S7, and a third gate signal to be supplied to the third switching element S3 and the sixth switching element S6 are generated. Specifically, in an area where the carrier signal of the thin line is higher than the duty ratio (duty), the second gate signal is on and the third gate signal is off. In an area where the carrier signal of the thin line is lower than the duty ratio (duty), the second gate signal is off and the third gate signal is on. The second gate signal and the third gate signal are complementary. Note that when the second gate signal and the third gate signal are switched on/off, a dead time period is set during which the second gate signal and the third gate signal are simultaneously off.

When the boost ratio is 2x or more, the control unit 40 alternates between modes a and b, inserting mode d between the two. That is, the control unit 40 switches between modes in the following order: mode a → mode d → mode b → mode d → mode a → mode d → mode b → mode d... While the duty ratio (duty) does not change, the periods of mode a and mode b are equal, and the voltages of the first flying capacitor C1 and the second flying capacitor C2 are each maintained at 1/4E. When the boost ratio is 2x or more, the higher the duty ratio (duty), the longer the period of mode d relative to the periods of mode a and mode b, and the amount of energy transmitted increases.

When the boost ratio is less than 2, the control unit 40 alternates between modes a and b, inserting mode c between the two. That is, the control unit 40 switches between modes in the following order: mode a → mode c → mode b → mode c → mode a → mode c → mode b → mode c.... While the duty ratio (duty) does not change, the periods of mode a and mode b are equal, and the voltages of the first flying capacitor C1 and the second flying capacitor C2 are each maintained at 1/4E. When the boost ratio is less than 2, the higher the duty ratio (duty), the shorter the period of mode c relative to the periods of mode a and mode b, and the amount of energy transmitted increases.

If the boost ratio is ideally maintained at 2x and the voltages of the first flying capacitor C1 and the second flying capacitor C2 are ideally maintained at 1/4E, respectively, the duty ratio duty will be maintained at 0.5.

When the total voltage of the voltage of the first flying capacitor C1 and the voltage of the second flying capacitor C2 falls below 1/2E, the control unit 40 increases the time of the charging mode of mode a or mode b to bring the total voltage closer to 1/2E. Conversely, when the total voltage of the voltage of the first flying capacitor C1 and the voltage of the second flying capacitor C2 exceeds 1/2E, the control unit 40 increases the time of the discharging mode of mode a or mode b to bring the total voltage closer to 1/2E.

The control unit 40 can also operate the DC/DC conversion device 3 as a normal boost chopper by alternately switching between mode c and mode d without using the first flying capacitor C1 and the second flying capacitor C2. In this case, the operating mode is not switched based on the boost ratio.

In the circuit configuration shown in FIG. 1, when the first flying capacitor C1 and the second flying capacitor C2 are precharged from the high-voltage DC power supply 2, the voltage E of the high-voltage DC power supply 2 is applied to both the first switching element S1 and the eighth switching element S8, and the first switching element S1 and the eighth switching element S8 may exceed their withstand voltage. When the low-voltage side capacitor C3 is not charged (when the voltage across the low-voltage side capacitor C3 is 0V), the voltage across the third switching element S3-sixth switching element S6, which are connected in series and are connected in parallel to the low-voltage side capacitor C3, also becomes 0V.

When the first flying capacitor C1 is not charged (the voltage across the first flying capacitor C1 is 0V), the voltages across the second switching element S2 and the third switching element S3, which are connected in series and are connected in parallel to the first flying capacitor C1, are also 0V. Similarly, when the second flying capacitor C2 is not charged (the voltage across the second flying capacitor C2 is 0V), the voltages across the sixth switching element S6 and the seventh switching element S7, which are connected in series and are connected in parallel to the second flying capacitor C2, are also 0V.

As a result, the voltage across the series-connected second switching element S2 and seventh switching element S7 becomes 0V, and the voltage E of the high-voltage side DC power supply 2 is applied to both the first switching element S1 and the eighth switching element S8. As described above, in this embodiment, MOSFETs with a withstand voltage of 150V are used for the first switching element S1 and the eighth switching element S8. Therefore, when the voltage E of the high-voltage side DC power supply 2 exceeds 300V, the first switching element S1 and the eighth switching element S8 exceed their withstand voltage.

The following describes a DC/DC conversion device 3 that has the function of safely precharging the first flying capacitor C1 and the second flying capacitor C2 while preventing the first switching element S1 and the eighth switching element S8 from exceeding their withstand voltages.

Figure 7 is a diagram for explaining the configuration of a DC/DC converter 3 with a soft precharge function according to an embodiment. The DC/DC converter 3 shown in Figure 7 has a configuration in which a switch circuit 50 is added to the DC/DC converter 3 shown in Figure 1. The switch circuit 50 is inserted in the path between the high-voltage side capacitor C4 and the high-voltage side DC power supply 2, and can electrically cut off the connection between the high-voltage side capacitor C4 and the high-voltage side DC power supply 2.

In the example shown in FIG. 7, the switch circuit 50 is inserted in the positive DC bus, but it may be inserted in the negative DC bus or in both. In the example shown in FIG. 7, a ninth switching element S9 is used as the switch circuit 50. More specifically, an N-channel MOSFET with a source terminal connected to the high-voltage side capacitor C4 and a drain terminal connected to the high-voltage side DC power source 2 is used as the ninth switching element S9.

Figure 8 is a diagram for explaining the operation of the DC/DC conversion device 3 shown in Figure 7 at startup. At startup of the DC/DC conversion device 3, the control unit 40 precharges the first flying capacitor C1 and the second flying capacitor C2 in three phases.

(1) In the first phase, the control unit 40 controls the switch circuit 50 to the off state and controls the first switching element S1 to the eighth switching element S8 so that the low-voltage side capacitor C3, the high-voltage side capacitor C4, the first flying capacitor C1, and the second flying capacitor C2 are charged from the low-voltage side DC power supply 1.

Specifically, the control unit 40 controls at least the third switching element S3 to the sixth switching element S6 to the off state. The control unit 40 may control the first switching element S1, the second switching element S2, the seventh switching element S7, and the eighth switching element S8 to the on state or to the off state. When controlling them to the on state, the high-voltage side capacitor C4 is charged from the low-voltage side DC power supply 1 via the first switching element S1, the second switching element S2, the seventh switching element S7, and the eighth switching element S8. When controlling them to the off state, the high-voltage side capacitor C4 is charged from the low-voltage side DC power supply 1 via the first diode D1, the second diode D2, the third diode D3, and the fourth diode D4.

The voltages of the low-voltage side capacitor C3 and the high-voltage side capacitor C4 rise to the voltage of the low-voltage side DC power supply 1. Because the first resistor R1 and the eighth resistor R8 are connected in series in parallel with the high-voltage side capacitor C4, the voltages of the first flying capacitor C1 and the second flying capacitor C2 each rise to 1/4 of the voltage of the high-voltage side capacitor C4 (= the voltage of the low-voltage side DC power supply 1).

When the voltage of the high-voltage side capacitor C4 rises to a voltage corresponding to the voltage of the low-voltage side DC power supply 1, the second phase can be entered. Note that the sequence may be such that the second phase is entered after a set time from startup.

(2) In the second phase, the control unit 40 controls the first switching element S1 to the eighth switching element S8 so that the voltage of the high-voltage side capacitor C4 is boosted. For example, the control unit 40 gradually boosts the voltage of the high-voltage side capacitor C4 according to the switching pattern of the first switching element S1 to the eighth switching element S8 when the boost ratio is less than 2 times as shown in FIG. 6.

When the voltage of the high-voltage side capacitor C4 rises to a voltage corresponding to the voltage E of the high-voltage side DC power supply 2, the third phase can be entered. The condition for entering the third phase does not necessarily require that the voltage of the high-voltage side capacitor C4 and the voltage E of the high-voltage side DC power supply 2 are the same, but it is sufficient that the voltage of the high-voltage side capacitor C4 and the voltage E of the high-voltage side DC power supply 2 are approximately within a predetermined range. In the circuit configuration shown in FIG. 7, when the voltage of the high-voltage side capacitor C4 becomes higher than the voltage E of the high-voltage side DC power supply 2 due to the ninth diode D9 of the ninth switching element S9 constituting the switch circuit 50, a current flows from the high-voltage side capacitor C4 side to the high-voltage side DC power supply 2 side, and the voltage of the high-voltage side capacitor C4 is clamped to the voltage E of the high-voltage side DC power supply 2.

When the voltage of the high-voltage side capacitor C4 rises to the voltage E of the high-voltage side DC power supply 2, the voltages of the first flying capacitor C1 and the second flying capacitor C2 each rise to 1/4 of the voltage E of the high-voltage side DC power supply 2.

(3) In the third phase, the control unit 40 turns on the switch circuit 50. This establishes electrical continuity between the flying capacitor unit 30 and the high-voltage side DC power supply 2. At the stage of electrical continuity, the first flying capacitor C1 and the second flying capacitor C2 are already precharged to 1/4E, so the first switching element S1 and the eighth switching element S8 do not exceed their withstand voltages.

Figures 9(a)-(f) are diagrams showing examples of the configuration of the switch circuit 50. In the circuit configuration shown in Figure 7, an N-channel MOSFET (ninth switching element S9) with a source terminal connected to the high-voltage side capacitor C4 and a drain terminal connected to the high-voltage side DC power supply 2 is used as the switch circuit 50. As described above, in this configuration example, the voltage of the high-voltage side capacitor C4 can be clamped so that it does not become higher than the voltage E of the high-voltage side DC power supply 2.

Figure 9 (a) shows an example in which the switch circuit 50 is configured as a bidirectional switch. The bidirectional switch is configured by connecting two N-channel MOSFETs (switching elements S9a, S9b) in series in the opposite directions. The source terminal of one N-channel MOSFET (switching element S9a) is connected to the high-voltage side capacitor C4, and the source terminal of the other N-channel MOSFET (switching element S9b) is connected to the high-voltage side DC power supply 2.

The drain terminals of the two N-channel MOSFETs (switching elements S9a, S9b) are connected to each other. In this configuration example, the cathode of the parasitic diode D9a of one N-channel MOSFET (switching element S9a) faces the cathode of the parasitic diode D9b of the other N-channel MOSFET (switching element S9b). Therefore, when the bidirectional switch is in the off state, it is possible to prevent current from flowing from the high-voltage side capacitor C4 to the high-voltage side DC power supply 2 via the parasitic diode, and from flowing from the high-voltage side DC power supply 2 to the high-voltage side capacitor C4.

Figure 9 (b) shows an example in which the switch circuit 50 is configured with a relay RY1. When relay RY1 is used, a parasitic diode is not formed. Therefore, when relay RY1 is in the off state, it is possible to block current from either direction.

When the high-voltage side DC power supply 2 is connected to a system power supply via an inverter (not shown), the high-voltage side DC power supply 2 is affected by ripple noise. When the voltage E of the high-voltage side DC power supply 2 fluctuates due to the influence of this ripple noise, the magnitude relationship between the voltage of the high-voltage side capacitor C4 and the voltage of the high-voltage side DC power supply 2 fluctuates, and there is a possibility that input and output of current will occur between the high-voltage side capacitor C4 and the high-voltage side DC power supply 2. By using the bidirectional switch shown in FIG. 9(a) or the relay RY1 shown in FIG. 9(b), it is possible to prevent input and output of this current.

Figure 9 (c) shows an example of a switch circuit 50 configured with a bidirectional switch, a tenth switching element S10, and a limiting resistor R9. The tenth switching element S10 and the limiting resistor R9 are connected in series. The tenth switching element S10 and the limiting resistor R9 connected in series are connected in parallel to the bidirectional switch described in Figure 9 (a). The tenth switching element S10 is an N-channel MOSFET whose source terminal is connected to the high-voltage side capacitor C4 and whose drain terminal is connected to the high-voltage side DC power source 2 via the limiting resistor R9.

The switch circuit 50 shown in FIG. 9(c) has an inrush current prevention function. That is, when the bidirectional switch is in the off state, current flows through the limiting resistor R9. When the control unit 40 connects the high-voltage side capacitor C4 and the high-voltage side DC power supply 2, it first turns on the tenth switching element S10, and after a predetermined time has elapsed, turns off the tenth switching element S10 and turns on the bidirectional switch. This makes it possible to prevent an inrush current from occurring when connecting the high-voltage side capacitor C4 and the high-voltage side DC power supply 2, even if a large difference in voltage between the two occurs.

Even if it becomes necessary to charge the high-voltage side capacitor C4, the first flying capacitor C1, and the second flying capacitor C2 from the high-voltage side DC power supply 2, if the switch circuit 50 has an inrush current prevention function, it is possible to prevent inrush current from flowing from the high-voltage side DC power supply 2 to the high-voltage side capacitor C4, the first flying capacitor C1, and the second flying capacitor C2.

In the configuration example shown in FIG. 9(c), similarly to the switch circuit 50 shown in FIG. 7, when the bidirectional switch is in the off state, the voltage of the high-voltage side capacitor C4 is clamped so that the voltage of the high-voltage side capacitor C4 does not become higher than the voltage E of the high-voltage side DC power supply 2.

The configuration shown in FIG. 9(d) is a configuration in which the bidirectional switch included in the configuration shown in FIG. 9(c) is replaced with a relay RY1. The configuration shown in FIG. 9(d) has the same effect as the configuration shown in FIG. 9(c).

9(e) is an example in which the switch circuit 50 is configured with a bidirectional switch, a tenth switching element S10, a limiting resistor R9, and an eleventh diode D11. The tenth switching element S10, the limiting resistor R9, and the eleventh diode D11 are connected in series. The tenth switching element S10, the limiting resistor R9, and the eleventh diode D11 connected in series are connected in parallel to the bidirectional switch described in FIG. 9(a). The tenth switching element S10 is an N-channel MOSFET whose source terminal is connected to the high-voltage side DC power supply 2 via the limiting resistor R9 and the eleventh diode D11, and whose drain terminal is connected to the low-voltage side capacitor C3. The eleventh diode D11 has an anode terminal connected to the limiting resistor R9, and a cathode terminal connected to the high-voltage side DC power supply 2.

The switch circuit 50 shown in FIG. 9(e) has an inrush current prevention function, and can prevent the occurrence of inrush current when conducting between the high-voltage side capacitor C4 and the high-voltage side DC power supply 2. In addition, when the bidirectional switch is in the off state, it can prevent input and output of current between the high-voltage side capacitor C4 and the high-voltage side DC power supply 2 due to fluctuations in the voltage E of the high-voltage side DC power supply 2.

The configuration shown in FIG. 9(f) is a configuration in which the bidirectional switch included in the configuration shown in FIG. 9(e) is replaced with a relay RY1. The configuration shown in FIG. 9(f) has the same effect as the configuration shown in FIG. 9(e).

Figure 10 is a diagram for explaining another configuration of a DC/DC converter 3 with a soft precharge function according to an embodiment. The DC/DC converter 3 shown in Figure 10 has a configuration in which another switch circuit 50a having an inrush current prevention function is added to the DC/DC converter 3 shown in Figure 7. The switch circuit 50a is inserted in the path between the low-voltage side DC power supply 1 and the low-voltage side capacitor C3, and can electrically cut off the connection between the low-voltage side DC power supply 1 and the low-voltage side capacitor C3.

In the example shown in FIG. 10, the switch circuit 50 shown in FIG. 9(f) is used as the switch circuit 50a. The switch circuit 50 shown in FIG. 9(e) may also be used. When starting up the DC/DC conversion device 3, the control unit 40 first turns on the tenth switching element S10, turns off the tenth switching element S10 after a predetermined time has elapsed, and turns on the relay RY1. This makes it possible to prevent inrush current from flowing from the low-voltage side DC power supply 1 to the low-voltage side capacitor C3, the high-voltage side capacitor C4, the first flying capacitor C1, and the second flying capacitor C2.

As described above, according to this embodiment, the DC/DC conversion device 3 is disconnected from the high-voltage side DC power supply 2, and the low-voltage side capacitor C3, the high-voltage side capacitor C4, the first flying capacitor C1, and the second flying capacitor C2 are charged from the low-voltage side DC power supply 1. After that, the voltages of the high-voltage side capacitor C4, the first flying capacitor C1, and the second flying capacitor C2 are gradually increased, so that the high-voltage side capacitor C4, the first flying capacitor C1, and the second flying capacitor C2 can be safely precharged. In other words, it is possible to prevent the first switching element S1 and the eighth switching element S8 from exceeding their withstand voltage due to the voltage of the high-voltage side DC power supply 2. In addition, it is possible to suppress the flow of inrush current during precharging.

The present disclosure has been described above based on the embodiments. The embodiments are merely examples, and it will be understood by those skilled in the art that various modifications are possible in the combination of each component and each processing process, and that such modifications are also within the scope of the present disclosure.

In the above-described embodiment, the flying capacitor section 30 is configured to have two three-level output flying capacitor circuits connected in series. In this regard, the flying capacitor section 30 is not limited to the configuration of the above-described embodiment, as long as it includes a plurality of switching elements connected in series and at least one flying capacitor, the high-voltage side DC power supply 2 is connected to both ends of the plurality of switching elements, and the low-voltage side DC power supply 1 is connected to both ends of a portion of the plurality of switching elements that make up the plurality of switching elements.

Figure 11 is a diagram for explaining the configuration of a DC/DC conversion device 3 with a soft precharge function according to a modified example. In this modified example, the flying capacitor section 30 has one flying capacitor circuit with a three-level output. The high-voltage side DC power supply 2 is connected to both ends of the first switching element S1 to the fourth switching element S4 that are connected in series.

The positive terminal of the low-voltage DC power supply 1 is connected to the connection point between the second switching element S2 and the third switching element S3 via the first reactor L1. The negative terminal of the low-voltage DC power supply 1 is connected to the lower terminal of the fourth switching element S4 via the second reactor L2.

In the circuit configuration shown in FIG. 11, when the first flying capacitor C1 is precharged from the high-voltage DC power supply 2, the voltage E of the high-voltage DC power supply 2 is applied to the first switching element S1, and the first switching element S1 may exceed its withstand voltage. When the low-voltage side capacitor C3 is not charged (when the voltage across the low-voltage side capacitor C3 is 0V), the voltage across the third switching element S3-fourth switching element S4, which are connected in series and are connected in parallel to the low-voltage side capacitor C3, is also 0V. When the first flying capacitor C1 is not charged (when the voltage across the first flying capacitor C1 is 0V), the voltage across the second switching element S2-third switching element S3, which are connected in series and are connected in parallel to the first flying capacitor C1, is also 0V.

As a result, the voltage across the series-connected second switching element S2 and fourth switching element S4 becomes 0V, and a state occurs in which the voltage E of the high-voltage DC power supply 2 is applied to one of the first switching elements S1. In response to this, if the first flying capacitor C1 is precharged using the soft precharge function described above, it is possible to prevent the first switching element S1 from exceeding its withstand voltage.

In the above embodiment, a one-stage flying capacitor circuit using four switching elements connected in series and one flying capacitor is given as an example of the configuration of each flying capacitor circuit constituting the flying capacitor section 30. In this regard, a flying capacitor circuit with more stages can also be used.

Figures 12(a)-(c) are diagrams showing configuration examples of flying capacitor circuits. Figure 12(a) shows a one-stage flying capacitor circuit. The flying capacitor circuit shown in Figure 12(a) has the same circuit configuration as that described in the above embodiment.

Figure 12(b) shows a two-stage flying capacitor circuit. The two-stage flying capacitor circuit includes six switching elements S12, S1, S2, S3, S4, and S42 connected in series, and two flying capacitors C11 and C12. The innermost flying capacitor C11 is connected in parallel to the two switching elements S2 and S3, and is controlled to maintain a voltage of 1/6E. The second innermost flying capacitor C12 is connected in parallel to the four switching elements S1, S2, S3, and S4, and is controlled to maintain a voltage of 1/6E.

Figure 12(c) shows a three-stage flying capacitor circuit. The three-stage flying capacitor circuit includes six switching elements S13, S12, S1, S2, S3, S4, S42, and S43 connected in series, and three flying capacitors C11, C12, and C13. The innermost flying capacitor C11 is connected in parallel to the two switching elements S2 and S3, and is controlled to maintain a voltage of 1/8E. The second innermost flying capacitor C12 is connected in parallel to the four switching elements S1, S2, S3, and S4, and is controlled to maintain a voltage of 2/8E. The third innermost flying capacitor C13 is connected in parallel to the six switching elements S12, S1, S2, S3, S4, and S42, and is controlled to maintain a voltage of 3/8E.

Figure 13 shows an N-stage (N is a natural number) flying capacitor circuit. The N-stage flying capacitor circuit includes (2N+2) switching elements S1n, ..., S13, S12, S1, S2, S3, S4, S42, S43, ..., S4n connected in series, and N flying capacitors C11, C12, C13, ..., C1n. The innermost flying capacitor C11 is connected in parallel to the two switching elements S2 and S3, and is controlled to maintain a voltage of 1/(2N+2)E. The second innermost flying capacitor C12 is connected in parallel to the four switching elements S1, S2, S3, and S4, and is controlled to maintain a voltage of 2/(2N+2)E. The third innermost flying capacitor C13 is connected in parallel to the six switching elements S12, S1, S2, S3, S4, and S42, and is controlled to maintain a voltage of 3/(2N+2)E. The outermost flying capacitor C1n is connected in parallel to 2N switching elements S1(n-1), ..., S13, S12, S1, S2, S3, S4, S42, S43, ..., S4(n-1), and is controlled to maintain a voltage of N/(2N+2)E.

In the first and second flying capacitor circuits shown in FIG. 7 and FIG. 10, the one-stage flying capacitor circuit shown in FIG. 12(a) is used. When the one-stage flying capacitor circuit is used, it is possible to generate a voltage of three levels (E, 1/2E, 0) between the midpoint of the first flying capacitor circuit and the midpoint of the second flying capacitor circuit. When the two-stage flying capacitor circuit shown in FIG. 12(b) is used, it is possible to generate a voltage of five levels (E, 2/3E, 1/2E, 1/3E, 0) between the midpoint of the first flying capacitor circuit and the midpoint of the second flying capacitor circuit. When the three-stage flying capacitor circuit shown in FIG. 12(c) is used, it is possible to generate a voltage of seven levels (E, 3/4E, 5/8E, 1/2E, 3/8E, 1/4E, 0) between the midpoint of the first flying capacitor circuit and the midpoint of the second flying capacitor circuit. By using the N-stage flying capacitor circuit shown in FIG. 13, it is possible to generate (2N+1) levels of voltage between the midpoint of the first flying capacitor circuit and the midpoint of the second flying capacitor circuit.

Increasing the number of stages in a flying capacitor circuit allows the use of cheaper switching elements with lower voltage resistance, but it also increases the number of switching elements used. Therefore, designers need only determine the optimal number of stages in the flying capacitor circuit, taking into account the total cost and total conversion efficiency. Also, in applications where the voltage of the high-voltage side DC section exceeds 1000V or exceeds 10,000V, it is effective to increase the number of stages in the flying capacitor circuit in order to reduce the voltage resistance of each switching element.

Regardless of the number of stages in the flying capacitor circuit, the switching elements at both ends of the flying capacitor section 30 can be prevented from exceeding their withstand voltage by precharging the flying capacitor with the soft precharge function described above.

The embodiment may be specified by the following:

[Item 1]
A low-voltage side capacitor (C3) connected in parallel to the low-voltage side DC power supply (1);
A high-voltage side capacitor (C4) connected in parallel to the high-voltage side DC power supply (2);
a flying capacitor section (30) including a plurality of switching elements (S1-S8) connected in series and at least one flying capacitor (C1-C2), the high-voltage side DC power supply (2) being connected across both ends of the plurality of switching elements (S1-S8) connected in series, and the low-voltage side DC power supply (1) being connected across both ends of a portion of a plurality of switching elements (S3-S6) constituting the plurality of switching elements (S1-S8) connected in series;
At least one reactor (L1-L2) inserted in a path between both ends of the low-voltage side capacitor (C3) and both ends of the part of the plurality of switching elements (S3-S6);
a switch circuit (50) inserted in a path between the high-voltage side capacitor (C4) and the high-voltage side DC power supply (2);
Equipped with
DC/DC converter (3).
This makes it possible to safely precharge the flying capacitors (C1-C2) from the low-voltage side DC power supply (1) rather than from the high-voltage side DC power supply (2).
[Item 2]
a plurality of resistors (R1-R8) connected in parallel with the plurality of switching elements (S1-S8) connected in series;
a control unit (40) that controls the plurality of switching elements (S1-S8) connected in series and the switch circuit (50);
Further equipped with
The control unit (40) performs, at the start-up of the DC/DC conversion device (3),
The switch circuit (50) is controlled to an off state, and the plurality of switching elements (S1-S8) connected in series are controlled so that the low-voltage side capacitor (C3), the high-voltage side capacitor (C4), and the at least one flying capacitor (C1-C2) are charged from the low-voltage side DC power supply (1);
After the voltage of the high-voltage side capacitor (C4) rises to a voltage corresponding to the voltage of the low-voltage side DC power supply (1), the plurality of switching elements (S1-S8) connected in series are controlled so that the voltage of the high-voltage side capacitor (C4) is boosted;
After the voltage of the high-voltage side capacitor (C4) rises to a voltage corresponding to the voltage of the high-voltage side DC power supply (2), the switch circuit (50) is controlled to be in an on state.
Item 2. A DC/DC conversion device (3) according to item 1.
This allows the voltage of the flying capacitors (C1-C2) to be gradually increased in accordance with the increase in voltage of the high-voltage side capacitor (C4), and allows the flying capacitors (C1-C2) to be safely precharged.
[Item 3]
The flying capacitor section (30) comprises:
a first switching element (S1), a second switching element (S2), a third switching element (S3), a fourth switching element (S4), a fifth switching element (S5), a sixth switching element (S6), a seventh switching element (S7), and an eighth switching element (S8) connected in series;
a first flying capacitor (C1) connected between a connection point between the first switching element (S1) and the second switching element (S2) and a connection point between the third switching element (S3) and the fourth switching element (S4);
a second flying capacitor (C2) connected between a connection point between the fifth switching element (S5) and the sixth switching element (S6) and a connection point between the seventh switching element (S7) and the eighth switching element (S8);
a positive terminal of the low-voltage side DC power supply (1) is electrically connected to a connection point between the second switching element (S2) and the third switching element (S3);
A negative terminal of the low-voltage side DC power supply (1) is electrically connected to a connection point between the sixth switching element (S6) and the seventh switching element (S7).
Item 2. A DC/DC conversion device (3) according to item 1.
This makes it possible to realize a three-level multilevel DC/DC converter (3). By connecting eight switching elements (S1-S8) in series in parallel with the high-voltage side DC power supply (2), it becomes possible to use switching elements with lower voltage resistance than before.
[Item 4]
a first resistor R1 to an eighth resistor R8 connected in parallel to the first switching element S1 to the eighth switching element S8, respectively;
The power supply circuit further includes a control unit (40) that controls the first switching element (S1) to the eighth switching element (S8) and the switch circuit (50),
The control unit (40) performs, at the start-up of the DC/DC conversion device (3),
The switch circuit (50), the third switching element (S3), the fourth switching element (S4), the fifth switching element (S5), and the sixth switching element (S6) are controlled to be in an off state,
After the voltage of the high-voltage side capacitor (C4) rises to a voltage corresponding to the voltage of the low-voltage side DC power source (1), the first switching element (S1) to the eighth switching element (S8) are controlled so that the voltage of the high-voltage side capacitor (C4) is boosted;
After the voltage of the high-voltage side capacitor (C4) rises to a voltage corresponding to the voltage of the high-voltage side DC power supply (2), the switch circuit (50) is controlled to be in an on state.
Item 3. A DC/DC conversion device (3) according to item 3.
This allows the voltages of the first flying capacitor (C1) and the second flying capacitor (C2) to be gradually increased in accordance with the increase in voltage of the high-voltage side capacitor (C4), and allows the first flying capacitor (C1) and the second flying capacitor (C2) to be safely pre-charged.
[Item 5]
The control unit (40)
a first mode in which the second switching element (S2), the fourth switching element (S4), the fifth switching element (S5), and the seventh switching element (S7) are controlled to an on state, and the first switching element (S1), the third switching element (S3), the sixth switching element (S6), and the eighth switching element (S8) are controlled to an off state;
a second mode in which the first switching element (S1), the third switching element (S3), the sixth switching element (S6), and the eighth switching element (S8) are controlled to an ON state and the second switching element (S2), the fourth switching element (S4), the fifth switching element (S5), and the seventh switching element (S7) are controlled to an OFF state;
a third mode in which the first switching element (S1), the second switching element (S2), the seventh switching element (S7), and the eighth switching element (S8) are controlled to an ON state, and the third switching element (S3), the fourth switching element (S4), the fifth switching element (S5), and the sixth switching element (S6) are controlled to an OFF state;
a fourth mode in which the third switching element (S3), the fourth switching element (S4), the fifth switching element (S5), and the sixth switching element (S6) are controlled to be in an on state, and the first switching element (S1), the second switching element (S2), the seventh switching element (S7), and the eighth switching element (S8) are controlled to be in an off state;
The voltage of the high-voltage side capacitor (C4) is boosted by using three modes, namely, the first mode, the second mode, the third mode, and the fourth mode.
5. A DC/DC conversion device (3) according to item 4.
This allows a highly efficient boost operation by combining three modes.
[Item 6]
The switch circuit (50)
A source terminal of the N-channel MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) (S9) is connected to the high-voltage side capacitor (C4) and a drain terminal of the N-channel MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) (S9) is connected to the high-voltage side DC power supply (2).
6. A DC/DC conversion device (3) according to any one of items 1 to 5.
According to this, the voltage of the high-voltage side capacitor (C4) can be clamped so that the voltage of the high-voltage side capacitor (C4) does not become higher than the voltage of the high-voltage side DC power supply (2). Also, the switch circuit (50) can be constructed at low cost.

1 Low-voltage side DC power supply, 2 High-voltage side DC power supply, 3 DC/DC conversion device, 30 Flying capacitor section, 40 Control section, 41 Voltage sensor, 50 Switch circuit, S1-S10 Switching elements, D1-D11 Diodes, C1 First flying capacitor, C2 Second flying capacitor, C3 Low-voltage side capacitor, C4 High-voltage side capacitor, L1 First reactor, L2 Second reactor, R1-R8 Resistor, R9 Limiting resistor, RY1 Relay.

Claims (4)

a low-voltage side capacitor connected in parallel to the low-voltage side DC power supply;
A high-voltage side capacitor connected in parallel to the high-voltage side DC power supply;
a flying capacitor unit including a plurality of switching elements connected in series and at least one flying capacitor, the high-voltage side DC power supply being connected to both ends of the plurality of switching elements connected in series, and the low-voltage side DC power supply being connected to both ends of a portion of the plurality of switching elements constituting the plurality of switching elements connected in series;
at least one reactor inserted in a path between both ends of the low-voltage side capacitor and both ends of the part of the plurality of switching elements;
a switch circuit inserted in a path between the high-voltage side capacitor and the high-voltage side DC power supply;
a plurality of resistors connected in parallel with the plurality of switching elements connected in series, respectively;
A control unit that controls the plurality of switching elements connected in series and the switch circuit;
Equipped with
When the DC/DC conversion device is started, the control unit
controlling the switch circuit to an off state and controlling the plurality of switching elements connected in series so that the low-voltage side capacitor, the high-voltage side capacitor, and the at least one flying capacitor are charged from the low-voltage side DC power supply;
After the voltage of the high-voltage side capacitor has increased to a voltage corresponding to the voltage of the low-voltage side DC power supply, the plurality of switching elements connected in series are controlled so that the voltage of the high-voltage side capacitor is further increased;
After the voltage of the high-voltage side capacitor has increased to a voltage corresponding to the voltage of the high-voltage side DC power supply, the switch circuit is controlled to an on state.
DC/DC conversion device. a low-voltage side capacitor connected in parallel to the low-voltage side DC power supply;
A high-voltage side capacitor connected in parallel to the high-voltage side DC power supply;
a flying capacitor unit including a plurality of switching elements connected in series and at least one flying capacitor, the high-voltage side DC power supply being connected to both ends of the plurality of switching elements connected in series, and the low-voltage side DC power supply being connected to both ends of a portion of the plurality of switching elements constituting the plurality of switching elements connected in series;
at least one reactor inserted in a path between both ends of the low-voltage side capacitor and both ends of the part of the plurality of switching elements;
a switch circuit inserted in a path between the high-voltage side capacitor and the high-voltage side DC power supply;
A DC/DC conversion device comprising :
The flying capacitor unit includes:
the plurality of switching elements connected in series, including a first switching element, a second switching element, a third switching element, a fourth switching element, a fifth switching element, a sixth switching element, a seventh switching element, and an eighth switching element;
a first flying capacitor, which is one of the at least one flying capacitor, connected between a connection point between the first switching element and the second switching element and a connection point between the third switching element and the fourth switching element;
a second flying capacitor, which is one of the at least one flying capacitor, connected between a connection point between the fifth switching element and the sixth switching element and a connection point between the seventh switching element and the eighth switching element;
The DC/DC conversion device includes:
a first resistor and an eighth resistor connected in parallel to the first switching element and the eighth switching element, respectively;
A control unit that controls the first switching element to the eighth switching element and the switch circuit,
a positive terminal of the low-voltage side DC power supply is electrically connected to a connection point between the second switching element and the third switching element,
a negative terminal of the low-voltage DC power supply is electrically connected to a connection point between the sixth switching element and the seventh switching element ,
When the DC/DC conversion device is started, the control unit
controlling the switch circuit, the third switching element, the fourth switching element, the fifth switching element, and the sixth switching element to an off state;
After the voltage of the high-voltage side capacitor has increased to a voltage corresponding to the voltage of the low-voltage side DC power supply, the first switching element-the eighth switching element are controlled so that the voltage of the high-voltage side capacitor is further increased;
After the voltage of the high-voltage side capacitor has increased to a voltage corresponding to the voltage of the high-voltage side DC power supply, the switch circuit is controlled to an on state.
DC/DC conversion device. The control unit is
a first mode in which the second switching element, the fourth switching element, the fifth switching element, and the seventh switching element are controlled to an on state, and the first switching element, the third switching element, the sixth switching element, and the eighth switching element are controlled to an off state;
a second mode in which the first switching element, the third switching element, the sixth switching element, and the eighth switching element are controlled to an on state, and the second switching element, the fourth switching element, the fifth switching element, and the seventh switching element are controlled to an off state;
a third mode in which the first switching element, the second switching element, the seventh switching element, and the eighth switching element are controlled to an on state, and the third switching element, the fourth switching element, the fifth switching element, and the sixth switching element are controlled to an off state;
a fourth mode in which the third switching element, the fourth switching element, the fifth switching element, and the sixth switching element are controlled to be in an on state, and the first switching element, the second switching element, the seventh switching element, and the eighth switching element are controlled to be in an off state;
further increasing the voltage of the high-voltage side capacitor by using three modes, namely, the first mode, the second mode, and the third mode or the fourth mode;
3. The DC/DC conversion device according to claim 2. The switch circuit includes:
A source terminal of the N-channel MOSFET is connected to the high-voltage side capacitor, and a drain terminal of the N-channel MOSFET is connected to the high-voltage side DC power supply.
The DC/DC conversion device according to claim 1 .

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