Power conversion device

Abstract

Provided is a power conversion device which is reduced in size. A power conversion device (1) comprises a DC-DC converter (2), a control device (3), and a second capacitor (C2). The DC-DC converter (2) has a positive electrode input terminal (21), a positive electrode output terminal (23), and a ground terminal (26). The DC-DC converter (2) has a first capacitor (C1) connected between the positive electrode output terminal (23) and the ground terminal (26). The control device (3) controls the DC-DC converter (2). The second capacitor (C2) is connected between the positive electrode input terminal (21) and positive electrode output terminal (23) of the DC-DC converter (2). Each of the first capacitor (C1) and the second capacitor (C2) is a capacitor having DC bias characteristics.

Description

Power Conversion Device

[0001] The present disclosure relates to a power conversion device, and more particularly to a power conversion device including a DC-DC converter.

[0002] Patent Document 1 discloses an inverter circuit and a DC-DC converter using a chopper circuit. The chopper circuit includes a power supply side half-bridge circuit, a load side half-bridge circuit, a reactor, and a control circuit. The inverter circuit and the DC-DC converter include a smoothing capacitor (first capacitor) connected between output terminals of the chopper circuit.

[0003] Japanese Patent Application Laid-Open No. 2005-295671

[0004] In a power conversion device including the DC-DC converter disclosed in Patent Document 1, the component size of the smoothing capacitor (first capacitor) connected between the output terminals is large, which may make it difficult to reduce the size of the power conversion device.

[0005] An object of the present disclosure is to provide a power conversion device that can be made smaller.

[0006] A power conversion device according to one aspect of the present disclosure includes a DC-DC converter, a control device, and a second capacitor. The DC-DC converter has a positive input terminal, a positive output terminal, and a ground terminal. The DC-DC converter has a first capacitor connected between the positive output terminal and the ground terminal. The control device controls the DC-DC converter. The second capacitor is connected between the positive input terminal and the positive output terminal of the DC-DC converter. Each of the first capacitor and the second capacitor has a DC bias characteristic.

[0007] The power conversion device of the present disclosure has the effect of enabling miniaturization.

[0008] FIG. 1 is a circuit diagram of a power conversion device according to the first embodiment. FIG. 2A is a circuit diagram of a first capacitor in the power conversion device according to the first embodiment. FIG. 2B is a circuit diagram of a second capacitor in the power conversion device according to the first embodiment. FIG. 3 is an operating waveform diagram of the power conversion device according to the first embodiment. FIG. 4 is a timing chart when the DC-DC converter in the power conversion device according to the first embodiment is operated in step-down mode. FIG. 5 is a timing chart when the DC-DC converter in the power conversion device according to the first embodiment is operated in step-up mode. FIG. 6 is a voltage characteristic diagram of the effective capacitance of the first capacitor in the power conversion device according to the first example and the power conversion device according to the first comparative example. FIG. 7A is a waveform diagram of the output voltage of the power conversion device according to the second example. FIG. 7B is a waveform diagram of the output voltage of the power conversion device according to the second comparative example. FIG. 7C is a waveform diagram of the output voltage of the power conversion device according to the third comparative example. FIG. 8 is a circuit diagram of a power conversion device according to the second embodiment. FIG. 9 is a circuit diagram of a power conversion device according to the third embodiment. FIG. 10 is a circuit diagram of a power conversion device according to the fourth embodiment.

[0009] First Embodiment A power conversion device 1 according to a first embodiment will be described below with reference to FIGS. 1 to 5. FIG.

[0010] (1) Configuration of the Power Conversion Device FIG. 1 is a circuit diagram of a power conversion device 1 according to a first embodiment. The power conversion device 1 includes a plurality of (three in FIG. 1 ) DC-DC converters 2, a control device 3, and a plurality of (three in FIG. 1 ) second capacitors C2. Each of the plurality of DC-DC converters 2 has a positive input terminal 21, a positive output terminal 23, and a ground terminal 26. Each of the plurality of DC-DC converters 2 has a first capacitor C1 connected between the positive output terminal 23 and the ground terminal 26. The control device 3 controls the DC-DC converters 2. The second capacitor C2 is connected between the positive input terminal 21 and the positive output terminal 23 of the DC-DC converter 2. Each of the first capacitor C1 and the second capacitor C2 has a DC bias characteristic. The "DC bias characteristic" refers to a characteristic in which the capacitance changes depending on the magnitude of the applied DC voltage.

[0011] According to the above configuration, it is possible to achieve miniaturization.

[0012] The positive input terminal 21 , the positive output terminal 23 and the ground terminal 26 do not have to have physical components (terminals), and may be, for example, part of a conductor portion included in a circuit board provided in the power conversion device 1 .

[0013] The power conversion device 1 further includes a first input terminal T1, a second input terminal T2, and a plurality of (three in FIG. 1) output terminals T3.

[0014] In the power conversion device 1, a DC power supply E1 is connected between a first input terminal T1 and a second input terminal T2, and a load 5 is connected to a plurality of output terminals T3. The load 5 is, for example, an AC load (a three-phase motor in the example of FIG. 1 ).

[0015] Furthermore, in the power conversion device 1, each of the plurality of DC-DC converters 2 further has a negative input terminal 22. In the power conversion device 1, the positive input terminals 21 of the plurality of DC-DC converters 2 are connected to the first input terminal, and the negative input terminals 22 of the plurality of DC-DC converters 2 are connected to the second input terminal T2.

[0016] The power conversion device 1 further includes a third capacitor C3. The third capacitor C3 is connected between the first input terminal T1 and the second input terminal T2.

[0017] (2) Details of the Power Conversion Device The power conversion device 1 according to the first embodiment is a three-phase inverter that converts direct current into three-phase alternating current.

[0018] In the power conversion device 1, for example, a high-potential output terminal (positive electrode) of a DC power supply E1 is connected to a first input terminal T1, and a low-potential output terminal (negative electrode) of the DC power supply E1 is connected to a second input terminal T2. The output voltage of the DC power supply E1 is, for example, 48 V. The output voltage of the DC power supply E1 is not limited to 48 V, and may be, for example, 141 V obtained by inputting an AC voltage of 12 V, 24 V, or 100 V to a diode bridge.

[0019] Hereinafter, with regard to the multiple DC-DC converters 2, the DC-DC converter 2 corresponding to the U phase may be referred to as DC-DC converter 2u, the DC-DC converter 2 corresponding to the V phase may be referred to as DC-DC converter 2v, and the DC-DC converter 2 corresponding to the W phase may be referred to as DC-DC converter 2w. Also, with regard to the multiple output terminals T3, the output terminal T3 connected to the U phase terminal of the load 5 may be referred to as output terminal T3u, the output terminal T3 connected to the V phase terminal of the load 5 may be referred to as output terminal T3v, and the output terminal T3 connected to the W phase terminal of the load 5 may be referred to as output terminal T3w.

[0020] In this embodiment, each of the plurality of DC-DC converters 2 is a bidirectional DC-DC converter 20. The bidirectional DC-DC converter 20 is a step-up / step-down converter capable of stepping up and stepping down in both directions.

[0021] Each of the multiple bidirectional DC-DC converters 20 has a negative input terminal 22, a negative output terminal 24, a first series circuit 201, a second series circuit 202, and an inductor L1. The negative output terminal 24 also serves as a ground terminal 26. In the first series circuit 201, a first switching element Q1 and a second switching element Q2 are connected in series between the positive input terminal 21 and the negative input terminal 22. In the second series circuit 202, a third switching element Q3 and a fourth switching element Q4 are connected in series between the positive output terminal 23 and the negative output terminal 24. The inductor L1 is connected between a connection point N1 (hereinafter also referred to as the first connection point N1) between the first switching element Q1 and the second switching element Q2 and a connection point N2 (hereinafter also referred to as the second connection point N2) between the third switching element Q3 and the fourth switching element Q4. The negative input terminal 22 and the negative output terminal 24 may not have physical components (terminals), and may be, for example, part of a conductor included in the circuit board.

[0022] In the bidirectional DC-DC converter 20, the first switching element Q1, the second switching element Q2, the third switching element Q3, and the fourth switching element Q4 each have a control terminal, a first main terminal, and a second main terminal. The control terminals of the first switching element Q1, the second switching element Q2, the third switching element Q3, and the fourth switching element Q4 are connected to the control device 3. In this embodiment, the first switching element Q1, the second switching element Q2, the third switching element Q3, and the fourth switching element Q4 are, for example, normally-off n-channel metal-oxide-semiconductor field effect transistors (MOSFETs). Therefore, the control terminal, the first main terminal, and the second main terminal of the first switching element Q1, the second switching element Q2, the third switching element Q3, and the fourth switching element Q4 are, respectively, a gate terminal, a drain terminal, and a source terminal.

[0023] In the first series circuit 201, a first main terminal of the first switching element Q1 is connected to the positive input terminal 21, a second main terminal of the first switching element Q1 is connected to the first main terminal of the second switching element Q2, and a second main terminal of the second switching element Q2 is connected to the negative input terminal 22. Therefore, in the first series circuit 201, the first switching element Q1 is a high-side switching element (P-side switching element), and the second switching element Q2 is a low-side switching element (N-side switching element). In the second series circuit 202, a first main terminal of the third switching element Q3 is connected to the positive output terminal 23, a second main terminal of the third switching element Q3 is connected to the first main terminal of the fourth switching element Q4, and a second main terminal of the fourth switching element Q4 is connected to the negative output terminal 24. Therefore, in the second series circuit 202, the third switching element Q3 is a high-side switching element, and the fourth switching element Q4 is a low-side switching element.

[0024] The bidirectional DC-DC converter 20 further includes a first diode D1, a second diode D2, a third diode D3, and a fourth diode D4. The first diode D1 is connected in anti-parallel to the first switching element Q1. The anode of the first diode D1 is connected to the second main terminal (source terminal) of the first switching element Q1, and the cathode of the first diode D1 is connected to the first main terminal (drain terminal) of the first switching element Q1. The second diode D2 is connected in anti-parallel to the second switching element Q2. The anode of the second diode D2 is connected to the second main terminal of the second switching element Q2, and the cathode of the second diode D2 is connected to the first main terminal of the second switching element Q2. The third diode D3 is connected in anti-parallel to the third switching element Q3. The third diode D3 has an anode connected to the second main terminal of the third switching element Q3 and a cathode connected to the first main terminal of the third switching element Q3. The fourth diode D4 is connected in anti-parallel to the fourth switching element Q4. The fourth diode D4 has an anode connected to the second main terminal of the fourth switching element Q4 and a cathode connected to the first main terminal of the fourth switching element Q4. The first to fourth diodes D4 are parasitic diodes of the n-channel MOSFETs that constitute the first to fourth switching elements Q1 to Q4, respectively, but are not limited to this and may be external diodes.

[0025] In this embodiment, the inductances of the multiple inductors L1 (three in FIG. 1 ) are the same. That is, the inductances of the three inductors L1 are the same. "The inductances of the three inductors L1 are the same" does not necessarily mean that the inductances of two of the three inductors L1 are completely equal to the inductance of the remaining inductor L1, but may mean that the inductance of each of the two inductors L1 is within a range of 80% to 120% of the inductance of the remaining inductor L1.

[0026] In each of the multiple DC-DC converters 2, the first capacitor C1 is connected between the positive output terminal 23 and the ground terminal 26 (negative output terminal 24). More specifically, in the example of Fig. 1, the first capacitor C1 is connected between the ground terminal 26 and a node 25 of the positive wiring portion between the positive output terminal 23 and the output terminal T3.

[0027] In each of the multiple DC-DC converters 2, the first capacitor C1 is a capacitor having the DC bias characteristics as described above. The first capacitor C1 includes a high-dielectric-constant multilayer ceramic capacitor 10 (see FIG. 2A). The dielectric material of the multilayer ceramic capacitor 10 is a ferroelectric material. The ferroelectric material is, for example, barium titanate (BaTiO ３ ), but is not limited to barium titanate. The dielectric constant of the dielectric material of a high dielectric constant multilayer ceramic capacitor is, for example, 2000 or more and 12000 or less. A "high dielectric constant multilayer ceramic capacitor" is, for example, a multilayer ceramic capacitor classified as Class 2 in the Japanese Industrial Standards or EIA Standards.

[0028] 2A is a circuit diagram of a first capacitor C1 in the power conversion device 1 according to the first embodiment. In each of the multiple DC-DC converters 2, the first capacitor C1 includes, for example, multiple (four in the example of FIG. 2A ) multilayer ceramic capacitors 10. In the example of FIG. 2A , the first capacitor C1 is configured such that the four multilayer ceramic capacitors 10 included in the first capacitor C1 are connected in series and parallel. The first capacitor C1 is not limited to a configuration including multiple multilayer ceramic capacitors 10, and may include at least one multilayer ceramic capacitor 10.

[0029] In the power conversion device 1, the capacitances of the multiple (three in FIG. 1 ) first capacitors C1 are the same. That is, the capacitances of the three first capacitors C1 are the same. "The capacitances of the three first capacitors C1 are the same" does not necessarily mean that the capacitances of two of the three first capacitors C1 are completely the same as the capacitance of the remaining first capacitor C1, but may mean that the capacitance of each of the two first capacitors C1 is within a range of 90% to 110% of the capacitance of the remaining first capacitor C1.

[0030] In the power conversion device 1, the plurality of DC-DC converters 2 are connected in parallel to the third capacitor C3. Therefore, in the bidirectional DC-DC converter 20, the first series circuit 201 is connected in parallel to the third capacitor C3.

[0031] In the bidirectional DC-DC converter 20, the second series circuit 202 is connected in parallel to the first capacitor C1.

[0032] The bidirectional DC-DC converter 20 is capable of a first conversion operation for converting a first input voltage into a first output voltage, and a second conversion operation for converting a second input voltage into a second output voltage. Each of the first conversion operation and the second conversion operation can be either a step-up operation (hereinafter also referred to as a step-up mode operation) or a step-down operation (hereinafter also referred to as a step-down mode operation). The power conversion device 1 performs the second conversion operation to regenerate energy from a three-phase motor, which is the load 5, when the three-phase motor is braked, for example.

[0033] The multiple DC-DC converters 2 are controlled by a control device 3. FIG. 3 is an operational waveform diagram of the power conversion device 1 according to the first embodiment. The output voltage of each of the multiple DC-DC converters 2 is, for example, a sinusoidal DC voltage (see FIG. 3). The output current of each of the multiple DC-DC converters 2 is, for example, a sinusoidal AC current (see FIG. 3). The current IL1 flowing through the inductor L1 in each of the multiple DC-DC converters 2 is, for example, a sinusoidal AC current (see FIG. 3). The power conversion device 1 outputs sinusoidal DC voltages that are 120° out of phase with each other from the three DC-DC converters 2u, 2v, and 2w. The power conversion device 1 also outputs sinusoidal AC currents that are 120° out of phase with each other from the three DC-DC converters 2u, 2v, and 2w.

[0034] In this embodiment, the control device 3 controls multiple DC-DC converters 2. More specifically, the control device 3 controls multiple first switching elements Q1, multiple second switching elements Q2, multiple third switching elements Q3, and multiple fourth switching elements Q4. The control device 3 includes a computer system. The computer system is primarily composed of a processor and memory as hardware. The processor executes a program recorded in the memory of the computer system to realize the functions of the control device 3 in the present disclosure. The processor of the computer system is composed of one or more electronic circuits including a semiconductor integrated circuit (IC, Integrated Circuit) or a large-scale integrated circuit (LSI, Large Scale Integration). The integrated circuits, such as ICs and LSIs, are referred to by different names depending on the degree of integration, and include integrated circuits called system LSIs, very large scale integrations (VLSIs), or ultra large scale integrations (ULSIs). Furthermore, a field-programmable gate array (FPGA), which is programmed after the LSI is manufactured, or a logic device capable of reconfiguring the connections within the LSI or the circuit partitions within the LSI, can also be employed as a processor. Multiple electronic circuits may be integrated into a single chip or distributed across multiple chips. Multiple chips may be integrated into a single device or distributed across multiple devices. The computer system referred to here includes a microcontroller having one or more processors and one or more memories. Therefore, the microcontroller is also composed of one or more electronic circuits, including a semiconductor integrated circuit or a large-scale integrated circuit.

[0035] FIG. 4 is a timing chart showing the operation of the DC-DC converter 2 in the power conversion device 1 according to the first embodiment when the converter is operated in step-down mode. FIG. 5 is a timing chart showing the operation of the DC-DC converter 2 in the power conversion device 1 according to the first embodiment when the converter is operated in step-up mode. The control device 3 outputs a plurality of first control signals S1 (see FIGS. 4 and 5), a plurality of second control signals S2 (see FIGS. 4 and 5), a plurality of third control signals S3 (see FIGS. 4 and 5), and a plurality of fourth control signals S4 (see FIGS. 4 and 5) that control the on / off of the plurality of first switching elements Q1, the plurality of second switching elements Q2, the plurality of third switching elements Q3, and the plurality of fourth switching elements Q4, respectively. The plurality of first control signals S1 correspond one-to-one to the plurality of first switching elements Q1. The plurality of second control signals S2 correspond one-to-one to the plurality of second switching elements Q2. The plurality of third control signals correspond one-to-one to the plurality of third switching elements Q3. The plurality of fourth control signals correspond one-to-one to the plurality of fourth switching elements Q4. Each of the first control signals, the second control signals, the third control signals, and the fourth control signals is, for example, a PWM (Pulse Width Modulation) signal whose potential level changes between a first potential level (hereinafter also referred to as a low level) and a second potential level (hereinafter also referred to as a high level) higher than the first potential level. Each of the first switching elements Q1 is turned on when a corresponding one of the first control signals S1 is at a high level and turned off when it is at a low level. Each of the second switching elements Q2 is turned on when a corresponding one of the second control signals S2 is at a high level and turned off when it is at a low level. Each of the third switching elements Q3 is turned on when a corresponding one of the third control signals S3 is at a high level and turned off when it is at a low level. Each of the fourth switching elements Q4 is turned on when a corresponding one of the fourth control signals S4 is at a high level and turned off when it is at a low level.

[0036] The control device 3 uses a triangular-wave carrier signal CA1 (see FIGS. 4 and 5) to generate a plurality of first control signals S1, a plurality of second control signals S2, a plurality of third control signals, and a plurality of fourth control signals S4. More specifically, the control device 3 generates the first control signal S1, the second control signal S2, the third control signal S3, and the fourth control signal S4 to be applied to the first switching element Q1, the second switching element Q2, the third switching element Q3, and the fourth switching element Q4 of the DC-DC converter 2u, respectively, based on, for example, the carrier signal CA1 and a U-phase voltage command. The control device 3 also generates the first control signal S1, the second control signal S2, the third control signal S3, and the fourth control signal S4 to be applied to the first switching element Q1, the second switching element Q2, the third switching element Q3, and the fourth switching element Q4 of the DC-DC converter 2v, respectively, based on, for example, the carrier signal CA1 and a V-phase voltage command. Furthermore, the control device 3 generates a first control signal S1, a second control signal S2, a third control signal S3, and a fourth control signal S4 to be applied to the first switching element Q1, the second switching element Q2, the third switching element Q3, and the fourth switching element Q4 of the DC-DC converter 2w, respectively, based on the carrier signal CA1 and the W-phase voltage command. The U-phase voltage command, the V-phase voltage command, and the W-phase voltage command are, for example, sinusoidal signals with phases that differ by 120° from each other, and their values ​​(voltage command values) change over time. Note that the waveform of the carrier signal CA1 is not limited to a triangular waveform and may be, for example, a sawtooth waveform. Furthermore, the U-phase voltage command, the V-phase voltage command, and the W-phase voltage command have the same cycle length. Furthermore, the U-phase voltage command, the V-phase voltage command, and the W-phase voltage command have a longer cycle length than the carrier signal CA1.

[0037] The duties of the first control signal S1, the second control signal S2, the third control signal S3 and the fourth control signal S4 given from the control device 3 to the first switching element Q1, the second switching element Q2, the third switching element Q3 and the fourth switching element Q4 of the DC-DC converter 2, respectively, change based on the voltage command of the phase corresponding to the DC-DC converter 2.

[0038] The control device 3 operates the DC-DC converter 2 in a step-down mode when the output voltage of the DC-DC converter 2 is less than the output voltage of the DC power supply E1 (for example, 48 V), and operates the DC-DC converter 2 in a step-up mode when the output voltage of the DC-DC converter 2 is equal to or greater than the output voltage of the DC power supply E1. The power conversion device 1 changes the output voltages of the multiple DC-DC converters 2 within a predetermined voltage range (for example, a range of 0 V to 100 V).

[0039] In this embodiment, each of the plurality of second capacitors C2 is a capacitor having a DC bias characteristic. Fig. 2B is a circuit diagram of the second capacitor C2 in the power conversion device 1 according to the first embodiment. Each of the plurality of second capacitors C2 includes a high dielectric constant multilayer ceramic capacitor 10 (see Fig. 2B ), similar to the first capacitor C1.

[0040] In this embodiment, each of the multiple second capacitors C2 includes, for example, multiple (four in the example of FIG. 2B ) multilayer ceramic capacitors 10. In the example of FIG. 2B , the second capacitor C2 is configured by connecting the four multilayer ceramic capacitors 10 included in the second capacitor C2 in series and parallel. The second capacitor C2 is not limited to a configuration including multiple multilayer ceramic capacitors 10, and may include at least one multilayer ceramic capacitor 10.

[0041] In this embodiment, the capacitance of the second capacitor C2 is the same as the capacitance of the first capacitor C1. Here, the capacitances of the second capacitor C2 and the first capacitor C1 refer to the capacitances when no DC voltage is applied. The phrase "the capacitance of the second capacitor C2 is the same as the capacitance of the first capacitor C1" does not necessarily mean that the capacitance of the second capacitor C2 exactly matches the capacitance of the first capacitor C1, but may mean that the capacitance of the second capacitor C2 is within a range of 90% to 110% of the capacitance of the first capacitor C1.

[0042] (3) Example of Operation of Power Conversion Device An example of operation of the power conversion device 1 will be briefly described below with reference to FIGS.

[0043] In the power conversion device 1, the control device 3 controls the multiple DC-DC converters 2, so that the three DC-DC converters 2u, 2v, and 2w output sinusoidal DC voltages that are 120° out of phase with each other. At this time, the output currents of the three DC-DC converters 2u, 2v, and 2w are sinusoidal AC currents that are 120° out of phase with each other. Furthermore, the current IL1 flowing through the inductor L1 in the three DC-DC converters 2u, 2v, and 2w is sinusoidal AC currents that are 120° out of phase with each other. Figure 3 shows an example of the output voltage, output current, and current IL1 of DC-DC converter 2u, one of the three DC-DC converters 2u, 2v, and 2w. 3 shows a case where the output voltage of DC power supply E1 is 48 V, the rotation speed of the three-phase motor serving as load 5 is 3000 rpm, the frequency of carrier signal CA1 is 100 kHz, the length of dead time period Td (see FIGS. 4 and 5) is 0.4 μs, the inductance of inductor L1 is 15 μH, the capacitance of first capacitor C1 is 2.5 μF, and the capacitance of second capacitor C2 is 2.5 μF. The number of poles of the three-phase motor is 10. In the example of FIG. 3, when the output voltage of DC-DC converter 2u is less than 48 V, control device 3 operates the DC-DC converter in step-down mode, and when the output voltage of DC-DC converter 2u is 48 V or higher, control device 3 operates the DC-DC converter in step-up mode.

[0044] 4 illustrates the carrier signal CA1, duty cycle Du1 of the first control signal S1, duty cycle Du3 of the third control signal S3, first control signal S1, second control signal S2, third control signal S3, fourth control signal S4, and current IL1 when the polarity of current IL1 flowing through inductor L1 is positive, when the control device 3 operates the DC-DC converter 2 in step-down mode. When operating the DC-DC converter 2 in step-down mode, the control device 3 controls the third switching element Q3 to be always on and the fourth switching element Q4 to be always off. The control device 3 compares the duty cycle Du1 corresponding to the voltage command with the carrier signal CA1 to generate the first control signal S1 to be applied to the first switching element Q1. The control device 3 also inverts the first control signal S1 to be applied to the first switching element Q1 and generates the second control signal S2 to be applied to the second switching element Q2. The control device 3 also sets a dead time Td between the high-level period of the first control signal S1 and the high-level period of the second control signal S2 so that the on-periods of the first switching element Q1 and the second switching element Q2 do not overlap. The control device 3 also compares the duty Du3 corresponding to the voltage command with the carrier signal CA1 to generate a third control signal S3 to be provided to the third switching element Q3. The control device 3 also inverts the third control signal S3 to be provided to the third switching element Q3 to generate a fourth control signal S4 to be provided to the fourth switching element Q4.

[0045] 5 illustrates the carrier signal CA1, duty cycle Du1 of the first control signal S1, duty cycle Du3 of the third control signal S3, first control signal S1, second control signal S2, third control signal S3, fourth control signal S4, and current IL1 when the polarity of current IL1 flowing through inductor L1 is positive when the control device 3 operates the DC-DC converter 2u in boost mode. When operating the DC-DC converter 2u in boost mode, the control device 3 controls the first switching element Q1 to be always on and the second switching element Q2 to be always off. The control device 3 compares the duty cycle Du3 corresponding to the voltage command with the carrier signal CA1 to generate the third control signal S3 to be applied to the third switching element Q3. The control device 3 also inverts the third control signal S3 to be applied to the third switching element Q3 to generate the fourth control signal S4 to be applied to the fourth switching element Q4. The control device 3 also sets a dead time Td between the high-level period of the third control signal S3 and the high-level period of the fourth control signal S4 so that the on periods of the third switching element Q3 and the third switching element Q3 do not overlap. The control device 3 also compares the duty Du1 corresponding to the voltage command with the carrier signal CA1 to generate the first control signal S1 to be applied to the first switching element Q1. The control device 3 also inverts the first control signal S1 to be applied to the first switching element Q1 to generate the second control signal S2 to be applied to the second switching element Q2.

[0046] In the above, the operation of the control device 3 has been described only in terms of the step-down mode in which the control device 3 controls the third switching element Q3 to be always on, and the step-up mode in which the control device 3 controls the first switching element Q1 to be always on. However, the control device 3 may also operate in the step-up / step-down mode in which the first to fourth switching elements Q1 to Q4 are switched on and off at all times.

[0047] (4) Characteristics Below, before describing the characteristics of the power conversion device 1 of Example 1, which is an example of the power conversion device 1 according to Embodiment 1, a power conversion device of Comparative Example 1 will be described. The power conversion device of Comparative Example 1 differs from the power conversion device 1 of Embodiment 1 in that it does not include the multiple second capacitors C2 of the power conversion device 1 of Embodiment 1.

[0048] In the power converter of Comparative Example 1, the first capacitor is configured using eight multilayer ceramic capacitors. Each of the eight multilayer ceramic capacitors is a high-dielectric-constant multilayer ceramic capacitor. Furthermore, each of the eight multilayer ceramic capacitors has the same capacitance and rated voltage specifications. FIG. 6 is a voltage characteristic diagram of the effective capacitance of the first capacitor in the power converter 1 of Example 1 and the power converter of Comparative Example 1. In the power converter of Comparative Example 1, as shown by "B1" in FIG. 6, the effective capacitance of the first capacitor decreases as the output voltage of the DC-DC converter 2 (the voltage across the first capacitor) increases. In the power converter of Comparative Example 1, the first capacitor is configured by connecting four series circuits, each of which connects two multilayer ceramic capacitors in series, in parallel to ensure an effective capacitance of 5 μF or more for the first capacitor when the output voltage of the DC-DC converter is changed between 0 V and 100 V. When a DC voltage is applied between the two terminals of the capacitor, the capacitance of the capacitor appears to decrease due to the DC bias characteristics of the capacitor. This capacitance after reduction is called the effective capacitance. For example, the first capacitor in the power conversion device of Comparative Example 1 consists of eight high-dielectric-constant multilayer ceramic capacitors, each with a capacitance of 10 μF, connected in two series and four parallel configurations. In Comparative Example 1, when the output voltage of the DC-DC converter is 0 V, the effective capacitance is 10 μF ÷ 2 × 4 = 20 μF. Also, in Comparative Example 1, when the output voltage of the DC-DC converter is 100 V, the inter-terminal voltage per high-dielectric-constant multilayer ceramic capacitor is 50 V. The DC bias characteristics of a high-dielectric-constant multilayer ceramic capacitor show a capacitance change rate of -75% when 50 V is applied, for example. In other words, when 50 V is applied, it only functions as a 2.5 μF capacitor. Therefore, the effective capacitance of the two series and four parallel configurations is 2.5 μF ÷ 2 × 4 = 5 μF.

[0049] Furthermore, in the power conversion device of Comparative Example 1, the voltage between the positive output terminal and the positive input terminal of the DC-DC converter, with the positive input terminal of the DC-DC converter as a reference, decreases as the output voltage of the DC-DC converter increases until the step-up ratio of the DC-DC converter reaches 1. In contrast, the power conversion device 1 of Example 1 includes a second capacitor C2 connected between the positive input terminal 21 and the positive output terminal 23 of the DC-DC converter 2.

[0050] In the power conversion device 1 of Example 1, as shown by "A1" in Fig. 6, the rate of change in effective capacitance when the output voltage of the DC-DC converter 2 is changed in the range of 0 V to 100 V is smaller than "B1" in Fig. 6. In the power conversion device 1 of Example 1, the first capacitor C1 is formed using four multilayer ceramic capacitors 10, and the second capacitor C2 is formed using four multilayer ceramic capacitors 10. More specifically, in the power conversion device 1 of Example 1, the first capacitor C1 is formed by connecting in parallel two series circuits, each of which connects two multilayer ceramic capacitors 10 in series, and the second capacitor C2 is formed by connecting in parallel two series circuits, each of which connects two multilayer ceramic capacitors 10 in series.

[0051] As can be seen from FIG. 6, the power conversion device 1 of Example 1 has a smaller rate of change in effective capacitance than the power conversion device of Comparative Example 1, and therefore it is possible to reduce the number of multilayer ceramic capacitors 10 required to ensure an effective capacitance of 5 μF.

[0052] In addition, below, the waveform of the output voltage of the power conversion device 1 of Example 2, the waveform of the output voltage of the power conversion device of Comparative Example 2, and the waveform of the output voltage of the power conversion device of Comparative Example 3 will be described with reference to Figures 7A, 7B, and 7C.

[0053] The power conversion devices of Comparative Example 2 and Comparative Example 3 differ from the power conversion device 1 in that they do not include the multiple second capacitors C2 of the power conversion device 1 of Embodiment 1. In the power conversion device of Comparative Example 2, the capacitance of the first capacitor is 2 μF, and the first capacitor is an ideal capacitor that does not have a DC bias characteristic. In the power conversion device of Comparative Example 3, the capacitance of the first capacitor is 2 μF, and the first capacitor has a DC bias characteristic. In the power conversion device 1 of Example 2, the capacitance of each of the first capacitor C1 and the second capacitor C2 is 1 μF, and each of the first capacitor C1 and the second capacitor C2 has a DC bias characteristic.

[0054] FIG. 7A shows the output voltage waveform of the DC-DC converter 2 of the power conversion device 1 of Example 2, FIG. 7B shows the output voltage waveform of the DC-DC converter of the power conversion device of Comparative Example 2, and FIG. 7C shows the output voltage waveform of the DC-DC converter of the power conversion device of Comparative Example 3. From FIGS. 7B and 7C , it can be seen that the DC-DC converter of the power conversion device of Comparative Example 3, which includes a first capacitor with DC bias characteristics, tends to have a larger ripple voltage as the output voltage increases, compared to the DC-DC converter of the power conversion device of Comparative Example 2, which includes a first capacitor without DC bias characteristics. Furthermore, from FIGS. 7A and 7C , it can be seen that the DC-DC converter 2 of the power conversion device of Example 2 can reduce ripple voltage compared to the DC-DC converter of the power conversion device of Comparative Example 3 in the high-voltage region where the output voltage is large. In the present disclosure, the "high-voltage region" is the region in the output voltage waveform where the voltage value of the output voltage is greater than half the voltage value of the input voltage of the DC-DC converter 2.

[0055] (5) Advantages The power conversion device 1 according to the first embodiment includes a DC-DC converter 2, a control device 3, and a second capacitor C2. The DC-DC converter 2 has a positive input terminal 21, a positive output terminal 23, and a ground terminal 26, and includes a first capacitor C1 connected between the positive output terminal 23 and the ground terminal 26. The second capacitor C2 is connected between the positive input terminal 21 and the positive output terminal 23 of the DC-DC converter 2. Each of the first capacitor C1 and the second capacitor C2 is a capacitor having a DC bias characteristic.

[0056] The above configuration enables the power conversion device 1 to be miniaturized. More specifically, in the power conversion device 1 according to the first embodiment, when the output voltage of the DC-DC converter 2 is changed, the DC bias characteristics of the first capacitor C1 can be mitigated by the DC bias characteristics of the second capacitor C2. As a result, the power conversion device 1 according to the first embodiment can reduce the rate of change of the effective capacitance within the output voltage range, thereby reducing the voltage ripple of the output voltage and reducing the capacitance of the first capacitor C1, thereby enabling miniaturization. Furthermore, the above configuration enables the rate of change of the effective capacitance within the output voltage range to be reduced, thereby reducing the voltage ripple of the output voltage. This also reduces torque ripple when the load is a motor. Furthermore, the power conversion device 1 according to the first embodiment can be miniaturized compared to a power conversion device that includes an electrolytic capacitor as the first capacitor but does not include a second capacitor, as in Comparative Example 2. Furthermore, the power conversion device 1 according to the first embodiment can achieve a longer life than a configuration that includes an electrolytic capacitor as the first capacitor.

[0057] In the power conversion device 1 according to the first embodiment, each of the first capacitor C1 and the second capacitor C2 includes a high dielectric constant multilayer ceramic capacitor 10.

[0058] According to the above configuration, it is possible to achieve further miniaturization.

[0059] Furthermore, in the power conversion device 1 according to the first embodiment, when no DC bias voltage is applied to each of the first capacitor C1 and the second capacitor C2, the capacitance of the second capacitor C2 is the same as the capacitance of the first capacitor C1.

[0060] According to the above configuration, the DC bias characteristics of the first capacitor C1 can be easily offset by the DC bias characteristics of the second capacitor C2, and the rate of change of the effective capacitance when the step-up ratio of the DC-DC converter 2 is 1 or less can be made smaller.

[0061] The power conversion device 1 according to the first embodiment also includes a plurality of DC-DC converters 2. The control device 3 controls the plurality of DC-DC converters 2. The power conversion device 1 also includes a plurality of second capacitors C2. The plurality of second capacitors C2 correspond one-to-one to the plurality of DC-DC converters 2. Each of the plurality of second capacitors C2 is connected between the positive input terminal 21 and the positive output terminal 23 of a corresponding one of the plurality of DC-DC converters 2.

[0062] According to the above configuration, the DC bias characteristics of the first capacitor C1 of each of the multiple DC-DC converters 2 can be mitigated by the DC bias characteristics of the corresponding second capacitor C2 among the multiple second capacitors C2, making it possible to reduce the voltage ripple of the output voltage.

[0063] Furthermore, in the power conversion device 1 according to the first embodiment, each of the plurality of DC-DC converters 2 includes a bidirectional DC-DC converter 20 .

[0064] According to the above configuration, for example, it is possible to regenerate energy generated by a load 5 connected to a plurality of DC-DC converters 2 using the plurality of DC-DC converters 2 .

[0065] Furthermore, in the power conversion device according to the present disclosure, feedback control may be performed by detecting the output voltage. In this case, if the magnitude of the output voltage ripple differs between the low-voltage region and the high-voltage region of the output voltage, it may be difficult to set a high feedback gain. This is because using a high gain when the ripple is large increases the risk of oscillation. According to the first embodiment, it is possible to keep the rate of change of the effective capacitance small, and the output voltage ripple does not become excessive in the high-voltage region as in the second embodiment. Therefore, it is possible to set a large feedback gain and increase the response speed of the power conversion device 1.

[0066] (Embodiment 2) A power conversion device 1A according to embodiment 2 will be described with reference to Fig. 8. Fig. 8 is a circuit diagram of the power conversion device 1A according to embodiment 2. Regarding the power conversion device 1A according to embodiment 2, components that are the same as those of the power conversion device 1 according to embodiment 1 (see Fig. 1) are denoted by the same reference numerals, and description thereof will be omitted.

[0067] (1) Configuration The power conversion device 1A of the second embodiment differs from the power conversion device 1 of the first embodiment in that it is provided with a plurality of DC-DC converters 2A instead of the plurality of DC-DC converters 2 in the power conversion device 1 of the first embodiment.

[0068] Each of the multiple DC-DC converters 2A is a step-down converter (step-down chopper). In the DC-DC converter 2A, an inductor L1 is connected between a connection point N1 between the first switching element Q1 and the second switching element Q2 and a positive output terminal 23. In the DC-DC converter 2A, the negative input terminal 22 also serves as a ground terminal 26. In the DC-DC converter 2A, a first capacitor C1 is connected between the positive output terminal 23 and the ground terminal 26 (negative input terminal 22). More specifically, in the example of FIG. 8 , the first capacitor C1 is connected between a node 25 of a positive wiring portion between the positive output terminal 23 and the output terminal T3 and the ground terminal 26.

[0069] The control device 3 controls the first switching element Q1 and the second switching element Q2 in the same manner as when the control device 3 operates the DC-DC converter 2 in the step-down mode in the power conversion device 1 of the first embodiment.

[0070] (2) Advantages The power conversion device 1A according to the second embodiment includes a second capacitor C2 connected between the positive input terminal 21 and the positive output terminal 23 of the DC-DC converter 2A. Each of the first capacitor C1 and the second capacitor C2 has a DC bias characteristic.

[0071] The above configuration allows for a reduction in the size of the power conversion device 1A. More specifically, in the power conversion device 1A according to the second embodiment, when the output voltage of the DC-DC converter 2A is changed, the DC bias characteristics of the first capacitor C1 can be mitigated by the DC bias characteristics of the second capacitor C2. As a result, the power conversion device 1A according to the second embodiment can reduce the rate of change of the effective capacitance within the output voltage range, thereby reducing the voltage ripple of the output voltage and reducing the capacitance of the first capacitor C1, thereby enabling a reduction in size. Furthermore, the above configuration allows for a reduction in the rate of change of the effective capacitance within the output voltage range, thereby reducing the voltage ripple of the output voltage. This also reduces torque ripple when the load is a motor. Furthermore, the power conversion device 1A according to the second embodiment allows for a reduction in size compared to a configuration including an electrolytic capacitor as the first capacitor.

[0072] (Embodiment 3) A power conversion device 1B according to embodiment 3 will be described with reference to Fig. 9. Fig. 9 is a circuit diagram of power conversion device 1B according to embodiment 3. Regarding power conversion device 1B according to embodiment 3, components similar to those of power conversion device 1 according to embodiment 1 (see Fig. 1) are denoted by the same reference numerals, and description thereof will be omitted.

[0073] (1) Configuration The power conversion device 1B of the third embodiment differs from the power conversion device 1 of the first embodiment in that the power conversion device 1B of the third embodiment includes a plurality of DC-DC converters 2B instead of the plurality of DC-DC converters 2 in the power conversion device 1 of the first embodiment.

[0074] Each of the plurality of DC-DC converters 2B differs from the DC-DC converter 2 in that it further includes a second inductor L2 different from the inductor L1 (hereinafter also referred to as the first inductor L1), and a switch SW2.

[0075] In each of the plurality of DC-DC converters 2B, a series circuit of a second inductor L2 and a switch SW2 is connected in parallel to the first inductor L1.

[0076] The inductance of the second inductor L2 is smaller than the inductance of the first inductor L1.

[0077] The switch SW2 is, for example, a bidirectional switch that includes, for example, two MOSFETs whose sources are connected to each other, and diodes that are connected in anti-parallel to the two MOSFETs one-to-one.

[0078] The switch SW2 is controlled by the control device 3. That is, the two MOSFETs included in the switch SW2 are controlled by the control device 3.

[0079] In the DC-DC converter 2B, the inductance between the first connection point N1 and the second connection point N2 can be changed by controlling the switch SW2 by the control device 3. For example, in the power conversion device 1B, immediately before turning on the fourth switching element Q4, the switch SW2 is turned on to pass a current through the second inductor L2, and the charge stored in the junction capacitance of the fourth switching element Q4 is extracted, thereby performing zero-volt switching on the fourth switching element Q4. This allows the power conversion device 1B to reduce switching loss and improve power conversion efficiency.

[0080] (2) Advantages The power conversion device 1B according to the third embodiment is provided with a second capacitor C2, similar to the power conversion device 1 according to the first embodiment, and each of the first capacitor C1 and the second capacitor C2 has a DC bias characteristic, which makes it possible to reduce the size of the device.

[0081] (Embodiment 4) A power conversion device 1C according to embodiment 4 will be described with reference to Fig. 10. Fig. 10 is a circuit diagram of the power conversion device 1C according to embodiment 4. With regard to the power conversion device 1C according to embodiment 4, components that are the same as those of the power conversion device 1 according to embodiment 1 (see Fig. 1) are denoted by the same reference numerals, and description thereof will be omitted.

[0082] (1) Configuration The power conversion device 1C of the fourth embodiment differs from the power conversion device 1 of the first embodiment in that it includes a plurality of DC-DC converters 2C instead of the plurality of DC-DC converters 2 in the power conversion device 1 of the first embodiment.

[0083] In the power conversion device 1C, each of the multiple DC-DC converters 2C is a DC-DC converter with a two-phase interleaved configuration. That is, each of the multiple DC-DC converters 2C has two DC-DC converters 2 (see FIG. 1), and the first capacitor C1 is shared by these two DC-DC converters 2. Each of the multiple DC-DC converters 2C has two sets of a first switching element Q1, a second switching element Q2, a third switching element Q3, a fourth switching element Q4, and an inductor L1.

[0084] In the following, the DC-DC converter 2C connected to the output terminal T3u will be referred to as the DC-DC converter 2Cu, the DC-DC converter 2C connected to the output terminal T3v will be referred to as the DC-DC converter 2Cv, and the DC-DC converter 2C connected to the output terminal T3w will be referred to as the DC-DC converter 2Cw.

[0085] The multiple DC-DC converters 2C are controlled by a control device 3. The control device 3 causes the phase of a carrier signal for generating the first control signal S1 to the fourth control signal S4 for one of the two DC-DC converters 2 in each of the multiple DC-DC converters 2 to differ by 180° from the phase of a carrier signal for generating the first control signal S1 to the fourth control signal S4 for the remaining DC-DC converter 2. As a result, in each of the multiple DC-DC converters 2C, the phase of the switching element to be turned on and off among the set of the first switching element Q1 to the fourth switching element Q4 is caused to differ by 180° from the phase of the switching element to be turned on and off among the remaining set of the first switching element Q1 to the fourth switching element Q4.

[0086] (2) Advantages The power conversion device 1C according to the fourth embodiment, like the power conversion device 1 according to the first embodiment, has a plurality of DC-DC converters 2C, each of which includes a second capacitor C2, and each of the first capacitor C1 and the second capacitor C2 has a DC bias characteristic, which allows for miniaturization. Note that, in each of the plurality of DC-DC converters 2C, the second capacitors C2 are connected to the same node, so they may be combined into a single second capacitor C2. In this case, in the example of FIG. 10, the number of second capacitors C2 in the power conversion device 1C is three.

[0087] Furthermore, in the power conversion device 1C according to the fourth embodiment, each of the plurality of DC-DC converters 2C is a DC-DC converter with a two-phase interleaved configuration.

[0088] According to the above configuration, it is possible to reduce the current ripple in the output current and the voltage ripple in the output voltage of each of the plurality of DC-DC converters 2C.

[0089] In addition, the power conversion device 1C of embodiment 4 further includes a third capacitor C3 connected between the first input terminal T1 and the second input terminal T2, and multiple DC-DC converters 2C are commonly connected to the third capacitor C3.

[0090] According to the above configuration, it is possible to reduce the current ripple of the input current and the voltage ripple of the input voltage of each of the plurality of DC-DC converters 2C.

[0091] In the power conversion device 1C according to the fourth embodiment, the case has been described in which each of the multiple DC-DC converters 2C is a DC-DC converter with a two-phase interleaved configuration, but each of the multiple DC-DC converters 2C may be a DC-DC converter with an interleaved configuration with more than two phases. For example, each of the multiple DC-DC converters 2C may be a DC-DC converter with a four-phase interleaved configuration.

[0092] (Other Modifications) The above-described first to fourth embodiments are merely examples of various embodiments of the present disclosure. The above-described first to fourth embodiments can be modified in various ways depending on the design, etc., as long as the object of the present disclosure can be achieved.

[0093] For example, each of the first switching element Q1, the second switching element Q2, the third switching element Q3, and the fourth switching element Q4 is not limited to an n-channel MOSFET and may be a p-channel MOSFET. Furthermore, each of the first switching element Q1, the second switching element Q2, the third switching element Q3, and the fourth switching element Q4 is a Si-based MOSFET, but is not limited to this and may be, for example, a SiC-based MOSFET. Furthermore, each of the first switching element Q1, the second switching element Q2, the third switching element Q3, and the fourth switching element Q4 is not limited to a MOSFET and may be, for example, a bipolar transistor, an IGBT (Insulated Gate Bipolar Transistor), or a GaN-based GIT (Gate Injection Transistor).

[0094] Furthermore, the circuit configuration of the bidirectional DC-DC converter 20 is not limited to the circuit configurations shown in FIGS. 1 and 9, and other circuit configurations may also be used.

[0095] Furthermore, although the power conversion device 1 includes a plurality of DC-DC converters 2, it is sufficient that the power conversion device 1 includes at least one DC-DC converter 2. It is also sufficient that the power conversion devices 1A, 1B, and 1C each include at least one DC-DC converter 2A, 2B, and 2C.

[0096] Furthermore, the power conversion device 1 includes a plurality of second capacitors C2 that correspond one-to-one to the plurality of DC-DC converters 2, but it is sufficient that the power conversion device 1 includes a second capacitor C2 that corresponds to at least one of the plurality of DC-DC converters 2. It is not essential that each of the power conversion devices 1A, 1B, and 1C includes a plurality of second capacitors C2, and it is sufficient that each of the power conversion devices 1A, 1B, and 1C includes at least one second capacitor C2.

[0097] (Aspects) The present specification discloses the following aspects.

[0098] A power conversion device (1; 1A; 1B; 1C) according to a first aspect includes a DC-DC converter (2; 2A; 2B), a control device (3), and a second capacitor (C2). The DC-DC converter (2; 2A; 2B; 2C) has a positive input terminal (21), a positive output terminal (23), and a ground terminal (26). The DC-DC converter (2; 2A; 2B; 2C) has a first capacitor (C1) connected between the positive output terminal (23) and the ground terminal (26). The control device (3) controls the DC-DC converter (2; 2A; 2B; 2C). The second capacitor (C2) is connected between the positive input terminal (21) and the positive output terminal (23) of the DC-DC converter (2; 2A; 2B; 2C). Each of the first capacitor (C1) and the second capacitor (C2) is a capacitor having a DC bias characteristic.

[0099] According to this aspect, it is possible to achieve miniaturization.

[0100] In the power conversion device (1; 1A; 1B; 1C) according to the second aspect, in the first aspect, each of the first capacitor (C1) and the second capacitor (C2) includes a high dielectric constant multilayer ceramic capacitor (10).

[0101] According to this aspect, it is possible to achieve further miniaturization.

[0102] In the power conversion device (1; 1A; 1B; 1C) according to the third aspect, in the second aspect, the dielectric material of the multilayer ceramic capacitor is a ferroelectric material.

[0103] A power conversion device (1; 1A; 1B; 1C) according to a fourth aspect is based on any one of the first to third aspects. When a DC bias voltage is not applied to each of the first capacitor (C1) and the second capacitor (C2), the capacitance of the second capacitor (C2) is the same as the capacitance of the first capacitor (C1).

[0104] According to this aspect, the DC bias characteristics of the first capacitor (C1) can be easily offset by the DC bias characteristics of the second capacitor (C2), and the rate of change in the effective capacitance when the step-up ratio of the DC-DC converter (2) is 1 or less can be made smaller.

[0105] A power conversion device (1; 1A; 1B; 1C) according to a fifth aspect is any one of the first to fourth aspects and includes a plurality of DC-DC converters (2; 2A; 2B; 2C). A control device (3) controls the plurality of DC-DC converters (2; 2A; 2B; 2C).

[0106] A power conversion device (1; 1A; 1B; 1C) according to a sixth aspect is the fifth aspect, and further includes a plurality of second capacitors (C2). The plurality of second capacitors (C2) correspond one-to-one to the plurality of DC-DC converters (2; 2A; 2B). Each of the plurality of second capacitors (C2) is connected between a positive input terminal (21) and a positive output terminal (23) of a corresponding DC-DC converter (2; 2A; 2B; 2C) among the plurality of DC-DC converters (2; 2A; 2B; 2C).

[0107] According to this aspect, the DC bias characteristics of the first capacitor (C1) of each of the plurality of DC-DC converters (2; 2A; 2B; 2C) can be alleviated by the DC bias characteristics of the corresponding second capacitor (C2) among the plurality of second capacitors (C2), thereby making it possible to reduce voltage ripple in the output voltage.

[0108] In a power conversion device (1; 1A; 1B; 1C) according to a seventh aspect, in the fifth or sixth aspect, each of the plurality of DC-DC converters (2; 2A; 2B; 2C) includes a bidirectional DC-DC converter (20).

[0109] According to this aspect, for example, it is possible to regenerate energy generated in a load (5) connected to a plurality of DC-DC converters (2; 2A; 2B; 2C) by the plurality of DC-DC converters (2; 2A; 2B; 2C).

[0110] In a power conversion device (1; 1A; 1B; 1C) according to an eighth aspect, in the seventh aspect, the bidirectional DC-DC converter (20) includes a negative input terminal (22), a negative output terminal (24), a first series circuit (201), a second series circuit (202), and an inductor (L1). The negative output terminal (24) also serves as a ground terminal (26). The first series circuit (201) includes a first switching element (Q1) and a second switching element (Q2) connected in series between the positive input terminal (21) and the negative input terminal (22). The second series circuit (202) includes a third switching element (Q3) and a fourth switching element (Q4) connected in series between the positive output terminal (23) and the negative output terminal (24). The inductor (L1) is connected between a first connection point (N1) between the first switching element (Q1) and the second switching element (Q2) and a second connection point (N2) between the third switching element (Q3) and the fourth switching element (Q4).

[0111] According to this aspect, it is possible to simultaneously suppress the surge voltage generated in the first switching element (Q1) and the surge voltage generated in the third switching element (Q3).

[0112] In a power conversion device (1C) according to a ninth aspect, in any one of the first to eighth aspects, the DC-DC converter (2C) is a DC-DC converter of a two-phase interleaved configuration.

[0113] According to this aspect, it is possible to reduce the current ripple of the output current and the voltage ripple of the output voltage of each of the plurality of DC-DC converters (2C).

[0114] According to the present disclosure, it is possible to reduce the size of a power conversion device. Thus, the power conversion device of the present disclosure is industrially useful.

[0115] 1, 1A, 1B, 1C Power conversion device 2, 2A, 2B, 2C DC-DC converter 20 Bidirectional DC-DC converter 21 Positive input terminal 22 Negative input terminal 23 Positive output terminal 24 Negative output terminal 26 Ground terminal 201 First series circuit 202 Second series circuit 3 Control device 5 Load 10 Multilayer ceramic capacitor T1 First input terminal T2 Second input terminal T3, T3u Output terminal T3, T3v Output terminal T3, T3w Output terminal C1 First capacitor C2 Second capacitor C3 Third capacitor D1 First diode D2 Second diode D3 Third diode D4 Fourth diode L1 Inductor IL1 Current Q1 First switching element Q2 Second switching element Q3 Third switching element Q4 Fourth switching element N1 First connection point N2 Second connection point

Claims

1. A power conversion device comprising: a DC-DC converter having a positive input terminal, a positive output terminal, and a ground terminal, the first capacitor being connected between the positive output terminal and the ground terminal; a control device that controls the DC-DC converter; and a second capacitor that is connected between the positive input terminal and the positive output terminal of the DC-DC converter, wherein each of the first capacitor and the second capacitor has DC bias characteristics.

2. The power conversion device according to claim 1, wherein each of the first capacitor and the second capacitor includes a high dielectric constant multilayer ceramic capacitor.

3. The power conversion device according to claim 2, wherein the dielectric material of the multilayer ceramic capacitor is a ferroelectric material.

4. A power conversion device according to any one of claims 1 to 3, wherein when no DC bias voltage is applied to each of the first capacitor and the second capacitor, the capacitance of the second capacitor is the same as the capacitance of the first capacitor.

5. The power conversion device according to any one of claims 1 to 4, comprising a plurality of the DC-DC converters, and the control device controls the plurality of DC-DC converters.

6. The power conversion device according to claim 5, comprising a plurality of second capacitors, the plurality of second capacitors corresponding one-to-one to the plurality of DC-DC converters, and each of the plurality of second capacitors being connected between the positive input terminal and the positive output terminal of a corresponding one of the plurality of DC-DC converters.

7. The power conversion device according to claim 5 or 6, wherein each of the plurality of DC-DC converters includes a bidirectional DC-DC converter.

8. The power conversion device according to claim 7, wherein the bidirectional DC-DC converter comprises: a negative input terminal; a negative output terminal that also serves as the ground terminal; a first series circuit in which a first switching element and a second switching element are connected in series between the positive input terminal and the negative input terminal; a second series circuit in which a third switching element and a fourth switching element are connected in series between the positive output terminal and the negative output terminal; and an inductor 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.

9. The power conversion device according to any one of claims 1 to 8, wherein the DC-DC converter is a DC-DC converter with a two-phase interleaved configuration.

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