Power converter

Abstract

To provide a power conversion device capable of stably operating.SOLUTION: A power conversion device includes: a first bridge circuit that is provided between a first line to which a first voltage is applied and a second line to which a second voltage lower than the first voltage is applied and includes a plurality of first switching elements; a second bridge circuit that is provided between the second line and a third line to which a third voltage lower than the second voltage is applied and includes a plurality of second switching elements; and a voltage output circuit for generating a predetermined DC voltage based on operation of the first and the second bridge circuits.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a power conversion device.

Background Art

[0002] As power conversion devices that convert a varying input voltage into a constant voltage through power conversion, those using a booster circuit, a high-frequency transformer (insulating transformer) or the like are known (see, for example, Patent Documents 1 and 2). In Patent Document 2, after an input voltage is boosted by a boost chopper (booster circuit), power is converted to a constant voltage using an inverter (bridge circuit) including a plurality of switching elements, an insulating transformer, a rectifier circuit, and the like.

Prior Art Literature

Patent Literature

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problem to be Solved by the Invention

[0004] When the output voltage of the booster circuit is high, the subsequent bridge circuit requires a switching element having a higher withstand voltage than the output voltage (high-withstand-voltage switching element). However, high-withstand-voltage switching elements are expensive, and have slow turn-off response for small currents, making high-frequency operation (high-speed switching) difficult. Furthermore, even when a high-withstand-voltage switching element is used, the element may be damaged due to turn-off surge.

[0005] The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide a power conversion device that can operate stably.

Means for Solving the Problem

[0006] The power conversion device of the present invention, which solves the aforementioned problems, comprises: a first bridge circuit provided between a first line to which a first voltage is applied and a second line to which a second voltage lower than the first voltage is applied, and including a plurality of first switching elements; a second bridge circuit provided between the second line and a third line to which a third voltage lower than the second voltage is applied, and including a plurality of second switching elements; and a voltage output circuit that generates a predetermined DC voltage based on the operation of the first and second bridge circuits. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a power conversion device that can operate stably. [Brief explanation of the drawing]

[0008] [Figure 1] This is a circuit diagram showing the configuration of power converter 1a, a comparative example. [Figure 2] This is a circuit diagram showing the configuration of the power converter 1b of the first embodiment. [Figure 3] This is a diagram illustrating the effectiveness of this embodiment. [Figure 4] This diagram shows the case where a turn-off surge occurs. [Figure 5] This is an explanatory diagram regarding the contents of the package. [Figure 6] This is an explanatory diagram of a modified example of the first embodiment. [Figure 7] This is a circuit diagram and waveform diagram showing part of the configuration of the power converter 1c of the second embodiment. [Figure 8] Figures 8A to 8D are explanatory diagrams of the rectification operation in the second embodiment. [Figure 9] This is a circuit diagram and waveform diagram showing part of the configuration of the power converter 1d of the third embodiment. [Figure 10] Figures 10A to 10D are explanatory diagrams of the rectification operation in the third embodiment. [Figure 11] This is an explanatory diagram of a modified example of the third embodiment. [Figure 12]It is a circuit diagram and a waveform diagram showing a part of the configuration of the power conversion device 1e according to the fourth embodiment. [Figure 13] It is an explanatory diagram of a modification of the fourth embodiment. [Figure 14] It is a circuit diagram and a waveform diagram showing a part of the configuration of the power conversion device 1f according to the fifth embodiment. [Figure 15] It is an explanatory diagram of a modification of the fifth embodiment. [Figure 16] FIG. 16A to FIG. 16F are explanatory diagrams of the sixth embodiment. [Figure 17] It is an explanatory diagram of an example of a voltage conversion circuit used in place of a booster circuit.

Mode for Carrying Out the Invention

[0009] At least the following matters will become apparent from the description of the present specification and the accompanying drawings.

[0010] <<<About the Power Conversion Device>>>[ The power conversion device of the present embodiment is, for example, a relatively large-capacity auxiliary power supply device that supplies power to loads such as lighting and air conditioning of railway vehicles. In such a power conversion device, it is necessary to insulate the power input side (input side) from the power output side (output side), and an insulating transformer is used to ensure insulation. As the insulating transformer, a high-frequency insulating transformer is applied for the purpose of reduction in size and weight. Furthermore, conversion using a high-frequency insulating transformer requires converting an input into high-frequency alternating current. For this reason, a bridge circuit formed of switching elements converts a direct current voltage into a high-frequency alternating current, which is input to the high-frequency insulating transformer. A DC-DC converter, which rectifies and smoothes the alternating current output thereof by a rectifier circuit and a smoothing circuit and converts it back to direct current, is generally used.

[0011] Before describing the power conversion device of the present embodiment, a comparative example will first be described.

[0012] <<Comparative Example>> FIG. 1 is a circuit diagram showing a configuration of a power converter 1a of a comparative example.

[0013] The power converter 1a of the comparative example includes a booster circuit 10, a resonant DC-DC converter 200, a three-phase inverter 30, and an LC filter 40. Terminals Ta and Tb shown in the figure are input terminals for an input voltage, where terminal Ta is a high-voltage side input terminal and terminal Tb is a low-voltage side input terminal. In the case of a railway vehicle, terminal Ta is a pantograph and terminal Tb is a wheel (rail), and a DC input voltage of, for example, 750V is applied between terminal Ta and terminal Tb. Note that this input voltage is not constant and fluctuates in a range of 400V to 1000V.

[0014] ==Booster Circuit 10== The booster circuit 10 is a circuit that transforms (boosts) a fluctuating input voltage to a constant voltage. In addition, by performing the boosting, the current is reduced, so that loss and heat generation can be suppressed. The booster circuit 10 is a three-level boost chopper, which generates a three-level voltage based on the input voltage and applies the voltage to a first line 110, a second line 120, and a third line 130 respectively. The booster circuit 10 includes a coupled reactor 11, capacitors C1 and C2, diodes D1 and D2, switching elements Q1 and Q2, and a control circuit 15.

[0015] The capacitor C1 is connected between the first line 110 and the second line 120, and the capacitor C2 is connected between the second line 120 and the third line 130. That is, the capacitor C1 and the capacitor C2 are connected in series.

[0016] Further, the diode D1 and the switching element Q1 are connected in series between the first line 110 and the second line 120 (that is, they are provided in parallel with the capacitor C1). A connection point between the diode D1 and the switching element Q1 is connected to the terminal Ta via the coupled reactor 11.

[0017] Furthermore, diode D2 and switching element Q2 are connected in series between the second line 120 and the third line 130 (i.e., in parallel with capacitor C2). The connection point between diode D2 and switching element Q2 is connected to terminal Tb via coupling reactor 11.

[0018] The switching elements Q1 and Q2 and the diodes D1 and D2 are all rated for 1200V. Note that voltage rating refers to the rated voltage; for example, in the case of a MOSFET, the source-drain voltage must be kept within that range (1200V in this case). In other words, applying a voltage exceeding the voltage rating may damage the components.

[0019] The control circuit 15 monitors the voltages at the nodes of capacitors C1 and C2, and controls the switching of switching elements Q1 and Q2.

[0020] The operation of this boost circuit 10 (3-level boost chopper) is well known, so a detailed description will be omitted. For example, the control circuit 15 alternately turns switching elements Q1 and Q2 on and off according to the voltages of capacitors C1 and C2. This repeatedly stores and releases energy in the coupling reactor 11, controlling the voltages of capacitors C1 and C2 to Vout / 2, respectively, to perform a boost operation. Vout is the output voltage of the boost circuit 10 (the voltage between the first line 110 and the third line 130), and is a higher voltage than the input voltage.

[0021] For example, when boosting an input voltage of 750V (450~1000V) to obtain an output voltage Vout of 1100V, the voltage applied to the first line 110 will be Vout (1100V), the voltage applied to the second line 120 will be Vout / 2 (550V), and the voltage applied to the third line 130 will be 0V.

[0022] ==Resonant DC-DC Converter 200== The resonant DC-DC converter 200 is a circuit that isolates the output side from the input side. It also transforms the output of the boost circuit 10 (DC voltage 1100V) to a different DC voltage. The resonant DC-DC converter 200 is located downstream of the boost circuit 10 and includes a bridge circuit 210, a resonant isolation circuit 220, a rectifier circuit 230, a smoothing circuit 240, and a control circuit 250.

[0023] The bridge circuit 210 is a circuit for converting the output voltage (DC voltage 1100V) of the boost circuit 10 into an AC voltage, and is composed of switching elements Qa to Qd. Switching elements Qa and Qc are connected in series between the first line 110 and the third line 130, and switching elements Qb and Qd are connected in series between the first line 110 and the third line 130.

[0024] Furthermore, one end of the primary winding L21 of the isolation transformer 221, described later, is connected to the connection point between switching element Qa and switching element Qc via a resonant capacitor C6. In this embodiment, "connection" refers to a state in which components are directly or indirectly connected in a way that allows them to conduct electricity, and the state in which they are electrically connected via the resonant capacitor C6 as described above is also referred to as connection. Additionally, the other end of the primary winding L21 of the isolation transformer 221 is connected to the connection point between switching element Qb and switching element Qd.

[0025] Of the switching elements Qa to Qd that constitute the bridge circuit 210, switching elements Qa and Qb are high-side elements, and switching elements Qc and Qd are low-side elements.

[0026] The resonant isolation circuit 220 is a circuit that constitutes the isolation portion of the resonant DC-DC converter 200, and is composed of an isolation transformer 221 and a resonant capacitor C6.

[0027] The isolation transformer 221 has a primary winding L21 on the primary side that generates magnetic flux, and a secondary winding L22 on the secondary side that is insulated from the primary winding L21 and is excited by the magnetic flux generated in the primary winding L21. As described above, one end of the primary winding L21 of the isolation transformer 221 is connected to the bridge circuit 210 via a resonant capacitor C6. The leakage inductance of the isolation transformer 221 is used as the resonant inductance, and the resonant isolation circuit 220 constitutes a series resonant circuit in which the resonant capacitor C6 and the resonant inductance are connected in series.

[0028] The rectifier circuit 230 rectifies the voltage induced in the secondary winding L22 of the isolation transformer 221 and supplies it to the subsequent smoothing circuit 240 (capacitor Ca). The rectifier circuit 230 is a full-wave rectifier circuit composed of four diodes Da to Dd.

[0029] The smoothing circuit 240 is a circuit that smooths the output of the rectifier circuit 230 to convert it to DC, and in this case, it is composed of a capacitor Ca.

[0030] The control circuit 250 is a circuit that controls the on / off state of the switching elements Qa to Qd of the bridge circuit 210 with a predetermined duty cycle. This allows control of the current flowing through the primary winding L21 of the isolation transformer 221. For example, when switching elements Qa and Qd are turned on and switching elements Qb and Qc are turned off, current flows through the path of switching element Qa → resonant capacitor C6 → primary winding L21 of the isolation transformer 221 → switching element Qd (see the solid arrow in Figure 3).

[0031] On the other hand, when switching elements Qa and Qd are turned off and switching elements Qb and Qc are turned on, current flows through the path of switching element Qb → primary winding L21 of isolation transformer 221 → resonant capacitor C6 → switching element Qc (see dashed arrow in Figure 3). In this way, the control circuit 250 controls the on / off state of switching elements Qa to Qd of the bridge circuit 210, which induces a voltage in the secondary winding L22 of isolation transformer 221, and the rectifier circuit 230 and smoothing circuit 240 produce a constant DC voltage.

[0032] ==3-phase inverter 30== The three-phase inverter 30 is a circuit that converts the output of the resonant DC-DC converter 200 into three-phase AC power required for in-vehicle equipment (air conditioning, lighting, etc.). The three-phase inverter 30 is equipped with switching elements Q5a, Q5b, Q6a, Q6b, Q7a, Q7b and a control circuit 35.

[0033] Switching elements Q5a, Q5b, Q6a, Q6b, Q7a, and Q7b constitute a three-phase full-bridge circuit. Switching elements Q5a, Q6a, and Q7a are the high-side switching elements, while switching elements Q5b, Q6b, and Q7b are the low-side switching elements. Like switching elements Q1 and Q2, switching elements Q5a, Q5b, Q6a, Q6b, Q7a, and Q7b have a voltage rating of 1200V.

[0034] The control circuit 35 is a circuit that controls the on / off state of the switching elements Q5a, Q5b, Q6a, Q6b, Q7a, and Q7b of the three-phase inverter 30, respectively.

[0035] ==LC filter 40== The LC filter 40 is a filter that removes harmonics from the output of the three-phase inverter 30 and outputs an AC voltage.

[0036] With the above configuration, the fluctuating input voltage (for example, the overhead line voltage of 750V) is boosted to a higher, constant voltage (for example, 1100V) in the boost circuit 10. The output of the boost circuit 10 is converted to AC by the resonant DC-DC converter 200, and then further transformed (stepped down) to a DC voltage (for example, 700V). Finally, it is converted back to AC voltage by the three-phase inverter 30 and output.

[0037] In this comparative example, since the output of the boost circuit 10 is 1100V, if the switching elements Qa to Qd of the bridge circuit 210 of the resonant DC-DC converter 200 have the same voltage rating (1200V) as the other switching elements (switching element Q1, etc.), there is a risk of them being destroyed. For this reason, it is necessary to use high-voltage-rated elements (for example, with a voltage rating of 1700V) for the switching elements Qa to Qd of the bridge circuit 210.

[0038] However, as will be described later, using such high-voltage switching elements makes high-frequency operation (high-speed switching) difficult due to the slow turn-off response for small currents. Furthermore, even when using high-voltage switching elements, there is a risk of damage due to turn-off surges when switching the output (1100V) of the boost circuit 10 with those elements. In addition, high-voltage switching elements are expensive and costly. Therefore, in this embodiment, as will be described later, a configuration is adopted that does not require the use of high-voltage switching elements. This ensures stable operation.

[0039] =====Implementation Method 1===== <<Regarding the configuration of the power converter>> Figure 2 is a circuit diagram showing the configuration of the power converter 1b of the first embodiment. Parts identical to those in the comparative example in Figure 1 are denoted by the same reference numerals, and their descriptions are omitted. As shown in the figure, the configuration of the resonant DC-DC converter in this embodiment differs from that of the comparative example.

[0040] The power converter 1b of the first embodiment includes a boost circuit 10, a resonant DC-DC converter 20, a three-phase inverter 30, and an LC filter 40.

[0041] ==Boost circuit 10== The boost circuit 10 is a 3-level boost chopper, the same as in the comparative example, and generates three levels of voltage based on the input voltage (750V). It applies the highest voltage (e.g., 1100V) to the first line 110, an intermediate level voltage (e.g., 550V) to the second line 120, and the lowest voltage (e.g., 0V) to the third line 130. The boost circuit 10 corresponds to a "converter," the voltage applied to the first line 110 corresponds to the "first voltage," the voltage applied to the second line 120 corresponds to the "second voltage," and the voltage applied to the third line 130 corresponds to the "third voltage." Switching elements Q1 and Q2 each correspond to a "third switching element."

[0042] ==Resonant DC-DC Converter 20== The resonant DC-DC converter 20 includes bridge circuits 21A, 21B, a resonant isolation circuit 22, a rectifier circuit 23, and a smoothing circuit 24. The resonant isolation circuit 22, the rectifier circuit 23, and the smoothing circuit 24 correspond to the "voltage output circuit." Also, similar to the comparative example, the resonant DC-DC converter 20 is a step-down converter, and the DC voltage it generates (a predetermined voltage) is lower than the output voltage of the step-up circuit 10. For example, the output voltage of the step-up circuit 10 (the voltage between the first line 110 and the third line 130) is 1100V, and the DC voltage generated by the resonant DC-DC converter 20 is 700V.

[0043] The bridge circuit 21A is a full-bridge circuit including switching elements Q3a to Q3d, and is located between the first line 110 and the second line 120. In other words, the bridge circuit 21A is located in parallel with the capacitor C1 of the boost circuit 10. Note that the bridge circuit 21A corresponds to the "first bridge circuit," and each of the switching elements Q3a to Q3d corresponds to the "first switching element."

[0044] Furthermore, the bridge circuit 21B is a full-bridge circuit including switching elements Q4a to Q4d, and is located between the second line 120 and the third line 130. In other words, the bridge circuit 21B is located in parallel with the capacitor C2 of the boost circuit 10. Note that the bridge circuit 21B corresponds to the "second bridge circuit," and each of the switching elements Q4a to Q4d corresponds to the "second switching element."

[0045] The resonant isolation circuit 22 is a circuit that constitutes the isolation portion of the resonant DC-DC converter 20, and is composed of isolation transformers 22A and 22B, and resonant capacitors C3 and C4.

[0046] The isolation transformer 22A has a primary winding L31 on the primary side that generates magnetic flux, and a secondary winding L32 on the secondary side that is insulated from the primary winding L31 and is excited by the magnetic flux generated in the primary winding L31. The primary winding L31 of the isolation transformer 22A is connected to the bridge circuit 21A via a resonant capacitor C3. That is, the resonant capacitor C3 is connected between the bridge circuit 21A and the primary winding L31 of the isolation transformer 22A. The isolation transformer 22A corresponds to the "first isolation transformer," and the resonant capacitor C3 corresponds to the "first resonant capacitor."

[0047] The isolation transformer 22B has a primary winding L41 on the primary side that generates magnetic flux, and a secondary winding L42 on the secondary side that is insulated from the primary winding L41 and is excited by the magnetic flux generated in the primary winding L41. The primary winding L41 of the isolation transformer 22B is connected to the bridge circuit 21B via a resonant capacitor C4. That is, the resonant capacitor C4 is connected between the bridge circuit 21B and the primary winding L41 of the isolation transformer 22B. The isolation transformer 22B corresponds to the "second isolation transformer," and the resonant capacitor C4 corresponds to the "second resonant capacitor."

[0048] The rectifier circuit 23 includes a diode bridge circuit 23A and a diode bridge circuit 23B. Diode bridge circuit 23A is a full-wave rectifier circuit composed of diodes D3a to D3d, which rectifies the voltage induced in the secondary winding L32 of the isolation transformer 22A and supplies it to capacitor C5a, which will be described later. Diode bridge circuit 23B is a full-wave rectifier circuit composed of diodes D4a to D4d, which rectifies the voltage induced in the secondary winding L42 of the isolation transformer 22B and supplies it to capacitor C5b, which will be described later. Note that diode bridge circuit 23A corresponds to the "first diode bridge circuit," and diode bridge circuit 23B corresponds to the "second diode bridge circuit."

[0049] The smoothing circuit 24 is a circuit that smooths the output of the rectifier circuit 23 to generate a constant DC voltage (for example, 700V). In this embodiment, the smoothing circuit 24 is configured by connecting a capacitor C5a that smooths the output of the diode bridge circuit 23A and a capacitor C5b that smooths the output of the diode bridge circuit 23B in series. Note that capacitor C5a corresponds to the "first capacitor" and capacitor C5b corresponds to the "second capacitor".

[0050] Furthermore, the control circuit 25 of this embodiment controls the on / off states of the switching elements Q3a to Q3d of the bridge circuit 21A and the switching elements Q4a to Q4d of the bridge circuit 21B, respectively. Note that the control circuit 25 corresponds to the "control circuit".

[0051] Furthermore, the three-phase inverter 30 and the LC filter 40 have the same configuration as in the comparative example. Note that the three-phase inverter 30 corresponds to the "inverter," and each of the switching elements (Q5a, Q5b, Q6a, Q6b, Q7a, Q7b) of the three-phase inverter 30 corresponds to the "fourth switching element."

[0052] As described above, the power converter of this embodiment has a structure (two-series structure) in which two configurations similar to those of the comparative resonant DC-DC converter 200 are arranged in series on the output side of the boost circuit 10. By doing so, the switching elements (switching elements Q3a~Q3d, Q4a~Q4d) of the bridge circuits 21A and 21B can be switched with a lower voltage rating (for example, 1200V) than the switching elements Qa~Qd (withstand voltage 1700V) of the comparative example, and as will be described later, stable operation becomes possible.

[0053] <<Regarding effectiveness>> Figure 3 is a diagram illustrating the effectiveness of this embodiment. For the sake of explanation and simplification, here, a pair of switching elements (high-side and low-side) constituting the bridge circuit will be described as switching elements (1) and (2), respectively, as shown in the figure. In this embodiment, switching elements Q3a, Q3d, Q4a, and Q4d correspond to switching element (1), and switching elements Q3b, Q3c, Q4b, and Q4c correspond to switching element (2). In the comparative example, switching elements Qa and Qd correspond to switching element (1), and switching elements Qb and Qc correspond to switching element (2). Switching elements (1) and switching elements (2) each have a high-side and a low-side, but here, for example, the high-side will be described.

[0054] Furthermore, in the waveform diagram of Figure 3, the ON command represents the gate voltage of the switching element, where voltage indicates the source-drain voltage and current indicates the current flowing through the switching element. Also, in Figure 3, the thick line shows the waveform of the comparative example, and the thin line shows the waveform of this embodiment. In reality, the magnitudes of the voltages and currents of each element differ between the comparative example and this embodiment, but they are shown as having the same magnitude in the figure.

[0055] As shown in the figure, switching element (1) and switching element (2) are controlled to alternately turn on and off. When switching element (1) is turned on (switching element (2) is turned off), current flows in the direction indicated by the solid arrow in the figure. On the other hand, when switching element (2) is turned on (switching element (1) is turned off), current flows in the direction indicated by the dashed arrow in the figure. When each switching element is turned on, a sinusoidal current flows, determined by the capacitor and inductor (LC) of the resonant circuit. In addition, a predetermined "dead time" is provided so that switching element (1) and switching element (2) do not turn on at the same time. During this dead time, current flows through the parasitic diode (body diode) of the switching element or the diode connected in antiparallel.

[0056] During normal operation, the turn-off (switching from on to off) is performed when the current is low, as shown in the diagram, thereby minimizing turn-off losses.

[0057] In the comparative example, 1100V is applied to the bridge circuit, so a high-voltage switching element (e.g., with a voltage rating of 1700V) is used in the bridge circuit. As a result, when trying to turn off a small current with such a high-voltage switching element, it takes time, as shown by the thick line in Figure 3.

[0058] In contrast, in this embodiment, bridge circuit 21A and bridge circuit 21B are arranged in series. Therefore, the voltage applied to each of the bridge circuits 21A and 21B is 550V, which is smaller than in the comparative example. Accordingly, switching elements (1) and (2) (specifically, switching elements Q3a to Q3d, Q4a to Q4d) can be used with a lower voltage rating (for example, a voltage rating of 1200V) than in the comparative example. Since low-voltage elements have smaller size and parasitic capacitance than high-voltage elements, the time required for interruption during turn-off can be shortened. Also, since the voltage between each line (between the first line 110 and the second line 120, and between the second line 120 and the third line 130) is 550V, there is a margin of safety in the voltage rating of each switching element.

[0059] Thus, a rapid power cut-off reduces dead time, leading to lower losses and improved operational stability. In other words, it allows for stable operation.

[0060] Figure 4 shows the case where a turn-off surge occurs. Here, the pair of switching elements (high-side and low-side) that make up the bridge circuit will be described as switching elements (1) and (2), respectively, as shown in the figure. The figure shows the relationship between the ON command (gate voltage), voltage (source-drain voltage), and current for switching element (1), and the same relationship applies to switching element (2).

[0061] When switching elements (1) and (2) are stopped, they do not necessarily stop at a time when the current is small. For example, if they stop when the current is large, such as during an emergency stop, a large turn-off surge (surge voltage) will occur between the source and drain, as shown in Figure 4.

[0062] In the comparative example, if the output of the boost circuit 10 is 1100V, even if a high-voltage (1700V) switching element is used, the element may be destroyed by the surge voltage. To prevent the surge voltage from exceeding the voltage rating of the switching element, the bus voltage needs to be lowered. If the bus voltage is low, it is difficult to keep the input voltage constant in the boost circuit 10.

[0063] In contrast, this embodiment uses a series configuration of bridge circuits with elements having a voltage rating of 1200V. The voltage between the lines is 550V, and as long as the surge voltage does not exceed the voltage rating of the switching element (1200V), there is margin in the operation of the boost circuit 10. For example, there is margin even if the boost voltage of the boost circuit 10 is increased to a voltage higher than 1100V. By increasing the voltage boost of the boost circuit 10, conduction losses can be reduced.

[0064] Furthermore, elements with a voltage rating of 1200V are cheaper than elements with a voltage rating of 1700V, and can also be used with the same voltage rating as the switching elements in other parts (boost circuit 10, 3-phase inverter 30). Specifically, switching elements Q1, Q2, Q3a~Q3d, Q4a~Q4d, Q5a, Q5b, Q6a, Q6b, Q7a, and Q7b have the same voltage rating. Here, "same" voltage rating includes acceptable differences due to manufacturing variations, etc. In other words, they do not have to be exactly the same, but can be approximately the same. This approach does not increase the number of element types, which is also effective in terms of management and procurement.

[0065] Furthermore, it is desirable that each switching element (at least switching elements Q3a to Q3d and switching elements Q4a to Q4) used in the power conversion device of this embodiment be formed from a wide-bandgap semiconductor. Examples of wide-bandgap semiconductors include silicon carbide (SiC) semiconductors and gallium nitride (GaN) semiconductors. Using such wide-bandgap semiconductors allows for the fabrication of high-voltage elements with low on-resistance. It also enables faster switching speeds and reduced switching losses. However, the wide-bandgap semiconductor is not limited; for example, semiconductors such as IGBTs (Insulated Gate Bipolar Transistors) or Si-based MOSFETs may also be used.

[0066] Furthermore, in this embodiment, two switching elements connected in series are housed (modularized) in a predetermined package. Figure 5 is an explanatory diagram of the package housing. As shown in Figure 5, the set of Q3a on the high side and Q3c on the low side (a set of two switching elements) is housed in package P1. Although not shown, the switching elements Q3b and Q3d, Q4a and Q4c, Q4b and Q4d, Q5a and Q5b, Q6a and Q6b, and Q7a and Q7b are also housed in packages similar to package P1. Since each of these switching elements has the same voltage rating, procurement and management are simplified.

[0067] Furthermore, diodes D1 and D2 of the boost circuit 10 may each be configured as switching elements. In this case, the functions of diodes D1 and D2 can be realized by turning off the switching elements and using the parasitic diodes (body diodes) of those switching elements or diodes connected in antiparallel. In this case as well, sourcing and management can be further simplified by housing the two series-connected switching elements of the boost circuit 10 (switching element Q1 and the switching element corresponding to diode D1, and switching element Q2 and the switching element corresponding to diode D2) in predetermined packages.

[0068] <<Variations of the first implementation form>> Figure 6 is an explanatory diagram of a modified example of the first embodiment. Figure 6 shows a part of the input side of the power converter, and parts with the same configuration as in Figure 2 are denoted by the same reference numerals and their descriptions are omitted. In the first embodiment described above, the bridge circuits 21A and 21B were full bridges, whereas in this modified example, they are composed of half bridges of switching elements Q3e and Q3f, and switching elements Q4e and Q4f. In this case, the capacitors of the boost circuit 10 can be arranged in series of four (four capacitors C1a, C1b, C2a, and C2b in series). The same effect can be obtained in this modified example as well.

[0069] Furthermore, in the first embodiment, the diode bridge circuits 23A and 23B of the rectifier circuit 23 were full-wave rectifier circuits, but the invention is not limited to this and may be configured as half-wave rectifier circuits.

[0070] =====Second Embodiment===== In the second embodiment, the configuration of the output side (rectifier circuit, smoothing circuit) of the resonant DC-DC converter 20 differs from that of the first embodiment.

[0071] Figure 7 is a circuit diagram and waveform diagram showing part of the configuration of the power converter 1c of the second embodiment, and Figures 8A to 8D are explanatory diagrams of the rectification operation in the second embodiment. Note that the waveform in Figure 7 schematically shows the operation, and the transient state of the switching element current when switching from on to off as shown in Figure 3 is omitted. Similarly, in the diagrams describing other embodiments thereafter, the transient state when switching between on and off will be omitted.

[0072] In Figure 7, for the sake of explanation, the switching elements of bridge circuits 21A and 21B are denoted as switching elements (1), (2), (3), and (4), and the diodes constituting the output diode bridge circuit are denoted as diodes (5), (6), (7), and (8). Specifically, switching elements Q3a and Q3d of bridge circuit 21A correspond to switching element (1), and switching elements Q3b and Q3c correspond to switching element (2). Also, switching elements Q4a and Q4d of bridge circuit 21B correspond to switching element (3), and switching elements Q4b and Q4c correspond to switching element (4). Furthermore, diodes D3a and D3d of diode bridge circuit 23A correspond to diode (5), and diodes D3b and D3c correspond to diode (6). Also, diodes D4a and D4d of diode bridge circuit 23B correspond to diode (7), and diodes D4b and D4c correspond to diode (8). Diodes (5), (6), (7), and (8) are each provided in pairs, forming a full-wave rectifier diode bridge circuit.

[0073] As shown in Figure 7, the power converter 1c of the second embodiment has a rectifier circuit 231 and a smoothing circuit 241.

[0074] The smoothing circuit 241 of the second embodiment is composed of one capacitor (capacitor C5).

[0075] The rectifier circuit 231 has a diode bridge circuit composed of two diodes (5) and two diodes (6), and a diode bridge circuit composed of two diodes (7) and two diodes (8), and these diode bridge circuits are provided in parallel with capacitor C5.

[0076] The diode bridge circuit, consisting of two diodes (5) and two diodes (6), is a circuit (full-wave rectifier circuit) that rectifies the voltage induced in the secondary winding L32 of the isolation transformer 22A and supplies it to capacitor C5, and corresponds to the "first diode bridge circuit".

[0077] Furthermore, the diode bridge circuit, composed of two diodes (7) and two diodes (8), is a circuit (full-wave rectifier circuit) that rectifies the voltage induced in the secondary winding L42 of the isolation transformer 22B and supplies it to capacitor C5, and corresponds to the "second diode bridge circuit".

[0078] When switching elements (1) and (2) are switched alternately, current flows alternately through diodes (5) and (6), as shown in Figures 8A and 8B, charging capacitor C5. Specifically, when switching element (1) is on and switching element (2) is off, current flows through diode (5), as shown in Figure 8A (and Figure 7). Also, when switching element (2) is on and switching element (1) is off, current flows through diode (6), as shown in Figure 8B (and Figure 7).

[0079] Similarly, when switching elements (3) and (4) are switched alternately, current flows alternately through diodes (7) and (8), charging capacitor C5, as shown in Figures 8C and 8D. Specifically, when switching element (3) is on and switching element (4) is off, current flows through diode (7), as shown in Figure 8C. Also, when switching element (2) is on and switching element (1) is off, current flows through diode (8), as shown in Figure 8D.

[0080] When the ON command timings of switching elements (1) and (3), and switching elements (2) and (4) coincide, current flows through diodes (5) and (7), and diodes (6) and (8) at the same time. On the other hand, when the ON command timings of switching elements (1) and (3), and switching elements (2) and (4) differ, the conduction timing (the timing of the current flow) of diodes (5) and (7), and diodes (6) and (8) will be staggered.

[0081] However, since the current paths are separated by diodes (5) and (7), and by diodes (6) and (8) (capacitor C5 is charged in each), the timing of conduction may be different. To average the current flowing to capacitor C5 by shifting the timing of the currents in diodes (5) and (7), and diodes (6) and (8), it is best to have a 90° phase difference between diodes (5) and (7) (and diodes (6) and (8)). In other words, it is best to have a 90° difference in the ON commands of switching elements (1) and (3), and switching elements (2) and (4).

[0082] Furthermore, since this example uses full-wave rectification, the current flowing through each of the diodes (5) to (8) is small.

[0083] Thus, in the second embodiment, a full-wave rectifier diode bridge circuit is provided in parallel. In this case as well, the same effects as in the first embodiment can be obtained.

[0084] =====Third Embodiment===== Figure 9 is a circuit diagram and waveform diagram showing part of the configuration of the power converter 1d of the third embodiment. Figures 10A to 10D are explanatory diagrams of the rectification operation in the third embodiment. In the third embodiment, a configuration is used in which half-wave rectification diode bridge circuits are provided in parallel.

[0085] In Figure 9, for the sake of explanation, the switching elements of the bridge circuits 21A and 21B are designated as switching elements (1), (2), (3), and (4) as in Figure 3, and the diodes constituting the output diode bridge are designated as diodes (5), (6), (7), and (8). Switching elements (1), (2), (3), and (4) are the same as in the second embodiment. In the third embodiment, diode D3a corresponds to diode (5), and diode D3c corresponds to diode (6). Also, diode D4a corresponds to diode (7), and diode D4c corresponds to diode (8). Furthermore, in the third embodiment, the same smoothing circuit 24 (series-connected capacitors C5a and C5b) as in the first embodiment is used. Note that capacitors C5a and C5b each correspond to "capacitor".

[0086] The rectifier circuit 232 of the third embodiment is provided with one diode each of (5), (6), (7), and (8), and these diodes constitute a diode bridge circuit (half-wave rectifier circuit).

[0087] In the rectifier circuit 232, the diode bridge circuit including diode (5) is a circuit that rectifies the voltage induced in the secondary winding L32 of the isolation transformer 22A and supplies it to capacitor C5a, and corresponds to the "first diode bridge circuit". Also, the diode bridge circuit including diode (7) is a circuit that rectifies the voltage induced in the secondary winding L42 of the isolation transformer 22B and supplies it to capacitor C5a, and corresponds to the "second diode bridge circuit".

[0088] Furthermore, the diode bridge circuit including diode (6) is a circuit that rectifies the voltage induced in the secondary winding L32 of the isolation transformer 22A and supplies it to capacitor C5b, and corresponds to the "first diode bridge circuit". Also, the diode bridge circuit including diode (8) is a circuit that rectifies the voltage induced in the secondary winding L42 of the isolation transformer 22B and supplies it to capacitor C5b, and corresponds to the "second diode bridge circuit".

[0089] When switching elements (1) and (2) are switched alternately, current flows alternately through diodes (5) and (6), as shown in Figures 10A and 10B. Specifically, when switching element (1) is on and switching element (2) is off, current flows through diode (5) and charges capacitor C5a, as shown in Figure 10A (and Figure 9). When switching element (2) is on and switching element (1) is off, current flows through diode (6) and charges capacitor C5b, as shown in Figure 10B (and Figure 9).

[0090] Similarly, when switching elements (3) and (4) are switched alternately, current flows alternately through diodes (7) and (8), as shown in Figures 10C and 10D. Specifically, when switching element (3) is on and switching element (4) is off, current flows through diode (7) and charges capacitor C5a, as shown in Figure 10C. When switching element (4) is on and switching element (3) is off, current flows through diode (8) and charges capacitor C5b, as shown in Figure 10D.

[0091] When the timing of the commands for switching elements (1) and (3), and (2) and (4) are almost identical, the current flowing through diodes (5) and (6) in conjunction with the driving of switching elements (1) and (2), and the current flowing through diodes (7) and (8) in conjunction with the driving of switching elements (3) and (4) will be at almost the same timing. When the timing of the commands for switching elements (1) and (3), and (2) and (4) are different, the timing of the conduction of diodes (5) and (7), and diodes (6) and (8) will be different.

[0092] However, since the flow paths are separated by diodes (5) and (7), and (6) and (8), the timings may be different.

[0093] Furthermore, in order to average the current flowing through each capacitor (capacitors C5a, C5b) by shifting the timing of the currents in diodes (5) and (7), and diodes (6) and (8), it is best to have a phase difference of 180° between diodes (5) and (7) (and between diodes (6) and (8)). In other words, it is best to have a phase difference of 180° between the ON commands of switching elements (1) and (3), and between switching elements (2) and (4).

[0094] In this third embodiment, the rectifier circuit 232 has fewer diodes than the second embodiment because the diode bridge circuit is composed of a half-wave rectifier circuit. Therefore, although the current flowing through each diode is larger, the number of components (number of packages) can be reduced.

[0095] <<Variations of the third implementation form>> Figure 11 is an explanatory diagram of a modified example of the third embodiment. Here, only the corresponding parts are shown. In this modified example, the rectifier circuit 233 has two diode bridges of diodes (5) to (8) in parallel. In this modified example as well, diode D3a corresponds to diode (5), and diode D3c corresponds to diode (6). Also, diode D4a corresponds to diode (7), and diode D4c corresponds to diode (8). In this case, the number of diodes is doubled compared to the third embodiment (Figure 9), but the current flowing through each diode can be reduced.

[0096] =====Fourth Embodiment===== Figure 12 shows a circuit diagram and waveform diagram illustrating a portion of the configuration of the power converter 1e according to the fourth embodiment.

[0097] In Figure 12, the switching elements of the bridge circuits 21A and 21B are designated as switching elements (1), (2), (3), and (4) as in Figure 3, and the diodes constituting the output diode bridge are designated as diodes (5) and (6). Switching elements (1), (2), (3), and (4) are the same as in the second embodiment. In the fourth embodiment, diodes D3a, D3d and diodes D4a, D4d correspond to diode (5), and diodes D3b, D3c and diodes D4b, D4c correspond to diode (6).

[0098] The power converter 1e of the fourth embodiment includes a rectifier circuit 234 and a smoothing circuit 241.

[0099] The smoothing circuit 241 is the same as in the second embodiment and includes a capacitor C5. Note that capacitor C5 corresponds to "capacitor".

[0100] The rectifier circuit 234 has two diodes (5) and two diodes (6), and these four diodes form a diode bridge circuit (full-wave rectifier circuit). In addition, the secondary winding L32 of isolation transformer 22A and the secondary winding L42 of isolation transformer 22B are commonly connected to this diode bridge circuit. This diode bridge circuit corresponds to a "diode bridge circuit" that rectifies the voltage induced in the secondary winding L32 of isolation transformer 22A and the secondary winding L42 of isolation transformer 22B.

[0101] When switching elements (1) and (2) are switched alternately, current flows alternately through diodes (5) and (6), charging capacitor C5. Specifically, when switching element (1) is turned on (switching element (2) is turned off), current flows through diode (5), and when switching element (2) is turned on (switching element (1) is turned off), current flows through diode (6).

[0102] Furthermore, when switching elements (3) and (4) are switched alternately, current flows alternately through diodes (5) and (6), charging capacitor C5. Specifically, when switching element (3) is turned on (switching element (4) is turned off), current flows through diode (5), and when switching element (4) is turned on (switching element (3) is turned off), current flows through diode (6).

[0103] When the ON command timings of switching elements (1) and (3), and (2) and (4) are nearly identical (phase difference of 0°), the timing at which current flows through diode (5) in conjunction with the driving of switching elements (1) and (3) will be nearly the same. Similarly, the timing at which current flows through diode (6) in conjunction with the driving of switching elements (2) and (4) will be nearly the same. In other words, diode (5) and diode (6) will not conduct simultaneously. If the ON command timing difference between switching elements (1) and (3), and (2) and (4) is large, and current attempts to flow through diode (5) and (6) simultaneously, a short circuit will occur and the condition will not be met.

[0104] Therefore, in the fourth embodiment, switching elements (1) and (3), and (2) and (4) are switched so that they turn on at the same timing. In other words, the control circuit 25 of the fourth embodiment controls the switching of each switching element in bridge circuits 21A and 21B so that the voltages applied to the primary windings (L31, L41) of isolation transformers 22A and 22B are in phase.

[0105] In the fourth embodiment, the diode bridge circuit composed of diodes (5) and (6) is a full-wave rectifier circuit. However, since the current based on the driving of switching elements (1) and (3) and the current based on the driving of switching elements (2) and (4) overlap, the current flowing through one diode is larger than in the second embodiment (Figure 7). However, the number of elements can be reduced compared to the second embodiment.

[0106] <<Variations of the 4th Implementation Form>> Figure 13 is an explanatory diagram of a modified example of the fourth embodiment. Here, only the corresponding parts are shown. In the rectifier circuit 235 of this modified example, two diode bridge combinations of diodes (5) and (6) are provided in parallel. In this modified example as well, diodes D3a, D3d and diodes D4a, D4d correspond to diode (5), and diodes D3b, D3c and diodes D4b, D4c correspond to diode (6). In this modified example, the current flowing through one diode can be reduced compared to the fourth embodiment.

[0107] =====Fifth Embodiment===== Figure 14 shows a circuit diagram and waveform diagram of part of the configuration of the power converter 1f of the fifth embodiment. This fifth embodiment differs from the fourth embodiment in that the diode bridge circuit is configured as a half-wave rectifier circuit.

[0108] In Figure 14, the switching elements of the bridge circuits 21A and 21B are designated as switching elements (1), (2), (3), and (4) as in Figure 3, and the diodes constituting the output diode bridge are designated as diodes (5) and (6). Switching elements (1), (2), (3), and (4) are the same as in the second embodiment. In the fifth embodiment, diodes D3a and D4a correspond to diode (5), and diodes D3c and D4c correspond to diode (6).

[0109] In the fifth embodiment, a rectifier circuit 236 and a smoothing circuit 24 are provided.

[0110] The smoothing circuit 24 is the same as in the first and third embodiments and consists of capacitors C5a and C5b connected in series. Capacitor C5a corresponds to the "first capacitor," and capacitor C5b corresponds to the "second capacitor."

[0111] The rectifier circuit 236 is equipped with one diode (5) and one diode (6). Diodes (5) and (6) are connected in series, and are also connected in parallel with capacitors C5a and C5b, which are connected in series. One end of the secondary winding L32 of isolation transformer 22A and one end of the secondary winding L42 of isolation transformer 22B are connected to the connection point of diodes (5) and (6). The other end of the secondary winding L32 of isolation transformer 22A and the other end of the secondary winding L42 of isolation transformer 22B are connected to the connection point of capacitors C5a and C5b.

[0112] The diode bridge circuit, composed of diodes (5), rectifies the voltages induced in the secondary winding L32 of isolation transformer 22A and the secondary winding L42 of isolation transformer 22B, and supplies them to capacitor C5a. In other words, this diode bridge circuit corresponds to the "first diode bridge circuit".

[0113] Furthermore, the diode bridge circuit, composed of diodes (6), rectifies the voltages induced in the secondary winding L32 of isolation transformer 22A and the secondary winding L42 of isolation transformer 22B and supplies them to capacitor C5b. In other words, this diode bridge circuit corresponds to the "second diode bridge circuit".

[0114] When switching elements (1) and (2) are switched alternately, current flows alternately through diodes (5) and (6), charging capacitors C5a and C5b respectively. Specifically, when switching element (1) is turned on (switching element (2) is turned off), current flows through diode (5) and charges capacitor C5a, and when switching element (2) is turned on (switching element (1) is turned off), current flows through diode (6) and charges capacitor C5b.

[0115] Furthermore, when switching elements (3) and (4) are switched alternately, current flows alternately through diodes (5) and (6), charging capacitors C5a and C5b respectively. Specifically, when switching element (3) is turned on (switching element (4) is turned off), current flows through diode (5) and charges capacitor C5a, and when switching element (4) is turned on (switching element (3) is turned off), current flows through diode (6) and charges capacitor C5b.

[0116] When the ON command timings of switching elements (1) and (3), and (2) and (4) are nearly identical (phase difference of 0°), the timing at which current flows through diode (5) in conjunction with the driving of switching elements (1) and (3) will be nearly the same. Similarly, the timing at which current flows through diode (6) in conjunction with the driving of switching elements (2) and (4) will be nearly the same. In other words, diode (5) and diode (6) will not conduct simultaneously. If the ON command timing difference between switching elements (1) and (3), and (2) and (4) is large, and current attempts to flow through diode (5) and (6) simultaneously, a short circuit will occur and the condition will not be met.

[0117] Therefore, in the fifth embodiment as in the fourth embodiment, switching elements (1) and (3), and (2) and (4) are switched on at the same timing. In other words, the control circuit 25 controls the switching of each switching element in bridge circuits 21A and 21B so that the voltages applied to the primary windings (L31, L41) of isolation transformers 22A and 22B are in phase.

[0118] In the fifth embodiment, the current based on the driving of switching elements (1) and (3) and the current based on the driving of switching elements (2) and (4) overlap, so the current flowing through one diode is larger compared to the third embodiment (half-wave rectifier circuit), but the number of elements (diodes) can be reduced compared to the third embodiment.

[0119] <<Variations of the Fifth Implementation Form>> Figure 15 is an explanatory diagram of a modified example of the fifth embodiment. Here, only the corresponding parts are shown. In the rectifier circuit 237 of this modified example, four diode bridge combinations of diodes (5) and (6) are provided in parallel. In this modified example as well, diodes D3a and D4a correspond to diode (5), and diodes D3c and D4c correspond to diode (6). In this modified example, the current flowing through each element can be reduced and the loss per element can be reduced compared to the fifth embodiment. In Figure 15, the current and loss per element are approximately the same as in the embodiments shown in Figures 7, 8, 11, and 13.

[0120] =====Sixth Implementation Method===== Figures 16A to 16F are explanatory diagrams of the sixth embodiment. In the sixth embodiment, the diodes constituting the diode bridge circuit are connected in reverse series.

[0121] Figures 16A and 16B show an example of a diode bridge circuit containing diodes in reverse series arranged in series. Here, a smoothing circuit 24 (capacitors C5a and C5b) is used as the smoothing circuit. Also, as in the embodiment described above, the diodes that make up the output side diode bridge are diodes (5), (6), (7), and (8). Note that diodes D3a and D3d correspond to diode (5), diodes D3b and D3c correspond to diode (6), diodes D4a and D4d correspond to diode (7), and diodes D4b and D4c correspond to diode (8).

[0122] For example, in Figure 16A, the anode of diode (5) is connected to one end of the secondary winding L32 of isolation transformer 22A, and the anode of diode (6) is connected to the other end of the secondary winding L32. The cathodes of diode (5) and diode (6) are connected to each other and also to one end of capacitor C5a. In addition, the midpoint of the secondary winding L32 of isolation transformer 22A is connected to the other end of capacitor C5a.

[0123] Furthermore, the anode of diode (7) is connected to one end of the secondary winding L42 of the isolation transformer 22B, and the anode of diode (8) is connected to the other end of the secondary winding L42. The cathodes of diode (7) and diode (8) are connected to each other and also to one end of capacitor C5b. Additionally, the midpoint of the secondary winding L42 of the isolation transformer 22B is connected to the other end of capacitor C5b.

[0124] Note that in Figure 16B, the polarity of each diode (anode and cathode) and the connection relationships to capacitors C5a and C5b are reversed compared to Figure 16A.

[0125] Figures 16C and 16D show an example of a diode bridge circuit containing diodes in reverse series arranged in parallel. In this example, a smoothing circuit 241 (capacitor C5) is used as the smoothing circuit. The diodes constituting the diode bridge are denoted as diodes (5), (6), (7), and (8). Note that diodes D3a and D3d correspond to diode (5), diodes D3b and D3c correspond to diode (6), diodes D4a and D4d correspond to diode (7), and diodes D4b and D4c correspond to diode (8).

[0126] For example, in Figure 16C, the anode of diode (5) is connected to one end of the secondary winding L32 of isolation transformer 22A, and the anode of diode (6) is connected to the other end of the secondary winding L32. The cathodes of diode (5) and diode (6) are connected to each other and also connected to one end of capacitor C5.

[0127] Furthermore, the anode of diode (7) is connected to one end of the secondary winding L42 of isolation transformer 22B, and the anode of diode (8) is connected to the other end of the secondary winding L42. The cathodes of diode (7) and diode (8) are connected to each other and also connected to one end of capacitor C5.

[0128] Furthermore, the midpoint of the secondary winding L32 of isolation transformer 22A and the midpoint of the secondary winding L42 of isolation transformer 22B are connected to the other end of capacitor C5.

[0129] Note that in Figure 16D, the polarity (anode and cathode) of each diode and the connection relationship to capacitor C5 are reversed compared to Figure 16C.

[0130] Figures 16E and 16F show an example of a diode bridge containing diodes in reverse series being shared in parallel. In this example as well, the smoothing circuit 241 (capacitor C5) is used as the smoothing circuit. The diodes constituting the diode bridge are denoted as diodes (5) and (6). Note that diodes D3a, D3d, D4a, and D4d correspond to diode (5), and diodes D3b, D3c, D4b, and D4c correspond to diode (6).

[0131] For example, in Figure 16E, the anode of diode (5) is connected to one end of the secondary winding L32 of isolation transformer 22A and one end of the secondary winding L42 of isolation transformer 22B, while the anode of diode (6) is connected to the other end of the secondary winding L32 of isolation transformer 22A and the other end of the secondary winding L42 of isolation transformer 22B. In addition, the cathodes of diode (5) and diode (6) are connected to each other and also to one end of capacitor C5, and the midpoint of the secondary winding L32 of isolation transformer 22A and the midpoint of the secondary winding L42 of isolation transformer 22B are connected to the other end of capacitor C5.

[0132] Note that in Figure 16F, the polarity of each diode (anode and cathode) and the connection relationship to capacitor C5 are reversed compared to Figure 16E.

[0133] Thus, in the sixth embodiment, the diodes constituting the diode bridge are connected in reverse series. This makes it possible to reduce the number of elements (diodes) and modules compared to the previously described embodiments.

[0134] =====Summary===== The above describes a power conversion device, which is one embodiment of the present invention. The power converter of this embodiment includes a boost circuit 10 (3-level boost chopper) that applies three levels of voltage to the first line 110 to the third line 130 based on the input voltage. It also includes a bridge circuit 21A provided between the first line 110 and the second line 120 and including switching elements Q3a to Q3d, a bridge circuit 21B provided between the second line 120 and the third line 130 and including switching elements Q4a to Q4d, and a voltage output circuit (resonant isolation circuit 22, rectifier circuit 23, smoothing circuit 24) that generates a predetermined DC voltage based on the operation of bridge circuits 21A and 21B. As a result, compared to the comparative example, switching elements Q3a to Q3d and Q4a to Q4d can be used with lower voltage ratings, and stable operation can be achieved.

[0135] Furthermore, the voltage output circuit includes an isolation transformer 22A with a primary winding L31 connected to the bridge circuit 21A, an isolation transformer 22B with a primary winding L41 connected to the bridge circuit 21B, a rectifier circuit 23 that rectifies the voltage induced in the isolation transformers 22A and 22B, and a smoothing circuit 24 that smooths the output of the rectifier circuit 23 to generate a predetermined DC voltage. This allows for power conversion based on the operation of the bridge circuits 21A and 21B while providing isolation between the input and output sides.

[0136] Furthermore, a resonant capacitor C3 is connected between the bridge circuit 21A and the primary winding L31 of the isolation transformer 22A, and a resonant capacitor C4 is connected between the bridge circuit 21B and the primary winding L41 of the isolation transformer 22B. This allows for the formation of a resonant circuit, thereby reducing switching losses.

[0137] Furthermore, in the first embodiment (Figure 2), the smoothing circuit 24 has capacitors C5a and C5b connected in series, and the rectifier circuit 23 has a diode bridge circuit 23A that rectifies the voltage induced in the secondary winding L32 of the isolation transformer 22A and supplies it to capacitor C5a, and a diode bridge circuit 23B that rectifies the voltage induced in the secondary winding L42 of the isolation transformer 22B and supplies it to capacitor C5b. This allows rectification to be performed with a series configuration of diode bridge circuits.

[0138] Furthermore, in the second embodiment (Figure 7), the smoothing circuit 241 has a capacitor C5, and the rectifier circuit 231 has a diode bridge circuit (a circuit composed of diodes (5) and (6)) that rectifies the voltage induced in the secondary winding L32 of the isolation transformer 22A and supplies it to the capacitor C5, and a diode bridge circuit (a circuit composed of diodes (7) and (8)) that rectifies the voltage induced in the secondary winding L42 of the isolation transformer 22B and supplies it to the capacitor C5. This allows rectification to be performed with a parallel configuration of diode bridge circuits.

[0139] Each of the diode bridge circuits described above may also be a full-wave rectifier circuit. In this case, the current flowing through each element (diode) can be reduced.

[0140] Furthermore, each diode bridge circuit may also be a half-wave rectifier circuit. In this case, the number of components can be reduced.

[0141] Furthermore, in the fourth embodiment (Figure 12), the smoothing circuit 241 has a capacitor C5, and the rectifier circuit 234 has a diode bridge circuit (diodes (5) to (8)) that rectifies the voltages induced in the secondary windings (L32, L42) of the isolation transformers 22A and 22B respectively and supplies them to the capacitor C5. This reduces the number of components.

[0142] Furthermore, in the fifth embodiment (Figure 14), the smoothing circuit 24 has capacitors C5a and C5b connected in series, and the rectifier circuit 236 has a diode bridge circuit (diode (5)) that rectifies the voltages induced in the secondary windings (L32, L42) of the isolation transformers 22A and 22B respectively and supplies them to capacitor C5a, and a diode bridge circuit (diode (6)) that rectifies the voltages induced in the secondary windings (L32, L42) of the isolation transformers 22A and 22B respectively and supplies them to capacitor C5b. This further reduces the number of elements.

[0143] Furthermore, in the fourth and fifth embodiments, the control circuit 25 controls the switching of each switching element in the bridge circuits 21A and 21B so that the voltages applied to the primary windings (L31 and L41) of the isolation transformers 22A and 22B are in phase. This ensures reliable rectification.

[0144] Furthermore, the voltage output circuit (resonant isolation circuit 22, rectifier circuit 23, smoothing circuit 24) is a step-down converter, and the voltage between the first line 110 and the third line 130 is higher than the output voltage of the voltage output circuit. This allows the output voltage of the boost circuit 10 to be increased and conduction losses to be reduced.

[0145] Furthermore, the boost circuit 10 includes switching elements Q1 and Q2, and the withstand voltage of switching elements Q3a to Q3d and switching elements Q4a to Q4d is the same as the withstand voltage of switching elements Q1 and Q2. This reduces the number of types of elements used.

[0146] Furthermore, the breakdown voltage of the switching elements Q5a, Q5b, Q6a, Q6b, Q7a, and Q7b of the three-phase inverter 30, which converts the output voltage of the voltage output circuit to AC voltage, is the same as that of the switching elements Q1, Q2, Q3a~Q3d, and Q4a~Q4d. This further reduces the number of types of elements used.

[0147] Furthermore, the diodes D1 and D2 of the boost circuit 10 can also be composed of switching elements. In that case, the switching elements of the boost circuit 10, the bridge circuits 21A and 21B, and the three-phase inverter 30 each include two switching elements connected in series, and it is desirable that these two switching elements be housed in a predetermined package. This simplifies procurement and management.

[0148] Furthermore, it is desirable that at least the switching elements of the bridge circuits 21A and 21B be made of wide-bandgap semiconductors such as SiC. This makes it possible to create high-voltage elements with low on-resistance. In addition, the switching speed can be increased and switching losses can be reduced.

[0149] The embodiments described above are provided to facilitate understanding of the present invention and are not intended to limit its interpretation. Furthermore, the present invention may be modified or improved without departing from its spirit, and it goes without saying that equivalents thereof are included.

[0150] For example, although the above-described embodiment described an application to a railway vehicle, the power conversion device of the present invention is not limited to railway vehicles and can be suitably used in systems with large voltage fluctuations on the input side (for example, wind power and solar power conditioner systems).

[0151] Furthermore, although the above embodiment described a resonant DC-DC converter using a series resonant circuit as the "power output circuit," it is not limited to this. For example, a parallel resonant converter, an inverter rectifier, or other isolation converters may also be used.

[0152] Furthermore, although the boost circuit 10 in the above-described embodiment was a 3-level boost chopper, it is not limited to this. For example, it may be a 2-level or 4-level or higher converter. Also, depending on the input voltage, it may be a buck circuit.

[0153] Figure 17 is an explanatory diagram of an example of a voltage conversion circuit used as an alternative to a boost circuit. In Figure 17, parts identical to those in Figures 1 and 2 are denoted by the same reference numerals and their descriptions are omitted. The voltage conversion circuit 10A shown in Figure 17 comprises a coupling reactor 11, a switching element Q1, a diode D1, capacitors C1 and C2, and resistors R1 and R2. Note that the switching element Q1 of the voltage conversion circuit 10A is connected to the third line 130 and not to the second line 120.

[0154] The coupling reactor 11, switching element Q1, and diode D1 generate two levels of voltage based on the input voltage, applying the higher voltage to the first line 110 and the lower voltage to the third line 130. In other words, the coupling reactor 11, switching element Q1, and diode D1 correspond to a two-level "converter".

[0155] Furthermore, resistor R1 is provided in parallel with capacitor C1 between the first line 110 and the second line 120, and resistor R2 is provided in parallel with capacitor C2 between the second line 120 and the third line 130. Resistors R1, R2 and capacitors C1, C2 generate a voltage (e.g., an intermediate voltage) by dividing the voltage of the first line 110 and the voltage of the third line 130 (the output of the "converter") and apply it to the second line 120. In other words, resistors R1, R2 and capacitors C1, C2 correspond to a "voltage divider circuit". Note that resistors R1 and R2 are provided to stabilize the voltage of the second line 120. Resistors R1 and R2 are optional, and voltage division can be performed by adjusting the capacitance of capacitors C1 and C2. Similarly in Figures 1 and 2, resistors may be provided between the first line 110 and the second line 120, and between the second line 120 and the third line 130.

[0156] Thus, the voltage conversion circuit 10A can output three levels of voltage using a two-level converter. As mentioned above, the converter may be a boost circuit or a buck circuit.

[0157] Furthermore, although the resonant DC-DC converter 20 in the above-described embodiment had two bridge circuits, it is not limited to two, and three or more may be provided depending on the number of lines. [Explanation of Symbols]

[0158] 1a~1f Power conversion device 10 Boost Circuit 10A Voltage Conversion Circuit 11. Bonding reactor 15 Control circuits 20. Resonant DC-DC Converter 21A, 21B bridge circuit 22 Resonant isolation circuit 22A, 22B Isolation Transformer 23 Rectifier circuit 23A, 23B Diode Bridge Circuit 24 Smoothing circuit 25 Control circuits 30 3-phase inverter 35 Control circuits 40 LC filter 110 Line 1 120 Second Line 130 Third Line 200 Resonant DC-DC Converter 210 Bridge Circuit 220 Resonant isolation circuit 230,231~237 Rectifier circuit 240,241 Smoothing circuit 250 Control circuits C1, C1a, C1b, C2, C2a, C2b, C5, C5a, C5b Capacitors C3, C4, C6 Resonant capacitors D1, D2, D3a~D3d, D4a~D4d diodes P1 Package Q1, Q2 switching elements Q3a~Q3f Switching elements Q4a~Q4f Switching elements Q5a, Q5b, Q6a, Q6b, Q7a, Q7b switching elements L21, L31, L41 Primary winding L22, L32, L42 Secondary winding Ta, Tb terminals

Claims

1. A first bridge circuit is provided between a first line to which a first voltage is applied and a second line to which a second voltage lower than the first voltage is applied, and includes a plurality of first switching elements. A second bridge circuit is provided between the second line and a third line to which a third voltage lower than the second voltage is applied, and includes a plurality of second switching elements. A voltage output circuit that generates a predetermined DC voltage based on the operation of the first and second bridge circuits, A converter that applies the first voltage to the first line, the second voltage to the second line, and the third voltage to the third line based on the input voltage, Equipped with, The converter includes a plurality of third switching elements, The breakdown voltage of the first and second switching elements is the same as that of the third switching element. Power converter.

2. A power conversion device according to claim 1, The system further includes an inverter which includes a plurality of fourth switching elements and converts the predetermined DC voltage into an AC voltage, The breakdown voltage of the fourth switching element is the same as that of the first to third switching elements. Power converter.

3. A power conversion device according to claim 2, Each of the aforementioned first to fourth switching elements includes two switching elements connected in series. The two switching elements are housed in a predetermined package. Power converter.

4. A power conversion device according to any one of claims 1 to 3, At least the first and second switching elements are formed of a wide-bandgap semiconductor. Power converter.

5. A power conversion device according to any one of claims 1 to 4, The aforementioned voltage output circuit is A first isolation transformer in which the primary winding is connected to the first bridge circuit, A second isolation transformer in which the primary winding is connected to the second bridge circuit, A rectifier circuit for rectifying the voltage induced in the secondary windings of the first and second isolation transformers, A smoothing circuit that smooths the output of the rectifier circuit to generate the predetermined DC voltage, A power conversion device having the following features.

6. A power conversion device according to claim 5, A first resonant capacitor connected between the first bridge circuit and the primary winding of the first isolation transformer, A second resonant capacitor connected between the second bridge circuit and the primary winding of the second isolation transformer, A power conversion device that includes a power converter.

7. A power conversion device according to claim 5 or 6, The smoothing circuit is It has a first capacitor and a second capacitor connected in series, The rectifier circuit described above is A first diode bridge circuit rectifies the voltage induced in the secondary winding of the first isolation transformer and supplies it to the first capacitor, A second diode bridge circuit rectifies the voltage induced in the secondary winding of the second isolation transformer and supplies it to the second capacitor, A power conversion device having the following features.

8. A power conversion device according to claim 5 or 6, The smoothing circuit has a capacitor, The rectifier circuit described above is A first diode bridge circuit rectifies the voltage induced in the secondary winding of the first isolation transformer and supplies it to the capacitor, A second diode bridge circuit rectifies the voltage induced in the secondary winding of the second isolation transformer and supplies it to the capacitor, A power conversion device having the following features.

9. A power conversion device according to claim 7 or 8, The first and second diode bridge circuits are full-wave rectifier circuits. Power converter.

10. A power conversion device according to claim 7 or 8, The first and second diode bridge circuits are half-wave rectifier circuits. Power converter.

11. A power conversion device according to claim 5 or 6, The smoothing circuit has a capacitor, The rectifier circuit described above is The diode bridge circuit rectifies the voltage induced in the secondary windings of the first and second isolation transformers and supplies it to the capacitor. Power converter.

12. A power conversion device according to claim 5 or 6, The smoothing circuit has a first capacitor and a second capacitor connected in series. The rectifier circuit described above is A first diode bridge circuit rectifies the voltage induced in the secondary windings of the first and second isolation transformers and supplies it to the first capacitor, A second diode bridge circuit rectifies the voltage induced in the secondary windings of the first and second isolation transformers and supplies it to the second capacitor, A power conversion device having the following features.

13. A power conversion device according to claim 11 or 12, The system includes a control circuit that controls the switching of the plurality of first and second switching elements so that the voltages applied to the primary windings of the first and second isolation transformers are in phase. Power converter.

14. A power conversion device according to any one of claims 1 to 13, The aforementioned voltage output circuit is a step-down converter. The voltage between the first line and the third line is higher than the predetermined voltage. Power converter.

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