Bidirectional multi-stage gallium nitride switch and power conversion device comprising same

Abstract

The present invention relates to a bidirectional switch using a multi-stage gallium nitride switch, and a power conversion device using same. The multi-stage-structured bidirectional gallium nitride switch according to the present invention is structured such that source terminals of two gallium nitride switches are connected to each other to be included in one package so as to control the flow of a bidirectional current, thereby enabling volume and costs to be reduced, and a common source terminal is configured to have a simplified power circuit of a gate driver and has no body diode, and thus a switching loss can be reduced.

Description

Bidirectional multi-stage gallium nitride switch and power conversion device including the same

[0001] The present disclosure relates to a power conversion device, and more particularly, to a power conversion device using a bidirectional gallium nitride switch as a switching element.

[0002] A power converter is a device that converts electrical energy into various forms, such as converting direct current or alternating current power into alternating current or direct current power, or converting voltage or frequency.

[0003] An inverter, one of the power conversion devices, is a device for converting direct current power into alternating current power, and may include a converter section and an inverter section.

[0004] For example, the converter unit receives direct current from an external power source and converts it into a current in the form of a radio wave, and the inverter unit receives the current in the form of a radio wave and converts it into an alternating current, which can then be transmitted to an external load or system.

[0005] For example, an inverter may include various types of electrical devices. For example, silicon-based switches may switch at high speeds to convert direct current (DC) power into alternating current (AC), and the inverter may alternately switch at different frequencies to convert DC current into a sinusoidal AC current.

[0006] However, silicon-based switches are not suitable for high-speed switching and can cause losses in low-power applications. Specifically, silicon-based bidirectional switches can incur losses due to the breakdown voltage generated when the body diode of the switch itself conducts. This can lead to losses in the entire circuit.

[0007] Additionally, two silicon-based switches are required to form a bidirectional switch. Therefore, a bidirectional switch composed of two switches also has the disadvantage of being bulky.

[0008] The present disclosure aims to provide a bidirectional gallium nitride switch capable of reducing switching loss by eliminating a body diode.

[0009] In addition, the present disclosure aims to provide a bidirectional switch capable of reducing package volume by including two switches in one package.

[0010] In addition, the present disclosure aims to provide an inverter utilizing a bidirectional gallium nitride switch configured in one package.

[0011] A bidirectional gallium nitride switch according to one aspect includes a first gallium nitride (GaN) switch and a second gallium nitride switch, each of which includes a gate, a drain, and a source terminal, and the drain terminal of the first gallium nitride switch and the drain terminal of the second gallium nitride switch are connected to each other, so that bidirectional current flow can be controlled by on / off control of the gate terminal of the first gallium nitride switch and the gate terminal of the second gallium nitride switch, respectively.

[0012] The first gallium nitride switch and the second gallium nitride switch are contained within the same package.

[0013] A power conversion device according to another aspect includes the bidirectional gallium nitride switch.

[0014] The power conversion device includes a primary full-bridge circuit connected to an input power source; a transformer that transmits the output of the full-bridge circuit to the secondary side; and a converter unit that transmits the secondary side output of the transformer to the output unit of the power conversion device.

[0015] The above power conversion device includes an insulated inverter that converts primary-side direct current power into secondary-side alternating current power.

[0016] The above converter unit includes a first bidirectional gallium nitride switch, a second bidirectional gallium nitride switch, a first capacitor, and a second capacitor.

[0017] The converter unit is connected between the first bidirectional gallium nitride switch and the second bidirectional gallium nitride switch, which are connected in series at one end of the secondary output of the transformer, and the other end of the secondary output of the transformer is connected between the first capacitor and the second capacitor, which are connected in series, and the first and second bidirectional gallium nitride switches and the first and second capacitors are connected in parallel with the output unit of the power conversion device.

[0018] The above power conversion device has a DAB (Dual Active Bridge) structure in which a transformer and an inductor connected in series with the transformer are connected between a primary side full bridge circuit and a secondary side full bridge circuit, and the primary side full bridge circuit includes third and fourth bidirectional gallium nitride switches.

[0019] The above primary side full bridge circuit includes first and second switching elements connected in series and third and fourth bidirectional gallium nitride switches connected in series in parallel with the input power supply.

[0020] The power conversion device includes: a primary side full-bridge circuit; a first inductor, a second inductor, and a third capacitor connected to the primary side full-bridge circuit and connected in series with each other; a transformer having a primary side connected in parallel with the first or second inductor; a fifth bidirectional gallium nitride switch connected in parallel with a secondary side of the transformer; a fourth capacitor connected in parallel with the fifth bidirectional gallium nitride switch; and a secondary side full-bridge circuit connected in parallel with the fourth capacitor.

[0021] By constructing a bidirectional switch using a gallium nitride switch suitable for high-speed switching, current flow with low switching loss can be realized.

[0022] Additionally, by fabricating a bidirectional switch as a single die with a common drain or common source structure and configuring it into a package, the overall switch volume can be reduced, thereby minimizing PCB volume. This can reduce the manufacturing cost of the power conversion device.

[0023] Figure 1 is an exemplary diagram of a power supply structure of a building in which solar modules are installed according to one embodiment.

[0024] FIG. 2 is an exemplary diagram of a solar module including a power conversion device according to one embodiment.

[0025] FIGS. 3A to 4D are structural diagrams of a bidirectional multi-stage gallium nitride switch according to one embodiment.

[0026] FIG. 5 is a circuit diagram of an inverter having a cycloconverter structure including a bidirectional multi-stage gallium nitride switch according to one embodiment.

[0027] FIG. 6 is a circuit diagram of an inverter of a DAB converter structure including a bidirectional multi-stage gallium nitride switch according to one embodiment.

[0028] FIG. 7 is a circuit diagram of an inverter having an LLC resonant converter structure including a bidirectional multi-stage gallium nitride switch according to one embodiment.

[0029] A bidirectional gallium nitride switch according to one aspect includes a first gallium nitride (GaN) switch and a second gallium nitride switch, each of which includes a gate, a drain, and a source terminal, and the drain terminal of the first gallium nitride switch and the drain terminal of the second gallium nitride switch are connected to each other, so that bidirectional current flow can be controlled by on / off control of the gate terminal of the first gallium nitride switch and the gate terminal of the second gallium nitride switch, respectively.

[0030] The above-described objects, means, and resulting effects of the present invention will become more apparent through the following detailed description, taken in conjunction with the accompanying drawings. Accordingly, those skilled in the art will be able to readily implement the technical concepts of the present invention. Furthermore, in describing the present invention, if a detailed description of known technology related to the present invention is deemed to unnecessarily obscure the gist of the invention, such detailed description will be omitted.

[0031] In this specification, terms such as “or,” “at least one,” and the like can refer to one of the words listed together, or a combination of two or more. For example, “or B” or “and at least one of B” can include only one of A or B, or can include both A and B.

[0032] In this specification, terms such as "first" and "second" may be used to describe various components, but the components should not be limited by these terms. Furthermore, these terms should not be construed to limit the order of each component, but rather may be used to distinguish one component from another. For example, a "first component" may be referred to as a "second component," and similarly, a "second component" may also be referred to as a "first component."

[0033] Hereinafter, a preferred embodiment according to the present invention will be described in detail with reference to the attached drawings.

[0034] Figure 1 is an exemplary diagram of a power supply structure of a building in which solar modules are installed according to one embodiment.

[0035] Referring to Fig. 1, a plurality of photovoltaic modules (2) are installed on the roof of a building (1) and can produce energy using solar energy.

[0036] When a plurality of solar modules (2) are connected, a solar module array can be formed. A solar module array is an assembly of a plurality of solar modules and can include one output terminal.

[0037] Meanwhile, the solar module (2) may include a power conversion device. For example, the power conversion device (110 in FIG. 2) controls the power conversion of the solar module (2) and may include an optimizer to optimize energy generation. The power conversion device (110 in FIG. 2) may monitor the status of the solar module (2), determine whether there is a failure, and transmit data to the outside. For example, the power conversion device (110 in FIG. 2) may be a device including a converter (i.e., a device that converts alternating current into direct current) and an inverter (i.e., a device that converts direct current into alternating current).

[0038] Additionally, the power conversion device (110 in FIG. 2) may stop operation by executing a rapid shutdown (RSD) function depending on the situation. In addition, at least one of the solar module (2) and the power conversion device may include a communication module for power line communication.

[0039] The solar module (2) may include a monitoring system or a rapid shutdown system (RSD system).

[0040] The inverter (6) can convert the power generated from the solar module (2) and supply the generated power into the building (1).

[0041] Meanwhile, commercial power transmitted through the power line (3) can be supplied to the building through the transformer (4).

[0042] A plurality of home appliances (7) can be operated by selectively receiving at least one of commercial electricity or power generated by a solar module (2). The power meter (5) can measure the amount of power consumed in the building (1).

[0043] Additionally, if a separate energy storage system (ESS) is installed in the building (1), the power generated from the solar module (100) can be stored in the energy storage system (ESS).

[0044] FIG. 2 is an exemplary diagram of a solar module including a power conversion device according to one embodiment.

[0045] FIG. 2 illustrates a solar module (100) and a power conversion device (110). Although FIG. 2 illustrates the power conversion device (110) as being included within the solar module (100), the present invention is not limited thereto. In other words, the power conversion device (110) may be an independent device from the solar module (100).

[0046] A solar module (100) is a module that generates electricity using solar energy. For example, a plurality of solar modules (100) may be connected to form a solar module array.

[0047] The power conversion device (110) can be connected to the solar module (100) to optimize the output voltage of the solar module (100). For example, the power conversion device (110) can optimize the output voltage so that the output of the solar module (100) is maximized.

[0048] For example, the power conversion device (110) may be a module-level power conversion device (Module Level Power Electronics, MLPE) configured in module units. Here, the module-level power conversion device may include a micro-inverter or a DC optimizer (or power optimizer).

[0049] A micro-inverter is a small solar inverter installed in a solar module (100). Unlike a string inverter that is centrally located and connected to multiple solar modules, a micro-inverter is a device that is independently connected to each solar module (100) to convert power. For example, if the power conversion device (110) is a micro-inverter, a single micro-inverter can be connected to a single solar module (100). In this case, the micro-inverter can convert power generated by the solar module (100), and the converted current can be output to a load or a power grid.

[0050] A DC optimizer (or power optimizer) is a device that converts direct current power into alternating current power, like an inverter. The DC optimizer is independently connected to a solar module (100), and is a device that combines and optimizes the power (direct current) generated by the solar module (100) and then transmits it to a main inverter (e.g., a string inverter) to convert it into alternating current power. For example, if the power conversion device (110) is a DC optimizer, a single DC optimizer can be connected to a single solar module (100). In this case, the DC optimizer can optimize the power output from the solar module (100) and output it to the main inverter. The current converted by the main inverter (e.g., converting direct current into alternating current) can be output to a load or a power grid.

[0051] The power conversion device (110) may be, but is not limited to, a module-level power conversion device (MLPE) connected to a solar module (100). For example, the power conversion device (110) may also be applied to a microinverter or a DC optimizer. In addition, the power conversion device (110) may be included in a converter or inverter.

[0052] The power conversion device (110) can optimize and output the output voltage of each connected solar module (100) through maximum power point tracking control. The power conversion device (110) can identify the maximum power point voltage by performing maximum power point tracking control that tracks the corresponding power and voltage when the solar module (100) generates maximum power. For example, the maximum power point tracking algorithm may be an algorithm that continuously adjusts the impedance of the solar module (100) or the solar module array so that the solar power generation system operates near the maximum power point when conditions such as irradiance, temperature, and load change.

[0053] For example, the power conversion device (110) may be connected to the solar modules (100) in a one-to-one correspondence, but is not limited thereto. As another example, the power conversion device (110) may be installed in the solar modules (100) in a many-to-one or many-to-many correspondence, depending on the structure adopted by the solar power generation system. The installation form of the power conversion device (110) and the solar modules (100) is not limited to either one. In addition, when a plurality of power conversion devices (110) are provided, the power conversion devices (110) may be connected in series with each other. If the power conversion device (110) is a DC optimizer, the power conversion devices (110) at both ends of the plurality of power conversion devices (110) connected in series may be connected to an inverter.

[0054] According to one embodiment of the present invention, the inverter may be a component installed in a power conversion system (PCS) to perform power conversion in order to supply power generated from a solar module (100) to a load or a grid. For example, the inverter may monitor various data received from the solar module (100), the power conversion device (110), the load, the power grid, etc.

[0055] FIGS. 3A to 4D are structural diagrams of a bidirectional multi-stage gallium nitride switch according to one embodiment.

[0056] Figure 3a shows a circuit diagram of a gallium nitride (GaN) switch.

[0057] For example, in a gallium nitride (GaN) switch, like other switching devices, the flow of current from the drain (DRAIN) to the source (SOURCE) can be controlled by turning the gate on and off.

[0058] Specifically, if the voltage applied to the gate is higher than a certain voltage (threshold voltage), the gate can be in an ON state where current flows from the drain to the source, and if it is lower than the threshold voltage, the gate can be in an OFF state where current does not flow from the drain to the source.

[0059] Figure 3b is a schematic structural diagram of a multi-stage bidirectional gallium nitride switch composed of the gallium nitride switch of Figure 3a.

[0060] For example, a bidirectional gallium nitride switch (600) may include a first gallium nitride switch (610) and a second gallium nitride switch (620).

[0061] A first gallium nitride switch (610) and a second gallium nitride switch (620) can be connected within a single package to form a bidirectional gallium nitride switch (600). At this time, the drain terminal of the first gallium nitride switch (610) and the drain terminal of the second gallium nitride switch (620) are connected to each other to form a structure that enables control of bidirectional current flow.

[0062] FIGS. 4A to 4D schematically illustrate the current flow of a bidirectional gallium nitride switch (600) according to the combination of the gate (G1) state of the first gallium nitride switch (610) and the gate (G2) state of the second gallium nitride switch (620).

[0063] Figure 4a shows a case where both the gate (G1) of the first gallium nitride switch (610) and the gate (G2) of the second gallium nitride switch (620) are in the ON state, i.e., both gate voltages are higher than the threshold voltage (V th1 <V gs1 , V th2 <V gs2 ) is shown. Since both the first gallium nitride switch (610) and the second gallium nitride switch (620) are in a conducting state, current can flow in both directions.

[0064] Figure 4b shows that the gate (G1) of the first gallium nitride switch (610) is in the ON state, i.e., the gate (G1) voltage is higher than the threshold voltage (V th1 <V gs1 ), and the gate (G2) of the second gallium nitride switch (620) is in the OFF state, i.e., the voltage between the gate (G2) and the source (S2) terminals is lower than zero voltage (0>V). gs2 ) is shown. At this time, the first gallium nitride switch (610) is in a conducting state, and the second gallium nitride switch (620) is in a diode-like state that conducts only in the direction of the first gallium nitride switch (610), so that current can flow only in the direction of the first gallium nitride switch (610) from the second gallium nitride switch (620). Here, the diode state of the second gallium nitride switch (620) is to help understand the current flow, and since it is not a body diode like a silicon-based switching element, a voltage drop due to the body diode also does not occur.

[0065] Figure 4c shows that the gate (G1) of the first gallium nitride switch (610) is in an OFF state, i.e., the voltage between the gate (G1) and the source (S1) terminals is lower than zero voltage (0>V). gs1 ) and when the gate (G2) of the second gallium nitride switch (620) is in the ON state, that is, when the gate (G2) voltage is higher than the threshold voltage (V th2 <V gs2 ) is shown. The first gallium nitride switch (610) becomes a diode-like state in the direction of the second gallium nitride switch (32-), and the second gallium nitride switch (620) becomes a conducting state, so that current can flow only in the direction from the first gallium nitride switch (610) to the second gallium nitride switch (620).

[0066] Figure 4d shows a case where both the gate (G1) of the first gallium nitride switch (610) and the gate (G2) of the second gallium nitride switch (620) are in the OFF state (0=V gs1 , 0=V gs2) is shown. At this time, since the channels of the first gallium nitride switch (610) and the second gallium nitride switch (620) are both closed, current cannot flow in any direction.

[0067] As described above, the bidirectional gallium nitride switch (610) having a multi-stage structure according to the present invention can reduce losses because breakdown voltage due to the body diode does not occur. In addition, since the distance between the source and drain of the first gallium nitride switch (610) and the drain and source of the second gallium nitride switch (620) is short, it is suitable for high-speed switching. In addition, since the two gallium nitride switches (610, 620) are included in a single package, the overall volume can be reduced.

[0068] FIGS. 5 to 7 illustrate embodiments of a power conversion device including the bidirectional gallium nitride switch of the multi-stage structure described above.

[0069] FIG. 5 is a circuit diagram of an inverter including a cyclo converter structure according to one embodiment.

[0070] Referring to FIG. 5, the inverter (500) may include a primary side full bridge circuit (510) connected to an input power source, a transformer (520), a secondary side bidirectional gallium nitride switch (530a, 530b), and a capacitor (540a, 540b) connected to an output section.

[0071] For example, the primary full bridge circuit (510) is connected in parallel with the input power and the input capacitor, and may include four switching elements. The four switching elements are connected in parallel with each other in a state where two of them are connected in series, and one end and the other end of the transformer (520) may be connected to the connection points of the switching elements connected in series in pairs, respectively.

[0072] For example, the input DC current can be converted into AC current by controlling the on / off of the switching elements included in the primary full bridge circuit (510).

[0073] For example, the transformer (520) can insulate the primary side and the secondary side to transmit the primary side power to the secondary side.

[0074] A primary side full bridge circuit (510) may be connected to the primary side of a transformer (520), and a bidirectional gallium nitride switch (530a, 530b) and a capacitor (540a, 540b) may be connected to the secondary side of the transformer (520).

[0075] Additionally, the first bidirectional gallium nitride switch (530a) and the second bidirectional gallium nitride switch (530b) are connected in series, and a secondary end of the transformer (520) can be connected between them.

[0076] Additionally, the first capacitor (540a) and the second capacitor (540b) may also be connected in series, and the secondary side of the transformer (520) may be connected therebetween.

[0077] Bidirectional gallium nitride switches (530a, 530b) connected in series and capacitors (540a, 540b) connected in series can each be connected in parallel to the output section.

[0078] An inverter (200) including a cycloconverter structure according to the present invention may include a bidirectional gallium nitride switch. Accordingly, it can be formed into a single package structure, thereby reducing the volume of the entire circuit. In addition, the effect of reducing the length of lines affected by noise in the entire circuit can be realized. In addition, through high-speed switching of the GaN element, the volume of passive elements (transformers, capacitors, inductors) can be minimized, and efficiency can be increased.

[0079] FIG. 6 is a circuit diagram of an inverter including a DAB structure according to one embodiment.

[0080] Referring to FIG. 6, the inverter (600) may include a DAB structure in which the primary side full bridge circuit (610) and the secondary side full bridge circuit (370) have a symmetrical structure.

[0081] For example, the primary full bridge circuit (610) includes four switching elements, which may be configured as bidirectional gallium nitride switches.

[0082] For example, the primary full-bridge circuit (610) may include two switching elements (612a, 612b) connected in parallel with the input power source and two bidirectional gallium nitride switches (614a, 614b) connected in parallel with the input power source. The two bidirectional gallium nitride switches, the third bidirectional gallium nitride switch (614a) and the fourth bidirectional gallium nitride switch (614b), may be connected in series, and the primary end of the transformer (620) may be connected between them.

[0083] The transformer (620) insulates the primary side and the secondary side to transmit the primary side current to the secondary side. For example, an inductor (630) may be connected in series to the primary side of the transformer (620).

[0084] On the secondary side of the transformer (620), two switching elements (640a, 640b) may be connected in series, and one end of the secondary output of the transformer (620) may be connected between them. In addition, on the secondary side of the transformer (620), two capacitors (650a, 650b) may be connected in series, and the other end of the secondary output of the transformer (620) may be connected between them.

[0085] For example, two switching elements (640a, 640b) and two capacitors (650a, 650b) may be connected in parallel, and another capacitor (360) may be connected in parallel to a secondary full bridge circuit (370).

[0086] An inverter (600) including a DAB structure according to the present invention may include a bidirectional gallium nitride switch on the primary side. Therefore, the inverter (600) can achieve high efficiency, a high voltage gain ratio, and miniaturization of passive components due to high-speed switching. Furthermore, the single-package structure can reduce volume and the influence of noise lines.

[0087] Fig. 7 is a circuit diagram of an LLC resonant inverter according to one embodiment.

[0088] Referring to FIG. 7, the inverter (700) may include a primary side full bridge circuit (710), a transformer (720), an LLC circuit (730), a fifth bidirectional gallium nitride switch (740), a capacitor (750), and a secondary side full bridge circuit (760).

[0089] For example, the primary full bridge circuit (710) includes four switching elements and can transmit current from the input power source to the transformer (720) through the LLC circuit (730).

[0090] For example, the LLC circuit (730) includes two inductors and one capacitor connected in series, and one of the two inductors can be connected in parallel with the primary side of the transformer (720).

[0091] The transformer (720) transmits the primary side current to the secondary side, and the primary side and the secondary side can be electrically insulated.

[0092] A fifth bidirectional gallium nitride switch (740) may be connected in parallel to the secondary side of the transformer (720). Additionally, a capacitor (750) may also be connected in parallel with the gallium nitride switch (740).

[0093] Additionally, the capacitor (750) and the secondary full bridge circuit (760) can also be connected in parallel so that the final converted current can be output.

[0094] The LLC resonant inverter (700) according to the present invention may include a bidirectional gallium nitride switch on the secondary side. Therefore, when using the inverter (700), miniaturization of passive components due to high efficiency, high voltage gain ratio, and high-speed switching can be achieved. In addition, the single package structure can reduce volume and the influence of noise lines can be reduced.

[0095] According to the bidirectional gallium nitride switch and the power conversion device including the bidirectional gallium nitride switch according to the present invention, losses due to voltage drops occurring in the body diode of conventional silicon-based switching devices can be reduced. Furthermore, since two gallium nitride switches are included in a single package, volume and cost can be reduced, and noise lines can be optimized.

[0096] While the detailed description of the present invention has described specific embodiments, it should be understood that various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention is not limited to the described embodiments, but should be determined by the claims and their equivalents.

Claims

1. A first gallium nitride (GaN) switch and a second gallium nitride switch each including a gate, a drain, and a source terminal, A bidirectional gallium nitride switch in which the drain terminal of the first gallium nitride switch and the drain terminal of the second gallium nitride switch are connected to each other, and bidirectional current flow can be controlled by controlling the on / off of the gate terminal of the first gallium nitride switch and the gate terminal of the second gallium nitride switch, respectively.

2. In paragraph 1, A bidirectional gallium nitride switch, wherein the first gallium nitride switch and the second gallium nitride switch are contained within the same package.

3. A power conversion device including a bidirectional gallium nitride switch according to paragraph 1.

4. In paragraph 3, The above power conversion device, Primary full bridge circuit connected to input power supply; A transformer that transmits the output of the above full bridge circuit to the secondary side; and A converter section that transmits the secondary output of the above transformer to the output section of the above power conversion device; A power conversion device comprising:

5. In paragraph 4, The above power conversion device, A power conversion device including an isolated inverter that converts primary-side direct current power into secondary-side alternating current power.

6. In paragraph 4, The above converter part, A power conversion device comprising a first bidirectional gallium nitride switch, a second bidirectional gallium nitride switch, a first capacitor, and a second capacitor.

7. In paragraph 6, The above converter part, One end of the secondary output of the above transformer is connected between the first bidirectional gallium nitride switch and the second bidirectional gallium nitride switch which are connected in series, The other end of the secondary output of the above transformer is connected between the first capacitor and the second capacitor connected in series, A power conversion device, wherein the first and second bidirectional gallium nitride switches and the first and second capacitors are connected in parallel with the output section of the power conversion device.

8. In paragraph 3, The above power conversion device, It is a DAB (Dual Active Bridge) structure in which a transformer and an inductor connected in series with the transformer are connected between the primary side full bridge circuit and the secondary side full bridge circuit. A power conversion device, wherein the above primary side full bridge circuit includes third and fourth bidirectional gallium nitride switches.

9. In paragraph 8, The above primary full bridge circuit is, A power conversion device, comprising first and second switching elements connected in series, and third and fourth bidirectional gallium nitride switches connected in series, the third and fourth bidirectional gallium nitride switches being connected in parallel with an input power source.

10. In paragraph 3, The above power conversion device, Primary full bridge circuit; A first inductor, a second inductor and a third capacitor connected in series with each other and connected to the above primary side full bridge circuit; A transformer having the primary side connected in parallel with the first or second inductor; A fifth bidirectional gallium nitride switch connected in parallel with the secondary side of the above transformer; a fourth capacitor connected in parallel with the fifth bidirectional gallium nitride switch; and A secondary full bridge circuit connected in parallel with the fourth capacitor; A power conversion device comprising:

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