Power Conversion Device

Abstract

To provide a power conversion device that enables stable control by appropriately setting the coupling rate of a coupling reactor.SOLUTION: A power conversion device (10) converts an input voltage (Vin) into a predetermined output voltage (Vout). The power conversion device (10) includes a coupling reactor (1) having a first reactor (L1) and a second reactor (L2) which are magnetically coupled to each other, a first switching element (Tr1), a second switching element (Tr2), a first capacitor (C1), a second capacitor (C2), and a controller (15). The coupling rate k of the coupling reactor (1) is set to a value that satisfies k≤Vin / (Vout-Vin).SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] Conventionally, some DC-DC converters have an interleaved circuit configuration in which converter circuits are arranged in parallel to achieve higher power. To reduce the size of this interleaved circuit configuration, it has been proposed to use a coupling reactor in which the reactors of each phase are magnetically coupled.

[0003] For example, Patent Documents 1 and 2 describe a power conversion device that converts a voltage input from a power supply into a predetermined voltage, and that has a coupling reactor in which two reactors are magnetically coupled to each other. In the power conversion device of Patent Document 2, the coupling rate of the coupling reactor is set to a predetermined value or less, thereby suppressing the ripple current that flows through a capacitor connected in parallel to the power supply. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6567236 [Patent Document 2] Patent No. 6763013 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in a power conversion device configured as described above, when the switching duty ratio is set to less than 50% and the device is driven in discontinuous conduction mode (DCM), a reverse current may flow through one of the two reactors. In this case, a dead band phenomenon may occur, in which the output voltage does not follow changes in the duty ratio. When this dead band phenomenon occurs, the control of the power conversion device becomes unstable, and there is a risk of the output voltage oscillating.

[0006] An object of the present invention is to provide a power conversion device that can be stably controlled by appropriately setting the coupling ratio of a coupling reactor. [Means for solving the problem]

[0007] In order to solve the above problems, a power conversion device according to a first aspect of the present invention is a power conversion device that converts an input voltage to a predetermined output voltage, and includes a coupling reactor having a first reactor and a second reactor that are magnetically coupled to each other, a first switching element connected to the output side of the first reactor, a second switching element connected to the output side of the second reactor, and a control unit that controls driving of the first switching element and the second switching element. A coupling ratio k of the coupling reactor is set to a value that satisfies Condition 1, k≦Vin / (Vout−Vin), where Vin is the input voltage and Vout is the output voltage.

[0008] According to the above configuration, by setting the coupling ratio k of the coupling reactor to a value that satisfies k≦Vin / (Vout−Vin), it is possible to prevent a reverse current from occurring in the first reactor or the second reactor. This prevents the occurrence of a dead band phenomenon in which the output voltage Vout does not follow changes in the on-duty ratio, and allows the power conversion device to be stably controlled by the control unit.

[0009] In the power conversion device according to the second aspect of the present invention, the coupling ratio k is set to a value that satisfies the second condition, k≦1 / (Bmax−1), where Bmax is the maximum value of the step-up ratio obtained by dividing the output voltage by the input voltage.

[0010] According to the above configuration, when the maximum value of the step-up ratio is Bmax, the coupling ratio k of the coupling reactor is set to a value that satisfies k≦1 / (Bmax−1), thereby making it possible to more reliably prevent the occurrence of the dead band phenomenon.

[0011] In the power conversion device according to aspect 3 of the present invention, the control unit turns off the first switching element when the on-duty ratio of the switching of the first switching element and the second switching element is less than 50%, and turns off the second switching element during a period when the first reactor is discharging to the output side.

[0012] According to the above configuration, when the on-duty ratio of the switching of the first switching element and the second switching element is less than 50%, even if the second switching element is turned off during the period when the first switching element is turned off and discharging from the first reactor to the output side, it is possible to prevent a reverse current from occurring in the second reactor.

[0013] The power conversion device according to a fourth aspect of the present invention further includes a first capacitor connected to the input side of the coupling reactor, and a second capacitor connected to the output side of the coupling reactor.

[0014] According to the above configuration, the ripple current can be removed by the first capacitor, and the energy stored in the coupling reactor is supplied to the second capacitor and then released, thereby increasing the output of the power conversion device.

[0015] The power conversion device according to a fifth aspect of the present invention further includes a first diode connected to the output side of the first switching element, and a second diode connected to the output side of the second switching element.

[0016] According to the above configuration, by connecting a first diode to the output side of the first switching element and connecting a second diode to the output side of the second switching element, it is possible to prevent a current from flowing back from the first capacitor to the coupling reactor.

[0017] In a power conversion device according to aspect 6 of the present invention, the first switching element and the second switching element are vertical MOS field effect transistors, and the drain of the first switching element is connected to the anode of the first diode, and the drain of the second switching element is connected to the anode of the second diode.

[0018] According to the above configuration, by using a vertical MOS field effect transistor as the switching element, it is possible to increase the breakdown voltage and perform high-speed switching.

[0019] A power conversion device according to a seventh aspect of the present invention further includes a third switching element connected to an output side of the first switching element and a fourth switching element connected to an output side of the second switching element. The control unit controls driving of the third switching element and the fourth switching element so that the third switching element is turned off when the first switching element is turned on, the third switching element is turned on when the first switching element is turned off, the fourth switching element is turned off when the second switching element is turned on, and the fourth switching element is turned on when the second switching element is turned off.

[0020] According to the above configuration, by connecting the third switching element to the output side of the first switching element and the fourth switching element to the output side of the second switching element, it is possible to prevent a current from flowing back from the first capacitor to the coupling reactor. Furthermore, since a synchronous rectification circuit configuration is formed, it is possible to improve the conversion efficiency compared to the power conversion device according to aspect 5. [Effects of the Invention]

[0021] According to one aspect of the present invention, by appropriately setting the coupling ratio of the coupling reactor, it is possible to realize a power conversion device that enables stable control. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a diagram showing a schematic configuration of a power supply device including a power conversion device according to an embodiment of the present invention; [Figure 2] 2 is a graph showing the relationship between the step-up ratio of the power conversion device of FIG. 1 and the coupling rate of a coupling reactor. [Figure 3] 2 is a diagram for explaining an example of the operation of the power conversion device 10 of FIG. [Figure 4] 2 is a graph showing the relationship between the time change in the on-duty ratio of switching of a first switching element and a second switching element and the time change in output voltage in the power conversion device of FIG. 1; [Figure 5] 1. FIG. 4 is a diagram showing a state in which a reverse current flows through a second reactor of the power conversion device of FIG. [Figure 6] 1. FIG. 5 is a diagram corresponding to FIG. 4 when a dead band phenomenon occurs in a coupling reactor of the power conversion device of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0023] A power supply device 100 including a power conversion device 10 according to an embodiment of the present invention will be described below with reference to FIGS.

[0024] <Outline of power supply configuration> Fig. 1 is a diagram showing a schematic configuration of a power supply device 100 including a power conversion device 10. As shown in Fig. 1, the power supply device 100 includes a power source E and the power conversion device 10. The power supply device 100 is mounted on a vehicle such as an electric vehicle or a hybrid vehicle, and is connected to a motor 30.

[0025] The power conversion device 10 is a device that converts a direct current input voltage Vin supplied from a power source E into a predetermined output voltage Vout. The power conversion device 10 is, for example, a DC-DC converter such as a boost converter. The power source E is, for example, a high-voltage power source of about 200 V. The power conversion device 10 is connected to an inverter 20 and supplies the inverter 20 with an output voltage Vout. Note that the power conversion device 10 is not limited to a DC-DC converter and may also be used in a power factor correction (PFC) circuit.

[0026] An inverter 20 is connected to the power supply device 100. A three-phase AC motor 30 is connected to the inverter 20. The inverter 20 converts the output voltage Vout supplied from the power conversion device 10 into a three-phase AC voltage and outputs it to the motor 30. The motor 30 functions as a drive source for the vehicle.

[0027] [Configuration of power conversion device] As shown in FIG. 1, the power conversion device 10 includes a coupling reactor 1, a first switching element Tr1, a second switching element Tr2, a first diode D1, a second diode D2, a first capacitor C1, a second capacitor C2, and a control unit 15.

[0028] An input terminal Pin of the power conversion device 10 is connected to the positive electrode of a power supply E. On the other hand, an input terminal Nin of the power conversion device 10 is connected to the negative electrode of the power supply E. In addition, an output terminal Pout of the power conversion device 10 is connected to an input terminal 21 on the positive electrode side of an inverter 20. On the other hand, an output terminal Nout of the power conversion device 10 is connected to an input terminal 22 on the negative electrode side of the inverter 20. The power conversion device 10 boosts an input voltage Vin input from the power supply E to a predetermined output voltage Vout.

[0029] The coupling reactor 1 is configured to include a first reactor L1 having a coil wound around a core 11, and a second reactor L2 having a coil wound around a core 11. The first reactor L1 and the second reactor L2 of the coupling reactor 1 are magnetically coupled to each other. The coupling reactor 1 is a differential coupling reactor in which the first reactor L1 and the second reactor L2 are wound in different directions.

[0030] An input terminal T11 of the first reactor L1 is connected to the positive electrode of a power supply E. An input terminal T21 of the second reactor L2 is connected to the positive electrode of the power supply E. A first switching element Tr1 and a first diode D1 are connected to an output terminal T12 of the first reactor L1. A second switching element Tr2 and a second diode D2 are connected to an output terminal T22 of the second reactor L2.

[0031] The first switching element Tr1 and the second switching element Tr2 are, for example, power MOSFETs (Metal-Oxide Semiconductor Field Effect Transistors). The on and off operations of the first switching element Tr1 and the second switching element Tr2 are controlled by the control unit 15. Note that the first switching element Tr1 and the second switching element Tr2 are not limited to power MOSFETs, and may also be IGBTs (Insulated Gate Bipolar Transistors).

[0032] A first body diode Db1 is formed between the source s1 and drain d1 of the first switching element Tr1. The first body diode Db1 is a parasitic diode of the first switching element Tr1. When the first switching element Tr1 is on, a current flows through a channel portion having a lower resistance than the first body diode Db1. On the other hand, when the first switching element Tr1 is off, a current flows through the first body diode Db1.

[0033] A second body diode Db2 is formed between the source s2 and drain d2 of the second switching element Tr2. The second body diode Db2 is a parasitic diode of the second switching element Tr2. When the second switching element Tr2 is on, a current flows through a channel portion having a lower resistance than the second body diode Db2. On the other hand, when the second switching element Tr2 is off, a current flows through the second body diode Db2.

[0034] The drain d1 of the first switching element Tr1 is connected to the output terminal T12 of the first reactor L1 and the anode of the first diode D1. The source s1 of the first switching element Tr1 is connected to the input terminal Nin and the output terminal Nout. The gate g1 of the first switching element Tr1 is connected to the control unit 15.

[0035] The drain d2 of the second switching element Tr2 is connected to the output terminal T22 of the second reactor L2 and the anode of the second diode D2. The source s2 of the second switching element Tr2 is connected to the input terminal Nin and the output terminal Nout. The gate g2 of the second switching element Tr2 is connected to the control unit 15.

[0036] One end P1 of the first capacitor C1 is connected between the input terminal Pin and the input-side terminal T11 of the first reactor L1. The other end N1 of the first capacitor C1 is connected between the input terminal Nin and the output terminal Nout. The first capacitor C1 is a smoothing capacitor that reduces ripples contained in the input voltage Vin supplied from the power source E to the power conversion device 10.

[0037] One end P2 of the second capacitor C2 is connected to the positive terminal 21 of the inverter 20 via the output terminal Pout. The other end N2 of the second capacitor C2 is connected to the negative terminal 22 of the inverter 20 via the output terminal Nout.

[0038] 1, the control unit 15 controls the on / off operation of the first switching element Tr1 by outputting a control signal Sig1. The control unit 15 also controls the on / off operation of the second switching element Tr2 by outputting a control signal Sig2. As a result, the control unit 15 supplies the energy stored in the first reactor L1 and the second reactor L2 to the inverter 20 via the second capacitor C2.

[0039] [Detailed configuration of coupling reactor] Next, the detailed configuration of the coupling reactor 1 will be described with reference to Fig. 2. Fig. 2 is a graph showing the relationship between the step-up ratio B of the power conversion device 10 of Fig. 1 and the coupling ratio k of the coupling reactor 1. As shown in Fig. 2, it can be seen that the larger the step-up ratio B, the smaller the boundary value of the coupling ratio k at which a reverse current occurs. Here, the step-up ratio B is defined as B = Vout / Vin.

[0040] In this embodiment, in order to prevent a reverse current from flowing through the first reactor L1 and the second reactor, the coupling ratio k of the coupling reactor 1 is set to satisfy condition 1 shown in the following equation (1).

[0041] k≦Vin / (Vout-Vin) (1) When the coupling ratio k of the coupling reactor 1 satisfies condition 1 shown in equation (1), the values ​​of the step-up ratio B and the coupling ratio k fall within the range of k≦1 / (B−1), as shown by the arrow indicating no reverse current in FIG. 2, and no reverse current flows through the first reactor L1 and the second reactor.

[0042] <Power conversion device operation> Next, an example of the operation of the power conversion device 10 will be described with reference to Fig. 3. Fig. 3 is a diagram for explaining an example of the operation of the power conversion device 10 of Fig. 1.

[0043] The power conversion device 10 shown in FIG. In operation mode 1, the first switching element Tr1 is on and the second switching element Tr2 is off. In operation mode 2, the first switching element Tr1 is turned off and the second switching element Tr2 is turned on. In operation mode 3, the first switching element Tr1 and the second switching element Tr2 are in an off state. In operation mode 4, the first switching element Tr1 and the second switching element Tr2 are in an ON state. In each of operation modes 1 to 4, the first reactor L1 and the second reactor L2 operate in a state where they are magnetically coupled to each other.

[0044] The control unit 15 drives the first switching element Tr1 and the second switching element Tr2 with a half-cycle shift, i.e., a 180° phase shift. When the on-duty ratio A of the switching of the first switching element Tr1 and the second switching element Tr2 is less than 50%, the control unit 15 controls the driving of the first switching element Tr1 and the second switching element Tr2 so that the pattern of operation mode 1 → operation mode 3 → operation mode 2 → operation mode 3 is repeated, for example.

[0045] On the other hand, when the on-duty ratio A of the switching of the first switching element Tr1 and the second switching element Tr2 is greater than 50%, the control unit 15 controls the driving of the first switching element Tr1 and the second switching element Tr2 so that the pattern of operation mode 1 → operation mode 4 → operation mode 2 → operation mode 4 is repeated. Also, when the on-duty ratio A of the switching of the first switching element Tr1 and the second switching element Tr2 is 50%, the control unit 15 alternately repeats operation mode 1 and operation mode 2. Note that the above-described operation pattern of the power conversion device 10 is an example and can be changed as appropriate.

[0046] [Occurrence of reverse current] Next, conditions under which a reverse current occurs in the first reactor L1 or the second reactor L2 of the coupling reactor 1 and conditions under which a reverse current does not occur will be described with reference to FIGS. 4 to 6 and Table 1. FIG. 4 is a graph showing the relationship between the time change in the on-duty ratio A of the switching of the first switching element Tr1 and the second switching element Tr2 and the time change in the output voltage Vout in the power conversion device 10 of FIG. 1. FIG. 5 is a diagram showing how a reverse current flows in the second reactor L2 of the power conversion device 10 of FIG. 1. FIG. 6 is a diagram equivalent to FIG. 4 showing a case in which a dead band phenomenon occurs in the coupling reactor 1 of the power conversion device 10 of FIG. 1. Here, the "dead band phenomenon" refers to a phenomenon in which the output voltage Vout does not follow changes in the on-duty ratio A. Furthermore, the region in which the dead band phenomenon occurs, as shown from time t2 to t3 in FIG. 6, is called the "dead band region."

[0047] Table 1 below shows the conditions under which a reverse current occurs. In Table 1, continuous conduction mode (CCM) refers to a mode in which a current flows continuously through the first reactor L1 or the second reactor L2. On the other hand, discontinuous conduction mode (DCM) refers to a mode in which the current flowing through the first reactor L1 or the second reactor L2 becomes zero for a period during one cycle.

[0048] [Table 1] As shown in Table 1, when the on-duty ratio A of the switching of the first switching element Tr1 and the second switching element Tr2 is 50% or more, no reverse current is generated in the first reactor L1 or the second reactor L2. Furthermore, when the first switching element Tr1 and the second switching element Tr2 are driven in the continuous current mode, no reverse current is generated in the first reactor L1 or the second reactor L2.

[0049] On the other hand, for example, when the on-duty ratio A of the switching of the first switching element Tr1 and the second switching element Tr2 is less than 50%, when the second switching element Tr2 is driven in the discontinuous current mode, as shown in FIG. 5, the reactor current I L2 A reverse current indicated by -1 occurs.

[0050] Specifically, when the state changes from the above-described operation mode 1 to operation mode 3, that is, when the first switching element Tr1 is turned off and the second switching element Tr2 is off during the period in which the first reactor L1 is discharging to the output side, the second body diode Db2 becomes conductive, causing a reverse current to be generated in the second reactor L2.

[0051] The reverse current in the second reactor L2 is the reactor current I L1 When -1 flows to the output side, the reactor current I flows in the direction that prevents power transmission to the phase that is transmitting power. L2 This occurs due to the flow of -1. As a result, as shown by t2 to t3 in Fig. 6, a dead band region appears in which the output voltage Vout does not follow the change in the on-duty ratio A of the switching of the first switching element Tr1 and the second switching element Tr2.

[0052] Here, it has been confirmed that the condition under which a reverse current occurs in the first reactor L1 or the second reactor L2 is expressed by the following equation (2) using the coupling ratio k, the input voltage Vin, and the output voltage Vout.

[0053] k>Vin / (Vout-Vin) (2) Therefore, in this embodiment, the value of the coupling ratio k is set to a value that satisfies condition 1 shown in equation (1) so as to eliminate the condition of equation (2), thereby preventing a reverse current from occurring in the coupling reactor 1. As a result, when the on-duty ratio A of the switching of the first switching element Tr1 and the second switching element Tr2 is less than 50%, even if the second switching element Tr2 is off during the period in which the first switching element Tr1 is turned off, no reverse current will flow in the second reactor L2 as shown in FIG.

[0054] Therefore, the first switching element Tr1 and the second switching element Tr2 can be driven without causing a dead band phenomenon in the power conversion device 10. That is, as shown in time 0 to t1 in Fig. 4, the output voltage Vout can be changed in accordance with the change in the on-duty ratio A of the switching of the first switching element Tr1 and the second switching element Tr2.

[0055] [Effects of the embodiment] According to the power conversion device 10 described above, by setting the coupling ratio k of the coupling reactor 1 to a value that satisfies condition 1 shown in equation (1), it is possible to prevent a reverse current from occurring in the first reactor L1 or the second reactor L2 of the coupling reactor 1.

[0056] As a result, when the on-duty ratio A of the switching of the first switching element Tr1 and the second switching element Tr2 is less than 50%, even if the first switching element Tr1 or the second switching element Tr2 is driven in the discontinuous current mode, it is possible to prevent the appearance of the dead band region in which the dead band phenomenon shown in Fig. 6 occurs. Therefore, the control unit 15 can stably control the power conversion device 10.

[0057] Furthermore, the first reactor L1 and the second reactor L2 of the coupling reactor 1 are configured by winding coils around a common core 11, which allows for a reduction in size and weight of the power conversion device 10. In particular, because the coupling reactor 1 is a differential coupling reactor, it is possible to cancel out the DC magnetic flux of each phase generated in the core 11, improving the tolerance for magnetic saturation. This allows for a reduction in the size of the core 11 while suppressing magnetic saturation.

[0058] Furthermore, ripple can be reduced by connecting the first capacitor C1 in parallel between the power supply E and the coupling reactor 1. Furthermore, by connecting the second capacitor C2 to the output side of the coupling reactor 1, the energy stored in the coupling reactor 1 can be supplied to the second capacitor C2 and then released to the inverter 20, thereby increasing the output of the power conversion device 10.

[0059] Furthermore, by connecting a first diode D1 to the output side of the first switching element Tr1 and a second diode D2 to the output side of the second switching element Tr2, it is possible to prevent current from flowing back from the second capacitor C2 to the coupling reactor 1 side.

[0060] Furthermore, by using a power MOSFET, which is a vertical MOS field effect transistor, as the first switching element Tr1 or the second switching element Tr2, it is possible to increase the breakdown voltage and perform high-speed switching.

[0061] [Modification] Next, a description will be given of a modified example of the power conversion device 10. In the modified example, the coupling rate k of the coupling reactor 1 is set to a value that satisfies condition 2 expressed by the following equation (3).

[0062] k≦1 / (Bmax-1) (3) Here, Bmax is the maximum value of the step-up ratio B of the power conversion device 10. In the power conversion device 10 of the modified example, the coupling factor k satisfies condition 2 when the step-up ratio B is maximum. For example, in FIG. 2, the maximum value Bmax of the step-up ratio B is 3.0. In this case, condition 2 becomes k≦0.5. Therefore, the power conversion device 10 of the modified example uses a coupling reactor 1 in which the coupling factor k is set to 0.5 or less.

[0063] The same effects as those of the above-described embodiment can be obtained with this modified power conversion device 10. That is, even if the first switching element Tr1 or the second switching element Tr2 is driven in the discontinuous current mode during a light load in which the on-duty ratio A of the switching of the first switching element Tr1 and the second switching element Tr2 is less than 50%, the dead band phenomenon shown in Fig. 6 can be prevented from occurring, and the power conversion device 10 can be stably controlled.

[0064] In particular, in the power conversion device 10 of the modified example, the step-up ratio B can be maximized, so that no backflow occurs in the coupling reactor 1 and a large output voltage Vout can be obtained from a small input voltage Vin.

[0065] Other Embodiments In the power conversion device 10 of the above embodiment, a case has been described in which one coupling reactor 1 is arranged in which a two-phase first reactor L1 and a two-phase second reactor L2 are magnetically coupled, but this is not limiting, and for example, two coupling reactors 1 each consisting of a four-phase reactor may be provided.

[0066] In the power conversion device 10 of the above-described embodiment, the first diode D1 is connected to the output side of the first reactor L1, and the second diode D2 is connected to the output side of the second reactor L2. However, this is not limiting. A synchronous rectification circuit configuration may be used in which a third switching element and a fourth switching element are arranged instead of the first diode D1 and the second diode D2. That is, the circuit configuration of the power conversion device 10 may be such that a third switching element is connected to the output side of the first switching element Tr1, and a fourth switching element is connected to the output side of the second switching element Tr2. FETs or the like may be used as the third switching element and the fourth switching element.

[0067] The on and off operations of the third switching element and the fourth switching element are controlled by the control unit 15. Specifically, the control unit 15 controls the third switching element to be on when the first switching element Tr1 is off, and the fourth switching element to be on when the second switching element Tr2 is off. The control unit 15 also controls the third switching element to be off when the first switching element Tr1 is on, and the fourth switching element to be off when the second switching element Tr2 is on. This prevents current from flowing back from the second capacitor C2 to the coupling reactor 1 when the first switching element Tr1 and the second switching element Tr2 are on.

[0068] In this case, by using a secondary battery as the power source E, the power conversion device 10 can convert the power generated by the motor 30 into direct current and charge the power source E. Furthermore, the synchronous rectification circuit configuration can improve conversion efficiency compared to the asynchronous rectification circuit configuration including the first diode D1 and the second diode D2.

[0069] In the power conversion device 10 of the above embodiment, the first capacitor C1 is connected in parallel between the power supply E and the coupling reactor 1, but this is not limiting, and the first capacitor C1 may be omitted.

[0070] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Explanation of symbols]

[0071] 1 Coupling reactor 10 Power conversion device 11 cores 15 Control Unit 20 Inverter 100 Power supply L1 First reactor L2 Second reactor Tr1 First switching element Tr2 Second switching element C1 First capacitor C2 Second capacitor D1 First diode D2 Second diode Vin Input voltage Vout Output voltage A On-duty ratio B Boost ratio k coupling rate

Claims

1. A power conversion device that converts an input voltage into a predetermined output voltage, a coupling reactor having a first reactor and a second reactor that are magnetically coupled to each other; a first switching element connected to an output side of the first reactor; a second switching element connected to the output side of the second reactor; a control unit that controls driving of the first switching element and the second switching element; Equipped with A power conversion device in which, depending on a value of a coupling rate k of the coupling reactor, when an on-duty ratio of switching of the first switching element and the second switching element is less than 50%, a reverse current is generated in the second reactor, causing a dead band phenomenon in which an output voltage does not follow a change in the on-duty ratio, The coupling ratio k is expressed as follows, where Vin is the input voltage and Vout is the output voltage: k≦Vin / (Vout-Vin) Condition 1 is satisfied, and When the maximum value of the step-up ratio obtained by dividing the output voltage by the input voltage is Bmax, k≦1 / (Bmax-1) is set to a value that satisfies condition 2 of The control unit a power conversion device that turns off the first switching element when an on-duty ratio of switching of the first switching element and the second switching element is less than 50%, and turns off the second switching element during a period in which the first reactor is discharging to an output side.

2. a first capacitor connected to the input side of the coupling reactor; a second capacitor connected to the output side of the coupling reactor; The power conversion device according to claim 1, further comprising:

3. a first diode connected to the output side of the first switching element; a second diode connected to the output side of the second switching element; The power conversion device according to claim 2, further comprising:

4. the first switching element and the second switching element are vertical MOS field effect transistors, the drain of the first switching element and the anode of the first diode are connected; 4. The power conversion device according to claim 3, wherein the drain of the second switching element and the anode of the second diode are connected together.

5. a third switching element connected to the output side of the first switching element; a fourth switching element connected to the output side of the second switching element; Further provided with The control unit 3. The power conversion device according to claim 2, wherein driving of the third switching element and the fourth switching element is controlled so that the third switching element is turned off when the first switching element is turned on, the third switching element is turned on when the first switching element is turned off, the fourth switching element is turned off when the second switching element is turned on, and the fourth switching element is turned on when the second switching element is turned off.

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