Power Conversion Equipment

Abstract

To suppress the occurrence of excess current via a transformer.SOLUTION: Power conversion equipment comprises a transformer having a first coil, a second coil and a third coil, a first switching circuit connected between an external power and the first coil, a second switching circuit connected between a main battery and the second coil, and a third switching circuit connected between an auxiliary battery and the third coil. The first switching circuit has a PFC circuit improving a power factor of AC power input from the external power, a smooth capacitor smoothing voltage of DC power output from the PFC circuit, and a relay provided on a power line between the smooth capacitor and the first coil.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Patent Document 1 discloses that in a power conversion device mounted on an electric vehicle capable of external charging, power is transmitted between an external power source, a main battery, and an auxiliary battery via a transformer. In the configuration described in Patent Document 1, the transformer has three windings, and transmits power via the transformer when power from the external power source is charged to the main battery, and transmits power via the transformer when power from the main battery is supplied to the auxiliary battery. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2021-164338 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the configuration described in Patent Document 1, if a short circuit occurs in the PFC circuit while power is being transmitted from the main battery to the auxiliary battery, current flows from the PFC circuit to the main battery circuit and the auxiliary battery circuit via the transformer, which may cause overcurrent to occur in the main battery circuit and the auxiliary battery circuit.

[0005] The present invention has been made in consideration of the above circumstances, and has an object to provide a power conversion device capable of suppressing the occurrence of an overcurrent through a transformer. [Means for solving the problem]

[0006] The present invention is a power conversion device comprising: a transformer having a first winding, a second winding, and a third winding; a first switching circuit connected between an external power source and the first winding and supplying power input from the external power source to the first winding; a second switching circuit connected between a main battery and the second winding and supplying power input from the first switching circuit through the transformer to the main battery and supplying power output from the main battery to the second winding; and a third switching circuit connected between an auxiliary battery and the third winding and supplying power input from the second switching circuit through the transformer to the auxiliary battery, wherein the first switching circuit has a PFC circuit that improves the power factor of AC power input from the external power source, a smoothing capacitor that smoothes the voltage of DC power output from the PFC circuit, and a relay provided in a power line between the smoothing capacitor and the first winding.

[0007] With this configuration, it is possible to selectively cut off the current path between the first winding and the smoothing capacitor by switching the open / closed state of the relay. Therefore, when the relay is in the open state, even if a short circuit occurs in the smoothing capacitor, the current path between the smoothing capacitor and the first winding is cut off, so that it is possible to prevent an overcurrent from flowing to the second switching circuit and the third switching circuit via the transformer.

[0008] In addition, the first switching circuit may further include a first bridge circuit that converts DC power output from the PFC circuit into AC power and supplies the AC power to the first winding, and the relay may be provided in a power line between the first bridge circuit and the first winding.

[0009] With this configuration, it is possible to selectively cut off the current path between the first winding and the first bridge circuit by switching the open / closed state of the relay. Therefore, when the relay is in the open state, even if a short circuit occurs in a switching element included in the first bridge circuit, the current path between the switching element and the first winding is cut off, so that it is possible to prevent an overcurrent from flowing to the second switching circuit and the third switching circuit via the transformer.

[0010] In addition, the main battery and the auxiliary battery may be mounted on an electric vehicle, and when the electric vehicle is traveling, the relay may be opened and power may be transmitted from the main battery to the auxiliary battery via the transformer.

[0011] According to this configuration, when power from the main battery is transmitted to the auxiliary battery while the electric vehicle is running, by setting the relay to an open state, it is possible to prevent overcurrent from flowing to the second switching circuit and the third switching circuit via the transformer even if a short circuit occurs on the first switching circuit side. Effect of the Invention

[0012] In the present invention, by switching the open / closed state of the relay, it is possible to selectively cut off the current path between the first winding and the smoothing capacitor. Therefore, when the relay is in the open state, even if a short circuit occurs in the smoothing capacitor, the current path between the smoothing capacitor and the first winding is cut off, so that it is possible to prevent an overcurrent from flowing to the second switching circuit and the third switching circuit via the transformer. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram illustrating a power conversion device according to an embodiment. [Diagram 2] FIG. 2 is a circuit diagram for explaining the location of a relay between a smoothing capacitor and a winding in a circuit on the PFC side. [Diagram 3]FIG. 3 is a circuit diagram for explaining the location of a relay between a switching element and a winding in a circuit on the PFC side. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, a power conversion device according to an embodiment of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiment described below.

[0015] FIG. 1 is a diagram showing a power conversion device in an embodiment. The power conversion device 1 is mounted on a vehicle Ve that can be externally charged. The vehicle Ve is an electric vehicle equipped with a battery that can be charged with power supplied from an external source, and a motor for driving that is driven using the power of the battery. For example, the vehicle Ve is a plug-in hybrid vehicle (PHEV) or an electric vehicle (BEV). The power conversion device 1 is used to supply power from an AC power source such as a commercial power source or a household power source to a battery mounted on the vehicle Ve, and to supply AC power from the battery mounted on the vehicle Ve to electrical devices outside the vehicle. In other words, the power conversion device 1 functions as a charger and an AC power supply.

[0016] The power conversion device 1 supplies power between an external power source 2, a main battery 3, and an auxiliary battery 4. The external power source 2 is an AC power source such as a commercial power source (system power source) or a household power source. The main battery 3 and the auxiliary battery 4 are DC power sources mounted on the vehicle Ve. The main battery 3 is a secondary battery that stores power to be supplied to a motor for driving, and supplies power for powering the motor and charges the battery with power generated by regenerative braking by the motor. The auxiliary battery 4 is a secondary battery that charges the battery with power to be supplied to auxiliary devices such as audio equipment, interior lights, and air conditioners mounted on the vehicle Ve. The power conversion device 1 supplies power supplied from the external power source 2 to the main battery 3 and the auxiliary battery 4. The power conversion device 1 also supplies power from the main battery 3 to the auxiliary battery 4. That is, the power conversion device 1 functions as an auxiliary DCDC in addition to a charger and an AC power feeder.

[0017] This power conversion device 1 includes a first switching circuit 10, a second switching circuit 20, a third switching circuit 30, and a transformer 40. A main battery 3 is connected to the second switching circuit 20. An auxiliary battery 4 is connected to the third switching circuit 30. When performing external charging, an external power source 2 is connected to the first switching circuit 10, as shown in Fig. 1. The power conversion device 1 transmits power between the external power source 2, the main battery 3, and the auxiliary battery 4 via the transformer 40.

[0018] The transformer 40 has a first winding 41, a second winding 42, and a third winding 43. The first winding 41, the second winding 42, and the third winding 43 are magnetically coupled to each other. Both ends of the first winding 41 are connected to the first switching circuit 10. Both ends of the second winding 42 are connected to the second switching circuit 20. Both ends of the third winding 43 are connected to the third switching circuit 30.

[0019] The first switching circuit 10 is connected between the external power supply 2 and the first winding 41, and supplies power supplied from the external power supply 2 to the first winding 41. The first switching circuit 10 includes a PFC circuit 11, a smoothing capacitor 12, a first bridge circuit 13, and a relay 14.

[0020] The PFC circuit 11 improves the power factor of AC power input from the external power source 2, converts the AC power to DC power, and outputs it to the first bridge circuit 13. During external charging, the external power source 2 is connected to the AC terminals of the PFC circuit 11. The first bridge circuit 13 is connected to the positive and negative terminals of the PFC circuit 11.

[0021] The smoothing capacitor 12 smoothes the voltage of the DC power output from the PFC circuit 11. The smoothing capacitor 12 is connected to the power line between the PFC circuit 11 and the first bridge circuit 13. This smoothing capacitor 12 is a first capacitor.

[0022] The first bridge circuit 13 is a full bridge circuit connected to the positive and negative terminals of the PFC circuit 11, and includes a switching arm 13a and a switching arm 13b. The switching arm 13a includes switching elements S1 and S2 connected in series. The switching arm 13b includes switching elements S3 and S4 connected in series. The switching arms 13a and 13b are connected in parallel. A smoothing capacitor 12 is connected in parallel to the switching arms 13a and 13b. An upper parallel connection point between the switching arms 13a and 13b and the smoothing capacitor 12 is connected to the positive terminal of the PFC circuit 11. A lower parallel connection point between the switching arms 13a and 13b and the smoothing capacitor 12 is connected to the negative terminal of the PFC circuit 11. A first winding 41 is connected between the connection point between the switching element S1 and the switching element S2 and the connection point between the switching element S3 and the switching element S4.

[0023] The relay 14 is provided in the power line between the first bridge circuit 13 and the first winding 41. The relay 14 is provided in the power line between one end of the first winding 41 and a connection point between the switching element S3 and the switching element S4. When the relay 14 is in a closed state (ON state), the first winding 41 and the first switching circuit 10 are electrically connected. On the other hand, when the relay 14 is in an open state (OFF state), the first winding 41 and the first switching circuit 10 are electrically disconnected from each other so that no current can pass between them.

[0024] The second switching circuit 20 is connected between the main battery 3 and the second winding 42, and supplies power from the main battery 3 to the second winding 42. The second switching circuit 20 includes a main capacitor 21 and a second bridge circuit 22.

[0025] The main engine capacitor 21 is connected between the positive and negative pole wires of the main engine battery 3. This main engine capacitor 21 is a second capacitor.

[0026] The second bridge circuit 22 is a full bridge circuit connected to the positive and negative terminals of the main battery 3, and includes a switching arm 22a and a switching arm 22b. The switching arm 22a includes switching elements S5 and S6 connected in series. The switching arm 22b includes switching elements S7 and S8 connected in series. The switching arms 22a and 22b are connected in parallel. The main capacitor 21 is connected in parallel to the switching arms 22a and 22b. The upper parallel connection point between the switching arms 22a and 22b and the main capacitor 21 is connected to the positive terminal of the main battery 3. The lower parallel connection point between the switching arms 22a and 22b and the main capacitor 21 is connected to the negative terminal of the main battery 3. In addition, a second winding 42 is connected between the connection point between the switching element S5 and the switching element S6 and the connection point between the switching element S7 and the switching element S8.

[0027] The third switching circuit 30 is connected between the auxiliary battery 4 and the third winding 43, and supplies power from the auxiliary battery 4 to the third winding 43. The third switching circuit 30 includes a third bridge circuit 31, an intermediate capacitor 32, and an auxiliary capacitor 33.

[0028] The third bridge circuit 31 includes a switching arm 31a and a switching arm 31b. The switching arm 31a includes switching elements S9 and S10 connected in series. The switching arm 31b includes switching elements S11 and S12 connected in series. The switching arms 31a and 31b are connected in parallel. An intermediate capacitor 32 is connected in parallel to the switching arms 31a and 31b. A third winding 43 is connected between a connection point between the switching element S9 and the switching element S10 and a connection point between the switching element S11 and the switching element S12.

[0029] The auxiliary capacitor 33 is connected between the lower parallel connection point of the switching arms 31a, 31b and the intermediate capacitor 32 and the midpoint of the third winding 43. The midpoint of the third winding 43 is connected to the positive terminal of the auxiliary battery 4. The lower parallel connection point of the switching arms 31a, 31b and the intermediate capacitor 32 is connected to the negative terminal of the auxiliary battery 4. The midpoint of the third winding 43 refers to a midpoint of the conductor that forms the third winding 43. The midpoint may be a center tap provided at the midpoint of the conductor that forms the third winding 43. The auxiliary capacitor 33 is the third capacitor, and the intermediate capacitor 32 is the fourth capacitor.

[0030] A diode is connected to each of the switching elements S1 to S12 with its anode terminal facing the lower end side of the switching element S1 to S12. Each of the switching elements S1 to S12 is composed of an IGBT (Insulated Gate Bipolar Transistor) or a MOSFET (Metal Oxide Semiconductor Field Effect Transistor).

[0031] Here, the operation of the power conversion device 1 will be described.

[0032] The operation of the power conversion device 1 differs depending on whether the vehicle Ve is stopped and supplies power between the external power source 2 and the main battery 3 (charger, AC power supply) or whether the vehicle Ve supplies power between the main battery 3 and the auxiliary battery 4 (auxiliary DCDC).

[0033] First, the operation of the power conversion device 1 when power is supplied between the external power source 2 and the main battery 3 while the vehicle Ve is stopped will be described. When the power conversion device 1 functions as a charger or AC power feeder, the external power source 2 is connected to the PFC circuit 11. For example, a charging plug on the external power source 2 side is connected to a charging port provided in the vehicle Ve. The input terminal of the power conversion device 1, i.e., the AC terminal of the PFC circuit 11, is provided at the charging port.

[0034] When the vehicle Ve is stopped and the main battery 3 is charged using the external power source 2, the power conversion device 1 closes the relay 14 and transmits power from the external power source 2 from the first switching circuit 10 to the second switching circuit 20 via the transformer 40.

[0035] In this case, the PFC circuit 11 controls the current flowing through the AC terminal of the PFC circuit 11 by switching operation so that the time waveform of the current flowing through the AC terminal of the PFC circuit 11 is made to approximate or coincide with the time waveform of the AC voltage output by the external power source 2. The PFC circuit 11 converts the AC power input from the external power source 2 into DC power and outputs it to the first bridge circuit 13 while performing an operation to improve the power factor. The PFC circuit 11 boosts the voltage of the power supplied from the external power source 2 and outputs it to the first bridge circuit 13. That is, the terminal voltage of the smoothing capacitor 12 is adjusted by the PFC circuit 11. At that time, the power conversion device 1 adjusts the output voltage of the PFC circuit 11 so that it is higher than the peak value of the voltage of the external power source 2. For example, the charging voltage of the main battery 3 is 350V, and the charging voltage of the auxiliary battery 4 is 14.5V. The output voltage of the PFC circuit 11 is adjusted to 400V.

[0036] The first bridge circuit 13 outputs an AC voltage to the first winding 41 by switching the DC voltage output from the PFC circuit 11. That is, the first bridge circuit 13 converts the DC power of the PFC circuit 11 into AC power and supplies it to the first winding 41. When transmitting power to the second switching circuit 20 via the transformer 40, the power is transmitted to the second switching circuit 20 depending on the difference between the switching timing of the first bridge circuit 13 and the switching timing of the second bridge circuit 22.

[0037] The second switching circuit 20 supplies the power transmitted from the first switching circuit 10 to the main battery 3. In this case, the second bridge circuit 22 converts the AC current transmitted from the second winding 42 into DC power and supplies it to the main battery 3. In this case, the second switching circuit 20 is capable of outputting power to the main battery 3 and also outputting power to a load circuit connected to the main battery 3.

[0038] In addition, when charging the main battery 3 with power from the external power source 2, it is also possible to charge the auxiliary battery 4 with power from the external power source 2. The power conversion device 1 transmits power from the external power source 2 from the first switching circuit 10 to the third switching circuit 30 via the transformer 40.

[0039] When power is transmitted to the third switching circuit 30 via the transformer 40, power is transmitted to the third switching circuit 30 according to the difference between the switching timing of the first bridge circuit 13 and the switching timing of the third bridge circuit 31.

[0040] The third switching circuit 30 supplies the power transmitted from the first switching circuit 10 to the auxiliary battery 4. In this case, the third switching circuit 30 first charges the intermediate capacitor 32 with the power supplied from the first switching circuit 10 via the transformer 40. Then, due to the switching operation of the third bridge circuit 31, power is output from the intermediate capacitor 32 to the auxiliary battery 4 via the midpoint of the third winding 43.

[0041] The terminal voltage of the intermediate capacitor 32 is adjusted by controlling a phase difference, which is a delay in the switching phase of the switching arms 31a, 31b of the third bridge circuit 31 relative to the switching phase of the switching arms 13a, 13b of the first bridge circuit 13. The third bridge circuit 31 outputs an AC voltage to the third winding 43 by switching the voltage to the intermediate capacitor 32. In the power conversion device 1, the switching arms 13a, 13b, 22a, 22b, 31a, 31b perform switching operations with the same duty ratio D. Therefore, a voltage that is "1-D" times the terminal voltage of the intermediate capacitor 32 appears across the auxiliary battery 4 and the auxiliary capacitor 33 due to the switching operation of the third bridge circuit 31. In this way, the third bridge circuit 31 supplies power to the auxiliary battery 4 via the intermediate capacitor 32 using the current transmitted from the first switching circuit 10. At that time, the third switching circuit 30 is capable of outputting electric power to the auxiliary battery 4 and also outputting electric power to the auxiliary equipment connected to the auxiliary battery 4.

[0042] In this configuration, in the first switching circuit 10 and the third switching circuit 30, the terminal voltage of the smoothing capacitor 12 is stepped down to the terminal voltage of the intermediate capacitor 32, and the terminal voltage of the intermediate capacitor 32 is stepped down to the terminal voltage of the auxiliary battery 4 and the auxiliary capacitor 33. In this manner, power is supplied by stepwise stepping down the voltage.

[0043] Next, the operation of the power conversion device 1 when power is supplied between the main battery 3 and the auxiliary battery 4 while the vehicle Ve is running will be described. When the power conversion device 1 functions as the auxiliary DCDC, the external power source 2 is disconnected from the PFC circuit 11, and the PFC circuit 11 stops switching operation. When power is supplied from the main battery 3 to the auxiliary battery 4 while the vehicle Ve is running, the power conversion device 1 opens the relay 14 and transmits the power of the main battery 3 from the second switching circuit 20 to the third switching circuit 30 via the transformer 40.

[0044] In this case, the second bridge circuit 22 outputs an AC voltage to the second winding 42 by switching on the DC voltage output from the main battery 3. The second bridge circuit 22 converts the DC power of the main battery 3 into AC power and supplies it to the second winding 42. Then, when transmitting power to the third switching circuit 30 via the transformer 40, power is transmitted to the third switching circuit 30 depending on the difference between the switching timing of the second bridge circuit 22 and the switching timing of the third bridge circuit 31.

[0045] The third switching circuit 30 supplies the power transmitted from the second switching circuit 20 to the auxiliary battery 4. In this case, similar to the above-mentioned external charging, the third switching circuit 30 first charges the intermediate capacitor 32 with the power supplied from the second switching circuit 20 via the transformer 40. Then, due to the switching operation of the third bridge circuit 31, power is output from the intermediate capacitor 32 to the auxiliary battery 4 via the midpoint of the third winding 43.

[0046] In this way, while the vehicle Ve is running, power is supplied from the main battery 3 to the auxiliary battery 4 with the relay 14 open, and the auxiliary battery 4 is charged. Even if a short circuit occurs in the smoothing capacitor 12 of the first switching circuit 10, the relay 14 is open, and the current path between the first winding 41 and the smoothing capacitor 12 is interrupted. By opening the relay 14 while the vehicle Ve is running, it is possible to prevent a current caused by a short circuit in the smoothing capacitor 12 from flowing to the first winding 41. Therefore, while the vehicle Ve is running, it is possible to prevent an overcurrent from occurring in the second switching circuit 20 on the main battery 3 side and the third switching circuit 30 on the auxiliary battery 4 side due to power transmission from the first switching circuit 10 via the transformer 40.

[0047] If the circuit does not include the relay 14, the main battery 3 side and the first switching circuit 10 are driven to maintain the terminal voltage of the smoothing capacitor 12 on the PFC side at 400 V, and therefore, when a short circuit occurs in the smoothing capacitor 12, the current flowing through the circuit on the main battery 3 side and the auxiliary battery 4 side increases. For example, in the case of a 1000 W output, the value of the current flowing through the circuit on the main battery 3 side increases from 4 Aac to 50 Aac, and the value of the current flowing through the circuit on the auxiliary battery 4 side increases from 50 Aac to 180 Aac. This current increase may cause the battery fuse to melt. In contrast, the power conversion device 1 including the relay 14 can prevent an overcurrent from flowing through the second switching circuit 20 and the third switching circuit 30 via the transformer 40.

[0048] As described above, according to the embodiment, when power is supplied from the main battery 3 to the auxiliary battery 4, the relay 14 is in an open state, which prevents power from being transmitted from the first switching circuit 10 to the second switching circuit 20 and the third switching circuit 30 via the transformer 40. As a result, if a short circuit occurs in the smoothing capacitor 12 of the first switching circuit 10, the relay 14 is in an open state, which prevents an overcurrent from flowing through the second switching circuit 20 and the third switching circuit 30.

[0049] Furthermore, the installation location of relay 14 is not limited to the above embodiment. As a measure against a short circuit of smoothing capacitor 12, relay 14 may be provided on the power line between smoothing capacitor 12 and first winding 41. In this case, relay 14 may be installed at first to sixth installation locations 14A to 14F as shown in FIG. 2.

[0050] The first installation location 14A is a power line between the connection point of the switching elements S1, S2 and the first winding 41. The second installation location 14B is a power line between the connection point of the switching elements S3, S4 and the first winding 41. The third installation location 14C is a power line connecting the upper sides of the switching arms 13a and 13b. The fourth installation location 14D is a power line connecting the lower sides of the switching arms 13a and 13b. The fifth installation location 14E is a power line connecting the upper sides of the switching arms 13a and the smoothing capacitor 12. The sixth installation location 14F is a power line connecting the upper sides of the switching arms 13b and the smoothing capacitor 12.

[0051] As a measure against a short circuit of the smoothing capacitor 12, it is sufficient that the relay 14 is provided in at least one of the first to sixth installation locations 14A to 14F. In other words, the number of the relay 14 is not limited to one, and it may be provided in a plurality of installation locations.

[0052] Furthermore, a short circuit in the first switching circuit 10 may occur not only in the smoothing capacitor 12, but also in the switching elements of the first bridge circuit 13. To prevent a short circuit in the switching elements S1 to S4 of the first bridge circuit 13, a relay 14 may be provided in the power line between the first bridge circuit 13 and the first winding 41. In this case, the relay 14 may be installed at first and second installation locations 14A and 14B as shown in FIG.

[0053] As a measure against a short circuit of the switching elements of the first bridge circuit 13, it is sufficient that a relay 14 is provided in at least one of the first and second installation locations 14A and 14B. In this case, the number of relays 14 is not limited to one, and relays 14 may be provided in both the first and second installation locations 14A and 14B. [Explanation of symbols]

[0054] 1 Power conversion device 2 External power supply 3 Main engine battery 4. Auxiliary battery 10 First switching circuit 11 PFC circuit 12 Smoothing capacitor 13 First bridge circuit 14 Relay 20 Second switching circuit 21 Main engine capacitor 22 Second bridge circuit 30 Third switching circuit 31 Third bridge circuit 32 Intermediate Capacitor 33 Auxiliary Capacitor 40 Trans 41 Winding No. 1 42 Second Winding 43 Third Winding

Claims

[Claim 1] a transformer having a first winding, a second winding, and a third winding; a first switching circuit connected between an external power supply and the first winding and configured to supply power input from the external power supply to the first winding; a second switching circuit connected between a main battery and the second winding, supplying the power input from the first switching circuit via the transformer to the main battery and supplying the power output from the main battery to the second winding; a third switching circuit connected between an auxiliary battery and the third winding and configured to supply the power input from the second switching circuit via the transformer to the auxiliary battery; A power conversion device comprising: The first switching circuit is a PFC circuit that corrects a power factor of the AC power input from the external power supply; a smoothing capacitor that smoothes the voltage of the DC power output from the PFC circuit; a first bridge circuit that converts the DC power output from the PFC circuit into AC power and supplies the AC power to the first winding; a relay provided in a power line between the smoothing capacitor and the first winding, The PFC circuit converts the AC power having a corrected power factor into DC power and outputs the DC power to the first bridge circuit; the smoothing capacitor is connected to a power line between the PFC circuit and the first bridge circuit, the first bridge circuit is a full bridge circuit connected to a positive terminal and a negative terminal of the PFC circuit, and has a first switching arm and a second switching arm connected in parallel; the smoothing capacitor is connected in parallel to the first switching arm and the second switching arm, the first switching arm has a first switching element and a second switching element connected in series; the second switching arm includes a third switching element and a fourth switching element connected in series; the first winding is connected between a connection point between the first switching element and the second switching element and a connection point between the third switching element and the fourth switching element, The relay is provided in at least one of a plurality of installation locations, The plurality of installation locations include: a power line connecting upper sides of the first switching arm and the second switching arm; a power line connecting a lower side of the first switching arm and a lower side of the second switching arm; a power line connecting the first switching arm and an upper side of the smoothing capacitor; a power line connecting the first switching arm and a lower side of the smoothing capacitor, The main battery and the auxiliary battery are mounted on an electric vehicle, When the electric vehicle is running, the relay is opened and power is transmitted from the main battery to the auxiliary battery via the transformer. A power conversion device comprising:

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