Power Conversion Device

Abstract

A power conversion device (14) has low-voltage side terminals (TL1, TL2) and high-voltage side terminals (TH1, TH2). The power conversion device comprises: a step-up operation unit that performs a step-up operation for stepping up a voltage that is input from the low-voltage side terminals and outputting the stepped-up voltage to the high-voltage side terminals; a step-down operation unit that performs a step-down operation for stepping down a voltage that is input from the high-voltage side terminals and outputting the stepped-down voltage to the low-voltage side terminals; and a control unit (24) that causes the step-up operation unit to perform the step-up operation and causes the step-down operation unit to perform the step-down operation, thereby performing a temperature rise control for raising the temperature of an object (13) to be raised in temperature.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Japanese Application No. 2022-094503, filed on June 10, 2022, the contents of which are incorporated herein by reference. [Technical Field]

[0002] The present disclosure relates to a power conversion device having a low-voltage side terminal and a high-voltage side terminal. [Background technology]

[0003] As this type of power conversion device, Patent Document 1 describes one that boosts the DC voltage of a battery and supplies the voltage to a capacitor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-42341 Summary of the Invention

[0005] For example, a heating control for raising the temperature of a battery may involve exchanging power between the battery and a capacitor. In this case, a portion of the exchanged power is converted into thermal energy, and the converted thermal energy is used to raise the temperature of the battery. However, since there is an upper limit to the voltage that can be applied to the battery and the capacitor, there is a possibility that the increase in the power exchanged in the heating control may be limited. As a result, there is a concern that the efficiency of the heating control may be reduced, such as the thermal energy used to raise the battery temperature may not be sufficiently increased.

[0006] The present disclosure has been made in view of the above-mentioned problems, and a main object of the present disclosure is to provide a power conversion device capable of improving the efficiency of temperature rise control.

[0007] The present disclosure provides a power conversion device having a low-voltage side terminal and a high-voltage side terminal, comprising: a boost operation unit that performs a boost operation of boosting a voltage input from the low-voltage side terminal and outputting the boosted voltage to the high-voltage side terminal; a step-down operation unit that performs a step-down operation of lowering a voltage input from the high-voltage side terminal and outputting the lowered voltage to the low-voltage side terminal; and a control unit that causes the boost operation unit to perform the step-up operation and also causes the step-down operation unit to perform the step-down operation, thereby performing temperature rise control to raise the temperature of an object to be heated.

[0008] Unlike the present disclosure, a possible temperature increase control is to alternately perform a voltage increase operation in which the voltage input from the low-voltage side terminal is increased and output to the high-voltage side terminal, and a voltage decrease operation in which the voltage input from the high-voltage side terminal is decreased and output to the low-voltage side terminal. As a result, power is exchanged between the low-voltage side terminal and the high-voltage side terminal. In this case, a portion of the exchanged power is converted into thermal energy and used to increase the temperature of the object to be heated.

[0009] In order to increase the thermal energy used to raise the temperature of the object to be heated, it is conceivable to increase the power exchanged during the heating control. Here, the power exchanged that is not converted into thermal energy is supplied to the low-voltage side terminal or the high-voltage side terminal. Specifically, during a period in which a voltage step-up operation is performed, power is supplied to the high-voltage side terminal. This increases the inter-terminal voltage of the high-voltage side terminal. Furthermore, during a period in which a voltage step-down operation is performed, power is supplied to the low-voltage side terminal. This increases the inter-terminal voltage of the low-voltage side terminal. In this case, the inter-terminal voltage of at least one of the low-voltage side terminal and the high-voltage side terminal may reach the upper limit voltage of the low-voltage side terminal or the high-voltage side terminal, potentially limiting the increase in the power exchanged during the heating control. As a result, there is a concern that the efficiency of the heating control may be reduced, such as by not being able to sufficiently increase the thermal energy used to raise the temperature of the object to be heated.

[0010] In this regard, according to the present disclosure, temperature rise control is performed by causing the boost operation unit to perform a boost operation and causing the buck operation unit to perform a buck operation. In this case, at the high-voltage side terminal, power is supplied from the low-voltage side terminal by the boost operation, while power is output to the low-voltage side terminal by the buck operation. At the low-voltage side terminal, power is supplied from the high-voltage side terminal by the buck operation, while power is output to the high-voltage side terminal by the boost operation. This allows power to be exchanged between the boost operation unit and the buck operation unit while suppressing changes in the terminal-to-terminal voltage of the low-voltage side terminal and the terminal-to-terminal voltage of the high-voltage side terminal. Therefore, the terminal-to-terminal voltage of the low-voltage side terminal and the high-voltage side terminal can be prevented from reaching an upper limit voltage during temperature rise control, while increasing the power exchanged during temperature rise control. As a result, the thermal energy used to raise the temperature of the object to be heated can be sufficiently increased, thereby improving the efficiency of temperature rise control. [Brief explanation of the drawings]

[0011] The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: [Figure 1] FIG. 1 is a configuration diagram of a vehicle according to a first embodiment; [Figure 2] FIG. 2 is a configuration diagram of a power conversion device; [Figure 3] FIG. 3 is a time chart showing an example of a voltage boosting operation. [Figure 4] FIG. 4 is a diagram showing a current path flowing through a power conversion device during a boost operation; [Figure 5] FIG. 5 is a time chart showing an example of a voltage step-down operation. [Figure 6] FIG. 6 is a diagram showing a current path through a power conversion device during a step-down operation; [Figure 7] FIG. 7 is a time chart showing an example of temperature rise control; [Figure 8] FIG. 8 is a diagram showing a method for setting the switching frequency. [Figure 9]FIG. 9 is a diagram showing a method for setting the lengths of the periods in Mode 2 and Mode 4. [Figure 10] FIG. 10 is a diagram showing the effect of temperature rise control; [Figure 11] FIG. 11 is a diagram showing the effect of temperature rise control; [Figure 12] FIG. 12 is a time chart showing an example of a voltage step-up operation and a voltage step-down operation according to the second embodiment; [Figure 13] FIG. 13 is a diagram showing a current path that flows through a power conversion device and ground during temperature rise control; [Figure 14] FIG. 14 is a time chart showing an example of temperature rise control; [Figure 15] FIG. 15 is a diagram showing the effect of suppressing the generation of noise current; [Figure 16] FIG. 16 is a configuration diagram of a power conversion device according to a third embodiment; [Figure 17] FIG. 17 is a configuration diagram of a power conversion device according to a fourth embodiment; [Figure 18] FIG. 18 is a time chart showing an example of a voltage step-down operation. [Figure 19] FIG. 19 is a diagram showing a current path that flows through a power conversion device and ground during a step-down operation; [Figure 20] FIG. 20 is a configuration diagram of a power conversion device according to another embodiment; [Figure 21] FIG. 21 is a configuration diagram of a power conversion device according to another embodiment; [Figure 22] FIG. 22 is a configuration diagram of a power conversion device according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] First Embodiment A first embodiment of a power conversion device according to the present disclosure will be described below with reference to the drawings. The power conversion device is mounted on a moving object such as a vehicle, an aircraft, or a ship. In this embodiment, the power conversion device is mounted on a vehicle. The vehicle is, for example, a hybrid vehicle equipped with a rotating electric machine and an engine, or an electric vehicle equipped with only the rotating electric machine of the rotating electric machine and engine.

[0013] As shown in FIG. 1, a vehicle 10 includes a rotating electric machine 11, an inverter 12, a battery 13, a power converter 14, and a heat transfer unit 15. The rotating electric machine 11 is connected to drive wheels and an engine serving as a main vehicle engine via a power split mechanism (not shown). The rotating electric machine 11 is connected to the inverter 12 and functions as a main vehicle engine, etc. The inverter 12 is a three-phase inverter and is connected to a battery 13 (for example, a lithium-ion secondary battery or a nickel-metal hydride secondary battery). For example, the rated voltage of the battery 13 is 600V to 800V.

[0014] The battery 13 is connected to an off-vehicle charger 16 provided outside the vehicle 10 via a power converter 14. The off-vehicle charger 16 is, for example, a DC quick charger. When the battery 13 is connected to the off-vehicle charger 16 via the power converter 14, it is charged by DC power input from the off-vehicle charger 16. For example, the charging voltage of the off-vehicle charger 16 is 300V to 400V.

[0015] The heat transfer unit 15 transfers thermal energy generated in the heat exchange target to the target to be heated. The heat transfer unit 15 is configured to absorb heat generated in the heat exchange target, which is the rotating electric machine 11, the inverter 12, the battery 13, and the power conversion device 14. The heat transfer unit 15 transfers the absorbed heat to the target to be heated, thereby increasing the temperature of the target to be heated. In this embodiment, the target to be heated is the battery 13. The heat transfer unit 15 may, for example, include a circulation path through which coolant circulates between the heat exchange target and the target to be heated, and the temperature of the target to be heated is increased via this coolant. Note that the heat transfer unit 15 may also be configured to use, for example, gas (air) as a cooling fluid. Alternatively, the heat transfer unit 15 may be, for example, a component such as a heat sink that contacts the heat exchange target and the target to be heated, without using a cooling fluid.

[0016] 2 shows the configuration of the power conversion device 14. The power conversion device 14 is provided with a high-voltage side terminal, i.e., a first high-voltage side terminal TH1 and a second high-voltage side terminal TH2, as high-voltage side terminals, and a first low-voltage side terminal TL1 and a second low-voltage side terminal TL2 as low-voltage side terminals. In this embodiment, the low-voltage side terminals TL1 and TL2 are connected to the off-vehicle charger 16, and the high-voltage side terminals TH1 and TH2 are connected to the battery 13.

[0017] The power conversion device 14 transforms the voltage input from either the low-voltage side terminals TL1, TL2 or the high-voltage side terminals TH1, TH2 and outputs the transformed voltage to the other terminal. In this embodiment, the power conversion device 14 functions as a boost converter with a boost ratio of 2, and doubles the charging voltage input from the off-vehicle charger 16 and outputs it to the battery 13. This charges the battery 13.

[0018] The power conversion device 14 includes a high-voltage side capacitor 20 and a low-voltage side capacitor 21. A first end of the high-voltage side capacitor 20 is connected to a first high-voltage side terminal TH1, and a second end of the high-voltage side capacitor 20 is connected to a second high-voltage side terminal TH2. A first end of the low-voltage side capacitor 21 is connected to a first low-voltage side terminal TL1, and a second end of the low-voltage side capacitor 21 is connected to a second low-voltage side terminal TL2.

[0019] The power conversion device 14 includes a high-voltage side voltage sensor 22, a low-voltage side voltage sensor 23, and a control device 24. The high-voltage side voltage sensor 22 detects the voltage VH between the high-voltage side terminals TH1 and TH2, and the low-voltage side voltage sensor 23 detects the voltage VL between the low-voltage side terminals TL1 and TL2. The detected values ​​of the voltage sensors 22 and 23 are input to the control device 24.

[0020] The power conversion device 14 includes a plurality of power conversion units. In this embodiment, the power conversion device 14 includes a first power conversion unit 30 and a second power conversion unit 40.

[0021] The first power conversion unit 30 includes a first upper arm unit 31, a first lower arm unit 32, and a first resonant unit 33. The first upper arm unit 31 and the first lower arm unit 32 are a series connection of voltage-controlled semiconductor switches. The first resonant unit 33 is a series connection of a first reactor 34 and a first capacitor 35. In this embodiment, N-channel MOSFETs having body diodes are used as the semiconductor switches of the first upper arm unit 31 and the first lower arm unit 32.

[0022] The drain of the upper switch QH1 of the first upper arm section 31 is connected to the high-voltage side first terminal TH1, and the source of the upper switch QH1 of the first upper arm section 31 is connected to the drain of the lower switch QH2 of the first upper arm section 31. The source of the lower switch QH2 of the first upper arm section 31 is connected to the low-voltage side first terminal TL1 and the drain of the upper switch QL1 of the first lower arm section 32. The drain of the lower switch QL2 of the first lower arm section 32 is connected to the source of the upper switch QL1 of the first lower arm section 32, and the source of the lower switch QL2 of the first lower arm section 32 is connected to the high-voltage side second terminal TH2 and the low-voltage side second terminal TL2. A first end of the first reactor 34 is connected to the connection point between the source of the upper switch QH1 and the drain of the lower switch QH2 in the first upper arm section 31. A second end of the first reactor 34 is connected to the first end of the first capacitor 35. A second end of the first capacitor 35 is connected to the connection point between the source of the upper switch QL1 and the drain of the lower switch QL2 in the first lower arm section 32.

[0023] The second power conversion unit 40 includes a second upper arm unit 41, a second lower arm unit 42, and a second resonant unit 43. The second upper arm unit 41 and the second lower arm unit 42 are a series connection of voltage-controlled semiconductor switches. The second resonant unit 43 is a series connection of a second reactor 44 and a second capacitor 45. In this embodiment, N-channel MOSFETs having body diodes are used as the semiconductor switches of the second upper arm unit 41 and the second lower arm unit 42.

[0024] The drain of the upper switch SH1 of the second upper arm section 41 is connected to the high-voltage side first terminal TH1, and the source of the upper switch SH1 of the second upper arm section 41 is connected to the drain of the lower switch SH2 of the second upper arm section 41. The source of the lower switch SH2 of the second upper arm section 41 is connected to the low-voltage side first terminal TL1 and the drain of the upper switch SL1 of the second lower arm section 42. The drain of the lower switch SL2 of the second lower arm section 42 is connected to the source of the upper switch SL1 of the second lower arm section 42, and the source of the lower switch SL2 of the second lower arm section 42 is connected to the high-voltage side second terminal TH2 and the low-voltage side second terminal TL2. A first end of the second reactor 44 is connected to the connection point between the source of the upper switch SH1 and the drain of the lower switch SH2 of the second upper arm section 41. A second end of the second reactor 44 is connected to the first end of the second capacitor 45. A second end of the second capacitor 45 is connected to the connection point between the source of the upper switch SL1 and the drain of the lower switch SL2 in the second lower arm section .

[0025] In this embodiment, the upper switches QH1, SH1 of each upper arm section 31, 41 correspond to the "upper arm first switch," and the lower switches QH2, SH2 of each upper arm section 31, 41 correspond to the "upper arm second switch." Furthermore, the upper switches QL1, SL1 of each lower arm section 32, 42 correspond to the "lower arm first switch," and the lower switches QL2, SL2 of each lower arm section 32, 42 correspond to the "lower arm second switch."

[0026] The control device 24 is mainly configured with a microcomputer. The functions provided by the control device 24 can be provided by, for example, software recorded in a physical memory device and a computer that executes the software, hardware, or a combination of these.

[0027] The control device 24 turns on and off the switches QH1, QH2, QL1, and QL2 of the first power conversion unit 30 to place the first power conversion unit 30 in one of Modes 1 to 4. In Mode 1, the upper switch QH1 of the first upper arm unit 31 and the upper switch QL1 of the first lower arm unit 32 are turned on, and the lower switch QH2 of the first upper arm unit 31 and the lower switch QL2 of the first lower arm unit 32 are turned off. In Mode 2, the upper switch QH1 of the first upper arm unit 31 and the lower switch QL2 of the first lower arm unit 32 are turned on, and the lower switch QH2 of the first upper arm unit 31 and the upper switch QL1 of the first lower arm unit 32 are turned off.

[0028] In Mode 3, the lower switch QH2 of the first upper arm portion 31 and the lower switch QL2 of the first lower arm portion 32 are turned on, and the upper switch QH1 of the first upper arm portion 31 and the upper switch QL1 of the first lower arm portion 32 are turned off. In Mode 4, the lower switch QH2 of the first upper arm portion 31 and the upper switch QL1 of the first lower arm portion 32 are turned on, and the upper switch QH1 of the first upper arm portion 31 and the lower switch QL2 of the first lower arm portion 32 are turned off.

[0029] As in the case of the first power conversion unit 30, the control device 24 turns on and off each of the switches SH1, SH2, SL1, and SL2 of the second power conversion unit 40 to place the second power conversion unit 40 in one of Modes 1 to 4.

[0030] The control device 24 causes each of the power conversion units 30, 40 to repeatedly perform one cycle of processing consisting of Modes 1 to 4, thereby causing each of the power conversion units 30, 40 to operate as either a step-up operation unit or a step-down operation unit. The step-up operation is an operation of stepping up the voltage input from the low-voltage side terminals TL1, TL2 and outputting the step-up voltage to the high-voltage side terminals TH1, TH2. The step-down operation is an operation of stepping down the voltage input from the high-voltage side terminals TH1, TH2 and outputting the step-down voltage to the low-voltage side terminals TL1, TL2. The control device 24 performs temperature rise control to raise the temperature of the battery 13, which is the target for temperature rise, by performing the step-up operation and the step-down operation. The temperature rise control will be described later.

[0031] First, a process for causing the first power conversion unit 30 to perform a boost operation will be described with reference to Figures 3 and 4. In Figure 3(a), a solid line indicates the on / off state of the upper switch QH1 of the first upper arm unit 31, and a dashed line indicates the on / off state of the lower switch QH2 of the first upper arm unit 31. In Figure 3(b), a solid line indicates the on / off state of the upper switch QL1 of the first lower arm unit 32, and a dashed line indicates the on / off state of the lower switch QL2 of the first lower arm unit 32. Figure 3(c) shows the transition of the current iQ flowing through the first resonance unit 33. Here, the sign of the current iQ flowing through the first resonance unit 33 is positive when the current flows from the first end of the first reactor 34 to the second end of the first reactor 34.

[0032] When the control device 24 operates the first power conversion unit 30 as a boost operation unit, it causes the first power conversion unit 30 to repeatedly perform processes consisting of Mode 1, Mode 2, Mode 3, and Mode 4 in this order. The switching period Tsw is the total period of Modes 1 to 4. Figures 4(a) to 4(d) show the current paths that flow through the power conversion device 14 during boost operation for each of Modes 1 to 4. Note that the second power conversion unit 40 and the like are not shown in Figure 4.

[0033] During a period in which the first power conversion unit 30 is in Mode 1, a current flows through a closed circuit including the first low-voltage side terminal TL1, the upper switch QL1 of the first lower arm unit 32, the first capacitor 35, the first reactor 34, the upper switch QH1 of the first upper arm unit 31, the high-voltage side capacitor 20, and the second low-voltage terminal TL2. In this case, the current flows in a direction in which the sign of the current iQ flowing through the first resonance unit 33 is negative. As a result, the first capacitor 35 is discharged, and power is supplied from the low-voltage side terminals TL1 and TL2 to the high-voltage side terminals TH1 and TH2. Note that the reason why the direction of the current during the period in Mode 1 is such that the sign of the current iQ flowing through the first resonance unit 33 is negative is because, as will be described later, the sign of the current iQ flowing through the first resonance unit 33 was negative during the immediately preceding period in Mode 4.

[0034] During the period when the first power conversion unit 30 is in Mode 2, a current flows through a closed circuit including the high-voltage side capacitor 20, the upper switch QH1 of the first upper arm unit 31, the first reactor 34, the first capacitor 35, and the lower switch QL2 of the first lower arm unit 32. During the period when the first power conversion unit 30 is in Mode 2, the direction of the current is reversed from the direction of the current flowing during the immediately preceding period when the first power conversion unit 30 is in Mode 1. In other words, the sign of the current iQ flowing through the first resonance unit 33 switches from negative to positive.

[0035] During the period when the first power conversion unit 30 is in Mode 3, a current flows through a closed circuit including the low-voltage side first terminal TL1, the lower switch QH2 of the first upper arm unit 31, the first reactor 34, the first capacitor 35, the lower switch QL2 of the first lower arm unit 32, and the low-voltage side second terminal TL2. In this case, the current flows in the same direction as the current flowing during the immediately preceding period when the first power conversion unit 30 is in Mode 2, and in a direction such that the sign of the current iQ flowing through the first resonance unit 33 is positive. This charges the first capacitor 35.

[0036] During the period when the first power conversion unit 30 is in Mode 4, a current flows through a closed circuit including the lower switch QH2 of the first upper arm unit 31, the upper switch QL1 of the first lower arm unit 32, the first capacitor 35, and the first reactor 34. During the period when the first power conversion unit 30 is in Mode 4, the direction of the current is reversed from the direction of the current flowing during the immediately preceding period when the first power conversion unit 30 is in Mode 3. In other words, the sign of the current iQ flowing through the first resonance unit 33 switches from positive to negative.

[0037] As a result of the above-described boost operation being performed in the first power conversion unit 30, the voltage input from the low-voltage side terminals TL1 and TL2 is boosted, and the boosted voltage is output to the high-voltage side terminals TH1 and TH2. In the boost operation, the longer the period in Mode 2 or Mode 4, the larger the amplitude of the current iQ flowing through the first resonance unit 33. In this case, the amount of power supplied from the low-voltage side terminals TL1 and TL2 to the high-voltage side terminals TH1 and TH2 increases.

[0038] Next, a process for causing the first power conversion unit 30 to perform a step-down operation will be described with reference to Figures 5 and 6. In Figure 5, (a) to (c) correspond to Figures 3(a) to (c) above.

[0039] When the control device 24 operates the first power conversion unit 30 as a step-down operation unit, it causes the first power conversion unit 30 to repeatedly perform processes consisting of Mode 1, Mode 4, Mode 3, and Mode 2 in this order. The switching period Tsw is the total period of Modes 1 to 4. Figures 6(a) to 6(d) show the current paths that flow through the power conversion device 14 during step-down operation for each period of Modes 1 to 4. Note that the second power conversion unit 40 and the like are not shown in Figure 6.

[0040] During a period in which the first power conversion unit 30 is in Mode 1, a current flows through a closed circuit including the high-voltage side first terminal TH1, the upper switch QH1 of the first upper arm unit 31, the first reactor 34, the first capacitor 35, the upper switch QL1 of the first lower arm unit 32, the low-voltage side capacitor 21, and the high-voltage side second terminal TH2. In this case, the current flows in a direction in which the sign of the current iQ flowing through the first resonance unit 33 is positive. As a result, the first capacitor 35 is charged, and power is supplied from the high-voltage side terminals TH1 and TH2 to the low-voltage side terminals TL1 and TL2. Note that the reason why the direction of the current during the period in Mode 1 is such that the sign of the current iQ flowing through the first resonance unit 33 is positive is because, as will be described later, the sign of the current iQ flowing through the first resonance unit 33 was positive during the immediately preceding period in Mode 2.

[0041] During the period when the first power conversion unit 30 is in Mode 4, a current flows through a closed circuit including the lower switch QH2 of the first upper arm unit 31, the upper switch QL1 of the first lower arm unit 32, the first capacitor 35, and the first reactor 34. During the period when the first power conversion unit 30 is in Mode 4, the direction of the current is reversed from the direction of the current flowing during the immediately preceding period when the first power conversion unit 30 is in Mode 1. In other words, the sign of the current iQ flowing through the first resonance unit 33 switches from positive to negative.

[0042] During the period when the first power conversion unit 30 is in Mode 3, a current flows through a closed circuit including the low-voltage side second terminal TL2, the lower switch QL2 of the first lower arm unit 32, the first capacitor 35, the first reactor 34, the lower switch QH2 of the first upper arm unit 31, and the low-voltage side first terminal TL1. In this case, the current flows in the same direction as the current flowing during the immediately preceding period when the first power conversion unit 30 is in Mode 4, and in a direction in which the sign of the current iQ flowing through the first resonance unit 33 is negative. This causes the first capacitor 35 to discharge.

[0043] During the period when the first power conversion unit 30 is in Mode 2, a current flows through a closed circuit including the high-voltage side capacitor 20, the upper switch QH1 of the first upper arm unit 31, the first reactor 34, the first capacitor 35, and the lower switch QL2 of the first lower arm unit 32. During the period when the first power conversion unit 30 is in Mode 2, the direction of the current is reversed from the direction of the current flowing during the immediately preceding period when the first power conversion unit 30 is in Mode 3. In other words, the sign of the current iQ flowing through the first resonance unit 33 switches from negative to positive.

[0044] As a result of the above-described step-down operation being performed in the first power conversion unit 30, the voltage input from the high-voltage side terminals TH1 and TH2 is stepped down, and the stepped-down voltage is output to the low-voltage side terminals TL1 and TL2. In the step-down operation, the longer the period in Mode 2 or Mode 4, the larger the amplitude of the current iQ flowing through the first resonance unit 33. In this case, the amount of power supplied from the high-voltage side terminals TH1 and TH2 to the low-voltage side terminals TL1 and TL2 increases.

[0045] Next, the temperature rise control will be described. Unlike the present embodiment, it is conceivable that the temperature rise control for raising the temperature of the battery 13, which is the target for temperature rise, involves alternately performing a voltage rise operation and a voltage drop operation. As a result, electric power is exchanged between the low-voltage side terminals TL1, TL2 and the high-voltage side terminals TH1, TH2. In this case, a portion of the exchanged electric power is converted into thermal energy, and the converted thermal energy is transferred to the battery 13 via the heat transfer unit 15. As a result, the thermal energy is used to raise the temperature of the battery 13.

[0046] In order to increase the thermal energy used to increase the temperature of the battery 13, it is conceivable to increase the electric power exchanged during the temperature rise control. However, the electric power exchanged that is not converted into thermal energy is supplied to the low-voltage side terminals TL1 and TL2 or the high-voltage side terminals TH1 and TH2. Specifically, during the voltage step-up operation, electric power is supplied to the high-voltage side terminals TH1 and TH2. This increases the inter-terminal voltage VH between the high-voltage side terminals TH1 and TH2. Furthermore, during the voltage step-down operation, electric power is supplied to the low-voltage side terminals TL1 and TL2. This increases the inter-terminal voltage VL between the low-voltage side terminals TL1 and TL2. In this case, the inter-terminal voltage VL between the low-voltage side terminals TL1 and TL2 may reach an upper limit voltage determined based on the withstand voltage of the low-voltage side capacitor 21, or the inter-terminal voltage VH between the high-voltage side terminals TH1 and TH2 may reach an upper limit voltage determined based on the withstand voltage of the high-voltage side capacitor 20. This may limit the increase in the electric power exchanged during the temperature rise control. As a result, there is a concern that the efficiency of the temperature increase control may decrease, such that the thermal energy used to increase the temperature of the battery 13 may not be increased sufficiently.

[0047] Therefore, in this embodiment, the control device 24 performs temperature rise control by causing one of the first power conversion unit 30 and the second power conversion unit 40 to perform a voltage step-up operation and the other to perform a voltage step-down operation. Here, with reference to Fig. 7, a description will be given of temperature rise control in the case where the first power conversion unit 30 performs a voltage step-up operation and the second power conversion unit 40 performs a voltage step-down operation.

[0048] 7(a) and 7(b) correspond to the above-mentioned FIGS. 3(a) and 3(b). In FIG. 7(c), a solid line indicates the on / off state of the upper switch SH1 of the second upper arm unit 41, and a dashed line indicates the on / off state of the lower switch SH2 of the second upper arm unit 41. In FIG. 7(d), a solid line indicates the on / off state of the upper switch SL1 of the second lower arm unit 42, and a dashed line indicates the on / off state of the lower switch SL2 of the second lower arm unit 42. In FIG. 7(e), a solid line indicates the change in current iQ flowing through the first resonance unit 33, and a dashed line indicates the change in current iS flowing through the second resonance unit 43. In FIG. 7(f), a solid line indicates the change in power PL supplied to the low-voltage side terminals TL1 and TL2, and a dashed line indicates the change in output power PH of the battery 13.

[0049] During the temperature rise control, the control device 24 operates the first power conversion unit 30 as a boost operation unit. That is, in the first power conversion unit 30, processes consisting of Mode 1, Mode 2, Mode 3, and Mode 4 are repeatedly performed in this order. In this case, power is supplied from the low-voltage side terminals TL1 and TL2 to the high-voltage side terminals TH1 and TH2. Meanwhile, during the temperature rise control, the control device 24 operates the second power conversion unit 40 as a buck operation unit. That is, in the second power conversion unit 40, processes consisting of Mode 1, Mode 4, Mode 3, and Mode 2 are repeatedly performed in this order. In this case, power is supplied from the high-voltage side terminals TH1 and TH2 to the low-voltage side terminals TL1 and TL2.

[0050] During temperature rise control, the control device 24 operates the first power conversion unit 30 as a boost operation unit and the second power conversion unit 40 as a buck operation unit. In this case, the supply of power to the low-voltage side terminals TL1 and TL2 by the buck operation and the output of power from the low-voltage side terminals TL1 and TL2 by the boost operation are performed in parallel. Also, the supply of power to the high-voltage side terminals TH1 and TH2 by the boost operation and the output of power from the high-voltage side terminals TH1 and TH2 by the buck operation are performed in parallel. This suppresses changes in the inter-terminal voltage VL between the low-voltage side terminals TL1 and TL2 and the inter-terminal voltage VH between the high-voltage side terminals TH1 and TH2 during temperature rise control.

[0051] During temperature rise control, a current circulates between the first power conversion unit 30 and the second power conversion unit 40. A current indicated by the transition of the current iQ flowing through the first resonance unit 33 flows through the first power conversion unit 30. As a result, the first power conversion unit 30 experiences switching losses associated with the on / off switching of the switches QH1, QH2, QL1, and QL2, as well as conduction losses associated with the current flowing through the switches QH1, QH2, QL1, and QL2. Meanwhile, a current indicated by the transition of the current iS flowing through the second resonance unit 43 flows through the second power conversion unit 40. As a result, the second power conversion unit 40 experiences switching losses associated with the on / off switching of the switches SH1, SH2, SL1, and SL2, as well as conduction losses associated with the current flowing through the switches SH1, SH2, SL1, and SL2. The switching loss and conduction loss occurring in each of the switches QH1, QH2, QL1, QL2, SH1, SH2, SL1, and SL2 are converted into thermal energy. The thermal energy is transferred to the battery 13 via the heat transfer unit 15. As a result, the temperature of the battery 13 rises.

[0052] In this embodiment, as shown in Figure 7(f), the power PL supplied to the low-voltage side terminals TL1, TL2 is maintained at approximately 0 W. Therefore, changes in the inter-terminal voltage VL of the low-voltage side terminals TL1, TL2 during the temperature rise control are suppressed. Furthermore, as in the case of the inter-terminal voltage VL of the low-voltage side terminals TL1, TL2, changes in the inter-terminal voltage VH of the high-voltage side terminals TH1, TH2 are also suppressed. The output power PH of the battery 13 is greater than 0 W because the amount of power converted into thermal energy by the temperature rise control is output from the battery 13.

[0053] The control device 24 sets the switching frequency fsw of each of the power conversion units 30, 40 when operating each of the power conversion units 30, 40 as either a step-up operation unit or a step-down operation unit. Here, the switching frequency fsw is the reciprocal of the switching period Tsw. In this embodiment, the control device 24 sets different values ​​of the switching frequency fsw when performing temperature rise control and when operating each of the power conversion units 30, 40 as only one of the step-up operation and the step-down operation.

[0054] A method for setting the switching frequency fsw of each power conversion unit 30, 40 will be described using Figure 8. Figure 8 shows the relationship between the switching frequency fsw and the impedance ZLC of each resonant unit 33, 43. The impedance ZLC of each resonant unit 33, 43 becomes minimum when the switching frequency fsw matches the resonant frequency fr. The resonant frequency fr of the first resonant unit 33 is determined by the inductance of the first reactor 34 and the capacitance of the first capacitor 35, and the resonant frequency fr of the second resonant unit 43 is determined by the inductance of the second reactor 44 and the capacitance of the second capacitor 45.

[0055] In the capacitive region where the switching frequency fsw is lower than the resonant frequency fr, the higher the switching frequency fsw, the lower the impedance ZLC of each resonant unit 33, 43. In the inductive region where the switching frequency fsw is higher than the resonant frequency fr, the higher the switching frequency fsw, the higher the impedance ZLC of each resonant unit 33, 43.

[0056] To operate the power conversion device 14 as a step-up / step-down converter, it is possible to cause each of the power conversion units 30, 40 to perform only one of the step-up operation and the step-down operation. In this case, in order to improve the ratio of output power to input power, it is desirable to set the switching frequency fsw to a frequency close to the resonant frequency fr at which the impedance ZLC of each of the resonant units 33, 43 is minimized. Therefore, in this embodiment, when the control device 24 causes each of the power conversion units 30, 40 to operate in only one of the step-up operation and the step-down operation, the control device 24 sets the switching frequency fsw of the first power conversion unit 30 to the resonant frequency fr of the first resonant unit 33 and sets the switching frequency fsw of the second power conversion unit 40 to the resonant frequency fr of the second resonant unit 43. The switching frequency fsw of the first and second power conversion units 30, 40 is not limited to being the resonant frequency fr of the first and second resonant units 33, 43, but may be a frequency close to the resonant frequency fr within a range in which a decrease in the ratio of output power to input power does not become a problem.

[0057] On the other hand, when temperature rise control is performed, in order to improve the efficiency of converting input power into thermal energy, it is desirable to set the switching frequency fsw so that the impedance ZLC of each resonance unit 33, 43 is greater than the minimum value. Therefore, when temperature rise control is performed, the control device 24 sets the switching frequency fsw of the first and second power conversion units 30, 40 to a value different from the resonance frequency fr of the first and second resonance units 33, 43.

[0058] Here, during the period when each power conversion unit 30, 40 is in either Mode 2 or Mode 4, the currents IQ, IS flowing through each resonance unit 33, 43 are controlled, thereby performing either a step-up operation or a step-down operation in each power conversion unit 30, 40. The currents IQ, IS flowing through each resonance unit 33, 43 are controlled by utilizing the inductance component of each resonance unit 33, 43. Therefore, it is believed that the controllability of the currents IQ, IS flowing through each resonance unit 33, 43 is improved by setting the switching frequency fsw of each power conversion unit 30, 40 to a value in the inductive region.

[0059] Therefore, when performing temperature rise control, the control device 24 sets the switching frequency fsw of the first power conversion unit 30 to be higher than the resonant frequency fr of the first resonant unit 33, and sets the switching frequency fsw of the second power conversion unit 40 to be higher than the resonant frequency fr of the second resonant unit 43. For example, the control device 24 sets the switching frequencies fsw of the first and second power conversion units 30, 40 to a value twice the resonant frequency fr of the first and second resonant units 33, 43. In this case, the switching frequencies fsw of the first and second power conversion units 30, 40 are set higher than the switching frequencies fsw when each of the power conversion units 30, 40 operates in only one of the step-up operation and the step-down operation. The switching frequency fsw of the first and second power conversion units 30, 40 is not limited to being set to a value twice the resonant frequency fr of the first and second resonant units 33, 43, but may also be set to a value such as 1.5, 3, or 4 times the resonant frequency fr of the first and second resonant units 33, 43.

[0060] During temperature rise control, an error may occur in the power supplied to at least one of the low-voltage side terminals TL1, TL2 and the high-voltage side terminals TH1, TH2. In this case, there is a concern that the power supplied from one of the low-voltage side terminals TL1, TL2 and the high-voltage side terminals TH1, TH2 to the other may be excessive, resulting in an overvoltage abnormality. There is also a concern that the power supplied from one of the low-voltage side terminals TL1, TL2 and the high-voltage side terminals TH1, TH2 to the other may be insufficient, resulting in an undervoltage abnormality. Therefore, it is desirable to control the inter-terminal voltage VL between the low-voltage side terminals TL1, TL2 and the inter-terminal voltage VH between the high-voltage side terminals TH1, TH2 while performing temperature rise control.

[0061] Here, the inter-terminal voltage VL between the low-voltage side terminals TL1 and TL2 changes depending on the power supplied to and output from the low-voltage side terminals TL1 and TL2. Similarly, the inter-terminal voltage VH between the high-voltage side terminals TH1 and TH2 changes depending on the power supplied to and output from the high-voltage side terminals TH1 and TH2. In this regard, it is believed that the inter-terminal voltage VL between the low-voltage side terminals TL1 and TL2 and the inter-terminal voltage VH between the high-voltage side terminals TH1 and TH2 can be controlled by adjusting the power exchanged through the voltage step-up operation and the voltage step-down operation.

[0062] Therefore, in the temperature rise control, the control device 24 sets the length of at least one of the periods corresponding to Mode 2 and Mode 4 in the voltage rise control based on at least one of the inter-terminal voltage VL between the low-voltage side terminals TL1 and TL2 and the inter-terminal voltage VH between the high-voltage side terminals TH1 and TH2. In this embodiment, the control device 24 acquires the inter-terminal voltage VL between the low-voltage side terminals TL1 and TL2 and the inter-terminal voltage VH between the high-voltage side terminals TH1 and TH2. The control device 24 may acquire the detected value of the low-voltage side voltage sensor 23 as the inter-terminal voltage VL between the low-voltage side terminals TL1 and TL2, and may acquire the detected value of the high-voltage side voltage sensor 22 as the inter-terminal voltage VH between the high-voltage side terminals TH1 and TH2. In the temperature rise control, the control device 24 sets the length of the periods corresponding to Mode 2 and Mode 4 in the voltage rise control based on the acquired inter-terminal voltages VH and VL. The control device 24 corresponds to the "acquisition unit."

[0063] Specifically, as shown in FIG. 9 , when the control device 24 determines that the inter-terminal voltage VL at the low-voltage side terminals TL1 and TL2 is equal to or greater than the first threshold value Va, the control device 24 extends the duration of the Mode 2 or Mode 4 in the power conversion unit 30 or 40 that performs the boost operation. This increases the power output from the low-voltage side terminals TL1 and TL2 through the boost operation. Furthermore, when the control device 24 determines that the inter-terminal voltage VL at the low-voltage side terminals TL1 and TL2 is equal to or greater than the first threshold value Va, the control device 24 shortens the duration of the Mode 2 or Mode 4 in the power conversion unit 30 or 40 that performs the buck operation. This reduces the power supplied to the low-voltage side terminals TL1 and TL2 through the buck operation. In this case, the inter-terminal voltage VL at the low-voltage side terminals TL1 and TL2 is lowered.

[0064] When the control device 24 determines that the inter-terminal voltage VL of the low-voltage side terminals TL1, TL2 is equal to or lower than a second threshold Vb, which is lower than the first threshold Va, the control device 24 shortens the duration of Mode 2 or Mode 4 in one of the power conversion units 30, 40 that performs the boost operation. This reduces the power output from the low-voltage side terminals TL1, TL2 due to the boost operation. When the control device 24 determines that the inter-terminal voltage VL of the low-voltage side terminals TL1, TL2 is equal to or lower than the second threshold Vb, the control device 24 extends the duration of Mode 2 or Mode 4 in one of the power conversion units 30, 40 that performs the buck operation. This increases the power supplied to the low-voltage side terminals TL1, TL2 due to the buck operation. In this case, the inter-terminal voltage VL of the low-voltage side terminals TL1, TL2 is increased.

[0065] When the control device 24 determines that the inter-terminal voltage VH of the high-voltage side terminals TH1, TH2 is equal to or greater than the third threshold Vc, it shortens the duration of the period in Mode 2 or Mode 4 in one of the power conversion units 30, 40 that performs the boost operation. This reduces the power supplied to the high-voltage side terminals TH1, TH2 by the boost operation. When the control device 24 determines that the inter-terminal voltage VH of the high-voltage side terminals TH1, TH2 is equal to or greater than the third threshold Vc, it extends the duration of the period in Mode 2 or Mode 4 in one of the power conversion units 30, 40 that performs the step-down operation. This increases the power output from the high-voltage side terminals TH1, TH2 by the step-down operation. In this case, the inter-terminal voltage VH of the high-voltage side terminals TH1, TH2 is reduced.

[0066] When the control device 24 determines that the inter-terminal voltage VH of the high-voltage side terminals TH1, TH2 is equal to or less than a fourth threshold Vd, which is lower than the third threshold Vc, the control device 24 extends the duration of the Mode 2 or Mode 4 in the power conversion unit 30, 40 that performs the boost operation. This increases the power supplied to the high-voltage side terminals TH1, TH2 through the boost operation. When the control device 24 determines that the inter-terminal voltage VH of the high-voltage side terminals TH1, TH2 is equal to or less than the fourth threshold Vd, the control device 24 shortens the duration of the Mode 2 or Mode 4 in the power conversion unit 30, 40 that performs the step-down operation. This reduces the power output from the high-voltage side terminals TH1, TH2 through the step-down operation. In this case, the inter-terminal voltage VH of the high-voltage side terminals TH1, TH2 is increased.

[0067] The control device 24 may repeatedly perform the process of setting the lengths of the periods in Mode 2 and Mode 4 in the voltage step-up operation and voltage step-down operation at a predetermined control cycle. The amount of change when the lengths of the periods in Mode 2 and Mode 4 are extended or shortened at each control cycle may be set to a fixed value or may be variably set based on the values ​​of the inter-terminal voltages VH and VL.

[0068] If the control device 24 determines that the inter-terminal voltage VL between the low-voltage side terminals TL1 and TL2 is within the first range and that the inter-terminal voltage VH between the high-voltage side terminals TH1 and TH2 is within the second range, the control device 24 may maintain the current lengths of the periods in Mode 2 and Mode 4. Here, the first range is a voltage range defined by first and second thresholds Va and Vb, and the second range is a voltage range defined by third and fourth thresholds Vc and Vd. If the control device 24 determines that the inter-terminal voltage VL between the low-voltage side terminals TL1 and TL2 is within the first range and that the inter-terminal voltage VH between the high-voltage side terminals TH1 and TH2 is within the second range, the control device 24 may set the lengths of the periods in Mode 2 and Mode 4 to initial settings instead of maintaining the current lengths. The initial setting value is the length of the period in which Mode 2 or Mode 4 was set before it was determined that the inter-terminal voltage VL of the low-voltage side terminals TL1 and TL2 was outside the first range, or that the inter-terminal voltage VH of the high-voltage side terminals TH1 and TH2 was outside the second range.

[0069] The first and second thresholds Va and Vb are preferably set based on the withstand voltages of the low-voltage side terminals TL1 and TL2, and the third and fourth thresholds Vc and Vd are preferably set based on the withstand voltages of the high-voltage side terminals TH1 and TH2.

[0070] According to the present embodiment described above in detail, the following effects can be obtained.

[0071] As temperature rise control, the first power conversion unit 30 performs a voltage step-up operation, and the second power conversion unit 40 performs a voltage step-down operation. In this case, at the high-voltage side terminals TH1, TH2, power is supplied from the low-voltage side terminals TL1, TL2 by the voltage step-up operation, while power is output to the low-voltage side terminals TL1, TL2 by the voltage step-down operation. Also, at the low-voltage side terminals TL1, TL2, power is supplied from the high-voltage side terminals TH1, TH2 by the voltage step-down operation, while power is output to the high-voltage side terminals TH1, TH2 by the voltage step-up operation. As a result, during temperature rise control, power is exchanged between the first power conversion unit 30 and the second power conversion unit 40 while changes in the inter-terminal voltage VL of the low-voltage side terminals TL1, TL2 and the inter-terminal voltage VH of the high-voltage side terminals TH1, TH2 are suppressed. Therefore, during the temperature rise control, the inter-terminal voltage VL between the low-voltage side terminals TL1 and TL2 and the inter-terminal voltage VH between the high-voltage side terminals TH1 and TH2 can be prevented from reaching the upper limit voltage, and the power exchanged during the temperature rise control can be increased. As a result, the thermal energy used to raise the temperature of the battery 13 can be sufficiently increased, and the efficiency of the temperature rise control can be improved.

[0072] The high-voltage side terminals TH1 and TH2 are connected to the battery 13, and the low-voltage side terminals TL1 and TL2 are connected to the off-vehicle charger 16. In this case, it is conceivable that the low temperature of the battery 13 will reduce the power that can be input to and output from the battery 13. Therefore, when the temperature of the battery 13 is low, there is a concern that the increase in power exchanged in the temperature rise control will be limited, reducing the efficiency of the temperature rise control.

[0073] In this regard, in the present embodiment, in which the voltage increase operation and the voltage decrease operation are performed in parallel as the temperature increase control, the power output from the battery 13 is the power converted into thermal energy by the temperature increase control. This makes it possible to suppress an increase in the power output from the battery 13 compared to the control of the comparative example in which the voltage increase operation and the voltage decrease operation are performed alternately as the temperature increase control. Therefore, even in a situation in which the power that can be input and output to the battery 13 is low due to a low temperature of the battery 13, it is possible to suppress the occurrence of a situation in which an increase in the power exchanged in the temperature increase control is restricted. As a result, the efficiency of the temperature increase control can be improved.

[0074] The power conversion device 14 has a function of charging the battery 13 by boosting the voltage input from the off-vehicle charger 16 and outputting the boosted voltage to the battery 13. In this case, there is a concern that a low ambient temperature around the power conversion device 14 may reduce the power that can be input to and output from the battery 13, lengthening the charging time for the battery 13. In this regard, by performing the temperature rise control of this embodiment, the temperature of the battery 13 can be quickly raised. As a result, the power that can be input to and output from the battery 13 is increased, and then the battery 13 is charged. As a result, it is possible to prevent the charging time for the battery 13 from becoming longer.

[0075] Specifically, Fig. 10 shows an example comparing the charging time of the battery 13 between a comparative example and this embodiment when the ambient temperature of the power conversion device 14 is -10 degrees. In the comparative example, the temperature rise control of this embodiment is not performed, and the battery 13 is charged while the temperature of the battery 13 remains low. On the other hand, in this embodiment, the temperature of the battery 13 is raised by the temperature rise control, and then the battery 13 is charged. In this case, the battery 13 is charged after the power that can be input to and output from the battery 13 is increased, so that the charging time of the battery 13 can be reduced by 35% compared to the comparative example.

[0076] The power conversion device 14 has both a function of charging the battery 13 and a function of increasing the temperature of the battery 13. Therefore, the power conversion device 14 used to charge the battery 13 can be used to perform temperature increase control to increase the temperature of the battery 13.

[0077] The switches QH1, QH2, QL1, and QL2 of the first power conversion unit 30 and the switches SH1, SH2, SL1, and SL2 of the second power conversion unit 40 are turned on and off to perform voltage step-up and voltage step-down operations. In this case, current circulates between the first power conversion unit 30 and the second power conversion unit 40. As a result, switching loss and conduction loss occurring in the switches QH1, QH2, QL1, QL2, SH1, SH2, SL1, and SL2 are converted into thermal energy.

[0078] Specifically, Fig. 11 shows the amount of thermal energy generated by the temperature increase control for each of the switches QH1, QH2, QL1, QL2, SH1, SH2, SL1, and SL2. In Fig. 11, the amount of thermal energy is shown as a ratio to a target value. The target value is the amount of thermal energy required to increase the temperature of the battery 13, and is set based on the thermal characteristics of each of the switches QH1, QH2, QL1, QL2, SH1, SH2, SL1, and SL2, such as the allowable power loss and operating temperature range.

[0079] By performing the temperature increase control, the switches QH1, QH2, QL1, QL2, SH1, SH2, SL1, and SL2 generate approximately the same amount of heat energy close to the target value. The heat energy generated in the switches QH1, QH2, QL1, QL2, SH1, SH2, SL1, and SL2 is transferred to the battery 13 via the heat transfer unit 15. This increases the temperature of the battery 13. Note that FIG. 11 is an example of operation, and the amount of heat energy generated in the switches QH1, QH2, QL1, QL2, SH1, SH2, SL1, and SL2 may vary depending on the operating conditions.

[0080] A different switching frequency fsw is set when only one of the step-up operation and the step-down operation is performed in each power conversion unit 30, 40 and when temperature rise control is performed. Specifically, when only one of the step-up operation and the step-down operation is performed in each power conversion unit 30, 40, the switching frequency fsw of the first and second power conversion units 30, 40 is set to the resonance frequency fr of the first and second resonance units 33, 43. This improves the ratio of output power to input power compared to when the switching frequency fsw is set to a frequency other than the resonance frequency fr. On the other hand, when temperature rise control is performed, the switching frequency fsw of the first and second power conversion units 30, 40 is set to a value that is different from the resonance frequency fr of the first and second resonance units 33, 43. This increases the switching loss caused by the on / off switching of each switch QH1, QH2, QL1, QL2, SH1, SH2, SL1, and SL2 compared to when the switching frequency fsw is set to the resonance frequency fr. As a result, the efficiency of converting input electric power into thermal energy can be improved.

[0081] When temperature rise control is performed, the switching frequency fsw of the first and second power conversion units 30, 40 is set higher than the resonant frequency fr of the first and second resonant units 33, 43. In this case, the switching frequency fsw of the first and second power conversion units 30, 40 is set to a value in the inductive region, thereby improving the controllability of the currents IQ, IS flowing through the first and second resonant units 33, 43. As a result, even in a situation where various values ​​are set for the inter-terminal voltages VL, VH, one of the power conversion units 30, 40 can be operated accurately as a step-up operation unit, and the other can be operated accurately as a step-down operation unit. As a result, temperature rise control can be performed accurately.

[0082] During temperature rise control, the lengths of the periods of Mode 2 and Mode 4 in the voltage step-up control and voltage step-down control are set based on the inter-terminal voltage VL between the low-voltage side terminals TL1 and TL2 and the inter-terminal voltage VH between the high-voltage side terminals TH1 and TH2. This makes it possible to control the inter-terminal voltage VL between the low-voltage side terminals TL1 and TL2 and the inter-terminal voltage VH between the high-voltage side terminals TH1 and TH2 while performing temperature rise control. As a result, it is possible to prevent overvoltage and undervoltage conditions from occurring during temperature rise control.

[0083] Second Embodiment The second embodiment will be described below, focusing on the differences from the first embodiment.

[0084] When temperature rise control is performed, a current may flow through stray capacitance between the power conversion device 14 and the ground. The ground may be, for example, a body earth formed by the metal body frame of the vehicle 10, and is a wiring path on the low potential side. The current flowing through the stray capacitance is a noise current that flows in or out of the power conversion device 14, and it is desirable that the noise current be kept below a regulated value.

[0085] In this regard, in the present embodiment, one of the power conversion units 30, 40 can operate as a boost operation unit, and the other can operate as a buck operation unit. Therefore, in the temperature rise control, the control device 24 synchronizes the boost operation of the power conversion unit operated as a boost operation unit with the buck operation of the power conversion unit operated as a buck operation unit.

[0086] More specifically, the description will be made with reference to Fig. 12. Fig. 12 shows a control example in which the step-down operation performed in the first power conversion unit 30 and the step-up operation performed in the second power conversion unit 40 are synchronized. Figs. 12(a) to (d) correspond to Figs. 7(a) to (d) above.

[0087] The on / off states of the upper switch QH1 of the first upper arm portion 31 and the lower switch SL2 of the second lower arm portion 42 are synchronized, and the on / off states of the lower switch QH2 of the first upper arm portion 31 and the upper switch SL1 of the second lower arm portion 42 are synchronized. Furthermore, the on / off states of the upper switch QL1 of the first lower arm portion 32 and the lower switch SH2 of the second upper arm portion 41 are synchronized, and the on / off states of the lower switch QL2 of the first lower arm portion 32 and the upper switch SH1 of the second upper arm portion 41 are synchronized.

[0088] Here, noise currents are generated at the timings when the switches QH1, QH2, QL1, QL2, SH1, SH2, SL1, and SL2 are turned on and off. Figures 13(a) to 13(d) show current paths that flow through the power conversion device 14 and ground at first to fourth timings t1 to t4, which are the timings at which noise currents are generated.

[0089] At a first timing t1, the upper switch QH1 of the first upper arm portion 31 and the lower switch SL2 of the second lower arm portion 42 are turned on, and the lower switch QH2 of the first upper arm portion 31 and the upper switch SL1 of the second lower arm portion 42 are turned off. The switches QL1, QL2 of the first lower arm portion 32 and the switches SH1, SH2 of the second upper arm portion 41 are not switched on or off.

[0090] In this case, a first outflow current ia1 flows through a stray capacitance 51 between the ground and the connection point between the source of the upper switch QH1 and the drain of the lower switch QH2 in the first upper arm section 31. The first outflow current ia1 is a current that flows in a direction from the power conversion device 14 toward the ground, and its magnitude is expressed by the following equation (e1):

[0091]

number

[0092] Furthermore, a first inflow current ib1 flows through a stray capacitance 52 between the ground and the connection point of the source of the upper switch SL1 and the drain of the lower switch SL2 in the second lower arm section 42. The first inflow current ib1 is a current that flows in a direction from the ground toward the power conversion device 14, and its magnitude is expressed by the following equation (e2):

[0093]

number

[0094] Here, according to the above equations (e1) and (e2), the magnitude of each current ia1, ib1 is the product of the capacitance values ​​CH1, CL2 of each stray capacitance 51, 52 and the amount of change in voltage applied to each stray capacitance 51, 52. Therefore, assuming a situation in which the capacitance values ​​CH1, CL2 of each stray capacitance 51, 52 are equal, the magnitude of the noise current increases as the difference between the amount of change in voltage caused by the on / off switching of each switch QH1, QH2 of the first upper arm portion 31 and the amount of change in voltage caused by the on / off switching of each switch SL1, SL2 of the second lower arm portion 42 increases.

[0095] At the second timing t2, the upper switch QL1 of the first lower arm portion 32 and the lower switch SH2 of the second upper arm portion 41 are turned on, and the lower switch QL2 of the first lower arm portion 32 and the upper switch SH1 of the second upper arm portion 41 are turned off. The switches QH1, QH2 of the first upper arm portion 31 and the switches SL1, SL2 of the second lower arm portion 42 are not switched on or off.

[0096] In this case, a second outflow current ia2 flows through a stray capacitance 53 between the ground and the connection point of the source of the upper switch QL1 and the drain of the lower switch QL2 in the first lower arm section 32. The second outflow current ia2 is a current that flows in a direction from the power conversion device 14 toward the ground, and its magnitude is expressed by the following equation (e3):

[0097]

number

[0098] Furthermore, a second incoming current ib2 flows through a stray capacitance 54 between the ground and the connection point of the source of the upper switch SH1 and the drain of the lower switch SH2 in the second upper arm portion 41. The second incoming current ib2 is a current that flows in a direction from the ground to the power conversion device 14, and its magnitude is expressed by the following equation (e4):

[0099]

number

[0100] Here, according to the above equations (e3) and (e4), the magnitude of each current ia2, ib2 is the product of the capacitance value CL1, CH2 of each stray capacitance 53, 54 and the amount of change in voltage applied to each stray capacitance 53, 54. Therefore, assuming a situation in which the capacitance values ​​CL1, CH2 of each stray capacitance 53, 54 are equal, the magnitude of the noise current increases as the difference between the amount of change in voltage caused by the on / off switching of each switch QL1, QL2 of the first lower arm portion 32 and the amount of change in voltage caused by the on / off switching of each switch SH1, SH2 of the second upper arm portion 41 increases.

[0101] At the third timing t3, the lower switch QH2 of the first upper arm portion 31 and the upper switch SL1 of the second lower arm portion 42 are turned on, and the upper switch QH1 of the first upper arm portion 31 and the lower switch SL2 of the second lower arm portion 42 are turned off. The switches QL1, QL2 of the first lower arm portion 32 and the switches SH1, SH2 of the second upper arm portion 41 are not switched on or off.

[0102] In this case, a third incoming current ib3 flows through a stray capacitance 51 between the ground and the connection point of the source of the upper switch QH1 and the drain of the lower switch QH2 in the first upper arm section 31. The third incoming current ib3 is a current that flows in a direction from the ground toward the power conversion device 14, and its magnitude is the same as that of the first outgoing current ia1. In other words, the magnitude of the third incoming current ib3 is expressed by the right side of the above equation (e1).

[0103] Furthermore, a third outflow current ia3 flows through a stray capacitance 52 between the ground and the connection point of the source of the upper switch SL1 and the drain of the lower switch SL2 in the second lower arm section 42. The third outflow current ia3 is a current that flows in the direction from the power conversion device 14 to the ground, and its magnitude is the same as that of the first inflow current ib1. In other words, the magnitude of the third outflow current ia3 is expressed by the right side of the above equation (e2).

[0104] The third outflow current ia3 and the third inflow current ib3 are currents that flow in opposite directions to each other and circulate between the first and second power conversion units 30, 40 via the ground. In this case, the current flowing out from the power conversion device 14 to the ground and the current flowing into the power conversion device 14 from the ground cancel each other out, and therefore, as in the case of the first timing t1, a noise current is generated according to the difference in magnitude between the third outflow current ia3 and the third inflow current ib3.

[0105] At a fourth timing t4, the lower switch QL2 of the first lower arm portion 32 and the upper switch SH1 of the second upper arm portion 41 are turned on, and the upper switch QL1 of the first lower arm portion 32 and the lower switch SH2 of the second upper arm portion 41 are turned off. The switches QH1, QH2 of the first upper arm portion 31 and the switches SL1, SL2 of the second lower arm portion 42 are not switched on or off.

[0106] In this case, a fourth incoming current ib4 flows through a stray capacitance 53 between the ground and the connection point of the source of the upper switch QL1 and the drain of the lower switch QL2 in the first lower arm section 32. The fourth incoming current ib4 is a current that flows in a direction from the ground toward the power conversion device 14, and its magnitude is the same as that of the second outgoing current ia2. In other words, the magnitude of the fourth incoming current ib4 is expressed by the right side of the above equation (e3).

[0107] Furthermore, a fourth outflow current ia4 flows through a stray capacitance 54 between the ground and the connection point of the source of the upper switch SH1 and the drain of the lower switch SH2 in the second upper arm section 41. The fourth outflow current ia4 is a current that flows in a direction from the power conversion device 14 toward the ground, and its magnitude is the same as that of the second inflow current ib2. In other words, the magnitude of the fourth outflow current ia4 is expressed by the right side of the above equation (e4).

[0108] The fourth outflow current ia4 and the fourth inflow current ib4 are currents that flow in opposite directions to each other and circulate between the first and second power conversion units 30, 40 via the ground. In this case, the current flowing out from the power conversion device 14 to the ground and the current flowing into the power conversion device 14 from the ground cancel each other out, and therefore, as in the case of the second timing t2, a noise current is generated according to the difference between the magnitude of the fourth outflow current ia4 and the magnitude of the fourth inflow current ib4.

[0109] Fig. 14 shows an example of temperature rise control in which the first power conversion unit 30 performs a voltage step-up operation and the second power conversion unit 40 performs a voltage step-down operation. Figs. 14(a) to (f) correspond to Figs. 7(a) to (f). In Fig. 14(e), the voltage step-up operation performed in the first power conversion unit 30 and the voltage step-down operation performed in the second power conversion unit 40 are synchronized, so that the transitions of the current iQ flowing through the first resonance unit 33 and the current iS flowing through the second resonance unit 43 overlap.

[0110] 7, in the present embodiment, the temperature of the battery 13 is increased while suppressing changes in the inter-terminal voltage VL between the low-voltage side terminals TL1 and TL2 and the inter-terminal voltage VH between the high-voltage side terminals TH1 and TH2 during the temperature increase control. In addition, noise currents generated during the temperature increase control are reduced.

[0111] Specifically, FIG. 15 shows a diagram comparing the magnitude of noise current between temperature rise control in which the voltage step-up operation and the voltage step-down operation are not synchronized and temperature rise control of this embodiment in which the voltage step-up operation and the voltage step-down operation are synchronized, when the terminal voltage VH of the high-voltage side terminals TH1 and TH2 is twice the terminal voltage VL of the low-voltage side terminals TL1 and TL2.

[0112] When the inter-terminal voltage VH of the high-voltage side terminals TH1, TH2 is twice the inter-terminal voltage VL of the low-voltage side terminals TL1, TL2, the magnitude of the first outflow current ia1 is CH1×dVL / dt from the above equation (e1). On the other hand, the magnitude of the first inflow current ib1 is CL2×dVL / dt from the above equation (e2). In this case, assuming a situation where the capacitance values ​​CH1 and CL2 of the stray capacitances 51 and 52 are the same, the magnitude of the first outflow current ia1 and the magnitude of the first inflow current ib1 will be the same, and almost no noise current will be generated.

[0113] 15, in this embodiment in which the step-up operation and the step-down operation are synchronized, the magnitude of the noise current is reduced to about 1 / 1000 of that in the case in which the step-up operation and the step-down operation are not synchronized. Therefore, it is possible to suppress the generation of noise current while performing the same temperature rise control as in the first embodiment.

[0114] 15 can vary depending on the inter-terminal voltage VH of the high-voltage side terminals TH1, TH2 and the inter-terminal voltage VL of the low-voltage side terminals TL1, TL2. Specifically, if the inter-terminal voltage VH of the high-voltage side terminals TH1, TH2 is not twice the inter-terminal voltage VL of the low-voltage side terminals TL1, TL2, the noise current increases when the voltage step-up operation and the voltage step-down operation are synchronized.

[0115] Third Embodiment The third embodiment will be described below, focusing on the differences from the second embodiment.

[0116] In this embodiment, as shown in Fig. 16, the power conversion device 14 includes a third power conversion unit 60 in addition to the first power conversion unit 30 and the second power conversion unit 40. Note that in Fig. 16, the control device 24 is not shown, and the same components as those shown in Fig. 2 are denoted by the same reference numerals for convenience.

[0117] The third power conversion unit 60 includes a third upper arm unit 61, a third lower arm unit 62, and a third resonant unit 63. The third upper arm unit 61 and the third lower arm unit 62 are a series connection of voltage-controlled semiconductor switches. The third resonant unit 63 is a series connection of a third reactor 64 and a third capacitor 65. In this embodiment, N-channel MOSFETs having body diodes are used as the semiconductor switches of the third upper arm unit 61 and the third lower arm unit 62.

[0118] The drain of the upper switch KH1 of the third upper arm section 61 is connected to the first high-voltage side terminal TH1, and the source of the upper switch KH1 of the third upper arm section 61 is connected to the drain of the lower switch KH2 of the third upper arm section 61. The source of the lower switch KH2 of the third upper arm section 61 is connected to the first low-voltage side terminal TL1 and the drain of the upper switch KL1 of the third lower arm section 62. The drain of the lower switch KL2 of the third lower arm section 62 is connected to the source of the upper switch KL1 of the third lower arm section 62, and the source of the lower switch KL2 of the third lower arm section 62 is connected to the second high-voltage side terminal TH2 and the second low-voltage side terminal TL2. A first end of the third reactor 64 is connected to the connection point between the source of the upper switch KH1 and the drain of the lower switch KH2 in the third upper arm section 61. A second end of the third reactor 64 is connected to a first end of the third capacitor 65. A second end of the third capacitor 65 is connected to the connection point between the source of the upper switch KL1 and the drain of the lower switch KL2 in the third lower arm section 62.

[0119] In this embodiment, the upper switch KH1 of the third upper arm portion 61 corresponds to the "upper arm first switch," and the lower switch KH2 of the third upper arm portion 61 corresponds to the "upper arm second switch." Furthermore, the upper switch KL1 of the third lower arm portion 62 corresponds to the "lower arm first switch," and the lower switch KL2 of the third lower arm portion 62 corresponds to the "lower arm second switch."

[0120] As in the case of the first power conversion unit 30, the control device 24 turns on and off the switches KH1, KH2, KL1, and KL2 of the third power conversion unit 60 to place the third power conversion unit 60 in one of Modes 1 to 4. The control device 24 causes the third power conversion unit 60 to repeatedly perform one cycle of processing consisting of Modes 1 to 4, thereby causing the third power conversion unit 60 to operate as either a step-up operation unit or a step-down operation unit.

[0121] Here, for example, as in the second embodiment, it is considered that temperature rise control may be performed to synchronize the voltage step-up operation of the first power conversion unit 30 and the voltage step-down operation of the second power conversion unit 40. In this case, the problem arises as to how to control the remaining third power conversion unit 60 during temperature rise control. In this embodiment, the control device 24 stops the operation of the third power conversion unit 60 during temperature rise control. This makes it possible to suppress the generation of noise currents due to the operation of the third power conversion unit 60.

[0122] <Modification of the third embodiment> In the temperature rise control, the control device 24 may operate the third power conversion unit 60 as either a step-up operation unit or a step-down operation unit, instead of stopping the operation of the third power conversion unit 60. In this case, the control device 24 may determine whether to operate the third power conversion unit 60 as a step-up operation unit or a step-down operation unit, based on the inter-terminal voltage VL of the low-voltage side terminals TL1, TL2 and the inter-terminal voltage VH of the high-voltage side terminals TH1, TH2.

[0123] Here, a method for determining whether the third power conversion unit 60 should operate as a step-up operation unit or a step-down operation unit will be described based on the concept explained above with reference to FIG. 9 . When the control device 24 determines that the inter-terminal voltage VL between the low-voltage side terminals TL1 and TL2 is equal to or greater than the first threshold value Va, it may operate the third power conversion unit 60 as a step-up operation unit. This reduces the inter-terminal voltage VL between the low-voltage side terminals TL1 and TL2. When the control device 24 determines that the inter-terminal voltage VL between the low-voltage side terminals TL1 and TL2 is equal to or less than the second threshold value Vb, it may operate the third power conversion unit 60 as a step-down operation unit. This increases the inter-terminal voltage VL between the low-voltage side terminals TL1 and TL2.

[0124] When the control device 24 determines that the inter-terminal voltage VH of the high-voltage side terminals TH1, TH2 is equal to or greater than the third threshold Vc, it may operate the third power conversion unit 60 as a step-down operation unit. This reduces the inter-terminal voltage VH of the high-voltage side terminals TH1, TH2. Furthermore, when the control device 24 determines that the inter-terminal voltage VH of the high-voltage side terminals TH1, TH2 is equal to or less than the fourth threshold Vd, it may operate the third power conversion unit 60 as a step-up operation unit. This increases the inter-terminal voltage VH of the high-voltage side terminals TH1, TH2.

[0125] According to this embodiment, during temperature rise control, the inter-terminal voltage VL of the low-voltage side terminals TL1, TL2 and the inter-terminal voltage VH of the high-voltage side terminals TH1, TH2 can be controlled using the third power conversion unit 60, which is not synchronized with the operation of the first and second power conversion units 30, 40. As a result, it is possible to prevent overvoltage and undervoltage states from occurring during temperature rise control.

[0126] <Fourth embodiment> The fourth embodiment will be described below, focusing on the differences from the third embodiment.

[0127] In this embodiment, as shown in Fig. 17, the power conversion device 14 includes a fourth power conversion unit 70 in addition to the first power conversion unit 30, the second power conversion unit 40, and the third power conversion unit 60. Note that in Fig. 17, the control device 24 is not shown, and the same components as those shown in Fig. 16 are denoted by the same reference numerals for convenience.

[0128] The fourth power conversion unit 70 includes a fourth upper arm unit 71, a fourth lower arm unit 72, and a fourth resonant unit 73. The fourth upper arm unit 71 and the fourth lower arm unit 72 are a series connection of voltage-controlled semiconductor switches. The fourth resonant unit 73 is a series connection of a fourth reactor 74 and a fourth capacitor 75. In this embodiment, N-channel MOSFETs having body diodes are used as the semiconductor switches of the fourth upper arm unit 71 and the fourth lower arm unit 72.

[0129] The drain of the upper switch RH1 of the fourth upper arm section 71 is connected to the high-voltage side first terminal TH1, and the source of the upper switch RH1 of the fourth upper arm section 71 is connected to the drain of the lower switch RH2 of the fourth upper arm section 71. The source of the lower switch RH2 of the fourth upper arm section 71 is connected to the low-voltage side first terminal TL1 and the drain of the upper switch RL1 of the fourth lower arm section 72. The drain of the lower switch RL2 of the fourth lower arm section 72 is connected to the source of the upper switch RL1 of the fourth lower arm section 72, and the source of the lower switch RL2 of the fourth lower arm section 72 is connected to the high-voltage side second terminal TH2 and the low-voltage side second terminal TL2. A first end of the fourth reactor 74 is connected to the connection point between the source of the upper switch RH1 and the drain of the lower switch RH2 in the fourth upper arm section 71. A second end of the fourth reactor 74 is connected to a first end of the fourth capacitor 75. A second end of the fourth capacitor 75 is connected to the connection point between the source of the upper switch RL1 of the fourth lower arm section 72 and the drain of the lower switch RL2.

[0130] In this embodiment, the upper switch RH1 of the fourth upper arm section 71 corresponds to the "upper arm first switch," and the lower switch RH2 of the fourth upper arm section 71 corresponds to the "upper arm second switch." Furthermore, the upper switch RL1 of the fourth lower arm section 72 corresponds to the "lower arm first switch," and the lower switch RL2 of the fourth lower arm section 72 corresponds to the "lower arm second switch."

[0131] As in the case of the first power conversion unit 30, the control device 24 turns on and off the switches RH1, RH2, RL1, and RL2 of the fourth power conversion unit 70 to place the fourth power conversion unit 70 in one of Modes 1 to 4. The control device 24 causes the fourth power conversion unit 70 to repeatedly perform one cycle of processing consisting of Modes 1 to 4, thereby causing the fourth power conversion unit 70 to operate as either a step-up operation unit or a step-down operation unit.

[0132] As explained above in Fig. 15 regarding the effect of suppressing the generation of noise current, when the operation of the power conversion unit performing the step-up operation and the operation of the power conversion unit performing the step-down operation are synchronized, noise current may increase. Therefore, there is still room for improvement in reducing noise current during temperature rise control.

[0133] In this embodiment, any two of the power conversion units 30, 40, 60, and 70 can operate as boost operation units, and the remaining two can operate as buck operation units. Therefore, in the temperature rise control, instead of synchronizing the operation of the power conversion unit performing the boost operation with the operation of the power conversion unit performing the buck operation, the control device 24 synchronizes the operation of the two power conversion units performing the boost operation and synchronizes the operation of the two power conversion units performing the buck operation. Specifically, the control device 24 synchronizes the operation of the third and fourth power conversion units 60 and 70 performing the boost operation and synchronizes the operation of the first and second power conversion units 30 and 40 performing the buck operation.

[0134] Fig. 18 shows an example of the operation of the first and second power conversion units 30 and 40 in which the voltage step-down operation is performed. Fig. 18(a) to (d) correspond to Fig. 7(a) to (d) above.

[0135] The on / off states of the upper switch QH1 of the first upper arm portion 31 and the lower switch SH2 of the second upper arm portion 41 are synchronized, and the on / off states of the lower switch QH2 of the first upper arm portion 31 and the upper switch SH1 of the second upper arm portion 41 are synchronized. Furthermore, the on / off states of the upper switch QL1 of the first lower arm portion 32 and the lower switch SL2 of the second lower arm portion 42 are synchronized, and the on / off states of the lower switch QL2 of the first lower arm portion 32 and the upper switch SL1 of the second lower arm portion 42 are synchronized.

[0136] 19(a) to 19(d) show current paths that flow through the power converter 14 and the ground at the fifth to eighth timings t5 to t8, which are timings at which noise currents are generated. For convenience, the same components as those shown in FIG. 13 are denoted by the same reference numerals.

[0137] At a fifth timing t5, the upper switch QH1 of the first upper arm portion 31 and the lower switch SH2 of the second upper arm portion 41 are turned on, and the lower switch QH2 of the first upper arm portion 31 and the upper switch SH1 of the second upper arm portion 41 are turned off. The switches QL1, QL2 of the first lower arm portion 32 and the switches SL1, SL2 of the second lower arm portion 42 are not switched on or off.

[0138] In this case, a fifth outflow current ia5 flows through stray capacitance 51 between the ground and the connection point of the source of the upper switch QH1 and the drain of the lower switch QH2 in the first upper arm section 31. The fifth outflow current ia5 is a current that flows in the direction from power conversion device 14 to ground, and its magnitude is the same as that of the first outflow current ia1. In other words, the magnitude of the fifth outflow current ia5 is expressed by the right side of the above equation (e1).

[0139] Furthermore, a fifth incoming current ib5 flows through a stray capacitance 54 between the ground and the connection point of the source of the upper switch SH1 and the drain of the lower switch SH2 in the second upper arm section 41. The fifth incoming current ib5 is a current that flows in a direction from the ground toward the power conversion device 14, and its magnitude is the same as that of the second incoming current ib2. In other words, the magnitude of the fifth incoming current ib5 is expressed by the right side of the above equation (e4).

[0140] The fifth outflow current ia5 and the fifth inflow current ib5 are currents flowing in opposite directions and circulate between the first and second power conversion units 30 and 40 via the ground. In this case, the current flowing out from the power conversion device 14 to the ground and the current flowing into the power conversion device 14 from the ground cancel each other out, so the difference between the magnitude of the fifth outflow current ia5 and the magnitude of the fifth inflow current ib5 becomes a noise current. Here, assuming that the capacitance values ​​CH1 and CH2 of the stray capacitances 51 and 54 are the same, the magnitude of the fifth outflow current ia5 and the magnitude of the fifth inflow current ib5 will be the same regardless of the values ​​of the inter-terminal voltages VH and VL. As a result, compared to the second embodiment, the difference between the magnitude of the fifth outflow current ia5 and the magnitude of the fifth inflow current ib5 is accurately reduced, thereby enabling accurate reduction of noise currents.

[0141] At the sixth timing t6, the upper switch QL1 of the first lower arm portion 32 and the lower switch SL2 of the second lower arm portion 42 are turned on, and the lower switch QL2 of the first lower arm portion 32 and the upper switch SL1 of the second lower arm portion 42 are turned off. The switches QH1, QH2 of the first upper arm portion 31 and the switches SH1, SH2 of the second upper arm portion 41 are not switched on or off.

[0142] In this case, a sixth outflow current ia6 flows through a stray capacitance 53 between the ground and the connection point of the source of the upper switch QL1 and the drain of the lower switch QL2 in the first lower arm section 32. The sixth outflow current ia6 is a current that flows in a direction from the power conversion device 14 toward the ground, and its magnitude is the same as that of the second outflow current ia2. In other words, the magnitude of the sixth outflow current ia6 is expressed by the right side of the above equation (e3).

[0143] Furthermore, a sixth incoming current ib6 flows through a stray capacitance 52 between the ground and the connection point of the source of the upper switch SL1 and the drain of the lower switch SL2 in the second lower arm section 42. The sixth incoming current ib6 is a current that flows in a direction from the ground toward the power conversion device 14, and its magnitude is the same as that of the first incoming current ib1. In other words, the magnitude of the sixth incoming current ib6 is expressed by the right side of the above equation (e2).

[0144] The sixth outflow current ia6 and the sixth inflow current ib6 are currents flowing in opposite directions and circulate between the first and second power conversion units 30 and 40 via the ground. In this case, the current flowing out from the power conversion device 14 to the ground and the current flowing into the power conversion device 14 from the ground cancel each other out, and the difference between the magnitude of the sixth outflow current ia6 and the magnitude of the sixth inflow current ib6 becomes a noise current. Here, assuming that the capacitance values ​​CL2 and CL1 of the stray capacitances 52 and 53 are the same, the magnitude of the sixth outflow current ia6 and the magnitude of the sixth inflow current ib6 are the same regardless of the values ​​of the inter-terminal voltages VH and VL. As a result, compared to the second embodiment, the difference between the magnitude of the sixth outflow current ia6 and the magnitude of the sixth inflow current ib6 is accurately reduced, thereby enabling accurate reduction of noise currents.

[0145] At seventh timing t7, the lower switch QH2 of the first upper arm portion 31 and the upper switch SH1 of the second upper arm portion 41 are turned on, and the upper switch QH1 of the first upper arm portion 31 and the lower switch SH2 of the second upper arm portion 41 are turned off. The switches QL1, QL2 of the first lower arm portion 32 and the switches SL1, SL2 of the second lower arm portion 42 are not switched on or off.

[0146] In this case, a seventh incoming current ib7 flows through a stray capacitance 51 between the ground and the connection point of the source of the upper switch QH1 and the drain of the lower switch QH2 in the first upper arm section 31. The seventh incoming current ib7 is a current that flows in a direction from the ground toward the power conversion device 14, and its magnitude is the same as that of the first outgoing current ia1. In other words, the magnitude of the seventh incoming current ib7 is expressed by the right side of the above equation (e1).

[0147] Furthermore, a seventh outflow current ia7 flows through a stray capacitance 54 between the ground and the connection point of the source of the upper switch SH1 and the drain of the lower switch SH2 in the second upper arm section 41. The seventh outflow current ia7 is a current that flows in a direction from the power conversion device 14 toward the ground, and its magnitude is the same as that of the second inflow current ib2. In other words, the magnitude of the seventh outflow current ia7 is expressed by the right side of the above equation (e4).

[0148] The seventh outflow current ia7 and the seventh inflow current ib7 are currents flowing in opposite directions and circulate between the first and second power conversion units 30 and 40 via the ground. In this case, the current flowing out from the power conversion device 14 to the ground and the current flowing into the power conversion device 14 from the ground cancel each other out, and the difference between the magnitude of the seventh outflow current ia7 and the magnitude of the seventh inflow current ib7 becomes a noise current. Here, assuming that the capacitance values ​​CH1 and CH2 of the stray capacitances 51 and 54 are the same, the magnitude of the seventh outflow current ia7 and the seventh inflow current ib7 will be the same regardless of the values ​​of the inter-terminal voltages VH and VL. As a result, compared to the second embodiment, the difference between the magnitude of the seventh outflow current ia7 and the seventh inflow current ib7 is accurately reduced, thereby accurately reducing the noise current.

[0149] At eighth timing t8, the lower switch QL2 of the first lower arm portion 32 and the upper switch SL1 of the second lower arm portion 42 are turned on, and the upper switch QL1 of the first lower arm portion 32 and the lower switch SL2 of the second lower arm portion 42 are turned off. The switches QH1, QH2 of the first upper arm portion 31 and the switches SH1, SH2 of the second upper arm portion 41 are not switched on or off.

[0150] In this case, an eighth incoming current ib8 flows through a stray capacitance 53 between the ground and the connection point of the source of the upper switch QL1 and the drain of the lower switch QL2 in the first lower arm section 32. The eighth incoming current ib8 is a current that flows in a direction from the ground toward the power conversion device 14, and its magnitude is the same as that of the second outgoing current ia2. In other words, the magnitude of the eighth incoming current ib8 is expressed by the right side of the above equation (e3).

[0151] Furthermore, an eighth outflow current ia8 flows through a stray capacitance 52 between the ground and the connection point of the source of the upper switch SL1 and the drain of the lower switch SL2 in the second lower arm section 42. The eighth outflow current ia8 is a current that flows in the direction from the power conversion device 14 to the ground, and its magnitude is the same as that of the first inflow current ib1. In other words, the magnitude of the eighth outflow current ia8 is expressed by the right side of the above equation (e2).

[0152] The eighth outflow current ia8 and the eighth inflow current ib8 are currents flowing in opposite directions and circulate between the first and second power conversion units 30 and 40 via the ground. In this case, the current flowing out from the power conversion device 14 to the ground and the current flowing into the power conversion device 14 from the ground cancel each other out, and the difference between the magnitude of the eighth outflow current ia8 and the magnitude of the eighth inflow current ib8 becomes a noise current. Here, assuming that the capacitance values ​​CL2 and CL1 of the stray capacitances 52 and 53 are the same, the magnitudes of the eighth outflow current ia8 and the eighth inflow current ib8 are the same regardless of the values ​​of the inter-terminal voltages VH and VL. As a result, compared to the second embodiment, the difference between the magnitude of the eighth outflow current ia8 and the magnitude of the eighth inflow current ib8 is accurately reduced, thereby enabling accurate reduction of noise currents.

[0153] The control device 24 synchronizes the operations of the third and fourth power conversion units 60 and 70 that perform the voltage step-down operation, just as it synchronizes the operations of the first and second power conversion units 30 and 40 that perform the voltage step-down operation. This ensures that noise currents are appropriately reduced even in the third and fourth power conversion units 60 and 70 that perform the voltage step-up operation. Therefore, the control device 24 synchronizes the operations of the third and fourth power conversion units 60 and 70 that perform the voltage step-up operation as temperature rise control, and synchronizes the operations of the first and second power conversion units 30 and 40 that perform the voltage step-down operation, thereby enabling more appropriate suppression of noise currents than in the second embodiment.

[0154] <Other embodiments> The above-described embodiments may be modified as follows.

[0155] The upper and lower switches included in each of the upper and lower arm sections 31, 32, 41, 42, 61, 62, 71, and 72 are not limited to a single semiconductor switch, and may be configured as a series connection of multiple semiconductor switches. Fig. 20 shows an example in which, in the configuration shown in Fig. 2, each of the switches QH1 and QH2 in the first upper arm section 31 and each of the switches QL1 and QL2 in the first lower arm section 32 are configured as a series connection of two N-channel MOSFETs. This allows each of the switches QH1, QH2, QL1, and QL2 to be a low-voltage element.

[0156] The upper and lower switches of each of the upper and lower arm units 31, 32, 41, 42, 61, 62, 71, and 72 may be configured as a parallel connection of multiple semiconductor switches. Fig. 21 shows an example in which, in the configuration shown in Fig. 2, each of the switches QH1 and QH2 of the first upper arm unit 31 and each of the switches QL1 and QL2 of the first lower arm unit 32 are configured as a parallel connection of two N-channel MOSFETs. This allows each of the switches QH1, QH2, QL1, and QL2 to be a low-current-capacity element.

[0157] The configuration of the resonance unit may be changed. Specifically, taking the first resonance unit 33 as an example, a first end of the first capacitor 35 may be connected to a connection point between the source of the upper switch QH1 and the drain of the lower switch QH2 in the first upper arm unit 31. A second end of the first capacitor 35 may be connected to a first end of the first reactor 34. A second end of the first reactor 34 may be connected to a connection point between the source of the upper switch QL1 and the drain of the lower switch QL2 in the first lower arm unit 32. As with the first resonance unit 33, the configurations of the second, third, and fourth resonance units 43, 63, and 73 may be changed.

[0158] In the fourth embodiment, the control device 24 is not limited to synchronizing the operations of two power conversion units that perform a step-up operation and synchronizing the operations of two power conversion units that perform a step-down operation. For example, the control device 24 may synchronize the step-up operation of the third power conversion unit 60 with the step-down operation of the first power conversion unit 30, and synchronize the step-up operation of the fourth power conversion unit 70 with the step-down operation of the second power conversion unit 40.

[0159] The power conversion device 14 may include five or more power conversion units. For example, if the power conversion device 14 includes six power conversion units, the number of pairs in which the operations of two power conversion units can be synchronized is three. In this case, various combinations of operations to be performed by the three pairs are conceivable. Here, to accurately suppress the generation of noise current, it is desirable that the operations of the two step-up operation units or the two step-down operation units in each pair be synchronized.

[0160] Therefore, the control device 24 may synchronize the boost operations of the two boost operation units in any two of the three pairs, and synchronize the buck operation of the two buck operation units in the remaining pair. In this case, the control device 24 may shorten the length of the period in which the boost operation units are in Mode 2 and Mode 4 compared to the length of the period in which the buck operation units are in Mode 2 and Mode 4, in order to balance the power exchanged during the temperature rise control.

[0161] Furthermore, in the temperature rise control, the control device 24 may synchronize the boost operations of the two boost operation units in one of the three pairs, and synchronize the buck operations of the two buck operation units in the remaining two pairs. In this case, the control device 24 may extend the length of the period in which the boost operation units are in Mode 2 and Mode 4 compared to the length of the period in which the buck operation units are in Mode 2 and Mode 4, in order to balance the power exchanged in the temperature rise control.

[0162] According to this embodiment, in each pair of two power conversion units capable of synchronizing the operations of the two boost operation units, or the operations of the two buck operation units are synchronized, thereby enabling the generation of noise current to be appropriately suppressed.

[0163] In the temperature rise control, the operation of synchronizing the operations of two power conversion units in a pair is not limited to synchronizing the operations of two step-up operation units and synchronizing the operations of two step-down operation units.

[0164] In the temperature rise control, the control device 24 may synchronize the boost operation of a boost operation unit other than the boost operation unit that operates in synchronization with the other boost operation units, among the boost operation units, with the buck operation of a buck operation unit other than the buck operation unit that operates in synchronization with the other buck operation units, among the buck operation units. Explaining the case where the power conversion device 14 is configured to include six power conversion units, the control device 24 may synchronize the boost operation of two boost operation units in one of three pairs. Then, the control device 24 may synchronize the buck operation of two buck operation units in one of the remaining two pairs, and synchronize the boost operation of the boost operation unit and the buck operation of the buck operation unit in the other pair.

[0165] In a configuration in which power conversion device 14 is provided with eight power conversion units, there are four pairs in which the operations of two power conversion units can be synchronized. In this case, control device 24 may synchronize the boost operations of the two boost operation units in any two of the four pairs, and synchronize the buck operation of the two buck operation units in the remaining two pairs. This allows temperature rise control to be performed while each boost operation unit operates in synchronization with the other boost operation units and while each buck operation unit operates in synchronization with the other buck operation units.

[0166] The power conversion unit is not limited to the first to fourth power conversion units 30, 40, 60, and 70, which include an upper arm unit, a lower arm unit, and a resonant unit. For example, the power conversion unit may be a non-insulated DC / DC converter. FIG. 22 shows an example in which the power conversion device 14 includes a fifth power conversion unit 80 instead of the first power conversion unit 30 and a sixth power conversion unit 90 instead of the second power conversion unit 40. The fifth power conversion unit 80 is a non-insulated DC / DC converter of a step-up chopper type including a fifth reactor 81, a step-up switch 82, and a step-up diode 83. The sixth power conversion unit 90 is a non-insulated DC / DC converter of a step-down chopper type including a sixth reactor 91, a step-down switch 92, and a step-down diode 93. In this case, the fifth power conversion unit 80 performs only a step-up operation, and the sixth power conversion unit 90 performs only a step-down operation. The power conversion unit may be a non-insulated DC / DC converter of a step-up / step-down chopper type.

[0167] The low-voltage side terminals TL1 and TL2 may be connected to a battery instead of being connected to the external charger 16. The high-voltage side terminals TH1 and TH2 may be connected to a DC side terminal of an AC / DC converter instead of being connected to the battery 13.

[0168] The upper and lower switches provided in the upper and lower arm portions 31, 32, 41, 42, 61, 62, 71, 72 are not limited to N-channel MOSFETs, and may be, for example, IGBTs with freewheel diodes connected in antiparallel.

[0169] The following describes characteristic configurations extracted from the above-described embodiments. [Configuration 1] In a power conversion device (14) having low-voltage side terminals (TL1, TL2) and high-voltage side terminals (TH1, TH2), a boost operation unit that performs a boost operation of boosting a voltage input from the low-voltage side terminal and outputting the voltage to the high-voltage side terminal; a step-down operation unit that performs a step-down operation of stepping down a voltage input from the high-voltage side terminal and outputting the voltage to the low-voltage side terminal; a control unit (24) that performs temperature increase control to increase the temperature of an object to be heated (13) by causing the voltage increase operation unit to perform the voltage increase operation and the voltage decrease operation unit to perform the voltage decrease operation. [Configuration 2] a plurality of power conversion units (30, 40, 60, 70) each including a series connection of upper-arm first switches (QH1, SH1, KH1, RH1) and upper-arm second switches (QH2, SH2, KH2, RH2), a series connection of lower-arm first switches (QL1, SL1, KL1, RL1) and lower-arm second switches (QL2, SL2, KL2, RL2), and a resonance unit (33, 43, 63, 73) which is a series connection of reactors (34, 44, 64, 74) and capacitors (35, 45, 65, 75); the high-voltage side terminals are a high-voltage side first terminal (TH1) on the high potential side and a high-voltage side second terminal (TH2) on the low potential side, the low-voltage side terminals are a low-voltage side first terminal (TL1) on the high potential side and a low-voltage side second terminal (TL2) on the low potential side, the resonator connects a connection point between the upper arm first switch and the upper arm second switch and a connection point between the lower arm first switch and the lower arm second switch, the upper arm first switch is connected to the high voltage side first terminal, a connection point between the upper arm second switch and the lower arm first switch is connected to the low voltage side first terminal, the lower arm second switch is connected to the high voltage side second terminal and the low voltage side second terminal, each of the power conversion units is configured to be operable as at least one of the step-up operation unit and the step-down operation unit by switching the upper arm first switch, the upper arm second switch, the lower arm first switch, and the lower arm second switch; The power conversion device according to configuration 1, wherein the control unit performs the temperature rise control by operating at least one of the power conversion units as the boost operation unit and operating at least one of the power conversion units as the buck operation unit. [Configuration 3] The power conversion device according to configuration 2, wherein, when performing the temperature rise control, the control unit sets the switching frequencies of the upper arm first switch, the upper arm second switch, the lower arm first switch, and the lower arm second switch provided in the boost operation unit to be higher than a resonant frequency of the resonant unit provided in the boost operation unit, and sets the switching frequencies of the upper arm first switch, the upper arm second switch, the lower arm first switch, and the lower arm second switch provided in the step-down operation unit to be higher than the resonant frequency of the resonant unit provided in the step-down operation unit. [Configuration 4] The power conversion device according to configuration 3, wherein when the control unit causes each of the power conversion units to operate as only one of the step-up operation unit and the step-down operation unit, the control unit sets the switching frequency to a frequency lower than a switching frequency when performing the temperature rise control and close to the resonant frequency. [Configuration 5] an acquisition unit that acquires an inter-terminal voltage of at least one of the low-voltage side terminal and the high-voltage side terminal; a state in which the upper arm second switch and the lower arm second switch are turned off and the upper arm first switch and the lower arm first switch are turned on is defined as Mode 1; a state in which the upper arm second switch and the lower arm first switch are turned off and the upper arm first switch and the lower arm second switch are turned on is defined as Mode 2; a state in which the upper arm first switch and the lower arm first switch are turned off and the upper arm second switch and the lower arm second switch are turned on is defined as Mode 3; In the case where the upper arm first switch and the lower arm second switch are turned off and the upper arm second switch and the lower arm first switch are turned on, Mode 4 is set as follows: In the temperature increase control, the control unit causing the step-up operation unit to repeatedly perform the processes consisting of Mode 1, Mode 2, Mode 3, and Mode 4 in this order, and causing the step-down operation unit to repeatedly perform the processes consisting of Mode 1, Mode 4, Mode 3, and Mode 2 in this order; The power conversion device according to any one of configurations 2 to 4, wherein the length of at least one of the period in which Mode 2 is used in the voltage step-up operation, the period in which Mode 4 is used in the voltage step-down operation, the period in which Mode 2 is used in the voltage step-down operation, and the period in which Mode 4 is used in the voltage step-down operation is set based on the acquired inter-terminal voltage. [Configuration 6] when the temperature rise control is performed, a plurality of the power conversion units among the power conversion units are operable as the step-up operation units, and a plurality of the power conversion units among the power conversion units are operable as the step-down operation units, 6. The power conversion device according to any one of configurations 2 to 5, wherein the control unit synchronizes the operations of the two step-up operation units and synchronizes the operations of the two step-down operation units in the temperature rise control. [Configuration 7] The power conversion device according to configuration 6, wherein the control unit synchronizes, in the temperature rise control, the boost operation of a boost operation unit other than a boost operation unit that operates in synchronization with other boost operation units among the boost operation units, and the buck operation of a buck operation unit other than a buck operation unit that operates in synchronization with other buck operation units among the buck operation units. [Configuration 8] 6. The power conversion device according to any one of configurations 2 to 5, wherein the control unit synchronizes the step-up operation of the step-up operation unit and the step-down operation of the step-down operation unit in the temperature rise control. [Configuration 9] The power conversion device according to any one of configurations 6 to 8, wherein the control unit stops operation of the power conversion units other than the power conversion units that operate in synchronization with the other power conversion units during the temperature rise control. [Configuration 10] The power conversion device according to any one of configurations 6 to 8, wherein the control unit operates, in the temperature rise control, a power conversion unit among the power conversion units other than a power conversion unit that operates in synchronization with the other power conversion units as the step-up operation unit or the step-down operation unit. [Configuration 11] the high-voltage side terminal is connected to a battery (13) that is the object to be heated; the boost operation unit boosts the voltage input from the low-voltage side terminal and outputs the boosted voltage to the battery, 11. The power conversion device according to any one of configurations 1 to 10, wherein the step-down operation unit performs the step-down operation by stepping down the voltage output from the battery and outputting the stepped-down voltage to the low-voltage side terminal. [Configuration 12] The low-voltage side terminal is connected to a charging device (16), 12. The power conversion device according to claim 11, wherein the boost operation unit boosts the voltage output from the charging device and outputs the boosted voltage to the battery, thereby charging the battery.

[0170] Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and equivalent modifications. In addition, various combinations and forms, including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure.

Claims

1. In a power conversion device (14) having low-voltage side terminals (TL1, TL2) and high-voltage side terminals (TH1, TH2), a boost operation unit that performs a boost operation of boosting a voltage input from the low-voltage side terminal and outputting the boosted voltage to the high-voltage side terminal; a step-down operation unit that performs a step-down operation of stepping down a voltage input from the high-voltage side terminal and outputting the stepped-down voltage to the low-voltage side terminal; a control unit (24) that performs temperature increase control to increase the temperature of an object to be heated (13) by causing the voltage increase operation unit to perform the voltage increase operation and the voltage decrease operation unit to perform the voltage decrease operation; a power conversion unit (30, 40, 60, 70) including a series connection of upper-arm first switches (QH1, SH1, KH1, RH1) and upper-arm second switches (QH2, SH2, KH2, RH2), a series connection of lower-arm first switches (QL1, SL1, KL1, RL1) and lower-arm second switches (QL2, SL2, KL2, RL2), and a resonance unit (33, 43, 63, 73) that is a series connection of reactors (34, 44, 64, 74) and capacitors (35, 45, 65, 75), The high-voltage side terminals are a high-voltage side first terminal (TH1) on the high potential side and a high-voltage side second terminal (TH2) on the low potential side, The low-voltage side terminals are a low-voltage side first terminal (TL1) on the high potential side and a low-voltage side second terminal (TL2) on the low potential side, the resonator connects a connection point between the upper arm first switch and the upper arm second switch and a connection point between the lower arm first switch and the lower arm second switch, the upper arm first switch is connected to the high voltage side first terminal, a connection point between the upper arm second switch and the lower arm first switch is connected to the low voltage side first terminal, the lower arm second switch is connected to the high voltage side second terminal and the low voltage side second terminal, The power converter includes a plurality of power converters, each of the power conversion units is configured to be operable as at least one of the step-up operation unit and the step-down operation unit by switching the upper arm first switch, the upper arm second switch, the lower arm first switch, and the lower arm second switch; The control unit performs the temperature rise control by operating at least one of the power conversion units as the boost operation unit and operating at least one of the power conversion units as the step-down operation unit.

2. In a power conversion device (14) having low-voltage side terminals (TL1, TL2) and high-voltage side terminals (TH1, TH2), a boost operation unit that performs a boost operation of boosting a voltage input from the low-voltage side terminal and outputting the boosted voltage to the high-voltage side terminal; a step-down operation unit that performs a step-down operation of stepping down a voltage input from the high-voltage side terminal and outputting the stepped-down voltage to the low-voltage side terminal; a control unit (24) that performs temperature increase control to increase the temperature of a temperature-increasing object (13) by causing the voltage-increasing operation unit to perform the voltage-increasing operation and the voltage-decreasing operation unit to perform the voltage-decreasing operation, The high-voltage side terminal is connected to a battery (13) that is the object to be heated, The low-voltage side terminal is connected to a charging device (16), the boost operation unit boosts the voltage output from the charging device and outputs the boosted voltage to the battery, thereby charging the battery; The step-down operation unit is a power conversion device that performs the step-down operation by stepping down a voltage output from the battery and outputting the stepped-down voltage to the low-voltage side terminal.

3. the power conversion unit (30, 40, 60, 70) includes a plurality of power conversion units (30, 40, 60, 70) each including a series connection of upper-arm first switches (QH1, SH1, KH1, RH1) and upper-arm second switches (QH2, SH2, KH2, RH2), a series connection of lower-arm first switches (QL1, SL1, KL1, RL1) and lower-arm second switches (QL2, SL2, KL2, RL2), and a resonance unit (33, 43, 63, 73) which is a series connection of reactors (34, 44, 64, 74) and capacitors (35, 45, 65, 75); The high-voltage side terminals are a high-voltage side first terminal (TH1) on the high potential side and a high-voltage side second terminal (TH2) on the low potential side, The low-voltage side terminals are a low-voltage side first terminal (TL1) on the high potential side and a low-voltage side second terminal (TL2) on the low potential side, the resonator connects a connection point between the upper arm first switch and the upper arm second switch and a connection point between the lower arm first switch and the lower arm second switch, the upper arm first switch is connected to the high voltage side first terminal, a connection point between the upper arm second switch and the lower arm first switch is connected to the low voltage side first terminal, the lower arm second switch is connected to the high voltage side second terminal and the low voltage side second terminal, each of the power conversion units is configured to be operable as at least one of the step-up operation unit and the step-down operation unit by switching the upper arm first switch, the upper arm second switch, the lower arm first switch, and the lower arm second switch; 3. The power conversion device according to claim 2, wherein the control unit performs the temperature rise control by operating at least one of the power conversion units as the step-up operation unit and operating at least one of the power conversion units as the step-down operation unit.

4. 4. The power conversion device according to claim 1, wherein, when performing the temperature rise control, the control unit sets the switching frequencies of the upper arm first switch, the upper arm second switch, the lower arm first switch, and the lower arm second switch provided in the voltage boost operation unit to be higher than a resonant frequency of the resonant unit provided in the voltage boost operation unit, and sets the switching frequencies of the upper arm first switch, the upper arm second switch, the lower arm first switch, and the lower arm second switch provided in the voltage step-down operation unit to be higher than a resonant frequency of the resonant unit provided in the voltage step-down operation unit.

5. 5. The power conversion device according to claim 4, wherein when the control unit causes each of the power conversion units to operate as only one of the step-up operation unit and the step-down operation unit, the control unit sets the switching frequency to a frequency lower than a switching frequency when performing the temperature rise control and close to the resonant frequency.

6. an acquisition unit that acquires an inter-terminal voltage of at least one of the low-voltage side terminal and the high-voltage side terminal; a state in which the upper arm second switch and the lower arm second switch are turned off and the upper arm first switch and the lower arm first switch are turned on is defined as Mode 1; a state in which the upper arm second switch and the lower arm first switch are turned off and the upper arm first switch and the lower arm second switch are turned on is defined as Mode 2; a state in which the upper arm first switch and the lower arm first switch are turned off and the upper arm second switch and the lower arm second switch are turned on is defined as Mode 3; When the state in which the upper arm first switch and the lower arm second switch are turned off and the upper arm second switch and the lower arm first switch are turned on is defined as Mode 4, In the temperature increase control, the control unit the step-up operation unit is caused to repeatedly perform the processes consisting of Mode 1, Mode 2, Mode 3, and Mode 4 in this order, and the step-down operation unit is caused to repeatedly perform the processes consisting of Mode 1, Mode 4, Mode 3, and Mode 2 in this order; 4. The power conversion device according to claim 1, wherein a length of at least one of a period during which Mode 2 is set in the voltage step-up operation, a period during which Mode 4 is set in the voltage step-down operation, a period during which Mode 2 is set in the voltage step-down operation, and a period during which Mode 4 is set in the voltage step-down operation is set based on the acquired inter-terminal voltage.

7. when the temperature rise control is performed, a plurality of the power conversion units among the power conversion units are operable as the step-up operation units, and a plurality of the power conversion units among the power conversion units are operable as the step-down operation units, The power conversion device according to claim 1 , wherein the control unit synchronizes the operations of the two step-up operation units and synchronizes the operations of the two step-down operation units in the temperature rise control.

8. 8. The power conversion device according to claim 7, wherein the control unit synchronizes, in the temperature rise control, the boost operation of a boost operation unit other than a boost operation unit that operates in synchronization with other boost operation units among the boost operation units, and the buck operation of a buck operation unit other than a buck operation unit that operates in synchronization with other buck operation units among the buck operation units.

9. The power conversion device according to claim 1 , wherein the control unit synchronizes the voltage step-up operation of the voltage step-up operation unit and the voltage step-down operation of the voltage step-down operation unit in the temperature rise control.

10. The control unit stops operation of the power conversion units other than the power conversion units that operate in synchronization with the other power conversion units among the power conversion units in the temperature rise control. The power conversion device according to any one of claims 7 to 9.

11. The power conversion device according to any one of claims 7 to 9, wherein the control unit operates a power conversion unit other than a power conversion unit that operates in synchronization with other power conversion units among the power conversion units as the step-up operation unit or the step-down operation unit during the temperature rise control.

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