Power Conversion Device

Abstract

An electric power converting device (2) is provided with: a plurality of electric power converting circuits (12) each of which is provided with a transformer (22), and each of which supplies direct-current power to a common rechargeable battery (3); and a control circuit (13) for controlling the electric power converting circuits (12). If the load voltage of the rechargeable battery 3 reaches to or above a predetermined threshold, the control circuit (13) selectively and sequentially operates the plurality of electric power converting circuits (12) in such a way that one electric power converting circuit (12) among the plurality of electric power converting circuits (12) operates and the operation of the other electric power converting circuits (12) is stopped.

Description

[Technical Field]

[0001] The present disclosure relates to a power conversion device, a control method for a power conversion device, and a charging system. [Background technology]

[0002] Electric vehicles and plug-in hybrid vehicles are equipped with an on-board power conversion device that converts AC power obtained from a commercial AC power source into DC power in order to charge on-board rechargeable batteries. For example, Patent Document 1 discloses a switching power supply device that can be used as a charging device for electric vehicles or hybrid vehicles. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6643678 [Patent Document 2] Patent No. 6509472 Summary of the Invention [Problem to be solved by the invention]

[0004] Some power conversion devices are configured as isolated circuits equipped with a transformer. In such power conversion devices, the temperature of the transformer core gradually increases as the power conversion device continues to operate. If the temperature of the transformer core increases excessively, external forces are applied to the core due to the thermal expansion of the transformer's components (such as the bobbin and potting), and stress is generated in the core due to an unbalanced temperature distribution in the core. These external forces and stresses may result in damage to the core.

[0005] For example, Patent Document 2 discloses a transformer equipped with a cooling water channel. Even if the transformer is cooled with cooling water as in Patent Document 2, depending on the magnitude of the current flowing through the transformer, heat may be generated that exceeds the cooling capacity of the transformer, which may damage the core.

[0006] An object of the present disclosure is to provide an isolated power conversion device including a transformer in which core damage due to overheating of the transformer is less likely than conventional power conversion devices. Another object of the present disclosure is to provide a control method for such a power conversion device. Another object of the present disclosure is to provide a charging system including such a power conversion device. [Means for solving the problem]

[0007] According to the power conversion device according to one aspect of the present disclosure, a plurality of power conversion circuits each including a transformer and each supplying DC power to a common load device; a control circuit for controlling each of the power conversion circuits, The control circuit selectively and sequentially operates the plurality of power conversion circuits so that, when the load voltage of the load device becomes equal to or greater than a first threshold, one of the plurality of power conversion circuits operates and the other power conversion circuits stop operating. [Effects of the Invention]

[0008] According to a power conversion device according to an aspect of the present disclosure, damage to the core due to overheating of the transformer can be made less likely than in the past. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a block diagram showing a configuration of a charging system including a power conversion device 2 according to a first embodiment. [Figure 2] 2 is a circuit diagram showing an exemplary configuration of power conversion circuits 12-1 to 12-3 of FIG. [Figure 3] 2 is a cross-sectional view showing an exemplary configuration of transformers 22-1 to 22-3 in FIG. [Figure 4] 2 is a vertical cross-sectional view of a housing 41 for explaining a cooling device of the power conversion device 2 of FIG. 1. FIG. [Figure 5] 2 is a cross-sectional view of a housing 41 for explaining a cooling device of the power conversion device 2 of FIG. 1. FIG. [Figure 6] 2 is a graph showing exemplary changes in load power and load voltage when charging the rechargeable battery 3 of FIG. 1. [Figure 7] 2 is a graph showing temperature characteristics of iron loss of core 52 of transformers 22-1 to 22-3 of FIG. [Figure 8] 2 is a diagram illustrating heat conduction between the transformers 22-1 to 22-3 in FIG. 1 when the transformers 22-1 to 22-3 are in thermal contact with each other. [Figure 9] FIG. 10 is a block diagram showing the configuration of a charging system including a power conversion device 2A according to a modified example of the first embodiment. [Figure 10] 10 is a vertical cross-sectional view of a housing 41 for explaining a cooling device of the power conversion device 2A of FIG. 9. FIG. [Figure 11] 10 is a cross-sectional view of a housing 41 for explaining a cooling device of the power conversion device 2A of FIG. 9. FIG. [Figure 12] 10 is a graph schematically showing a change over time in temperature of core 52 of transformers 22-1 to 22-3 when power conversion device 2 of FIG. 1 is switched from heavy load operation to light load operation. [Figure 13] 10 is a flowchart showing a charging control process executed by a control circuit 13 of a power conversion device 2 according to a second embodiment. [Figure 14] 14 is a timing chart showing the operation of power conversion circuits 12-1 to 12-3 when the charge control process of FIG. 13 is executed. [Figure 15] FIG. 10 is a block diagram showing the configuration of a charging system including a power conversion device 2B according to a first modified example of the second embodiment. [Figure 16] 16 is a flowchart showing a charging control process executed by a control circuit 13B of a power conversion device 2B of FIG. [Figure 17] 17 is a graph showing a schematic change over time in temperature of core 52 of transformers 22-1 to 22-3 when the charge control process of FIG. 16 is executed. [Figure 18] 17 is a timing chart showing the operation of the power conversion circuits 12-1 to 12-3 when the charge control process of FIG. 16 is executed. [Figure 19] FIG. 10 is a block diagram showing the configuration of a charging system including a power conversion device 2C according to a second modification of the second embodiment. [Figure 20] 20 is a flowchart showing a charging control process executed by a control circuit 13C of a power conversion device 2C of FIG. 19. [Figure 21] FIG. 10 is a block diagram showing the configuration of a charging system including a power conversion device 2D according to a third modification of the second embodiment. [Figure 22] 22 is a flowchart showing a charging control process executed by a control circuit 13D of a power conversion device 2D of FIG. 21. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. However, the configurations described below are merely examples of the present disclosure, and the present disclosure is not limited to the following embodiments. Various modifications can be made to the embodiments other than these embodiments according to the design, etc., as long as they do not deviate from the technical concept of the present disclosure.

[0011] [First embodiment] In each embodiment of the present disclosure, a power conversion device including a plurality of power conversion circuits each including a transformer and supplying DC power to a common load device will be described. In a first embodiment, a power conversion device will be described in which, when only one of the plurality of power conversion circuits is operated, the power conversion circuit including the transformer with the highest cooling performance is operated to prevent the transformer from overheating.

[0012] [Configuration of the first embodiment] Fig. 1 is a block diagram showing the configuration of a charging system including a power conversion device 2 according to a first embodiment. The charging system of Fig. 1 includes the power conversion device 2 and a rechargeable battery 3. The power conversion device 2 converts AC power supplied from an AC power source 1, such as a commercial AC power source, into DC power and supplies it to the rechargeable battery 3 for charging. The charging system of Fig. 1 is mounted on, for example, an electric vehicle or a plug-in hybrid vehicle.

[0013] The power conversion device 2 includes a distributor 11, switches SW-1 to SW-3, power conversion circuits 12-1 to 12-3, and a control circuit 13. The power conversion device 2 further includes a housing 41, a heat sink 45, and a pump 46, as will be described later with reference to FIGS.

[0014] The distributor 11 distributes 100V or 200V AC power supplied from the AC power supply 1 into LN1-phase, LN2-phase, and LN3-phase AC power, and supplies the distributed AC power to the power conversion circuits 12-1-12-3 via the switches SW-1-SW-3, respectively. The AC power supply 1 is, for example, a three-phase AC power supply, and the LN1-phase, LN2-phase, and LN3-phase are, for example, the AC power of each phase of the three-phase AC power.

[0015] The switch SW-1 passes or blocks the LN1-phase AC power supplied from the distributor 11 to the power conversion circuit 12-1. The switch SW-2 passes or blocks the LN2-phase AC power supplied from the distributor 11 to the power conversion circuit 12-2. The switch SW-3 passes or blocks the LN3-phase AC power supplied from the distributor 11 to the power conversion circuit 12-3. The switches SW-1 to SW-3 are, for example, mechanical relays.

[0016] The power conversion circuit 12-1 converts LN1-phase AC power to DC power, the power conversion circuit 12-2 converts LN2-phase AC power to DC power, and the power conversion circuit 12-3 converts LN3-phase AC power to DC power. The power conversion circuits 12-1 to 12-3 each supply DC power to a rechargeable battery 3, which is a common load device. The power conversion circuits 12-1 to 12-3 generate an output voltage equal to the load voltage required to charge the rechargeable battery 3. The power conversion circuit 12-1 includes a primary side circuit 21-1, a transformer 22-1, and a secondary side circuit 23-1. The power conversion circuit 12-2 includes a primary side circuit 21-2, a transformer 22-2, and a secondary side circuit 23-2. The power conversion circuit 12-3 includes a primary side circuit 21-3, a transformer 22-3, and a secondary side circuit 23-3. In this way, the power conversion circuits 12-1 to 12-3 are configured as insulated circuits each including a transformer 22-1 to 22-3. The output terminals of the power conversion circuits 12-1 to 12-3 are connected to the rechargeable battery 3 in parallel.

[0017] The control circuit 13 receives from the rechargeable battery 3 a control signal indicating the magnitude of the load current and load voltage required to charge the rechargeable battery 3. The control circuit 13 controls the switches SW-1 to SW-3 and the power conversion circuits 12-1 to 12-3 to operate one, two, or three of the power conversion circuits 12-1 to 12-3 according to the magnitude of the required load current and load voltage. When operating one of the power conversion circuits 12-1 to 12-3, the control circuit 13 turns on the switches SW-1 to SW-3 corresponding to that power conversion circuit and performs switching operations on the switching elements Q1 to Q4 (described later with reference to FIG. 2) of that power conversion circuit at a predetermined cycle. On the other hand, when stopping the operation of one of the power conversion circuits 12-1 to 12-3, the control circuit 13 turns off the switches SW-1 to SW-3 corresponding to that power conversion circuit and stops the switching operations of the switching elements Q1 to Q4 of that power conversion circuit. The control circuit 13 is configured, for example, by a microcomputer equipped with a CPU and memory.

[0018] In this specification, switches SW-1 to SW-3 are also collectively referred to as "switches SW." In addition, in this specification, power conversion circuits 12-1 to 12-3 are also collectively referred to as "power conversion circuits 12." In addition, in this specification, primary side circuits 21-1 to 21-3 are also collectively referred to as "primary side circuits 21." In addition, in this specification, transformers 22-1 to 22-3 are also collectively referred to as "transformers 22." In addition, in this specification, secondary side circuits 23-1 to 23-3 are also collectively referred to as "secondary side circuits 23."

[0019] FIG. 2 is a circuit diagram showing an exemplary configuration of the power conversion circuits 12-1 to 12-3 of FIG.

[0020] Referring to FIG. 2, the primary side circuit 21 includes diodes D1 to D4, capacitors C1 and C2, a power factor correction circuit 31, and switching elements Q1 to Q4. The diodes D1 to D4 rectify AC power of LN1 phase, LN2 phase, or LN3 phase input via one of the switches SW-1 to SW-3. The capacitor C1 smoothes the power rectified by the diodes D1 to D4. The power factor correction circuit 31 suppresses harmonics in the rectified and smoothed DC power to improve its power factor. The switching elements Q1 to Q4 form a full-bridge inverter circuit and convert the DC power output from the power factor correction circuit 31 into AC power. The switching elements Q1 to Q4 are, for example, N-channel MOSFETs. The switching elements Q1 to Q4 are turned on / off in accordance with control signals applied to their gates from the control circuit 13. The capacitor C2 is connected between the switching elements Q1 to Q4 and the primary winding L1 of the transformer 22.

[0021] 2, the transformer 22 includes a primary winding L1 and a secondary winding L2. The primary winding L1 and the secondary winding L2 each have a magnetizing inductance. The transformer 22 further includes a leakage inductance L3. The configuration of the transformer 22 will be described in further detail with reference to FIG. 3.

[0022] 2, the secondary side circuit 23 includes diodes D5 to D8 and a capacitor C3. The diodes D5 to D8 rectify the AC power generated in the secondary winding L2 of the transformer 22. The capacitor C3 smoothes the power rectified by the diodes D5 to D8. The rectified and smoothed DC power is supplied to the rechargeable battery 3.

[0023] The excitation inductance of the primary winding L1 of the transformer 22, leakage inductance L3, and capacitor C2 constitute an LLC resonant circuit. Therefore, the switching elements Q1 to Q4 and capacitor C2 of the primary side circuit 21, the transformer 22, and the secondary side circuit 23 constitute an LLC resonant DC / DC converter circuit. LLC resonant DC / DC converter circuits are widely used in high-efficiency power supply devices such as industrial switching power supplies, on-board charging devices, and power converters. The control circuit 13 monitors the load voltage required to charge the rechargeable battery 3 and controls the power conversion circuits 12-1 to 12-3 using a frequency modulation method that changes the switching frequency of the switching elements Q1 to Q4 to bring the output voltages of the power conversion circuits 12-1 to 12-3 closer to the load voltage. The power conversion circuits 12-1 to 12-3 can reduce switching loss by operating the switching elements Q1 to Q4 using zero-voltage switching. Furthermore, the power conversion circuits 12-1 to 12-3 generate switching currents that are close to sine waves, thereby reducing surge currents and voltages and reducing noise.

[0024] 3 is a cross-sectional view showing an exemplary configuration of the transformers 22-1 to 22-3 in FIG. 1. As described above, the transformer 22 includes the primary winding L1 and the secondary winding L2, as well as a bobbin 51, a core 52, and a potting 53. The primary winding L1 and the secondary winding L2 are wound around the bobbin 51. The core 52 is made of core portions 52a and 52b, which sandwich the bobbin 51 around which the primary winding L1 and the secondary winding L2 are wound. The core 52 is made of, for example, ferrite. The core 52 is embedded in a potting 53 made of silicone rubber or the like. Copper loss occurs in the primary winding L1 and the secondary winding L2, and iron loss occurs in the core 52. These losses cause the temperatures of the primary winding L1, the secondary winding L2, and the core 52 to rise. Heat from the primary winding L1, secondary winding L2, and core 52 is dissipated to the outside through the potting 53. Furthermore, by conducting heat between the core portions 52a and 52b, the temperature difference between the core portions 52a and 52b can be reduced. While the thermal conductivity of materials typically used for the potting 53 is approximately 1 to 2 W / (m·K), the ferrite used for the core 52 has a thermal conductivity of 5 W / (m·K), providing high heat dissipation. The thickness of the potting 53 around the core 52 may be constant or may vary depending on the location. In the example shown in FIG. 3, the potting 53 at the bottom of the transformer 22 is thinner than other portions to facilitate heat dissipation from the core 52 to an external thermal conductor (e.g., the wall 44b of the chamber 44 in FIG. 4).

[0025] Fig. 4 is a vertical cross-sectional view of the housing 41 for explaining the cooling device of the power conversion device 2 of Fig. 1. Fig. 5 is a horizontal cross-sectional view of the housing 41 for explaining the cooling device of the power conversion device 2 of Fig. 1. Fig. 5 shows a cross section taken along line A-A' in Fig. 4. As shown in Figs. 4 and 5, the power conversion device 2 further includes the housing 41, a heat sink 45, and a pump 46.

[0026] The housing 41 protects the components therein from water, dust, noise, and the like. The housing 41 is configured by fitting together multiple parts formed by aluminum die-casting or the like. The housing 41 includes chambers 42 to 44. The chambers 42 and 43 house the components of the power conversion device 2 shown in FIG. 1. A coolant 44a, such as cooling water or an antifreeze liquid called LLC (Long Life Coolant), circulates inside the chamber 44. The coolant 44a is in thermal contact with the components of the power conversion device 2 via walls 44b and 44c of the chamber 44. The chamber 44 is connected to a heat sink 45 and a pump 46 outside the housing 41 via an inlet 44d and an outlet 44e. The coolant 44a circulates through the chamber 44, the heat sink 45, and the pump 46 by the pump 46. Heat generated by heat-generating components (such as the primary circuit 21, the transformer 22, and the secondary circuit 23) of the power conversion device 2 is transferred to the coolant 44a through the walls 44b and 44c, and the heat in the coolant 44a is dissipated from the heat sink 45. The chamber 44 may be provided with one or more fins 44f to improve cooling performance.

[0027] For the sake of explanation, Figures 4 and 5 show only the primary side circuit 21, the transformer 22, and the secondary side circuit 23 of the power conversion circuit 12 among the components of the power conversion device 2 shown in Figure 1, and omit the other components.

[0028] 5 also schematically shows the footprints of the primary side circuit 21, transformer 22, and secondary side circuit 23 of the power conversion circuit 12. The example of Fig. 5 shows a case where the power conversion circuits 12-1 to 12-3 have the same configuration, and therefore the primary side circuits 21-1 to 21-3 have the same dimensions, the transformers 22-1 to 22-3 have the same dimensions, and the secondary side circuits 23-1 to 23-3 have the same dimensions.

[0029] As shown in Fig. 5, the chamber 44 includes flow paths F1 to F3 for flowing the coolant 44a, which are in thermal contact with at least the transformers 22-1 to 22-3, respectively. The flow paths F1 to F3 may further be in thermal contact with the primary-side circuits 21-1 to 21-3 and the secondary-side circuits 23-1 to 23-3, respectively. The primary-side circuits 21-1 to 21-3, the transformers 22-1 to 22-3, and the secondary-side circuits 23-1 to 23-3 are in thermal contact with the flow paths F1 to F3 via a wall portion 44b of the chamber 44 (see Fig. 4). In the example of Fig. 5, the flow paths F1 to F3 may be at least partially connected to each other.

[0030] The housing 41, the heat radiator 45, and the pump 46 constitute a cooling device for the power conversion device 2, and cool the heat-generating components of the power conversion device 2.

[0031] [Operation of the first embodiment] The magnitude of the load voltage required to charge the rechargeable battery 3 varies from the minimum voltage of the rechargeable battery 3 to the fully charged voltage depending on the state of charge of the rechargeable battery 3, i.e., the charged voltage (hereinafter referred to as "the voltage of the rechargeable battery 3"). The magnitude of the load current and load power required to charge the rechargeable battery 3 also varies depending on the state of charge of the rechargeable battery 3. The power conversion device 2 changes the number of operating power conversion circuits 12-1 to 12-3 depending on the magnitude of the load current or load power required to charge the rechargeable battery 3. Generally, the power conversion device 2 operates all of the power conversion circuits 12-1 to 12-3 in a heavy load state where a large current or large power is required to charge the rechargeable battery 3, and operates only one of the power conversion circuits 12-1 to 12-3 in a light load state where a small current or small power is required to charge the rechargeable battery 3. In this specification, the operation of the power conversion device 2 when all of the power conversion circuits 12-1 to 12-3 are operated is called "heavy load operation," and the operation of the power conversion device 2 when only one of the power conversion circuits 12-1 to 12-3 is operated is called "light load operation."

[0032] FIG. 6 is a graph showing exemplary changes in load power and load voltage when charging the rechargeable battery 3 in FIG. 1. When the power conversion device 2 starts charging the rechargeable battery 3, it first operates all of the power conversion circuits 12-1 to 12-3 (heavy load operation). However, during the period from time t0 to t1, when the voltage of the rechargeable battery 3 is low, the power conversion device 2 operates all of the power conversion circuits 12-1 to 12-3 but charges the rechargeable battery 3 with low power to prevent deterioration of the rechargeable battery 3. At this time, the power conversion device 2 charges the rechargeable battery 3 with a constant current, and the load power gradually increases as the load voltage increases. As charging of the rechargeable battery 3 continues, at time t1, when the load voltage required to charge the rechargeable battery 3 reaches a predetermined threshold value Th0 that is higher than the lower limit voltage of the rechargeable battery 3, the power conversion device 2 increases the output power of the power conversion circuits 12-1 to 12-3 and charges the rechargeable battery 3 with a constant, high power. As the voltage of the rechargeable battery 3 further increases and approaches the fully charged voltage Th, the voltage drop due to the internal resistance and current of the rechargeable battery 3 is superimposed on the load voltage, causing an excessive voltage to be applied to the rechargeable battery 3, potentially damaging the rechargeable battery 3 and shortening its lifespan. Therefore, when the load voltage reaches the fully charged voltage Th at time t2, the power conversion device 2 operates only one of the power conversion circuits 12-1 to 12-3 and stops the operation of the other power conversion circuits (light load operation). By reducing the number of operating power conversion circuits 12-1 to 12-3 and reducing the output current, the voltage drop of the rechargeable battery 3 decreases, resulting in a temporary drop in the load voltage. Thereafter, the operating power conversion circuits gradually reduce the current flowing through the rechargeable battery 3. By reducing the current flowing through the rechargeable battery 3, the voltage drop of the rechargeable battery 3 also decreases further, and the voltage of the rechargeable battery 3 approaches the fully charged voltage Th.

[0033] As described above, the magnitudes of the load voltage, load current, and load power required to charge the rechargeable battery 3 all change depending on the state of charge of the rechargeable battery 3. Therefore, changes in the load current and load power are correlated with changes in the load voltage. In an embodiment of the present disclosure, the power conversion device 2 changes the number of operating power conversion circuits 12-1 to 12-3 depending on the magnitude of the load voltage, instead of the magnitude of the load current or load power.

[0034] FIG. 7 is a graph showing the temperature characteristics of iron loss in the core 52 of each of the transformers 22-1 to 22-3 in FIG. 1. In the transformer 22, copper loss occurs when current flows through the primary winding L1 and the secondary winding L2, and iron loss occurs when magnetic flux flows through the core 52. Because magnetic flux is generated when an excitation current flows through the primary winding L1, increasing the excitation current increases the magnetic flux and iron loss. Furthermore, the excitation current increases as the output voltage increases, and the excitation current also increases as the output current decreases. Therefore, as the voltage of the rechargeable battery 3 approaches full charge and the output current of the power conversion circuit 12 decreases, iron loss increases, and heat generation in the core 52 also increases. Materials such as ferrite typically used for the core 52 of the transformer 22 have the temperature characteristics of iron loss shown in FIG. 4. Iron loss is minimized at temperatures between 80 and 90°C. During operation of the power conversion circuit 12, when the temperature of the core 52 exceeds 80 to 90°C, iron loss increases, and the temperature of the core 52 further rises. As the temperature of the core 52 rises, iron loss increases again. Repeating this cycle can cause thermal runaway, potentially damaging the core 52 of the transformer 22. To mitigate thermal runaway in the transformer 22, it is important to reduce or manage the heat generated by the transformer 22.

[0035] When the power conversion circuit 12 is operating, the primary current of the transformer 22 includes a current component that contributes to the generation of magnetic flux (i.e., an excitation current) and a current component that contributes to the generation of a secondary current. During heavy load operation, the latter current component is dominant, and the power conversion circuit 12 operates with high efficiency. On the other hand, during light load operation, the output power and output current decrease, the resonant current decreases, and the excitation current that does not contribute to the generation of a secondary current becomes dominant, resulting in a decrease in the efficiency of the power conversion circuit 12. Therefore, during light load operation, by operating only one power conversion circuit rather than operating all of the power conversion circuits 12-1 to 12-3, it is possible to reduce the amount of decrease in the output current of the operating power conversion circuit and alleviate the decrease in efficiency.

[0036] As described below, when operating only one of the multiple power conversion circuits 12 under light load operation, the power conversion device 2 of the first embodiment operates the power conversion circuit 12 equipped with the transformer 22 having the highest cooling performance.

[0037] As shown in FIG. 4, the bottom surface of the transformer 22 is in thermal contact with the flow paths F1 to F3 via the wall 44b of the chamber 44. Also, referring to FIG. 5, the entire bottom surface of the transformer 22-2 faces the flow path F2, while the transformers 22-1 and 22-3 have portions of their bottom surfaces facing the flow paths F1 and F3. Therefore, the area of ​​the transformer 22-2 in thermal contact with the flow path F2 is larger than the areas of the transformers 22-1 and 22-3 in thermal contact with the flow paths F1 and F3, respectively. This results in the cooling performance of the transformer 22-2 being higher than the cooling performance of the transformers 22-1 and 22-3. When the power conversion device 2 operates under light load, i.e., when the load voltage of the rechargeable battery 3 becomes equal to or greater than a predetermined threshold value Th, the control circuit 13 activates the power conversion circuit 12 having the transformer 22 with the largest area of ​​thermal contact with the flow paths F1 to F3 among the multiple power conversion circuits 12, and stops the operation of the other power conversion circuits 12. 5, when the power conversion device 2 is operating under a light load, the control circuit 13 operates only the power conversion circuit 12-2 and stops the operations of the power conversion circuits 12-1 and 12-3. By operating the power conversion circuit 12 having the transformer 22 with the largest area in thermal contact with the flow paths F1 to F3 in this manner, the power conversion circuit 12 having the transformer 22 with the highest cooling performance operates, making it more unlikely than ever that the core 52 will be damaged due to overheating of the transformer 22.

[0038] FIG. 8 illustrates heat conduction between the transformers 22-1 to 22-3 in FIG. 1 when the transformers 22-1 to 22-3 are in thermal contact with one another. The transformer 22 of a power conversion circuit 12 that is stopped approaches the temperature of the coolant 44a in a relatively short time. Therefore, by arranging the transformers 22 of each power conversion circuit 12 in thermal contact with one another, heat can be dissipated from the transformer 22 of the operating power conversion circuit 12 to the transformer 22 of the stopped power conversion circuit 12. In particular, by contacting the transformers 22 of multiple stopped power conversion circuits 12 with the transformer 22 of the operating power conversion circuit 12, cooling performance is improved compared to when only the transformer 22 of a single stopped power conversion circuit 12 is in contact. When the power conversion device 2 is operating under light load, the control circuit 13 operates one of the multiple power conversion circuits 12 that has a transformer 22 in thermal contact with at least two other transformers 22, and stops the operation of the other power conversion circuits 12. 8, when the power conversion device 2 operates under a light load, the control circuit 13 operates only the power conversion circuit 12-2 including the transformer 22-2, and stops the operation of the power conversion circuits 12-1 and 12-3 including the transformers 22-1 and 22-3. By operating one power conversion circuit 12 including a transformer 22 that is in thermal contact with at least two other transformers 22 in this manner, the power conversion circuit 12 including the transformer 22 with the highest cooling performance operates, making it less likely than ever that the core 52 will be damaged due to overheating of the transformer 22.

[0039] By arranging the transformers 22 of each power conversion circuit 12 so that they are in thermal contact with one another, it is possible to operate the power conversion circuit 12 equipped with the transformer 22 having the highest cooling performance, even if there is no difference in the area of ​​the region in thermal contact with the flow paths F1 to F3 of each transformer 22. Furthermore, by arranging each transformer 22 so that the transformer 22 having the largest area in thermal contact with the flow paths F1 to F3 is in thermal contact with at least two other transformers 22, it is possible to further improve the cooling performance of the transformers 22.

[0040] [Modification of the first embodiment] Fig. 9 is a block diagram showing the configuration of a charging system including a power conversion device 2A according to a modification of the first embodiment. The power conversion device 2A includes a control circuit 13A instead of the control circuit 13 of Fig. 1, and further includes valves 47-1 to 47-3. As will be described later with reference to Figs. 10 and 11, the valves 47-1 to 47-3 allow or block the passage of the coolant 44a flowing through the flow paths F1 to F3. The valves 47-1 to 47-3 are, for example, solenoid valves. The control circuit 13A controls the switches SW-1 to SW-3 and the power conversion circuits 12-1 to 12-3 in the same way as the control circuit 13 of Fig. 1, and further controls the opening and closing of the valves 47-1 to 47-3.

[0041] In this specification, the valves 47-1 to 47-3 are also collectively referred to as "valves 47."

[0042] Fig. 10 is a vertical cross-sectional view of the housing 41 for explaining the cooling device of the power conversion device 2A of Fig. 9. Fig. 11 is a horizontal cross-sectional view of the housing 41 for explaining the cooling device of the power conversion device 2A of Fig. 9. Fig. 11 shows a cross section taken along line BB' in Fig. 10. The chamber 44 has a partition plate 44g that separates the flow paths F1 to F3 from each other. Valves 47-1 to 47-3 are provided in the flow paths F1 to F3, respectively, and allow or block the passage of the cooling liquid 44a flowing through the flow paths F1 to F3.

[0043] Closing any one of valves 47-1 to 47-3 increases the flow rate of the flow path in which the open valve 47 is located compared to when all valves 47-1 to 47-3 are open, thereby improving the cooling performance of the transformer 22 in thermal contact with that flow path. When power conversion device 2A operates under light load, control circuit 13A operates one of the multiple power conversion circuits 12 and stops the operation of the other power conversion circuits 12, as described above. Furthermore, when power conversion device 2A operates under light load, control circuit 13A opens the valves in the flow paths F1 to F3 that are in thermal contact with the transformer 22 of the operating power conversion circuit 12 and closes the valves in the flow paths F1 to F3 that are in thermal contact with the transformer 22 of the stopped power conversion circuit 12. The example in FIG. 11 shows a case where only valve 47-2 is open and valves 47-1 and 47-3 are closed. In this way, by increasing the flow rate of the flow paths F1 to F3 that are in thermal contact with the transformer 22 of the power conversion circuit 12 during operation, the cooling performance of the transformer 22 of the power conversion circuit 12 during operation is improved, making it less likely than before that the core 52 will be damaged due to overheating of the transformer 22.

[0044] As an example, the inventors have determined that when core 52 core loss is maximized, increasing the flow rate from 4 liters / minute to 6 liters / minute reduces the core 52 temperature by 20°C.

[0045] 10 and 11, the valve 47 is provided upstream of the transformer 22, but the valve 47 may be provided at any position along the flow paths F1 to F3, for example, downstream of the transformer 22.

[0046] The valve 47 does not need to completely block the flow paths F1 to F3, but can increase the flow rate of the open flow paths by partially restricting the flow.

[0047] By using the valves 47, it is possible to effectively cool the transformers 22 of the operating power conversion circuits 12 even when there is no difference in the areas of the regions of the transformers 22 in thermal contact with the flow paths F1 to F3. Furthermore, when the control circuit 13A operates the power conversion circuit 12 including the transformer 22 having the largest area of ​​the region in thermal contact with the flow paths F1 to F3, and stops the operation of the other power conversion circuits 12, it may open the valves 47 provided in the flow paths F1 to F3 that are in thermal contact with the transformers 22 of the operating power conversion circuit 12 and close the valves 47 provided in the flow paths F1 to F3 that are in thermal contact with the transformers 22 of the stopped power conversion circuit 12. This further improves the cooling performance of the transformers 22.

[0048] By using the valves 47, the transformers 22 of the power conversion circuits 12 in operation can be cooled effectively even when the transformers 22 of the power conversion circuits 12 are not in thermal contact with each other. Furthermore, when the control circuit 13A operates one power conversion circuit 12 including a transformer 22 in thermal contact with at least two other transformers 22 and stops the operation of the other power conversion circuit 12, the control circuit 13A may open the valves 47 provided in the flow paths F1 to F3 in thermal contact with the transformers 22 of the operating power conversion circuit 12 and close the valves 47 provided in the flow paths F1 to F3 in thermal contact with the transformers 22 of the stopped power conversion circuit 12. This further improves the cooling performance of the transformers 22.

[0049] [Effects of the first embodiment] As described above, according to the power conversion device 2, 2A of the first embodiment, when only one of the multiple power conversion circuits 12 is operated, it is possible to operate the power conversion circuit 12 equipped with the transformer 22 having the highest cooling performance. This makes it less likely than conventional to damage the core 52 due to overheating of the transformer 22, and improves the reliability of the power conversion device 2, 2A.

[0050] [Second embodiment] In the second embodiment, a power conversion device that selectively and sequentially operates a plurality of power conversion circuits to prevent overheating of a transformer will be described.

[0051] 12 is a graph showing a change over time in the temperature of the cores 52 of the transformers 22-1 to 22-3 when the power conversion device 2 shown in FIG. 1 is switched from heavy-load operation to light-load operation. FIG. 12 shows a case where the transformers 22-1 to 22-3 of the power conversion device 2 shown in FIG. 1 do not have sufficient cooling performance. When the power conversion device 2 is operating under heavy load, that is, when all the power conversion circuits 12-1 to 12-3 are operating, the temperatures of the cores 52 of the transformers 22-1 to 22-3 are equal to each other. On the other hand, when the power conversion device 2 is operating under light load, in the example shown in FIG. 12, when only the power conversion circuit 12-1 is operating and the operations of the power conversion circuits 12-2 and 12-3 are stopped, the temperature of the core 52 of the transformer 22-1 rises approximately linearly at a rate of approximately 0.01°C / sec, and the temperatures of the cores 52 of the transformers 22-2 and 22-3 fall linearly at a rate of approximately 0.1°C / sec. 12 continues, there is a risk that the core 52 of the transformer 22-1 will overheat and be damaged. For this reason, in the second embodiment, when the power conversion device 2 operates under a light load, that is, when the load voltage of the rechargeable battery 3 becomes equal to or higher than the threshold value Th, the control circuit 13 selectively and sequentially operates the multiple power conversion circuits 12 so that one of the multiple power conversion circuits 12 operates and the other power conversion circuits 12 stop operating.

[0052] First, a case where the power conversion device according to the second embodiment has the same configuration as the power conversion device 2 in FIG. 1 will be described.

[0053] FIG. 13 is a flowchart showing a charging control process executed by the control circuit 13 of the power conversion device 2 according to the second embodiment.

[0054] In step S1, the control circuit 13 determines whether the magnitude of the load voltage required to charge the rechargeable battery 3 is equal to or greater than a predetermined threshold value Th, and if the result is YES, the process proceeds to step S3, and if the result is NO, the process proceeds to step S2. The threshold value Th is set to the fully charged voltage of the rechargeable battery 3, for example, as described with reference to FIG.

[0055] In step S2, the control circuit 13 turns on all the power conversion circuits 12-1 to 12-3 to operate them (heavy load operation), and then periodically returns to step S1.

[0056] In step S3, control circuit 13 stops the operations of all power conversion circuits 12-1 to 12-3.

[0057] In step S4, control circuit 13 selects one of power conversion circuits 12-1 to 12-3.

[0058] In step S5, the control circuit 13 turns on the selected power conversion circuit 12 to operate it (light load operation), and starts supplying power to the rechargeable battery 3.

[0059] In step S6, the control circuit 13 starts measuring the operation time of the selected power conversion circuit 12.

[0060] In step S7, the control circuit 13 determines whether the rechargeable battery 3 has reached full charge, and if YES, the process proceeds to step S10, and if NO, the process proceeds to step S8.

[0061] In step S8, the control circuit 13 determines whether the operating time for the selected power conversion circuit 12, i.e., the predetermined time period for the selected power conversion circuit 12, has expired, and if YES, proceeds to step S9, and if NO, returns to step S7.

[0062] In step S9, the control circuit 13 selects the next power conversion circuit 12 from the power conversion circuits 12-1 to 12-3 in a predetermined order, and returns to step S5. By repeating steps S5 to S9, for example, the power conversion circuit 12-2 operates after the power conversion circuit 12-1, the power conversion circuit 12-3 operates after the power conversion circuit 12-2, the power conversion circuit 12-1 operates after the power conversion circuit 12-3, and so on, with the power conversion circuits 12-1 to 12-3 operating selectively and sequentially in the same manner.

[0063] In step S10, control circuit 13 stops the operations of all power conversion circuits 12-1 to 12-3.

[0064] 14 is a timing chart showing the operation of power conversion circuits 12-1 to 12-3 when the charge control process of FIG. 13 is executed. In step S2 of FIG. 13, power conversion device 2 operates under heavy load, and in steps S3 to S9 of FIG. 13, power conversion device 2 operates under light load. When power conversion device 2 operates under light load, control circuit 13 switches the operating power conversion circuit 12 among power conversion circuits 12-1 to 12-3 every time a predetermined time period elapses. As a result, when power conversion device 2 operates under light load, power conversion circuits 12-1 to 12-3 operate for, for example, the same time period each. Of the entire time period during which power conversion device 2 operates under light load, each of power conversion circuits 12-1 to 12-3 operates for 1 / 3 of the time period and stops operating for the remaining 2 / 3 of the time period. 12, the rate at which the temperature of the core 52 of the transformer 22 in the stopped power conversion circuit 12 drops is ten times faster than the rate at which the temperature of the core 52 of the transformer 22 in the operating power conversion circuit 12. Therefore, as shown in FIG. 14, when the power conversion device 2 operates under a light load, the temperature of the core 52 does not effectively rise by switching the operating power conversion circuit 12.

[0065] 13 is determined based on the rate of temperature rise of the core 52, the rate of temperature fall of the core 52, the upper limit of the temperature at which thermal runaway does not occur, etc. The time period of step S8 in FIG. 13 may be set to, for example, one or two minutes in order to distribute the temperature rise of the core 52.

[0066] The time period of step S8 in FIG. 13 may be the same or different for the multiple power conversion circuits 12. In the latter case, when the power conversion device 2 operates under a light load, the control circuit 13 may selectively and sequentially operate the multiple power conversion circuits 12 so that the total operating times of the power conversion circuits 12 over a predetermined long time period are equal to each other. Furthermore, when the power conversion device 2 operates under a light load, the control circuit 13 may selectively and sequentially operate the multiple power conversion circuits 12 so that a longer operating time is allocated to the power conversion circuit 12 having a transformer 22 with higher cooling performance. For example, as described above, a transformer 22 in thermal contact with the flow paths F1 to F3 over a larger area has higher cooling performance, and a transformer 22 in thermal contact with more transformers 22 has higher cooling performance.

[0067] In this way, by selectively and sequentially operating the multiple power conversion circuits 12 based on their operating times, it is possible to make it less likely than before that the core 52 will be damaged due to overheating of the transformer 22. By selectively and sequentially operating the multiple power conversion circuits 12, it is possible to distribute the deterioration of the circuits and devices that occurs when the circuits are used continuously for a long period of time, which contributes to extending the life of the product.

[0068] [First Modification of the Second Embodiment] Fig. 15 is a block diagram showing the configuration of a charging system including a power conversion device 2B according to a first modification of the second embodiment. Power conversion device 2B includes a control circuit 13B instead of control circuit 13 in Fig. 1, and further includes temperature sensors 14-1 to 14-3. Temperature sensors 14-1 to 14-3 measure the temperatures of cores 52 of transformers 22-1 to 22-3, respectively. Control circuit 13B executes a charging control process, which will be described with reference to Fig. 16, based on the temperatures of cores 52 measured by temperature sensors 14-1 to 14-3.

[0069] Fig. 16 is a flowchart showing a charge control process executed by control circuit 13B of power conversion device 2B of Fig. 15. The charge control process of Fig. 16 includes steps S21 to S22 instead of steps S6 and S8 of Fig. 13. Control circuit 13B proceeds to step S7 after step S5, and if step S7 is NO, proceeds to step S21.

[0070] In step S21, the control circuit 13B measures the temperature Temp of the core 52 of the transformer 22 in the selected power conversion circuit 12.

[0071] In step S22, control circuit 13B determines whether temperature Temp is equal to or greater than a predetermined threshold value ThA, and if YES, proceeds to step S9, and if NO, returns to step S7. Threshold value ThA may be set to, for example, 80°C to 90°C, which is the temperature at which the iron loss of core 52 shown in Fig. 7 is minimized, that is, the temperature at which the iron loss of core 52 begins to increase.

[0072] By executing the charge control process of Figure 16, when the power conversion device 2B is operating under light load, the control circuit 13B switches the operating power conversion circuit 12 each time the temperature of the transformer 22 of the operating power conversion circuit 12 becomes equal to or higher than the threshold value ThA.

[0073] FIG. 17 is a graph schematically illustrating temporal changes in the temperature of core 52 of transformers 22-1 to 22-3 when the charge control process of FIG. 16 is executed. FIG. 18 is a timing chart illustrating the operation of power conversion circuits 12-1 to 12-3 when the charge control process of FIG. 16 is executed. In step S2 of FIG. 16, power conversion device 2B operates under heavy load, and in steps S3 to S5, S7, S21, S22, and S9 of FIG. 16, power conversion device 2B operates under light load. In the example of FIG. 18, when light load operation starts, power conversion circuit 12-1 operates first. The temperature of core 52 of transformer 22-1 rises due to iron loss of core 52, etc. Control circuit 13B monitors the temperature of core 52 of transformer 22-1, and when the temperature of core 52 becomes equal to or higher than threshold value ThA, stops operation of power conversion circuit 12-1 and starts operation of power conversion circuit 12-2. As a result, the temperature of core 52 of transformer 22-1 of power conversion circuit 12-1, which has been stopped, begins to decrease and quickly approaches the temperature of coolant 44a. Core 52 of transformer 22-2 of power conversion circuit 12-2 is cooled before power conversion circuit 12-2 starts operating, but its temperature gradually rises once power conversion circuit 12-2 starts operating. Control circuit 13B monitors the temperature of core 52 of transformer 22-2, and when the temperature of core 52 exceeds threshold value ThA, it stops operation of power conversion circuit 12-2 and starts operation of power conversion circuit 12-3. When power conversion device 2B operates under a light load, iron loss in core 52 increases significantly, but an unbalanced temperature distribution in core 52 does not occur. This makes core 52 less likely to be damaged, resulting in a highly reliable power conversion device 2B.

[0074] 7, the control circuit 13B may switch the power conversion circuit 12 to operate in a temperature range of about 80 to 90° C. where the iron loss is minimized, for example, 70 to 100° C. This allows the power conversion device 2B to operate with high efficiency even during light load operation where efficiency generally decreases.

[0075] In this way, by selectively and sequentially operating the multiple power conversion circuits 12 based on the temperature of the transformers 22, damage to the core 52 due to overheating of the transformers 22 can be made less likely than in the past.

[0076] [Second Modification of the Second Embodiment] Fig. 19 is a block diagram showing the configuration of a charging system including a power conversion device 2C according to a second modification of the second embodiment. The power conversion device 2C includes a control circuit 13C instead of the control circuit 13 in Fig. 1, and further includes a current sensor 15. The current sensor 15 measures the input current of each power conversion circuit 12. The control circuit 13C executes a charging control process, which will be described with reference to Fig. 20, based on the input current measured by the current sensor 15.

[0077] Fig. 20 is a flowchart showing a charge control process executed by control circuit 13C of power conversion device 2C of Fig. 19. The charge control process of Fig. 20 includes steps S31 to S33 instead of steps S21 to S22 of Fig. 16. When step S7 is NO, control circuit 13C proceeds to step S31.

[0078] In step S31, the control circuit 13C measures the input current Iin of the selected power conversion circuit 12.

[0079] In step S32, the control circuit 13C sets the input current threshold value ThB based on the magnitude of the load current required to charge the rechargeable battery 3.

[0080] In step S33, the control circuit 13C determines whether the input current Iin is equal to or greater than the threshold value ThB, and if YES, the process proceeds to step S9, and if NO, the process returns to step S7.

[0081] By executing the charging control process of Figure 20, when the power conversion device 2C is operating under light load, the control circuit 13C switches the operating power conversion circuit 12 each time the input current of the operating power conversion circuit 12 becomes equal to or greater than a threshold value ThB determined based on the load current of the rechargeable battery 3.

[0082] Generally, the output current of the power conversion circuit 12 is controlled based on the magnitude of the load current required to charge the rechargeable battery 3. However, when iron loss in the core 52 of the transformer 22 increases and the efficiency of the power conversion circuit 12 decreases, the desired output current cannot be achieved without increasing the input current. Therefore, the control circuit 13C measures the input current Iin of the primary side circuit 21 of the transformer 22 and switches the operating power conversion circuit 12 when the input current Iin exceeds a predetermined threshold value ThB. As described with reference to FIG. 6 , during light-load operation, the load current required to charge the rechargeable battery 3 gradually decreases, so the control circuit 13C recalculates the threshold value ThB when the load current changes. In this way, by selectively and sequentially operating multiple power conversion circuits 12 based on their input current Iin, damage to the core 52 due to overheating of the transformer 22 can be made less likely than in the past.

[0083] Furthermore, when power conversion device 2C operates under a light load, only one of power conversion circuits 12-1 to 12-3 operates, and therefore the input current of each of power conversion circuits 12-1 to 12-3 can be measured using one current sensor 15 provided upstream of distributor 11 as shown in Fig. 19. Alternatively, a current sensor for measuring the input current of each of power conversion circuits 12-1 to 12-3 may be provided for each of power conversion circuits 12-1 to 12-3.

[0084] [Third Modification of the Second Embodiment] Fig. 21 is a block diagram showing the configuration of a charging system including a power conversion device 2D according to a third modification of the second embodiment. The power conversion device 2D includes a control circuit 13D instead of the control circuit 13 in Fig. 1, and further includes a power sensor 16. The power sensor 16 measures the input power of each power conversion circuit 12. The power sensor 16 may be a single sensor or may be a combination of a current sensor and a voltage sensor. The control circuit 13D executes a charging control process, which will be described with reference to Fig. 22, based on the input power measured by the power sensor 16.

[0085] Fig. 22 is a flowchart showing a charge control process executed by control circuit 13D of power conversion device 2D of Fig. 21. The charge control process of Fig. 22 includes steps S41 to S43 instead of steps S21 to S22 of Fig. 16. When step S7 is NO, control circuit 13D proceeds to step S41.

[0086] In step S41, the control circuit 13D measures the input power Pin of the selected power conversion circuit 12.

[0087] In step S42, the control circuit 13D calculates the efficiency Eff=Pout / Pin of the selected power conversion circuit 12 based on the input power Pin and the load power Pout required to charge the rechargeable battery 3. The control circuit 13D may receive a control signal from the rechargeable battery 3 indicating the magnitude of the load current and load voltage required to charge the rechargeable battery 3, and calculate the load power Pout based on the load current and load voltage. The control circuit 13D may also receive a control signal from the rechargeable battery 3 indicating the magnitude of the load power Pout.

[0088] In step S43, the control circuit 13D determines whether the efficiency Eff is equal to or less than a predetermined threshold value ThC, and if YES, the process proceeds to step S9, and if NO, the process returns to step S7.

[0089] By executing the charging control process of Figure 22, when the power conversion device 2D operates under light load, the control circuit 13D calculates the efficiency of the operating power conversion circuit 12 based on the input power of the operating power conversion circuit 12 and the load power of the rechargeable battery 3, and switches the operating power conversion circuit 12 each time the efficiency becomes equal to or less than the threshold value ThC.

[0090] In this way, by selectively and sequentially operating the plurality of power conversion circuits 12 based on their efficiencies Eff, damage to the core 52 due to overheating of the transformer 22 can be made less likely than in the past.

[0091] Furthermore, when power conversion device 2D operates under a light load, only one of power conversion circuits 12-1 to 12-3 operates, and therefore, the input power of each of power conversion circuits 12-1 to 12-3 can be measured using one power sensor 16 provided upstream of distributor 11 as shown in Fig. 21. Alternatively, a power sensor for measuring the input power of each of power conversion circuits 12-1 to 12-3 may be provided for each of power conversion circuits 12-1 to 12-3.

[0092] [Effects of the second embodiment] According to the power conversion device 2, 2B to 2D of the second embodiment, by selectively and sequentially operating multiple power conversion circuits 12, damage to the core 52 due to overheating of the transformer 22 can be made less likely than in the past, and its reliability can be improved.

[0093] According to the power conversion devices 2, 2B to 2D of the second embodiment, even if a cooling device such as that shown in Figures 4 and 5 is not provided, by selectively and sequentially operating multiple power conversion circuits 12, the temperature of the core 52 of the transformer 22 becomes less likely to rise than in the past.

[0094] For example, even if a transformer has a cooling water channel as in Patent Document 2, cooling only a portion of the core can cause a large temperature difference in the core, which can cause stress in the core and lead to damage. On the other hand, in the power conversion device 2, 2B to 2D according to the second embodiment, by selectively and sequentially operating a plurality of power conversion circuits 12, the temperature of the core 52 of the transformer 22 is less likely to rise, and therefore a large temperature difference is less likely to occur. This makes it possible to make damage to the core 52 less likely than before.

[0095] [Other variations] 9 to 11 may be applied to the power conversion devices 2, 2B to 2D according to the second embodiment. In this case, the control circuits 13, 13B to 13D open the valves provided in the flow paths F1 to F3 that are in thermal contact with the transformer 22 of the power conversion circuit 12 that is in operation, and close the valves provided in the flow paths F1 to F3 that are in thermal contact with the transformer 22 of the power conversion circuit 12 that is not in operation. This further improves the cooling performance of the transformer 22.

[0096] In the above description, the power conversion device 2 transitions from heavy load operation to light load operation when the load voltage required to charge the rechargeable battery 3 reaches the fully charged voltage Th of the rechargeable battery 3, but this is not limiting. The power conversion device 2 may also transition from heavy load operation to light load operation when the load voltage reaches or exceeds a predetermined threshold value that is lower than the fully charged voltage Th.

[0097] In the above description, the power conversion device 2 transitions from heavy load operation to light load operation based on the load voltage required to charge the rechargeable battery 3, but this is not limiting. The power conversion device 2 may also transition from heavy load operation to light load operation based on the load current or load power required to charge the rechargeable battery 3.

[0098] The above explanation has mainly been about preventing overheating of the transformer 22, but the power conversion device according to an embodiment of the present disclosure may also be configured to prevent overheating of the primary side circuit 21, the secondary side circuit 23, and / or other heat-generating components.

[0099] Although FIG. 1 and other figures illustrate a case in which the power conversion device 2 receives three-phase AC power from, for example, a three-phase AC power source 1, the power conversion device according to an embodiment of the present disclosure may be configured to receive power from one or more single-phase AC power sources, or may be configured to receive power from a single two-phase AC power source. When the power conversion device receives power from a single single-phase AC power source, the distributor 11 may supply the same AC power to the three power conversion circuits 12. When the power conversion device receives power from two single-phase AC power sources, the distributor 11 may supply AC power from one AC power source to one power conversion circuit 12 and AC power from the other AC power source to the other power conversion circuit 12. In this case, the control circuit 13 stops operation of the remaining power conversion circuit 12. When the power conversion device receives power from three single-phase AC power sources, the distributor 11 may supply AC power from each AC power source to each power conversion circuit 12 in a one-to-one relationship. Furthermore, when the power conversion device receives power from a two-phase AC power source, the distributor 11 may supply AC power of one phase to one power conversion circuit 12 and AC power of the other phase to another power conversion circuit 12. In this case, the control circuit 13 stops the operation of the remaining power conversion circuit 12.

[0100] The power conversion device according to the embodiment of the present disclosure may be configured to receive power from one or more DC power sources. In this case, the distributor 11 supplies power to the three power conversion circuits 12 in the same manner as when receiving power from one or more single-phase AC power sources, and the diodes D1 to D4 and the power factor correction circuit 31 of the primary side circuit 21 of each power conversion circuit 12 are omitted.

[0101] A power conversion device according to an embodiment of the present disclosure may include two or four or more power conversion circuits.

[0102] The power conversion device according to the embodiment of the present disclosure is not limited to the power conversion circuit 12 including an LLC resonant DC / DC converter circuit, and may include any power conversion circuit including a transformer.

[0103] The power conversion device according to the embodiment of the present disclosure may be configured to supply DC power to any load device, not limited to the rechargeable battery 3, where the magnitude of the load voltage varies. [Industrial Applicability]

[0104] A power conversion device according to an aspect of the present disclosure is applicable to, for example, an on-board charging system for an electric vehicle or a plug-in hybrid vehicle. [Explanation of symbols]

[0105] 1 AC power supply 2,2A~2D Power conversion device 3 Rechargeable batteries 11 Distributor 12-1~12-3 Power conversion circuit 13, 13A to 13D control circuit 14-1~14-3 Temperature sensors 15 Current Sensor 16 Power Sensor 21-1~21-3 Primary side circuit 22-1~22-3 Transformer 23-1~23-3 Secondary side circuit 31 Power factor correction circuit 41 Case 42, 43, 44 Chambers 44a Coolant 44b,44c wall 44d Inlet 44e Outlet 44f Fin 44g Divider 45 Heatsink 46 Pump 47-1~47-3 Valves 51 Bobbin 52 cores 53 Potting C1~C3 capacitors D1~D8 diodes L1 Primary winding L2 Secondary winding L3 leakage inductance Q1~Q4 switching elements SW-1 to SW-3 switches

Claims

1. a plurality of power conversion circuits each including a transformer and each supplying DC power to a common load device; a plurality of temperature sensors that measure the temperatures of the transformers of the power conversion circuits; a control circuit for controlling each of the power conversion circuits, the control circuit selectively and sequentially operates the plurality of power conversion circuits such that, when a load voltage of the load device becomes equal to or greater than a first threshold, one of the plurality of power conversion circuits operates and the other power conversion circuits stop operating; Selectively and sequentially operating the plurality of power conversion circuits includes switching the operating power conversion circuit every time the load voltage of the load device becomes equal to or higher than the first threshold value and the temperature of the transformer of the operating power conversion circuit becomes equal to or higher than a second threshold value. Power conversion device.

2. the control circuit switches the operating power conversion circuit every time a first time period elapses when a load voltage of the load device becomes equal to or higher than the first threshold value; The power conversion device according to claim 1 .

3. when a load voltage of the load device becomes equal to or greater than the first threshold, the control circuit selectively and sequentially operates the plurality of power conversion circuits so that total operation time lengths of the power conversion circuits over a second time period are equal to each other; The power conversion device according to claim 1 .

4. the control circuit selectively and sequentially operates the plurality of power conversion circuits so as to allocate a longer operating time to a power conversion circuit having a transformer with higher cooling performance when a load voltage of the load device becomes equal to or higher than the first threshold value; The power conversion device according to claim 1 .

5. the power conversion device further includes at least one current sensor for measuring an input current of each of the power conversion circuits; the control circuit switches the operating power conversion circuit each time an input current of the operating power conversion circuit becomes equal to or greater than a third threshold determined based on a load current of the load device when a load voltage of the load device becomes equal to or greater than the first threshold; The power conversion device according to claim 1 .

6. the power conversion device further includes at least one power sensor for measuring input power of each of the power conversion circuits; the control circuit calculates an efficiency of the power conversion circuit in operation based on an input power of the power conversion circuit in operation and a load power of the load device when a load voltage of the load device becomes equal to or higher than the first threshold, and switches an operating power conversion circuit every time the efficiency becomes equal to or lower than a fourth threshold. The power conversion device according to claim 1 .

7. the power conversion device includes three power conversion circuits; The three power conversion circuits convert AC power of each phase of three-phase AC power supplied from a three-phase AC power source into DC power, respectively. The power conversion device according to any one of claims 1 to 6.

8. the power converter further comprising a cooling device having at least one flow path for a coolant, the at least one flow path being in thermal contact with a transformer of each of the power converter circuits; The power conversion device according to any one of claims 1 to 7.

9. the cooling device further includes a plurality of flow paths for the cooling liquid, and a plurality of valves respectively provided in the plurality of flow paths; the control circuit opens a valve provided in a flow path that is in thermal contact with a transformer of the power conversion circuit that is in operation, and closes a valve provided in a flow path that is in thermal contact with a transformer of the power conversion circuit that is not in operation. The power converter according to claim 8.

10. A power conversion device according to any one of claims 1 to 9; a rechargeable battery that is charged by receiving DC power from the plurality of power conversion circuits as a load device common to the plurality of power conversion circuits of the power conversion device; Charging system.

11. A control method for a power conversion device including a plurality of power conversion circuits, each of which includes a transformer and supplies DC power to a common load device, comprising: the power conversion device further includes a plurality of temperature sensors that measure temperatures of the transformers of the power conversion circuits, respectively; The control method includes selectively and sequentially operating the plurality of power conversion circuits such that, when a load voltage of the load device becomes equal to or greater than a first threshold, one of the plurality of power conversion circuits operates and the other power conversion circuits stop operating; Selectively and sequentially operating the plurality of power conversion circuits includes switching the operating power conversion circuit every time the load voltage of the load device becomes equal to or higher than the first threshold value and the temperature of the transformer of the operating power conversion circuit becomes equal to or higher than a second threshold value. A method for controlling a power conversion device.

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