converter

Abstract

To appropriately operate a converter in which switching elements are provided in parallel.SOLUTION: A converter comprises a control circuit. Based on a current detected by a current sensor, the control circuit calculates a first differential value by subtracting a first temperature estimated value from a first temperature of a first target switching element and a second differential value by subtracting a second temperature estimated value from a second temperature of a second target switching element. In a case where the first differential value is higher than a first threshold and the second differentia value is lower than a second threshold, an on-duty ratio of the second target switching element is caused to rise in relative to an on-duty ratio of the first target switching element. In a case where the first differential value is higher than a third threshold and the second differential value is higher than a fourth threshold, the on-duty ratio of the first target switching element is caused to rise in relative to the on-duty ratio of the second target switching element.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to a converter.

[0002] Patent Document 1 discloses a motor drive device that includes a plurality of converters. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-152954 Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, a converter has a high-side switching element provided between a coil and a high-potential output wiring, and a low-side switching element provided between the coil and a low-potential wiring. The high-side switching element may be provided with multiple switching elements connected in parallel. The low-side switching element may be provided with multiple switching elements connected in parallel. This specification proposes a technique for properly operating a converter in which switching elements are connected in parallel. [Means for solving the problem]

[0005] A first converter disclosed in this specification includes a high-potential input wiring, a high-potential output wiring, a low-potential wiring, a connection point, a coil connected between the high-potential input wiring and the connection point, a first diode having a cathode connected to the high-potential output wiring and an anode connected to the connection point, a first switching element connected in parallel with the first diode, a second diode having a cathode connected to the high-potential output wiring and an anode connected to the connection point, a second switching element connected in parallel with the second diode, a third diode having a cathode connected to the connection point and an anode connected to the low-potential wiring, a third switching element connected in parallel with the third diode, a fourth diode having a cathode connected to the connection point and an anode connected to the low-potential wiring, a fourth switching element connected in parallel with the fourth diode, a current sensor detecting a current flowing through the coil, a first temperature sensor, a second temperature sensor, and a control circuit, wherein one of the first switching element and the third switching element is a first target switching element. The second target switching element is one of the second switching element and the fourth switching element that is connected in parallel to the first target switching element. The first temperature sensor detects a first temperature that is the temperature of the first target switching element. The second temperature sensor detects a second temperature that is the temperature of the second target switching element. The control circuit calculates a first temperature estimate that is the temperature estimate of the first target switching element and a second temperature estimate that is the temperature estimate of the second target switching element based on the current detected by the current sensor. The control circuit also calculates a first difference value by subtracting the first temperature estimate from the first temperature and a second difference value by subtracting the second temperature estimate from the second temperature. The control circuit also increases the on-duty ratio of the second target switching element relatively to the on-duty ratio of the first target switching element when the first difference value is higher than a first threshold and the second difference value is lower than a second threshold.Furthermore, when the first difference value is lower than a third threshold value and the second difference value is higher than a fourth threshold value, the control circuit increases the on-duty ratio of the first target switching element relatively to the on-duty ratio of the second target switching element.

[0006] A current may flow unevenly in one of a first target switching element and a second target switching element connected in parallel to each other. The control circuit calculates a first differential value and a second differential value and determines whether a current imbalance occurs in the first target switching element and the second target switching element based on the first differential value and the second differential value. If the first differential value is higher than a first threshold value and the second differential value is lower than a second threshold value, it is considered that the temperature of the first target switching element is higher than an expected temperature, and a current is flowing unevenly in the first target switching element. In this case, the control circuit increases the on-duty ratio of the second target switching element relative to the on-duty ratio of the first target switching element, thereby increasing the current flowing in the second target switching element. Furthermore, if the first differential value is lower than a third threshold value and the second differential value is higher than a fourth threshold value, it is considered that the temperature of the second target switching element is higher than an expected temperature, and a current is flowing unevenly in the second target switching element. In this case, the control circuit increases the on-duty ratio of the first target switching element relative to the on-duty ratio of the second target switching element, thereby increasing the current flowing through the first target switching element. In this way, the control circuit performs control so that the current flowing through the first target switching element and the current flowing through the second target switching element are balanced. This prevents a high current from flowing disproportionately through either the first target switching element or the second target switching element.

[0007] The second converter disclosed in this specification includes a high-potential input wiring, a high-potential output wiring, a low-potential wiring, a connection point, a coil connected between the high-potential input wiring and the connection point, a first diode having a cathode connected to the high-potential output wiring and an anode connected to the connection point, a first switching element connected in parallel with the first diode, a second diode having a cathode connected to the high-potential output wiring and an anode connected to the connection point, a second switching element connected in parallel with the second diode, a third diode having a cathode connected to the connection point and an anode connected to the low-potential wiring, a third switching element connected in parallel with the third diode, a fourth diode having a cathode connected to the connection point and an anode connected to the low-potential wiring, a fourth switching element connected in parallel with the fourth diode, a current sensor detecting a current flowing through the coil, a temperature sensor, and a control circuit. Any of the first switching element, the second switching element, the third switching element, and the fourth switching element is a target switching element. The temperature sensor detects the temperature of the target switching element. The control circuit calculates an estimated temperature value of the target switching element based on the current flowing through the current sensor. The control circuit also calculates a difference value by subtracting the estimated temperature value from the temperature detected by the temperature sensor. The control circuit also implements output limiting when the difference value is higher than a first threshold value and when the difference value is lower than a second threshold value that is lower than the first threshold value.

[0008] When one of multiple switching elements connected in parallel to each other suffers an open circuit fault, a high current flows through the other switching element. The control circuit calculates a difference value and determines whether an open circuit fault has occurred in the switching element based on the difference value. If the difference value is higher than a first threshold, the target switching element is at a high temperature. In this case, it is considered that the switching element connected in parallel to the target switching element has suffered an open circuit fault, and a high current is flowing through the target switching element. On the other hand, if the difference value is lower than a second threshold, it is considered that the target switching element is at a low temperature. In this case, it is considered that the target switching element has suffered an open circuit fault, and a high current is flowing through the switching element connected in parallel to the target switching element. The control circuit implements output limitation in these cases. Therefore, output limitation can be implemented when an open circuit fault has occurred in any of the switching elements. [Brief explanation of the drawings]

[0009] [Figure 1] Converter circuit diagram. [Figure 2] 6 is a graph showing changes in the state of each switching element during operation of the converter. [Figure 3] 1 is a flowchart showing a process of the first embodiment. [Figure 4] 10 is a flowchart showing the processing of the second embodiment. DETAILED DESCRIPTION OF THE INVENTION [Example]

[0010] A converter 10 according to a first embodiment shown in FIG. 1 is mounted on a charging facility for an electric vehicle. The converter 10 has input terminals 11a and 11b and output terminals 13a and 13b. A direct current input voltage Vin (e.g., DC 400 V) is applied between the input terminals 11a and 11b from the outside. The converter 10 boosts the input voltage Vin applied between the input terminals 11a and 11b, and outputs the boosted voltage (e.g., DC 800 V) as an output voltage Vout between the output terminals 13a and 13b. An electric vehicle 90 is connected to the output terminals 13a and 13b. When the output voltage Vout of the converter 10 is supplied to the electric vehicle 90, a battery 92 of the electric vehicle 90 is charged.

[0011] The converter 10 has a high-potential input wiring 12, a low-potential wiring 14, and a high-potential output wiring 16. The low-potential wiring 14 is connected to the input terminal 11b and the output terminal 13b. The high-potential input wiring 12 is connected to the input terminal 11a. Therefore, the high-potential input wiring 12 has a potential higher than the low-potential wiring 14 by a voltage Vin. A smoothing capacitor 51 is connected between the high-potential input wiring 12 and the low-potential wiring 14. The high-potential output wiring 16 is connected to the output terminal 13a. Therefore, the high-potential output wiring 16 has a potential higher than the low-potential wiring 14 by a voltage Vout. A smoothing capacitor 50 is connected between the high-potential output wiring 16 and the low-potential wiring 14.

[0012] The converter 10 has a coil 18, a connection point 19, and a current sensor 20. The coil 18 is connected between the high potential input wiring 12 and the connection point 19. The current sensor 20 is installed on the wiring between the coil 18 and the connection point 19. The current sensor 20 detects the current IL flowing through the coil 18. The current sensor 20 may be installed at any position as long as it can detect the current IL flowing through the coil 18. For example, the current sensor 20 may be installed on the high potential input wiring 12.

[0013] The converter 10 includes switching elements 21-24, diodes 31-34, and temperature sensors 41-44.

[0014] The cathode of diode 31 is connected to high-potential output wiring 16, and the anode of diode 31 is connected to node 19. The cathode of diode 32 is connected to high-potential output wiring 16, and the anode of diode 32 is connected to node 19. The cathode of diode 33 is connected to node 19, and the anode of diode 33 is connected to low-potential wiring 14. The cathode of diode 34 is connected to node 19, and the anode of diode 34 is connected to low-potential wiring 14.

[0015] The switching elements 21 to 24 are configured by IGBTs (insulated gate bipolar transistors). The switching elements 21 to 24 may be configured by other switching elements such as MOSFETs (metal-oxide-semiconductor field effect transistors). The switching element 21 is provided on the same semiconductor substrate as the diode 31. The collector of the switching element 21 is connected to the high-potential output wiring 16, and the emitter of the switching element 21 is connected to the connection point 19. That is, the switching element 21 is connected in parallel to the diode 31. The switching element 22 is provided on the same semiconductor substrate as the diode 32. The collector of the switching element 22 is connected to the high-potential output wiring 16, and the emitter of the switching element 22 is connected to the connection point 19. That is, the switching element 22 is connected in parallel to the switching element 21 and the diodes 31 and 32. The switching element 23 is provided on the same semiconductor substrate as the diode 33. The collector of the switching element 23 is connected to the connection point 19, and the emitter of the switching element 23 is connected to the low-potential wiring 14. That is, the switching element 23 is connected in parallel to the diode 33. The switching element 24 is provided on the same semiconductor substrate as the diode 34. The collector of the switching element 24 is connected to the connection point 19, and the emitter of the switching element 24 is connected to the low-potential wiring 14. That is, the switching element 24 is connected in parallel to the switching element 23 and the diodes 33 and 34.

[0016] The temperature sensor 41 detects the temperature of the switching element 21. The temperature sensor detects the temperature of the switching element 22. The temperature sensor 43 detects the temperature of the switching element . The temperature sensor 44 detects the temperature of the switching element .

[0017] The converter 10 has a control circuit 52. The control circuit 52 is connected to the temperature sensors 41 to 44. The detection values ​​of the temperature sensors 41 to 44 are input to the control circuit 52. The control circuit 52 is connected to the current sensor 20. The value of the current IL detected by the current sensor 20 is input to the control circuit 52. The control circuit 52 is connected to the gates of the switching elements 21 to 24. The control circuit 52 controls the switching elements 21 to 24.

[0018] 2, the control circuit 52 controls the switching elements 21 to 24 so that a first on-time Pon1, a first dead time Pd1, a second on-time Pon2, and a second dead time Pd2 are repeated in this order. During the first on-time Pon1, the control circuit 52 turns on the switching elements 21 and 22 and turns off the switching elements 23 and 24. During the first dead time Pd1, the control circuit 52 turns off the switching elements 21 to 24. During the second on-time Pon2, the control circuit 52 turns on the switching elements 23 and 24 and turns off the switching elements 21 and 22. During the second dead time Pd2, the control circuit 52 turns off the switching elements 21 to 24.

[0019] The converter 10 can perform step-up and step-down operations. In step-up operation, the converter 10 steps up the input voltage Vin and outputs the resulting voltage as the output voltage Vout. In step-down operation, the converter 10 steps down the output voltage Vout and outputs the resulting voltage as the input voltage Vin. The current paths differ between step-up operation and step-down operation. The operation of the converter 10 will be described below for both step-up operation and step-down operation.

[0020] (Boost operation) In the boost operation, during the second on-time Pon2, a current flows from the high potential input wiring 12 to the low potential wiring 14 via the coil 18 and the switching elements 23 and 24. During the second dead time Pd2, the first on-time Pon1, and the first dead time Pd1, a current flows from the high potential input wiring 12 to the high potential output wiring 16 via the coil 18 and the diodes 31 and 32. In the boost operation, this current flow supplies power from the input side to the output side.

[0021] 3 during each second on-time Pon2 during the boost operation. In the boost operation, the first target switching element is the switching element 23, and the second target switching element is the switching element 24.

[0022] In step S2, the control circuit 52 reads the current IL detected by the current sensor 20. Next, the control circuit 52 calculates an estimated temperature value Tp23 of the switching element 23 and an estimated temperature value Tp24 of the switching element 24 based on the current IL. During the second on-time Pon2 during the boost operation, the current IL branches off to flow through the switching elements 23 and 24, so the estimated temperature values ​​Tp23 and Tp24 of the switching elements 23 and 24 can be calculated from the current IL. The estimated temperature values ​​Tp23 and Tp24 are calculated according to a predetermined calculation method. The estimated temperature values ​​Tp23 and Tp24 are calculated assuming that the current IL flows evenly distributed through the switching elements 23 and 24.

[0023] In step S4, the control circuit 52 reads temperatures T23, T24 (i.e., measured temperatures) of the switching elements 23, 24 detected by the temperature sensors 43, 44. The control circuit 52 calculates a first difference value ΔT23 by subtracting the estimated temperature value Tp23 from the measured temperature T23. The control circuit 52 also calculates a second difference value ΔT24 by subtracting the estimated temperature value Tp24 from the measured temperature T24.

[0024] In step S6, the control circuit 52 determines whether the first difference value ΔT23 is higher than the threshold value ΔTa and whether the second difference value ΔT24 is lower than the threshold value ΔTb. The threshold value ΔTa is a positive value, and the threshold value ΔTb is a negative value. The absolute values ​​of the threshold values ​​ΔTa and ΔTb may be equal. A YES result in step S6 means that the switching element 23 is hotter than expected (i.e., a higher current than expected is flowing through the switching element 23) and that the switching element 24 is colder than expected (i.e., a lower current than expected is flowing through the switching element 24).

[0025] If the determination in step S6 is YES, the control circuit 52 changes the settings of the on-duty ratios of the switching elements 23 and 24 in step S8. The on-duty ratio is the ratio of the period during which the switching element is on during a control period. Here, the control circuit 52 increases the on-duty ratio of the switching element 24 relative to the on-duty ratio of the switching element 23. For example, as indicated by the dashed line G1 in FIG. 2, the on-duty ratio of the switching element 24 may be increased relative to the on-duty ratio of the switching element 23 by increasing the on-duty ratio of the switching element 24. Alternatively, as indicated by the dashed line G2 in FIG. 2, the on-duty ratio of the switching element 24 may be increased relative to the on-duty ratio of the switching element 23 by decreasing the on-duty ratio of the switching element 23. After changing the settings of the on-duty ratios in step S8, the control circuit 52 subsequently controls each switching element according to the changed on-duty ratio. Therefore, after the on-duty ratio is changed, the current flowing through the switching element 23 decreases and the current flowing through the switching element 24 increases compared to before the on-duty ratio was changed.

[0026] If the determination in step S6 is NO, the control circuit 52 executes step S10. In step S10, the control circuit 52 determines whether the first difference value ΔT23 is lower than the threshold value ΔTc and whether the second difference value ΔT24 is higher than the threshold value ΔTd. The threshold value ΔTc is a negative value, and the threshold value ΔTd is a positive value. The absolute value of the threshold value ΔTc and the absolute value of the threshold value ΔTd may be equal. The threshold value ΔTc may be the same value as the threshold value ΔTb, and the threshold value ΔTd may be the same value as the threshold value ΔTa. A determination of YES in step S10 means that the switching element 24 is hotter than expected (i.e., a higher current than expected is flowing through the switching element 24) and that the switching element 23 is colder than expected (i.e., a lower current than expected is flowing through the switching element 23).

[0027] If the determination in step S10 is YES, in step S12, control circuit 52 changes the settings of the on-duty ratios of switching elements 23 and 24. Here, control circuit 52 increases the on-duty ratio of switching element 23 relatively to the on-duty ratio of switching element 24. After changing the setting of the on-duty ratio in step S12, control circuit 52 thereafter executes control in accordance with the changed on-duty ratio. Therefore, after the on-duty ratio is changed, the current flowing through switching element 24 decreases and the current flowing through switching element 23 increases compared to before the on-duty ratio was changed.

[0028] If the result of step S10 is NO, the control circuit 52 skips steps S8 and S12. If the result of step S10 is NO, it means that currents are flowing in an appropriate balance through the switching elements 23 and 24. Therefore, in this case, the control circuit 52 does not change the setting of the on-duty ratio.

[0029] 3, the control circuit 52 adjusts the on-duty ratios of the switching elements 23 and 24 so that the currents flowing through the switching elements 23 and 24 are properly balanced. This makes it possible to prevent the current from flowing unevenly through one of the switching elements 23 and 24.

[0030] (Step-down operation) In the step-up operation, during the first on-time Pon1, a current flows from the high-potential output wiring 16 to the low-potential wiring 14 via the switching elements 21 and 22 and the coil 18. During the first dead time Pd1, the second on-time Pon2, and the second dead time Pd2, a current flows from the low-potential wiring 14 to the high-potential input wiring 12 via the diodes 33 and 34. In the step-down operation, this current flow supplies power from the output side to the input side.

[0031] 3 during each first on-time Pon1 of the step-down operation. In the step-down operation, the first target switching element is the switching element 21, and the second target switching element is the switching element 22.

[0032] In step S2, the control circuit 52 reads the current IL detected by the current sensor 20, and calculates the estimated temperature value Tp21 of the switching element 21 and the estimated temperature value Tp22 of the switching element 22 based on the current IL.

[0033] In step S4, the control circuit 52 reads the temperatures T21, T22 (i.e., the actually measured temperatures) of the switching elements 21, 22 detected by the temperature sensors 41, 42, and calculates a first difference value ΔT21 (=T21-Tp21) and a second difference value ΔT22 (=T22-Tp22).

[0034] When the first difference value ΔT21 is higher than the threshold value ΔTa and the second difference value ΔT22 is lower than the threshold value ΔTb (i.e., when the answer is YES in step S6), the control circuit 52 increases the on-duty ratio of the switching element 22 relative to the on-duty ratio of the switching element 21 in step S8. When the first difference value ΔT21 is lower than the threshold value ΔTc and the second difference value ΔT22 is higher than the threshold value ΔTd (i.e., when the answer is YES in step S10), the control circuit 52 increases the on-duty ratio of the switching element 21 relative to the on-duty ratio of the switching element 22 in step S12. When the answer is NO in step S10, the control circuit 52 does not change the on-duty ratio. Since the control circuit 52 adjusts each on-duty ratio in this manner, biased current flow to one of the switching elements 21 and 22 is suppressed.

[0035] In the first embodiment, the control circuit 52 executes the process of Fig. 3 for each of the voltage step-up operation and the voltage step-down operation. However, the control circuit 52 may execute the process of Fig. 3 for only one of the voltage step-up operation and the voltage step-down operation. [Example]

[0036] The converter of the second embodiment does not have temperature sensors 42, 44. Furthermore, the converter of the second embodiment does not execute the process of Fig. 3. Furthermore, the converter of the second embodiment executes the process of Fig. 4. Except for other points, the converter of the second embodiment has a common configuration with the converter of the first embodiment.

[0037] (Boost operation) In the converter of the second embodiment, the control circuit 52 executes the process shown in Fig. 4 during each second on-time Pon2 in the voltage step-up operation. Note that in the voltage step-up operation, the switching element 23 is the target switching element.

[0038] In step S102, the control circuit 52 reads the current IL detected by the current sensor 20. Next, the control circuit 52 calculates the estimated temperature value Tp23 of the switching element 23 based on the current IL. The estimated temperature value Tp23 is calculated assuming that the current IL flows through the switching elements 23, 24 while being evenly distributed.

[0039] In step S104, the control circuit 52 reads the temperature T23 (i.e., the measured temperature) of the switching element 23 detected by the temperature sensor 43. The control circuit 52 calculates a difference value ΔT23 by subtracting the estimated temperature value Tp23 from the measured temperature T23.

[0040] In step S106, the control circuit 52 determines whether the difference value ΔT23 is higher than the threshold value ΔTA. The threshold value ΔTA is a positive, relatively large value. A YES result in step S106 means that the switching element 24 is at a high temperature (i.e., the switching element 24 has an open circuit fault and a large current is flowing through the switching element 23).

[0041] If the determination in step S106 is NO, the control circuit 52 executes step S108. In step S108, the control circuit 52 determines whether the difference value ΔT23 is lower than the threshold value ΔTB. The threshold value ΔTB is a negative value, and its absolute value is relatively large. The absolute values ​​of the threshold values ​​TA and TB may be equal. A determination of YES in step S108 means that the switching element 23 is at a low temperature (i.e., the switching element 23 has an open circuit fault and a large current is flowing through the switching element 24).

[0042] If the answer is YES in step S106 or step S108, the control circuit 52 implements output limitation in step S110. Note that, when limiting the output, the control circuit 52 changes the control method for each switching element so that the current IL is smaller than normal. In this way, if either switching element 23 or 24 has an open circuit fault, the load on the remaining switching element is reduced by limiting the output. If the answer is NO in step S108, the control circuit 52 skips step S110 and continues normal operation.

[0043] (Step-down operation) In the converter of the second embodiment, the control circuit 52 executes the process shown in Fig. 4 during each first on-time Pon1 in the step-down operation. Note that in the step-down operation, the switching element 21 is the target switching element.

[0044] In step S102, the control circuit 52 reads the current IL detected by the current sensor 20. Next, the control circuit 52 calculates the estimated temperature value Tp21 of the switching element 21 based on the current IL.

[0045] In step S104, the control circuit 52 reads the temperature T21 (i.e., the measured temperature) of the switching element 21 detected by the temperature sensor 41. The control circuit 52 calculates a difference value ΔT21 by subtracting the estimated temperature value Tp21 from the measured temperature T21.

[0046] In step S106, the control circuit 52 determines whether the difference value ΔT21 is higher than the threshold value ΔTA. A YES result in step S106 means that the switching element 21 is at a high temperature (i.e., the switching element 22 has an open circuit failure and a large current is flowing through the switching element 21). In step S108, the control circuit 52 determines whether the difference value ΔT21 is lower than the threshold value ΔTB. A YES result in step S108 means that the switching element 21 is at a low temperature (i.e., the switching element 21 has an open circuit failure and a large current is flowing through the switching element 22). If the result in step S106 or step S108 is YES, the control circuit 52 implements output limitation in step S110. If the result in step S108 is NO, the control circuit 52 skips step S110 and continues normal operation.

[0047] As described above, according to the configuration of Example 2, it is possible to detect open circuit faults in both of the parallel-connected switching elements by using a temperature sensor provided in one of the parallel-connected switching elements. Since it is not necessary to provide a temperature sensor in every switching element, the converter can be made smaller.

[0048] In the second embodiment, the control circuit 52 executes the process of Fig. 4 for each of the voltage step-up operation and the voltage step-down operation. However, the control circuit 52 may execute the process of Fig. 4 for only one of the voltage step-up operation and the voltage step-down operation.

[0049] Although the embodiments have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. The technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technology exemplified in this specification or drawings simultaneously achieves multiple objectives, and achieving one of these objectives itself has technical utility. [Explanation of symbols]

[0050] 10: Converter 12: High potential input wiring 14:Low potential wiring 16: High potential output wiring 18: Coil 19: Connection point 20: Current sensor 21 to 24: Switching elements 31~34: Diodes

Claims

1. A converter comprising: A high potential input wiring; High potential output wiring; Low potential wiring; A connection point and a coil connected between the high-potential input wiring and the connection point; a first diode having a cathode connected to the high-potential output wiring and an anode connected to the connection point; a first switching element connected in parallel to the first diode; a second diode having a cathode connected to the high-potential output wiring and an anode connected to the connection point; a second switching element connected in parallel to the second diode; a third diode having a cathode connected to the connection point and an anode connected to the low potential wiring; a third switching element connected in parallel to the third diode; a fourth diode having a cathode connected to the connection point and an anode connected to the low potential wiring; a fourth switching element connected in parallel to the fourth diode; a current sensor for detecting a current flowing through the coil; a first temperature sensor; A second temperature sensor; control circuit, and one of the first switching element and the third switching element is a first target switching element, one of the second switching element and the fourth switching element that is connected in parallel to the first target switching element is a second target switching element, the first temperature sensor detects a first temperature that is a temperature of the first target switching element; the second temperature sensor detects a second temperature that is the temperature of the second target switching element; The control circuit calculating a first temperature estimate value, which is a temperature estimate value of the first target switching element, and a second temperature estimate value, which is a temperature estimate value of the second target switching element, based on the current detected by the current sensor; calculating a first difference value by subtracting the first temperature estimated value from the first temperature and a second difference value by subtracting the second temperature estimated value from the second temperature; When the first difference value is higher than a first threshold value and the second difference value is lower than a second threshold value, an on-duty ratio of the second target switching element is increased relatively to an on-duty ratio of the first target switching element; When the first difference value is lower than a third threshold value and the second difference value is higher than a fourth threshold value, the on-duty ratio of the first target switching element is increased relatively to the on-duty ratio of the second target switching element. converter.

2. A converter comprising: A high potential input wiring; High potential output wiring; Low potential wiring; A connection point and a coil connected between the high-potential input wiring and the connection point; a first diode having a cathode connected to the high-potential output wiring and an anode connected to the connection point; a first switching element connected in parallel to the first diode; a second diode having a cathode connected to the high-potential output wiring and an anode connected to the connection point; a second switching element connected in parallel to the second diode; a third diode having a cathode connected to the connection point and an anode connected to the low potential wiring; a third switching element connected in parallel to the third diode; a fourth diode having a cathode connected to the connection point and an anode connected to the low potential wiring; a fourth switching element connected in parallel to the fourth diode; a current sensor for detecting a current flowing through the coil; A temperature sensor; control circuit, and any one of the first switching element, the second switching element, the third switching element, and the fourth switching element is a target switching element; the temperature sensor detects the temperature of the target switching element; The control circuit calculating an estimated temperature value of the target switching element based on the current detected by the current sensor; calculating a difference value by subtracting the estimated temperature value from the temperature detected by the temperature sensor; When the difference value is higher than a first threshold value and when the difference value is lower than a second threshold value that is lower than the first threshold value, an output limitation is implemented. converter.

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