DRIVE DEVICE FOR SWITCHES

Abstract

Drive device for a plurality of switches (S1p-S4p, S1n-S4n) connected in parallel, the drive device comprising: a plurality of drivers (41-44; 61-64) configured to switch the respective switches on or off, a temperature acquiring device (30a) configured to acquire a value of a temperature parameter correlated with a temperature of at least one of the switches, a selection device (30b) configured to select at least one of the switches (S1p-S4p, S1n-S4n) as at least one drive target switch, and a drive control device (30c) configured to cause at least one of the drivers (41-44; 61-64): to switch on the at least one drive target switch during a predetermined ON period and then to switch off the at least one drive target switch in each target switching cycle, wherein the target switching cycle is defined as a product of a reference switching cycle and the number of the selected at least one drive target switch, wherein the selection device (30b) is configured to adjust the number of the selected at least one drive target switch according to the value of the temperature parameter, wherein the selection device (30b) is configured: to determine whether the value of the temperature parameter is higher than a temperature threshold, and to increase the number of the selected at least one drive target switch when it is determined that the value of the temperature parameter is higher than the temperature threshold, and wherein the switches (S1p-S4p, S1n-S4n) comprise at least first, second, third and fourth switches connected in parallel to each other, and the at least first, second, third and fourth switches are divided into a first group of first and second switches and a second group of third and fourth switches, the drivers (41-44; 61-64) have at least first, second, third and fourth drivers, the selection device (30b) is configured, upon determining that the value of the temperature parameter is higher than the temperature threshold value, while the number of the selected at least one drive target switch has reached an upper limit: selecting the first and second switches of the first group as the first and second drive target switches and the third and fourth switches of the second group as the third and fourth drive target switches, wherein the first to fourth drive target switches form the at least one drive target switch, wherein the target switching cycle is defined as the product of the reference switching cycle and the number of selected switches in each of the first and second groups, and the drive control device (30c) is configured: to cause each of the first and second drivers to: turning on the corresponding one of the first and second drive target switches during a corresponding one of the first and second ON periods as the ON period and thereafter turning off the corresponding one of the first and second drive target switches in each target switching cycle, and to cause each of the third and fourth drivers to: turning on the corresponding one of the third and fourth drive target switches during a corresponding one of predetermined third and fourth ON periods as the ON period and thereafter turning off the corresponding one of the third and fourth drive target switches in each target switching cycle while each of the first and second ON periods of the first group is not overlapped with each of the third and fourth ON periods of the second group.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to drive devices for switches connected in parallel. BACKGROUND

[0002] For example, JP 2007 - 11 087 A discloses such a drive device for driving switches that are connected in parallel to each other.

[0003] JP 2010 124 586 A discloses a DC-DC converter. To prevent a temperature increase of a switching element without suppressing the throughput of the DC-DC converter, the drive is switched from a drive through only one branch of a single phase to a drive with alternating phase branches depending on an increase in the temperatures of the corresponding switching elements of the phase branches. SUMMARY

[0004] An increase in the temperature of a switch can lead to an increase in the switch's ON-resistance. Therefore, an increase in the switching frequency of a specified switch in parallel-connected circuits leads to an increase in the temperature of the specified switch, which leads to an increase in the conduction loss of the specified switch based on its ON-resistance. Therefore, there is room for improvement in parallel-connected drive switches.

[0005] In view of the circumstances described above, an exemplary embodiment of the present disclosure aims to provide driving devices for switches connected in parallel, each of which is capable of preventing an increase in the conduction loss of a specified switch in the parallel-connected switches.

[0006] This object is achieved by a drive device as specified in patent claim 1, 2 or 3.

[0007] An advantageous embodiment is specified in the dependent patent claim.

[0008] According to a first exemplary embodiment of the present disclosure, a drive device is provided for a plurality of switches connected in parallel to one another. The drive device includes a plurality of drivers configured to turn the respective switches on or off, and a temperature acquiring device configured to acquire a value of a temperature parameter correlated with a temperature of at least one of the switches. The drive device includes a selecting device configured to select at least one of the switches as at least one drive target switch. The drive device includes a drive controlling device configured to cause at least one of the drivers to turn on the at least one drive target switch during a predetermined ON period and thereafter to turn off the at least one drive target switch in each target switching cycle.The target switching cycle, such as the target switching frequency, is defined as a product of a reference switching cycle and the number of the selected at least one drive target switch. The selection device is configured to adjust the number of the selected at least one drive target switch according to the value of the temperature parameter.

[0009] According to a second exemplary embodiment of the present disclosure, the drivers include at least first and second drivers, and the selection device is configured to select a first switch and a second switch among the switches as the first and second drive target switches that constitute the at least one drive target switch. The drive control device is configured to cause the first driver to turn on the first drive target switch for a predetermined first ON period as the ON period and thereafter to turn off the first drive target switch in each target switching cycle.The drive control device is also configured to cause the second driver to turn on the second drive target switch during a predetermined second ON period as the ON period and thereafter turn off the second drive target switch in each target switching cycle while the first ON period of the first drive target switch is not overlapped with the second ON period of the second drive target switch.

[0010] The selection device according to each of the first and second exemplary embodiments of the present disclosure adjusts the number of the selected at least one drive target switch according to the value of the temperature parameter.

[0011] This prevents a specified switch from being intensively turned on or off, thereby minimizing any increase in the temperature of the specified switch and thus minimizing any increase in the ON resistance of the specified switch. This therefore leads to lower conduction losses in the switches.

[0012] According to a third exemplary embodiment of the present disclosure, the selection device is configured to determine whether the value of the temperature parameter is higher than a temperature threshold, and to increase the number of the selected at least one drive target switch when it is determined that the value of the temperature parameter is higher than the temperature threshold.

[0013] Increasing the number of the selected at least one drive target switch results in a reduction in the temperature of the selected at least one drive target switch, which results in a reduction in the conduction loss generated by the at least one drive target switch.

[0014] According to a fourth exemplary embodiment of the present disclosure, the selection device is configured to determine whether the value of the temperature parameter is lower than a reference temperature, the reference temperature being set to be lower than the temperature threshold, and to decrease the number of the selected at least one drive target switch upon determining that the value of the temperature parameter is equal to or lower than the reference temperature.

[0015] A reduction in the number of selected at least one drive target switch results in a reduction in the line loss generated by the switches.

[0016] According to a fifth exemplary embodiment of the present disclosure, the switches include at least first, second, third, and fourth switches connected in parallel, and the at least first, second, third, and fourth switches are divided into a first group of first and second switches and a second group of third and fourth switches. The drivers include at least first, second, third, and fourth drivers.The selection device is configured, upon determining that the value of the temperature parameter is higher than the temperature threshold while the number of the selected at least one drive target switch has reached an upper limit, to select the first and second switches of the first group as the first and second drive target switches and the third and fourth switches of the second group as the third and fourth drive target switches, wherein the first to fourth drive target switches form the at least one drive target switch. The target switching cycle is defined as the product of the reference switching cycle and the number of selected switches in each of the first and second groups. The drive control device is configured. (1) to cause each of the first and second drivers to turn on the corresponding one of the first and second drive target switches during a corresponding one of the first and second ON periods as the ON period and thereafter to turn off the corresponding one of the first and second drive target switches in each target switching cycle, (2) cause each of the third and fourth drivers to turn on the corresponding one of the third and fourth drive target switches during a corresponding one of predetermined third and fourth ON periods as the ON period and thereafter turn off the corresponding one of the third and fourth drive target switches in each target switching cycle such that each of the first and second ON periods of the first group is not overlapped with each of the third and fourth ON periods of the second group.

[0017] This configuration allows a predetermined current to be distributed to flow through both the first and second switches in the first group and the predetermined current to flow through both the third and fourth switches in the second group. This reduces the level of the distributed current flowing through each of the first and fourth switches compared to the level of the predetermined current flowing concentratedly through one of the first to fourth switches. This therefore reduces the temperature of each of the first to fourth switches to be equal to or less than the temperature threshold, thereby reducing the conduction loss generated by each of the first to fourth switches.In addition, the fifth exemplary embodiment leads to a reduction in switching loss compared to the comparison arrangement that in each target switching cycle all of the first to fourth switches are turned on or off simultaneously.

[0018] According to a sixth exemplary embodiment of the present disclosure, a plurality of temperature ranges that differ from each other are defined as determination temperature ranges. The selection device is configured (1) periodically perform a determination task that determines one of the temperature ranges to which the value of the temperature parameter belongs, (2) to determine whether one of the determination temperature ranges to which the value of the temperature parameter determined in a current determination task belongs is higher than one of the determination temperature ranges to which the value of the temperature parameter determined in a previous determination task belongs, (3) increase the number of at least one drive target switch selected upon determining that one of the determination temperature ranges to which the value of the temperature parameter determined in the current determination task belongs is higher than one of the determination temperature ranges to which the value of the temperature parameter determined in the previous determination task belongs, (4) reduce the number of the at least one drive target switch selected upon determining that one of the determination temperature ranges to which the value of the temperature parameter selected in the current determination task belongs is lower than one of the determination temperature ranges to which the temperature of one of the first and second switches determined in the previous determination task belongs.

[0019] This increases or decreases the number of the selected at least one drive target switch depending on whether one of the determination temperature ranges to which the temperature parameter determined in the current determination task belongs is higher than one of the determination temperature ranges to which the temperature parameter determined in the previous determination task belongs. This prevents a specified switch from being intensively turned on or off, thereby suppressing an increase in the temperature of the specified switch and suppressing an increase in the ON resistance value of the specified switch. This therefore leads to a lower conduction loss of the switches.

[0020] According to a seventh exemplary embodiment of the present disclosure, the switches include at least first, second, third, and fourth switches connected in parallel to each other, and the at least first, second, third, and fourth switches are divided into a first group of first and second switches and a second group of third and fourth switches. The drivers include at least first, second, third, and fourth drivers, and an upper limit of the highest temperature range in the determination temperature ranges is defined as the temperature threshold.

[0021] The selection device is configured to select the first and second switches of the first group as the first and second drive target switches and the third and fourth switches of the second group as the third and fourth drive target switches upon determining that the value of the temperature parameter is higher than the temperature threshold. The first to fourth drive target switches form the at least one drive target switch, and the target switching cycle is defined as the product of the reference switching cycle and the number of selected switches in each of the first and second groups.

[0022] The drive control device is configured (1) to cause, in each target switching cycle, each of the first and second drivers to turn on the corresponding one of the first and second drive target switches during a corresponding one of the first and second ON periods as the ON period and thereafter to turn off the corresponding one of the first and second drive target switches, (2) to cause, in each target switching cycle, each of the third and fourth drivers to turn on the corresponding one of the third and fourth drive target switches during a corresponding one of predetermined third and fourth ON periods as the ON period and thereafter to turn off the corresponding one of the third and fourth drive target switches while each of the first and second ON periods of the first group is not overlapped with each of the third and fourth ON periods of the second group.

[0023] This configuration allows a predetermined current to be distributed to flow through both the first and second switches in the first group, and the predetermined current to flow through both the third and fourth switches of the second group. This reduces the level of the distributed current flowing through each of the first to fourth switches compared to the level of the predetermined current flowing intensively through any one of the first to fourth switches. This therefore reduces the temperature of each of the first to fourth switches to be equal to or lower than the temperature threshold, thereby reducing conduction loss of each of the first to fourth switches.In addition, the seventh exemplary embodiment leads to a reduction in switching loss compared to the comparison arrangement that all of the first to fourth switches are turned on or off simultaneously in each target switching cycle.

[0024] The drive device according to an eighth exemplary embodiment of the present disclosure further includes a plurality of power supply circuits for supplying electric power to the respective drivers, and a power supply control device configured to cause at least one of the power supply circuits to supply the electric power only to at least one of the drivers corresponding to the at least one drive target switch. The drive control device is configured to cause the at least one of the drivers to which electric power is supplied from the at least one power supply circuit to turn on or off the corresponding at least one drive target switch.

[0025] If all the power supply circuits supplying electric power to the respective drivers are switched off while at least one of the switches as the at least one drive target switch is not selected, standby power of the unselected driver(s) corresponding to the unselected switching would be wasted.

[0026] In this regard, the power supply control device according to the eighth exemplary embodiment is configured to cause at least one of the power supply circuits to supply the electric power only to the at least one of the drivers corresponding to the at least one drive target switch. This configuration therefore results in lower power consumption of the drivers while suppressing an increase in the temperature of the at least one drive target switch.

[0027] The above-described and / or other features and / or advantages of various embodiments of the present disclosure will become further apparent in view of the following description taken in conjunction with the accompanying drawings. Various embodiments of the present disclosure may include and / or exclude different features and / or advantages, where applicable. In addition, various embodiments of the present disclosure may combine one or more features of other embodiments, where applicable. The description of features and / or advantages of particular embodiments should not be construed as a limitation of other embodiments or the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Other aspects of the present disclosure will become apparent from the following description of embodiments with reference to the accompanying drawings, in which: Fig. 1 is a circuit diagram schematically illustrating an overall configuration of a power conversion system according to a first embodiment of the present disclosure, Fig. 2 shows a flowchart schematically illustrating a drive routine performed by a Fig. 1 illustrated control device is executed, Fig. 3 shows a timing diagram schematically illustrating how a first sub-branch switch is driven over time, Fig. 4 shows a time loss diagram schematically illustrating how first and second sub-branch switches are driven over time, Fig. 5 shows a timing diagram schematically showing how first to third sub-branch switches are driven over time, Fig. 6 shows a timing diagram schematically illustrating how first to fourth sub-branch switches are driven over time, Fig. 7 shows a timing diagram schematically illustrating how the first and second sub-branch switches of a first group and the third and fourth sub-branch switches of a second group are driven over time, Fig. 8 shows a graph schematically illustrating an example of the relationship between a collector current flowing through an IGBT and the collector-emitter voltage across the IGBT, Fig. 9 is a flowchart schematically illustrating a drive routine executed by a controller of a power conversion system according to a second embodiment of the present disclosure, and Fig. 10 is a timing diagram schematically illustrating how the first and second sub-branch switches of the first group, the third and fourth sub-branch switches of the second group, and fifth and sixth sub-branch switches are driven over time according to a modification of each embodiment. DETAILED DESCRIPTION OF EMBODIMENTS

[0029] Embodiments of the present disclosure will be described below with reference to the accompanying drawings. In the embodiments, like parts are omitted or simplified across the embodiments to which the same reference numerals are assigned to avoid redundant description.

[0030] First, a power conversion system CS having a drive apparatus according to the first embodiment of the present disclosure will be described below with reference to the accompanying drawings.

[0031] According to Fig. 1, the power conversion system CS is installed, for example, in a vehicle. The power conversion system CS includes a voltage converter 10, which is an example of a boost converter, and a control system 100 for controlling the boost converter 10.

[0032] The boost converter 10 is designed, for example, as a chopper booster and operable to boost an output voltage from a direct current (DC) power source PS, such as a battery, and output the boosted voltage to at least one electrical load EL, such as an inverter. The DC power source PS has opposing positive and negative terminals.

[0033] The boost converter 10 has a positive input terminal Cip, a negative input terminal Cin, a positive output terminal Cop, and a negative output terminal Con. The boost converter 10 includes, for example, an inductor, i.e., a choke coil, 11 and a first capacitor 12. The inductor 11 has opposite first and second ends, and the first capacitor 12 has opposite first and second electrodes, i.e., first and second ends.

[0034] The first end of the inductor 11 is connected to the positive terminal of the DC power source PS via the positive input terminal Cip. The first electrode of the first capacitor 12 is connected to the positive input terminal Cip, and the second electrode of the first capacitor 12 is connected to the negative terminal of the DC power source PS via the negative input terminal Cin. This results in the first capacitor 12 being connected in parallel with the DC power source PS.

[0035] The boost converter 10 has a first parallel circuit arrangement 10a1 consisting of first to fourth upper-branch switches S1p, S2p, S3p, and S4p. The boost converter 10 also has a second parallel circuit arrangement 10a2 consisting of first to fourth lower-branch switches S1n, S2n, S3n, and S4n.

[0036] The first upper-branch switch S1p and the first sub-branch switch S1n are connected in series, and the second upper-branch switch S2p and the second sub-branch switch S2n are connected in series. Likewise, the third upper-branch switch S3p and the third sub-branch switch S3n are connected in series, and the fourth upper-branch switch S4p and the fourth sub-branch switch S4n are connected in series.

[0037] The boost converter 10 further comprises freewheeling diodes or flywheel diodes D1p, D2p, D3p, D4p, D1n, D2n, D3n and D4n, which are connected antiparallel to the respective switches S1p, S2p, S3p, S4p, S1n, S2n, S3n and S4n.

[0038] For example, the first embodiment uses IGBTs, as an example of semiconductor switches, as the upper and lower branch switches S1p, S2p, S3p, S4p, S1n, S2n, S3n, and S4n. MOSFETs or bipolar transistors can also be used as the upper and lower branch switches S1p, S2p, S3p, S4p, S1n, S2n, S3n, and S4n. When MOSFETs are used individually as the upper and lower branch switches S1p, S2p, S3p, S4p, S1n, S2n, S3n, and S4n, the intrinsic diodes of the MOSFETs can be used as the freewheeling diodes.

[0039] The connection point between the first upper and lower branch switches S1p and S1n and the connection point between the second upper and lower branch switches S2p ​​and S2n are connected to the second end of the induction coil 11. Likewise, the connection point between the third upper and lower branch switches S3p and S3n and the connection point between the fourth upper and lower branch switches S4p and S4n are connected to the second end of the induction coil 11.

[0040] The collectors of the first to fourth upper-branch switches S1p to S4p are connected to the positive output terminal Cop of the boost converter 10. The emitters of the first to fourth sub-branch switches S1n to S4n are connected to both the negative input and positive output terminals Cin and Con of the boost converter 10 via a common signal ground line.

[0041] The boost converter 10n includes a second capacitor 13. The second capacitor 13 has opposite first and second electrodes, i.e., first and second ends. The first end of the second capacitor 13 is connected to the positive output terminal Cop of the boost converter 10, and the second end of the second capacitor 13 is connected to the negative output terminal Con of the boost converter 10. That is, the second capacitor 13 is connected in parallel to the pair of first upper and lower branch switches (S1p, S1n), the pair of second upper and lower branch switches (S2p, S2n), the pair of third upper and lower branch switches (S3p, S3n), and the pair of fourth upper and lower branch switches (S4p, S4n).

[0042] The at least one electrical load EL is connected to the positive and negative output terminals Cop and Con of the boost converter 10 such that the voltage boosted by the boost converter 10 is applied to the at least one electrical load EL. The first embodiment uses an inverter as an example of an electrical load; the inverter converts the DC voltage boosted by the boost converter 10 into an AC voltage and outputs the AC voltage, for example, to a motor (not shown) connected thereto. The motor (not shown) is driven based on the AC voltage to output torque.

[0043] The control system 100 includes a temperature sensor 20, an input voltage sensor 21, an output voltage sensor 22, and a controller 30. The temperature sensor 20 consists, for example, of a temperature-sensitive diode 20a. For example, the temperature sensor 20 is arranged close to the first sub-branch switch S1n as a temperature detection target. For example, the switches S1p to S4n are mounted on a chip, and the temperature sensor 20 is also mounted on the same chip.

[0044] Specifically, the temperature sensor 20 is configured to measure the temperature of the first sub-branch switch S1n and output a temperature measurement signal indicative of the measured temperature to a first driver described later.

[0045] The input voltage sensor 21 is connected across the first capacitor 12 to serve as an input voltage measuring unit. Specifically, the input voltage sensor 21 is operable to measure the voltage across the first and second electrodes of the first capacitor 12 as an input voltage Vin to the boost converter 10. The input voltage sensor 21 is connected to the controller 30 and outputs the measured input voltage Vin to the controller 30.

[0046] The output voltage sensor 22 is connected across the second capacitor 13 to serve as an output voltage measuring unit. Specifically, the output voltage sensor 22 is operable to measure the voltage across the first and second electrodes of the second capacitor 13 as an output voltage Vout of the boost converter 10. The output voltage sensor 12 is connected to the controller 30 and outputs the measured output voltage Vout to the controller 30.

[0047] The control device 30 is connected to the input voltage sensor 21 and the output voltage sensor 22. The control device 30 receives the input voltage sensor Vin of the boost converter 10 measured by the input voltage sensor 21 and the output voltage Vout of the boost converter 10 measured by the output voltage sensor 22.

[0048] The control device 30 essentially consists of at least one microcomputer circuit, including, for example, a CPU, a ROM, a RAM, and other known peripheral devices. The CPU of the control device 30 executes software programs, stored, for example, in the ROM, to perform various tasks and / or routines. Specifically, the CPU of the control device 30 executes at least one software program, stored, for example, in the ROM, to execute a drive routine described later, to implement at least a temperature acquisition device 30a, a selection device 30b, a drive control device 30c, and a power supply control device 30d.

[0049] These functional modules 30a, 30b, 30c and 30d may each be implemented by an electronic circuit such as a hardware unit, or may be implemented by at least one digital circuit having a plurality of logic circuits, at least one analog circuit, or at least one analog and digital hybrid circuit.

[0050] The control device 30 performs a control task in a boost mode, ie, a step-up mode, to perform ON-OFF control of the first to fourth sub-branch switches S1b to S4n while maintaining the first to fourth upper-branch switches S1p to S4p in an OFF state. This boost-mode control task causes the output voltage Vout of the boost converter 10 to track a target voltage Vtg.

[0051] In particular, the controller 30 determines a duty cycle, ie, a duty or duty cycle, Duty of each of the first to fourth sub-branch switches S1n to S4n as a function of the input voltage Vin, the output voltage Vout, and the target voltage Vtgt when controlling the boost converter 10 to operate in the boost mode.

[0052] The duty cycle Duty of each of the first to fourth sub-branch switches S1n to S4n represents the ratio of an ON time Lon to the total time of each reference switching cycle Lsw for a corresponding one of the first to fourth sub-branch switches S1n to S4n; the duty cycle Duty is expressed as Lon / Lsw. Specifically, the controller 30 increases the duty cycle Duty of each of the first to fourth sub-branch switches S1n to S4n with an increase in the target voltage Vtgt.

[0053] The power control system 100 also includes first, second, third, and fourth drivers 41, 42, 43, and 44 provided for the respective first, second, third, and fourth switches S1n, S2n, S3n, and S4n. The control terminals, i.e., the gates, of the first to fourth sub-branch switches S1n to S4n are connected to the respective first to fourth drivers 41 to 44. The control terminals, i.e., the gates, of the first to fourth sub-branch switches S1n to S4n are connected to the respective first to fourth drivers 41 to 44. Each of the first to fourth drivers 41 to 44, which is made of, for example, an integrated circuit (IC), is configured to be driven based on an externally supplied electric power thereto.

[0054] The power control system 100 further includes first to fourth power supply circuits (PSCs) 51, 52, 53 and 54, a photocoupler 60 and first to fourth transformers 61, 62, 63 and 64.

[0055] The first to fourth power supply circuits 51 to 54, each of which is composed of an IC, for example, are connected to the controller 30. Each of the first to fourth transformers 61 to 64 consists of a primary coil and a secondary coil that is magnetically coupled to the primary coil when the primary coil is energized. The primary coil of each of the first to fourth transformers 61 to 64 is connected to the corresponding one of the first to fourth power supply circuits 51 to 54. The secondary coil of each of the first to fourth transformers 61 to 64 is connected to the corresponding one of the first to fourth drivers 41 to 44.

[0056] Specifically, the controller 30 generates drive signals D1, D2, D3, and D4 for the respective first to fourth sub-branch switches S1n, S2n, S3n, and S4n based on the determined duty cycles of the respective first to fourth switches S1n, S2n, S3n, and S4n. Then, the controller 30 sends the drive signals D1 to D4 to the respective first to fourth power supply circuits 51 to 54.

[0057] Each of the first to fourth power supply circuits 51 to 54 is connected to a corresponding one of constant voltage sources CVS.

[0058] The first power supply circuit 51 is configured to supply a constant voltage based on the corresponding constant voltage source CVS to the first transformer 61 in accordance with the drive signal D1 sent from the controller 30. The second power supply circuit 52 is configured to supply a constant voltage based on the corresponding constant voltage source CVS to the second transformer 62 in accordance with the drive signal D2 sent from the controller 30.

[0059] The third power supply circuit 53 is configured to supply a constant voltage based on the corresponding constant voltage source CVS to the third transformer 63 in accordance with the drive signal D3 sent from the controller 30. The fourth power supply circuit 44 is configured to supply a constant voltage based on the corresponding constant voltage source CVS to the fourth transformer 64 in accordance with the drive signal D4 sent from the controller 30.

[0060] Each of the first to fourth transformers 61 to 64 is configured to convert the constant voltage into a predetermined drive voltage for a corresponding one of the first to fourth sub-branch switches S1n to S4n, while the corresponding transformer is electrically isolated from the corresponding sub-branch switch. Then, each of the first to fourth transformers 61 to 64 is configured to apply the drive voltage to the control terminal, i.e., the gate, of the corresponding one of the first to fourth sub-branch switches S1n to S4n, thereby driving the corresponding one of the first to fourth sub-branch switches S1n to S4n.

[0061] That is, the control device 30 controls the drive signals D1 to D4 to control ON-OFF switching operations of the first to fourth sub-branch switches S1n to S4n.

[0062] It should be noted that, as described above, the first to fourth transformers electrically isolate the set of boost converter 10 and first to fourth drivers 61 to 64 from the set of controller 30 and first to fourth power supply circuits 51 to 54.

[0063] The set of boost converter 10n and first to fourth drivers 61 to 64 constitutes a high-voltage system because the input voltage Vin supplied from DC power source PS is higher than the constant voltage supplied from each constant-voltage source CVS. For the same reason, the set of controller 30 and first to fourth power supply circuits 51 to 54 constitutes a low-voltage system. In other words, the power conversion system CS according to the first embodiment is configured such that the first to fourth transformers 61 to 64 electrically isolate the high- and low-voltage systems from each other.

[0064] In addition, the temperature sensor 20 according to the first embodiment is connected to the first driver 41, for example, so that the temperature sensor 20 is configured to output the temperature measurement signal indicating the measured temperature of the first sub-branch switch S1n to the first driver 41.

[0065] The first driver 41 is connected to the photocoupler 60, which is an electrical isolation device, and the photocoupler 60 is connected to the controller 30.

[0066] Specifically, the first driver 41 is configured to convert the value of the measurement signal indicating the measured temperature of the first sub-branch switch S1n into a digital temperature measurement value. The first driver 41 is then configured to transmit the digital temperature measurement value to the control device 30 via the photocoupler 60, while the first driver 41 is electrically isolated from the control device 30. That is, the photocoupler 60 serves to transmit data between the high- and low-voltage systems while maintaining electrical isolation between the high- and low-voltage systems.

[0067] Upon receiving the digital temperature measurement value via the photocoupler 60, the controller 30 acquires the digital temperature measurement value as temperature information regarding the first sub-branch switch S1n and calculates, as a temperature parameter indicating the temperature of the first to fourth sub-branch switches S1n to S4n, a switch temperature Tsw1 of the first sub-branch switch S1n as a function of the temperature information.

[0068] The following is a driving routine for the first to fourth sub-branch switches S1n to S4n in the boost mode with reference to Fig. 2. The controller 30 is programmed to execute the drive routine, for example, at a predetermined period. In other words, the controller 30 functions as the temperature acquisition device 30a, the selection device 30b, the drive control device 30c, and the power supply control device 30d described above to perform the subsequent processing of the drive routine.

[0069] When starting the drive routine, the controller 30 serves, for example, as the temperature acquiring means 30a to acquire, as the temperature information regarding the first sub-branch switch S1n, the digital temperature measurement value indicating the measured temperature of the first sub-branch switch S1n via the first driver 41 and the photocoupler 60 in step S8.

[0070] Thereafter, the control device 30 serves, for example, as the temperature acquiring device 30a to calculate the switch temperature Tsw1 of the first sub-branch switch S1n as a function of the temperature information.

[0071] Subsequently, the controller 30 serves, for example, as the selector 30b to determine whether the calculated switch temperature Tsw1 is equal to or lower than a first threshold value Tth1 in step S10. Note that the temperature range defined from a predetermined allowable lower limit temperature of the first to fourth sub-branch switches S1n to S4n up to and including the first threshold value Tth1 is set as a first determination temperature range according to the first embodiment. The allowable lower limit temperature represents that when the temperature of each of the first to fourth sub-branch switches S1n to S4n is maintained equal to or higher than the allowable lower limit temperature, the reliability of the corresponding one of the first to fourth sub-branch switches S1n to S4n is maintained.

[0072] If it is determined that the calculated switch temperature Tsw1 is equal to or less than the first threshold value Tth1 (YES in step S10), the controller 30 determines that the switch temperature Tsw1 calculated in the current drive routine belongs to the first determination temperature range. Then, the drive routine proceeds to step S11.

[0073] In step S11, the controller 30 serves, for example, as the selector 30b to select the first driver 41 from the first to fourth drivers 41 to 44. Then, in step S11, the controller 30 serves, for example, as the power supply control means 30d to cause the first power supply circuit 51 to supply the constant voltage only to the selected first driver 41. This causes the first driver 41 to be activated, so that the first sub-branch switch S1n is selected as a drive target switch.

[0074] Thereafter, the control device 30 serves, for example, as the drive control device 30c to control the first driver 41 via the first power supply circuit 51, to turn on only the first sub-branch switch S1n during the ON time Lon in each reference switching cycle Lsw and to turn off the first sub-branch switch S1n after the elapse of the ON time Lon (see Fig. 3).

[0075] Otherwise, upon determining that the calculated switch temperature Tsw1 is higher than the first threshold Tth1 (NO in step S10), the controller 30 serves, for example, as the selector 30b to determine in step S12 whether the switch temperature Tsw1 is higher than the first threshold Tth1 and equal to or less than the second threshold Tth2; the second threshold Tth2 is set to be higher than the first threshold Tth1. Note that the temperature range defined from the first threshold Tth1 exclusive to the second threshold Tth2 is set as a second determination temperature range according to the first embodiment; the second determination temperature range is adjacent to the first determination temperature range.

[0076] If it is determined that the switch temperature Tsw1 is higher than the first threshold Tth1 and equal to or lower than the second threshold Tth2 (YES in step S12), the controller 30 determines that the switch temperature Tsw1 calculated in the current drive routine belongs to the second determination temperature range. The drive routine then proceeds to step S13.

[0077] In step S13, the controller 30 serves, for example, as the selector 30b to select the first and second drivers 41 and 42 from the first to fourth drivers 41 to 44. Then, in step S13, the controller serves, for example, as the power supply control means 30s to cause the first and second power supply circuits 51 and 52 to supply the constant voltages only to the selected first and second drivers 41 and 42. This causes the first and second drivers 41 and 42 to be activated, so that the first and second sub-branch switches S1n and S2n are each selected as a drive target switch.

[0078] Specifically, in step S13, the control device 30 serves, for example, as the drive control device 30c for controlling the first and second drivers 41 and 42 via the first and second power supply circuits 51 and 52 to 1. every two reference switching cycles, which are expressed as (2 x Lsw) (see Fig. 4) to switch on the first sub-branch switch S1n during the ON period of the drive signal, ie drive pulse, D1 and to switch off the first sub-branch switch S1n after the ON period Lon has elapsed, 2. every two switching cycles (2 x Lsw) to switch on the second sub-branch switch S2n during the ON time period Lon of the drive pulse D2 and to switch off the second sub-branch switch S2n after the ON time period Lon has elapsed, while maintaining a reference switching cycle Lsw between the ON start time of each drive pulse D1 and the ON start time of the drive pulse D2 which is adjacent to the corresponding drive pulse D1 (see Fig. 4).

[0079] In other words, the control device 30 alternately switches on the first sub-branch switch S1n and the second sub-branch switch S2n every two reference switching cycles (2 x Lsw) so that the ON period of the first sub-branch switch S1n does not overlap with the ON period of the second sub-branch switch S2n.

[0080] Otherwise, upon determining that the switch temperature Tsw1 is higher than the second threshold Tth2 (NO in step S12), the controller 30 serves, for example, as the selector 30b to determine in step S14 whether the switch temperature Tsw1 is higher than the second threshold Tth2 and equal to or lower than a third threshold Tth3; the third threshold Tth3 is set to be higher than the second threshold Tth2. Note that the temperature range defined from the second threshold Tth2 excluding the third threshold Tth3 is set as a third determination temperature range according to the first embodiment; the third determination temperature range is adjacent to the second determination temperature range.

[0081] If it is determined that the switch temperature Tsw1 is higher than the second threshold Tth2 and equal to or lower than the third threshold Tth3 (YES in step S14), the controller 30 determines that the switch temperature Tsw1 calculated in the current drive routine belongs to the third determination temperature range. Then, the drive routine proceeds to step S15.

[0082] In step S15, the controller 30 serves, for example, as the selector 30b to select the first to third drivers 41 to 43 from the first to fourth drivers 41 to 44. Then, in step S15, the controller 30 serves, for example, as the power supply control means 30d to cause the first to third power supply circuits 51 to 53 to supply the constant voltages only to the selected first to third drivers 41 to 43. This causes the first to third drivers 41 to 43 to be activated, so that the first to third sub-branch switches S1n to S3n are each selected as a drive target switch.

[0083] Specifically, in step S15, the control device 30 serves, for example, as the drive control device 30c for controlling the first to third drivers 41 to 43 via the first to third power supply circuits 51 to 53 to 1. all three reference switching cycles, which are expressed as (3 x Lsw) (see Fig. 5) to switch on the first sub-branch switch S1n during the ON time Lon of the drive pulse D1 and to switch off the first sub-branch switch S1n after the ON time Lon has elapsed, 2. every three switching cycles (3 x Lsw) to switch on the second sub-branch switch S2n during the ON time period Lon of the drive pulse D2 and to switch off the second sub-branch switch S2n after the ON time period Lon has elapsed, while a reference switching cycle Lsw is maintained between the ON start time of each drive pulse D1 and the ON start time of the entry pulse D2 which is adjacent to the corresponding drive pulse D1 (see Fig. 5), is maintained, 3. every three switching cycles (3 x Lsw) to switch on the third sub-branch switch S3n during the on-time period Lon of the drive pulse D3 and to switch off the third sub-branch switch S3n after the on-time period Lon has elapsed, while a reference switching cycle Lsw is maintained between the on-start time of each drive pulse D2 and the on-start time of the drive pulse D3 which is adjacent to the corresponding drive pulse D2 (see Fig. 5), is retained.

[0084] In other words, the control device 30 turns on the first sub-branch switch S1n, the second sub-branch switch S2n and the third sub-branch switch S3n every three reference switching cycles (3 x Lsw) so that the ON period of the first sub-branch switch S1n, the ON period of the second sub-branch switch S2n and the ON period of the third sub-branch switch S3n do not overlap each other.

[0085] Otherwise, upon determining that the switch temperature Tsw1 is higher than the third threshold Tth3 (NO in step S14), the controller 30 serves, for example, as the selector 30b to determine in step S16 whether the switch temperature Tsw1 is higher than the third threshold Tth3 and equal to or lower than a fourth threshold Tth4; the fourth threshold Tth4 is set to be higher than the third threshold Tth3. Note that the temperature range defined from the third threshold Tth3 exclusive to the fourth threshold Tth4 is set as a fourth determination temperature range according to the first embodiment; the fourth temperature determination range is adjacent to the third temperature range.The fourth threshold value Tth4 is set to a predetermined allowable upper limit temperature, such as 150°C, of ​​the first to fourth sub-branch switches S1n to S4n, for example. The allowable upper limit temperature represents that when the temperature of each of the first to fourth sub-branch switches S1n to S4n is maintained at or below the allowable upper limit temperature, the reliability of the corresponding one of the first to fourth sub-branch switches S1n to S4n is maintained.

[0086] If it is determined that the switch temperature Tsw1 is higher than the third threshold Tth3 and equal to or lower than the fourth threshold Tth4 (YES in step S16), the controller 30 determines that the switch temperature Tsw1 calculated in the current drive routine belongs to the fourth determination temperature range. Then, the drive routine proceeds to step S17.

[0087] In step S17, the controller 30 serves, for example, as the selector 30b to select all of the first to fourth drivers 41 to 44. Then, in step S17, the controller 30 serves, for example, as the power supply control means 30d to cause all of the first to fourth power supply circuits 51 to 54 to supply the constant voltages to all of the first to fourth drivers 41 to 44. This causes the first to fourth drivers 41 to 44 to be activated, so that the first to fourth sub-branch switches S1n to S4n are each selected as a drive target switch.

[0088] Specifically, in step S17, the control device 30 serves, for example, as the drive control device 30c for controlling the first to fourth drivers 41 to 44 via the first to fourth power supply circuits 51 to 54 to 1. all four reference cycles, which are expressed as (4x Lsw) (see Fig. 6) to switch on the first sub-branch switch S1n during the ON time Lon of the drive pulse D1 and to switch off the first sub-branch switch S1n after the ON time Lon has elapsed, 2. every four switching cycles (4x Lsw) to switch on the second sub-branch switch S2n during the ON time period Lon of the drive pulse D2 and to switch off the second sub-branch switch S2n after the ON time period Lon has elapsed, while maintaining a reference switching cycle Lsw between the ON start time of each drive pulse D1 and the ON start time of the drive pulse D2 that is adjacent to the corresponding drive pulse D1 (see Fig. 6), 3. every four switching cycles (4x Lsw) to switch on the third sub-branch switch S3n during the ON time period Lon of the drive pulse D3 and to switch off the third sub-branch switch S3n after the ON time period Lon has elapsed, while maintaining a reference switching cycle Lsw between the ON start time of each drive pulse D2 and the ON start time of the drive pulse D3 that is adjacent to the corresponding drive pulse D2 (see Fig. 6), 4. every four switching cycles (4x Lsw) to switch on the fourth sub-branch switch S4n during the ON time period Lon of the drive pulse D4 and to switch off the fourth sub-branch switch S4n after the ON time period Lon has elapsed, while maintaining a reference switching cycle Lsw between the ON start time of each drive pulse D3 and the ON start time of the drive pulse D4 that is adjacent to the corresponding drive pulse D3 (see Fig. 6).

[0089] In other words, the control device 30 switches on the first sub-branch switch S1n, the second sub-branch switch S2n, the third sub-branch switch S3n and the fourth sub-branch switch S4n alternately every four reference switching cycles (4x Lsw) so that the ON period of the first sub-branch switch S1n, the ON period of the second sub-branch switch S2n, the ON period of the third sub-branch switch S3n and the ON period of the fourth sub-branch switch S4n do not overlap each other.

[0090] Otherwise, if it is determined that the switch temperature Tsw1 is higher than the fourth threshold Tth4 (NO in step S16), the controller 30 determines that the switch temperature Tsw4 calculated in the current drive routine has exceeded the fourth threshold, which serves as a temperature threshold, for example. Then, the drive routine proceeds to step S18.

[0091] In step S18, the controller 30 serves, for example, as the power supply controller 30b to cause all of the first to fourth power supply circuits 51 to 54 to supply the constant voltages to all of the first to fourth drivers 41 to 44. This results in the first to fourth drivers 41 to 44 being activated, so that the first to fourth sub-branch switches S1n to S4n are each selected as a drive target switch.

[0092] Specifically, in step S18, the control device 30 serves, for example, as the drive control device 30c for controlling the first to fourth drivers 41 to 44 via the first to fourth power supply circuits 51 to 54 to 1. every two reference switching cycles, which are expressed as (2x Lsw), to switch on a pair of the first and second sub-branch switches S1n and S2n during the identical ON times Lon of the drive pulses D1 and D2, and to switch off the pair of the first and second sub-branch switches S1n and S2n after the ON times Lon have elapsed (see Fig. 7), 2. every two reference switching cycles, which are expressed as (2x Lsw), to turn on a pair of the third and fourth sub-branch switches S3n and S4n during the respective identical ON periods Lon of the drive pulses D3 and D4 and to turn off the pair of the third and fourth sub-branch switches S3n and S4n after the elapse of the ON periods Lon, while maintaining a reference switching cycle Lsw between the ON start time of each drive pulse D1, D2 and the ON start time of the drive pulse S3, D4 which is adjacent to the corresponding drive pulses D1, D2.

[0093] In other words, the control device 30 alternately switches on the pair, i.e., the first group, of the first and second sub-branch switches S1n and S2n and the pair, i.e., the second group, of the third and fourth sub-branch switches S3n and S4n every two reference switching cycles (2x Lsw) so that the ON periods of the first group of the first and second sub-branch switches S1n and S2n and the ON periods of the second group of the third and fourth sub-branch switches S3n and S4n do not overlap. Note that the ON period for the first group of the first and second sub-branch switches S1n and S2n and the ON period for the second group of the third and fourth sub-branch switches S3n and S4n are set, for example, to be identical to each other.

[0094] That is, the processing in step S18 enables a current based on the power source PS to be distributed so that it flows through both of the first and second sub-branch switches S1n and S2n every two reference switching cycles (2x Lsw). This reduced the level of current flowing through each of the first and second switches S1n and S2n based on the processing in step S18 compared to the level of current flowing through each of the first and second switches S1n and S2n based on the processing in step S17. This therefore allows the switch temperature Tsw1 of the first sub-branch switch S1n to become equal to or lower than the fourth threshold Tth4, resulting in a lower conduction loss of at least the first sub-branch switch S1n.

[0095] Below is an example of how the first to fourth switches are configured according to the Fig. 2. In the following example, it is assumed that the determination in step S12 in the previous drive routine was positive.

[0096] If, in the current drive routine, the determination in step S12 is changed to negative and the determination in step S14 is affirmative in the current drive routine, the drive target switches are changed from the first and second sub-branch switches S1n and S2n to the first to third sub-branch switches S1n to S3n (see step S15). This increases the number of drive target switches by one.

[0097] On the other hand, in the current drive routine, if the determination in step S10 is changed to affirmative, the drive target switches are changed from the first and second sub-branch switches S1n and S2n to the first sub-branch switch S1n (see step S11). This reduces the number of drive target switches by one.

[0098] Otherwise, if the determination in step S12 in the current drive routine is also affirmative, the number of drive target switches is kept unchanged because it is determined that the determination temperature range to which the switch temperature Tsw1 belongs is unchanged.

[0099] The power conversion system CS according to the first embodiment described above is configured to adjust the frequency at which the first sub-branch switch S1n is alternately turned on and off according to the switch temperature Tsw1 of the first sub-branch switch S1n. That is, this configuration increases the number of drive target switches to thereby reduce the frequency of on-off confirmations of the first sub-branch switch S1n as the switch temperature Tsw1 of the first sub-branch switch S1n increases.

[0100] This means that, as it is in Fig. 8, when a collector current Ic flowing through an IGBT has a value Ia, the collector-emitter voltage Vce across the IGBT is changed between a value V(25°C) and a value V(100°C) depending on a change in the temperature of the IGBT between 25°C and 100°C. This means that Fig. Figure 9 shows that the ON resistance of the IGBT exhibits a temperature dependence.

[0101] Preventing an increase in the temperature of the first sub-branch switch S1n as a specified switch therefore reduces the ON resistance of the first sub-branch switch S1n, resulting in a reduction in conduction loss of the first sub-branch switch S1n. This therefore reduces the overall loss in the boost converter 10.

[0102] Additionally, the power conversion system CS according to the first embodiment is configured to selectively power at least one of the first to fourth drivers 41 to 44 corresponding to the at least one drive target switch. This configuration therefore results in lower power consumption of the power conversion system CS while suppressing an increase in the temperature of the first sub-branch switch S1n. Second embodiment

[0103] Hereinafter, a power conversion system according to the second embodiment of the present disclosure will be described with reference to Fig. 9. The configuration and functions of the power conversion system according to the second embodiment differ substantially from those of the power conversion system CS according to the first embodiment in the following points. Therefore, the different points will be mainly described below, while the same reference numerals are assigned to the same parts between the first and second embodiments.

[0104] The following is a drive routine for the first to fourth sub-branch switches S1n to S4n of the boost mode with reference to Fig. 9. The control device 30 is programmed to execute the drive routine, for example, in a predetermined period. The same steps between the Fig. 9 illustrated drive routine and the one in Fig. 2, which are assigned the same step numbers, are omitted or simplified in the description.

[0105] When starting the drive routine, the control device 30 performs the processings in steps S8 and S9, and serves, for example, as the selecting device 30b to determine in step S20 whether the first sub-branch switch S1n in the first to fourth sub-branch switches S1n to S4n is selected only as the at least one drive target switch.

[0106] Upon determining that only the first sub-branch switch S1n among the first to fourth sub-branch switches S1n to S4n is selected as the at least one drive target switch (YES in step S20), the controller 30 serves, for example, as the selector 30b to determine in step S21 whether the switch temperature Tsw1 calculated in the current drive routine is higher than the fourth threshold value Tth4. The processing in step S21 aims to determine whether there is a temperature situation where an increase in the number of drive target switches is required.

[0107] If it determines that the switch temperature Tsw1 calculated in the current drive routine is equal to or lower than the fourth threshold Tth4 (NO in step S21), the controller 30 determines that there is no temperature situation requiring an increase in the number of drive target switches. Then, the drive routine proceeds to step S11.

[0108] In step S11, as described above, the controller 30 selects the first driver 41 from the first to fourth drivers 41-44 and causes the first power supply circuit 51 to apply the constant voltage only to the selected first driver 41. This results in the first driver 41 being activated, so that the first sub-branch switch S1n is selected as a first drive target switch. Then, the controller 30 controls the first driver 41 via the first power supply circuit 51 to turn on only the first sub-branch switch S1n during the ON time Lon and to turn off the first sub-branch switch S1n after the elapse of the time Lon in each reference switching cycle Lsw (see Fig. 3).

[0109] Otherwise, if it is determined that the switch temperature Tsw1 calculated in the current drive routine is higher than the fourth threshold Tth4 (YES in step S21), the controller 30 determines that there is a temperature situation where an increase in the number of drive target switches is required. Then, the drive routine proceeds to step S13.

[0110] In step S13, as described above, the controller 30 selects the first and second drivers 41 and 42 from the first to fourth drivers 41 to 44, and causes the first and second power supply circuits 51 and 52 to apply the constant voltages only to the selected first and second drivers 41 and 42. This causes the first and second drivers 41 and 42 to be activated, so that the first and second sub-branch switches S1n and S2n are each selected as a drive target switch.

[0111] In particular, as it is in Fig. 4, the control device 30 alternately switches on the first sub-branch switch S1n and the second sub-branch switch S2n every two reference switching cycles (2x Lsw) so that the ON duration of the first sub-branch switching element S1n does not overlap with the ON duration of the second sub-branch switch S2n.

[0112] Otherwise, upon determining that not only the first sub-branch switch S1n in the first to fourth sub-branch switches S1n to S4n is selected as the at least one drive target switch (NO in step S20), the control device 30 serves, for example, as the selecting device 30b to determine in step S22 whether only the first and second sub-branch switches S1n and S2n selected in step S13 are driven as the drive target switches.

[0113] When determining that only the first and second sub-branch switches S1n and S2n selected in step S13 are driven as the drive target switches (YES in step S22), the control device 30 serves, for example, as the selector 30b to determine in step S23 whether the switch temperature Tsw1 is higher than the fourth threshold value Tth4.

[0114] Upon determining that the switch temperature Tsw1 is equal to or lower than the fourth threshold Tth4 (NO in step S23), the controller 30 serves, for example, as the selector 30b to determine in step S24 whether the switch temperature Tsw1 is equal to or lower than a predetermined reference temperature Tα set to be lower than the fourth threshold Tth4. The processing in step S24 aims to determine whether there is a temperature situation in which a reduction in the number of drive target switches is permitted.

[0115] If it is determined that the switch temperature Tsw1 is higher than the predetermined reference temperature Tα (NO in step S24), the controller 30 determines that there is no temperature situation in which a reduction in the number of drive target switches is permitted. Then, the controller 30 terminates the drive routine so that the first and second sub-branch switches S1n and S2n are continuously driven as the drive target switches (see step S13).

[0116] Otherwise, upon determining that the switch temperature Tsw1 is equal to or lower than the predetermined reference temperature Tα (YES in step S24), the controller 30 determines that there is a temperature situation where a reduction in the number of drive target switches is permitted. Then, the drive routine proceeds to step S11, and the controller 30 performs the processing in step S11 so that the target drive switches are reduced from the first and second sub-branch switches S1n and S2n to the first sub-branch switch S1n.

[0117] Otherwise, if it is determined that the switch temperature Tsw1 is higher than the fourth threshold Tth4 (YES in step S23), the controller 30 determines that there is a temperature situation where an increase in the number of drive target switches is required. Then, the drive routine proceeds to step S15.

[0118] In step S15, as described above, the controller 30 selects the first to third drivers 41 to 43 from the first to fourth drivers 41 to 44, and causes the first to third power supply circuits 51 to 53 to apply the constant voltages only to the selected first to third drivers 41 to 43. This causes the first to third drivers 41 to 43 to be activated, so that the first to third sub-branch switches S1n to S3n are each selected as a drive target switch.

[0119] In other words, the control device 30 switches on the first sub-branch switch S1n, the second sub-branch switch S2n and the third sub-branch switch S3n alternately every three reference switching cycles (3x Lsw) so that the ON time period of the first sub-branch switch S1n, the ON time period of the second sub-branch switch S2n and the ON time period of the third sub-branch switch S3n do not overlap each other (see Fig. 5).

[0120] Otherwise, when determining that not only the first and second sub-branch switches S1n and S2n selected in step S13 are driven as the drive target switches (NO in step S22), the control device 30 serves, for example, as the selector 30b to determine in step S25 whether only the first to third sub-branch switches S1n to S3n selected in step S15 are selected as the drive target switches.

[0121] Upon determining that only the first to third sub-branch switches S1n to S3n selected in step S15 are driven as the drive target switches (YES in step S25), the controller 30 determines in step S26 whether the switch temperature Tsw1 is higher than the fourth threshold value Tth4.

[0122] Upon determining that the switch temperature Tsw1 is equal to or lower than the fourth threshold Tth4 (NO in step S26), the controller 30 serves, for example, as the selector 30b to determine whether the switch temperature Tsw1 is equal to or lower than the predetermined reference temperature Tα in step S27.

[0123] Upon determining that the switch temperature Tsw1 is higher than the predetermined reference temperature Tα (NO in step S27), the controller 30 determines that there is no temperature situation in which a reduction in the number of drive target switches is permitted. Then, the controller 30 terminates the drive routine so that the first to third sub-branch switches S1n to S3n are continuously driven as the drive target switches (see step S15).

[0124] Otherwise, upon determining that the switch temperature Tsw1 is equal to or lower than the predetermined reference temperature Tα (YES in step S27), the controller 30 determines that there is a temperature situation where a reduction in the number of drive target switches is permitted. Then, the drive routine proceeds to step S13, and the controller 30 executes the processing in step S13 so that the drive target switches are reduced from the first to third sub-branch switches S1n to S3n to the first and second sub-branch switches S1n and S2n.

[0125] Otherwise, if it is determined that the switch temperature Tsw1 is higher than the fourth threshold Tth4 (YES in step S26), the controller 30 determines that there is a temperature situation where an increase in the number of drive target switches is required. Then, the drive routine proceeds to step S17.

[0126] In step S17, as described above, the controller 30 causes all of the first to fourth power supply circuits 51 to 54 to apply the constant voltages to all of the first to fourth drivers 41 to 44. This results in the first to fourth drivers 41 to 44 being activated, so that the first to fourth sub-branch switches S1n to S4n are each selected as a drive target switch.

[0127] In particular, the control device 30 switches the first sub-branch switch S1n, the second sub-branch switch S2n, the third sub-branch switch S3n and the fourth sub-branch switch S4n on and off every four reference switching cycles (4x Lsw) such that the ON time period of the first sub-branch switch S1n, the ON time period of the second sub-branch switch S2n, the ON time period of the third sub-branch switch S3n and the ON time period of the fourth sub-branch switch S4n do not overlap each other (see Fig. 6).

[0128] Otherwise, upon determining that not only the first to third sub-branch switches S1n to S3n selected in step S15 are driven as the drive target switches (NO in step S25), the controller 30 serves, for example, as the selector 30b to determine in step S28 whether only the first to fourth sub-branch switches S1n to S4n selected in step S17 are driven as the drive target switches.

[0129] When determining that only the first to fourth sub-branch switches S1n to S4n selected in step S17 are driven as the drive target switches (YES in step S28), the controller 30 serves, for example, as the selector 30b to determine in step S29 whether the switch temperature Tsw1 is higher than the fourth threshold value Tth4.

[0130] Upon determining that the switch temperature Tsw1 is equal to or lower than the fourth threshold Tth4 (NO in step S29), the controller 30 determines in step S30 whether the switch temperature Tsw1 is equal to or lower than the predetermined reference temperature Tα.

[0131] If it is determined that the switch temperature Tsw1 is higher than the predetermined reference temperature Tα (NO in step S30), the controller 30 determines that there is no temperature situation in which a reduction in the number of drive target switches is permitted. Then, the controller 30 terminates the drive routine so that the first to fourth sub-branch switches S1n to S4n are continuously driven as the drive target switches (see step S17).

[0132] Otherwise, upon determining that the switch temperature Tsw1 is equal to or lower than the predetermined reference temperature Tα (YES in step S30), the controller 30 determines that there is a temperature situation where a reduction in the number of drive target switches is permitted. Then, the drive routine proceeds to step S15, and the controller 30 executes the processing in step S15 so that the target drive switches are reduced from the first to fourth sub-branch switches S1n to S4n to the first to third sub-branch switches S1n to S3n.

[0133] Otherwise, if it is determined that the switch temperature Tsw1 is higher than the fourth threshold Tth4 (YES in step S29), the drive routine proceeds to step S18.

[0134] In step S18, as described above, the controller 30 causes all of the first to fourth power supply circuits 51 to 54 to apply the constant voltages to all of the first to fourth drivers 41 to 44. This results in the first to fourth drivers 41 to 44 being activated, so that the first to fourth sub-branch switches S1n to S4n are each selected as a drive target switch.

[0135] In particular, the control device 30 alternately switches on the pair, ie the first group, of the first and second sub-branch switches S1n and S2n and the pair, ie the second group, of the third and fourth sub-branch switches S3n and S4n every two reference switching cycles (2x Lsw), so that the ON periods of the first group, the first and second sub-branch switches S1n and S2n and the ON periods of the second group, the third and fourth sub-branch switches S3n and S4n are not overlapped (see Fig. 7).

[0136] Otherwise, if it is determined that not only the first to fourth sub-branch switches S1n to S4n selected in step S17 are driven as the drive target switches (NO in step S28), the controller determines that the pair of first and second sub-branch switches S1n and S2n and the pair of third and fourth sub-branch switches S3n and S4n selected in step S18 are driven as the drive target switches. Then, the drive routine proceeds to step S31.

[0137] In step S31, the controller 30 determines whether the switch temperature Tsw1 is equal to or lower than the predetermined reference temperature Tα.

[0138] Upon determining that the switch temperature Tsw1 is higher than the predetermined reference temperature Tα (NO in step S31), the controller 30 ends the drive routine so that the pair of first and second sub-branch switches S1n and S2n and the pair of third and fourth sub-branch switches S3n and S4n selected in step S18 are continuously driven as the drive target switches.

[0139] Otherwise, if it is determined that the switch temperature Tsw1 is equal to or lower than the predetermined reference temperature Tα (YES in step S31), the drive routine proceeds to step S17. In step S17, the controller 30 executes the processing in step S17 so that the first to fourth sub-branch switches S1n to S4n are driven in step S17 as described above.

[0140] The power conversion system according to the second embodiment described above is configured 1. increase the number of drive target switches to thereby reduce the frequency of on / off confirmations of the first sub-branch switch S1n when the switch temperature Tsw1 of the first sub-branch switch S1 increases, 2. Continuously use each of the sub-branch switches S1n to S4n selected as the target drive switches until the switch temperature Tsw1 reaches the fourth threshold Tth4. This configuration therefore prevents an increase in the temperature of the first sub-branch switch S1n as a specified switch while suppressing an increase in the number of drive target switches, resulting in a reduction in conduction loss of each of the first to fourth sub-branch switches S1n to S4n.

[0141] The present disclosure is not limited to the embodiments described above, and may be modified within the scope thereof.

[0142] The number of sub-branch switches is not limited to four, and can be set to two, three, five or more.

[0143] When there are first to sixth sub-branch switches S1n to S6n provided in the power conversion system, and when the control device 30 Fig. 2, the first to sixth sub-branch switches S1n to S6n are driven by the processing in step S18 of the drive routine. Note that there are first to sixth drivers and first to sixth power supply circuits provided in the power conversion system for the respective first to sixth sub-branch switches S1n to S6n.

[0144] Specifically, the controller 30 controls the first to sixth drivers via the first to sixth power supply circuits to 1. all three reference switching cycles, which are expressed as (3x Lsw) (see Fig. 10) to switch on a pair of the first and second sub-branch switches S1n and S2n during the respective identical ON periods Lon of the drive pulses D1 and D2 and to switch off the pair of the first and second sub-branch switches S1n and S2n after the ON periods Lon have elapsed, 2. every three reference switching cycles, expressed as (3x Lsw), to turn on a pair of the third and fourth sub-branch switches S3n and S4n during the respective identical ON periods Lon of the drive pulses D3 and D4 and to turn off the pair of the third and fourth sub-branch switches S3n and S4n after the ON periods Lon have elapsed, while maintaining a reference switching cycle Lsw between the ON start time of each drive pulse D1, D2 and the ON start time of the drive pulse D3, D4 adjacent to the corresponding drive pulse D1, D2, 3. every three reference switching cycles expressed as (3x Lsw), turn on a pair of the fifth and sixth sub-branch switches S5n and S6n during the respective identical ON periods Lon of the drive pulses D5 and D6 and turn off the pair of the fifth and sixth sub-branch switches S5n and S6n after the elapse of the ON periods Lon, while maintaining a reference switching cycle Lsw between the ON start time of each drive pulse D3, D4 and the ON start time of the drive pulse D5, D6 adjacent to the corresponding drive pulse D3, D4.

[0145] In other words, the control device 30 switches on the pair, i.e. the first group, of the first and second sub-branch switches S1n and S2n, the pair, i.e. the second group, of the third and fourth sub-branch switches S3n and S4n and the pair, i.e. the third group, of the fifth and sixth sub-branch switches S5n and S6n alternately every three reference switching cycles (3x Lsw) so that the ON periods of the first group, the first and second sub-branch switches S1n and S2n, the ON periods of the second group, the third and fourth sub-branch switches S3n and S4n and the ON periods of the third group, the fifth and sixth sub-branch switches S5n and S6n are not overlapped with each other.It should be noted that the ON period for the first group of the first and second sub-branch switches S1n and S2n, the ON period for the second group of the third and fourth sub-branch switches S3n and S4n, and the ON period for the third group of the fifth and sixth sub-branch switches S5n and S6n are set to be identical to each other, for example.

[0146] Each of the first and second embodiments is configured such that the minimum number of sub-branch switches selected as at least one drive target switch is set to one, but it may be set to two or more provided that the number of sub-branch switches is two or more.

[0147] According to Fig. 7, the ON period of one of the first and second sub-branch switches S1n and S2n in the first group can be set to be shorter than the ON period of the other thereof. This modification also allows a current based on the power source PS to be distributed to flow through both of the first and second sub-branch switches S1n and S2n while the first and second sub-branch switches S1n and S2n are both in the ON state. This therefore reduces the level of current flowing through the first and second switches S1n and S2n, resulting in a lower conduction loss of each of the first and second sub-branch switches S1n and S2n.

[0148] Likewise, according to Fig. 7 the ON period of one of the third and fourth sub-branch switches S3n and S4n in the second group is set to be shorter than the ON period of the other thereof.

[0149] The temperature sensor 20 is provided for the sub-branch switch S1n selected from the first to fourth sub-branch switches S1n to S4n, but the present disclosure is not limited thereto. Specifically, first to fourth temperature sensors may be provided for the respective first to fourth sub-branch switches S1n to S4n. According to this modification, the control device 30 may select the highest temperature of the temperatures of the first to fourth sub-branch switches S1n to S4n measured by the first to fourth temperature sensors as the switch temperature Tsw1 in each of the Fig. 2 and Fig. Select the drive routines illustrated in 9.

[0150] The temperature sensor 20 may consist of another temperature-sensitive device such as a thermistor.

[0151] The boost converter may be operable to step down an output voltage from the positive and negative output terminals Cop and Con and output the stepped down voltage to the positive and negative input terminals Cip and Cin.

[0152] In particular, the control device 30 can perform a control task in a buck mode to perform ON / OFF control of the first to fourth upper-branch switches S1p to S4p while maintaining the first to fourth lower-branch switches S1n to S4n in the OFF state. This control task in the buck mode causes the bucked voltage to track a target voltage. That is, in the buck mode, the control device 30, when controlling the first to fourth upper-branch switches S1p to S4p, performs one of the Fig. 2 illustrated drive routine and the one in Fig. 9 illustrated drive routine.

[0153] The first to fourth upper-branch switches S1p to S4p and the first to fourth sub-branch switches S1n to S4n constituting the boost converter 10 can be cooled by a coolant circulated in a cooling device (not shown). According to this modification, the controller 30 may acquire the temperature of the coolant as a temperature parameter indicating the temperature of one of the first to fourth sub-branch switches S1n to S4n, instead of the switch temperature Tsw1; the temperature of the coolant has a positive correlation with the temperature of the first sub-branch switch S1n.Similarly, the controller 30 may acquire the flow rate of the coolant as a temperature parameter indicating the temperature of one of the first to fourth sub-branch switches S1n to S4n, instead of the switch temperature Tsw1; the flow rate of the coolant has a negative correlation with the temperature of the first sub-branch switch S1n.

[0154] Each of the first and second embodiments uses the boost converter 10 composed of a plurality of switches as a power converter, but they may use another type of power converter operable to convert an input voltage into a predetermined output voltage, such as an inverter for converting an input DC voltage into a predetermined AC voltage, or a DC-DC buck converter.

[0155] As described above, MOSFETs such as N-channel MOSFETs can be used for the respective switches of the boost converter 10 according to each embodiment. Each of the power conversion systems according to the first and second embodiments can be installed in a machine other than a vehicle.

[0156] As described above, in a drive device for switches connected in parallel, drivers respectively turn the switches on or off. A temperature acquiring device acquires a value of a temperature parameter that correlates with a temperature of at least one of the first and second switches. A selecting device selects at least one of the switches as at least one drive target switch. A driver causes at least one of the drivers to turn on the at least one drive target switch during an ON period and thereafter to turn off the at least one drive target switch in each target switching cycle. The selecting device adjusts the number of selected at least one drive target switch based on the value of the temperature parameter.

Claims

[1] Drive unit for a plurality of switches (S1p-S4p, S1n-S4n) connected in parallel, the drive unit comprising: a large number of drivers (41-44; 61-64) configured to turn the respective switches on or off, a temperature procurement device (30a) configured to procure a value of a temperature parameter that correlates with a temperature of at least one of the switches, a selection device (30b) which is configured to select at least one of the switches (S1p-S4p, S1n-S4n) as at least one drive target switch, and a drive control device (30c) configured to cause at least one of the drivers (41-44; 61-64): to switch on the at least one drive target switch for a predetermined ON duration and then to switch off the at least one drive target switch in each target switching cycle, wherein the target switching cycle is defined as a product of a reference switching cycle and the number of selected at least one drive target switch, wherein the selection device (30b) is configured to adjust the number of selected at least one drive target switches according to the value of the temperature parameter, wherein the selection device (30b) is configured: to determine whether the value of the temperature parameter is higher than a temperature threshold value, and to increase the number of selected at least one drive target switch if it is determined that the value of the temperature parameter is higher than the temperature threshold, and wherein the switches (S1p-S4p, S1n-S4n) have at least first, second, third and fourth switches that are connected in parallel to each other, and which at least the first, second, third and fourth switches are divided into a first group of the first and second switches and a second group of the third and fourth switches, the drivers (41-44; 61-64) must include at least the first, second, third and fourth drivers, the selection device (30b) is configured when it is determined that the value of the temperature parameter is higher than the temperature threshold value, while the number of selected at least one drive target switch has reached an upper limit: to select the first and second switches of the first group as the first and second target drive switches and the third and fourth switches of the second group as the third and fourth target drive switches, wherein the first to fourth target drive switches constitute the at least one target drive switch, wherein the target switching cycle is defined as the product of the reference switching cycle and the number of selected switches in each of the first and second groups, and the drive control unit (30c) is configured: to cause each of the first and second drivers to: to switch on the corresponding first and second drive target switches during a corresponding first and second ON duration as the ON duration and then to switch off the corresponding first and second drive target switches in each target switching cycle, and to cause each of the third and fourth drivers to: to switch on the corresponding third and fourth drive target switches during a corresponding predetermined third and fourth ON duration as the ON duration and then to switch off the corresponding third and fourth drive target switches in each target switching cycle, while each of the first and second ON durations of the first group does not overlap with each of the third and fourth ON durations of the second group. [2] Drive unit for a plurality of switches (S1p-S4p, S1n-S4n) connected in parallel, the drive unit comprising: a large number of drivers (41-44; 61-64) configured to turn the respective switches on or off, a temperature procurement device (30a) configured to procure a value of a temperature parameter that correlates with a temperature of at least one of the switches, a selection device (30b) which is configured to select at least one of the switches (S1p-S4p, S1n-S4n) as at least one drive target switch, and a drive control device (30c) configured to cause at least one of the drivers (41-44; 61-64): to switch on the at least one drive target switch for a predetermined ON duration and then to switch off the at least one drive target switch in each target switching cycle, wherein the target switching cycle is defined as a product of a reference switching cycle and the number of selected at least one drive target switch, wherein the selection device (30b) is configured to adjust the number of selected at least one drive target switches according to the value of the temperature parameter, wherein the selection device (30b) is configured: to determine whether the value of the temperature parameter is higher than a temperature threshold value, and to increase the number of selected at least one drive target switch if it is determined that the value of the temperature parameter is higher than the temperature threshold, and wherein the selection device (30b) is configured: to determine whether the value of the temperature parameter is lower than a reference temperature, where the reference temperature is set such that it is lower than the temperature threshold, and to reduce the number of selected at least one drive target switch when determining that the value of the temperature parameter is equal to or lower than the reference temperature, wherein the switches (S1p-S4p, S1n-S4n) have at least first, second, third and fourth switches that are connected in parallel to each other, and which at least the first, second, third and fourth switches are divided into a first group of the first and second switches and a second group of the third and fourth switches, the drivers (41-44; 61-64) must include at least the first, second, third and fourth drivers, the selection device (30b) is configured when it is determined that the value of the temperature parameter is higher than the temperature threshold value, while the number of selected at least one drive target switch has reached an upper limit: to select the first and second switches of the first group as the first and second target drive switches and the third and fourth switches of the second group as the third and fourth target drive switches, wherein the first to fourth target drive switches constitute the at least one target drive switch, wherein the target switching cycle is defined as the product of the reference switching cycle and the number of selected switches in each of the first and second groups, and the drive control unit (30c) is configured: to cause each of the first and second drivers to: In each target switching cycle, the corresponding first and second drive target switches are switched on for a corresponding ON duration of the first and second ON durations, and then the corresponding first and second drive target switches are switched off. to cause each of the third and fourth drivers to: In each target switching cycle, the corresponding third and fourth drive target switches are switched on during a corresponding predetermined third and fourth ON duration as the ON duration, and then the corresponding third and fourth drive target switches are switched off, while each of the first and second ON durations of the first group does not overlap with each of the third and fourth ON durations of the second group. [3] Drive unit for a plurality of switches (S1p-S4p, S1n-S4n) connected in parallel, the drive unit comprising: a large number of drivers (41-44; 61-64) configured to turn the respective switches on or off, a temperature procurement device (30a) configured to procure a value of a temperature parameter that correlates with a temperature of at least one of the switches, a selection device (30b) which is configured to select at least one of the switches (S1p-S4p, S1n-S4n) as at least one drive target switch, and a drive control device (30c) configured to cause at least one of the drivers (41-44; 61-64): to switch on the at least one drive target switch for a predetermined ON duration and then to switch off the at least one drive target switch in each target switching cycle, wherein the target switching cycle is defined as a product of a reference switching cycle and the number of selected at least one drive target switch, wherein the selection device (30b) is configured to adjust the number of selected at least one drive target switches according to the value of the temperature parameter, wherein: several temperature ranges, which differ from each other, are defined as determination temperature ranges, and the selection device (30b) is configured: periodically perform a determination task that determines one of the temperature ranges to which the value of the temperature parameter belongs, to determine whether one of the temperature ranges to which the value of the temperature parameter being determined in a current determination task belongs is higher than one of the temperature ranges to which the value of the temperature parameter belonging was determined in a previous determination task, to increase the number of at least one selected drive target switch when it is determined that one of the determination temperature ranges to which the value of the temperature parameter being determined in the current determination task belongs is higher than one of the determination temperature ranges to which the value of the temperature parameter being determined in the previous determination task belongs, and to reduce the number of at least one selected drive target switch when it is determined that one of the determination temperature ranges to which the value of the temperature parameter being determined in the current determination task belongs is lower than one of the determination temperature ranges to which the temperature of one of the first and second switches belonging to which the previous determination task belongs, and wherein: the switches (S1p-S4p, S1n-S4n) have at least the first, second, third and fourth switches that are connected in parallel to each other, which at least the first, second, third and fourth switches are divided into a first group of the first and second switches and a second group of the third and fourth switches, the drivers (41-44; 61-64) must include at least the first, second, third and fourth drivers, and an upper limit of the highest temperature range in the specified temperature ranges is defined as the temperature threshold value, the selection device (30b) is configured when it is determined that the value of the temperature parameter is higher than the temperature threshold: to select the first and second switches of the first group as the first and second target drive switches and the third and fourth switches of the second group as the third and fourth target drive switches, wherein the first to fourth target drive switches constitute the at least one target drive switch, wherein the target switching cycle is defined as the product of the reference switching cycle and the number of selected switches in each of the first and second groups, and the drive control unit (30c) is configured: to cause each of the first and second drivers to: in each target switching cycle, switches on the corresponding first and second drive target switches for a corresponding ON duration of the first and second ON durations and then switches off the corresponding first and second drive target switches, to cause each of the third and fourth drivers to: In each target switching cycle, the corresponding third and fourth drive target switches are switched on during a corresponding predetermined third and fourth ON duration as the ON duration, and then the corresponding third and fourth drive target switches are switched off, while each of the first and second ON durations of the first group does not overlap with each of the third and fourth ON durations of the second group. [4] Drive unit according to one of claims 1 to 3, further comprising: a variety of power supply circuits for supplying electrical power to the respective drivers (41-44; 61-64) and a power supply control device configured to cause at least one of the power supply circuits to supply electrical power only to at least one of the drivers (41-44; 61-64) in accordance with the at least one drive target switch, wherein the drive control unit (30c) is configured: to cause at least one of the drivers, to which electrical power is supplied from at least one power supply circuit, to switch the corresponding at least one drive target switch on or off.

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