DC-DC converter

Abstract

DC-DC converter (10), with a DC-DC conversion circuit (20) with a plurality of parallel interconnected unit circuits (20a to 20d), each comprising a switching element (26a to 26d) from the plurality of unit circuits (20a to 20d), a control device (30) which is configured to control the operation of the switching elements (26a to 26d) of the plurality of unit circuits (20a to 20d), and a plurality of temperature sensors (32a to 32d) which are connected to the control unit (30) and are configured to measure the respective temperatures (T1 to T4) of the switching elements (26a to 26d) of the plurality of unit circuits (20a to 20d), wherein the control device (30) is configured to to obtain the respective temperatures (T1 to T4) of the switching elements (26a to 26d) of the plurality of unit circuits (20a to 20d) from the plurality of temperature sensors (32a to 32d), while the control device controls all of the switching elements (26a to 26d) of the plurality of unit circuits (20a to 20d), to determine at least one maintenance target switching element from the switching elements (26a to 26d) of the plurality of unit circuits (20a to 20d) based on the respective temperatures (T1 to T4) of the switching elements (26a to 26d) of the plurality of unit circuits (20a to 20d) such that the at least one maintenance target switching element comprises a switching element whose temperature is the highest among the switching elements (26a to 26d) of the plurality of unit circuits (20a to 20d), and to control at least one non-maintenance target switching element differently from the at least one maintenance target switching element in order to adjust an output current of the DC-DC conversion circuit to a setpoint (Ct), and wherein determining at least one conservation target switching element is determining all of at least one switching element whose temperature is higher by a predetermined value than a lowest temperature among the switching elements (26a to 26d) of the plurality of unit circuits (20a to 20d) than that which comprises at least one conservation target switching element.

Description

Technical field

[0001] The technology revealed herein relates to a DC-DC converter. background

[0002] Japanese patent application disclosure number 2011-19338 (JP 2011-19338A) discloses a DC-DC converter. This DC-DC converter comprises a DC-DC conversion circuit including a plurality of switching elements connected in parallel, a control device that controls the operation of the plurality of switching elements, and a plurality of temperature sensors connected to the control device for measuring the respective temperatures of the plurality of switching elements. The control device activates only a portion of the plurality of control elements to initiate control of the DC-DC conversion circuit and increases the number of switching elements to be activated when the measured temperature of the activated switching element exceeds a threshold.According to such a configuration, the number of switching elements to be controlled can be changed according to the strength of a load, thereby reducing losses in the switching elements (e.g. switching losses) compared to a configuration that always controls all of the switching elements.

[0003] In the aforementioned DC-DC converter, since only a portion of the numerous switching elements can be activated in any given situation, differences in usage frequencies arise among these elements. Normally, deterioration of a switching element and its peripheral structure (hereafter referred to simply as "switching element deterioration") progresses more rapidly with higher usage frequencies. Therefore, when differences in usage frequencies occur among the numerous switching elements, deterioration in some elements may progress earlier, resulting in the premature termination of the DC-DC converter's product life, even though the deterioration of another switching element remains within an acceptable range.In this respect, in the DC-DC converter of the JP 2011-19 338 A, the switching element to be controlled is changed randomly or periodically when a part of the multitude of switching elements is controlled, and this makes it possible to use the multitude of switching elements with the same frequency.

[0004] Further prior art can be found in DE 10 2013 203 830 A1, which describes methods and systems for controlling the operation of a boost converter. The boost converter includes an input, an output, and a plurality of paths that electrically connect the input to the output. The boost converter also includes a plurality of switches arranged along the paths to control the current flow between the input and the output. The system includes a control element. The control element receives a desired current to be delivered to the output. Based at least in part on the desired current, the control element determines which path to use. The control element controls the switches based at least in part on this determination of which path to use.

[0005] Further state of the art can be found in US 2014 / 0223949A1, which describes a control unit for switching an energy supply circuit and a heat pump unit. Further state of the art can be found in US 2011 / 0080151A1, which describes a system and method for multiphase voltage control. Summary

[0006] Manufacturing variations occur in industrial products. A DC-DC converter, which has a multitude of switching elements, is not exempt from manufacturing variations among these elements (including their peripheral structures). This means that even if the numerous switching elements are used with the same frequency, deterioration of the elements due to manufacturing variations will progress at different rates. If the deterioration of one switching element exceeds the permissible range, the product life of the DC-DC converter ends at that stage, even if the deterioration of other switching elements remains within the permissible range.In other words, the product life of the DC-DC converter can be improved if degrees of deterioration among the multitude of switching elements can be made uniform or consistent, regardless of manufacturing variations.

[0007] The present disclosure provides a technique for a DC-DC converter including a plurality of switching elements, in which degrees of degradation among the plurality of switching elements can be made uniform or consistent.

[0008] A DC-DC converter disclosed herein may comprise a DC-DC conversion circuit including a plurality of switching elements connected in parallel, a control device configured to control the operation of the plurality of switching elements, and a plurality of temperature sensors connected to the control device, configured to measure the respective temperatures of the plurality of switching elements.The control device can be configured to obtain the respective temperatures of the plurality of switching elements from the plurality of temperature sensors, while controlling all of the plurality of switching elements, to determine at least one maintenance target switching element from the plurality of switching elements based on the respective temperatures of the plurality of switching elements such that the at least one maintenance target switching element includes a switching element whose temperature is the highest among the plurality of switching elements, and to control at least one non-maintenance target switching element differently from the at least one maintenance target switching element in order to adjust or set an output current of the DC-DC conversion circuit to a setpoint.

[0009] In the aforementioned DC-DC converter, the control unit performs the following steps: determining the temperatures of the plurality of switching elements, identifying at least one maintenance target switching element, and activating at least one non-maintenance target switching element. During the determination phase, the control unit ascertains the temperatures of all the plurality of switching elements while activating all of them. The temperatures obtained in this process correspond to the degrees of actual deterioration of the respective switching elements, with the temperature of the switching element being higher for those with a greater degree of deterioration. During the identification phase, the control unit selects the at least one maintenance target switching element from the plurality of switching elements based on the temperatures of all the switching elements.If at least one maintenance target switching element is determined in this process, this maintenance target switching element includes at least one switching element whose temperature is the highest among the multitude of switching elements. That is, the switching element with a particularly high degree of deterioration among the multitude of switching elements is determined as the maintenance target switching element. Then, when activated, the control device activates the at least one non-maintenance target switching element among the multitude of switching elements, which is different from the at least one maintenance target switching element, in order to set or adjust the output current of the DC-DC conversion circuit to the setpoint. That is, the control device maintains or preserves the current.The switching element with the highest degree of degradation is protected, and only the switching element with a lower degree of degradation is activated to control the operation of the DC-DC conversion circuit. This configuration reduces the frequency of use for the switching element with the higher degree of degradation while increasing the frequency of use for the switching element with the lower degree of degradation, thus ensuring a uniform degree of degradation across the multiple switching elements. Brief description of the drawings Fig. Figure 1 shows an energy system 100 of a fuel cell vehicle. Fig. Figure 2 shows an example of control signals G1 to G4 to be output by a control unit 30. Fig. Figure 3 shows a pulse width W of the control signal G1 and a current flowing into a choke coil 22a. Fig. Figure 4 shows the pulse width W of the control signal G1 and the current flowing into the choke coil 22a. The pulse width W in Fig. 4 is wider than the pulse width W in Fig. 3. Fig. Figure 5 is a flow diagram showing the flow of an initial operation through the control device 30. Fig. Figure 6 is a flow diagram showing the flow of continuous operation through the control device 30. Fig. Table 7 shows examples of temperatures T1 to T4 of switching elements 26a to 26d. Fig. Figure 8 shows changes in the temperatures T1 to T4 of the switching elements 26a to 26d caused by aging in the present embodiment. Fig. Figure 9 shows changes in the temperatures T1 to T4 of the switching elements 26a to 26d caused by aging in a comparative example. Detailed description

[0010] Representative non-limiting examples of the present disclosure are now described in more detail with reference to the attached drawings. This detailed description is intended only to inform a person skilled in the art of further details for carrying out preferred aspects of the present teachings and is not intended to limit the scope of the claims. Furthermore, each of the additional features and teachings disclosed below can be used separately or in combination with other features and teachings to provide improved DC-DC converters.

[0011] Furthermore, combinations of features and steps disclosed in the following detailed description are not necessary to carry out the present disclosure in the broadest sense and are instead taught merely to describe, in particular, representative examples of the present disclosure. Moreover, various features of the representative examples described above and below, as well as of the various independent and dependent claims, can be combined in ways not specifically and explicitly listed to provide additional useful embodiments of the present teachings.

[0012] It is intended that all features disclosed herein and / or in the claims are disclosed separately and independently of one another for the purposes of the original written disclosure and for the purposes of limiting the claimed subject matter, irrespective of the combinations of features in the exemplary embodiments and / or the claims. Furthermore, it is intended that all ranges of values ​​or indications of groups of units disclose every possible intermediate value or unit for the purposes of the original written disclosure and for the purposes of limiting the claimed subject matter.

[0013] A DC-DC converter 10 (hereinafter referred to as converter 10) of an exemplary embodiment is described with reference to the drawings. Fig. Figure 1 shows an energy system 100 for a fuel cell vehicle, which is an application example of the converter 10. In particular, the converter 10 is not limited to the energy system 100 for the fuel cell vehicle, but can be applied to various other energy systems and energy conversion devices.

[0014] First, the energy system 100 is described. The energy system 100 comprises a fuel cell battery 102, the converter 10, an inverter 106, and a motor 108. The fuel cell battery 102 is a primary energy source in the energy system 100 and provides DC energy through the reaction of hydrogen and oxygen. The fuel cell battery 102 is electrically connected to the motor 108 via the main relay 104, the converter 10, and the inverter 106. The main relay 104 is a relay with contacts that electrically connects and disconnects the fuel cell battery 102 and the converter 10.

[0015] Converter 10 is a step-up DC-DC converter that increases the voltage of the DC energy from the fuel cell battery 102 and supplies it to inverter 106. Details of converter 10 are given below. Inverter 106 is a three-phase inverter including a variety of switching elements and converts the DC energy from converter 10 into three-phase AC energy, which it supplies to motor 108. Inverter 106 can freely adjust the voltage and frequency of the three-phase AC energy supplied to motor 108. Motor 108 is a drive machine for the energy system 100 and is connected to the drive wheels of the fuel cell vehicle. Motor 108 is driven by the three-phase AC energy from inverter 106. Accordingly, in the energy system 100, the energy is supplied from the fuel cell battery 102 to the motor 108 by means of the main relays 104, the converter 10, and the inverter 106.

[0016] The energy system 100 further comprises a second DC-DC converter 110 and a battery 112. The battery 112 is a second energy source in the energy system 100 and comprises a number of rechargeable battery cells (for example, lithium-ion cells). The battery 112 is electrically connected to the inverter 106 and the converter 10 via the second DC-DC converter 110. The second DC-DC converter 110 is a step-down-boost DC-DC converter and can increase the voltage of DC energy from the battery 112 and supply it to the inverter 106. Furthermore, the second DC-DC converter 110 can decrease the DC energy from the inverter 106 or the converter 10 and supply it to the battery 112. The energy system 100 can supply energy from battery 112 to motor 108 instead of, or in addition to, the energy from fuel cell battery 102, and thus power motor 108. Battery 112 is primarily charged by energy from fuel cell battery 102.Additionally, the energy system 100 can charge the battery 112 using energy generated by the motor 108, for example, when the fuel cell vehicle decelerates or brakes.

[0017] Next, the converter 10 is described. The converter 10 comprises a DC-DC conversion circuit 20 (hereinafter referred to as conversion circuit 20), a control device 30, a plurality of temperature sensors 32a to 32d, and a plurality of current sensors 34a to 34d. The conversion circuit 20 comprises a plurality of unit circuits 20a to 20d connected in parallel. The plurality of unit circuits 20a to 20d includes a first unit circuit 20a, a second unit circuit 20b, a third unit circuit 20c, and a fourth unit circuit 20d. The unit circuits 20a to 20d have an identical structure, and each of the unit circuits 20a to 20d comprises a circuit structure that functions as a step-up DC-DC converter.

[0018] For example, the first unit circuit 20a comprises an inductor 22a, a diode 24a, and a switching element 26a. One end of the inductor 22a is electrically connected to a positive terminal of the fuel cell battery 102 via the main relay 104. Another end of the inductor 22a is electrically connected to an anode of the diode 24a and to an end of the switching element 26a. A cathode of the diode 24a is electrically connected to a high-potential side (upper arm) of the inverter 106, and another end of the switching element 26a is connected to a low-potential side (lower arm) of the inverter 106. Furthermore, the other end of the switching element 26a is connected to a negative terminal of the fuel cell battery 102 via the main relay 104. According to this configuration, the first unit circuit 20a can increase or raise the voltage of the DC energy from the fuel cell battery 102 by intermittently or by switching the switching element 26a.is switched on intermittently and can supply the increased or boosted energy to the inverter 106.

[0019] Similarly, the second to fourth unit circuits 20b to 20d each comprise choke coils 22b to 22d, diodes 24b to 24d, and switching elements 26b to 26d, and have the same configuration as the first unit circuit 20a. Furthermore, the respective second to fourth unit circuits 20b to 20d can increase the voltage of the DC energy from the fuel cell battery 102 by intermittently switching on the switching elements 26b to 26d, and can supply the increased energy to the inverter 106. In this disclosure, "controlling a switching element" typically means switching the switching element on intermittently.

[0020] In the present embodiment, the conversion circuit 20 comprises the four unit circuits 20a to 20d; however, the conversion circuit 20 may simply need to comprise at least two unit circuits. The technology disclosed herein can be suitably applied to various DC-DC converters with two or more switching elements connected in parallel. Hereinafter, the switching element 26a of the first unit circuit 20a may be referred to as a first switching element 26a. Similarly, the switching elements 26b to 26d of the second to fourth unit circuits 20b to 20d may each be referred to as a second switching element 26b, a third switching element 26c, and a fourth switching element 26d, respectively.Although the switching elements 26a to 26d are not particularly restricted, they can be MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) or IGBTs (Insulated-Gate Bipolar Transistors).

[0021] The array of temperature sensors 32a to 32d measures the respective temperatures of the array of switching elements 26a to 26d. The array of temperature sensors 32a to 32d comprises a first temperature sensor 32a, a second temperature sensor 32b, a third temperature sensor 32c, and a fourth temperature sensor 32d. The first temperature sensor 32a is located near (or integrated with) the first switching element 26a and measures a temperature T1 of the first switching element 26a. Similarly, the second to fourth temperature sensors 32b to 32d each measure temperatures T2 to T4 of the second to fourth switching elements 26b to 26d. The array of temperature sensors 32a to 32d is connected to the control unit 30, and the temperatures T1 to T4 measured by the array of temperature sensors 32a to 32d are communicated to the control unit 30.In particular, configurations of the multitude of temperature sensors 32a to 32d are not particularly limited.

[0022] The plurality of current sensors 34a to 34d measures the currents flowing into the plurality of inductors 22a to 22d. The plurality of current sensors 34a to 34d comprises a first current sensor 34a, a second current sensor 34b, a third current sensor 34c, and a fourth current sensor 34d. The first current sensor 34a is located near the inductor 22a of the first unit circuit 20a and measures a current value C1 flowing into the inductor 22a. Similarly, the second to fourth current sensors 34b to 34d measure current values ​​C2 to C4 flowing into the inductors 22b to 22d of the second to fourth unit circuits 20b to 20d. The multitude of current sensors 34a to 34d is connected to the control unit 30, and the current values ​​C1 to C4 measured by the multitude of current sensors 34a to 34d are communicated to the control unit 30.The control unit 30 can detect or identify an instantaneous current flowing into each of the choke coils 22a to 22d, and an average current thereof and a total output current of the conversion circuit 20 based on the measured current values ​​C1 to C4.

[0023] The control unit 30 controls the output current of the conversion circuit 20 by controlling the operation of the plurality of switching elements 26a to 26d. The control unit 30 outputs control signals G1 to G4 for the plurality of switching elements 26a to 26d based on a setpoint Ct of the output current. Although this is only an example, the setpoint Ct of the output current can be communicated by a main control unit of the fuel cell vehicle. The control signal G1 is a signal for switching the first switching element 26a on and off. Similarly, the control signals G2 to G4 are signals for switching the second to fourth switching elements 26b to 26d on and off. The control signals G1 to G4, which the control unit 30 is to output, are input at the respective switching elements 26a to 26d.

[0024] Fig. Figure 2 shows an example of the control signals G1 to G4. As in Fig. As shown in Figure 2, the control device 30 periodically outputs high-level pulse signals (H) as the control signals G1 to G4. The switching elements 26a to 26d are switched on when the control signals G1 to G4 are at the high level (H), and the switching elements 26a to 26d are switched off when the control signals G1 to G4 are at a low level (L). Therefore, the respective switching elements 26a to 26d are switched on intermittently, i.e., with interruptions. For the four control signals G1 to G4, although a cycle period P of the pulse signals is constant, a phase difference of one-quarter of a cycle period (i.e., P / 4) is provided between them. A pulse width W of each of the control signals G1 to G4 corresponds to the output current of the conversion circuit 20. That is, the output current of the conversion circuit 20 is higher for larger pulse widths W.The control unit 30 changes the pulse widths W of the control signals G1 to G4 based on the current values ​​C1 to C4 measured by the multitude of current sensors 34a to 34d in such a way that the output current of the conversion circuit 20 is controlled to the setpoint Ct.

[0025] A relationship between the control signal G1 and the current flowing into the choke coil 22a of the first unit circuit 20a is established with reference to Fig. 3 and Fig. 4 described. In particular, similar relationships apply to the interactions between the control signals G2 to G4 and the currents flowing into the choke coils 22b to 22d of the second to fourth unit circuits 20b to 20d. As in Fig. 3 and Fig. As shown in Figure 4, while the control signal G1 is at the high level (H), the current C1 flowing into the inductor 22a gradually increases because the first switching element 26a is switched on. During this period A, the inductor 22a is charged with energy using the energy or power from the fuel cell battery 102. Subsequently, when the control signal G1 switches to the low level, the current flowing into the inductor 22a gradually decreases because the switching element 26a is switched off. During this period B, the energy charged into the inductor 22a is supplied to the inverter 106 along with the energy or power from the fuel cell battery 102. As described above, when the switching element 26a is periodically switched on and off, the current flowing into the inductor 22a periodically changes its magnitude.

[0026] In Fig. 3 and Fig. 4. The pulse width W of the control signal G1 is different. As in Fig. As shown in Figure 3, since the current flowing into the choke coil 22a is relatively small when the pulse width W is relatively narrow, the current flows intermittently, i.e., not continuously, into the choke coil 22a. Such a condition is referred to herein as the interrupted operating mode. On the other hand, as shown in Figure 3, the current flows intermittently, i.e., not continuously. Fig. Figure 4 shows that, since the current flowing into the choke coil 22a is relatively large when the pulse width W is relatively wide, the current flows continuously into the choke coil 22a. Such a state is hereafter referred to as continuous operating mode or uninterrupted operating mode.

[0027] Next, a flow of processes carried out by the control unit 30 will be described with reference to Fig. 5 and Fig. 6 described. The control unit 30 performs an initial operation, which is described in Fig. Figure 5 shows what happens when a user starts using the fuel cell vehicle and then switches to continuous operation as shown in Figure 5. Fig. 6 shown. In step S2 of the Fig. 5. When the user switches on a main switch (not shown) of the fuel cell vehicle (Yes), the main relays 104 of the energy system 100 are switched on in a subsequent step S4. As a result, the conversion circuit 20 is electrically connected to the fuel cell battery 102, which is the energy source. The operation of the main relays 104 can be controlled by the control unit 30 of the converter 10, or by another control unit provided in the fuel cell vehicle. At the same time, a warm-up operation of the fuel cell battery 102 is also initiated.

[0028] Proceeding to step S6, the control unit 30 sets a setpoint Ct0 for the output current of the conversion circuit 20. The setpoint Ct0 set in this step S6 is used only during initial operation and is pre-stored in the control unit 30. In particular, the setpoint Ct0 can be received by the other control unit provided in the fuel cell vehicle. Proceeding to step S8, the control unit 30 then activates all of the multiple switching elements 26a to 26d to control the output current of the conversion circuit 20 to the setpoint Ct0. In this embodiment, the four switching elements 26a to 26d are activated with the same duty cycle, so that the average current flowing into each of the inductors 22a to 22d becomes 1 / 4 of the setpoint Ct0 and is identical among them.Furthermore, the average current flowing into each of the switching elements 26a to 26d is also the same among them.

[0029] Continuing from step S10, the control unit 30 next determines whether the current flowing into each of the choke coils 22a to 22d is in interrupted operating mode (see Fig. 3) is in or out of the open-circuit mode based on the current values ​​C1 to C4 measured by the current sensors 34a to 34d. Furthermore, if in open-circuit mode (Yes), the control unit 30 proceeds to step S12. If not in open-circuit mode (No), the control unit 30 returns to step S6 to reset the setpoint Ct0 and decreases the setpoint Ct0. The processes from step S6 to step S10 are repeated until the current flowing into each of the chokes 22a to 22d is in open-circuit mode. As a result, over time, as the control unit 30 progresses to the subsequent step S12, it controls all of the plurality of switching elements 26a to 26d, and the currents flow in open-circuit mode into all of the chokes 22a to 22d. The average current flowing into the multitude of switching elements 26a to 26d is adjusted to a relatively small value, oradjusted by setting a smaller value than the setpoint Ct0 of the output current when the current flows into each of the choke coils 22a to 22d in the interrupted operating mode.

[0030] Progressing to step S12, the control device 30 attains or procures the temperatures T1 to T4 of the switching elements 26a to 26d. As a result, the control device 30 reaches the respective temperatures T1 to T4 of the switching elements 26a to 26d while all of the switching elements 26a to 26d are being controlled. The processes from step S6 to step S12 are an example of attaining the respective temperatures as described in the claims. In the conversion circuit 20, a temperature increase during electrical conduction of the switching elements 26a to 26d increases as the deterioration of the switching elements 26a to 26d and their peripheral structures (such as an adjacent solder layer) increases. Therefore, the temperature T1 of the first switching element 26a, which is reached in this step S12, corresponds to a degree of actual deterioration in the first switching element 26a.Similarly, the respective temperatures T2 to T4 correspond to the degrees of actual deterioration in the second to fourth switching elements 26b to 26d.

[0031] The temperatures T1 to T4 of the switching elements 26a to 26d can depend not only on the degree of deterioration in the switching elements 26a to 26d, but also on the magnitudes of the currents flowing into the switching elements 26a to 26d and the switching losses generated in the switching elements 26a to 26d. That is, unless the currents flowing into the respective switching elements 26a to 26d are equal, a temperature difference corresponding to a difference in the currents will occur at temperatures T1 to T4 of the switching elements 26a to 26d. Furthermore, unless the switching frequencies of the respective switching elements 26a to 26d are equal, a temperature difference corresponding to a difference in the switching frequencies will occur at temperatures T1 to T4 of the switching elements 26a to 26d.Regarding this point, in the aforementioned step S12, all of the switching elements 26a to 26d are switched with the same duty cycle, and the average currents and switching frequencies are the same for all of the switching elements 26a to 26d. Therefore, the degrees of deterioration of the switching elements 26a to 26d are more accurately reflected by the temperatures T1 to T4 obtained in step S12 as described above.

[0032] Furthermore, the temperatures T1 to T4 of the switching elements 26a to 26d also depend on a difference in heat dissipation efficiency that may exist among the switching elements 26a to 26d, such as a difference in positional relationships between each of the switching elements 26a to 26d and a cooler. For example, cooling water flows into the cooler, and the temperature of the cooling water is higher in an area located on the downstream side of the cooling water flow than in an area located on the upstream side. Due to such a temperature difference in the cooling water, the temperature difference between temperatures T1 to T4 of the plurality of switching elements 26a to 26d can be generated.Regarding this point, in the aforementioned step S12, the setpoint Ct0 of the output current is adjusted to a smaller value when the currents flowing into the respective choke coils 22a to 22d enter the open-circuit mode. As a result, the amount of heat generated at each of the switching elements 26a to 26d becomes relatively small, and consequently, the increase in the temperature of the cooling water flowing into the radiator also becomes relatively small. Therefore, the aforementioned influence caused by the temperature difference in the cooling water is suppressed, and the temperatures T1 to T4 obtained in step S12 more accurately reflect the degree of deterioration of the switching elements 26a to 26d.

[0033] In the subsequent step S14, the control unit 30 establishes or creates a sequence of temperatures T1 to T4 for the plurality of switching elements 26a to 26d. As an example, as shown in Fig. Figure 7 shows that the respective temperatures T1 to T4 of the first to fourth switching elements 26a to 26d were 120, 113, 108, and 103 °C, respectively. In this case, the temperature T1 of the first switching element 26a is the highest, the temperature T2 of the second switching element 26b is the second highest, the temperature T3 of the third switching element 26c is the third highest, and the temperature T4 of the fourth switching element 26d is the lowest. In particular, SW1 to SW4 denote in Fig. 7 each the first to fourth switching elements 26a to 26d.

[0034] In a subsequent step S16, the control unit 30 determines whether the temperature difference between the highest temperature (T1 = 120 °C) and the lowest temperature (T4 = 103 °C) is equal to or greater than a predetermined value. Although this is merely an example, the predetermined value in this embodiment is set to 5 °C. In particular, this predetermined value could be set arbitrarily within a range, for example, from 1 to 10 °C. If the temperature difference is equal to or greater than the predetermined value (Yes), the control unit 30 proceeds to step S18. If the temperature difference is less than the predetermined value (No), the process described in step S16 is interrupted. Fig. The initial operation shown in step 5 is completed, and the control unit 30 proceeds to the step shown in Fig. The continuous operation shown in section 6 continues.

[0035] In a subsequent step S18, the control unit 30 determines the switching element with the highest temperature among the plurality of switching elements 26a to 26d as a maintenance target switching element and stops the operation of this switching element. For example, in the Fig. In the example shown in Figure 7, since the temperature T1 of the first switching element 26a is the highest, the first switching element 26a is designated as the maintenance target switching element. Afterwards, the control device 30 returns to step S16 and repeats the processes of steps S16 and S18 for the remaining switching elements. For example, in the example shown in Figure 7, the temperature T1 of the first switching element 26a is determined as the maintenance target switching element. Fig. In the example shown in Figure 7, a temperature difference (+10 °C) between the second highest temperature T2 and the lowest temperature T4 is greater than the predetermined value (5 °C), thereby determining the second switching element 26b as the maintenance target switching element. The third switching element 26c is likewise determined as the maintenance target switching element when the processes of steps S16 and S18 are repeated further. As above, in the processes of steps S14 to S18, the maintenance target switching element or elements are determined from the plurality of switching elements 26a to 26d based on the respective temperatures T1 to T4 of the plurality of switching elements 26a to 26d. The processes of steps S14 to S18 are an example of determining at least one maintenance target switching element as described in the claims.

[0036] The aforementioned in Fig. The initial operation described in section 5 is completed within a short period of time (e.g., 1 second) after the user switches on the main switch of the fuel cell vehicle. Afterwards, the control unit 30 switches to the mode described in section 5. Fig. 6 shown continuous operation. In step S22 of the Fig. In step 6, the control unit 30 obtains the setpoint Ct of the output current of the conversion circuit 20. The setpoint Ct is determined, for example, based on accelerator operation by the user, a vehicle state, and the like, by a main control unit (not shown) of the fuel cell vehicle. Next, in step S24, the control unit 30 determines a number of switching elements to be controlled based on the setpoint Ct obtained in step S22. Although this is only an example, if the setpoint Ct is relatively small, the number of switching elements to be controlled is determined to be one or two, and if the setpoint Ct is relatively large, the number of switching elements to be controlled is determined to be three or four. That is, the number of switching elements to be controlled increases as the setpoint Ct becomes larger.

[0037] Next, in step S26, a determination is made as to whether the number of switching elements to be controlled, as determined in step S24, is equal to or less than a certain number of non-maintenance target switching elements. A non-maintenance target switching element is a switching element that has not been determined as the maintenance target switching element from among the plurality of switching elements 26a to 26d. If the number of switching elements to be controlled is equal to or less than the number of non-maintenance target switching elements, the control device 30 proceeds to step S28 and controls only the non-maintenance target switching elements to control the output current of the conversion circuit 20 at which the setpoint Ct is to be (regulation or feedback control). The process of step S28 is an example of controlling at least one non-maintenance target switching element as described in the claims.On the other hand, if the number of switching elements to be controlled exceeds the number of non-maintenance target switching elements, the control device 30 proceeds to step S30. In step S30, the control device 30 controls not only the non-maintenance target switching elements but also one, more, or all of the switching elements 26a to 26d, including the maintenance target switching elements, in order to control the output current of the conversion circuit 20 to be at the setpoint Ct (regulation or feedback control). Therefore, by determining the maintenance target switching element, it is possible to avoid sacrificing the performance of the conversion circuit 20. The process of step S30 is an example of controlling both the at least one maintenance target switching element and the at least one non-maintenance target switching element to set or adjust the output current of the DC-DC conversion circuit to the setpoint, as described in the claims.The control unit 30 repeatedly executes the in . Fig. 6 continuous operation shown, while the main relays 104 are switched on.

[0038] As described above, in the converter 10 of the present embodiment, initial operation is carried out to determine the maintenance target switching element before continuous operation. During initial operation, the control unit 30 reaches the temperatures T1 to T4 of the plurality of switching elements 26a to 26d while activating all of the plurality of switching elements 26a to 26d (steps S8 to S12 in Fig. 5) The temperatures T1 to T4 correspond to the actual degrees of deterioration of the switching elements 26a to 26d, and the temperatures T1 to T4 of the switching elements 26a to 26d are higher for greater degrees of deterioration in the switching elements 26a to 26d. In particular, the deterioration of the switching elements 26a to 26d referred to here is not only the deterioration of the switching elements 26a to 26d themselves, but also the deterioration of peripheral structures related to the switching elements 26a to 26d, such as a solder layer adjacent to the switching elements 26a to 26d. For example, if a break or crack occurs in the solder layer adjacent to the switching elements 26a to 26d, the heat dissipation efficiency of the switching elements 26a to 26d via the solder layer deteriorates.

[0039] During initial operation, the control unit 30 further determines the maintenance target switching element from the plurality of switching elements based on the temperatures T1 to T4 of the plurality of switching elements 26a to 26d (steps S14 to S18 in Fig. 5) In these processes, the switching element with the highest temperature is determined as the maintenance target switching element if the temperature difference between the switching element with the highest temperature and the switching element with the lowest temperature is equal to or greater than the predetermined value. In particular, by the control device 30 of the present embodiment, which repeats these processes with respect to the remaining switching elements, all of the switching elements with a temperature that is equal to or greater than the predetermined value higher than that of the switching element with the lowest temperature are determined as the maintenance target switching element.According to such a configuration, the frequency of use of the non-maintenance-target switching elements is higher by providing a greater number of switching elements than the maintenance-target switching elements, and the degrees of deterioration can be made uniform among the multitude of switching elements in an early phase of the product life. However, the control device 30 does not necessarily have to perform steps S14 to S18 in . Fig. Repeat step 5, and only the switching element with the highest temperature can be determined as the maintenance target switching element.

[0040] During continuous operation following initial operation, the control unit 30 activates the non-maintenance target switching elements, in addition to the maintenance target switching elements, from the plurality of switching elements 26a to 26d in order to control the output current of the conversion circuit 20, at which the setpoint Ct is to be (steps S22 and S28 in Fig. 6) That is, the control device 30 maintains, protects, or preserves the switching element with the particularly high degree of deterioration and uses only the switching elements with lower degrees of deterioration to control the operation of the conversion circuit 20. As a result, the frequency of use of the switching element with the higher degree of deterioration is reduced, while the frequency of use of the switching elements with the lower degree of deterioration is increased, resulting in a standardization or uniformity of deterioration among the multitude of switching elements.In particular, if the use of the non-maintenance target switching elements alone is insufficient to bring the output current of the conversion circuit 20 to its setpoint Ct, the control device 30 can control one or more or all of the plurality of switching elements 26a to 26d including the maintenance target switching elements (steps S24, S26 and S30 in . Fig. 6).

[0041] In the converter 10 of the present embodiment, the initial operation of a determination of the maintenance target switching element (see Fig. 5) is carried out upon activation of the energy system 100. Since the determination of the maintenance target switching element is based on the temperatures T1 to T4 of the plurality of switching elements 26a to 26d, there is a risk that the maintenance target switching element cannot be correctly determined if a temperature difference is generated among the plurality of switching elements 26a to 26d before initial operation. In this regard, at the time of activation of the energy system 100, the temperatures T1 to T4 of all the switching elements 26a to 26d are normally sufficiently low, and a significant temperature difference will not exist among them. Therefore, the timing of activation of the energy system 100 allows for a correct determination of the maintenance target switching element.However, the process of determining the conservation target switching element is not limited to taking place during the activation of energy system 100 and can be carried out at another suitable time.

[0042] Next, the effects of the converter 10 of the present embodiment will be discussed with reference to Fig. 8 and Fig. 9 described. Fig. Figure 8 schematically shows changes in the temperatures T1 to T4 of the switching elements 26a to 26d caused by aging during continuous operation of the converter 10 of the present embodiment. Fig. Figure 9 schematically shows changes in the temperatures T1 to T4 of the switching elements 26a to 26d caused by aging in a comparative example. In the case of the Fig. In the comparative example shown in Figure 9, all of the switching elements 26a to 26d are used with equal frequency, without determining any conservation target switching element. Fig. 8 and Fig. Figure 9 shows a vertical axis T representing the strengths / heights or extents of temperatures T1 to T4, and a horizontal axis Y representing time. Furthermore, a graph of the Fig. 9 in Fig. 8 shown by dashed lines. As the comparative example of the Fig. Figure 9 shows that the temperatures T1 to T4 of the switching elements 26a to 26d rise at different rates, even though all of the switching elements 26a to 26d are used with the same frequency. This is because product quality variations among the conversion circuits 20, which are industrial products, cannot be avoided, and product quality variations also exist among the multitude of switching elements 26a to 26d (including their peripheral structures). Furthermore, in the Fig. In the comparative example shown in Figure 9, the temperature T4 of the fourth switching element 26d is a permissible limit temperature Tx at a time Y1. In this case, the product life of the conversion circuit 20 is terminated, even though the temperatures T1 to T3 of the other switching elements 26a to 26c are still lower than the permissible limit temperature Tx.

[0043] On the other hand, in the present case Fig.In the embodiment shown in Figure 8, the first to third switching elements 26a to 26c are initially designated as the maintenance target switching elements. As a result, the frequency of use of the first to third switching elements 26a to 26c is reduced, and their deterioration is thereby suppressed. On the other hand, the deterioration of the fourth switching element 26d is increased because its frequency of use is increased. Subsequently, when the temperature T4 of the fourth switching element 26d approaches the temperature T3 of the third switching element 26c, the third switching element 26c is no longer designated as the maintenance target switching element. As a result, the third switching element 26c deteriorates at a comparable rate to the fourth switching element 26d because its frequency of use is increased.Similarly, the second switching element 26b is no longer designated as the maintenance target switching element, after which the first switching element 26a is no longer designated as the maintenance target switching element. In this phase, the degrees of deterioration across the multitude of switching elements 26a to 26d are made uniform. As a result, the product life of the conversion circuit 20 is improved or increased from time Y1 to time Y2.

[0044] The disclosure described above provides the following technical items. A DC-DC converter (10) is disclosed herein. The DC-DC converter can comprise a DC-DC conversion circuit (20) having a plurality of switching elements (26a to 26d) connected in parallel, a control device (30) configured to control the operation of the plurality of switching elements, and a plurality of temperature sensors (32a to 32d) connected to the control device, configured to measure the respective temperatures (T1 to T4) of the plurality of switching elements.The control device is configured to obtain the respective temperatures of the plurality of switching elements from the plurality of temperature sensors, while the control unit controls all of the plurality of switching elements, to determine at least one maintenance target switching element from the plurality of switching elements based on the respective temperatures of the plurality of switching elements such that the at least one maintenance target switching element includes a switching element whose temperature is the highest among the plurality of switching elements, and to control at least one non-maintenance target switching element different from the at least one maintenance target switching element in order to set or adjust an output current of the DC-DC conversion circuit to a setpoint (Ct).

[0045] In the aforementioned DC-DC converter, the designation of at least one maintenance target switching element can include designating all switching elements whose temperature is higher than a predetermined value than the lowest temperature among the plurality of switching elements as the at least one maintenance target switching element. According to this configuration, the frequency of use of the non-maintenance target switching element is increased, since a plurality of switching elements are designated as the maintenance target switching elements, and the degrees of degradation among the plurality of switching elements can be leveled out or made uniform in an early stage of the product life.

[0046] In the aforementioned DC-DC converter, the control device can further be configured to control both the at least one maintenance target switching element and the at least one non-maintenance target switching element in order to adjust the output current of the DC-DC conversion circuit to the setpoint if controlling only the at least one non-maintenance target switching element is insufficient to allow the output current of the DC-DC conversion circuit to reach the setpoint. According to this configuration, the degrees of degradation among the multiple switching elements can be equalized or made uniform without sacrificing the performance of the DC-DC converter.

[0047] In the aforementioned DC-DC converter, the DC-DC conversion circuit can further comprise a plurality of inductors (22a to 22d), each connected to a corresponding plurality of switching elements. In this case, the attainment of the respective temperatures during the energizing of all the plurality of switching elements can be achieved by interrupting or non-continuously flowing an electric current through each of the plurality of inductors when the control device obtains the respective temperatures of the plurality of switching elements from the plurality of temperature sensors. According to this configuration, when the respective temperatures are obtained, the current flowing into each of the switching elements is limited to a relatively small range, and the amount of heat generated at each of the switching elements can be made relatively small.As a result, the influence that may exist among the multitude of switching elements due to differences in heat dissipation efficiency (e.g., differences in their positional relationship to the cooler) is suppressed, and the temperatures obtained when the multitude of switching elements are reached more accurately reflect the degree of deterioration of the switching elements.

[0048] A control device of a DC-DC converter is configured to obtain the respective temperatures of a plurality of switching elements from a plurality of temperature sensors, while controlling all of the plurality of switching elements, to determine at least one maintenance target switching element from the plurality of switching elements based on the respective temperatures of the plurality of switching elements such that the at least one maintenance target switching element includes a switching element whose temperature is the highest among the plurality of switching elements, and to control at least one non-maintenance target switching element different from the at least one maintenance target switching element in order to adjust an output current of a DC-DC conversion circuit to a setpoint.

Claims

[1] DC-DC converter (10), with a DC-DC conversion circuit (20) with a plurality of parallel interconnected unit circuits (20a to 20d), each comprising a switching element (26a to 26d) from the plurality of unit circuits (20a to 20d), a control device (30) which is configured to control the operation of the switching elements (26a to 26d) of the plurality of unit circuits (20a to 20d), and a plurality of temperature sensors (32a to 32d) which are connected to the control unit (30) and are configured to measure the respective temperatures (T1 to T4) of the switching elements (26a to 26d) of the plurality of unit circuits (20a to 20d), wherein the control device (30) is configured to to obtain the respective temperatures (T1 to T4) of the switching elements (26a to 26d) of the plurality of unit circuits (20a to 20d) from the plurality of temperature sensors (32a to 32d), while the control device controls all of the switching elements (26a to 26d) of the plurality of unit circuits (20a to 20d), to determine at least one maintenance target switching element from the switching elements (26a to 26d) of the plurality of unit circuits (20a to 20d) based on the respective temperatures (T1 to T4) of the switching elements (26a to 26d) of the plurality of unit circuits (20a to 20d) such that the at least one maintenance target switching element comprises a switching element whose temperature is the highest among the switching elements (26a to 26d) of the plurality of unit circuits (20a to 20d), and to control at least one non-maintenance target switching element differently from the at least one maintenance target switching element in order to adjust an output current of the DC-DC conversion circuit to a setpoint (Ct), and wherein determining at least one conservation target switching element is determining all of at least one switching element whose temperature is higher by a predetermined value than a lowest temperature among the switching elements (26a to 26d) of the plurality of unit circuits (20a to 20d) than that which comprises at least one conservation target switching element. [2] DC-DC converter (10) according to claim 1, wherein the control device (30) is further configured to control both the at least one maintenance target switching element and the at least one non-maintenance target switching element in order to adjust the output current of the DC-DC conversion circuit (20) to the setpoint (Ct) when controlling only the at least one non-maintenance target switching element is not sufficient to allow the output current of the DC-DC conversion circuit (20) to reach the setpoint (Ct). [3] DC-DC converter (10), with a DC-DC conversion circuit (20) with a plurality of parallel interconnected unit circuits (20a to 20d), each comprising a switching element (26a to 26d) from the plurality of unit circuits (20a to 20d), a control device (30) which is configured to control the operation of the switching elements (26a to 26d) of the plurality of unit circuits (20a to 20d), and a plurality of temperature sensors (32a to 32d) which are connected to the control unit (30) and are configured to measure the respective temperatures (T1 to T4) of the switching elements (26a to 26d) of the plurality of unit circuits (20a to 20d), wherein the control device (30) is configured to to obtain the respective temperatures (T1 to T4) of the switching elements (26a to 26d) of the plurality of unit circuits (20a to 20d) from the plurality of temperature sensors (32a to 32d), while the control device controls all of the switching elements (26a to 26d) of the plurality of unit circuits (20a to 20d), to determine at least one maintenance target switching element from the switching elements (26a to 26d) of the plurality of unit circuits (20a to 20d) based on the respective temperatures (T1 to T4) of the switching elements (26a to 26d) of the plurality of unit circuits (20a to 20d) such that the at least one maintenance target switching element comprises a switching element whose temperature is the highest among the switching elements (26a to 26d) of the plurality of unit circuits (20a to 20d), to control at least one non-maintenance target switching element differently from the at least one maintenance target switching element in order to adjust an output current of the DC-DC conversion circuit to a setpoint (Ct), and to to control both the at least one maintenance target switching element and the at least one non-maintenance target switching element in order to adjust the output current of the DC-DC conversion circuit (20) to the setpoint (Ct) if controlling only the at least one non-maintenance target switching element is not sufficient to make the output current of the DC-DC conversion circuit (20) reach the setpoint (Ct), and wherein the DC-DC conversion circuit (20) further comprises a plurality of choke coils (22a to 22d), each of which is connected to a corresponding switching element (26a to 26d) of the plurality of unit circuits (20a to 20d), and The attainment of the respective temperatures (T1 to T4) during the actuation of all the switching elements (26a to 26d) of the plurality of unit circuits (20a to 20d) is carried out in such a way that an electric current flows interrupted through each of the plurality of choke coils (22a to 22d) when the control device (30) attains the respective temperatures (T1 to T4) of the switching elements (26a to 26d) of the plurality of unit circuits (20a to 20d) from the plurality of temperature sensors (32a to 32d).

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