Power conversion device

Abstract

To prevent a load that requires a large current temporarily at start-up or during operation from being unable to start or being stopped.SOLUTION: When a current I detected by a current detection unit Si is equal to or greater than an overcurrent threshold Ith, the duty ratio of a drive signal that drives a power element SW is reduced, and the higher the temperature T detected by the temperature detection unit St, the more the overcurrent threshold Ith and the integration threshold IGth are lowered. An integrated value IG of power P, which is the multiplied value of the current I detected by the current detection unit Si and the voltage V detected by the voltage detection unit Sv, is calculated, and when the integrated value IG of power P is equal to or greater than the integration threshold IGth, the overcurrent threshold Ith is lowered to a predetermined value Iα.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a power conversion device that drives a power element to convert input power into a predetermined power and supplies the power to a load. [Background technology]

[0002] There is a power conversion device that, when the current flowing through a power element is equal to or greater than an overcurrent threshold, reduces the duty ratio of a drive signal that drives the power element, thereby reducing the on-time of the power element and suppressing failure of the power element due to a rise in temperature of the power element.

[0003] Incidentally, a load that includes a compressor, such as a high-pressure cleaner, temporarily requires a large current when it is started or during operation.

[0004] Furthermore, the higher the temperature of the power element, the lower the rated current of the power element. Therefore, in order to prevent the power element from failing due to an increase in temperature of the power element, it may be possible to set the overcurrent threshold to a relatively low value.

[0005] Therefore, in the above-mentioned power conversion device, when supplying power to a load that temporarily requires a large current at start-up or during operation and the overcurrent threshold is set to a relatively low value, the current required to drive the load cannot be supplied to the load, and the load may be unable to start or may stop operating. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2016-208614 A Summary of the Invention [Problem to be solved by the invention]

[0007] An object of one aspect of the present invention is to provide a power conversion device that can prevent a load that temporarily requires a large current at start-up or during operation from being unable to start or being stopped from operating. [Means for solving the problem]

[0008] One form of the power conversion device according to the present invention is a power conversion device that converts input power to a predetermined power and supplies it to a load, and includes a power element, a temperature detection unit that detects the temperature of the power element, a current detection unit that detects the current output from the power conversion device, a voltage detection unit that detects the voltage output from the power conversion device, and a control unit that controls the drive of the power element.

[0009] The control unit includes a drive signal generation unit that generates a drive signal to drive the power element; a drive signal correction unit that reduces a duty ratio of the drive signal when the current detected by the current detection unit is equal to or greater than an overcurrent threshold; a first threshold variable unit that increases the overcurrent threshold and the integration threshold as the temperature detected by the temperature detection unit decreases and decreases the overcurrent threshold and the integration threshold as the temperature detected by the temperature detection unit increases; and a second threshold variable unit that calculates an integrated power value, which is the multiplication value of the current detected by the current detection unit and the voltage detected by the voltage detection unit, or an integrated current value detected by the current detection unit, and reduces the overcurrent threshold to a predetermined value when the integrated power value or the integrated current value is equal to or greater than the integration threshold.

[0010] According to the drive signal correction section, a temperature rise in the power element can be suppressed, and therefore, breakdown of the power element due to a temperature rise in the power element can be suppressed.

[0011] Moreover, the first threshold variable unit can vary the overcurrent threshold to a relatively high value when the temperature of the power element is relatively low. This makes it possible to prevent the duty ratio of the drive signal from being reduced when the temperature of the power element is relatively low, thereby reducing the occurrence of the current output from the power conversion device to the load being smaller than the current required to drive the load, and thus preventing the load from being unable to start or being stopped from being driven.

[0012] Moreover, according to the second threshold variable unit, when the integrated value of the power or the integrated value of the current is equal to or greater than the integrated threshold, it is assumed that the temperature of the power element has risen, and the overcurrent threshold can be varied to a relatively low value. As a result, even if the time it takes for the temperature detected by the temperature detection unit to follow the actual temperature of the power element is longer than the time it takes to start up the load, it is possible to estimate that the temperature of the power element has risen and reduce the duty ratio of the drive signal to suppress the current flowing through the power element, thereby suppressing the temperature rise of the power element and suppressing the breakdown of the power element due to the temperature rise of the power element.

[0013] The control unit may also be configured to store first information indicating a correspondence relationship between the temperature of the power element and a rated current of the power element in the case where the power element does not break down even when the power element is continuously driven for a predetermined time, the rated current of the power element indicated in the first information being a value that decreases as the temperature of the power element increases, and the first threshold variable unit may be configured to refer to the first information every time a first predetermined time elapses, and to set the rated current of the power element corresponding to the temperature detected by the temperature detection unit as a new overcurrent threshold.

[0014] This makes it possible to change the overcurrent threshold to a relatively high value when the temperature detected by the temperature detection unit is relatively low.

[0015] The control unit may also be configured to store second information indicating a correspondence between the temperature of the power element and the integrated threshold value, the integrated threshold value indicated in the second information being a value that becomes smaller as the temperature of the power element increases, and the second threshold value variable unit may be configured to refer to the second information every time a first predetermined time period elapses and set the integrated threshold value corresponding to the temperature detected by the temperature detection unit as the new integrated threshold value.

[0016] This makes it possible to change the integration threshold value to a relatively high value when the temperature detected by the temperature detection unit is relatively low.

[0017] The drive signal correction unit may be configured by software.

[0018] This makes it possible to reduce the number of hardware components that make up the power conversion device compared to when the drive signal correction unit is configured from hardware, thereby making it possible to reduce the size of the power conversion device.

[0019] The power conversion device may be mounted on a vehicle.

[0020] This makes it possible to prevent the load used in the vehicle from being unable to start or being stopped from being driven. Effect of the Invention

[0021] According to the present invention, it is possible to prevent a load that requires a large current temporarily at the time of startup or during operation from being unable to start or being stopped from operating. [Brief description of the drawings]

[0022] [Figure 1] 1 is a diagram illustrating an example of a power conversion device according to an embodiment; [Diagram 2] 5A and 5B are diagrams illustrating an example of a current detected by a current detection unit and a drive signal. [Diagram 3] 10 is a flowchart showing an example of an operation of a control unit. [Figure 4]11 is a diagram showing an example of first information, second information, an integrated value of power, and an overcurrent threshold value. FIG. [Diagram 5] FIG. 13 is a diagram illustrating a modified example of the drive signal correction unit. [Figure 6] 10 is a flowchart showing a modified example of the operation of the control unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Hereinafter, the embodiments will be described in detail with reference to the drawings.

[0024] FIG. 1 is a diagram illustrating an example of a power conversion device according to an embodiment.

[0025] The power conversion device 1 shown in Fig. 1 is mounted on a vehicle Ve, such as an electric vehicle or a plug-in hybrid vehicle, and includes a DC-DC converter 2 that converts the DC voltage of a battery B into a predetermined DC voltage, and an AC inverter 3 that converts the DC power output from the DCDC converter 2 into AC power and supplies it to a load Lo. The load Lo is an electrical device that temporarily requires a large current at start-up or during operation, and is, for example, a home appliance such as a high-pressure washer, a freezer, a portable air conditioner, a vacuum cleaner, or an induction heating (IH) cooker. Although the power conversion device 1 shown in Fig. 1 is configured to be provided in the vehicle Ve, it does not have to be provided in the vehicle Ve.

[0026] The AC inverter 3 includes power elements SW1 to SW4, inductors L1 and L2, a capacitor C, a temperature detector St, a voltage detector Sv, and a current detector Si. Note that the power elements SW1 to SW4 shown in Fig. 1 are IGBTs (Insulated Gate Bipolar Transistors) with diodes connected in parallel, but may be configured with other semiconductor elements such as MOSFETs (Metal Oxide Semiconductor Field Effect Transistors). Note that when the power elements SW1 to SW4 are not distinguished from one another, they are referred to as "power elements SW."

[0027] The collector terminals of the power elements SW1 and SW3 are connected to one output terminal of the DCDC converter 2, and the emitter terminals of the power elements SW2 and SW4 are connected to the other output terminal of the DCDC converter 2. The connection point between the emitter terminal of the power element SW1 and the collector terminal of the power element SW2 is connected to one input terminal of the load Lo via the inductor L1 and one terminal of the capacitor C. The connection point between the emitter terminal of the power element SW3 and the collector terminal of the power element SW4 is connected to the other input terminal of the load Lo via the inductor L2 and the other terminal of the capacitor C.

[0028] The temperature detection unit St is, for example, a thermistor, detects the temperature T of the power element SW, and sends the detected temperature T to the control unit 4. In this embodiment, the temperature detection unit St indirectly measures (estimates) the temperatures of the power elements SW1 to SW4. Note that the time it takes for the temperature T detected by the temperature detection unit St to follow the actual temperature of the power element SW varies depending on the thickness of the case (resin) packaging the power element SW and the distance between the power element SW and the temperature detection unit St. The temperature detection unit St may take the average value of the temperatures of the power elements SW1 to SW4 as the temperature T, or may use the temperature of a specific power element SW, for example, the temperature of a power element SW that is most likely to rise in temperature due to the cooling structure, such as being farthest from the flow path of the coolant, or due to the characteristics of the circuit, such as the time during which the current flows or the current value is large, as the temperature T.

[0029] The voltage detection unit Sv is configured, for example, by a plurality of voltage dividing resistors connected in series, detects the voltage V output from the AC inverter 3 (power conversion device 1) to the load Lo, and sends the detected voltage V to the control unit 4.

[0030] The current detection unit Si is configured with, for example, a Hall element, a current transformer, or a shunt resistor, detects the current I output from the AC inverter 3 (power conversion device 1) to the load Lo, and sends the detected current I to the control unit 4.

[0031] In this embodiment, the control unit 4 is configured by, for example, a microcomputer including a processor and a storage unit, and includes a drive signal generation unit 41, a drive signal correction unit 42, a first threshold variable unit 43, and a second threshold variable unit 44. For example, the drive signal generation unit 41, the drive signal correction unit 42, the first threshold variable unit 43, and the second threshold variable unit 44 are realized by executing a program stored in the storage unit by the processor. That is, the drive signal generation unit 41, the drive signal correction unit 42, the first threshold variable unit 43, and the second threshold variable unit 44 are configured by software. As a result, compared to a case in which the drive signal correction unit 42 and the like are configured by hardware, the number of hardware components constituting the power conversion device 1 can be reduced, and the power conversion device 1 can be made smaller. Note that the present invention is not limited to a configuration in which the drive signal generation unit 41, the drive signal correction unit 42, the first threshold variable unit 43, and the second threshold variable unit 44 are configured by software, and may be configured by hardware or a combination of software and hardware.

[0032] The control unit 4 also stores in advance, as information to be described later, first information indicating a correspondence relationship between the temperature of the power element SW and the rated current of the power element SW when the power element does not break down even if the power element SW is continuously driven for a predetermined time, and second information indicating a correspondence relationship between the temperature of the power element SW and an integrated threshold value IGth. The rated current of the power element SW indicated in the first information is set to a value that decreases as the temperature of the power element SW increases. The integrated threshold value IGth indicated in the second information is set to a value that decreases as the temperature of the power element SW increases.

[0033] The drive signal generating unit 41 generates a drive signal S1 for driving the power element SW1, a drive signal S2 for driving the power element SW2, a drive signal S3 for driving the power element SW3, and a drive signal S4 for driving the power element SW4. For example, the drive signal generating unit 41 generates a pulse signal corresponding to a comparison result between a first sine wave and a triangular wave and a pulse signal obtained by inverting the pulse signal as the drive signals S1 and S2, and generates a pulse signal corresponding to a comparison result between a second sine wave, which is 180 degrees out of phase with the first sine wave, and the triangular wave and a pulse signal obtained by inverting the pulse signal as the drive signals S3 and S4. When the drive signals S1 to S4 are not distinguished from each other, they are referred to as "drive signals S."

[0034] When the current I detected by the current detection unit Si is smaller than the overcurrent threshold Ith, the drive signal correction unit 42 does not change the duty ratio of the drive signal S and outputs the drive signal S as it is to the gate terminal of the power element SW as a corrected drive signal S', and when the current I detected by the current detection unit Si is equal to or greater than the overcurrent threshold Ith, the drive signal correction unit 42 reduces the duty ratio of the drive signal S and outputs the drive signal S with the reduced duty ratio as a corrected drive signal S' to the gate terminal of the power element SW. As a result, when the current I detected by the current detection unit Si is equal to or greater than the overcurrent threshold Ith, that is, when the temperature of the power element SW is relatively high, the duty ratio of the drive signal S is reduced to suppress the current flowing through the power element SW, thereby suppressing a temperature rise of the power element SW and suppressing a failure of the power element SW due to a temperature rise of the power element SW.

[0035] Here, FIG. 2(a) is a diagram showing an example of the current I detected by the current detection unit Si, FIG. 2(b) is a diagram showing an example of a pulse signal corresponding to a comparison result between the current I and the overcurrent threshold Ith, FIG. 2(c) is a diagram showing an example of a drive signal S output from the drive signal generation unit 41 generated to satisfy the required output, and FIG. 2(d) is a diagram showing an example of a drive signal S' output from the drive signal correction unit 42 in which the duty ratio of the drive signal S is reduced to protect the power element SW. Note that the horizontal axis of the two-dimensional coordinate system shown in FIG. 2(a) indicates time, and the vertical axis indicates current. The solid line shown in FIG. 2(a) indicates the current I detected by the current detection unit Si, and the broken line indicates the overcurrent threshold Ith. Also, the horizontal axis of the two-dimensional coordinate system shown in FIG. 2(b) to FIG. 2(d) indicates time, and the vertical axis indicates voltage. The solid line shown in Fig. 2(b) indicates a pulse signal corresponding to the comparison result between the current I and the overcurrent threshold Ith, the solid line shown in Fig. 2(c) indicates the drive signal S output from the drive signal generation unit 41, and the solid line shown in Fig. 2(d) indicates the drive signal S' output from the drive signal correction unit 42. It is also assumed that the time axes of Fig. 2(a) to Fig. 2(d) are the same.

[0036] First, when the current I shown in FIG. 2(a) is smaller than the overcurrent threshold Ith, the drive signal correction unit 42 sets the pulse signal shown in FIG. 2(b) to a high level, and when the current I shown in FIG. 2(a) is equal to or greater than the overcurrent threshold Ith, the drive signal correction unit 42 sets the pulse signal shown in FIG. 2(b) to a low level.

[0037] Next, when the pulse signal shown in FIG. 2(b) and the drive signal S shown in FIG. 2(c) are both at a high level, the drive signal correction unit 42 outputs a high-level drive signal S' as shown in FIG. 2(d), and when at least one of the pulse signal shown in FIG. 2(b) and the drive signal S shown in FIG. 2(c) is at a low level, the drive signal correction unit 42 outputs a low-level drive signal S' as shown in FIG. 2(d).

[0038] In the AC inverter of the present embodiment, for example, when the drive signals S1 and S4 are at a high level and the current I becomes equal to or greater than the overcurrent threshold Ith, it is desirable to set the drive signal S' so that only one of the drive signals S1 and S4 is at a low level. That is, by maintaining one of the drive signals S1 and S4 at a high level, the return path of the current that continues to flow through the inductors L1 and L2 shown in FIG. 1 is secured as "inductor L1 → load Lo → inductor L2 → power element SW4 → diode of power element SW2 → inductor L1" or "inductor L1 → load Lo → inductor L2 → diode of power element SW3 → power element SW1 → inductor L1". Similarly, when the drive signals S2 and S3 are at a high level and the current I becomes equal to or greater than the overcurrent threshold Ith, it is desirable to set the drive signal S' so that only one of the drive signals S2 and S3 is at a low level. In addition, in the case of a circuit in which another return path can be formed or a circuit in which a return path is not required, all the drive signals S may be corrected to the drive signal S'.

[0039] As a result, when the current I is equal to or greater than the overcurrent threshold Ith, the current I decreases, the temperature rise of the power element SW is mitigated, and failure of the power element SW due to the temperature rise of the power element SW can be suppressed.

[0040] 1 increases the overcurrent threshold Ith and the integration threshold IGth every time the first predetermined time elapses as the temperature T detected by the temperature detection unit St decreases, and decreases the overcurrent threshold Ith and the integration threshold IGth every time the temperature T detected by the temperature detection unit St increases. Note that the first predetermined time is, for example, the time it takes for the temperature T detected by the temperature detection unit St to follow the actual temperature of the power element SW.

[0041] For example, when the control unit 4 is started, the first threshold variable unit 43 refers to the first information to determine the rated current corresponding to the temperature T detected by the temperature detection unit St as the initial value of the overcurrent threshold Ith, and also refers to the second information to determine the integrated threshold IGth corresponding to the temperature T detected by the temperature detection unit St as the initial value of the integrated threshold IGth.

[0042] In addition, each time a first predetermined time has elapsed since the control unit 4 was started, the first threshold variable unit 43 refers to the first information and sets the rated current corresponding to the temperature T detected by the temperature detection unit St as a new overcurrent threshold Ith, and also refers to the second information and sets the integrated threshold IGth corresponding to the temperature T detected by the temperature detection unit St as a new integrated threshold IGth.

[0043] This allows the overcurrent threshold Ith and the integration threshold IGth to be changed to relatively high values ​​when the temperature of the power element SW is relatively low. Therefore, when the temperature of the power element SW is relatively low, the duty ratio of the drive signal S can be prevented from becoming unnecessarily small, so that the current output from the power conversion device 1 to the load Lo can be prevented from becoming smaller than the current required to drive the load Lo, and the load Lo can be prevented from becoming unable to start or being stopped from being driven.

[0044] The second threshold variable unit 44 calculates an integrated value IG of the power P, which is a multiplication value of the current I detected by the current detection unit Si and the voltage V detected by the voltage detection unit Sv, every time a second predetermined time (e.g., a clock cycle of the processor) shorter than the first predetermined time elapses, and when the integrated value IG of the power P is equal to or greater than the integrated threshold IGth, the overcurrent threshold Ith is lowered to a predetermined value Iα. In the present invention, the integrated value IG of the power P is considered to be approximately proportional to the temperature rise of the power element SW caused by the current I flowing. Therefore, although it takes time for the temperature T detected by the temperature detection unit St to follow the actual temperature of the power element SW, the current temperature is estimated by using the integrated value IG. Note that in this embodiment, for example, the integrated threshold IGth is determined based on the difference between the allowable operating temperature of the power element SW and the temperature T detected by the temperature detection unit St, and the predetermined value Iα is a current value allowed at the allowable operating temperature. In other words, in this case, regardless of the temperature T detected by the temperature detection unit St, when the integrated value IG of the power P becomes equal to or greater than the integrated threshold IGth, it is estimated that the temperature of the power element SW has reached the allowable operating temperature, and the overcurrent threshold Ith is lowered to a current value allowable at the allowable operating temperature. Note that the integrated threshold IGth and the predetermined value Iα are not limited to the values ​​described above, and may be values ​​taking a predetermined safety factor into consideration.

[0045] As a result, when the integrated value IG of the power P is equal to or greater than the integrated threshold IGth, it is assumed that the temperature of the power element SW has risen, and the overcurrent threshold Ith can be varied to a relatively low value. In addition, the overcurrent threshold Ith can be varied at a timing different from that of the first threshold variable unit 43. Therefore, even if the time required for the temperature T detected by the temperature detection unit St to follow the actual temperature of the power element SW is longer than the time required for the load Lo to start up, it is possible to estimate that the temperature of the power element SW has risen and reduce the duty ratio of the drive signal S to suppress the current flowing through the power element SW, thereby suppressing the temperature rise of the power element SW and suppressing the failure of the power element SW due to the temperature rise of the power element SW.

[0046] 3 is a flowchart showing an example of the operation of the control unit 4. When the control unit 4 is started, the control unit 4 starts measuring a first predetermined time and executes the process of step STP1. The control unit 4 also repeatedly measures the first predetermined time. It also takes a second predetermined time to execute the processes of steps STP4 to STP6.

[0047] First, the first threshold value variable part 43 of the control part 4 acquires the temperature T detected by the temperature detection part St (step STP1).

[0048] Next, the first threshold variable unit 43 refers to the first information to determine an overcurrent threshold Ith corresponding to the temperature T, and refers to the second information to determine an integrated threshold IGth corresponding to the temperature T, and sets the determined overcurrent threshold Ith and integrated threshold IGth as new overcurrent threshold Ith and new integrated threshold IGth (step STP2).

[0049] Next, if the first threshold variable unit 43 determines that the first predetermined time has not elapsed (step STP3: No), it executes the processing from step STP4 onwards, and if it determines that the first predetermined time has elapsed (step STP3: Yes), it executes the processing of steps STP1 to STP3 again.

[0050] In addition, the second threshold variable unit 44 of the control unit 4 calculates the integrated value IG of the power P (step STP4), and if the integrated value IG of the power P is smaller than the integrated threshold IGth (step STP5: No), it returns to the processing of step STP3, and if the integrated value IG of the power P is greater than or equal to the integrated threshold IGth (step STP5: Yes), it lowers the overcurrent threshold Ith to a predetermined value Iα (step STP6), and returns to the processing of step STP3.

[0051] Fig. 4(a) is a diagram showing an example of the first information. The horizontal axis of the two-dimensional coordinate system shown in Fig. 4(a) indicates temperature, and the vertical axis indicates current. The solid line shown in Fig. 4(a) is the first information showing the correspondence between the temperature of the power element SW and the rated current of the power element SW. The rated current of the power element SW shown in the first information in Fig. 4(a) is a value that decreases as the temperature of the power element SW increases.

[0052] For example, when the first threshold variable unit 43 acquires temperature T1 as the temperature T detected by the temperature detection unit St during startup of the control unit 4, the first threshold variable unit 43 refers to the first information shown in Fig. 4(a) and determines a relatively large rated current It1 corresponding to temperature T1 as the overcurrent threshold Ith. As a result, when the load Lo and the control unit 4 start up simultaneously and the temperature T detected by the temperature detection unit St is temperature T1, the overcurrent threshold Ith can be set to a relatively large value, so that the current flowing from the power conversion device 1 to the load Lo is not restricted, and it is possible to prevent the load Lo from becoming unable to start up.

[0053] Next, when the first predetermined time has elapsed since the start-up of the control unit 4, the first threshold variable unit 43 acquires a temperature T2 higher than the temperature T1 as the temperature T detected by the temperature detection unit St, and refers to the first information shown in Fig. 4(a) to determine a rated current It2 lower than the rated current It1 corresponding to the temperature T2 as a new overcurrent threshold Ith. As a result, in a case where the load Lo and the control unit 4 are started simultaneously and the temperature T detected by the temperature detection unit St when the first predetermined time has elapsed since the start-up is the temperature T2, the new overcurrent threshold Ith can be set to a value lower than the overcurrent threshold Ith at the time of start-up, so that the current flowing from the power conversion device 1 to the load Lo (the current flowing to the power element SW) can be limited, and the failure of the power element SW due to the temperature rise of the power element SW can be suppressed.

[0054] Fig. 4(b) is a diagram showing an example of the second information. The horizontal axis of the two-dimensional coordinate system shown in Fig. 4(b) indicates temperature, and the vertical axis indicates the integrated threshold value IGth. The solid line shown in Fig. 4(b) is the second information showing the correspondence relationship between the temperature of the power element SW and the integrated threshold value IGth. The integrated threshold value IGth shown in the second information in Fig. 4(b) is a value that decreases as the temperature of the power element SW increases.

[0055] FIG. 4(c) is a diagram showing an example of an integrated value IG of power P. The horizontal axis of the two-dimensional coordinate system shown in FIG. 4(c) indicates time, and the vertical axis indicates power. The solid line shown in FIG. 4(c) shows how the integrated value IG increases over time, the dashed line shown in FIG. 4(c) indicates the integrated threshold value IGth_t1 shown in FIG. 4(b), and the dashed double-dashed line shown in FIG. 4(c) indicates the integrated threshold value IGth_t2 shown in FIG. 4(b). The integrated threshold value IGth_t1>the integrated threshold value IGth_t2. That is, the solid line in FIG. 4(c) has two patterns, one for the case where the temperature of the power element SW is T1 and the other for the case where the temperature is T2, but in order to simplify the illustration, the pattern of increase in the integrated value IG is shown as being the same.

[0056] FIG. 4(d) is a diagram showing an example of an overcurrent threshold Ith. In addition, the horizontal axis of the two-dimensional coordinate system shown in FIG. 4(d) indicates time, and the vertical axis indicates current. The dashed line shown in FIG. 4(d) indicates the overcurrent threshold Ith. In addition, time t0 shown in FIG. 4(c) and time t0 shown in FIG. 4(d) are assumed to be the same time, and time t1 shown in FIG. 4(c) and time t1 shown in FIG. 4(d) are assumed to be the same time, with time t0<time t1.

[0057] For example, when the first threshold variable unit 43 acquires a temperature T1 as the temperature T detected by the temperature detection unit St at the time of starting up the control unit 4, the first threshold variable unit 43 refers to the second information shown in Fig. 4(b) and determines a relatively large integrated threshold IGth_t1 corresponding to the temperature T1 as the integrated threshold IGth. In this case, as shown in Fig. 4(c), when the integrated value IG of the power P becomes equal to or greater than the integrated threshold IGth_t1 at time t1 after a predetermined time has elapsed since the start-up of the control unit 4, the second threshold variable unit 44 determines that the temperature of the power element SW has risen from T1 to a predetermined temperature (allowable use temperature), and lowers the overcurrent threshold Ith (overcurrent threshold Ith1) at the temperature T1 to a predetermined value Iα at time t1, as shown in Fig. 4(d). As a result, when the load Lo and the control unit 4 start up simultaneously and the temperature T detected by the temperature detection unit St is temperature T1, the integrated threshold IGth can be set to a relatively large value, so that the overcurrent threshold Ith is less likely to decrease, making it less likely that the current flowing from the power conversion device 1 to the load Lo is restricted, and it is possible to prevent the load Lo from being unable to start up.

[0058] Alternatively, when the first threshold variable unit 43 obtains a temperature T2 higher than the temperature T1 as the temperature T detected by the temperature detection unit St at the time of starting up the control unit 4, the first threshold variable unit 43 refers to the second information shown in Fig. 4(b) and obtains a relatively small integrated threshold IGth_t2 corresponding to the temperature T2 as the integrated threshold IGth. In this case, as shown in Fig. 4(c), when the integrated value IG of the power P becomes equal to or greater than the integrated threshold IGth_t2 at time t0 after a predetermined time has elapsed since the start-up of the control unit 4, the second threshold variable unit 44 determines that the temperature of the power element SW has risen from T2 to a predetermined temperature (allowable use temperature), and reduces the overcurrent threshold Ith (overcurrent threshold Ith2) at the temperature T2 to a predetermined value Iα at time t0, as shown in Fig. 4(d). As a result, when the load Lo and the control unit 4 start up simultaneously and the temperature T detected by the temperature detection unit St is temperature T2, the integrated threshold IGth can be set to a relatively small value, so that the overcurrent threshold Ith is more likely to be lowered, making it easier to limit the current flowing from the power conversion device 1 to the load Lo, and suppressing failure of the power element SW due to a rise in temperature of the power element SW.

[0059] In this way, according to the power conversion device 1 of the embodiment, when the temperature of the power element SW is relatively low, the overcurrent protection of the power element SW can be relaxed, and when the temperature of the power element SW is relatively high, the overcurrent protection of the power element SW is actively performed, so that it is possible to reduce the failure of the power element SW due to the temperature rise of the power element SW while suppressing the load Lo from being unable to start or being stopped. Also, even if it takes time for the temperature T detected by the temperature detection unit St to follow the actual temperature of the power element SW, it is possible to reduce the failure of the power element SW due to the temperature rise of the power element SW.

[0060] Moreover, the power conversion device 1 of the embodiment is configured to be mounted on a vehicle Ve.

[0061] This makes it possible to prevent the load Lo used in the vehicle Ve from being unable to start or being stopped from driving, even though the actual temperature of the power element SW is relatively low. In general, the load Lo used in the vehicle Ve is often a home appliance, and it is difficult to specify which load is being used, so it is difficult to estimate the current required to drive the load Lo. Therefore, it is preferable to employ the power conversion device 1 of the embodiment as a power conversion device for supplying power to the load Lo used in the vehicle Ve.

[0062] Furthermore, according to the power conversion device 1 of the embodiment, there is no need to adopt expensive power elements to improve the heat resistance performance of the power element SW, so that the start-up performance of the load Lo can be improved while suppressing an increase in the manufacturing cost of the power conversion device 1.

[0063] The present invention is not limited to the above-described embodiment, and various improvements and modifications are possible without departing from the gist of the present invention.

[0064] <Variation 1> Fig. 5 is a diagram showing a modified example of the drive signal correction section 42. In Fig. 5, the same components as those shown in Fig. 1 are given the same reference numerals, and the description thereof will be omitted.

[0065] The drive signal correction unit 42 shown in FIG. 5 is configured using hardware.

[0066] The drive signal correction unit 42 shown in FIG. 5 is configured, for example, by an IC (Integrated Circuit), and includes a comparator Cmp, an AND circuit LC1, and an AND circuit LC3.

[0067] The first threshold variable unit 43 or the second threshold variable unit 44 is connected to the positive input terminal of the comparator Cmp, and one outputs while the other does not, thereby selectively inputting the overcurrent threshold Ith. The selective input may also be achieved by providing a switch or the like for switching the connection. The current I detected by the current detection unit Si is input to the negative input terminal of the comparator Cmp. If the current I is smaller than the overcurrent threshold Ith, the signal output from the output terminal of the comparator Cmp becomes high level, and if the current I is equal to or greater than the overcurrent threshold Ith, the signal output from the output terminal of the comparator Cmp becomes low level.

[0068] The AND circuit LC1 outputs a high-level drive signal S1' when the drive signal S1 generated by the drive signal generating unit 41 and the signal output from the comparator Cmp are both at a high level, and outputs a low-level drive signal S1' when one of the drive signal S1 generated by the drive signal generating unit 41 and the signal output from the comparator Cmp is at a low level.

[0069] The drive signal S2 is input to the power element SW2 without any correction by the drive signal correction unit 42 in order to ensure a return path for the current that continues to flow through the inductors L1 and L2 even when the current I becomes equal to or exceeds the overcurrent threshold Ith when the drive signals S2 and S3 are at a high level.

[0070] The AND circuit LC3 outputs a high-level drive signal S3' when the drive signal S3 generated by the drive signal generating unit 41 and the signal output from the comparator Cmp are both at a high level, and outputs a low-level drive signal S3' when one of the drive signal S3 generated by the drive signal generating unit 41 and the signal output from the comparator Cmp is at a low level.

[0071] The drive signal S4 is input to the power element SW4 without any correction by the drive signal correction unit 42 in order to ensure a return path for the current that continues to flow through the inductors L1 and L2 even when the current I becomes equal to or exceeds the overcurrent threshold Ith when the drive signals S1 and S4 are at a high level.

[0072] That is, the drive signal correction unit 42 shown in FIG. 5, like the drive signal correction unit 42 shown in FIG. 1, has the function of reducing the duty ratio of the drive signal S when the current I detected by the current detection unit Si is equal to or greater than the overcurrent threshold Ith.

[0073] In this embodiment, the drive signals S2 and S4 are input to the power elements SW2 and SW4 without being corrected by the drive signal correction unit 42, but the reverse may also be true. That is, the drive signals S1 and S3 may be input to the power elements SW1 and SW3 without being corrected by the drive signal correction unit 42, and the drive signals S2 and S4 may be corrected by the drive signal correction unit 42 and the drive signals S2' and S4' may be input to the power elements SW2 and SW4. In addition, in the case of a circuit in which a return path can be formed or a circuit that does not require a return path, all drive signals S may be corrected to drive signals S'.

[0074] <Variation 2> 6 is a flowchart showing a modified example of the operation of the control unit 4. Note that steps STP1, STP3, and STP6 shown in FIG. 6 are similar to steps STP1, STP3, and STP6 shown in FIG.

[0075] First, the first threshold value variable part 43 of the control part 4 acquires the temperature T detected by the temperature detection part St (step STP1).

[0076] Next, the first threshold variable unit 43 determines an overcurrent threshold Ith corresponding to the temperature T with reference to the first information, and determines an integrated threshold IGth corresponding to the temperature T with reference to the second information, and sets the determined overcurrent threshold Ith and integrated threshold IGth as new overcurrent threshold Ith and new integrated threshold IGth (step STP2'). Note that the second information used in step STP2' is, for example, the second information shown in FIG. 3(b) in which the parameter of the integrated threshold IGth corresponding to the temperature of the power element SW is changed from power to current. The integrated value IG of the current I is also considered to be approximately proportional to the temperature rise of the power element SW caused by the flow of the current I, similar to the integrated value of the power P.

[0077] Next, if the first threshold variable unit 43 determines that the first predetermined time has not elapsed (step STP3: No), it executes the processing from step STP4' onwards, and if it determines that the first predetermined time has elapsed (step STP3: Yes), it executes the processing of steps STP1 to STP3 again.

[0078] In addition, the second threshold variable unit 44 of the control unit 4 calculates the integrated value IG of the current I detected by the current detection unit Si (step STP4'), and if the integrated value IG of the current I is smaller than the integrated threshold IGth (step STP5': No), it returns to the processing of step STP3, and if the integrated value IG of the current I is greater than or equal to the integrated threshold IGth (step STP5': Yes), it lowers the overcurrent threshold Ith to a predetermined value Iα (step STP6), and returns to the processing of step STP3.

[0079] <Modification 3> In the above embodiment, the target for protecting the power conversion device 1 from overcurrent is the power element SW provided in the AC inverter 3, but it may be the power element provided in the DC-DC converter 2, or both. [Explanation of symbols]

[0080] 1 Power conversion device 2 DC-DC converter 3. AC Inverter 4. Control section 41 Drive signal generator 42 Drive signal correction section 43 First threshold variable section 44 Second threshold variable section Vehicle B Battery Lo load SW1~SW4 Power elements L1, L2 inductors C Capacitor St Temperature detection section Sv voltage detection section Si current detection section

Claims

1. A power conversion device that converts input power into a predetermined power and supplies the power to a load, A power element; a temperature detection unit for detecting a temperature of the power element; A current detection unit that detects a current output from the power conversion device; A voltage detection unit that detects a voltage output from the power conversion device; A control unit that controls the driving of the power element; Equipped with The control unit is a drive signal generating unit that generates a drive signal for driving the power element; a drive signal correction unit that reduces a duty ratio of the drive signal when the current detected by the current detection unit is equal to or greater than an overcurrent threshold; a first threshold value varying unit that increases the overcurrent threshold value and the integration threshold value as the temperature detected by the temperature detecting unit becomes lower, and decreases the overcurrent threshold value and the integration threshold value as the temperature detected by the temperature detecting unit becomes higher; a second threshold value varying unit that calculates an integrated value of power, which is a multiplication value of a current detected by the current detection unit and a voltage detected by the voltage detection unit, or an integrated value of a current detected by the current detection unit, and reduces the overcurrent threshold value to a predetermined value when the integrated value of power or the integrated value of current is equal to or greater than the integration threshold value; A power conversion device comprising:

2. The power conversion device according to claim 1, the control unit stores first information indicating a correspondence relationship between a temperature of the power element and a rated current of the power element when the power element does not break down even when the power element is continuously driven for a predetermined time; the rated current of the power element indicated in the first information is a value that decreases as the temperature of the power element increases, The first threshold value changing unit refers to the first information every time a first predetermined time elapses, and sets a rated current of the power element corresponding to a temperature detected by the temperature detection unit as a new overcurrent threshold value. Power conversion equipment.

3. The power conversion device according to claim 1, the control unit stores second information indicating a correspondence relationship between the temperature of the power element and the integration threshold value; the integrated threshold value indicated in the second information is a value that decreases as the temperature of the power element increases, The second threshold value changing unit refers to the second information every time a first predetermined time period elapses, and sets the integrated threshold value corresponding to the temperature detected by the temperature detection unit as a new integrated threshold value. Power conversion equipment.

4. The power conversion device according to claim 1, The drive signal correction unit is configured by software. Power conversion equipment.

5. The power conversion device according to claim 1, The power conversion device is mounted on a vehicle. Power conversion equipment.

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