Power conversion device

Abstract

To provide a power conversion device with a simpler configuration, without requiring a central control unit to operate a plurality of DC-DC converters in parallel.SOLUTION: First and second control units (51, 52) of first and second DC-DC converters (21, 22) connected in parallel control first and second output voltages so that first and second output currents do not exceed first and second current control values, respectively. A power capacity of the second DC-DC converter (22) is smaller than that of the first DC-DC converter (21), and the second current control value is lower than the first current control value. The first control unit (51) controls the first output voltage to be constant at a first voltage value until the first output current reaches the first current control value, and the second control unit (52) controls the second output voltage to be constant at a second voltage value lower than the first voltage value, and switches the second output voltage from the second voltage value to a third voltage value higher than the first voltage value when a load current increases to a predetermined value equal to or less than the second current control value.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a power conversion device. [Background technology]

[0002] Patent Document 1 discloses a power conversion device in which two DC-DC converters (a first power conversion unit and a second power conversion unit) that convert power between a first conduction path and a second conduction path are connected in parallel. This power conversion device can switch to a first operating state in which only the second power conversion unit of the first and second power conversion units operates when the value of the output current output through the second conduction path is less than a first threshold. The power conversion device of Patent Document 1 can switch to a second operating state in which at least the first power conversion unit of the first and second power conversion units operates when the value of the output current is equal to or greater than the first threshold or equal to or greater than a second threshold that is greater than the first threshold. With this configuration, the technology of Patent Document 1 enables a power conversion device in which multiple DC-DC converters are connected in parallel to operate according to the load state. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2021-182447 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the power conversion device of Patent Document 1 requires a central control unit for parallel operation that transmits control signals to each of the parallel-connected DC-DC converters to coordinate the parallel operation of the DC-DC converters. It also requires signal lines connecting the central control unit to each of the DC-DC converters. This complicates the internal configuration of the power conversion device.

[0005] The present invention has been made in view of the above problems, and its object is to provide a power conversion device that does not require a central control unit for operating multiple DC-DC converters in parallel and has a simpler internal configuration. [Means for solving the problem]

[0006] A power conversion device according to one aspect of the present invention includes first and second DC-DC converters connected in parallel and having different power capacities, and outputs a load current to a load. The first DC-DC converter has a first control unit that controls its first output voltage so that its first output current does not exceed a first current control value. The second DC-DC converter has a power capacity smaller than that of the first DC-DC converter and a second control unit that controls its second output voltage so that its second output current does not exceed a second current control value that is lower than the first current control value. The first control unit starts outputting the first output current from the first DC-DC converter and controls the first output voltage to be constant at a first voltage value until the first output current reaches the first current control value. The second control unit controls the second output voltage to a constant second voltage value lower than the first voltage value, and when the load current increases to a predetermined value equal to or lower than the second current control value after the first output current starts to be output, switches the second output voltage from the second voltage value to a third voltage value higher than the first voltage value, and starts outputting the second output current from the second DC-DC converter. [Effects of the Invention]

[0007] According to one aspect of the present invention, a central control unit for operating a plurality of DC-DC converters in parallel is not required, and the configuration within the power conversion device can be further simplified. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a block diagram that schematically illustrates an in-vehicle power supply system that includes a power conversion device according to an embodiment. [Figure 2] FIG. 2 is a block diagram showing an example of the configuration of the power conversion device according to the first embodiment. [Figure 3] FIG. 3 is a graph showing an example of the current-voltage characteristics of the first power conversion unit and the second power conversion unit when each of the first power conversion unit and the second power conversion unit of the power conversion device according to the first embodiment is operated independently. [Figure 4] FIG. 4 is a graph showing the relationship between the output current (load current) of the entire power conversion device according to the first embodiment and the first output current and the second output current. [Figure 5] FIG. 5 is a diagram for explaining the characteristics of the operation of the power conversion device according to the first embodiment when the load current changes slowly and when it changes suddenly. [Figure 6] FIG. 6 is a graph showing the relationship between the overall output current of the power conversion device according to the modification of the first embodiment and the first output current and the second output current. [Figure 7] FIG. 7 is a graph showing the relationship between the overall output current of the power conversion device according to the second embodiment and the first output current and the second output current. [Figure 8] FIG. 8 is a graph showing the relationship between the overall output current of the power conversion device according to the third embodiment and the first output current and the second output current. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the description of the drawings, the same parts are designated by the same reference numerals and the description thereof will be omitted.

[0010] (First embodiment) First, an outline of an on-board power supply system including a power conversion device according to a first embodiment of the present invention will be described. An on-board power supply system 100 shown in Fig. 1 can function as an on-board DC voltage supply system mounted on a vehicle such as an electric vehicle. The power supply system 100 can supply a constant DC voltage to a load 102. The power supply system 100 includes a power conversion device 20 and a battery 101.

[0011] The load 102 may be any electrical device mounted on a vehicle, such as an accessory device required to operate an engine or a motor (such as a starter motor, an alternator, or a radiator cooling fan). The type and number of the load 102 are not limited, and may include an electric power steering system, an electric parking brake, lighting, a wiper drive unit, a navigation device, etc.

[0012] The battery 101 is a battery (e.g., a secondary battery) that supplies a high voltage (e.g., 300 V). A positive terminal on the high potential side of the battery 101 is electrically connected to the positive electrode side of the first conductive path 10. A negative terminal on the low potential side of the battery 101 is electrically connected to the negative electrode side of the first conductive path 10.

[0013] The power conversion device 20 includes a plurality of DC-DC converters 21 to 2n. The plurality of DC-DC converters 21 to 2n are connected in parallel between a first conduction path 10 and a second conduction path 30. The power conversion device 20 is a device that performs power conversion between the first conduction path 10 and the second conduction path 30. The power conversion device 20 can step down an input voltage input from a battery 101 via the first conduction path 10, and apply an output voltage to the second conduction path 30 that is lower than the voltage of the first conduction path 10.

[0014] In this specification, unless otherwise specified, voltage refers to a potential difference from a reference potential. For example, the voltage of the first conductive path 10 refers to a potential difference between the positive terminal and the negative terminal of the first conductive path 10, and the voltage of the second conductive path 30 refers to a potential difference between the second conductive path 30 and the reference potential. In the following example, the conductive path that generates the reference potential on the first conductive path 10 side and the conductive path that generates the reference potential on the second conductive path 30 side are insulated. Each of the multiple DC-DC converters 21 to 2n converts a DC voltage input from the battery 101 to a predetermined output voltage and outputs it from its respective output terminal. With the above configuration, the power conversion device 20 outputs a load current to the load 102.

[0015] In a power conversion device 20 according to one embodiment, a current control value is set for each of the plurality of DC-DC converters 21-2n as the maximum current value that can be output. Each of the plurality of DC-DC converters 21-2n has a control unit that controls its own output voltage so that its output current does not exceed the current control value. The power capacity and current control value of a first DC-DC converter 21 included in the plurality of DC-DC converters 21-2n differ from the power capacity and current control value of a second DC-DC converter 22 included in the plurality of DC-DC converters 21-2n.

[0016] In the following description, a power conversion device according to a first embodiment of the present invention will be described with reference to the drawings. In the description of the drawings, the same parts are given the same reference numerals and detailed description thereof will be omitted.

[0017] 2 is a block diagram showing an example of the configuration of a power conversion device 20 according to the first embodiment. The power conversion device 20 has two DC-DC converters (first and second DC-DC converters) 21 and 22 connected in parallel. Specifically, a first power conversion unit 41 of the first DC-DC converter 21 and a second power conversion unit 42 of the second DC-DC converter 22 are connected in parallel between a first conduction path 10 and a second conduction path 30.

[0018] The first DC-DC converter 21 has a first power conversion unit 41 that performs power conversion, a first control unit 51 that is a control unit within the first DC-DC converter, a first voltage value detection unit 61, and a first current value detection unit 71.

[0019] The first power conversion unit 41 converts power input from the first conductive path 10 via the first input path 11 and outputs the power to the second conductive path 30 via the first output path 31. The first input path 11 is a conductive path branched from the first conductive path 10, and one end is electrically connected to the first conductive path 10 and the other end is electrically connected to the first power conversion unit 41. The first output path 31 has one end electrically connected to the first current value detection unit 71 and the other end electrically connected to the second conductive path 30.

[0020] The first voltage value detection unit 61 detects the voltage value of the first output path 31 and inputs a signal indicating the voltage value to the first control unit 51. When the first power conversion unit 41 performs a power conversion operation, the first voltage value detection unit 61 detects the voltage value of the first output voltage that the first power conversion unit 41 applies to the first output path 31.

[0021] The first current value detection unit 71 is located midway along the first output path 31. The first current value detection unit 71 detects the value of a current flowing through the first output path 31 and inputs a signal indicating the current value to the first control unit 51. When the first power conversion unit 41 performs a power conversion operation (specifically, a step-down operation), the first current value detection unit 71 detects the current value of the first output current that the first power conversion unit 41 outputs via the first output path 31.

[0022] The first control unit 51 is configured as a control device having an information processing function, and is configured, for example, by a microcomputer including an internal memory. The internal memory stores programs to be executed by the first control unit 51, necessary parameters, etc. The first control unit 51 calculates setting values ​​necessary for the operation of the first power conversion unit 41, and sets them in the first power conversion unit 41.

[0023] The first control unit 51 sets a first current control value as the maximum current value that can be output by the first power conversion unit 41. The first control unit 51 controls the first output voltage that is the output voltage of the first power conversion unit 41 so that the first output current that is the output current of the first power conversion unit 41 does not exceed the first current control value. Details of the operation of the first control unit 51 to control the first output voltage will be described later.

[0024] When the first power conversion unit 41 is operated independently, the current-voltage characteristics of the first power conversion unit 41 are constant, and in this embodiment, the first output voltage relative to the first output current is constant.

[0025] The second DC-DC converter 22 has a second power conversion unit 42 that performs power conversion, a second control unit 52 that is a control unit within the second DC-DC converter, a second voltage value detection unit 62, and a second current value detection unit 72. In the first embodiment, the power capacity of the second DC-DC converter 22 is smaller than the power capacity of the first DC-DC converter.

[0026] The second power conversion unit 42 converts power input from the first conductive path 10 via the second input path 12 and outputs the power to the second conductive path 30 via the second output path 32. The second input path 12 is a conductive path branched off from the first conductive path 10, with one end electrically connected to the first conductive path 10 and the other end electrically connected to the second power conversion unit 42. The second output path 32 has one end electrically connected to the second current value detection unit 72 and the other end electrically connected to the second conductive path 30.

[0027] The second voltage value detection unit 62 detects the voltage value of the second output path 32 and inputs a signal indicating the voltage value to the second control unit 52. When the second power conversion unit 42 performs a power conversion operation, the second voltage value detection unit 62 detects the voltage value of the second output voltage that the second power conversion unit 42 applies to the second output path 32.

[0028] The second current value detection unit 72 is located midway along the second output path 32. The second current value detection unit 72 detects the value of a current flowing through the second output path 32 and inputs a signal indicating the current value to the second control unit 52. When the second power conversion unit 42 performs a power conversion operation (specifically, a step-down operation), the second current value detection unit 72 detects the current value of the second output current that the second power conversion unit 42 outputs via the second output path 32.

[0029] The second control unit 52 is configured as a control device having an information processing function, and is configured, for example, by a microcomputer including an internal memory. The internal memory stores programs to be executed by the second control unit 52, necessary parameters, etc. The second control unit 52 calculates setting values ​​necessary for the operation of the second power conversion unit 42, and sets them in the second power conversion unit 42.

[0030] The second control unit 52 sets the second current control value as the maximum current value that the second power conversion unit 42 can output. In the first embodiment, the second current control value is set to a value lower than the first current control value. The second control unit 52 controls the second output voltage, which is the output voltage of the second power conversion unit 42, so that the second output current, which is the output current of the second power conversion unit 42, does not exceed the second current control value. Details of the operation of the second control unit 52 to control the second output voltage will be described later.

[0031] When the second power conversion unit 42 is operated independently, the current-voltage characteristics of the second power conversion unit 42 are constant, and in this embodiment, the value of the second output voltage relative to the value of the second output current is constant.

[0032] The second control unit 52 is also connected to a load current value detection unit 80 included in the power conversion device 20. The load current value detection unit 80 is located midway along the second conduction path 30. The load current value detection unit 80 detects the value of a current flowing through the second conduction path 30 and inputs a signal indicating the current value to the second control unit 52. When the first and second power conversion units 41 and 42 perform a power conversion operation (specifically, a step-down operation), the load current value detection unit 80 detects the value of an output current output from the power conversion device 20 via the second output path 32. The output current output from the power conversion device 20 via the second output path 32 is a load current output to a load 102 connected to the power conversion device 20. That is, the load current value detection unit 80 detects the current value of the load current.

[0033] (Operations of the first control unit and the second control unit) The operations of the first control unit 51 and the second control unit 52 in the first embodiment will be described with reference to Figures 3 to 5. In the following description, the first current control value of the first power conversion unit 41 is set to 200 A, and the second current control value of the second power conversion unit 42 is set to 100 A. Note that the values ​​of the first current control value and the second current control value are not limited, as long as the second current control value is set to a value lower than the first current control value.

[0034] Fig. 3 is a graph showing an example of the current-voltage characteristics of the first power conversion unit 41 and the second power conversion unit 42 when each of the first power conversion unit 41 and the second power conversion unit 42 of the power conversion device 20 according to the first embodiment is operated independently. The horizontal axis of Fig. 3 represents the values ​​of the first output current and the second output current, and the vertical axis represents the values ​​of the first output voltage and the second output voltage. In Fig. 3, the solid line graph represents the value of the first output voltage, and the dashed line graph represents the value of the second output voltage.

[0035] Fig. 4 is a graph showing the relationship between the overall output current (load current) of the power conversion device 20 according to the first embodiment and the first and second output currents. The horizontal axis of Fig. 4 shows the output current of the power conversion device 20, i.e., the value of the load current IL output from the power conversion device 20 to the load 102, and the vertical axis shows the values ​​of the first output current Io1 and the second output current Io2.

[0036] 3 and 4, the first control unit 51 starts outputting the first output current Io1 from the first DC-DC converter 21, and controls the first output voltage to be constant at 14 V (first voltage value) until the first output current Io1 reaches the first current control value of 200 A. Furthermore, the second control unit 52 controls the second output voltage to be constant at 13 V (second voltage value) that is lower than 14 V (first voltage value).

[0037] Thereafter, when the load current IL increases to 100 A (second current control value) after the first output current Io1 (load current IL) starts to be output, the second control unit 52 switches the second output voltage from 13 V (second voltage value) to 15 V (third voltage value), which is higher than 14 V (first voltage value). Note that the values ​​of the first voltage value to the third voltage value are not limited, and it is sufficient that the second voltage value is lower than the first voltage value and the third voltage value is higher than the first voltage value. As a result, until the load current IL increases from 0 A to 100 A (second current control value), the first power conversion unit 41, which has a higher output voltage than the second power conversion unit 42, outputs the first output current Io1 alone as the load current IL. In other words, until the load current IL increases from 0 A to 100 A (second current control value), the first power conversion unit 41 alone bears the load current IL.

[0038] When the load current IL increases to 100 A (second current control value) and the second output voltage switches to 15 V (third voltage value), the second power conversion unit 42, which has a higher output voltage than the first power conversion unit 41, starts outputting the second output current Io2. Thereafter, the second power conversion unit 42 increases the second output current Io2 until the second output voltage is consumed. In FIG. 4, when the load current IL increases to 100 A (second current control value) and the second output voltage switches to 15 V (third voltage value), the second output current Io2 suddenly increases to 100 A, which is the second current control value. At the same time, the first output current Io1 decreases to 0 A.

[0039] Then, when the load current IL further increases after the second output current Io2 reaches the second current control value of 100 A, the first output current Io1 of the first power conversion unit 41 starts to increase again from 0 A while the second power conversion unit 42 continues to output the second output current Io2 at a constant value of 100 A (second current control value). Thereafter, when the first output current Io1 reaches the first current control value of 200 A, the first control unit 51 reduces the first output voltage so that the first output current Io1 does not exceed the first current control value of 200 A. In this way, the first power conversion unit 41 can compensate for the increase in the load current IL from when the second output current Io2 reaches 100 A (second current control value) to a total of 300 A.

[0040] In this way, in the power conversion device 20 of the first embodiment, when the load current reaches the second current control value, a state in which power is output only from the first power conversion unit 41 and a state in which power is output from both the first and second power conversion units 41, 42 are switched.

[0041] In the power conversion device 20 according to the first embodiment, the first output current is output only from the first power conversion unit 41 until the load current reaches a predetermined value equal to or less than the second current control value. When the load current increases and reaches the second current control value, the second control unit 52 switches the second output voltage from the second voltage value to a third voltage value higher than the first voltage value. Therefore, the second power conversion unit 42 outputs the second output current before the load current exceeds the first current control value. This makes it possible to suppress a voltage drop from the first output voltage to the second output voltage when the load current increases.

[0042] The power conversion device 20 according to the first embodiment can better handle sudden changes in the load current by switching the second output voltage from the second voltage value to a third voltage value higher than the first voltage value when the load current increases to the second current control value. Fig. 5 is a diagram illustrating the characteristics of the operation of the power conversion device 20 according to the first embodiment when the load current IL changes slowly and when it changes suddenly. The horizontal axis of each graph in Fig. 5 represents the elapsed time t as the load current IL increases from 0 to 300 A, and the vertical axis represents the values ​​of the first output current Io1 and the second output current Io2 as the load current IL increases from 0 to 300 A.

[0043] The graph in the upper right of Figure 5 shows the relationship between the elapsed time t and the first output current Io1 and the second output current Io2 in the power conversion device 20 according to the first embodiment when the load current IL increases slowly from 0 to 300 A at 100 A / sec.

[0044] 5, the first control unit 51 controls the first output voltage to be constant at 14 V (first voltage value) until the first output current Io1 reaches the first current control value of 100 A at an elapsed time t of 1 sec. The second control unit 52 controls the second output voltage to be constant at 13 V (second voltage value), which is lower than 14 V (first voltage value). When the load current IL (=first output current Io1) reaches the second current control value of 100 A at an elapsed time t of 1 sec, the second control unit 52 switches the second output voltage from 13 V (second voltage value) to 15 V (third voltage value), which is higher than 14 V (first voltage value).

[0045] When the elapsed time t reaches 1 sec and the second output voltage is switched to 15 V (third voltage value), the second output current Io2 suddenly increases to the second current control value of 100 A. At the same time, the first output current Io1 decreases to 0 A.

[0046] When the load current IL increases further after the elapsed time t reaches 1 sec, the first output current Io1 of the first power conversion unit 41 starts to increase again from 0 A while the second power conversion unit 42 continues to output the second output current Io2 at a constant value of 100 A (second current control value). Then, when the elapsed time t reaches 3 sec and the first output current Io1 reaches the first current control value of 200 A, the first control unit 51 reduces the first output voltage so that the first output current Io1 does not exceed the first current control value of 200 A. This allows the first power conversion unit 41 to compensate for the increase in the load current IL from the elapsed time t = 1 sec when the second output current Io2 reaches 100 A (second current control value) to the elapsed time t = 3 sec when the load current IL reaches 300 A.

[0047] Next, the graph in the upper left of FIG. 5 shows an example of the relationship between the elapsed time t and the first output current Io1 and the second output current Io2 when the timing at which the second control unit 52 switches the second output voltage is later than in the graph in the upper right of FIG.

[0048] 5, for example, when the load current IL (=first output current Io1) reaches 150 A (first current value), which is higher than the second current control value of 100 A (at elapsed time t=1.5 sec), the second control unit 52 switches the second output voltage from 13 V (second voltage value) to 15 V (third voltage value), which is higher than 14 V (first voltage value). Note that the first current value is not particularly limited, and may be any value higher than 100 A (second current control value) and lower than 200 A (first current control value).

[0049] When the elapsed time t reaches 1.5 seconds and the second output voltage is switched to 15 V (third voltage value), the second output current Io2 suddenly increases to the second current control value of 100 A. At the same time, the first output current Io1 decreases to 50 A.

[0050] When the load current IL increases further after the elapsed time t reaches 1.5 seconds, the second power conversion unit 42 continues to output the second output current Io2 at a constant value of 100 A (second current control value), while the first output current Io1 of the first power conversion unit 41 starts to increase again from 50 A. Then, when the elapsed time t reaches 3 seconds and the first output current Io1 reaches the first current control value of 200 A, the first control unit 51 reduces the first output voltage so that the first output current Io1 does not exceed the first current control value of 200 A. This allows the first power conversion unit 41 to compensate for the increase in the load current IL from the elapsed time t = 1.5 seconds when the second output current Io2 reaches 100 A (second current control value) to the elapsed time t = 3 seconds when the load current IL reaches 300 A.

[0051] That is, when the load current IL increases slowly, even if the timing at which the second control unit 52 switches the second output voltage is later than the timing at which the load current becomes the second control value, the second power conversion unit 42 can start outputting the second output current before the load current exceeds the first current control value. Therefore, even if the timing at which the second control unit 52 switches the second output voltage is later than the timing at which the load current becomes the second current control value, it is possible to suppress a voltage drop from the first output voltage to the second output voltage when the load current increases.

[0052] Next, the graph in the lower right of Figure 5 shows the relationship between the elapsed time t and the first output current Io1 and the second output current Io2 in the power conversion device 20 of the first embodiment when the load current IL increases suddenly from 0 to 300 A at 100 A / msec.

[0053] 5, the first control unit 51 controls the first output voltage to be constant at 14 V (first voltage value) until the first output current Io1 reaches the first current control value of 200 A at an elapsed time t of 2 msec. The second control unit 52 controls the second output voltage to be constant at 13 V (second voltage value), which is lower than 14 V (first voltage value). When the load current IL (=first output current Io1) reaches the second current control value of 100 A at an elapsed time t of 1 msec, the second control unit 52 switches the second output voltage from 13 V (second voltage value) to 15 V (third voltage value), which is higher than 14 V (first voltage value).

[0054] Ideally, when the elapsed time t reaches 1 msec and the second output voltage switches to 15 V (third voltage value), the second power conversion unit 42 preferably starts outputting the second output current Io2 at approximately the same timing (elapsed time t≈1 msec). However, if the load current is changing rapidly, there is a delay in the timing at which the second power conversion unit 42 starts outputting the second output current relative to the rate of increase in the load current. For this reason, in the graph at the bottom right of FIG. 5, when the elapsed time t reaches 1 msec and the second output voltage switches to 15 V, the second output current Io2 suddenly increases to 100 A, the second current control value, at the elapsed time t=2 msec. At the same time, the first output current Io1 decreases to 100 A.

[0055] When the load current IL increases further after the elapsed time t reaches 2 msec, the first output current Io1 of the first power conversion unit 41 starts to increase again from 100 A while the second power conversion unit 42 continues to output the second output current Io2 at a constant value of 100 A (second current control value). Then, when the elapsed time t reaches 3 msec and the first output current Io1 again reaches the first current control value of 200 A, the first control unit 51 reduces the first output voltage so that the first output current Io1 does not exceed the first current control value of 200 A. This allows the first power conversion unit 41 to compensate for the increase in the load current IL from the elapsed time t = 2 msec when the second output current Io2 reaches 100 A (second current control value) to the elapsed time t = 3 sec when the load current IL reaches 300 A.

[0056] Next, the graph on the bottom left of FIG. 5 shows an example of the relationship between the elapsed time t and the first output current Io1 and the second output current Io2 when the timing at which the second control unit 52 switches the second output voltage is later than in the graph on the bottom right of FIG.

[0057] For example, in the graph at the lower left of Figure 5, when the elapsed time t reaches 1.5 msec, at which time the load current IL (=first output current Io1) becomes 150 A (first current value), which is higher than the second current control value of 100 A, the second control unit 52 switches the second output voltage from 13 V (second voltage value) to 15 V (third voltage value), which is higher than 14 V (first voltage value).

[0058] Ideally, when the second output voltage is switched to 15 V (third voltage value) at elapsed time t=1.5 msec, the second power conversion unit 42 preferably starts outputting the second output current Io2 at approximately the same timing (elapsed time t≈1.5 msec). However, when the load current is changing rapidly, there is a delay in the timing at which the second power conversion unit 42 starts outputting the second output current relative to the rate of increase in the load current. For this reason, in the graph at the bottom left of FIG. 5, when the second output voltage is switched to 15 V at elapsed time t=1.5 msec, the second output current Io2 suddenly increases to 100 A, the second current control value, at elapsed time t=2.5 msec. That is, in the graph at the bottom left of FIG. 5, the output of the second output current Io2 does not start until elapsed time t=2.5 msec, and the first output current Io1 is output alone as the load current IL.

[0059] Here, the first output current Io1 becomes the first current control value of 200 A when the elapsed time t reaches 2 msec. If the load current IL further increases after the elapsed time t reaches 2 msec, the first power conversion unit 41 continues to output the first output current Io1 at a constant value of 200 A (first current control value). Therefore, during the period t1 from the elapsed time t=2 msec to the elapsed time t=2.5 msec when the output of the second output current Io2 starts, the increase in the load current IL cannot be compensated for.

[0060] 5, when the elapsed time t reaches 2.5 msec, the second output current Io2 suddenly increases to the second current control value of 100 A. At the same time, the first output current Io1 decreases to 150 A.

[0061] When the load current IL increases further after the elapsed time t reaches 2.5 msec, the first output current Io1 of the first power conversion unit 41 starts to increase again from 150 A while the second power conversion unit 42 continues to output the second output current Io2 at a constant value of 100 A (second current control value). Then, when the first output current Io1 reaches the first current control value of 200 A again at the elapsed time t reaches 3 msec, the first control unit 51 reduces the first output voltage so that the first output current Io1 does not exceed the first current control value of 200 A. Therefore, in the graph at the lower left of FIG. 5 , the first power conversion unit 41 cannot compensate for the increase in the load current IL from the elapsed time t reaches 2 msec, when the first output current Io1 reaches 200 A (first current control value), to the elapsed time t reaches 3 sec, when the load current IL reaches 300 A.

[0062] That is, when the load current increases suddenly, if the timing at which the second control unit 52 switches the second output voltage is later than the timing at which the load current reaches the second current control value, the increase in the load current may not be compensated for. Therefore, in the power conversion device 20 according to the first embodiment, by switching the second output voltage from the second voltage value to a third voltage value higher than the first voltage value when the load current increases to the second current control value, it is possible to better respond to sudden changes in the load current.

[0063] (Operation and effect of the first embodiment) As described above, according to the first embodiment, the following advantageous effects can be obtained.

[0064] A power conversion device 20 according to the first embodiment includes first and second DC-DC converters 21 and 22 connected in parallel and having different power capacities, and outputs a load current to a load. The power capacity of the second DC-DC converter 22 is smaller than that of the first DC-DC converter 21. The first DC-DC converter 21 includes a first control unit 51 that controls its own output voltage, a first output voltage, so that its own output current, a first output current, does not exceed a first current control value. The second DC-DC converter 21 includes a second control unit 52 that controls its own output voltage, a second output current, so that its own output current, a second output current, does not exceed a second current control value that is lower than the first current control value. The first control unit 51 starts outputting the first output current from the first DC-DC converter 21 and controls the first output voltage to be constant at a first voltage value until the first output current reaches the first current control value. The second control unit 52 controls the second output voltage to a constant second voltage value lower than the first voltage value, and when the load current increases to a predetermined value equal to or lower than the second current control value after the first output current starts to be output, the second control unit 52 switches the second output voltage from the second voltage value to a third voltage value higher than the first voltage value, and starts outputting the second output current from the second DC-DC converter.

[0065] According to the power conversion device 20 of the first embodiment, the first power conversion unit 41, which has a higher output voltage than the second power conversion unit 42, outputs the first output current as the load current alone until the load current decreases from 0 A to a predetermined value equal to or less than the second current control value. That is, the first power conversion unit 41 alone undertakes the load current until the load current decreases from 0 A to a predetermined value equal to or less than the second current control value. Thereafter, when the load current increases to a predetermined value and the second output voltage switches to a third voltage value, the second power conversion unit 42, which has a higher output voltage than the first power conversion unit 41, starts outputting the second output current. That is, when the load current increases to a predetermined value, the load current is output from both the first power conversion unit 41 and the second power conversion unit 42.

[0066] If the load current further increases after the second output current reaches the second current control value, the first output current of the first power conversion unit 41 starts to increase again. Then, when the first output current reaches the first current control value, the first control unit 51 reduces the first output voltage so that the first output current does not exceed the first current control value.

[0067] As a result, the power conversion device 20 can appropriately control each of the first and second DC-DC converters 21, 22 in accordance with the load current output from the power conversion device 20, without having a central control unit for parallel operation that transmits control signals to each of the parallel-connected first and second DC-DC converters 21, 22 to coordinate and operate them in parallel. The power conversion device 20 does not require a central control unit and signal lines connecting the first and second DC-DC converters 21, 22. This further simplifies the internal configuration of the power conversion device 20. This allows the power conversion device 20 to reduce its manufacturing cost. The power conversion device 20 can save space for installing signal lines. This eliminates the influence of noise on the signal lines, thereby suppressing malfunctions in vehicles under high noise conditions.

[0068] Furthermore, the first control unit 51 of the power conversion device 20 according to the first embodiment controls the first output voltage to a first voltage value, and the second control unit 52 controls the second output voltage to a second voltage value lower than the first voltage value. When the first output current reaches the first current control value, the first control unit 51 reduces the first output voltage.

[0069] As a result, until the load current reaches the first current control value, only the first DC-DC converter 21, which has a larger power capacity, outputs the first output current. When the load current increases to the first current control value, the first control unit 51 reduces the first output voltage, causing the second DC-DC converter 22, which has a smaller power capacity, to also output the second output current. The power conversion device 20 first operates only the first DC-DC converter 21 to output power, and only when the load increases does it operate the second DC-DC converter 22, which has a smaller power capacity, to output power. This reduces the frequency at which the second DC-DC converter 22 operates, making it possible to select components with a shorter lifespan than the first DC-DC converter 21.

[0070] Furthermore, in the power conversion device 20 according to the first embodiment, the predetermined value is set to be equal to or less than the second current control value. When the load current increases suddenly, the timing at which the second control unit 52 switches the second output voltage and starts outputting the second output current is delayed relative to the rate of increase in the load current. Therefore, if the timing at which the second control unit 52 switches the second output voltage is later than the timing at which the load current reaches the second current control value, it may not be possible to compensate for the increase in the load current. Therefore, in the power conversion device 20 according to the first embodiment, by switching the second output voltage from the second voltage value to a third voltage value higher than the first voltage value when the load current increases to a predetermined value equal to or less than the second current control value, it is possible to better respond to sudden changes in the load current.

[0071] (Variation) In the power conversion device 20 according to the first embodiment, the second control unit may switch the second output voltage from 13 V (second voltage value) to 15 V (third voltage value) higher than 14 V (first voltage value) at the timing when the load current increases to a predetermined value lower than the second current control value. FIG. 6 is a graph showing a second example of the relationship between the overall output current (load current) of the power conversion device 20 according to the first embodiment and the first and second output currents. The horizontal axis of FIG. 6 represents the output current of the power conversion device 20, i.e., the value of the load current IL output from the power conversion device 20 to the load 102, and the vertical axis represents the values ​​of the first output current Io1 and the second output current Io2.

[0072] 6, the first control unit 51 starts outputting the first output current Io1 from the first DC-DC converter 21, and controls the first output voltage to be constant at 14 V (first voltage value) until the first output current Io1 reaches 50 A (predetermined value P) which is lower than the second current control value of 100 A. Furthermore, the second control unit 52 controls the second output voltage to be constant at 13 V (second voltage value) which is lower than 14 V (first voltage value).

[0073] Thereafter, when the load current IL increases to 50 A (predetermined value P) after the first output current (load current IL) starts to be output, the second control unit 52 switches the second output voltage from 13 V (second voltage value) to 15 V (third voltage value), which is higher than 14 V (first voltage value). As a result, the first power conversion unit 41, which has a higher output voltage than the second power conversion unit 42, outputs the first output current Io1 alone as the load current IL until the load current IL increases from 0 A to 50 A (predetermined value P). In other words, the first power conversion unit 41 alone bears the load current IL until the load current IL increases from 0 A to 50 A (predetermined value P).

[0074] When the load current IL increases from 0 A to 50 A (predetermined value P) and the second output voltage switches to 15 V (third voltage value), the second power conversion unit 42, which has a higher output voltage than the first power conversion unit 41, starts outputting the second output current Io2. Thereafter, the second power conversion unit 42 increases the second output current Io2 until the second output voltage is consumed. For this reason, if the predetermined value P is set to a too low value, the load current IL is output from both the first power conversion unit 41 and the second power conversion unit 42 under light load conditions, reducing the power conversion efficiency of the entire power conversion device 20. For this reason, the predetermined value P is set in advance to a value lower than the second current control value and that allows the first and second DC-DC converters 21, 22 to be used efficiently.

[0075] In Figure 6, when the load current IL increases to 50 A (predetermined value P) and the second output voltage is switched to 15 V (third voltage value), and then the load current IL increases further, the first power conversion unit 41 continues to output the first output current Io1 at a constant value of 50 A (predetermined value P), while the second output current Io2 increases until it reaches the second current control value of 100 A.

[0076] Then, when the load current IL increases further after the second output current Io2 reaches the second current control value of 100 A, the first output current Io1 of the first power conversion unit 41 starts to increase again from 50 A while the second power conversion unit 42 continues to output the second output current Io2 at a constant value of 100 A (second current control value). After that, when the first output current Io1 reaches the first current control value of 200 A, the first control unit 51 reduces the first output voltage so that the first output current Io1 does not exceed the first current control value of 200 A.

[0077] As a result, the second power conversion unit 42 can compensate for the increase in the load current IL from when the load current IL reaches 50 A (predetermined value P) until the second output current Io2 reaches 100 A (second current control value). Also, the first power conversion unit 41 can compensate for the increase in the load current IL from when the second output current Io2 reaches 100 A (second current control value) up to a total of 300 A.

[0078] (Effects of modified examples) As described above, according to the modified example of the first embodiment, the following advantageous effects can be obtained.

[0079] As described above, in the power conversion device 20 according to the modification of the first embodiment, the predetermined value may be set to a value lower than the second current control value. In this case, the first control unit 51 of the power conversion device 20 starts outputting the first output current from the first DC-DC converter 21 and controls the first output voltage to be constant at the first voltage value until the first output current reaches the first current control value. The second control unit 52 controls the second output voltage to be constant at a second voltage value lower than the first voltage value. When the load current increases to a predetermined value lower than the second current control value after starting output of the first output current, the second control unit 52 switches the second output voltage from the second voltage value to a third voltage value higher than the first voltage value and starts outputting the second output current from the second DC-DC converter.

[0080] In the power conversion device 20 according to the modification of the first embodiment, when the load current increases to a predetermined value smaller than the second current control value and the load current further increases after the second output voltage is switched, the first DC-DC converter 21 continues to output a constant first output current, while the second DC-DC converter 22 increases the second output current until it reaches the second current control value. Because the predetermined value and the second current control value are lower than the first current control value, if the load current further increases after the second output current reaches the second current control value, the power conversion device 20 can output the first output current from the first DC-DC converter 21 until the first output current reaches the first current control value, while continuing to output the second output current from the second DC-DC converter 22 at a constant second current control value. As a result, when the load current increases to a predetermined value smaller than the second current control value and the load current further increases after the second output power is switched, even if the response of the output of the second output current from the second DC-DC converter 22 becomes slow, the first output current can be output from the first DC-DC converter 21, thereby stabilizing the output voltage of the entire power conversion device 20.

[0081] (Second embodiment) A second embodiment to which the present invention is applied will be described below with reference to the drawings. In the drawings, the same parts are given the same reference numerals and detailed description will be omitted. The power conversion device according to the second embodiment differs from the power conversion device according to the first embodiment in the operation of the first control unit 51 and the second control unit 52. The rest of the configuration is the same as the power conversion device 20 shown in FIG. 2. Therefore, the different parts will be mainly described, and a repeated description of the same parts will be omitted.

[0082] An example of the operation of the first control unit 51 and the second control unit 52 of the power conversion device 20 according to the second embodiment will be described with reference to FIG.

[0083] Fig. 7 is a graph showing the relationship between the overall output current of the power conversion device according to the second embodiment and the first and second output currents. The horizontal axis of Fig. 7 shows the output current of the power conversion device 20, i.e., the value of the load current IL output from the power conversion device 20 to the load 102, and the vertical axis shows the values ​​of the first output current Io1 and the second output current Io2.

[0084] 7, the first control unit 51 starts outputting the first output current Io1 from the first DC-DC converter 21, and controls the first output voltage to be constant at 14 V (first voltage value) until the first output current Io1 reaches the first current control value of 200 A. The second control unit 52 controls the second output voltage to be constant at 13 V (second voltage value) that is lower than 14 V (first voltage value).

[0085] Thereafter, when the load current IL increases to 200 A (first current control value) after the first output current Io1 (load current IL) starts to be output, the second control unit 52 switches the second output voltage from 13 V (second voltage value) to 15 V (third voltage value), which is higher than 14 V (first voltage value).

[0086] As a result, until the load current IL changes from 0 A to 200 A (first current control value), the first power conversion unit 41, which has a higher output voltage than the second power conversion unit 42, outputs the first output current Io1 solely as the load current IL. In other words, until the load current IL changes from 0 A to 200 A (first current control value), the first power conversion unit 41 solely undertakes the load current IL.

[0087] When the load current IL increases to 200 A (first current control value) and the second output voltage switches to 15 V (third voltage value), the second power conversion unit 42, which has a higher output voltage than the first power conversion unit 41, starts outputting the second output current Io2. Thereafter, the second power conversion unit 42 increases the second output current Io2 until the second output voltage is consumed.

[0088] 7, when the load current IL increases to 200 A (first current control value) and the second output voltage is switched to 15 V (third voltage value), and then the load current IL further increases, the first control unit 51 reduces the first output voltage so that the first output current Io1 does not exceed the first current control value of 200 A. Furthermore, while the first power conversion unit 41 continues to output the first output current Io1 at a constant value of 200 A (first current control value), the second output current Io2 increases until it reaches the second current control value of 100 A.

[0089] Thereafter, when the second output current Io2 reaches the second current control value of 100 A, the second control unit 52 reduces the second output voltage so that the second output current Io2 does not exceed the second current control value of 100 A. This allows the second power conversion unit 42 to compensate for the increase in the load current IL from when the first output current Io1 reaches 200 A (first current control value) to a total of 300 A.

[0090] (Operation and effect of the second embodiment) As described above, according to the second embodiment, the following advantageous effects can be obtained.

[0091] In the power conversion device 20 according to the second embodiment, a first control unit 51 starts outputting a first output current from the first DC-DC converter 21 and controls the first output voltage to be constant at a first voltage value until the first output current reaches a first current control value. A second control unit 52 controls the second output voltage to be constant at a second voltage value lower than the first voltage value. When the load current increases to the first current control value after the first output current starts to be output, the second control unit 52 switches the second output voltage from the second voltage value to a third voltage value higher than the first voltage value and starts outputting the second output current from the second DC-DC converter 22. The power capacity of the second DC-DC converter 22 is smaller than the power capacity of the first DC-DC converter 21, and the second current control value is lower than the first current control value.

[0092] In the power conversion device 20 according to the second embodiment, the first DC-DC converter 21, which has a higher output voltage than the second DC-DC converter 22, independently outputs the first output current as the load current until the load current increases from 0 A to the first current control value. That is, the first DC-DC converter 21 independently undertakes the load current until the load current increases from 0 A to the first current control value. Thereafter, when the load current increases to the first current control value and the second output voltage switches to a third voltage value, the second DC-DC converter 22, which has a higher output voltage than the first DC-DC converter 21, begins to output the second output current. That is, when the load current increases to the first current control value, the load current is output from both the first DC-DC converter 21 and the second DC-DC converter 22.

[0093] In the power conversion device 20 according to the second embodiment, when the load current increases to the first current control value and the second output voltage is switched and the load current further increases, the first DC-DC converter 21 continues to output the first output current at a constant first current control value, while the second DC-DC converter 22 gradually increases the second output current until it reaches the second current control value. This enables the power conversion device 20 to output the load current more stably.

[0094] (Third embodiment) A third embodiment to which the present invention is applied will be described below with reference to the drawings. In the drawings, the same parts are given the same reference numerals and detailed description will be omitted. The power conversion device according to the third embodiment differs from the power conversion device according to the second embodiment in that the power capacity of the first DC-DC converter 21 is smaller than the power capacity of the second DC-DC converter 22, and the first current control value is lower than the second current control value. The rest of the configuration is the same as the power conversion device 20 shown in FIG. 2. Therefore, the different parts will be mainly described, and a repeated description of the same parts will be omitted.

[0095] An example of the operation of the first control unit 51 and the second control unit 52 of the power conversion device 20 according to the third embodiment will be described with reference to Fig. 8. In the following description, the first current control value of the first power conversion unit 41 is set to 100 A, and the second current control value of the second power conversion unit 42 is set to 200 A. Note that the values ​​of the first current control value and the second current control value are not limited, as long as the first current control value is set to a value lower than the second current control value.

[0096] Fig. 8 is a graph showing the relationship between the output current (load current) of the power conversion device 20 according to the third embodiment and the first and second output voltages. The horizontal axis of Fig. 8 represents the output current of the power conversion device 20, i.e., the value of the load current output from the power conversion device 20 to the load 102, and the vertical axis represents the values ​​of the first and second output voltages.

[0097] 8, the first control unit 51 starts outputting the first output current Io1 from the first DC-DC converter 21, and controls the first output voltage to be constant at 14 V (first voltage value) until the first output current Io1 reaches the first current control value of 100 A. The second control unit 52 controls the second output voltage to be constant at 13 V (second voltage value) that is lower than 14 V (first voltage value).

[0098] Thereafter, when the load current IL increases to 100 A (first current control value) after the first output current Io1 (load current IL) starts to be output, the second control unit 52 switches the second output voltage from 13 V (second voltage value) to 15 V (third voltage value), which is higher than 14 V (first voltage value).

[0099] As a result, until the load current IL changes from 0 A to 100 A (first current control value), the first power conversion unit 41, which has a higher output voltage than the second power conversion unit 42, outputs the first output current Io1 solely as the load current IL. In other words, until the load current IL changes from 0 A to 100 A (first current control value), the first power conversion unit 41 solely undertakes the load current IL.

[0100] When the load current IL increases to 100 A (first current control value) and the second output voltage switches to 15 V (third voltage value), the second power conversion unit 42, which has a higher output voltage than the first power conversion unit 41, starts outputting the second output current Io2. Thereafter, the second power conversion unit 42 increases the second output current Io2 until the second output voltage is consumed.

[0101] 7, when the load current IL increases to 100 A (first current control value) and the second output voltage is switched to 15 V (third voltage value), and then the load current IL further increases, the first control unit 51 reduces the first output voltage so that the first output current Io1 does not exceed the first current control value of 200 A. Also, while the first power conversion unit 41 continues to output the first output current Io1 at a constant value of 100 A (first current control value), the second output current Io2 increases until it reaches the second current control value of 200 A.

[0102] Thereafter, when the second output current Io2 reaches the second current control value of 200 A, the second control unit 52 reduces the second output voltage so that the second output current Io2 does not exceed the second current control value of 200 A. This allows the second power conversion unit 42 to compensate for the increase in the load current IL from when the first output current Io1 reaches 100 A (first current control value) to a total of 300 A.

[0103] (Operation and effect of the third embodiment) As described above, according to the third embodiment, the following advantageous effects can be obtained.

[0104] A power conversion device 20 according to the third embodiment starts outputting a first output current from a first DC-DC converter 21 and controls the first output voltage to be constant at a first voltage value until the first output current reaches a first current control value. A second control unit 52 controls the second output voltage to be constant at a second voltage value lower than the first voltage value. When the load current increases to the first current control value after the first output current starts to be output, the second control unit 52 switches the second output voltage from the second voltage value to a third voltage value higher than the first voltage value and starts outputting the second output current from a second DC-DC converter 22. The power capacity of the first DC-DC converter 21 is smaller than the power capacity of the second DC-DC converter 22, and the first current control value is lower than the second current control value.

[0105] In the power conversion device 20 according to the third embodiment, the first DC-DC converter 21, which has a higher output voltage than the second DC-DC converter 22, solely outputs the first output current as the load current until the load current increases from 0 A to the first current control value. That is, until the load current increases from 0 A to the first current control value, the first DC-DC converter 21, which has a smaller power capacity, solely undertakes the load current. Thereafter, when the load current increases to the first current control value and the second output voltage switches to a third voltage value, the second DC-DC converter 22, which has a higher output voltage than the first DC-DC converter 21, begins to output the second output current. That is, when the load current increases to the first current control value, the load current is output from both the first DC-DC converter 21 and the second DC-DC converter 22.

[0106] In the power conversion device 20 according to the third embodiment, when the load current increases to the first current control value and the second output voltage is switched, the first DC-DC converter 21 continues to output a constant first output current at the first current control value, while the second DC-DC converter 22, whose power capacity is larger than that of the first DC-DC converter 21, gradually increases the second output current until it reaches the second current control value. As a result, the power conversion device 20 operates only the first DC-DC converter 21, which has a smaller power capacity, under light load conditions, and operates the second DC-DC converter 22, which has a larger power capacity, when the load current increases to or exceeds the first current control value. The fact that the power capacity of the first DC-DC converter 21 is smaller than that of the second DC-DC converter 22 means that the first DC-DC converter 21 is more efficient under light load conditions than the second DC-DC converter. For example, when comparing a 10W output product with a rated capacity of 100W with a 10W output product with a rated capacity of 1000W, the 10W output product will be more efficient. This improves the overall power conversion efficiency.

[0107] Although the embodiments of the present invention have been described above, the descriptions and drawings that form part of this disclosure should not be understood to limit the present invention. Various alternative embodiments, examples, and operating techniques will become apparent to those skilled in the art from this disclosure. [Explanation of symbols]

[0108] 20 Power conversion device 21 First DC-DC converter 22 Second DC-DC Converter 51 First Control Section 52 Second Control Section

Claims

1. A power conversion device including first and second DC-DC converters connected in parallel and having different power capacities, and outputting a load current to a load, the power capacity of the second DC-DC converter is smaller than the power capacity of the first DC-DC converter; the first DC-DC converter has a first control unit that controls a first output voltage that is its own output voltage so that a first output current that is its own output current does not exceed a first current control value; the second DC-DC converter has a second control unit that controls a second output voltage that is its own output voltage so that a second output current that is its own output current does not exceed a second current control value that is lower than the first current control value; the first control unit starts outputting the first output current from the first DC-DC converter and controls the first output voltage to be constant at a first voltage value until the first output current becomes the first current control value; The second control unit is controlling the second output voltage to a constant second voltage value lower than the first voltage value; When the load current increases to a predetermined value equal to or less than the second current control value after the first output current starts to be output, the second output voltage is switched from the second voltage value to a third voltage value higher than the first voltage value, and the second DC-DC converter starts to output the second output current. Power conversion device.

2. The predetermined value is set to a value lower than the second current control value. The power conversion device according to claim 1 .

3. A power conversion device including first and second DC-DC converters connected in parallel and having different power capacities, and outputting a load current to a load, the first DC-DC converter has a first control unit that controls a first output voltage that is its own output voltage so that a value of a first output current that is its own output current does not exceed a first current control value; the second DC-DC converter has a second control unit that controls a second output voltage that is its own output voltage so that a value of a second output current that is its own output current does not exceed a second current control value that is different from the first current control value; the first control unit starts outputting the first output current from the first DC-DC converter and controls the first output voltage to be constant at a first voltage value until the first output current becomes the first current control value; The second control unit is controlling the second output voltage to a constant second voltage value lower than the first voltage value; When the load current increases to the first current control value after the first output current starts to be output, the second output voltage is switched from the second voltage value to a third voltage value higher than the first voltage value, and the second DC-DC converter starts to output the second output current. Power conversion device.

4. the power capacity of the second DC-DC converter is smaller than the power capacity of the first DC-DC converter; The second current control value is lower than the first current control value. The power conversion device according to claim 3 .

5. the power capacity of the first DC-DC converter is smaller than the power capacity of the second DC-DC converter; The first current control value is lower than the second current control value. The power conversion device according to claim 3 .

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