Power converter

Abstract

To provide an electric power conversion device that includes a step-up unit and a step-down unit, has an intermediate capacitor for supplying power to the step-down unit located on the output side of the step-up unit, and can reduce the cost of the intermediate capacitor and perform miniaturization of the electric power conversion device.SOLUTION: An electric power conversion device 1 includes a step-up chopper circuit 10, a step-down chopper circuit 20, an intermediate capacitor 15 that is located on the output side of the step-up chopper circuit 10 and supplies power to the step-down chopper circuit 20, and a drive controller 30. The drive controller 30 controls a switching operation of at least one pair of a pair of step-up-side switching elements 13, 14 and a pair of step-down-side switching elements 23, 24 so that an ON-period of the step-up-side upper arm switching element 13 electrically connected to a positive electrode side of the intermediate capacitor 15 and an ON-period of the step-down-side upper arm switching element 23 electrically connected to the positive electrode side of the intermediate capacitor 15 overlap each other.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a power conversion device having a booster section and a buck section that perform voltage conversion according to an output voltage command.

Background Art

[0002] A power conversion device having a booster section and a buck section that perform voltage conversion according to an output voltage command is known. As an example of such a power conversion device, for example, Patent Document 1 discloses a DC-DC converter provided with a buck chopper and a boost chopper.

[0003] In the DC-DC converter, as shown in FIG. 9 of Patent Document 1, the buck chopper and the boost chopper are connected so as to boost the input voltage and then lower it. The boost chopper includes an input capacitor connected between a positive input terminal and a negative input terminal to which an input voltage is applied, a series circuit of a reactor and a switching element connected in parallel with the input capacitor, and a series circuit of a freewheeling diode and an intermediate capacitor connected in parallel with the switching element. The buck chopper includes a series circuit of a switching element and a freewheeling diode connected in parallel with the intermediate capacitor, and a series circuit of a reactor and an output capacitor connected in parallel with the freewheeling diode.

[0004] That is, in the circuit shown in FIG. 9, the boost chopper and the buck chopper are connected via an intermediate capacitor. By driving the switching element of the boost chopper, the intermediate capacitor is charged to boost the input voltage. On the other hand, by driving the switching element of the buck chopper, the boosted input voltage is lowered and output.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] By the way, in a configuration where a boost chopper and a buck chopper are connected via an intermediate capacitor, as shown in Figure 9 of Patent Document 1, the current flowing through the intermediate capacitor fluctuates significantly. Therefore, it is necessary to ensure a certain level of capacitance for the intermediate capacitor.

[0007] Therefore, in the circuit configuration described above, it is necessary to use a relatively large capacitor as the intermediate capacitor. Consequently, it becomes necessary to use an expensive capacitor as the intermediate capacitor, and the power conversion device equipped with the intermediate capacitor becomes larger.

[0008] The object of the present invention is to realize a power conversion device that includes a boost unit and a buck unit, wherein an intermediate capacitor that supplies power to the buck unit is located on the output side of the boost unit, and which reduces the cost of the intermediate capacitor and enables miniaturization of the power conversion device. [Means for solving the problem]

[0009] A power conversion device according to one embodiment of the present invention comprises: a boost unit electrically connected to a DC power supply and boosting the input voltage in accordance with an output voltage command; a buck unit connected in series with the output side of the boost circuit and lowering the input voltage in accordance with the output voltage command; an intermediate capacitor located on the output side of the boost unit and supplying power to the buck unit; and a drive control unit that controls the driving of the boost unit and the buck unit, respectively. The boost unit has a pair of boost-side switching elements electrically connected in parallel with the intermediate capacitor and electrically connected in series with each other. The buck unit has a pair of buck-side switching elements electrically connected in parallel with the intermediate capacitor and electrically connected in series with each other. The drive control unit controls the switching operation of at least one of the pair of boost-side switching elements and the pair of buck-side switching elements such that the ON period when the boost-side upper arm switching element, which is electrically connected to the positive electrode side of the intermediate capacitor, is ON, overlaps with the ON period when the buck-side upper arm switching element, which is electrically connected to the positive electrode side of the intermediate capacitor, is ON (first configuration).

[0010] In this circuit configuration, where a pair of boost-side switching elements and a pair of buck-side switching elements are electrically connected in parallel to an intermediate capacitor located on the output side of the boost-up section and supplying power to the buck-down section, current flows through the intermediate capacitor when the boost-up section boosts the input voltage, while current flows through the intermediate capacitor when the buck-down section lowers the voltage. Therefore, the current flowing through the intermediate capacitor fluctuates significantly depending on the operation of the boost-up section and the buck-down section.

[0011] In contrast, the drive control unit controls the switching operation of at least one of the pair of boost-side switching elements and the pair of buck-side switching elements so that the ON period when the boost-side upper arm switching element is ON overlaps with the ON period when the buck-side upper arm switching element is ON, thereby providing a period during which current flows directly from the boost unit to the buck unit. Therefore, fluctuations in the current flowing through the intermediate capacitor due to the operation of the boost unit and the buck unit can be suppressed.

[0012] Therefore, since the capacitance of the intermediate capacitor can be reduced, the cost of the intermediate capacitor can be reduced and the power conversion device can be made smaller.

[0013] The drive control unit controls the switching operation of at least one of the pair of boost-side switching elements and the pair of buck-side switching elements so that the center of the ON period of the boost-side upper arm switching element coincides with the center of the ON period of the buck-side upper arm switching element (second configuration).

[0014] This allows the on-periods of the boost-side upper arm switching element and the on-periods of the buck-side upper arm switching element to overlap more reliably and over a wider range when operating the boost-up and buck-down sections. Therefore, the period during which current flows directly from the boost-up section to the buck-down section can be extended when the boost-up and buck-down sections are operating. Consequently, fluctuations in the current flowing through the intermediate capacitor due to the operation of the boost-up and buck-down sections can be suppressed.

[0015] Therefore, since the capacitance of the intermediate capacitor can be reduced, the cost of the intermediate capacitor can be further reduced, and the power conversion device can be made smaller.

[0016] In the first configuration described above, the drive control unit changes the timing of the switching operation of the pair of boost-side switching elements to a timing different from the timing of the switching operation determined according to the output voltage command, so that the ON period of the boost-side upper arm switching element overlaps with the ON period of the buck-side upper arm switching element (third configuration).

[0017] This allows the drive of a pair of boost-side switching elements to be controlled when operating the boost-side and buck-side sections, making it easy to overlap the on-period of the boost-side upper arm switching element with the on-period of the buck-side upper arm switching element. Thus, the configuration of claim 1 can be easily realized.

[0018] In any one of the first to third configurations described above, the drive control unit includes a command signal processing unit that converts a command signal for generating a drive signal to be input to a switching element among the pair of boost-side switching elements and the pair of buck-side switching elements such that the phase of the command signal is shifted relative to the triangular wave of the carrier frequency; a triangular wave comparison unit that compares the converted command signal with the triangular wave; and a drive signal generation unit that generates the drive signal using the comparison result from the triangular wave comparison unit (fourth configuration).

[0019] This allows the command signal to be converted to realize the first configuration. Therefore, the first configuration can be easily realized compared to changing the carrier frequency used when creating the drive signal input to the switching element. [Effects of the Invention]

[0020] A power conversion device according to an embodiment of the present invention includes a boosting section, a bucking section, an intermediate capacitor located on the output side of the boosting section and supplying power to the bucking section, and a drive control section that controls the driving of the boosting section and the bucking section, respectively. The drive control section controls the switching operation of at least one of a pair of boosting-side switching elements and a pair of bucking-side switching elements so that the on-period of the boosting-side upper-arm switching element of the boosting section and the on-period of the bucking-side upper-arm switching element of the bucking section overlap.

[0021] Thereby, a period during which current directly flows from the boosting section to the bucking section can be provided during the operation of the boosting section and the bucking section. Therefore, fluctuations in the current flowing through the intermediate capacitor due to the operation of the boosting section and the bucking section can be suppressed. Accordingly, the capacitance of the intermediate capacitor can be reduced, so that the cost of the intermediate capacitor can be reduced and the power conversion device can be miniaturized.

Brief Description of Drawings

[0022] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of a power conversion device according to Embodiment 1. [Figure 2] FIG. 2 is a functional block diagram showing a schematic configuration of a boost chopper drive control section. [Figure 3] FIG. 3 is a diagram schematically showing a state of comparison between a signal generated by a command signal processing section and a triangular wave in a boost chopper drive control section. [Figure 4] FIG. 4 is a functional block diagram showing a schematic configuration of a buck chopper drive control section. [Figure 5] FIG. 5 is a diagram showing an example of the direction of current flowing in a boost chopper circuit and a buck chopper circuit of a power conversion device. [Figure 6] FIG. 6 is a diagram showing an example of changes in current flowing through each position of a boost chopper circuit and a buck chopper circuit of a power conversion device when the on-period of the boosting-side upper-arm switching element and the on-period of the bucking-side upper-arm switching element do not overlap. [Figure 7]Figure 7 shows an example of the change in current flowing through each position of the boost chopper circuit and buck chopper circuit of a power converter when the center of the ON period of the boost-side upper arm switching element and the center of the ON period of the buck-side upper arm switching element are aligned. [Figure 8] Figure 8 is a functional block diagram showing an example of the schematic configuration of the boost chopper drive control unit of the power conversion device according to Embodiment 2. [Figure 9] Figure 9 schematically shows a comparison between a signal generated by the command signal processing unit and a triangular wave with a phase shift of 180 degrees in the boost chopper drive control unit. [Figure 10] Figure 10 shows an example of switching operation when the duty cycle of the boost-side upper arm switching element is greater than the duty cycle of the buck-side upper arm switching element. [Modes for carrying out the invention]

[0023] Embodiments of the present invention will be described in detail below with reference to the drawings. The same or corresponding parts in the drawings are denoted by the same reference numerals, and their descriptions will not be repeated.

[0024] [Embodiment 1] (Overall structure) Figure 1 shows a schematic configuration of a power converter 1 according to Embodiment 1 of the present invention. This power converter 1 boosts the input voltage, then steps it down to output a predetermined output voltage. The power converter 1 can be used, for example, as a battery test system (BTS) for testing inverters and batteries.

[0025] The power converter 1 includes a boost chopper circuit 10 (boost unit), a buck chopper circuit 20 (buck unit), and a drive control unit 30. The boost chopper circuit 10 is connected to a DC power supply (not shown) and boosts the input voltage obtained from the DC power supply. The buck chopper circuit 20 reduces the voltage boosted by the boost chopper circuit 10.

[0026] The boost chopper circuit 10 includes an input capacitor 11, a reactor 12, a pair of boost-side switching elements 13 and 14, an intermediate capacitor 15, and freewheeling diodes 16 and 17.

[0027] The input capacitor 11 electrically connects the positive and negative terminals of the DC power supply. The pair of boost-side switching elements 13 and 14 are electrically connected in series. The midpoint of the pair of boost-side switching elements 13 and 14 is electrically connected to the positive terminal of the input capacitor 11 via the reactor 12. One end point of the pair of boost-side switching elements 13 and 14 is electrically connected to the negative terminal of the input capacitor 11.

[0028] Of the pair of boost-side switching elements 13 and 14, the switching element 14 that is electrically connected in parallel to the input-side capacitor 11 is the boost-side lower arm switching element. Of the pair of boost-side switching elements 13 and 14, the other switching element 13 is the boost-side upper arm switching element.

[0029] The freewheel diode 16 is electrically connected in parallel to the boost-side upper arm switching element 13. The freewheel diode 17 is electrically connected in parallel to the boost-side lower arm switching element 14. The freewheel diodes 16 and 17 are provided so that current flows when a reverse potential exceeding the breakdown voltage is applied to the pair of boost-side switching elements 13 and 14.

[0030] The intermediate capacitor 15 is electrically connected in parallel to the pair of boost-side switching elements 13 and 14. The boost-side upper arm switching element 13 is electrically connected to the positive side of the intermediate capacitor 15. The boost-side lower arm switching element 14 is electrically connected to the negative side of the intermediate capacitor 15.

[0031] The boost chopper circuit 10 having the above configuration drives a pair of boost-side switching elements 13 and 14, thereby causing the current input from a DC power supply (not shown) to flow through an intermediate capacitor 15, and boosting the voltage input from the DC power supply.

[0032] Furthermore, the pair of boost-side switching elements 13 and 14 are driven and controlled so that only one of the boost-side switching elements is turned on.

[0033] The step-down chopper circuit 20 includes an output capacitor 21, a reactor 22, a pair of step-down switching elements 23 and 24, and freewheeling diodes 26 and 27.

[0034] The pair of buck-side switching elements 23 and 24 are electrically connected in series and electrically connected in parallel to the intermediate capacitor 15 of the boost chopper circuit 10. The midpoint of the pair of buck-side switching elements 23 and 24 is electrically connected to the positive terminal of the output side capacitor 21 via the reactor 22. One endpoint of the pair of buck-side switching elements 23 and 24 is electrically connected to the negative terminal of the output side capacitor 21.

[0035] Of the pair of step-down switching elements 23 and 24, the switching element 24 that is electrically connected in parallel to the output capacitor 21 is the step-down lower arm switching element. Of the pair of step-down switching elements 23 and 24, the other switching element 23 is the step-down upper arm switching element.

[0036] The freewheel diode 26 is electrically connected in parallel to the step-down upper arm switching element 23. The freewheel diode 27 is electrically connected in parallel to the step-down lower arm switching element 24. The freewheel diodes 26 and 27 are provided so that current flows when a reverse potential exceeding the breakdown voltage is applied to the pair of step-down switching elements 23 and 24.

[0037] The step-down chopper circuit 20 having the above configuration drives a pair of step-down switching elements 23 and 24 to supply current from the step-up chopper circuit 10 to the reactor 22, thereby stepping down the output voltage of the step-up chopper circuit 10.

[0038] The drive control unit 30 controls the driving of a pair of boost-side switching elements 13 and 14 in the boost chopper circuit 10 and a pair of buck-side switching elements 23 and 24 in the buck chopper circuit 20, respectively. Specifically, the drive control unit 30 comprises a boost chopper drive control unit 31 and a buck chopper drive control unit 36.

[0039] The boost chopper drive control unit 31 boosts the output voltage of the boost chopper circuit 10 to a voltage corresponding to the boost voltage command by driving a pair of boost-side switching elements 13 and 14 based on a boost voltage command input from a controller (not shown). In other words, the boost chopper drive control unit 31 generates drive signals for the pair of boost-side switching elements 13 and 14 based on the boost voltage command. The boost voltage command is generated in a controller (not shown) according to an output voltage command, which will be described later.

[0040] Furthermore, the boost chopper drive control unit 31 generates a drive signal to control the driving of a pair of boost-side switching elements 13 and 14 such that the period during which the buck-side upper arm switching element 23 of the buck chopper circuit 20 is ON (hereinafter referred to as the ON period) overlaps with the ON period of the boost-side upper arm switching element 13 of the boost chopper circuit 10.

[0041] The detailed configuration of the boost chopper drive control unit 31 will be described later.

[0042] The buck chopper drive control unit 36 ​​drives a pair of buck-side switching elements 23 and 24 based on an output voltage command input from a controller (not shown), thereby reducing the output voltage of the buck chopper circuit 20 to a voltage corresponding to the output voltage command. In other words, the buck chopper drive control unit 36 ​​generates drive signals for the pair of buck-side switching elements 23 and 24 based on the output voltage command.

[0043] The detailed configuration of the step-down chopper drive control unit 36 ​​will be described later.

[0044] (Drive control unit) Next, the configuration of the drive control unit 30 will be described in detail using Figures 2 to 4. Figure 2 is a functional block diagram showing the schematic configuration of the boost chopper drive control unit 31. Figure 3 is a schematic diagram showing the comparison between the signal generated by the command signal processing unit 32 and the triangular wave in the boost chopper drive control unit 31. Figure 4 is a block diagram showing the schematic configuration of the buck chopper drive control unit 36. As described above, the drive control unit 30 includes a boost chopper drive control unit 31 and a buck chopper drive control unit 36.

[0045] As shown in Figure 2, the boost chopper drive control unit 31 includes a command signal processing unit 32, a triangular wave comparison unit 33, and a drive signal generation unit 34.

[0046] The command signal processing unit 32 converts the boost voltage command input to the boost chopper drive control unit 31 into a command signal that can be compared with a triangular wave of the carrier frequency using the triangular wave comparison unit 33, which will be described later. Specifically, the command signal processing unit 32 includes a subtractor 32a, a PI calculation unit 32b, a limiter 32c, a signal inverter 32d, and a scale conversion unit 32e.

[0047] The subtractor 32a calculates the difference between the boost voltage command and the output voltage of the boost chopper circuit 10. The PI calculation unit 32b performs a PI calculation on the difference obtained by the subtractor 32a. The limiter 32c cuts off values ​​above a predetermined value in the calculation result of the PI calculation unit 32b. The signal inversion unit 32d inverts the sign of the signal. The scale conversion unit 32e scales the signal so that the inverted signal is within the positive range. This generates the command signal that will be input to the triangular wave comparison unit 33, which will be described later.

[0048] The command signal processing unit 32 can be configured in any way that allows it to convert the difference between the boosted voltage command and the output voltage of the boost chopper circuit 10 into a signal comparable to a triangular wave of the carrier frequency.

[0049] As described above, the command signal processing unit 32 performs signal processing, which allows the command signal input to the triangular wave comparison unit 33 to be converted from a dashed line to a solid line, as shown in Figure 3(a). In other words, the command signal processing unit 32 converts the command signal for generating the drive signal input to the switching element that changes the timing of the switching operation, so that the phase of the carrier frequency is shifted relative to the triangular wave.

[0050] The triangular wave comparison unit 33 compares the command signal output from the command signal processing unit 32 with the carrier frequency triangular wave and generates a rectangular wave signal where the intersection of the two is the falling or rising edge. Figure 3(b) shows an example of a rectangular wave signal generated by the triangular wave comparison unit 33. As described above, the signal conversion performed in the command signal processing unit 32 causes the phase of the rectangular wave signal obtained by the triangular wave comparison unit 33 to shift (180 degrees in the example shown in the figure), as shown in Figure 3(b).

[0051] The drive signal generation unit 34 uses the square wave signal output from the triangular wave comparison unit 33 to generate drive signals for the pair of boost-side switching elements 13 and 14. Specifically, the drive signal generation unit 34 uses the square wave signal as the drive signal for the boost-side upper arm switching element 13. The drive signal generation unit 34 generates a signal by inverting the on / off state of the square wave signal and uses it as the drive signal for the boost-side lower arm switching element 14.

[0052] With the configuration of the boost chopper drive control unit 31 described above, it is possible to generate a drive signal with a different phase from the drive signal generated based on the boost voltage command. In other words, the boost chopper drive control unit 31 changes the timing of the switching operation of the pair of boost-side switching elements 13 and 14 to a timing different from the timing of the switching operation determined according to the output voltage command that forms the basis of the boost voltage command. As a result, as will be described in more detail later, it is possible to provide a period during the operation of the boost chopper circuit 10 and the buck chopper circuit 20 in which both the boost-side upper arm switching element 13 and the buck-side upper arm switching element 23 are in the ON state.

[0053] As shown in Figure 4, the step-down chopper drive control unit 36 ​​includes a command signal processing unit 37, a triangular wave comparison unit 38, and a drive signal generation unit 39.

[0054] The command signal processing unit 37 converts the output voltage command input to the step-down chopper drive control unit 36 ​​into a signal that can be compared with a triangular wave of the carrier frequency using the triangular wave comparison unit 38, which will be described later. Specifically, the command signal processing unit 37 includes a subtractor 37a, a PI calculation unit 37b, and a limiter 37c.

[0055] The subtractor 37a calculates the difference between the output voltage command and the output voltage of the step-down chopper circuit 20. The PI calculation unit 37b performs a PI calculation on the difference obtained by the subtractor 37a. The limiter 37c cuts off values ​​above a predetermined value in the calculation result of the PI calculation unit 37b.

[0056] The triangular wave comparison unit 38 compares the signal output from the command signal processing unit 37 with the carrier frequency triangular wave and generates a square wave signal where the intersection of the two is the falling or rising edge.

[0057] The drive signal generation unit 39 uses the square wave signal output from the triangular wave comparison unit 38 to generate drive signals for the pair of step-down switching elements 23 and 24. Specifically, the drive signal generation unit 39 uses the square wave signal as the drive signal for the step-down upper arm switching element 23. The drive signal generation unit 39 generates a signal by inverting the on / off state of the square wave signal to use as the drive signal for the step-down lower arm switching element 24.

[0058] (Operation of the power converter) Next, the operation of the power converter 1 having the above configuration will be explained using Figures 5 to 7. Figure 5 is a diagram showing an example of the direction of current flowing through the boost chopper circuit 10 and the buck chopper circuit 20 of the power converter 1. Figure 6 is a diagram showing an example of the change in current flowing through each position of the boost chopper circuit 10 and the buck chopper circuit 20 of the power converter 1 when the on-period of the boost-side upper arm switching element 13 and the on-period of the buck-side upper arm switching element 23 do not overlap. Figure 7 is a diagram showing an example of the change in current flowing through each position of the boost chopper circuit 10 and the buck chopper circuit 20 of the power converter 1 when the center of the on-period of the boost-side upper arm switching element 13 and the center of the on-period of the buck-side upper arm switching element 23 are aligned.

[0059] In the boost chopper circuit 10 of the power converter 1, when the boost-side upper arm switching element 13 is turned ON, current flows from the input-side capacitor 11 through the reactor 12 and the boost-side upper arm switching element 13 to the intermediate capacitor 15, as shown by the solid arrows A and B in Figure 5. This increases the input voltage. At this time, the boost-side lower arm switching element 14 is OFF.

[0060] On the other hand, when the boost-side upper arm switching element 13 is turned off, the boost-side lower arm switching element 14 is turned on, and current flows from the reactor 12 to the boost-side lower arm switching element 14 and then to the input side capacitor 11.

[0061] In the step-down chopper circuit 20 of the power converter 1, when the step-down upper arm switching element 23 is turned ON, current flows from the intermediate capacitor 15 through the step-down upper arm switching element 23 to the reactor 22, as shown by the solid arrows C and D in Figure 5. This allows the output voltage of the boost chopper circuit 10 to be stepped down. At this time, the step-down lower arm switching element 24 is in the OFF state.

[0062] The current flowing through the reactor 22 then flows through the output capacitor 21. The output current is smoothed by the reactor 22 and the output capacitor 21. The direction of the output current flow is indicated by the solid arrow F in Figure 5.

[0063] On the other hand, when the step-down upper arm switching element 23 is turned off, the step-down lower arm switching element 24 is turned on, and no current flows through the step-down chopper circuit 20.

[0064] Figure 6 shows the current changes at each position within the boost chopper circuit 10 and the buck chopper circuit 20 as described above. Figure 6 is a diagram showing an example of the current changes indicated by the solid arrows A to E in Figure 5. The solid arrow E represents the current flowing through the intermediate capacitor 15. In Figure 6, the case where current flows in the direction of the solid arrows shown in Figure 5 is shown as a positive current. In Figure 6, 13 indicates the switching operation of the boost-side upper arm switching element 13, and 23 indicates the switching operation of the buck-side upper arm switching element 23. In the case shown in Figure 6, the pair of boost-side switching elements 13, 14 and the pair of buck-side switching elements 23, 24 are each driven with a duty cycle of 50%.

[0065] As shown in Figure 6, when the boost-side upper arm switching element 13 is in the off state, the current indicated by solid arrow A increases and the current indicated by solid arrow B does not flow. On the other hand, when the boost-side upper arm switching element 13 is in the on state, the current indicated by solid arrow A decreases and the current indicated by solid arrow B flows but gradually decreases.

[0066] When the step-down upper arm switching element 23 is ON, the current indicated by the solid arrow D increases and the current indicated by the solid arrow C gradually increases. On the other hand, when the step-down upper arm switching element 23 is OFF, the current indicated by the solid arrow D decreases and no current flows as indicated by the solid arrow C.

[0067] When the center of the ON period of the boost-side upper arm switching element 13 is 180 degrees out of phase with the center of the ON period of the buck-side upper arm switching element 23, as shown in Figure 6, the current indicated by the solid arrow E is the sum of the current indicated by the solid arrow C that flows when the intermediate capacitor 15 is discharged and the current that flows when the intermediate capacitor 15 is charged (flowing in the opposite direction to the current indicated by the solid arrow B). In other words, the current indicated by the solid arrow E is the current that flows through the intermediate capacitor 15 during charging and discharging. The center of the ON period is the point in time midway between the start and end of the ON period.

[0068] Thus, when the on-periods of the boost-side upper arm switching element 13 and the buck-side upper arm switching element 23 do not overlap, a current flows through the intermediate capacitor 15, as shown by the solid arrow E in Figure 6. Because the current flowing through the intermediate capacitor 15 fluctuates significantly, the intermediate capacitor 15 needs to have a capacitance that can withstand these current fluctuations.

[0069] In contrast, in this embodiment, the boost chopper drive control unit 31 controls the driving of the pair of boost-side switching elements 13 and 14 so that the ON period of the boost-side upper arm switching element 13 and the ON period of the buck-side upper arm switching element 23 overlap. Specifically, as described above, the boost chopper drive control unit 31 generates a drive signal using the command signal obtained by the command signal processing unit 32, thereby generating a drive signal with a different phase from the drive signal generated based on the boost voltage command.

[0070] For example, when a pair of boost-side switching elements 13, 14 and a pair of buck-side switching elements 23, 24 are each driven with a duty cycle of 50%, the boost chopper drive control unit 31 can shift the phase of the drive signals of the pair of boost-side switching elements 13, 14 by 180 degrees, so that the center of the ON period of the boost-side upper arm switching element 13 and the center of the ON period of the buck-side upper arm switching element 23 coincide. As a result, the ON period of the boost-side upper arm switching element 13 and the ON period of the buck-side upper arm switching element 23 overlap.

[0071] As described above, when the phases of the drive signals of the pair of boost-side switching elements 13 and 14 are shifted by 180 degrees, and the center of the ON period of the boost-side upper arm switching element 13 coincides with the center of the ON period of the buck-side upper arm switching element 23, current flows through each position of the boost chopper circuit 10 and the buck chopper circuit 20 as shown in Figure 7. That is, the phases of the currents indicated by solid arrows A and B are shifted by 180 degrees with respect to the phases of the currents indicated by solid arrows A and B in Figure 6, respectively.

[0072] As a result, the current indicated by the solid arrow E, i.e., the current flowing through the intermediate capacitor 15, cancels out and is reduced, as shown in Figure 7. In other words, by controlling the drive of the pair of boost-side switching elements 13 and 14 as described above, it is possible to create a period in which current flows directly from the boost chopper circuit 10 to the buck chopper circuit 20, thereby suppressing fluctuations in the current flowing through the intermediate capacitor 15.

[0073] Therefore, fluctuations in the current flowing through the intermediate capacitor 15 during charging and discharging can be suppressed. As a result, the capacitance of the intermediate capacitor 15 can be reduced, which can lead to a reduction in the cost of the intermediate capacitor 15 and a miniaturization of the power converter.

[0074] The power converter 1 according to this embodiment includes a boost chopper circuit 10 electrically connected to a DC power supply and boosting the input voltage according to an output voltage command, a buck chopper circuit 20 electrically connected to the output side of the boost chopper circuit 10 and outputting a voltage reduced according to the output voltage command, an intermediate capacitor 15 located on the output side of the boost chopper circuit 10 and supplying power to the buck chopper circuit 20, and a drive control unit 30 that controls the driving of the boost chopper circuit 10 and the buck chopper circuit 20, respectively. The boost chopper circuit 10 has a pair of boost-side switching elements 13, 14 electrically connected in parallel to the intermediate capacitor 15 and electrically connected in series with each other. The buck chopper circuit 20 has a pair of buck-side switching elements 23, 24 electrically connected in parallel to the intermediate capacitor 15 and electrically connected in series with each other. The drive control unit 30 controls the switching operation of at least one of the pair of boost-side switching elements 13, 14 and the pair of buck-side switching elements 23, 24 such that the ON period when the boost-side upper arm switching element 13, which is electrically connected to the positive side of the intermediate capacitor 15, is ON, overlaps with the ON period when the buck-side upper arm switching element 23, which is electrically connected to the positive side of the intermediate capacitor 15, is ON.

[0075] In this circuit configuration, where a pair of boost-side switching elements 13, 14 and a pair of buck-side switching elements 23, 24 are electrically connected in parallel to an intermediate capacitor 15 located on the output side of the boost chopper circuit 10 and supplying power to the buck chopper circuit 20, current flows through the intermediate capacitor 15 when the input voltage is boosted by the boost chopper circuit 10, and current also flows through the intermediate capacitor 15 when the voltage is stepped down by the buck chopper circuit 20. Therefore, the current flowing through the intermediate capacitor 15 fluctuates significantly depending on the operation of the boost chopper circuit 10 and the buck chopper circuit 20.

[0076] In response to this, the drive control unit 30 controls the switching operation of at least one of the pair of boost-side switching elements 13, 14 and the pair of buck-side switching elements 23, 24 so that the ON period of the boost-side upper arm switching element 13 and the ON period of the buck-side upper arm switching element 23 overlap, thereby providing a period during which current flows directly from the boost chopper circuit 10 to the buck chopper circuit 20. Therefore, fluctuations in the current flowing through the intermediate capacitor 15 due to the operation of the boost chopper circuit 10 and the buck chopper circuit 20 can be suppressed.

[0077] Therefore, the capacitance of the intermediate capacitor 15 can be reduced, which in turn reduces the cost of the intermediate capacitor 15 and miniaturizes the power converter 1.

[0078] Furthermore, in this embodiment, the drive control unit 30 controls the switching operation of at least one of the pair of boost-side switching elements 13, 14 and the pair of buck-side switching elements 23, 24 so that the center of the ON period of the boost-side upper arm switching element 13 coincides with the center of the ON period of the buck-side upper arm switching element 23.

[0079] This allows the on-periods of the boost-side upper arm switching element 13 and the buck-side upper arm switching element 23 to overlap more reliably and over a wider range when operating the boost chopper circuit 10 and the buck chopper circuit 20. As a result, the period during which current flows directly from the boost chopper circuit 10 to the buck chopper circuit 20 can be extended. Therefore, fluctuations in the current flowing through the intermediate capacitor 15 due to the operation of the boost chopper circuit 10 and the buck chopper circuit 20 can be suppressed.

[0080] Therefore, the capacitance of the intermediate capacitor 15 can be reduced, which in turn reduces the cost of the intermediate capacitor 15 and allows the power converter 1 to be made smaller.

[0081] Furthermore, in this embodiment, the drive control unit 30 changes the timing of the switching operation of the pair of boost-side switching elements 13 and 14 to a timing different from the switching operation timing determined according to the output voltage command, so that the ON period of the boost-side upper arm switching element 13 overlaps with the ON period of the buck-side upper arm switching element 23.

[0082] This allows the drive of the pair of boost-side switching elements 13 and 14 to be controlled when operating the boost chopper circuit 10 and the buck chopper circuit 20, making it easy to overlap the on-period of the boost-side upper arm switching element 13 and the on-period of the buck-side upper arm switching element 23. Therefore, the configuration of this embodiment can be easily realized.

[0083] Furthermore, in this embodiment, the drive control unit 30 includes a command signal processing unit 32 that converts a command signal for generating a drive signal input to a pair of boost-side switching elements 13 and 14 so that its phase is shifted relative to the triangular wave of the carrier frequency; a triangular wave comparison unit 33 that compares the converted command signal with the triangular wave; and a drive signal generation unit 34 that generates the drive signal using the comparison result from the triangular wave comparison unit 33.

[0084] This allows the configuration of this embodiment to be realized by converting the command signal. Therefore, the configuration of this embodiment can be easily realized compared to the case where the carrier frequency used when generating the drive signal input to the switching element is changed.

[0085] [Embodiment 2] Figure 8 is a functional block diagram showing an example of the schematic configuration of the boost chopper drive control unit 131 of the power converter according to Embodiment 2. In this embodiment, the boost chopper drive control unit 131 differs from the configuration of Embodiment 1 in that it generates a phase-shifted signal by changing the phase of the triangular wave of the carrier frequency. In the following, components similar to those in Embodiment 1 are denoted by the same reference numerals and their descriptions are omitted, and only components different from Embodiment 1 will be described.

[0086] As shown in Figure 8, the drive control unit 130 includes a boost chopper drive control unit 131 and a buck chopper drive control unit 36. The boost chopper drive control unit 131 has the same configuration as the buck chopper drive control unit 36. That is, the boost chopper drive control unit 131 includes a command signal processing unit 132, a triangular wave comparison unit 33, and a drive signal generation unit 34.

[0087] The command signal processing unit 132, like the command signal processing unit 37 of the step-down chopper drive control unit 36, includes a subtractor 132a, a PI calculation unit 132b, and a limiter 132c. The subtractor 132a has the same function as the subtractor 32a in Embodiment 1. The PI calculation unit 132b has the same function as the PI calculation unit 32b in Embodiment 1. The limiter 132c has the same function as the limiter 32c in Embodiment 1. Therefore, a detailed explanation of the configuration of the command signal processing unit 132 is omitted.

[0088] The command signal generated by the command signal processing unit 132 is input to the triangular wave comparison unit 33. The triangular wave signal input to the triangular wave comparison unit 33 is a signal whose phase is shifted by 180 degrees relative to the triangular wave signal input to the triangular wave comparison unit 38 of the step-down chopper drive control unit 36. The triangular wave signal with a phase shift of 180 degrees is generated by the phase conversion unit 140. In other words, the drive control unit 130 has a phase conversion unit 140.

[0089] Figure 9 schematically shows how the boost chopper drive control unit 131 compares the command signal generated by the command signal processing unit 132 with a triangular wave that is 180 degrees out of phase. As shown by the solid line in Figure 9(a), the triangular wave comparison unit 33 receives a signal that is 180 degrees out of phase with the triangular wave signal shown by the dashed line (the signal input to the triangular wave comparison unit 33 of the buck chopper drive control unit 36).

[0090] The drive signal generation unit 34 generates a drive signal for a pair of boost-side switching elements 13 and 14 based on the comparison result by the triangular wave comparison unit 33. The generated drive signal (solid line in Figure 9(b)) is 180 degrees out of phase compared to the drive signal generated using the triangular wave signal before the phase shift (dashed line in Figure 9(b)), as shown in Figure 9(b).

[0091] In this embodiment, the boost chopper drive control unit 131 can generate a drive signal that is 180 degrees out of phase with respect to the drive signal generated by the buck chopper drive control unit 36.

[0092] (Other embodiments) Although embodiments of the present invention have been described above, the embodiments described above are merely examples for carrying out the present invention. Therefore, the invention is not limited to the embodiments described above, and it is possible to carry out the invention by appropriately modifying the embodiments described above without departing from the spirit of the invention.

[0093] In each of the above embodiments, the switching operation when a pair of boost-side switching elements 13, 14 and a pair of buck-side switching elements 23, 24 are driven with a duty cycle of 50% has been described. However, the pair of boost-side switching elements and the pair of buck-side switching elements may also switch with a duty cycle other than 50%. Even when the pair of boost-side switching elements and the pair of buck-side switching elements switch with a duty cycle other than 50%, the boost chopper drive control unit only needs to drive the pair of boost-side switching elements so that the on-period of the boost-side upper arm switching element and the on-period of the buck-side upper arm switching element overlap.

[0094] For example, as shown in Figure 10, the boost chopper drive control unit may drive and control the pair of boost-side switching elements such that the on-period of the boost-side upper arm switching element 13 and the on-period of the buck-side upper arm switching element 23 overlap, by making the duty cycle of the boost-side upper arm switching element 13 larger than the duty cycle of the buck-side upper arm switching element 23. In Figure 10, the dashed lines represent the centers of the on-periods of the boost-side upper arm switching element 13 and the buck-side upper arm switching element 23.

[0095] In each of the above embodiments, the boost chopper drive control units 31 and 131 generate drive signals for a pair of boost-side switching elements 13 and 14 such that the center of the ON period of the boost-side upper arm switching element 13 coincides with the center of the ON period of the buck-side upper arm switching element 23. However, the boost chopper drive control unit does not need to generate drive signals for a pair of boost-side switching elements such that the centers of their ON periods coincide, as long as the ON periods of the boost-side upper arm switching element and the ON period of the buck-side upper arm switching element overlap. In other words, the configuration is not limited to shifting the phase of the command signal or carrier frequency triangular wave by 180 degrees, as in each of the above embodiments, but the phase of the command signal or carrier frequency triangular wave may be shifted by an angle other than 180 degrees.

[0096] In each of the above embodiments, the boost chopper drive control units 31 and 131 generate drive signals for a pair of boost-side switching elements 13 and 14 such that the on-period of the boost-side upper arm switching element 13 and the on-period of the buck-side upper arm switching element 23 overlap. However, the buck chopper drive control unit may generate drive signals for a pair of buck-side switching elements such that the on-period of the boost-side upper arm switching element and the on-period of the buck-side upper arm switching element overlap. In this case, the buck chopper drive control unit only needs to have a configuration that shifts the phase of the command signal or the triangular wave of the carrier frequency, as in the boost chopper drive control units 31 and 131 of each of the above embodiments. Alternatively, the boost chopper drive control unit and the buck chopper drive control unit may generate drive signals for a pair of boost-side switching elements and a pair of buck-side switching elements such that the on-period of the boost-side upper arm switching element and the on-period of the buck-side upper arm switching element overlap. [Industrial applicability]

[0097] The present invention can be used in a power conversion device comprising a boost chopper circuit and a buck chopper circuit, wherein an intermediate capacitor that supplies power to the buck chopper circuit is located on the output side of the boost chopper circuit. [Explanation of symbols]

[0098] 1. Power converter 10. Boost chopper circuit (boost section) 11 Input capacitor 12, 22 Reactors 13. Boost-side upper arm switching element (boost-side switching element) 14. Boost-side lower arm switching element (boost-side switching element) 15 Intermediate Capacitor 16, 17, 26, 27 Freewheeling diodes 20. Step-down chopper circuit (step-down section) 21 Output capacitor 23. Step-down upper arm switching element (step-down switching element) 24. Step-down lower arm switching element (step-down switching element) 30, 130 Drive control unit 31, 131 Boost Chopper Drive Control Unit 32, 37, 132 Command signal processing unit 32a, 37a, 132a Subtractors 32b, 37b, 132b PI calculation section 32c, 37c, 132c limiter 32d Signal Inversion Section 32e Scale conversion section 33, 38 Triangular wave comparison section 34, 39 Drive signal generation unit 36 Step-down chopper drive control unit 140 Phase conversion section

Claims

1. A boost converter is electrically connected to a DC power supply and boosts the input voltage according to the output voltage command, A step-down unit is electrically connected to the output side of the step-up unit and outputs a stepped-down voltage according to the output voltage command, An intermediate capacitor located on the output side of the boost section and supplying power to the step-down section, A drive control unit that controls the driving of the boost unit and the buck unit, respectively, A power conversion device equipped with, The boost unit has a pair of boost-side switching elements that are electrically connected in parallel to the intermediate capacitor and electrically connected in series to each other. The step-down section has a pair of step-down switching elements that are electrically connected in parallel to the intermediate capacitor and electrically connected in series to each other. The drive control unit controls the switching operation of at least one of the pair of boost-side switching elements and the pair of buck-side switching elements such that the on-period when the boost-side upper arm switching element, which is electrically connected to the positive terminal side of the intermediate capacitor, is in the ON state overlaps with the on-period when the buck-side upper arm switching element, which is electrically connected to the positive terminal side of the intermediate capacitor, is in the ON state. Power converter.

2. In the power conversion device according to claim 1, The drive control unit controls the switching operation of at least one of the pair of boost-side switching elements and the pair of buck-side switching elements such that the center of the ON period of the boost-side upper arm switching element coincides with the center of the ON period of the buck-side upper arm switching element. Power converter.

3. In the power conversion device according to claim 1, The drive control unit changes the timing of the switching operation of the pair of boost-side switching elements to a timing different from the timing of the switching operation determined according to the output voltage command, so that the ON period of the boost-side upper arm switching element overlaps with the ON period of the buck-side upper arm switching element. Power converter.

4. In a power conversion device according to any one of claims 1 to 3, The drive control unit, A command signal processing unit converts a command signal for generating a drive signal input to a switching element among the pair of boost-side switching elements and the pair of buck-side switching elements, such that the phase of the command signal is shifted relative to the triangular wave of the carrier frequency, A triangular wave comparison unit compares the converted command signal with the triangular wave, A drive signal generation unit generates the drive signal using the comparison results from the aforementioned triangular wave comparison unit, Having, Power converter.

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