Power conversion device

Abstract

To provide a power conversion device that can correct a control target value to avoid an operating region in which the control accuracy of output voltage and current decreases.SOLUTION: One aspect of the disclosed technology is illustrated by a power conversion device described below. The power conversion device includes a first capacitor, a second capacitor, a first switching unit, a second switching unit, a transformer, and a control unit that controls switching of the first switching unit and the second switching unit. The control unit determines a corrected target value by correcting a control target value for a second voltage such that the difference between the command value and a third voltage obtained by dividing the first voltage by a turns ratio between a first winding and a second winding included in the transformer is equal to or greater than a predetermined difference.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] Conventionally, in a bidirectional DC / DC converter, which is a power conversion device, circuit operation has been achieved by utilizing current flow through a switching element and a body diode, as described in Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-205001 A Summary of the Invention [Problem to be solved by the invention]

[0004] In an isolated DC / DC converter, due to the relationship between the input DC power supply voltage, the output voltage, and the turns ratio of the transformer, there is a risk that the control accuracy of the output voltage and current will decrease in an operating region where the DC power supply voltage and the output voltage are close to each other.

[0005] An object of one aspect of the disclosed technique is to provide a power conversion device capable of correcting a control target value so as to avoid an operating region in which the control accuracy of the output voltage and current decreases. [Means for solving the problem]

[0006] One aspect of the disclosed technology is exemplified by a power conversion device as follows. The power conversion device includes a first capacitor that smoothes an input first voltage, a second capacitor that smoothes an output second voltage, a first switching unit connected to the first capacitor, a second switching unit connected to the second capacitor, a transformer disposed between the first switching unit and the second switching unit, and a control unit that controls switching of the first switching unit and the second switching unit. The control unit determines a corrected target value by correcting a control target value for the second voltage such that a difference between the control target value and a third voltage obtained by dividing the first voltage by a turns ratio between a first winding and a second winding included in the transformer is equal to or greater than a predetermined difference.

[0007] According to the present power conversion device, the difference between the third voltage and the control target value is ensured by adding a correction value. As a result, the difference between the third voltage and the output voltage becomes equal to or greater than the predetermined difference, so that the control target value can be corrected to avoid an operating region in which control accuracy decreases. Here, the corrected target value may be determined by adding a correction value to the third voltage. Furthermore, when the absolute value of the difference between the control target value and the third voltage is less than a first threshold value, the corrected target value may be determined by adding a correction value to the control target value.

[0008] The power conversion device may further include the following feature. When a difference between the control target value and the third voltage becomes equal to or greater than a second threshold value that is greater than the first threshold value after determining the corrected target value, the control unit interrupts the process of adding the correction value to the control target value, and sets the control target value to the corrected target value. By including such a feature, the power conversion device is prevented from frequently and repeatedly interrupting and resuming the addition of the correction value to the control target value.

[0009] The power conversion device may further include the following feature: the control unit controls the first switching unit and the second switching unit so as to output a voltage corresponding to the corrected target value. By providing such a feature, the power conversion device of the present invention can avoid an operating region in which the control accuracy of the output voltage and current decreases.

[0010] The power conversion device may include, instead of the transformer, a transformer disposed between the first switching unit and the second switching unit, capable of switching a turn ratio between a first winding and a second winding included in the transformer. The control unit may cause the transformer to change the turn ratio so that a difference between a third voltage obtained by dividing the first voltage by the turn ratio and a control target value related to the second voltage becomes equal to or greater than a predetermined difference. By providing such a feature, the power conversion device can make the difference between the third voltage and the output voltage equal to or greater than the predetermined difference. As a result, the power conversion device can avoid an operating region in which control accuracy decreases. Effect of the Invention

[0011] According to the disclosed technique, the control target value can be corrected so as to avoid an operating region in which the control accuracy deteriorates. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic configuration diagram of a power conversion device according to an embodiment. [Diagram 2] FIG. 2 is a control block diagram realized by the control unit according to the embodiment. [Diagram 3] FIG. 3 is a diagram illustrating a configuration in which the DC power supply voltage on the input / output terminal pair connected to an EV is converted in consideration of the turns ratio of a transformer. [Figure 4] FIG. 4 is a first diagram illustrating an example of the correction process by the command value generating unit. [Diagram 5] FIG. 5 is a second diagram illustrating an example of the correction process by the command value generating unit. [Figure 6] FIG. 6 is a control block diagram realized by a control unit according to the first modified example. [Figure 7]FIG. 7 is a first diagram illustrating an example of the correction process by the command value generating unit. [Figure 8] FIG. 8 is a second diagram illustrating an example of the correction process by the command value generating unit. [Figure 9] FIG. 9 is a first diagram showing another example of the correction process by the command value generating unit. [Figure 10] FIG. 10 is a second diagram showing another example of the correction process by the command value generating unit. [Figure 11] FIG. 11 is a diagram showing a schematic configuration of a DC / DC converter according to a second modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] <Application Examples> An application example of the present invention will be described below with reference to the drawings. The present invention is applied to a power conversion device 1 including an isolated bidirectional DC / DC converter 10 shown in Fig. 1. The power conversion device 1 comprises the DC / DC converter 10, a control unit 20, and two pairs of input / output terminals 13 (13p, 13m) and an input / output terminal pair 14 (14p, 14m). Capacitors C1 and C2 for smoothing the input voltage are connected between the input / output terminals 13m, 13p, and between the input / output terminals 14m, 14p, respectively.

[0014] The DC / DC converter 10 is an insulated bidirectional DC / DC converter whose main components are a transformer TR, two reactors Lr1 and Lr2, and two full-bridge circuits 11 and 12. The reactors Lr1 and Lr2 generate AC power under the control of the full-bridge circuits 11 and 12, and the capacitors C1 and C2 smooth the AC power into DC power. An insulating transformer can be used as the transformer TR, but a non-insulating transformer may also be used.

[0015] The full bridge circuit 12 of the DC / DC converter 10 is a series-connected switching element. The inverter circuit includes a leg L3 having a switching element Q5 and a switching element Q7 connected in series, and a leg L4 having a switching element Q6 and a switching element Q8 connected in series. As shown in the figure, a diode Dn (n=5 to 8) is connected in parallel between the terminals of the switching element Qn (n=5 to 8) of each leg. In addition, both of the legs L3 and L4 are connected to an input / output terminal pair 14. A connection point p3 between the switching element Q5 and the switching element Q7 of the leg L3 is connected to one end of the winding Wn2 of the transformer TR via a reactor Lr2, and a connection point p4 between the switching element Q6 and the switching element Q8 of the leg L4 is connected to the other end of the winding Wn2 of the transformer TR.

[0016] 2 shows an example of a control block diagram realized by the control unit 20. The control unit 20 includes a command value generating section 22, a control section 23, and a PWM generating section 24.

[0017] As can be understood by referring to formula (1) described later, in the DC / DC converter 10, in an operating region where V1 / n obtained by dividing the input voltage V1 by the turns ratio n between the windings Wn1 and Wn2 included in the transformer TR and the output side DC bus voltage V2 are close in value, the amount of change in current per unit time with respect to the change in the duty ratio or phase shift amount becomes small, which may reduce the control accuracy of the DC / DC converter 10. Therefore, in this application example, a corrected target value is determined such that the difference between V1 / n obtained by dividing the voltage V1 input to the DC / DC converter 10 by the turns ratio n and the control target value related to the output voltage is equal to or greater than a predetermined difference.

[0018] According to this application example, since the difference between V1 / n and the corrected target value can be secured, the control target value can be corrected so as to avoid an operating region in which the control accuracy of the DC / DC converter 10 decreases.

[0019] [Embodiment] Hereinafter, the power conversion device 1 according to the embodiment of the present invention will be described in more detail with reference to the drawings.

[0020] <Configuration of power conversion device> FIG. 1 is a schematic diagram of a power conversion device according to an embodiment. The power conversion device 1 according to this embodiment is a device capable of bidirectional power conversion. As shown in the figure, the power conversion device 1 includes a DC / DC converter 10, a control unit 20, and two pairs of input / output terminal pairs 13 (13p, 13m) and an input / output terminal pair 14 (14p, 14m). In the input / output terminal pairs 13 and 14, the input / output terminals 13p and 14p are high-potential input / output terminals, and the input / output terminals 13m and 14m are low-potential input / output terminals. In FIG. 1, the voltage of the input / output terminal pair 13 is V1, and the voltage of the input / output terminal pair 14 is V2. A capacitor C1 for smoothing the input / output voltage is connected between the input / output terminals 13m and 13p. Similarly, a capacitor C2 for smoothing the input / output voltage is connected between the input / output terminals 14m and 14p. Electrolytic capacitors can be used as the capacitors C1 and C2.

[0021] The DC / DC converter 10 is an insulated bidirectional DC / DC converter whose main components are a transformer TR, two reactors Lr1 and Lr2, and two full bridge circuits 11 and 12. Hereinafter, the full bridge circuit 11 on the left side and the full bridge circuit 12 on the right side in FIG. 1 will be referred to as the full bridge circuit 11 and the full bridge circuit 12, respectively. Similarly, the reactors Lr1 and Lr2 on the left side and the right side in FIG. 1 will be referred to as the reactor Lr1 and the reactor Lr2, respectively, and the winding Wn1 on the left side and the winding Wn2 on the right side in FIG. 1 of the transformer TR will be referred to as the winding Wn1 and the winding Wn2, respectively. In addition, the input / output terminal pair 13 (13p, 13m) and the input / output terminal pair 14 (14p, 14m) on the left side and the right side in FIG. 1 will be referred to as the input / output terminal pair 13 and the input / output terminal pair 14, respectively. The reactors Lr1 and Lr2 are connected to the windings Wn1 and Wn2 of the transformer TR. The leakage inductance of the wire Wn2 may be utilized. The transformer TR of the DC / DC converter 10 does not need to have a turns ratio of 1:1.

[0022] The full-bridge circuit 11 of the DC / DC converter 10 includes a leg L1 having a switching element Q1 and a switching element Q3 connected in series, and a leg L2 having a switching element Q2 and a switching element Q4 connected in series. As shown in the figure, a diode Dn (n=1 to 4) is connected in parallel between the terminals of the switching element Qn (n=1 to 4) of each leg. Each leg is connected to an input / output terminal pair 13, and a connection point p1 between the switching element Q1 and the switching element Q3 of the leg L1 is connected to one end of the winding Wn1 of the transformer TR via a reactor Lr1. A connection point p2 between the switching element Q2 and the switching element Q4 of the leg L2 is connected to the other end of the winding Wn1 of the transformer TR.

[0023] The full bridge circuit 12 of the DC / DC converter 10 includes a leg L3 having a switching element Q5 and a switching element Q7 connected in series, and a leg L4 having a switching element Q6 and a switching element Q8 connected in series. As shown in the figure, a diode Dn (n=5 to 8) is connected in parallel between the terminals of the switching element Qn (n=5 to 8) of each leg. In addition, both the leg L3 and the leg L4 are connected to an input / output terminal pair 14. In addition, a connection point p3 between the switching element Q5 and the switching element Q7 of the leg L3 is connected to one end of the winding Wn2 of the transformer TR via a reactor Lr2, and a connection point p4 between the switching element Q6 and the switching element Q8 of the leg L4 is connected to the other end of the winding Wn2 of the transformer TR.

[0024] The semiconductor material of the switching elements Q1 to Q8 may be, but is not limited to, gallium nitride (GaN), silicon (Si), silicon carbide (SiC), etc. The semiconductor switching elements may be, for example, a metal oxide semiconductor field effect transistor (MOSFET) or an insulated gate bipolar transistor (IGBT). The diodes D1 to D8 are connected in antiparallel to these semiconductor switching elements used as the switching elements Q1 to Q8. The DC / DC converter 10 may be provided with various sensors (not shown) for measuring the magnitude of input / output voltages and input / output currents.

[0025] The control unit 20 is a unit that controls the DC / DC converter 10 (ON / OFF of each switching element in the DC / DC converter 10) by changing the level of a control signal to each switching element in the DC / DC converter 10. Hereinafter, the control signal for the switching element Qn (n=1 to 8) will be referred to as a control signal Gn.

[0026] The control unit 20 is composed of a processor (in this embodiment, a microcontroller), a gate driver, etc., and the control unit 20 may receive outputs from the various sensors described above.

[0027] The control unit 20 is configured (programmed) to determine whether the DC / DC converter 10 should operate as one of the following four types of converters based on the input data (current value, voltage value), and to control the DC / DC converter 10 to operate as the determined converter. Input / output terminal pair 13 is the primary side boost converter Input / output terminal pair 13 is the primary side of the step-down converter Input / output terminal pair 14 is the primary side boost converter Input / output terminal pair 14 is the primary side of the step-down converter

[0028] In addition, control unit 20 is configured (programmed) to instantly change the control content for DC / DC converter 10 (such as changing from control that causes DC / DC converter 10 to operate as a step-up converter on the input / output terminal pair 13 side as the primary side to control that causes DC / DC converter 10 to operate as a step-down converter on the input / output terminal pair 14 side as the primary side).

[0029] Fig. 2 is a control block diagram realized by a control unit 20 according to the embodiment. As shown in Fig. 2, in this embodiment, a DC / DC converter 10 is connected to an EV2 (electrically-driven automobile) and an inverter 30. The inverter 30 is a device that performs AC / DC conversion, and electrically connects the DC / DC converter 10 (direct current) to an AC power system 3. Examples of the EV2 include a BEV (Battery Electric Vehicle) that runs only on battery power, a PHV (Plug-in Hybrid Vehicle) that uses both a battery and an internal combustion engine, an FCV (Fuel Cell Vehicle) that runs on fuel cell power, and various other types of electrically-driven automobiles. However, the DC / DC converter 10 is not limited to being used with such an EV 2, and may be connected to, for example, a home storage battery, a solar cell (PV), etc. Furthermore, the DC / DC converter 10 may be used, for example, for controlling the running of an electric vehicle that runs on DC power, or for controlling various other electric devices.

[0030] The control unit 20 controls the DC / DC converter 10 according to command values ​​sent from a higher-level device. The command values ​​sent from the higher-level device to the control unit 20 are values ​​determined based on the remaining charge of the EV 2 and the power consumption of the load 4. The control unit 20 includes a CPU (Central Processing Unit), a ROM (read only memory), and a RAM (Random Access Memory ) and an input / output interface, and the CPU executes a computer program stored in the storage device to realize each of the functional blocks shown below. Using each of the functional blocks shown below, the control unit 20 generates a PWM signal according to a command value sent from a higher-level device and sends it to the DC / DC converter 10. The command value sent from the higher-level device is an example of a "control target value."

[0031] 2, the control unit 20 realizes a command value generating section 22, a control section 23, and a PWM generating section 24 by executing a computer program. The command value generating section 22 generates a command value to be output to the control section 23 based on a command value received from a higher-level device. The control section 23 instructs the PWM generating section 24 to generate a PWM signal based on the command value received from the command value generating section 22. The PWM generating section 24 generates a PWM signal according to the instruction received from the control section 23, and supplies the generated PWM signal to the DC / DC converter 10.

[0032] FIG. 3 is a diagram illustrating a configuration in which the DC power supply voltage on the input / output terminal pair 13 side connected to EV2 is converted taking into consideration the turns ratio of the transformer TR. In FIG. 3, the excitation inductance of the transformer TR is ignored. In FIG. 3, the turns ratio of the transformer TR is set to n (the number of turns of the winding Wn1 / the number of turns of the winding Wn2). Using the turns ratio n, the DC power supply voltage can be expressed as V1 / n. In FIG. 3, Lr is the inductance component of the full-bridge circuit 12. The current I L A differential equation for the average of one switching period of the switching element Qn (n=1 to 8) can be expressed by the following formula (1). Note that in the following formula (1), the internal loss of the DC / DC converter 10 is ignored.

number

[0033] In formula (1), a 1 , a 2 , a 3D is one of the values ​​"0", "1", or "-1" and varies depending on the circuit topology and the switching pattern of the switching element Qn (n = 1 to 8). 1 , D 2 , D 3 is the ratio with respect to one switching period. Referring to formula (1), it can be seen that in an operating region where V1 / n and V2 are close to each other, the amount of change in current per unit time with respect to the change in the duty ratio or the amount of phase shift becomes small, and therefore the control accuracy of the DC / DC converter 10 tends to decrease. In this embodiment, in order to avoid such an operating region, the following configuration is adopted.

[0034] The command value generating unit 22 ensures the difference between V1 / n and the DC bus voltage V2 by adding the correction value to the command value received from the higher-level device. In other words, the command value generating unit 22 applies the correction value to avoid an operating region in which the control accuracy decreases.

[0035] 4 and 5 are diagrams showing an example of the correction process by the command value generating unit 22. In FIG. 4 and FIG. 5, the vertical axis indicates voltage, and the horizontal axis indicates time. The "lower limit value" in FIG. 4 and FIG. 5 indicates the lower limit value of the DC bus voltage V2. Moreover, the graph G1 in FIG. 4 and the graph G3 in FIG. 5 indicate the command value received from the upper device. The graph GH1 in FIG. 4 and the graph GH2 in FIG. 5 indicate the correction value corrected by the command value generating unit 22. The graph G2 in FIG. 4 and the graph G4 in FIG. 5 indicate V1 / n calculated based on the measured value of the voltage V1 between the input / output terminals 13p and 13m. In the example of FIG. 4 and FIG. 5, it is assumed that the lower limit value of the DC bus voltage V2 is received as the command value from the upper device.

[0036] 4, V1 / n illustrated by graph G2 increases with time. In the period from time 0 to less than time T1, V1 / n is less than the lower limit even if the correction value is added, so the command value generating unit 22 outputs the command value received from the higher-level device to the control unit 23 as is.

[0037] When the result of adding the correction value to V1 / n at time T1 is equal to or greater than the lower limit, the command value generating unit 22 adds the correction value H1 to V1 / n to determine a corrected command value, and outputs the determined corrected command value. The correction value H1 is appropriately determined at the time of design so as to avoid an operating region where the control accuracy decreases.

[0038] 5, V1 / n illustrated by graph G4 decreases with time. In the period from time 0 to less than time T2, the result of adding the correction value H1 to V1 / n is equal to or greater than the lower limit, so the command value generating unit 22 adds the correction value H1 to V1 / n to determine the corrected command value. The command value generating unit 22 outputs the determined corrected command value.

[0039] In the period after time T2, even if the correction value H1 is added to V1 / n, the result is less than the lower limit value, and therefore the command value generating unit 22 outputs the command value received from the higher-level device as is.

[0040] <Effects of the embodiment> In this embodiment, when the result of adding the correction value H1 to V1 / n, which is obtained by dividing the DC power supply voltage by the turns ratio of the transformer TR, is equal to or greater than the lower limit of the DC bus voltage V2, the command value generating unit 22 adds the correction value H1 to V1 / n to determine the command value after correction. Since the difference between the command value and V1 / n can be secured by adding the correction value H1, this embodiment makes it possible to correct the control target value so as to avoid an operating region in which the control accuracy of the output voltage and current of the DC / DC converter 10 decreases. Furthermore, this embodiment makes it possible to avoid an operating region in which the control accuracy of the output voltage and current of the DC / DC converter 10 decreases by controlling the DC / DC converter 10 to output power according to the control target value in this way.

[0041] [First Modification] In the embodiment described above, the correction value H1 is added to V1 / n to determine the corrected command value. In the first modified example, a configuration in which a command value is corrected using two threshold values ​​will be described. Components common to the embodiment will be given the same reference numerals, and descriptions thereof will be omitted. Hereinafter, the first modified example will be described with reference to the drawings.

[0042] 6 is a control block diagram realized by a control unit 20A according to a first modified example. The control unit 20A differs from the control unit 20 according to the embodiment in that the control unit 20A has a command value generating unit 22A instead of the command value generating unit 22.

[0043] When the absolute value of the difference between V1 / n and the command value received from the higher-level device is less than a first threshold, the command value generating unit 22A adds a correction value to the command value to ensure the difference between V1 / n and the DC bus voltage V2. When the absolute value of the difference between V1 / n and the command value becomes equal to or greater than a second threshold that is greater than the first threshold, the command value generating unit 22A stops adding the correction value to the command value and outputs the command value.

[0044] 7 and 8 are diagrams showing an example of the correction process by the command value generating unit 22A. In FIG. 7 and FIG. 8, the vertical axis indicates voltage, and the horizontal axis indicates time. The "lower limit value" in FIG. 7 and FIG. 8 indicates the lower limit value of the DC bus voltage V2. Moreover, the graph G5 in FIG. 7 and the graph G7 in FIG. 8 indicate the command value received from the upper device. The graph G6 in FIG. 7 and the graph G8 in FIG. 8 indicate V1 / n calculated based on the measured value of the voltage V1 between the input / output terminals 13p and 13m. The graph GH3 in FIG. 7 and the graph GH4 in FIG. 8 indicate the command value after correction by the command value generating unit 22A. In the example of FIG. 7 and FIG. 8, it is assumed that the lower limit value of the DC bus voltage V2 is received as the command value from the upper device.

[0045] 7, V1 / n illustrated by the graph G6 increases over time. In the period from time 0 to less than time T3, the absolute value of the difference between the lower limit value of the DC bus voltage V2 and V1 / n is greater than the first threshold value, so the command value generating unit 22A outputs the command value received from the higher-level device to the control unit 23 as is.

[0046] At time T3, the absolute value of the difference between the lower limit value of the DC bus voltage V2 and V1 / n becomes smaller than the first threshold value. Therefore, the command value generating unit 22A adds the correction value H2 to the command value to determine the corrected command value, and outputs the determined corrected command value. The correction value H2 is, for example, a value equal to or greater than the first threshold value.

[0047] At time T4, the absolute value of the difference between the lower limit value of the DC bus voltage V2 and V1 / n is greater than the first threshold but less than the second threshold that is greater than the first threshold. Therefore, the command value generator 22A adds the correction value H2 to the command value to determine a corrected command value, and outputs the determined corrected command value.

[0048] At time T5, the absolute value of the difference between the lower limit value of the DC bus voltage V2 and V1 / n becomes equal to or greater than the second threshold value, which is greater than the absolute value of the first threshold value. Therefore, the command value generating unit 22A stops adding the correction value H2 to the command value and outputs the command value received from the upper device.

[0049] 8, V1 / n illustrated by the graph G8 decreases over time. In the period from time 0 to less than time T6, the absolute value of the difference between the lower limit value of the DC bus voltage V2 and V1 / n is greater than the first threshold value, so the command value generating unit 22A outputs the command value received from the higher-level device to the control unit 23 as is.

[0050] At time T6, the absolute value of the difference between the lower limit value of the DC bus voltage V2 and V1 / n is smaller than the first threshold value. Therefore, the command value generator 22A adds the correction value H2 to V1 / n to determine a corrected command value, and outputs the determined corrected command value.

[0051] During the period from time T6 to time T7, the absolute value of the difference between the lower limit value of the DC bus voltage V2 and V1 / n is greater than the first threshold but less than the second threshold that is greater than the first threshold. Therefore, the command value generator 22A adds the correction value H2 to the command value to determine the corrected command value, and outputs the determined corrected command value.

[0052] After time T7, the absolute value of the difference between the lower limit value of the DC bus voltage V2 and V1 / n becomes equal to or greater than the second threshold value, which is greater than the absolute value of the first threshold value. Therefore, the command value generating unit 22A stops adding the correction value H2 to the command value and outputs the command value received from the upper device.

[0053] 9 and 10 are diagrams showing another example of the correction process by the command value generating unit 22A. In FIG. 9 and FIG. 10, the vertical axis indicates voltage, and the horizontal axis indicates time. The "lower limit value" in FIG. 9 and FIG. 10 indicates the lower limit value of the DC bus voltage V2. Moreover, the graph G9 in FIG. 9 and the graph G11 in FIG. 10 indicate the command value received from the upper device. The graph G10 in FIG. 9 and the graph G12 in FIG. 10 indicate V1 / n calculated based on the measured value of the voltage V1 between the input / output terminals 13p and 13m. The graph GH5 in FIG. 9 and the graph GH6 in FIG. 10 indicate the command value after correction by the command value generating unit 22A. In the example of FIG. 9 and FIG. 10, it is assumed that the lower limit value of the DC bus voltage V2 is received as the command value from the upper device.

[0054] 9, V1 / n illustrated by graph G10 increases with time from time 0 to time T6, and decreases with time after time T6. In the period from time 0 to before time T6, the absolute value of the difference between the command value and V1 / n is greater than the first threshold value, so the command value generating unit 22A outputs the command value received from the higher-level device to the control unit 23 as is.

[0055] At time T6, the absolute value of the difference between the command value and V1 / n becomes smaller than the first threshold value. Therefore, the command value generating unit 22A adds the correction value H2 to the command value to determine the corrected command value, and outputs the determined corrected command value.

[0056] During the period from time T6 to less than time T7, the absolute value of the difference between the command value and V1 / n is greater than the first threshold but less than a second threshold that is greater than the first threshold. Therefore, the command value generating unit 22A adds the correction value H2 to the command value to determine a corrected command value, and outputs the determined corrected command value.

[0057] After time T7, the absolute value of the difference between the command value and V1 / n becomes equal to or greater than the second threshold value, which is greater than the absolute value of the first threshold value. Therefore, the command value generating unit 22A stops adding the correction value H2 to the command value, and outputs the command value received from the higher-level device.

[0058] 10, V1 / n illustrated by graph G12 decreases with time from time 0 to time T8, and increases with time after time T8. In the period from time 0 to before time T8, the absolute value of the difference between the command value and V1 / n is greater than the first threshold value, so the command value generating unit 22A outputs the command value received from the higher-level device to the control unit 23 as is.

[0059] At time T8, the absolute value of the difference between the command value and V1 / n becomes smaller than the first threshold value. Therefore, the command value generating unit 22A adds the correction value H2 to the command value to determine the corrected command value, and outputs the determined corrected command value.

[0060] During the period from time T8 to time T9, the absolute value of the difference with respect to the command value V1 / n is greater than the first threshold value but less than a second threshold value that is greater than the first threshold value. Therefore, the command value generating unit 22A adds the correction value H2 to the command value to determine a corrected command value, and sets the determined corrected command value Output.

[0061] After time T9, the absolute value of the difference between the command value and V1 / n becomes equal to or greater than the second threshold value, which is greater than the absolute value of the first threshold value. Therefore, the command value generating unit 22A stops adding the correction value H2 to the command value, and outputs the command value received from the higher-level device.

[0062] According to the first modification, when the absolute value of the difference between the command value and V1 / n becomes equal to or greater than the second threshold value after application of the correction value H2 starts, addition of the correction value H2 to the command value is stopped. Therefore, an unnecessary increase in the DC bus voltage V2 can be suppressed. As a result, for example, a decrease in the conversion efficiency of the inverter 30 is suppressed. Also, according to the first modification, by ensuring the difference between the command value and V1 / n, an operating region in which the control accuracy of the DC / DC converter 10 decreases can be avoided.

[0063] [Second Modification] In the above-described embodiment, the difference between the command value and V1 / n is ensured by using a correction value to avoid the operating region where the control accuracy of the DC / DC converter 10 decreases, but the means for avoiding the operating region where the control accuracy of the DC / DC converter 10 decreases is not limited to the method of using a correction value. In the second modification, a configuration is described in which the turns ratio of the transformer TR is changed by switching the taps to avoid the operating region where the control accuracy of the DC / DC converter 10 decreases. The same reference numerals are used to denote components common to the embodiment and the first modification, and the description thereof is omitted. Hereinafter, the second modification will be described with reference to the drawings.

[0064] 11 is a diagram showing a schematic configuration of a DC / DC converter 10A according to Modification 2. The DC / DC converter 10A differs from the DC / DC converter 10 according to the embodiment in that it includes a transformer TRA instead of the transformer TR.

[0065] The transformer TRA has a tap that changes the turns ratio n between the winding Wn1 and the winding Wn2. The tap operates in response to an instruction from the control unit 20, thereby changing the turns ratio n between the winding Wn1 and the winding Wn2.

[0066] When the absolute value of the difference between the command value and V1 / n becomes equal to or less than the first threshold, the control unit 20 sends an instruction to the transformer TRA to drive the tap, thereby changing the turns ratio n so that the absolute value of the difference between the command value and V1 / n becomes equal to or more than the first threshold. By changing the turns ratio n, it is possible to avoid an operating region where the control accuracy of the DC / DC converter 10 decreases.

[0067] The embodiments and modifications disclosed above can be combined with each other.

[0068] <Appendix 1> a first capacitor (C1) for smoothing an input first voltage; a second capacitor (C2) for smoothing the second voltage to be output; a first switching unit (11) connected to the first capacitor (C1); a second switching unit (12) connected to the second capacitor (C2); a transformer (TR) disposed between the switching unit (11) and the second switching unit (12); a control unit (20) that controls switching of the first switching unit (11) and the second switching unit (12), The control unit (20) determining a corrected target value by correcting a control target value for the second voltage such that a difference between a third voltage obtained by dividing the first voltage by a turns ratio between a first winding (Wn1) and a second winding (Wn2) included in the transformer (TR) and the control target value becomes equal to or greater than a predetermined difference; Power conversion device (1). <Appendix 2> The control unit (20) determines the corrected target value by adding a correction value to the third voltage. The power conversion device (1) as described in appendix 1. <Appendix 3> When an absolute value of a difference between the control target value and the third voltage is less than a first threshold value, the control unit (20) adds a correction value to the control target value to determine the corrected target value. The power conversion device (1) as described in appendix 1. <Appendix 4> When a difference between the control target value and the third voltage becomes equal to or greater than a second threshold value that is greater than the first threshold value after determining the corrected target value, the control unit (20) interrupts the process of adding the correction value to the control target value and sets the control target value to the corrected target value. The power conversion device (1) as described in Appendix 3. <Appendix 5> the control unit (20) controls switching of the first switching unit (11) and the second switching unit (12) so as to output a voltage according to the corrected target value. 5. A power conversion device according to any one of claims 1 to 4. <Appendix 6> a first capacitor (C1) for smoothing an input first voltage; a second capacitor (C2) for smoothing the second voltage to be output; a first switching unit (11) connected to the first capacitor (C1); a second switching unit (12) connected to the second capacitor (C1); a transformer (TRA) disposed between the first switching unit (11) and the second switching unit (12), the transformer (TRA) being capable of switching a turn ratio between a first winding (Wn1) and a second winding (Wn2) included in the transformer (TRA); a control unit (20) that controls switching of the first switching unit (11) and the second switching unit (12), The control unit (20) causing the transformer (TRA) to change the turns ratio so that a difference between a third voltage obtained by dividing the first voltage by the turns ratio and a control target value related to the second voltage becomes equal to or larger than a predetermined difference; Power conversion device (1). [Explanation of symbols]

[0069] 1. Power conversion device 2··EV 3...Power system 4. Load 10. DC / DC converter 10A DC / DC Converter 11. Full bridge circuit 12. Full bridge circuit 20. Control unit 20A··Control unit 21...Ammeter 22 Command value generator 22A Command value generator 23 Control section 24...PWM generation section 30. Inverter 13 Input / Output Terminal Pair 14 Input / Output Terminal Pair 13p Input / output terminal 13m...Input / output terminal 14p Input / output terminal 14m...Input / output terminal C1 Capacitor C2 Capacitor TR··Transformer TRA...Trans Lr1 Reactor Lr2 Reactor Q1 Switching element Q2 Switching element Q3 Switching element Q4 Switching element Q5 Switching element Q6 Switching element Q7 Switching element Q8 Switching element

Claims

1. a first capacitor for smoothing an input first voltage; a second capacitor for smoothing the second voltage to be output; a first switching unit connected to the first capacitor; a second switching unit connected to the second capacitor; A transformer disposed between the first switching unit and the second switching unit; A control unit that controls switching of the first switching unit and the second switching unit, The control unit is determining a corrected target value by correcting a control target value for the second voltage such that a difference between a third voltage obtained by dividing the first voltage by a turns ratio between a first winding and a second winding included in the transformer and the control target value becomes equal to or larger than a predetermined difference; Power conversion equipment.

2. The control unit determines the corrected target value by adding a correction value to the third voltage. The power conversion device according to claim 1 .

3. the control unit, when an absolute value of a difference between the control target value and the third voltage is less than a first threshold, adds a correction value to the control target value to determine the corrected target value. The power conversion device according to claim 1 .

4. When a difference between the control target value and the third voltage becomes equal to or greater than a second threshold value that is greater than the first threshold value after determining the corrected target value, the control unit interrupts a process of adding the correction value to the control target value and sets the control target value to the corrected target value. The power conversion device according to claim 3 .

5. The control unit controls switching of the first switching unit and the second switching unit so as to output a voltage according to the corrected target value. The power conversion device according to claim 1 .

6. a first capacitor for smoothing an input first voltage; a second capacitor for smoothing the second voltage to be output; a first switching unit connected to the first capacitor; a second switching unit connected to the second capacitor; a transformer disposed between the first switching unit and the second switching unit, the transformer being capable of switching a turns ratio between a first winding and a second winding included in the transformer; A control unit that controls switching of the first switching unit and the second switching unit, The control unit is causing the transformer to change the turns ratio so that a difference between a third voltage obtained by dividing the first voltage by the turns ratio and a control target value related to the second voltage becomes equal to or larger than a predetermined difference; Power conversion equipment.

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