Power conversion device and power conversion system

Abstract

To provide a power conversion device that can match a current command value and an output current value as much as possible within a predetermined range including 0A.SOLUTION: The power conversion device comprises: a conversion unit that has a plurality of bidirectional DC / DC converters; and a control unit that sends current command values to each of the plurality of bidirectional DC / DC converters. The plurality of bidirectional DC / DC converters are classified into one of a first group and a second group. When a first current command value received from a host device is within a predetermined range including 0A, the control unit sends a positive current command value to the bidirectional DC / DC converter belonging to the first group, and sends a negative current command value determined to be the first current command value within the predetermined range when the positive current command value is added thereto, to the bidirectional DC / DC converter belonging to the second group.SELECTED DRAWING: Figure 3

Description

[Technical field]

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

[0002] Conventionally, in a bidirectional DC / DC converter, which is a power conversion device, a technology has been proposed in which two pairs of bidirectional DC / DC converters are provided to smoothly perform operations from charging to discharging or vice versa, as described in Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-093910 A Summary of the Invention [Problem to be solved by the invention]

[0004] In a bidirectional DC / DC converter, an error may occur between the current command value and the output current value near the output current of 0A due to current measurement error, control delay, the effect of the excitation current, and other factors.

[0005] An object of one aspect of the disclosed technique is to provide a power conversion device and a power conversion system that can make a current command value and an output current value match as closely as possible within a predetermined range including 0 A. [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 conversion unit having a plurality of bidirectional DC / DC converters, and a control unit that sends a current command value to each of the plurality of bidirectional DC / DC converters. Each of the plurality of bidirectional DC / DC converters is classified into either a first group or a second group. When a first current command value received from a higher-level device is within a predetermined range including 0 A, the control unit sends a positive current command value to the bidirectional DC / DC converters belonging to the first group, and sends a negative current command value to the bidirectional DC / DC converters belonging to the second group, the negative current command value being determined so that when added to the positive current command value, the first current command value falls within the predetermined range.

[0007] In the present power conversion device, the bidirectional DC / DC converter belonging to the first group to which a positive current command value is sent and the bidirectional DC / DC converter belonging to the second group to which a negative current command value is sent are offset by a measurement error of the current in the bidirectional DC / DC converter, a delay in control, and an influence of the excitation current. Therefore, according to the present power conversion device, the first current command value and the output current value within a predetermined range including 0 A can be made to match as much as possible. Here, when the first current command value is within the predetermined range, the case where the charging operation and the discharging operation by the conversion unit are switched may be included. The predetermined range may be specified by a first threshold value. Then, when the absolute value of the first current command value becomes equal to or less than the absolute value of the first threshold value, the control unit may send the positive current command value to the bidirectional DC / DC converter belonging to the first group and send the negative current command value to the bidirectional DC / DC converter belonging to the second group.

[0008] The power conversion device may further include the following feature: The predetermined range may be defined by the first threshold and a second threshold that is greater than the first threshold. When the absolute value of the first current command value becomes equal to or greater than the absolute value of the second threshold value, the control unit may stop sending a positive current command value to the bidirectional DC / DC converters belonging to the first group, stop sending the negative current command value to the bidirectional DC / DC converters belonging to the second group, and send current command values ​​distributed to arbitrary values ​​without changing the sign of the first current command value to the bidirectional DC / DC converters belonging to the first group and the bidirectional DC / DC converters belonging to the second group. By providing this feature, the power conversion device is suppressed from frequently and repeatedly interrupting and resuming the sending of the positive current command value and the negative current command value.

[0009] Furthermore, the power conversion device may further include the following feature: A total number of the plurality of bidirectional DC / DC converters is N (N is an integer equal to or greater than 2), and the number of the bidirectional DC / DC converters belonging to the first group and the number of the bidirectional DC / DC converters belonging to the second group are both equal to or greater than 1. By classifying the plurality of bidirectional DC / DC converters in this manner, the bidirectional DC / DC converters can be classified into both the first group and the second group, and ultimately the offsetting effect by the first group and the second group can be made more effective. Effect of the Invention

[0010] According to the disclosed technique, it is possible to make the current command value and the output current value match as closely as possible within a predetermined range including 0 A. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic configuration diagram of a power conversion device according to an embodiment. [Diagram 2] FIG. 2 is a schematic configuration diagram of a bidirectional DC / DC converter according to an embodiment. [Diagram 3] FIG. 3 is a control block diagram realized by the control unit. [Figure 4]FIG. 4 is a diagram illustrating an example of a current command value sent to the bidirectional DC / DC converter and a current value output by the bidirectional DC / DC converter. [Diagram 5] FIG. 5 is a diagram showing an example of a management table stored in the storage unit by the current command value division control unit 22. As shown in FIG. [Figure 6] FIG. 6 is a diagram showing an example of a time-series change in the current command value sent by the current command value division control unit. [Figure 7] FIG. 7 is a diagram illustrating a current value to be output to the conversion unit and an output current value from the conversion unit. [Figure 8] FIG. 8 is a functional block diagram realized by a control unit according to the first modified example. [Figure 9] FIG. 9 is a diagram showing an example of fluctuations in the current command value sent by the current command value division control unit to the bidirectional DC / DC converter in the first modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] [Application example] Hereinafter, application examples of the present invention will be described with reference to the drawings. The present invention is applied to a power conversion device 1 shown in FIG. 1, for example. The power conversion device 1 includes a conversion section 5 including DC / DC converters 10A and 10B, and a control unit 20. When the DC / DC converters 10A and 10B are not distinguished from each other, they are also referred to as DC / DC converters 10. As shown in FIG. 2, the DC / DC converter 10 includes 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 and 13p, and between the input / output terminals 14m and 14p, respectively.

[0013] As shown in FIG. 2, the DC / DC converter 10 includes a transformer TR and two reactors L This is an isolated bidirectional DC / DC converter whose main components are reactors r1 and Lr2 and two full-bridge circuits 11 and 12. Reactors Lr1 and Lr2 generate AC power under the control of full-bridge circuits 11 and 12, and capacitors C1 and C2 smooth the AC power into DC power. An isolated transformer can be used as the transformer TR, but a non-isolated reactor may also be used.

[0014] 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. In addition, both the leg L1 and the leg L2 are connected to an input / output terminal pair 13. 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, and 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.

[0015] 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.

[0016] 4 illustrates a current command value (graph G1) and a current value (graph G2) of a current output by the DC / DC converter 10. When outputting a current close to 0 A, such as when switching from charging to discharging, the current value of the current output by the DC / DC converter 10 may deviate from the current command value. In this application example, the following configuration is adopted to suppress such deviation.

[0017] A control block diagram realized by the control unit 20 is illustrated in Fig. 3. The control unit 20 includes a current command value division control unit 22, a control unit 23, a PWM generating unit 24, and a charge / discharge switching control unit 25. The DC / DC converters 10A and 10B are classified into either group A or group B, and the current command value division control unit 22 stores this classification in a storage unit of the control unit 20. When the current command value received from the higher-level device is within a predetermined range including 0A, the current command value division control unit 22 sends a positive current command value to the DC / DC converter 10A classified into group A, and sends a negative current command value to the DC / DC converter 10B classified into group B. Here, the positive current command value and the negative current command value are determined so that the current value to be output from the conversion unit 5 is obtained by adding the positive current command value and the negative current command value.

[0018] In this application example, current command value division control unit 22 sends a positive current command value to DC / DC converter 10A classified into group A and a negative current command value to DC / DC converter 10B classified into group B in this way, thereby canceling out the influences of measurement error by ammeter 21, control delay of control unit 20, excitation current by transformer TR, etc. that may occur in each of DC / DC converters 10A, 10B. Furthermore, according to this application example, the difference between the current command value near 0 A and the current value output by power conversion device 1 is suppressed as much as possible.

[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 configuration diagram of a power conversion device 1 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 conversion unit 5 and a control unit 20. The conversion unit 5 includes DC / DC converters 10A, 10B. The DC / DC converters 10A, 10B are connected in parallel between an EV2 (electrically-driven automobile) and an inverter 30.

[0021] The control unit 20 sends a current command value related to the output current to each of the DC / DC converters 10A and 10B. The current command value sent by the control unit 20 to each of the DC / DC converters 10A and 10B is 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) A microcomputer can be considered to be a computer equipped with memory devices such as a microcontroller, RAM (Random Access Memory), and an input / output interface.

[0022] EV2 includes BEVs (Battery Electric Vehicles) that run on battery power only, PHVs (Plug-in Hybrid Vehicles) that use both a battery and an internal combustion engine, FCVs (Fuel Cell Vehicles) that run on fuel cell power, and various other types of electric vehicles. 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, 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.

[0023] FIG. 2 is a schematic diagram of a DC / DC converter 10 according to an embodiment. FIG. 2 also illustrates a control unit 20. As illustrated, the DC / DC converter 10 includes two pairs of input / output terminals 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, 14p are high-potential input / output terminals, and the input / output terminals 13m, 14m are low-potential input / output terminals. A capacitor C1 for smoothing the input / output voltage is connected between the input / output terminals 13m, 13p. Similarly, a capacitor C2 for smoothing the input / output voltage is connected between the input / output terminals 14m, 14p. Electrolytic capacitors can be used as the capacitors C1 and C2.

[0024] 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. 2 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. 2 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. 2 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. 2 will be referred to as the input / output terminal pair 13 and the input / output terminal pair 14, respectively. The reactors Lr1 and Lr2 may utilize leakage inductance of the windings Wn1 and Wn2 of the transformer TR. The transformer TR of the DC / DC converter 10 does not need to have a turns ratio of 1:1. However, in the following, the configuration and operation of the power conversion device 1 will be described assuming that the turns ratio of the transformer TR is 1:1.

[0025] 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.

[0026] 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.

[0027] 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), an insulated gate bipolar transistor (IGBT), etc. The diodes D1 to D8 are connected in antiparallel to these semiconductor switching elements used as the switching elements Q1 to Q8.

[0028] The DC / DC converter 10 is equipped with various sensors (not shown) for measuring the magnitude of the input / output voltages and the input / output currents.

[0029] 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.

[0030] The control unit 20 is composed of a processor (in this embodiment, a microcontroller), a gate driver, etc., and receives outputs from the various sensors described above.

[0031] 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

[0032] 3 is a control block diagram realized by the control unit 20. The control unit 20 controls the DC / DC converter 10 in accordance with a current command value sent from a higher-level device. The control unit 20 includes a CPU (Central Processing Unit), storage devices such as a ROM (Read Only Memory) and a RAM (Random Access Memory), and an input / output interface. The CPU executes a computer program stored in the storage device to realize each of the functional blocks shown below. The control unit 20 uses each of the functional blocks shown below to generate a PWM signal according to a current command value sent from a higher-level device and sends the PWM signal to the DC / DC converter 10.

[0033] 3, the control unit 20 realizes a current command value division control unit 22, a control unit 23, a PWM generating unit 24, and a charge / discharge switching control unit 25. Each functional block in the control unit 20 will be described below.

[0034] The current command value division control unit 22 performs a process of dividing a current command value sent from a higher-level device. The DC / DC converter 10 of this embodiment performs two-phase interleaved control using two full-bridge insulated DC / DC circuits. For this reason, the current command value division control unit 22 divides the current command value from the higher-level device for each phase. Then, the current command value division control unit 22 sends the current command value divided for each phase to the control unit 23 and the charge / discharge switching control unit 25.

[0035] The control unit 23 generates a phase shift amount based on the difference between the actual current value of the electric path between the EV2 and the DC / DC converter 10 measured by the ammeter 21 and the current command value sent from the current command value division control unit 22. The phase shift amount is the phase difference of the pulse-like control signal related to the ON / OFF of each switching element included in the legs L1 to L4.

[0036] The PWM generating unit 24 generates a PWM signal based on the phase shift amount generated by the control unit 23. When generating the PWM signal, the PWM generating unit 24 uses a step-up / step-down signal output from a higher-level device and a charge / discharge signal output from a charge / discharge switching control unit 25. By using these signals, the PWM generating unit 24 generates a PWM signal of a switching pattern for causing the DC / DC converter 10 to perform a step-up operation, a step-down operation, a charge operation, or a discharge operation. The PWM signal generated by the PWM generating unit 24 is sent to the DC / DC converter 10 and operates each of the switching elements Q1 to Q8.

[0037] The charge / discharge switching control unit 25 generates a charge / discharge signal based on a command output from a higher-level device. For example, the charge / discharge switching control unit 25 selects whether the DC / DC converter 10 should perform a charging operation or a discharging operation based on a current command value output from the higher-level device. Then, the charge / discharge switching control unit 25 outputs a signal according to the selection result.

[0038] <Operation of power conversion device 1> The operation of the power conversion device 1 according to this embodiment will be described below.

[0039] Fig. 4 is a diagram illustrating a current command value sent to the bidirectional DC / DC converter 10 and a current value output by the bidirectional DC / DC converter 10. The upper part of Fig. 4 illustrates the current command value sent to the DC / DC converter 10 and the current value output by the DC / DC converter 10. The lower part of Fig. 4 illustrates the charging and discharging states of the DC / DC converter 10. In the example of Fig. 4, the DC / DC converter 10 is switched from charging to discharging at time T1.

[0040] 4 illustrates graph G1 showing the time series change in the current command value sent to the DC / DC converter 10, and graph G2 showing the time series change in the current value output by the DC / DC converter 10. As can be understood by referring to FIG. 4, when a current of about 0 A is output, such as when switching from charging to discharging, a deviation in the current value occurs with respect to the current command value. Such a deviation occurs due to a measurement error by the ammeter 21, as illustrated by arrow A1, a measurement error by the ammeter 21, as illustrated by arrow A2, and a measurement error by the ammeter 21, as illustrated by arrow A3. This is considered to be caused by a control delay of the control unit 20, an excitation current of the transformer TR, etc. In this embodiment, in order to suppress the deviation between the current command value and the current value near 0 A as much as possible, the following configuration is adopted.

[0041] <Control by current command value division control unit 22> The current command value division control unit 22 manages the DC / DC converters 10A and 10B by dividing them into groups. The current command value division control unit 22 stores information related to the grouped DC / DC converters 10A and 10B in, for example, a non-volatile storage unit. FIG. 5 is a diagram showing an example of a management table 511 stored in the storage unit by the current command value division control unit 22. The management table 511 includes items of "group" and "DC / DC converter". The "group" stores information indicating the group into which the DC / DC converters 10A and 10B are divided. The "DC / DC converter" stores information indicating the DC / DC converter. In FIG. 5, the "first DC / DC converter" is exemplified by the DC / DC converter 10A, and the "second DC / DC converter" is exemplified by the DC / DC converter 10B. In the example of FIG. 5, the DC / DC converter 10A is classified into group A, and the DC / DC converter 10B is classified into group B.

[0042] The current command value division control unit 22 sends a current command value to the DC / DC converter 10. Sending the current command value to the DC / DC converter 10 includes sending the current command value to the control unit 23 to cause the control unit 23 to generate a phase shift amount, and supplying the PWM signal generated by the PWM generation unit 24 based on the generated phase shift amount to the DC / DC converter 10. Here, when the current command value is near 0 A, the current command value division control unit 22 sends a positive current command value to the DC / DC converter 10A classified in group A, and sends a negative current command value to the DC / DC converter 10B classified in group B. Near 0 A can be, for example, a predetermined range set in advance with 0 A as the center. When the conversion unit 5 is caused to output a current of 0 A, the absolute value of the positive current command value sent by the current command value division control unit 22 becomes equal to the absolute value of the negative current command value.

[0043] Fig. 6 is a diagram showing an example of a time-series change in the current command value sent by current command value division control unit 22. In Fig. 6, graph G3 illustrates a current command value for DC / DC converter 10A classified into group A. Graph G4 illustrates a current command value for DC / DC converter 10B classified into group B. When causing conversion unit 5 to output a current of 0 A (for example, at the time of switching between charging and discharging as illustrated in Fig. 4), current command value division control unit 22 sends current command value P1 to DC / DC converter 10A and sends current command value P2 to DC / DC converter 10B. Current command value P1 and current command value P2 are, for example, values ​​whose absolute values ​​are equal and whose positive and negative signs are opposite to each other. In this way, current command value P1 is sent to DC / DC converter 10A, and current command value P2 is sent to DC / DC converter 10B, whereby the output current of DC / DC converter 10A and the output current of DC / DC converter 10B are offset, and the output current value from DC / DC converters 10A, 10B as a whole can approach the desired current value of 0 A. Note that when current command value division control unit 22 causes conversion unit 5 to output a current close to 0 A (for example, the period from time T0 to T2 in FIG. 6), it may send current command values ​​to each of DC / DC converters 10A, 10B so that the sum of the current command value sent to DC / DC converter 10A and the current command value sent to DC / DC converter 10B becomes the power value to be output by conversion unit 5.

[0044] 7 is a diagram illustrating a current value to be output to the conversion unit 5 and an output current value from the conversion unit 5. The current value to be output to the power conversion device 1 corresponds to, for example, the current command value in FIG. 4. FIG. 7 illustrates an output current value from the power conversion device 1 in a case where a current command value determined by the current command value division control unit 22 so that the sum of the current command values ​​becomes the current value to be output from the power conversion device 1 is sent to each of the DC / DC converters 10A and 10B. 7, a graph G5 illustrates an example of a current value output by the power conversion device 1, and a graph G6 illustrates an example of an output current value from the power conversion device 1.

[0045] Referring to Figure 7, it can be seen that the measurement error by ammeter 21 (arrow A3 in Figure 7) that occurs in each of DC / DC converters 10A, 10B, the control delay by control unit 20 (arrow A4 in Figure 7), the excitation current by transformer TR, etc. are offset, and the output current value from DC / DC converters 10A, 10B as a whole near 0 A approaches as close as possible to the current value output by DC / DC converters 10A, 10B as a whole.

[0046] <Effects of the embodiment> In this embodiment, a positive current command value is sent to DC / DC converter 10A, and a negative current command value is sent to DC / DC converter 10B. Here, the positive current command value and the negative current command value are added together to obtain a current value to be output by conversion unit 5. By sending such a current command value, the influences of measurement error by ammeter 21, control delay of control unit 20, excitation current by transformer TR, etc., which may occur in each of DC / DC converters 10A and 10B, are offset. Therefore, according to this embodiment, the difference between the current command value near 0 A and the current value output by conversion unit 5 is suppressed as much as possible.

[0047] According to this embodiment, when switching between charging and discharging, the conversion unit 5 can be caused to output a current of 0 A more accurately. Therefore, the connection between the EV 2 and the power grid 3 can be controlled with higher accuracy.

[0048] [First Modification] In the embodiment described above, when current command value division control unit 22 causes conversion unit 5 to output a current of 0 A, it sends current command values ​​having opposite positive and negative values ​​but equal absolute values ​​to each of DC / DC converters 10A, 10B. In the first modified example, a configuration is described in which it is determined based on a threshold value whether or not to send different current command values ​​to DC / DC converters 10A, 10B. Components common to the embodiment are denoted by the same reference numerals, and descriptions thereof are omitted. Hereinafter, the first modified example will be described with reference to the drawings.

[0049] 8 is a functional 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 includes a current command value division control unit 22A instead of the current command value division control unit 22.

[0050] Current command value division control unit 22A differs from current command value division control unit 22 in that it determines whether or not to send different current command values ​​to DC / DC converters 10A and 10B based on a threshold value. When the absolute value of the current command value received from the higher-level device becomes less than a first threshold value, current command value division control unit 22A sends a positive current command value to DC / DC converter 10A and sends a negative current command value to DC / DC converter 10B. Note that current command value division control unit 22A may determine the positive current command value and the negative current command value so that the sum of the positive current command value and the negative current command value becomes the current value to be output from power conversion device 1.

[0051] Furthermore, in a state in which a positive current command value is sent to DC / DC converter 10A and a negative current command value is sent to DC / DC converter 10B, when the absolute value of the current command value received from the higher-level device becomes equal to or greater than a second threshold value that is greater than the first threshold value, current command value division control unit 22A stops sending the positive current command value to DC / DC converter 10A and the negative current command value to DC / DC converter 10B. Then, current command value division control unit 22A distributes the current command value received from the higher-level device to any value without changing the sign thereof and sends it to DC / DC converters 10A and 10B. The first threshold value and the second threshold value are determined as appropriate, taking into consideration abnormality detection of DC / DC converters 10A and 10B and measurement error of ammeter 21. The determined first threshold value and second threshold value are stored in, for example, a storage device included in the control unit 20A.

[0052] Fig. 9 is a diagram showing an example of fluctuations in the current command value sent by current command value division control unit 22A to DC / DC converters 10A, 10B in the first modified example. In Fig. 9, graph G11 illustrates a current value to be output from power conversion device 1. Graph G12 illustrates a current command value sent to DC / DC converter 10A. Graph G13 illustrates a current command value sent to DC / DC converter 10B.

[0053] Until time T11, the absolute value of the current value to be output from power conversion device 1 is greater than the absolute value of the first threshold value. Therefore, current command value division control unit 22A distributes the current command value received from the higher-level device to an arbitrary value without changing the sign thereof, and sends the distributed value to DC / DC converters 10A and 10B.

[0054] Between time T11 and time T12, the absolute value of the current value output by power conversion device 1 is less than the absolute value of the first threshold. Therefore, current command value division control unit 22A divides the current command value to be sent to DC / DC converters 10A and 10B into positive and negative values. Current command value division control unit 22A sends, for example, a positive current command value to DC / DC converter 10A and a negative current command value to DC / DC converter 10B.

[0055] Between time T12 and time T13, the absolute value of the current to be output from power conversion device 1 is equal to or greater than the first threshold value but is less than the second threshold value. Therefore, current command value division control unit 22A continues to send a positive current command value to DC / DC converter 10A and a negative current command value to DC / DC converter 10B.

[0056] After time T13, the absolute value of the current to be output from power conversion device 1 is equal to or greater than the second threshold. Therefore, current command value division control unit 22A stops sending a positive current command value to DC / DC converter 10A and a negative current command value to DC / DC converter 10B. Then, current command value division control unit 22A distributes the current command value received from the higher-level device to an arbitrary value without changing the sign of the current command value and sends it to DC / DC converters 10A and 10B.

[0057] In the first modification, when the absolute value of the current value to be outputted from the power conversion device 1 is less than the absolute value of the first threshold, the current command value division control unit 22A sends a positive current command value to the DC / DC converter 10A and sends a negative current command value to the DC / DC converter 10B. Then, when the absolute value of the current value to be outputted from the power conversion device 1 becomes equal to or greater than the absolute value of the second threshold after the current command value division control unit 22A starts sending the positive current command value to the DC / DC converter 10A and the negative current command value to the DC / DC converter 10B, the current command value division control unit 22A stops sending the positive current command value to the DC / DC converter 10A and the negative current command value to the DC / DC converter 10B. The second threshold is set to have an absolute value larger than the first threshold. Therefore, according to the first modification, frequent switching between sending the positive current command value and the negative current command value separately to the DC / DC converters 10A and 10B and sending the current command value received from the upper device to the DC / DC converters 10A and 10B is suppressed.

[0058] [Other variations] In the embodiment and the first modified example described above, the power conversion device 1 includes the isolated DC / DC converter 10. However, the DC / DC converter included in the power conversion device 1 is not limited to being an isolated type. The DC / DC converter included in the power conversion device 1 may be a non-isolated type.

[0059] In the above-described embodiment and the first modified example, the power conversion device 1 includes two DC / DC converters 10, namely, DC / DC converters 10A and 10B. However, the number of DC / DC converters 10 included in the power conversion device 1 is not limited to two. The power conversion device 1 may include two or more DC / DC converters 10. The two or more DC / DC converters 10 may be classified into two groups (group A and group B). Here, it is preferable that the number of DC / DC converters 10 classified into group A is equal to the number of DC / DC converters 10 classified into group B. For example, when the total number of DC / DC converters 10 included in the conversion unit 5 is an even number (2N (N is an integer equal to or greater than 1)), it is preferable that the number of DC / DC converters 10 classified into group A and the number of DC / DC converters 10 classified into group B are each N. Furthermore, for example, when the total number of DC / DC converters 10 included in conversion unit 5 is an odd number (2N+1 (N is an integer equal to or greater than 1)), the number of DC / DC converters 10 classified into group A and the number of DC / DC converters 10 classified into group B are preferably N and N+1, respectively. Then, current command value division control unit 22 may send a positive current command value to DC / DC converters 10 classified into group A, and send a negative current command value to DC / DC converters 10 classified into group B. By classifying a plurality of DC / DC converters 10 in this manner, the numbers of DC / DC converters 10 classified into group A and group B can be made as equal as possible, and thus the above-mentioned offsetting effect by group A and group B can be made more effective.

[0060] In the above-described embodiment, the conversion unit 5 having the DC / DC converters 10A, 10B and the control unit 20 are realized as one power conversion device, but the conversion unit 5 and the control unit 20 may be separate devices. That is, the technology according to the present embodiment and each modification may be realized by a power conversion system including a conversion device having the DC / DC converters 10A, 10B, and a control device having the control unit 20.

[0061] The embodiments and modifications disclosed above can be combined with each other.

[0062] <Appendix 1> A conversion unit (5) having a plurality of bidirectional DC / DC converters (10A, 10B); a control unit (20) that sends a current command value to each of the plurality of bidirectional DC / DC converters (10A, 10B), Each of the plurality of bidirectional DC / DC converters (10A, 10B) is classified into either a first group (group A) or a second group (group B), When a first current command value received from a higher-level device is within a predetermined range including 0 A, the control unit (20) sends a positive current command value to the bidirectional DC / DC converter (10A) belonging to the first group (group A), and sends a negative current command value to the bidirectional DC / DC converter (10B) belonging to the second group (group B), the negative current command value being determined so as to result in the first current command value being within the predetermined range when added to the positive current command value. Power conversion device (1). <Appendix 2> When the first current command value is within a predetermined range, the conversion unit (5) switches between a charging operation and a discharging operation. The power conversion device (1) as described in appendix 1. <Appendix 3> the predetermined range is defined by a first threshold value; when the absolute value of the first current command value becomes equal to or less than the absolute value of the first threshold value, the control unit (20) sends the positive current command value to the bidirectional DC / DC converter (10A) belonging to the first group (group A) and sends the negative current command value to the bidirectional DC / DC converter (10B) belonging to the second group (group B). The power conversion device (1) according to appendix 1 or 2. <Appendix 4> the predetermined range is defined by the first threshold and a second threshold greater than the first threshold, when the absolute value of the first current command value becomes equal to or greater than the absolute value of a second threshold value, the control unit (20) stops sending a positive current command value to the bidirectional DC / DC converter (10A) belonging to the first group (group A), stops sending the negative current command value to the bidirectional DC / DC converter (10B) belonging to the second group (group A), and sends a current command value distributed to an arbitrary value without changing the sign of the first current command value to the bidirectional DC / DC converter (10A) belonging to the first group (group A) and the bidirectional DC / DC converter (10B) belonging to the second group (group B). The power conversion device (1) as described in appendix 3. <Appendix 5> The total number of the plurality of bidirectional DC / DC converters (10) is N (N is an integer equal to or greater than 2), the number of the bidirectional DC / DC converters (10) belonging to the first group (group A) and the number of the bidirectional DC / DC converters (10) belonging to the second group (group B) are both 1 or more; A power conversion device (1) according to any one of appendix 1 to 4. <Appendix 6> A conversion device (5) having a plurality of bidirectional DC / DC converters (10); a control device (20) that sends a current command value to each of the plurality of bidirectional DC / DC converters (10) included in the conversion device (5), Each of the plurality of bidirectional DC / DC converters (10) is classified into either a first group or a second group, When a first current command value received from a higher-level device is within a predetermined range including 0 A, the control device (20) sends a positive current command value to the bidirectional DC / DC converters (10) belonging to the first group, and sends a negative current command value to the bidirectional DC / DC converters (10) belonging to the second group, the negative current command value being determined so as to result in the first current command value being within the predetermined range when added to the positive current command value. Power conversion systems. [Explanation of symbols]

[0063] 1. Power conversion device 2··EV 3...Power system 4. Load 5. Conversion section 10. DC / DC converter 11. Full bridge circuit 12. Full bridge circuit 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 20. Control unit 21...Ammeter 22 Current command value division control unit 22A Current command value division control unit 23 Control section 24...PWM generation section 25 Charge / discharge switching control unit 30. Inverter 511 Management table C1 Capacitor C2 Capacitor TR··Transformer 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 conversion unit having a plurality of bidirectional DC / DC converters; a control unit that sends a current command value to each of the plurality of bidirectional DC / DC converters, Each of the plurality of bidirectional DC / DC converters is classified into either a first group or a second group, when a first current command value received from a higher-level device is within a predetermined range including 0 A, the control unit sends a positive current command value to the bidirectional DC / DC converters belonging to the first group, and sends a negative current command value to the bidirectional DC / DC converters belonging to the second group, the negative current command value being determined so as to result in the first current command value being within the predetermined range when added to the positive current command value. Power conversion equipment.

2. When the first current command value is within the predetermined range, the converter switches between a charging operation and a discharging operation. The power conversion device according to claim 1 .

3. the predetermined range is defined by a first threshold value; when the absolute value of the first current command value becomes equal to or less than the absolute value of the first threshold value, the control unit sends the positive current command value to the bidirectional DC / DC converters belonging to the first group, and sends the negative current command value to the bidirectional DC / DC converters belonging to the second group. The power conversion device according to claim 1 .

4. the predetermined range is defined by the first threshold and a second threshold greater than the first threshold, when the absolute value of the first current command value becomes equal to or greater than the absolute value of the second threshold value, the control unit stops sending a positive current command value to the bidirectional DC / DC converters belonging to the first group, stops sending the negative current command value to the bidirectional DC / DC converters belonging to the second group, and sends a current command value obtained by distributing the first current command value to any value without changing the sign of the first current command value to the bidirectional DC / DC converters belonging to the first group and the bidirectional DC / DC converters belonging to the second group. The power conversion device according to claim 3 .

5. a total number of the plurality of bidirectional DC / DC converters is N (N is an integer equal to or greater than 2), the number of the bidirectional DC / DC converters belonging to the first group and the number of the bidirectional DC / DC converters belonging to the second group are both equal to or greater than 1; The power conversion device according to claim 1 .

6. A conversion device having a plurality of bidirectional DC / DC converters; a control device that sends a current command value to each of the plurality of bidirectional DC / DC converters included in the conversion device, Each of the plurality of bidirectional DC / DC converters is classified into either a first group or a second group, When a first current command value received from a higher-level device is within a predetermined range including 0 A, the control device sends a positive current command value to the bidirectional DC / DC converters belonging to the first group, and determines that when added to the positive current command value, the first current command value falls within the predetermined range for the bidirectional DC / DC converters belonging to the second group. Send the negative current command value obtained by Power conversion systems.

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