Power supply system and control method thereof

Abstract

In a power supply system (10) and a control method thereof, at least one of a plurality of batteries (12a to 12d) is identified as a battery on the charging side, and the remaining batteries are identified as batteries on the discharging side. Next, a current difference between a current flowing out of the battery on the discharging side and a current flowing into the battery on the charging side is determined based on currents (I1 to I4) measured by a plurality of current measuring instruments (26a to 26d). Next, a transformation ratio (Tr) of a voltage converter connected to the battery on the discharging side is determined based on the determined current difference.

Description

Technical Field

[0001] The present invention relates to a power supply system in which a plurality of chargeable and dischargeable power storage units are connected in parallel via a voltage converter, and a control method thereof. Background Art

[0002] For example, Japanese Patent Application Laid-Open No. 2016-25791 discloses a power supply system in which a plurality of chargeable and dischargeable batteries (power storage units) are connected in parallel with each other via a voltage converter. Summary of the Invention

[0003] However, when multiple storage units with different voltages or SOCs are connected in parallel, charging and discharging are performed between the multiple storage units, with current flowing proportional to the voltage difference between the storage units, to equalize the voltages or SOCs. In this case, when simply connecting multiple storage units, if the voltage difference is negligibly small, there is no problem with simply connecting the storage units in parallel.

[0004] However, when multiple storage units with large voltage differences are connected in parallel, a large current flows due to this voltage difference. Furthermore, even when multiple storage units are connected in parallel via a voltage converter, a large current flows when the voltage converter's switching element is turned on. Meanwhile, when the switching element is turned off, a high voltage is generated due to the wiring inductance. This high current and high voltage may cause degradation of the storage units.

[0005] The present invention has been made in view of such technical problems, and an object of the present invention is to provide a power supply system and a control method thereof that can equalize the voltages or SOCs of a plurality of power storage units connected in parallel while preventing degradation of the power storage units.

[0006] The present invention relates to a power supply system and a control method thereof, wherein the power supply system has multiple storage units, multiple voltage converters and multiple current measuring instruments, wherein the multiple storage units are capable of charging and discharging; the input sides of the multiple voltage converters are connected to the multiple storage units, the output sides of the multiple voltage converters are connected in parallel to each other, the multiple voltage converters convert the voltages of the multiple storage units connected to the input sides at an arbitrary transformation rate, and output the converted voltages to the output sides; the multiple current measuring instruments are connected to the input sides of the multiple voltage converters to measure the currents flowing from the multiple storage units to the input sides.

[0007] In this case, the power supply system further includes a storage unit determination unit, a current difference determination unit, and a transformation ratio determination unit, wherein the storage unit determination unit determines at least one of the plurality of storage units as a reference storage unit on the charging side, and determines the remaining storage units as remaining storage units on the discharging side; the current difference determination unit determines the current difference between the current flowing out of the remaining storage unit and the current flowing out of the reference storage unit based on the current measured by the plurality of current measuring instruments; and the transformation ratio determination unit determines the transformation ratio of the voltage converter connected to the remaining storage unit based on the determined current difference.

[0008] In addition, the control method of the power supply system includes the following steps: using a storage unit determination unit to determine that at least one of the multiple storage units is a reference storage unit on the charging side, and determining that the remaining storage units are remaining storage units on the discharging side; using a current difference determination unit to determine the current difference between the current flowing out of the remaining storage unit and the current flowing out of the reference storage unit based on the current measured by the multiple current measuring instruments; and using a transformation ratio determination unit to determine the transformation ratio of the voltage converter connected to the remaining storage unit based on the determined current difference.

[0009] According to the present invention, the current difference between the current flowing from the surplus power storage unit and the current flowing from the reference power storage unit is fed back to determine the voltage conversion ratio of the voltage converter connected to the surplus power storage unit to reduce the current difference. Consequently, when multiple power storage units are connected in parallel via the voltage converter, the voltages or SOCs of the multiple parallel-connected power storage units can be equalized while preventing degradation of the power storage units. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a configuration diagram of a power supply system according to this embodiment.

[0011] Figure 2A This is a circuit diagram of a buck or boost-boost voltage converter. Figure 2B This is the circuit diagram of a step-down voltage converter. Figure 2C This is a circuit diagram of a buck-boost voltage converter.

[0012] Figure 3 It is a timing diagram showing the step-up and step-down operation.

[0013] Figure 4 It is a schematic diagram showing Figure 1 Circuit diagram of the power supply system.

[0014] Figure 5A is a timing chart of each current when the control method of this embodiment is not used. Figure 5BThis is a timing chart of each current when the control method of this embodiment is used.

[0015] Figure 6 This is a diagram showing a classified list of the charge and discharge states of each battery.

[0016] Figure 7 This is a sequence diagram of the control method according to this embodiment.

[0017] Figure 8 The diagram shows Figure 7 Flowchart of a portion of a control method.

[0018] Figure 9A This is a diagram explaining the process of making each battery voltage consistent with the reference voltage. Figure 9B This is a diagram illustrating actual control processing.

[0019] Figure 10 1 is a timing chart illustrating the discharge process.

[0020] Figure 11 is a block diagram schematically illustrating an equalization unit.

[0021] Figure 12 It is a block diagram illustrating the control method according to this embodiment.

[0022] Figure 13 It is a timing chart illustrating the relationship between the target current and the second current.

[0023] Figure 14 This is a timing chart showing the temporal changes in each battery voltage, each current, and each voltage reduction rate.

[0024] Figure 15 This is an explanatory diagram showing the settable range of the pressure reduction rate.

[0025] Figures 16A to 16D This is an explanatory diagram showing a problem when control using the current difference is not performed.

[0026] Figure 17 It is a time chart showing the temporal changes of the vehicle speed, various currents, and various SOCs of the electric vehicle. DETAILED DESCRIPTION

[0027] Hereinafter, preferred embodiments of the power supply system and control method thereof according to the present invention will be described with reference to the accompanying drawings. Figure 1 While explaining.

[0028] [1. Schematic Structure of This Embodiment]

[0029] like Figure 1As shown, the power supply system 10 according to this embodiment includes a plurality of batteries 12a to 12d (power storage units), an equalization unit 14, a control device 16, a motor generator ECU (MG-ECU) 18, and a power drive unit (PDU) 20. Figure 1 The middle figure shows a configuration with four batteries 12a to 12d (hereinafter also referred to as first to fourth batteries 12a to 12d). At least two batteries may be configured in the power supply system 10. The power supply system 10 is suitable for use in a power supply system for an electric vehicle 22, such as a two-wheeled vehicle or a four-wheeled vehicle.

[0030] The plurality of batteries 12a to 12d are chargeable and dischargeable storage units that can be attached to and detached from the power supply system 10. The plurality of batteries 12a to 12d are respectively housed in a battery pack (not shown) that includes a battery management system (BMU), and the plurality of batteries 12a to 12d can be attached to and detached from the power supply system 10 by attaching and detaching the battery pack to and from the power supply system 10, wherein the battery management system (BMU) is used to monitor the batteries 12a to 12d. In addition, in the present embodiment, at least one of the plurality of batteries 12a to 12d only needs to be attachable to and detachable from the power supply system 10. In addition, each battery pack, the equalization unit 14, the control device 16, the MG-ECU 18, and the PDU 20 can transmit and receive signals or information via a communication line (not shown) that constitutes a Controller Area Network (CAN).

[0031] The equalizing unit 14 includes a plurality of voltage converters 24 a to 24 d , a plurality of current measuring instruments 26 a to 26 d , a plurality of input-side voltage measuring instruments (voltage measuring instruments) 28 a to 28 d , an output-side voltage measuring instrument 30 , and a plurality of temperature sensors 32 .

[0032] The plurality of voltage converters 24a to 24d are, for example, DC / DC converters each having an input side 34 as a primary side and an output side 36 as a secondary side. The converters convert the voltages (battery voltages V1 to V4) of the batteries 12a to 12d connected to the input side 34 at an arbitrary voltage conversion rate Tr (voltage step-up rate Tru or voltage step-down rate Trd (hereinafter also referred to as voltage step-down rate R)) and output the converted voltage (output voltage V0) to the output side 36. Figure 1The middle figure shows a case where four voltage converters 24a to 24d (hereinafter referred to as first to fourth voltage converters 24a to 24d) are arranged in equalization unit 14, corresponding to first to fourth batteries 12a to 12d. The following description describes a case where the first to fourth voltage converters 24a to 24d step down the battery voltages V1 to V4 of the first to fourth batteries 12a to 12d at arbitrary step-down rates R1 to R4, and output the stepped-down battery voltages V1 to V4 as output voltage V0 to output side 36.

[0033] The input sides 34 of the first to fourth voltage converters 24a to 24d are connected to any one of the first to fourth batteries 12a to 12d. Specifically, the positive terminals of the first to fourth batteries 12a to 12d are connected to the positive terminals 38p of the input sides 34 of the first to fourth voltage converters 24a to 24d, and the negative terminals of the first to fourth batteries 12a to 12d are connected to the negative terminals 38m of the input sides 34 of the first to fourth voltage converters 24a to 24d. Furthermore, the output sides 36 of the first to fourth voltage converters 24a to 24d are connected in parallel to each other and are therefore connected in parallel to the PDU 20. In this case, the positive terminals 40 p of the output sides 36 of the first to fourth voltage converters 24 a to 24 d are connected to the positive terminal of the PDU 20 , and the negative terminals 40 m of the output sides 36 of the first to fourth voltage converters 24 a to 24 d are connected to the negative terminal of the PDU 20 .

[0034] Multiple input-side voltage measuring instruments 28a-28d (hereinafter also referred to as the first to fourth voltage measuring instruments 28a-28d) are voltage sensors connected between the positive and negative terminals of the first to fourth batteries 12a-12d on the input side 34 of the first to fourth voltage converters 24a-24d. Furthermore, multiple current measuring instruments 26a-26d (hereinafter also referred to as the first to fourth current measuring instruments 26a-26d) are current sensors connected between the positive terminals of the first to fourth batteries 12a-12d and the positive terminals 38p of the first to fourth voltage converters 24a-24d on the input side 34 of the first to fourth voltage converters 24a-24d. The output-side voltage measuring instrument 30 is a voltage sensor connected between the positive and negative terminals of the PDU 20 on the output side 36 of the first to fourth voltage converters 24a-24d.

[0035] The plurality of temperature sensors 32 detect the temperature of the switching elements 42H and 42L (see FIG. Figures 2A to 2C ) temperature. In addition, Figure 1 The middle figure shows a case where two temperature sensors 32 are provided.

[0036] The PDU 20 is configured to include a three-phase bridge inverter. On the input side of the PDU 20, the first to fourth voltage converters 24a to 24d are connected in parallel. On the output side of the PDU 20, a three-phase AC motor 44 is electrically connected as a load of the power supply system 10. During power operation, DC power is supplied to the PDU 20 from the first to fourth batteries 12a to 12d via the first to fourth voltage converters 24a to 24d. The PDU 20 converts the DC power into three-phase AC power and supplies it to the motor 44. This allows the motor 44 to be driven to allow the electric vehicle 22 to travel. On the other hand, during regeneration, the PDU 20 converts the AC power generated by the motor 44 into DC power. This allows the first to fourth batteries 12a to 12d to be charged with DC power via the first to fourth voltage converters 24a to 24d.

[0037] The MG-ECU 18 (power storage unit determination unit) is an ECU (electronic control unit) for controlling the PDU 20 and motor 44. It can exchange signals and information with the control unit 16 and PDU 20. Specifically, the MG-ECU 18 supplies control signals (signals indicating torque command values) for operating the switching elements 42H and 42L that make up the PDU 20. Meanwhile, the PDU 20 transmits information such as its status. The motor 44 transmits information such as its status. Based on information transmitted from the PDU 20 and motor 44, the MG-ECU 18 calculates the requested output of the motor 44 and transmits the calculated requested output to the control unit 16.

[0038] The control device 16 is an ECU for controlling the equalization unit 14 and includes a control unit 46 (storage unit determination unit, current difference determination unit, and transformation ratio determination unit), an instruction unit 48, and a table 50. The control unit 46 obtains the battery voltages V1 to V4 of the first to fourth batteries 12a to 12d measured by the first to fourth voltage measuring instruments 28a to 28d, the first to fourth currents I1 to I4 measured by the first to fourth current measuring instruments 26a to 26d, the output voltage V0 (load voltage) measured by the output-side voltage measuring instrument 30, and the temperatures of the first to fourth voltage converters 24a to 24d measured by the plurality of temperature sensors 32. Furthermore, the control unit 46 calculates (determines) the transformation ratio Tr and other parameters based on a target value (target current Itar) for the current flowing through the input side 34, as requested by the MG-ECU 18 and stored in the table 50. The command unit 48 outputs a command signal (a gate signal supplied to the switching elements 42H and 42L of the first to fourth voltage converters 24a to 24d) to the equalization unit 14 based on the transformation rate Tr determined by the control unit 46. The details of the processing performed by the control device 16 and the MG-ECU 18 will be described later.

[0039] [2. Specific Examples of the First to Fourth Voltage Converters 24a to 24d]

[0040] Figures 2A to 2C Yes Figure 1 The first to fourth voltage converters 24a to 24d are, for example, step-down or step-up / step-down types (see Figure 2A ), step-down type (refer to Figure 2B ), or buck-boost type (refer to Figure 2C The structure and operation of these DC / DC converters are well known, so here we will discuss the DC / DC converters in detail. Figures 2A to 2C The connection relationship between the various components in the circuit diagram is briefly described.

[0041] exist Figure 2A In the example, a capacitor 52 is connected between the positive terminal 38p and the negative terminal 38m on the input side 34. Two circuits, each consisting of two switching elements 42H and 42L connected in series and a coil 54, are connected in parallel to the capacitor 52. In each circuit, the switching element 42H on one side is the high-voltage switching element and is connected to the positive terminal 38p of the capacitor 52. The switching element 42L on the other side is the low-voltage switching element and is connected to the negative terminal 38m of the capacitor 52 and the negative terminal 40m on the output side 36. One end of the coil 54 is connected to the midpoint between the two switching elements 42H and 42L. The other end of the coil 54 is connected to the positive terminal 40p on the output side 36. Furthermore, a capacitor 56 is connected between the positive terminal 40p and the negative terminal 40m on the output side 36. The switching elements 42H and 42L are configured by connecting a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) 58 and a Zener diode 60 as a parasitic diode in parallel.

[0042] exist Figure 2B In FIG. 5 , a capacitor 52 is connected between the positive terminal 38p and the negative terminal 38m on the input side 34. Two switching elements 42H and 42L connected in series are connected in parallel to the capacitor 52. Switching element 42H is a high-voltage switching element and is connected to the positive terminal 38p of the capacitor 52. Switching element 42L is a low-voltage switching element and is connected to the negative terminal 38m of the capacitor 52 and the negative terminal 40m on the output side 36. A series circuit of a coil 54 and a resistor 62 is connected between the midpoint between the two switching elements 42H and 42L and the positive terminal 40p on the output side 36. Furthermore, a capacitor 56 is connected between the positive terminal 40p and the negative terminal 40m on the output side 36.

[0043] exist Figure 2C In the embodiment, a capacitor 52 is connected between the positive terminal 38p and the negative terminal 38m of the input side 34. The positive terminal 38p side of the capacitor 52 is connected to the midpoint of the two switching elements 42H and 42L connected in series via a series circuit of a coil 64 and a resistor 66. A capacitor 68 is connected in parallel to the two switching elements 42H and 42L. In addition, a capacitor 68 having the same structure as the capacitor 68 is connected in parallel to the output side 36 of the capacitor 68. Figure 2B Same circuit.

[0044] In any circuit configuration, the transformation rate Tr ( Figure 2A The boost rate Tru or the buck rate R, Figure 2B The pressure reduction rate R, Figure 2C The step-up rate Tru or step-down rate R).

[0045] Figure 3 As an example, Figure 2B The timing diagram of the gate signal supplied to the gate terminals of the switching elements 42H and 42L in the step-down circuit. Here, when the period of the gate signal is T, the gate signal supplied to the switching element 42H on the high side is ( Figure 3 The time of the high level of "Hi side duty ratio" is U, and the gate signal ( Figure 3 When the high-level time of the "Lo-side duty ratio" is D and the dead time (dead time) between the time U and the time D is Td, the period T is expressed by the following formula (1).

[0046] T=U+D+Td×2 (1)

[0047] When the voltage on the input side 34 (battery voltages V1 to V4) is Vin and the voltage on the output side 36 (output voltage V0) is Vout, the voltage reduction rate R is expressed by the following equation (2).

[0048] R=Vout / Vin (2)

[0049] Furthermore, the times U and D are expressed by the following equations (3) and (4), respectively.

[0050] U=T×R (3)

[0051] D=T×(1-R) ​​(4)

[0052] Therefore, by designating the voltage reduction rate R by the control unit 46 and supplying a gate signal corresponding to the voltage reduction rate R from the instruction unit 48 to the equalization unit 14 to drive the first to fourth voltage converters 24a to 24d, a desired output voltage V0 can be obtained.

[0053] [3. Characteristic Functions of This Embodiment]

[0054] <3.1 Overview of the Charging and Discharging Method of the Present Embodiment>

[0055] Next, refer to Figures 4 to 17 The characteristic functions of the power supply system 10 and the control method thereof according to the present embodiment (hereinafter also referred to as the characteristic functions of the present embodiment) will be described. The characteristic function of this embodiment is that, when first to fourth batteries 12a to 12d having different voltages or SOCs are connected in parallel and first to fourth currents I1 to I4 flow between the first to fourth batteries 12a to 12d to equalize their voltages or SOCs, the first to fourth currents I1 to I4 flowing from the first to fourth batteries 12a to 12d to the input side 34 are fed back to the control device 16. The control unit 46 of the control device 16 determines the current difference between the current flowing from the battery on the charging side (reference storage unit) and the current flowing from the battery on the discharging side (surplus storage unit), determines a voltage reduction rate R that reduces the determined current difference, and controls the first to fourth voltage converters 24a to 24d at the determined voltage reduction rate R, thereby achieving equalization of the voltages or SOCs of the batteries 12a to 12d while preventing degradation of the batteries 12a to 12d.

[0056] Figure 4 It is schematically represented Figure 1 The circuit diagram of the power supply system 10. Figure 4 In the circuit diagram, the equalization unit 14 and the like are omitted, and the diagram shows a case where a series circuit of the first to fourth batteries 12a to 12d and resistors 70a to 70d (hereinafter also referred to as the first to fourth resistors 70a to 70d) representing the internal resistance (resistance value r) of the first to fourth batteries 12a to 12d is connected in parallel, and a load 72 (motor 44) is connected to the positive electrode side of the first to fourth batteries 12a to 12d.

[0057] Here, the current flowing into the load 72 is represented by It (hereinafter also referred to as the load current). Furthermore, the voltage difference between the positive electrode side of the series circuit of the first battery 12a and the first resistor 70a and the positive electrode side of the series circuit of the second battery 12b and the second resistor 70b is represented by Vd1. The voltage difference between the positive electrode side of the series circuit of the first battery 12a and the first resistor 70a and the positive electrode side of the series circuit of the third battery 12c and the third resistor 70c is represented by Vd2. The voltage difference between the positive electrode side of the series circuit of the first battery 12a and the first resistor 70a and the positive electrode side of the series circuit of the fourth battery 12d and the fourth resistor 70d is represented by Vd3.

[0058] First, if Figure 4 As shown in the circuit diagram on the lower left side of FIG, in a closed circuit formed by connecting the series circuit of the first battery 12a and the first resistor 70a and the series circuit of the second battery 12b and the second resistor 70b in parallel, the first current I1 and the second current I2 are expressed by the following equations (5) and (6) based on Kirchhoff's law.

[0059] I1=It / 2+Vd1 / (4×r) (5)

[0060] I2=It / 2-Vd1 / (4×r) (6)

[0061] In addition, in a closed circuit formed by connecting in parallel a series circuit of the first battery 12a and the first resistor 70a, a series circuit of the second battery 12b and the second resistor 70b, and a series circuit of the third battery 12c and the third resistor 70c, the first to third currents I1 to I3 are expressed by the following equations (7) to (9) based on Kirchhoff's laws.

[0062] I1=It / 3+(Vd1+Vd2) / (6×r) (7)

[0063] I2=It / 3+(-2×Vd1+Vd2) / (6×r) (8)

[0064] I3=It / 3+(Vd1-2×Vd2) / (6×r) (9)

[0065] And, in Figure 4 In the circuit diagram on the upper side, in the case of a closed circuit without connecting the load 72, the first to fourth currents I1 to I4 are expressed by the following equations (10) to (13) based on Kirchhoff's law.

[0066] I1=It / 4+(Vd1+Vd2+Vd3) / (8×r) (10)

[0067] I2=It / 4+(-3×Vd1+Vd2+Vd3) / (8×r) (11)

[0068] I3=It / 4+(Vd1-3×Vd2+Vd3) / (8×r) (12)

[0069] I4=It / 4+(Vd1+Vd2-3×Vd3) / (8×r) (13)

[0070] Thus, the first to fourth currents I1 to I4 include voltage differences Vd1 to Vd3. Therefore, theoretically, if the first to fourth currents I1 to I4 are measured by the first to fourth current measuring instruments 26a to 26d and the measured first to fourth currents I1 to I4 are fed back to the control device 16, the desired voltage differences Vd1 to Vd3 can be adjusted based on the first to fourth currents I1 to I4.

[0071] Figure 5A and Figure 5B 1 is a timing chart showing an example of temporal changes of the first current I1 , the second current I2 , and the load current It. Figure 5A This shows a case where the first current I1 and the second current I2 are not fed back. Figure 5B The case where the first current I1 and the second current I2 are fed back is shown.

[0072] exist Figure 5A In the period from time point t0 to time point t1, there is no load 72 (refer to Figure 4 ) state, It = 0. In this case, due to the voltage difference Vd1, a current difference of 2×A occurs between the first current I1 and the second current I2. During this period, the first current I1 is a negative current, i.e., a charging current, while the second current I2 is a positive current, i.e., a discharging current. In other words, since there is no load 72, the second current I2 flowing from the second battery 12b flows into the first battery 12a as the first current I1, charging the first battery 12a.

[0073] In addition, Figure 5A In the period from time t1 to time t2, the system is in a power running state with load 72 present. Due to voltage difference Vd1, a current difference of 2×B occurs between first current I1 and second current I2. During this period, both first current I1 and second current I2 are discharge currents. That is, the first current I1 and second current I2 flowing from first battery 12a and second battery 12b flow as load current It to load 72.

[0074] And, in Figure 5AIn the period from time t2 to time t3, the load 72 is in a regenerative state, and charging of the first and second batteries 12a, 12b occurs from the load 72. In this case, a current difference of 2×C occurs between the first and second currents I1, I2, due to the voltage difference Vd1. During this period, both the first and second currents I1, I2 are charging currents. In other words, the load current It is split into the first and second currents I1, I2, and flows into the first and second batteries 12a, 12b.

[0075] And, in Figure 5A In the period after time t3 , similar to the period from t0 to t1 , It=0, and a current difference of 2×A is generated between the first current I1 and the second current I2 due to the voltage difference Vd1 .

[0076] However, in Figure 5A In the example, A≠B≠C and the first current I1 and the second current I2 are not fed back to the control device 16 (refer to Figure 1 ), therefore, it is unknown how the current difference changes due to the operation of the first to fourth voltage converters 24a to 24d. As a result, the first current I1 or the second current I2 may become large, causing the first battery 12a or the second battery 12b to deteriorate.

[0077] In contrast, in Figure 5B In this case, the first current I1 and the second current I2 are fed back to the control device 16, and the voltage difference Vd1 is controlled to reduce the current difference between the fed-back first current I1 and the second current I2. Consequently, during the period t1 to t3 when the load 72 is present, the current difference gradually decreases and reaches zero, that is, the first current I1 and the second current I2 change so that they have the same current value as the load current It. This prevents the first current I1 or the second current I2 from becoming excessive and degrading the first battery 12a or the second battery 12b. Furthermore, a certain current difference is maintained during the period t0 to t1 and the period after t3 when the load 72 is absent.

[0078] Figure 6 The diagram shows the first to fourth batteries 12a to 12d (see Figure 1 and Figure 4 ). Here, the charging and discharging methods are described when the number N of batteries 12a to 12d constituting the power supply system 10 is N = 4 (first to fourth batteries 12a to 12d), N = 3 (first to third batteries 12a to 12c), and N = 2 (first and second batteries 12a and 12b).

[0079] In addition, Figure 6 In FIG, MPP1 to MPP4 represent the first to fourth batteries 12a to 12d. Figure 6 In the diagram, “3H1L” and other symbols indicate the number of batteries on the discharge side (remaining storage unit) (the number before “H”) and the number of batteries on the charge side (reference storage unit) (the number before “L”). Figure 6 , the target values ​​of the first to fourth currents I1 to I4 (target current Itar) are indicated below the graphic symbols representing the first to fourth batteries 12a to 12d (indicated by battery). Here, the target current Itar of the battery on the discharge side is indicated by a symbol such as "Id".

[0080] The target current Itar represents the target value of the current flowing from the battery on the discharge side. The target current for the battery on the charge side is set to 0 [A]. Therefore, the actual current value (actual current) flowing from the first to fourth batteries 12a to 12d may differ from the target current. For example, when charging and discharging in the "1H3L" state, the target currents of the first to fourth currents I1 to I4 are set to 3.0 × Id [A], 0.0 [A], 0.0 [A], and 0.0 [A]. In contrast, the actual currents of the first to fourth currents I1 to I4 are +2.25 × Id [A], -0.75 × Id [A], -0.75 × Id [A], and -0.75 × Id [A]. In addition, regarding the positive and negative signs added to the 1st to 4th currents I1 to I4, the direction of flow from the 1st to 4th batteries 12a to 12d to the 1st to 4th voltage converters 24a to 24d is set to positive (+), and the direction of flow from the 1st to 4th voltage converters 24a to 24d to the 1st to 4th batteries 12a to 12d is set to negative (-).

[0081] In Form 50 (ref. Figure 1 ) is preset in the target current Itar. The control unit 46 changes each target current Itar according to the number of batteries (reference storage units) on the charging side, the number of batteries (remaining storage units) on the discharging side, the total current flowing from the plurality of batteries 12a to 12d, etc. Figure 6 The number of batteries on the charging side and the number of batteries on the discharging side are changed sequentially from the upper side to the lower side of the list. More specifically, the first to fourth batteries 12a to 12d are charged and discharged by sequentially reducing the number of batteries on the discharging side.

[0082] Specifically, when N=4, charging and discharging are performed by switching the number of batteries on the charging and discharging sides in the order of "3H1L" → "2H2L" → "1H3L" → "0H4L". Furthermore, when N=3, charging and discharging are performed by switching the number of batteries on the charging and discharging sides in the order of "2H1L" → "1H2L" → "0H3L". When N=2, charging and discharging are performed by switching the number of batteries on the charging and discharging sides in the order of "1H1L" → "0H2L".

[0083] Furthermore, during charging and discharging in this embodiment, the voltage converter connected to the battery on the charging side is set to a relatively high step-down rate (e.g., R = 0.94). While maintaining the voltage difference between the battery on the charging side and the battery on the discharging side, current is passed from the battery on the discharging side to the battery on the charging side, thereby charging the battery on the charging side. In this case, the step-down rate R of the voltage converter connected to the battery on the discharging side is set to be relatively lower than the step-down rate R of the voltage converter connected to the battery on the charging side.

[0084] However, as the battery voltage of the discharge-side battery decreases due to current flowing from the discharge-side battery to the charge-side battery, the voltage step-down rate R of the voltage converter connected to the discharge-side battery gradually increases over time. Therefore, when the voltage step-down rate R of the voltage converter connected to the discharge-side battery reaches the maximum settable rate (e.g., an upper limit of R = 0.96) taking into account the dead time Td, it becomes difficult to control the voltage converter.

[0085] Therefore, in this embodiment, if Figure 6 As shown, before the voltage reduction rate R of the voltage converter of the battery connected to the discharge side reaches the maximum voltage reduction rate, the voltage converter is sequentially Figure 6 By switching from the upper state to the lower state, the first to fourth batteries 12a to 12d are smoothly charged and discharged while avoiding difficulty in controlling the first to fourth voltage converters 24a to 24d. A specific charge and discharge control method will be described later.

[0086] <3.2 Specific Control Method of This Embodiment>

[0087] Figure 7 This is a sequence diagram showing charge and discharge control of the first to fourth batteries 12 a to 12 d when the power supply system 10 according to the present embodiment is applied to the electric vehicle 22 , more specifically, when the motor 44 is used as a driving source for the wheels of the electric vehicle 22 . Figure 8 It means in Figure 7 Flowchart of the operation of the equalization unit 14 and the control device 16 in the charge and discharge control. Figure 9Aand Figure 9B As shown, the charge and discharge control will be described in the case where the battery voltage V1 of the first battery 12a is the lowest and the battery voltages V1 to V4 increase in the order of the first to fourth batteries 12a to 12d.

[0088] First, refer to Figure 7 The overall flow of charge and discharge control will be described below. When the ignition switch (IG) of the electric vehicle 22 (not shown) is turned on, the MG-ECU 18 issues a start command to each BMU in step S1. In response, each BMU starts in accordance with the start command from the MG-ECU 18 in step S2.

[0089] Furthermore, in steps S1 and S2, the MG-ECU 18 also performs a numbering process for each BMU, assigning the four batteries 12a to 12d to the first to fourth batteries 12a to 12d. Consequently, the four batteries 12a to 12d are assigned to any of the first to fourth batteries 12a to 12d. The MG-ECU 18 also notifies the control unit 46 of the control device 16 of the result of the numbering process.

[0090] However, the first to fourth voltage converters 24a to 24d include capacitors 52, 56, and 68 (see Figures 2A to 2C ). Therefore, if Figure 10 As shown, even when electric vehicle 22 is parked and the ignition switch is turned off at time t4, a certain voltage is generated by the charge stored in capacitors 52, 56, and 68, or more specifically, by the charge stored between equalization unit 14 and PDU 20. Therefore, for example, during the period from time t5, when the ignition switch is turned on, to time t6, control unit 46 of control device 16 instructs command unit 48 in step S3 to drive switching elements 42H and 42L to discharge the charge from capacitors 52, 56, and 68. In response, command unit 48 supplies a gate signal to equalization unit 14 in accordance with the instruction from control unit 46, turning on switching elements 42H and 42L in step S4. As a result, the charge from capacitors 52, 56, and 68 is discharged during the period from time t5 to time t6, thereby reducing output voltage V0 to approximately 0 [V].

[0091] In addition, Figure 7 In the embodiment, the discharge process of steps S3 and S4 is performed after step S2. Figure 10 The discharge process is performed after the time point t5 of FIG. 1 and before the process of step S9 described later (time point t7).

[0092] In step S5, a voltage sensor (not shown) in the battery pack detects the voltages of the first to fourth batteries 12a to 12d (battery voltages V1 to V4). Based on this, in step S6, the equalization unit 14 can grasp the voltages V1 to V4 of the batteries. Figure 9A , the battery voltages detected by the voltage sensors are shown as V1can to V4can. Furthermore, the detection results of the voltage sensors are transmitted from each battery pack to the control device 16. The control device 16 transfers the detection results to the MG-ECU 18.

[0093] In step S7, the MG-ECU 18 determines how to control the charge and discharge of the first to fourth batteries 12a to 12d based on the result of the numbering process and the detection results of the battery voltages V1 to V4. In this case, the MG-ECU 18 determines that N = 4 based on the result of the numbering process and determines the charge and discharge control according to the first to fourth batteries 12a to 12d. Figure 6 MG-ECU 18 performs charge and discharge control with N=4. Furthermore, MG-ECU 18 determines that among the first to fourth batteries 12a to 12d, first battery 12a, which has the lowest battery voltage V1 to V4, is the battery on the charge side (reference storage unit), and determines that the remaining second to fourth batteries 12b to 12d are the batteries on the discharge side (remaining storage units). MG-ECU 18 then instructs control device 16 to begin charge and discharge control of first to fourth batteries 12a to 12d.

[0094] In step S8, the control unit 46 of the control device 16 executes a control process for charge and discharge control according to the instruction from the MG-ECU 18, and instructs the instruction unit 48 to output a gate signal. In response, the instruction unit 48 starts supplying the gate signal to the equalization unit 14 according to the instruction from the control unit 46. As a result, in step S9, the equalization unit 14 drives the switching elements 42H and 42L according to the received gate signal, thereby starting the charge and discharge control (equalization control) from time point t7. That is, at Figure 10 During the period of t5 to t7, the initial processing of the charge and discharge control is performed. Figure 7 The processing of steps S1 to S8.

[0095] In step S10, the MG-ECU 18 instructs each battery pack to execute a pre-charge process to charge a capacitor (not shown) within the battery pack. Consequently, in step S11, each battery pack charges the capacitor according to the instruction from the MG-ECU 18. Furthermore, steps S10 and S11 may also be used to charge capacitors 52, 56, and 68 of the voltage converters 24a to 24d. Furthermore, in this embodiment, steps S10 and S11 may be included in the initial processing.

[0096] In step S12, the MG-ECU 18 instructs each battery pack to turn on a switch element (not shown) in the battery pack. In step S13, each battery pack turns on the switch element in accordance with the instruction from the MG-ECU 18. Figure 10 At time t8, the switching element is turned on. This electrically connects the first to fourth batteries 12a to 12d and the first to fourth voltage converters 24a to 24d. As a result, after time t8, current can flow from the first to fourth batteries 12a to 12d to the first to fourth voltage converters 24a to 24d, allowing charging and discharging of the first to fourth batteries 12a to 12d.

[0097] After this, when the ignition switch of the electric vehicle 22 is turned off, the switching elements of each battery pack are turned off in step S14. As a result, the charge and discharge control (equalization control) is also stopped in step S15. Figure 7 In the process, the control device 16 may be responsible for processing steps S1, S7, S11, and S13.

[0098] Figure 8 Yes Figure 7 Flowchart of the specific method of equalization control. That is, Figure 8 The flowchart illustrates the flow of actions of the control device 16 and the equalization unit 14 during the period from step S9 to step S15.

[0099] First, in step S21, the MG-ECU 18 or the control unit 46 determines that the battery with the lowest battery voltage among the first to fourth batteries 12a to 12d is the battery on the charging side (reference storage unit). Figure 9A As shown in FIG. 1 , the battery voltage V1 (V1can) of the first battery 12a is the lowest, so the control unit 46 determines that the first battery 12a is the battery on the charging side. Figure 7 From steps S9 to S12, the switching elements of each battery pack are in the off state. Therefore, the first to fourth batteries 12a to 12d and the first to fourth voltage converters 24a to 24d are not electrically connected. In this case, the MG-ECU 18 or the control unit 46 can identify the first battery 12a as the battery to be charged based on the battery voltages V1 to V4 (V1can to V4can) of the first to fourth batteries 12a to 12d detected by voltage sensors (not shown) within each battery pack.

[0100] Next, the control unit 46 sets a reference voltage Vref based on the battery voltage V1 of the first battery 12a. Specifically, the reference voltage Vref is calculated according to the following equation (14) using the battery voltage V1 of the first battery 12a and the voltage reduction rate R1 of the first voltage converter 24a connected to the first battery 12a.

[0101] Vref=R1×(lowest battery voltage (V1))(14)

[0102] As described above, considering the dead time Td, the upper limit of the voltage reduction rate R is 0.96. Therefore, the control unit 46 sets R1 to 0.94, for example. Next, the control unit 46 sets the values ​​(initial values) of the battery voltages V1 to V4 of the first to fourth batteries 12a to 12d used in the charge and discharge process to the reference voltage Vref, thereby aligning the values ​​of the battery voltages V1 to V4. Consequently, the voltage difference between the first to fourth batteries 12a to 12d is temporarily set to 0 [V].

[0103] Then, as a result of the processing of steps S10 to S13, the 1st to 4th batteries 12a to 12d and the 1st to 4th voltage converters 24a to 24d are electrically connected, so that the battery voltages V1 to V4 of the 1st to 4th batteries 12a to 12d can be measured by the 1st to 4th voltage measuring instruments 28a to 28d and the 1st to 4th currents I1 to I4 can be measured by the 1st to 4th current measuring instruments 26a to 26d. In this case, in step S22, the control unit 46 obtains the battery voltages V1 to V4 of the 1st to 4th batteries 12a to 12d from the 1st to 4th voltage measuring instruments 28a to 28d, and obtains the 1st to 4th currents I1 to I4 from the 1st to 4th current measuring instruments 26a to 26d.

[0104] In the next step S23 , the control unit 46 calculates the current difference between the first to fourth currents I1 to I4 using the acquired first to fourth currents I1 to I4 . Figure 11 is a block diagram schematically illustrating the equalization unit 14, Figure 12 1 is a block diagram illustrating the charge and discharge control of the control device 16 and the equalization unit 14. Figure 12 In the embodiment, the “controlled object” refers to the power supply system 10 including the equalization unit 14. Figure 12 In FIG. 1 , “s” in each of “kp+kds” and “1 / s” is a complex variable in Laplace transform.

[0105] exist Figure 11 and Figure 12 In the example, the control unit 46 uses the first battery 12a as the battery on the charging side (reference storage unit) and the second to fourth batteries 12b to 12d as the batteries on the discharging side (surplus storage units). Therefore, the control unit 46 subtracts the second to fourth currents I2 to I4 from the first current I1.

[0106] In the next step S24, the control unit 46 determines whether the current charge and discharge state meets the requirements based on the acquired battery voltages V1 to V4. Figure 6 In this case, the control unit 46 determines that Figure 6The status of "3H1L".

[0107] Next, as shown in the following equations (15) to (17), the control unit 46 calculates the current difference between the first current I1 and the second to fourth currents I2 to I4 by adding the target currents Itar2 to Itar4 to the current difference obtained by subtraction in step S23. The current differences ΔI2 to ΔI4 in equations (15) to (17) are the target currents (target operating currents) used to actually control the first to fourth voltage converters 24a to 24d. That is, the control unit 46 can set each target operating current ΔI2 to ΔI4 by adding the target currents Itar2 to Itar4 to each current difference.

[0108] ΔI2=I1-I2+Itar2 (15)

[0109] ΔI3=I1-I3+Itar3 (16)

[0110] ΔI4=I1-I4+Itar4 (17)

[0111] In the following step S25, the control unit 46 uses the target operating currents (current differences) ΔI2 to ΔI4 calculated in step S24 to calculate voltage differences Vd1 to Vd3 between the battery voltage V1 of the first battery 12a and the battery voltages V2 to V4 of the second to fourth batteries 12b to 12d, as shown in the following equations (18) to (20). In equations (18) to (20), "∫" represents an integral symbol. Furthermore, kp and kd are fixed coefficients used in feedback control. Furthermore, ΔI2p to ΔI4p represent the previous target operating currents.

[0112] Vd1=∫{kp×ΔI2+kd×(ΔI2-ΔI2p)} (18)

[0113] Vd2=∫{kp×ΔI3+kd×(ΔI3-ΔI3p)} (19)

[0114] Vd3=∫{kp×ΔI4+kd×(ΔI4-ΔI4p)} (20)

[0115] In the next step S26, the control unit 46 calculates the voltage reduction rates R2 to R4 using the calculated voltage differences Vd1 to Vd3. In step S27, the command unit 48 outputs a gate signal based on the voltage reduction rates R1 to R4 to the equalization unit 14. Based on this, the switching elements 42H and 42L of the first to fourth voltage converters 24a to 24d are driven based on the received gate signal. As a result, in step S28, the voltage reduction rates R2 to R4 are calculated. Figure 9B The voltage differences Vd1 to Vd3 shown change the current values ​​of the first to fourth currents I1 to I4.

[0116] In the next step S29, the control unit 46 determines whether to stop the equalization control. If the control unit 46 does not reach step S15, it determines to continue the equalization control (step S29: No), returns to step S22, and executes the processing of steps S22 to S29 again. Therefore, each time the processing of steps S22 to S29 is repeatedly executed, the states of the first to fourth batteries 12a to 12d change from Figure 6 The "3H1L" is switched to the state of "2H2L", "1H3L", and "0H4L". After that, when the process reaches step S15, the control unit 46 stops the equalization control (step S29: Yes).

[0117] Figure 13 Yes Figure 8 The timing diagram of the effect of the control process is shown in FIG. Target current Itar is set at time t9, and the switching elements 42H and 42L are driven according to the voltage difference Vd1 based on the target current Itar. As a result, the second current I2 quickly rises toward the target current Itar as time passes after time t9. In this case, by appropriately setting the fixed coefficients kp and kd, the time when the second current I2 converges to the target current Itar can be shortened. In addition, Figure 13 The difference between the target current Itar and the second current I2 at any time point t10 is the target operating current (current difference) ΔI2. The area of ​​the portion surrounded by the target current Itar and the second current I2 between time points t9 and t10 represents the voltage difference Vd1.

[0118] <3.3 Necessity of Voltage Reduction Rate R in Charge and Discharge Control>

[0119] Next, in this embodiment, while referring to Figures 14 to 16D The necessity of considering the pressure reduction rate R will be explained. Figure 14 1 to 4 currents I1 to I4, battery voltages V1 to V4, and step-down rates R1 to R4 under charge and discharge control in this embodiment. Figure 6 The following describes a case where N=4 and the battery on the discharge side and the battery on the charge side are switched in the order of “3H1L” → “2H2L” → “1H3L” → “0H4L” at time points t11, t12, t13, and t14.

[0120] In this case, the first battery on the charging side is the fourth battery 12d, and the voltage reduction rate R4 of the fourth voltage converter 24d connected to the fourth battery 12d is fixed at R4 = 0.91. Therefore, the first to third batteries 12a to 12c are initially the batteries on the discharging side.

[0121] First, during the period from t11 to t12, the first to third currents I1 to I3 are discharge currents (positive currents), and the fourth current I4 is a charge current (negative current). As a result, the step-down rates R1 to R3 of the first to third voltage converters 24a to 24c increase over time. Then, at time t12, when the step-down rates R2 and R3 of the second and third voltage converters 24b and 24c reach approximately 0.96 (the upper limit of the settable step-down rate), the voltage is switched from "3H1L" to "2H2L."

[0122] Consequently, during the period from t12 to t13, the first and third batteries 12a and 12c are switched to the discharging side, while the second and fourth batteries 12b and 12d are switched to the charging side. Specifically, the first and third currents I1 and I3 are discharging currents, while the second and fourth currents I2 and I4 are charging currents. As a result, the step-down rates R1 and R3 of the first and third voltage converters 24a and 24c increase over time. Meanwhile, since the second battery 12b has been switched to the charging side, the step-down rate R2 of the second voltage converter 24b decreases to the step-down rate R4 (0.91) of the fourth voltage converter 24d. Then, at time t13, when the step-down rate R3 of the third voltage converter 24c reaches approximately 0.96, the system switches from "2H2L" to "1H3L."

[0123] Consequently, during the period from t13 to t14, the first battery 12a is switched to the discharge-side battery, while the second to fourth batteries 12b to 12d are switched to the charge-side batteries. Specifically, the first current I1 becomes the discharge current, while the second to fourth currents I2 to I4 become the charge current. As a result, the voltage reduction rate R1 of the first voltage converter 24a increases over time. Meanwhile, since the third battery 12c has been switched to the charge-side battery, the voltage reduction rate R3 of the third voltage converter 24c decreases to the voltage reduction rates R2 and R4 (0.91) of the second and fourth voltage converters 24b and 24d, respectively. Then, at time t14, when the voltage reduction rate R1 of the first voltage converter 24a reaches approximately 0.96, it switches from "1H3L" to "0H4L." Consequently, charge and discharge control is completed.

[0124] This charge and discharge control needs to consider the voltage reduction rate R (R1 to R4) for the following reasons. Figure 15As shown, for example, let the battery voltages V1 to V4 of the first to fourth batteries 12a to 12d in a fully charged state be Vi [V], and let the voltage reduction rates R1 to R4, corresponding to the dead time Td, be 0.31. Furthermore, taking into account the dead time Td, the adjustable range of the battery voltages V1 to V4 (the settable range of the voltage reduction rates R1 to R4) is 0.75 × Vi [V] to 0.96 × Vi [V] (R1 to R4 = 0.75 to 0.96). Furthermore, let the reference voltage Vref be 0.94 × Vi [V] (R = 0.94).

[0125] In this embodiment, if Figure 16A As shown in FIG, while maintaining the voltage difference between the battery on the charging side and the battery on the discharging side as a reference, current flows from the battery on the discharging side to the battery on the charging side, thereby charging the battery on the charging side. Figure 16A In the "1H3L" state, first battery 12a is the battery on the discharge side, and second to fourth batteries 12b-12d are the batteries on the charge side. Therefore, the initial step-down rate R1 of first voltage converter 24a is set to 0.81, and the step-down rates R2-R4 of second to fourth voltage converters 24b-24d are set (fixed) to 0.94. Furthermore, the voltage difference between first battery 12a and second to fourth batteries 12b-12d is set to Vd [V].

[0126] When the current is caused to flow from the first battery 12a on the discharge side to the second to fourth batteries 12b to 12d on the charge side while maintaining the voltage difference, Figure 16B As shown in FIG. 1 , the battery voltage V1 or SOC of the first battery 12a decreases, and the voltage reduction rate R1 increases. Figure 16C As shown in FIG. 1 , if the step-down rate R1 of the first voltage converter 24a reaches 0.96 and the voltage difference is maintained, the step-down rate R1 is saturated and does not rise from 0.96, making it difficult to control charge and discharge. Figure 16D As shown, the voltage difference decreases instead, and the absolute values ​​of the target currents of the first to fourth currents I1 to I4 also decrease.

[0127] Therefore, in this embodiment, if Figure 14 As shown, before the step-down rate R of the voltage converter connected to the battery on the discharge side reaches the upper limit value (R=0.96) taking into account the dead time Td, the combination of the number of batteries on the discharge side and the number of batteries on the charge side is changed, thereby avoiding a state where charge and discharge control is difficult.

[0128] <3.4 Application Example to Electric Vehicle 22>

[0129] Figure 17This is a timing diagram showing the temporal changes in vehicle speed, current, and SOC when the power supply system 10 according to this embodiment is installed in an electric vehicle 22. In this case, electric vehicle 22, which started before time t15, came to a stop from time t15 to time t16, and then began accelerating from time t16. Thereafter, electric vehicle 22 began cruising from time t17, decelerated from time t18, and came to a stop at time t19.

[0130] In this case, by implementing the above-mentioned charge and discharge control, charge and discharge are performed between the battery on the discharge side and the battery on the charge side when the electric vehicle 22 is parked (the period from t15 to t16 and the period after time t19) and when it is cruising (a part of the period from t17 to t18). Figure 17 In FIG. 1 , the current flowing out of the battery on the discharge side and the SOC are shown by the dotted line, and the current flowing into the battery on the charge side and the SOC are shown by the solid line.

[0131] [4. Effects of this embodiment]

[0132] As described above, the present embodiment is a power supply system 10 and a control method thereof, wherein the power supply system 10 has a plurality of batteries 12a to 12d (storage units), a plurality of voltage converters 24a to 24d and a plurality of current measuring instruments 26a to 26d, wherein the plurality of batteries 12a to 12d are capable of charge and discharge; the input sides 34 of the plurality of voltage converters 24a to 24d are connected to the plurality of batteries 12a to 12d, and the output sides 36 thereof are connected in parallel with each other, and the voltages V1 to V4 of the plurality of batteries 12a to 12d connected to the input side 34 are converted at an arbitrary transformation rate Tr, and the converted voltage V0 is output to the output side 36; the plurality of current measuring instruments 26a to 26d are connected to the input sides 34 of the plurality of voltage converters 24a to 24d, and measure the currents I1 to I4 flowing from the plurality of batteries 12a to 12d to the input side 34.

[0133] In this case, the power supply system 10 has a storage unit determination unit (MG-ECU18, control unit 46), a current difference determination unit (control unit 46) and a transformation ratio determination unit (control unit 46), wherein the storage unit determination unit determines at least one battery among the multiple batteries 12a~12d as a battery on the charging side (reference storage unit) and determines the remaining batteries as batteries on the discharging side (remaining storage units); the current difference determination unit determines the current difference between the current flowing out of the battery on the discharging side and the current flowing out of the battery on the charging side based on the currents I1~I4 measured by the multiple current measuring instruments 26a~26d; and the transformation ratio determination unit determines the transformation ratio Tr of the voltage converter connected to the battery on the discharging side based on the determined current difference.

[0134] In addition, the control method of the power supply system 10 includes the following steps: a step of using the MG-ECU 18 or the control unit 46 to determine that at least one of the multiple batteries 12a to 12d is a battery on the charging side, and determining that the remaining batteries are batteries on the discharging side (step S7); a step of using the control unit 46 to determine the current difference between the current flowing out of the battery on the discharging side and the current flowing out of the battery on the charging side based on the currents I1 to I4 measured by the multiple current measuring instruments 26a to 26d (steps S23 and S24); and a step of determining the transformation rate Tr of the voltage converter connected to the battery on the discharging side based on the determined current difference by the control unit 46 (step S26).

[0135] In this way, the current difference between the current flowing from the discharge-side battery and the current flowing from the charge-side battery is fed back, and the voltage conversion ratio Tr of the voltage converter connected to the discharge-side battery is determined to minimize this current difference. As a result, when multiple batteries 12a-12d are connected in parallel via voltage converters 24a-24d, the battery voltages V1-V4 or SOC of the multiple batteries 12a-12d connected in parallel can be equalized while preventing degradation of the batteries 12a-12d.

[0136] In this case, the MG-ECU 18 or the control unit 46 identifies the battery with the lowest voltage among the plurality of batteries 12a to 12d as the battery on the charging side and identifies the remaining batteries as the batteries on the discharging side.

[0137] The control unit 46 calculates the current difference by subtracting the current flowing from the discharging battery from the current flowing from the charging battery and adding the subtracted current to the target current Itar. This feedback control allows charge and discharge control to be performed while preventing the current flowing from each battery 12a to 12d from being excessive.

[0138] The target current Itar is a current value set according to the number of batteries 12a to 12d, the number of batteries on the charging side, or the total current flowing from the batteries 12a to 12d.

[0139] Furthermore, the control unit 46 calculates the voltage difference between the battery voltage of the battery on the charging side and the battery voltage of the battery on the discharging side based on the current difference, and uses the calculated voltage difference to determine the transformation ratio Tr of the voltage converter connected to the battery on the discharging side. By using the voltage difference reflecting the current difference to determine the transformation ratio Tr, it is possible to prevent excessive current from flowing from each battery 12a-12d, effectively suppressing degradation of the batteries 12a-12d.

[0140] The above description has mainly focused on the case where voltage converters 24a to 24d are controlled using the step-down rate R. Of course, in this embodiment, voltage converters 24a to 24d can also be appropriately controlled using the step-up rate Tru.

[0141] In addition, the present invention is not limited to the above-mentioned embodiment, and it is of course possible to adopt various structures based on the contents described in this specification.

Claims

1. A power supply system comprising a plurality of power storage units, a plurality of voltage converters, and a plurality of current measuring instruments, wherein: The plurality of power storage units are capable of charge and discharge; The input sides of the plurality of voltage converters are connected to any one of the plurality of power storage units, the output sides of the plurality of voltage converters are connected in parallel, the plurality of voltage converters convert the voltage of the power storage unit connected to the input side at an arbitrary transformation ratio, and output the converted voltage to the output side; The plurality of current measuring instruments are respectively connected to the input sides of the plurality of voltage converters to measure the current flowing between the plurality of power storage units and the corresponding plurality of voltage converters. It is characterized by: It also includes a storage unit determination unit, a current difference determination unit, and a transformation ratio determination unit, wherein: The power storage unit specifying unit specifies at least one of the plurality of power storage units as a reference power storage unit on a charge side, and specifies at least one remaining power storage unit as a remaining power storage unit on a discharge side; The current difference determination unit determines a current difference between a first current and a second current based on the currents measured by the plurality of current measuring instruments, wherein the first current is a current flowing between the reference power storage unit and the voltage converter connected to the reference power storage unit, and the second current is a current flowing between the surplus power storage unit and the voltage converter connected to the surplus power storage unit; The transformation ratio determination unit determines a transformation ratio of the voltage converter connected to the surplus power storage unit based on the determined current difference.

2. The power supply system according to claim 1, wherein: The power storage unit identification unit identifies the power storage unit having the lowest voltage among the plurality of power storage units as the reference power storage unit.

3. The power supply system according to claim 1, wherein: The current difference determination unit calculates the current difference by subtracting the second current from the first current and adding the subtracted first current to a target current.

4. The power supply system according to claim 3, characterized in that: The target current is a current value set according to the number of the plurality of power storage units, the number of the reference power storage units, or the total sum of the currents flowing between the plurality of power storage units and the corresponding plurality of voltage converters.

5. The power supply system according to any one of claims 1 to 4, characterized in that: The transformation ratio determination unit calculates a voltage difference between the voltage of the reference power storage unit and the voltage of the surplus power storage unit based on the current difference, and determines a transformation ratio of the voltage converter connected to the surplus power storage unit using the calculated voltage difference.

6. A method for controlling a power supply system comprising a plurality of power storage units, a plurality of voltage converters, and a plurality of current measuring instruments, wherein: The plurality of power storage units are capable of charge and discharge; The input sides of the plurality of voltage converters are connected to any one of the plurality of power storage units, the output sides of the plurality of voltage converters are connected in parallel, the plurality of voltage converters convert the voltage of the power storage unit connected to the input side at an arbitrary transformation ratio, and output the converted voltage to the output side; The plurality of current measuring instruments are respectively connected to the input sides of the plurality of voltage converters to measure the current flowing between the plurality of power storage units and the corresponding plurality of voltage converters. It is characterized by: The control method of the power supply system comprises the following steps: a step of determining, using a storage unit determination unit, at least one of the plurality of storage units as a reference storage unit on a charge side, and determining at least one remaining storage unit as a remaining storage unit on a discharge side; a step of determining, using a current difference determining unit, a current difference between a first current and a second current based on the currents measured by the plurality of current measuring instruments, wherein the first current is a current flowing between the reference power storage unit and the voltage converter connected to the reference power storage unit, and the second current is a current flowing between the surplus power storage unit and the voltage converter connected to the surplus power storage unit; The step of determining, using a transformation ratio determination unit, a transformation ratio of the voltage converter connected to the surplus power storage unit based on the determined current difference.

Images