Electricity storage device and power conversion device equipped with the electricity storage device

Abstract

The power storage device (10) includes a plurality of units (12) connected in series with one another and a control unit (11). Each of the plurality of units (12) includes a plurality of power storage elements (43) and a unit control unit (31) supplied with power from the plurality of power storage elements. When an index value representing the degree of variation in voltage or state of charge among the plurality of units (12) exceeds an upper limit value, the control unit (11) operates the unit control unit (31) of a unit having a relatively high voltage or state of charge in a first operation mode and operates the unit control unit (31) of a unit having a relatively low voltage or state of charge in a second operation mode that consumes less power than the first operation mode.

Description

[Technical Field]

[0001] The present disclosure relates to a power storage device and a power conversion device including the power storage device. [Background technology]

[0002] A power storage device has a large number of storage elements connected in series and parallel. To maintain the performance of the power storage device, it is necessary to keep the voltages of the many series-connected storage elements uniform. For this reason, the power storage device has a circuit for balancing the voltages of the storage elements.

[0003] The energy storage device disclosed in International Publication No. 2017 / 073018 (Patent Document 1) includes a plurality of energy storage units connected in series, each of which includes a battery pack in which a plurality of energy storage elements are connected in series. Furthermore, in the energy storage device disclosed in this document, each energy storage unit includes a cell rebalancing circuit and a unit rebalancing circuit to equalize the voltage or remaining capacity of each energy storage element within the energy storage device. The cell rebalancing circuit reduces the voltage and remaining capacity of each high-voltage energy storage element by passing current from the high-voltage energy storage element to a discharge resistor corresponding to each energy storage element in order to equalize the voltage and remaining capacity of each energy storage element constituting the battery pack within the storage battery unit. The unit rebalancing circuit reduces the voltage and remaining capacity of the high-voltage battery pack by passing current from the high-voltage battery pack to a discharge resistor corresponding to each unit in order to equalize the voltage between the energy storage units connected in series. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2017 / 073018 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, the energy storage device disclosed in International Publication No. 2017 / 073018 (Patent Document 1) requires that the high-voltage battery pack discharge enough energy to equalize the voltages between the battery units, and therefore requires a large discharge resistor with a rated power and rated voltage that allows such discharge. Even if the battery pack is connected to the discharge resistor via a DC / DC converter that converts the voltage to a low voltage, the rated power and rated voltage of the components that make up the DC / DC converter must be large. This poses a problem of increasing the size of the entire energy storage device.

[0006] The present disclosure has been made in consideration of the above-mentioned problems, and its purpose is to provide an energy storage device including a plurality of energy storage units connected in series, which can equalize the voltage or state of charge between the energy storage units without having a dedicated discharge resistor for discharging the energy storage units. [Means for solving the problem]

[0007] In one embodiment, the power storage device includes a positive electrode and a negative electrode, a plurality of units connected in series between the positive electrode and the negative electrode, and one or more control units. Each of the plurality of units includes a positive node and a negative node, and a plurality of power storage units connected in series between the positive node and the negative node. Module and, a switch connected in series with a plurality of power storage modules between a positive node and a negative node; and a unit control section. Each of the plurality of power storage modules includes a plurality of power storage elements and a power storage element balancing circuit. The storage element balancing circuit is By discharging one or more of the plurality of storage elements, The unit control unit balances the voltages or charge states of the plurality of storage elements. Module The power supply is supplied from the power supply 10 and has a first operation mode and a second operation mode which consumes less power than the first operation mode. The unit control unit is connected to one or more control units via a communication line. The unit control unit is configured to collect the status of its own unit, including the voltage or charge state of each storage element in its own unit, operate the switch in its own unit based on the status of its own unit and an operation command from the one or more control units, determine the storage element to be discharged by the storage element balancing circuit for each storage module, and issue a command to the control circuit of the storage element balancing circuit. When an index value representing the degree of variation in voltage or state of charge among multiple units exceeds an upper limit value while charging or discharging of the power storage device is stopped, one or more control units operate the unit control units of units with relatively high voltage or state of charge in a first operating mode and operate the unit control units of units with relatively low voltage or state of charge in a second operating mode. [Effects of the Invention]

[0008] According to the above embodiment, the voltage or state of charge among multiple units can be equalized by operating the unit control unit of a unit with a relatively high voltage or state of charge in a first operating mode and operating the unit control unit of a unit with a relatively low voltage or state of charge in the second operating mode. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram illustrating an example of a configuration of a power conversion device according to the present disclosure. [Figure 2] FIG. 1 is a diagram showing an example of the relationship between the SOC and OCV of a LIB. [Figure 3] FIG. 1 is a diagram showing an example of the relationship between the SOC and the OCV of an EDLC. [Figure 4] FIG. 2 is a diagram illustrating an example of the configuration of the power storage module of FIG. [Figure 5] 2 is a diagram illustrating an example of a power supply-related configuration of a unit control unit in FIG. 1; [Figure 6] 10 is a flowchart illustrating a process of unit voltage balance control. [Figure 7] 7 is a flowchart illustrating the operation mode control process in step S115 of FIG. 6. [Figure 8] 10 is a diagram illustrating an example of the configuration of power supplies in a unit control unit in a power storage device according to a second embodiment. FIG. [Figure 9] 10 is a flowchart illustrating a process of unit voltage balance control using a power supply mode. [Figure 10] 10 is a flowchart illustrating the process of power supply mode control in step S135 of FIG. 9. [Figure 11] 11 is a flowchart illustrating a process of SOC balance control between units using operation modes in the power storage device of the third embodiment. [Figure 12] 12 is a flowchart illustrating the operation mode control process in step S155 of FIG. 11. [Figure 13]11 is a flowchart illustrating processing of SOC balance control between units using a power supply mode in the power storage device of the third embodiment. [Figure 14] 14 is a flowchart illustrating the process of power supply mode control in step S175 of FIG. 13. [Figure 15] FIG. 10 is a diagram illustrating a configuration example of a unit in a power storage device according to a fourth embodiment. [Figure 16] 10 is a diagram illustrating an example of the configuration of power supplies of a bank control unit and a unit control unit in a power storage device according to a fourth embodiment. FIG. [Figure 17] 17 is a diagram illustrating an example of the internal configuration of the unit power supply unit of FIG. 16. [Figure 18] FIG. 13 is a diagram illustrating a configuration example of a power storage device according to a fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Each embodiment will be described in detail below with reference to the drawings. The same or corresponding parts will be denoted by the same reference characters and description thereof will not be repeated.

[0011] Embodiment 1 [Configuration of power conversion device 100] 1 is a diagram showing an example of the configuration of a power conversion device 100 according to the present disclosure. The power conversion device 100 includes a power storage device 10, a power converter 20, and a control device 21 that controls the power converter 20. The power conversion device 100 is connected to a power system 1 and operates to exchange active power between the power system 1 and the power storage device 10. The power conversion device 100 may also have a function of supplying reactive power to the power system.

[0012] The power converter 20 has a DC end 22 connected to the power storage device 10 and an AC end 23 connected to the power grid 1. The power converter 20 may be, for example, a modular multilevel converter in which a plurality of unit converters are cascaded.

[0013] The circuit configuration of power converter 20 is not limited to the form shown in Fig. 1. For example, in Fig. 1, two DC terminals are connected to the positive electrode P1 and negative electrode N1 of power storage device 10, but three or more terminals of the DC terminals may be connected to three or more terminals of power storage device 10. Furthermore, power converter 20 may be separated into a DC-DC converter and a DC-AC converter. Furthermore, a transformer may be provided between AC terminal 22 and power grid 1, and the voltage level of AC terminal 23 may be stepped up to the voltage level of power grid 1 by the transformer.

[0014] The control device 21 generates command values ​​for controlling the power converter 20 and the storage device 10 based on information about the storage device 10 received from the storage device control unit 11 provided in the storage device 10, information about the power system 1, and the like.

[0015] [Configuration of Power Storage Device 10] 1, the power storage device 10 includes a plurality of units 12a to 12c (three in FIG. 1) connected in series between a positive electrode P1 and a negative electrode N1, a power storage device control unit 11 that manages and controls the power storage device 10, and a switch 13 that disconnects the power storage device 10 from the power converter 20. The switch 13 and the units 12a to 12c are connected in series.

[0016] The unit 12a includes a unit control unit 31a that manages and controls the unit 12a, a plurality of (three in FIG. 1) power storage modules 41a to 41c connected in series with each other, a series switch 32a connected in series with the power storage modules 41a to 41c, and a parallel switch 33a connected in parallel with the power storage modules 41a to 41c and the switch 32a as a whole. The positive node of the series-connected power storage modules 41a to 41c is designated as P2, and the negative node is designated as N2.

[0017] Although not shown in Fig. 1 for simplicity, units 12b and 12c have the same configuration as unit 12a. That is, unit 12b includes a unit control unit 31b, power storage modules 41a to 41c, a series switch 32b, and a parallel switch 33b. Unit 12c includes a unit control unit 31c, power storage modules 41a to 41c, a series switch 32c, and a parallel switch 33c.

[0018] In FIG. 1, for simplicity, the number of units connected in series and the number of storage modules connected in series are both set to three, but the number of units connected in series and the number of storage modules connected in series in each unit may each be any number equal to or greater than two.

[0019] Furthermore, hereinafter, when referring collectively to the units 12a to 12c, the power storage modules 41a to 41c, the unit control units 31a to 31c, the series switches 32a to 32c, and the parallel switches 33a to 33c, or when referring to any one of them, they will be referred to as the unit 12, the power storage module 41, the unit control unit 31, the series switch 32, and the parallel switch 33, respectively. The series switch 32 and the parallel switch 33 will also be simply referred to as the switches 32 and 33. The parallel switch 33 will also be referred to as a bypass switch.

[0020] The power storage module 41a includes a module control unit 42a that monitors and controls the power storage module 41a, and a plurality of power storage elements 43a of the same type. In FIG. 1, the plurality of power storage elements 43a are connected in series, but this is not limited to this. For example, a set of a plurality of power storage elements connected in parallel may be further connected in series. Alternatively, a set of a plurality of power storage elements connected in series may be further connected in parallel.

[0021] Although not shown in Figure 1 for simplicity, power storage modules 41b and 41c have the same configuration as power storage module 41a. That is, power storage module 41b includes a module control unit 42b and a plurality of power storage elements 43b. Power storage module 41c includes a module control unit 42c and a plurality of power storage elements 43c. Hereinafter, module control units 42a to 42c and power storage elements 43a to 43c will be referred to as module control unit 42 and power storage element 43, respectively, when referring to them collectively or when referring to any one of them.

[0022] In each power storage module 41, the module control unit 42 has various functions related to the power storage elements 43 and the power storage module 41. Specifically, the module control unit 42 functions as a voltage detector, a temperature measuring device, a current detector, and a state of charge (SOC) calculator. Furthermore, the module control unit 42 has a function of detecting abnormalities in the power storage elements 43 from these measured values ​​and calculation results, a power storage element balance control function of suppressing variations in voltage or SOC of the power storage elements 43, a communication function with the unit control unit 31, etc.

[0023] In the present disclosure, the energy storage device 10 is provided with an energy storage device control unit 11, each unit 12 constituting the energy storage device 10 is provided with a unit control unit 31, and each energy storage module 41 constituting the unit 12 is provided with a module control unit 42. That is, the energy storage device control unit 11, the unit control unit 31, and the module control unit 42 are provided hierarchically. However, the control units do not necessarily have to be configured in this manner. In addition, since each of the above control units may primarily perform monitoring or management, they may of course be referred to as a monitoring device or a management device. Furthermore, the division of functions is not fixed, and the above multiple control units may appropriately divide the functions.

[0024] The storage element 43 may be any of a storage battery cell, an electric double layer capacitor (EDLC), a lithium ion capacitor (LIC), etc. The storage element 43 is not particularly limited as long as it can store energy and electrically input and output the stored energy. The storage elements 43 in the unit 12 are made of the same type of elements and are managed so that their voltages or SOCs are equal, although there are variations in their characteristics. If the storage element 43 is a lithium ion battery (LIB), an EDLC, or a LIC, it is common for the open circuit voltage (OCV) to increase as the SOC increases.

[0025] Regarding the series switch 32 and the parallel switch 33, in a normal state, the series switch 32 is closed and the parallel switch 33 is open. When the series switch 32 is closed, current can flow to each storage module 41 of the unit 12. When both the series switch 32 and the parallel switch 33 of a unit 12 are open, no current flows to the energy storage device 10. By opening the series switch 32 and closing the parallel switch 33 in a certain unit 12, current can be bypassed through the switch 32 of that unit 12 and the multiple storage modules 41 in that unit 12 and flow to other units 12. As a result, charging and discharging of the energy storage device 10 becomes possible. Hereinafter, a unit 12 in which the series switch 32 is open and the parallel switch 33 is closed is referred to as a bypassed unit 12.

[0026] The series switch 32 may be any of a type that can be opened and closed by an external signal, such as an electromagnetic contactor; a type that can be opened and closed manually, such as a no-fuse circuit breaker, or a type that can only be opened by an external signal; a semiconductor switch, semiconductor current limiter, or disconnector, and is selected depending on the functions required of the system. The series switch 32 may also be configured by combining two or more of the above types. A switch that can be quickly closed and has current interruption capabilities is used for the parallel switch 33. A high-speed switch may be combined with a type that can be opened and closed by an external signal, such as an electromagnetic contactor. Furthermore, a fuse may be provided in series with the energy storage module 41 and the series switch 32 to interrupt short-circuit current.

[0027] Each unit control unit 31 has a communication function with each module control unit 42 in its own unit 12, and collects the status of each storage element 43 from each module control unit 42 via wired or wireless communication line 38. Furthermore, when each unit control unit 31 itself detects the voltage, current, temperature, etc. of its own unit 12, it monitors these detected values ​​and operates the series switch 32 and the parallel switch 33 based on these detection results. Furthermore, each unit control unit 31 has a communication function with the power storage device control unit 11, and receives operation commands for the switches 32 and 33 from the power storage device control unit 11 via wired or wireless communication line 14, issues an alarm to the power storage device control unit 11 about an abnormality in its own unit 12, and transmits the voltage, temperature, SOC, etc. of its own unit 12.

[0028] The switches 13 connected in series with the multiple units 12 are closed under normal conditions. The switches 13 may be contactors that can be opened and closed by external signals, circuit breakers that can be opened and closed manually or that can only be opened by external signals, semiconductor switches, semiconductor current limiters, disconnectors, etc., and are selected depending on the functions required of the system. The switches 13 may also be configured by combining two or more of the above types. The switches 13 may also be provided not only on the positive electrode P1 side but also on the negative electrode N1 side of the multiple units 12 of the energy storage device 10. Alternatively, the switches 13 may be provided only on the negative electrode N1 side of the multiple units 12.

[0029] Although not shown in FIG. 1, the electricity storage device 10 may also be provided with a fuse in series with the switch 13 and the plurality of units 12.

[0030] The power storage device control unit 11 has a communication function with each unit control unit 31. As described above, the power storage device control unit 11 collects the status of each unit 12 from each unit control unit 31 via the communication line 14 and transmits operation commands for the switches 32 and 33 of each unit 12. Furthermore, when the power storage device control unit 11 itself detects the voltage, current, temperature, etc. of the power storage device 10, the power storage device control unit 11 monitors these detected values ​​and operates the switch 13 based on these detection results. Furthermore, the power storage device control unit 11 has a communication function for communicating with the control device 21 that controls the power converter 20. The power storage device control unit 11 receives operation commands for the power storage device 10 from the control device 21 and transmits the status of the power storage device 10 and the occurrence of any abnormalities to the control device 21.

[0031] [SOC variation of storage element 43] When the energy storage device 10 is configured with the same type of energy storage elements 43, ideally, charging and discharging the energy storage device 10 would not increase SOC variation if the initial SOCs of the elements 43 are consistent. However, if the energy storage elements 43 vary in capacity, internal resistance, temperature, or other characteristics, or if their initial SOCs differ, SOC variation may increase even when the energy storage elements 43 are connected in series. If the energy storage device 10 is used with large variations, some of the energy storage elements 43 may exceed the upper limit voltage when the energy storage device 10 is charged to nearly 100% SOC, or some of the energy storage elements 43 may fall below the lower limit voltage when the energy storage device 10 is discharged to nearly 0% SOC. This raises the risk of some of the energy storage elements 43 deteriorating or failing. On the other hand, if the energy storage device 10 is charged and discharged so that all of the energy storage elements 43 are maintained between the upper limit voltage and the lower limit voltage, the usable SOC range is reduced. To solve this problem, the module control unit 42 is provided with a storage element balancing circuit (50 in FIG. 4) that suppresses variations in SOC.

[0032] Fig. 2 is a diagram showing an example of the relationship between the SOC and OCV of a LIB, and Fig. 3 is a diagram showing an example of the relationship between the SOC and OCV of an EDLC.

[0033] As shown in Figures 2 and 3, in LIBs and EDLCs, the OCV also increases as the SOC increases from 0% (fully discharged) to 100% (fully charged). Generally, when charging or discharging of an energy storage element is suspended, the terminal voltage changes for a while. The voltage at the point when the suspension continues and the terminal voltage change stops corresponds to the OCV. There are multiple time constants for the terminal voltage change, ranging from long to short. The time constant varies depending on the type of energy storage element, temperature, SOC, etc., but in the case of LIBs, for example, the time constant is approximately 100 seconds. Therefore, it takes more than 1000 seconds for the terminal voltage of the energy storage element to stabilize. Furthermore, because energy storage elements have a DC resistance component, the terminal voltage is higher than the OCV when charging and lower than the OCV when discharging.

[0034] However, in energy storage elements such as LIBs, EDLCs, and LICs, where the SOC-OCV curve increases monotonically, the difference between the terminal voltage and OCV of each energy storage element is not thought to be large, and energy storage element operation is also managed using terminal voltages, so the energy storage element balancing circuit may suppress SOC variations by balancing the terminal voltages.

[0035] The storage element balancing circuit (50 in FIG. 4) of the module control unit 42 connects a resistor (RA in FIG. 4) to a storage element 43 whose terminal voltage is higher than a reference voltage, for example, to discharge the energy. The storage element 43 to which the resistor (RA in FIG. 4) is connected is determined by the unit control unit 31, and a command is sent to the module control unit 42. This makes it possible to suppress SOC variations among the storage elements 43 in the unit 12.

[0036] Incidentally, if the energy storage device 10 is a low-voltage device of 1500 V or less, it is possible for the energy storage device control unit 11, rather than the unit control unit 31, to determine the energy storage element 43 to which the resistor is connected and issue a command to the module control unit 42. However, this is not easy for high voltages such as 3 kV to 30 kV. The reason for this is as follows. When a high-voltage energy storage device 10 is configured by connecting low-voltage units 12 in series, the devices within the units 12 are manufactured as low-voltage devices, and therefore the unit control unit 31 and the module control unit 42 are constructed as a low-voltage system. However, because the energy storage device 10 is a high-voltage system, the unit control unit 31 and the energy storage device control unit 11 must be mutually insulated using, for example, optical communication. In this case, only limited signals can be exchanged between the unit control unit 31 and the energy storage device control unit 11.

[0037] [Configuration example of the power storage module 41] Fig. 4 is a diagram showing an example of the configuration of the power storage module 41 of Fig. 1. Referring to Fig. 4, the power storage module 41 includes n power storage elements 43_1 to 43_n connected in series, and a module control unit 42. The module control unit 42 includes a power storage element balancing circuit 50, a voltage detection circuit 51, a current detection circuit 53, a temperature detector 54, a processing circuit 55, and a communication circuit 56.

[0038] The energy storage element balancing circuit 50 includes n resistance elements RA_1 to RA_n and n switches SW_1 to SW_n corresponding to the n energy storage elements 43_1 to 43_n, respectively. The ith (1≦i≦n) resistance element RA_i and switch SW_i are connected in series with each other and in parallel with the corresponding ith energy storage element 43_i. Each of the n energy storage elements 43_1 to 43_n is normally controlled to an open state, and when the voltage of the corresponding energy storage element 43 is higher than the average value, the corresponding energy storage element 43 is controlled to a closed state, thereby discharging the corresponding energy storage element 43.

[0039] The voltage detection circuit 51 is connected to both ends of each of the n storage elements 43_1 to 43_n, detects the voltage of each storage element 43, and outputs the detection result to the processing circuit 55.

[0040] Current detection circuit 53 uses current detector 52 to detect the currents output from n power storage elements 43_1 to 43_n, and outputs the detection result to processing circuit 55.

[0041] The temperature detector 54 detects the temperature inside the power storage module 41 and outputs the detection result to the processing circuit 55.

[0042] The processing circuit 55 is configured as a microprocessor including a CPU (Central Processing Unit) and a memory. At least a part of the processing circuit 55 may be configured by an FPGA (Field Programmable Gate Array), an ASIC (Application Specific Integrated Circuit), or a combination of these.

[0043] The processing circuit 55 has (i) an SOC calculation function that calculates the SOC of the power storage module 41 based on the detection result of the voltage detection circuit 51, (ii) an abnormality detection function that detects an abnormality in the power storage module 41 based on the detection results of the voltage detection circuit 51, the current detection circuit 53, and the temperature detector 54, and (iii) a balance control function that balances the voltages of the n power storage elements 43_1 to 43_n based on the detection result of the voltage detection circuit 51. Furthermore, the processing circuit 55 communicates with the unit control unit 31 via a communication circuit 56.

[0044] [Power Supply Related Configuration of Unit Control Unit 31] Fig. 5 is a diagram showing an example of the power supply-related configuration of the unit control unit 31 of Fig. 1. In Fig. 5, together with the unit control unit 31, power storage modules 41a, 41b, and 41c, series switch 32, and parallel switch 33 that constitute unit 12 are also shown. As shown in Fig. 5, the unit control unit 31 has, as its power supply-related configuration, a unit power supply unit 61 connected between the positive side node P2 and the negative side node N2 of unit 12 via a diode 63, and a unit control power supply unit 62.

[0045] 5, the positive-side node P2 is connected to the positive input terminal of the DC-DC converter 65 via a forward diode 63 and a switch 64. The negative-side node N2 is connected to the negative input terminal of the DC-DC converter 65. The positive electrode of the control power storage device 66 is connected to the positive output terminal of the DC-DC converter 65 via a switch 67. The negative electrode of the control power storage device 66 is connected to the negative output terminal of the DC-DC converter 65.

[0046] When switch 64 is closed, power is supplied from power storage modules 41a to 41c to DC-DC converter 65, and the voltage of power storage modules 41a to 41c is converted by DC-DC converter 65 to a voltage compatible with the input of unit control power supply section 62. When switch 67 is closed, control power storage device 66 is connected to the output of DC-DC converter 65. This allows unit control section 31 to continue operating for a certain period of time even if switch 64 is open or output power is not obtained from DC-DC converter 65.

[0047] Diode 63 is provided to prevent reverse current from unit power supply section 61 to power storage module 41. In the case of Fig. 5, diode 63 is inserted on the positive side node P2 side, but it may also be inserted on the negative side node N2 side.

[0048] The switches 64 and 67 are composed of contactors, relays, etc. In Fig. 5, single-pole switches 64 and 67 are used and inserted on the positive side, but they may also be inserted on the negative side. Alternatively, double-pole switches 64 and 67 may be used to open and close both the positive and negative sides.

[0049] The specifications of the DC-DC converter 65 are not particularly limited, and either an insulated or non-insulated type is possible.

[0050] The control power storage device 66 is a storage battery, an EDLC, or the like. An initial charging circuit may be further provided for initially charging the control power storage device 66. A DC-DC converter may be further provided for converting the output voltage of the control power storage device 66, so that the output voltage of the DC-DC converter 65 and the voltage from the control power storage device 66 can be controlled independently.

[0051] The unit control power supply section 62 generates and supplies control power of a value appropriate for a processing circuit 68 for a controller in the unit control section 31, a communication circuit 69, a detector (not shown), and the like.

[0052] [Operation mode of unit control unit 31] When power is being supplied from the power storage module 41 to the unit control unit 31 and the module control unit 42, if charging / discharging of the power storage device 10 via the positive electrode P1 and the negative electrode N1 is suspended for a long period of time, the SOC of the power storage module 41 will decrease due to the power supply to the unit control unit 31 and the module control unit 42. While the unit control unit 31 and the module control unit 42 cannot be stopped while charging / discharging of the power storage module 41 is suspended, power consumption can be reduced by limiting their functions or by operating the unit control unit 31 and the module control unit 42 to intermittently monitor the state of the storage battery.

[0053] Therefore, the unit control unit 31 is provided with an operation mode that can reduce power consumption while charging / discharging of the power storage module 41 is suspended. The operation mode of the unit control unit 31 (hereinafter sometimes referred to as the "unit control unit operation mode") is commanded by the power storage device control unit 11 based on the operating state of the power conversion device 100, which operates in accordance with commands from the control device 21 or a higher-level computer. The unit control unit 31 controls the unit control power supply unit 62, the detector, and the controller according to the operation mode of the unit control unit.

[0054] The unit control unit 31 has at least two operation modes: a normal mode and a power-saving mode. In this disclosure, the normal mode is also referred to as a first operation mode, and the power-saving mode is also referred to as a second operation mode. When charging or discharging of the power storage module 41 is suspended, the state of the power storage element 43 rarely changes suddenly, and the states of the switches 32 and 33 do not change, so the operation mode can be transitioned from the normal mode to the power-saving mode.

[0055] In the power saving mode, power consumption can be reduced by stopping the functions of the power storage module control unit 42 and limiting the functions of the unit control unit 31. Specifically, in the power saving mode, the unit control unit 31 reduces power consumption by maintaining the open / closed states of the switches 32 and 33, reducing the number of communication signals with the power storage device control unit 11, and shifting communication with the power storage device control unit 11 to intermittent communication, etc. By having three or more operation modes with different power consumption, it is of course possible to use different operation modes depending on the expected downtime, the degree of need to monitor the power storage elements, and the management level of the power storage elements.

[0056] [SOC variation suppression between units] The power storage device control unit 11 receives a detected value of the voltage V12 (also referred to as the unit voltage V12) between the positive-side node P2 and the negative-side node N2 of each unit 12 from each unit control unit 31, and monitors the voltage variation between the units based on the received voltage V12. In this embodiment, the range of the distribution of the unit voltage V12 (the difference between the maximum and minimum values) is used as an index value indicating the degree of voltage variation, but this is not limiting. For example, the variance of the unit voltage V12 may be used as an index value for voltage variation.

[0057] When the voltage variation reaches an upper limit value (ΔV1) of the voltage variation, which is a level at which there is concern about a decrease in the usable SOC range of the power storage device 10 or deviation from the upper or lower limit voltage of the power storage element 43, the power storage device control unit 11 performs unit voltage balance control during the power saving mode. In the unit voltage balance control, the power storage device control unit 11 continues to instruct the unit control unit 31 of the unit 12 whose voltage V12 is relatively low to use the power saving mode and to instruct the unit control unit 31 of the unit 12 whose voltage V12 is relatively high to use the normal mode until the voltage variation becomes less than the allowable value (ΔV2).

[0058] 6 is a flowchart illustrating the unit voltage balance control process. The unit voltage balance control process will be described below with reference to FIGS.

[0059] 6, power storage device control unit 11 determines whether the unit control unit operation mode is the power saving mode. If the unit control unit operation mode is the power saving mode (YES in step S111), power storage device control unit 11 proceeds to step S112.

[0060] In step S112, the power storage device control unit 11 compares the unit voltages V12 received from the units 12 to calculate a maximum value Vmax, a minimum value Vmin, and a distribution range Vdif. The distribution range Vdif is expressed as follows: Vdif = Vmax - Vmin (1) It is calculated as follows.

[0061] In the next step S113, the power storage device control unit 11 compares the distribution range Vdif with the upper limit value ΔV1, and if Vdif>ΔV1 (YES in step S113), it determines that the voltage variation between units is large and unit voltage balance control is necessary, and proceeds to step S114.

[0062] After calculating the average value Vave of the unit voltage V12 of each unit in step S114, the power storage device control unit 11 performs an operation mode control process in the next step S115.

[0063] Fig. 7 is a flowchart illustrating the process of the operation mode control in step S115 in Fig. 6. First, in step S121, the power storage device control unit 11 selects a unit to be processed from all the units 12 in order, and performs the process from step S122 onwards on the selected unit.

[0064] In step S122, the power storage device control unit 11 compares the unit voltage V12 of the selected unit 12 with the average value Vave, and if V12>Vave (YES in step S112), the process proceeds to step S123. In step S123, the power storage device control unit 11 changes the unit control unit operation mode of the selected unit from the power saving mode to the normal mode.

[0065] On the other hand, if V12>Vave is not satisfied (NO in step S122), power storage device control unit 11 proceeds to step S124. In step S124, power storage device control unit 11 maintains the unit control unit operation mode of the selected unit in the power saving mode.

[0066] After steps S123 and S124 are completed, the power storage device control unit 11 advances the process to step S125. In step S125, the power storage device control unit 11 determines whether or not there are any unprocessed units. If there are no unprocessed units (YES in step S125), the operation mode control process ends. If there are unprocessed units (NO in step S125), the power storage device control unit 11 returns the process to step S121 and selects a unit to be processed from the unprocessed units. Thereafter, the above process is performed on the selected unit.

[0067] In this way, in the operation mode control process of step S115 in Fig. 6, power storage device control unit 11 changes the unit control unit operation mode from the power saving mode to the normal mode for units whose unit voltage V12 is greater than the average value Vave, and maintains the unit control unit operation mode in the power saving mode for units whose unit voltage V12 is equal to or less than the average value Vave. After step S115 in Fig. 6 is completed, the process proceeds to step S116.

[0068] Returning to FIG. 6, in step S113, if Vdif>ΔV1 is not satisfied, that is, if Vdif≦ΔV1 (NO in step S113), power storage device control unit 11 advances the process to step S117.

[0069] In step S117, the power storage device control unit 11 compares the distribution range Vdif with the allowable value ΔV2, and if Vdif<ΔV2 (YES in step S117), it determines that the voltage variation between units is small and voltage balance control is unnecessary, and proceeds to step S119. Step S119 is a process of not performing operation mode control. If operation mode control was performed in the previous process, the power storage device control unit 11 resets it, and then proceeds to step S116.

[0070] On the other hand, if Vdif<ΔV2 is not satisfied, that is, if Vdif≧ΔV2 (NO in step S117), the power storage device control unit 11 proceeds to step S118. In step S118, the power storage device control unit 11 determines whether or not operation mode control was being performed in the previous process. If operation mode control is being performed (YES in step S118), the power storage device control unit 11 proceeds to step S114 and continues operation mode control. On the other hand, if operation mode control is not being performed (NO in step S118), the power storage device control unit 11 proceeds to step S119 and continues not performing operation mode control.

[0071] If the normal mode is selected in the first step S111 (NO in step S111), the power storage device control unit 11 cannot transition to the power saving mode. In this case, the power storage device control unit 11 advances the process to step S119 and continues not to perform the operation mode control.

[0072] Since the operation mode (normal mode or power saving mode) of each unit has been determined in steps S115 and S119 above, in the next step S116, power storage device control unit 11 instructs each unit control unit 31 to select the operation mode, and then the process ends.

[0073] A specific example of processing when charging and discharging are suspended and the mode transitions to the power saving mode will be described below. In the following description, the power storage device 10 includes three units 12a, 12b, and 12c, and the unit voltages V12 of the units 12a, 12b, and 12c will be referred to as V12a, V12b, and V12c, respectively.

[0074] 6, it is assumed that power storage device control unit 11 calculates Vmax=V12a, Vmin=V12b, and Vdif=V12a-V12b. Furthermore, it is assumed that power storage device control unit 11 determines in step S113 that Vdif>ΔV1 (YES in step S113). In this case, power storage device control unit 11 calculates average value Vave of unit voltage V12 in step S114, and then proceeds to the operation mode control in step S115.

[0075] In step S122 of FIG. 7, the power storage device control unit 11 compares the unit voltages V12a, V12b, and V12c of the units 12a, 12b, and 12c with the average value Vave. As a result, it is determined that the unit voltages V12a and V12c are greater than the average value Vave, and the unit voltage V12b is smaller than the average value Vave. In this case, the power storage device control unit 11 transitions the unit 12b from the normal mode to the power saving mode as scheduled. This reduces the power supplied to the unit power supply unit 61 of the unit 12b, thereby suppressing a decrease in the SOC of the unit 12b. On the other hand, the operation mode control is performed on the units 12a and 12c, so the normal mode continues without transitioning to the power saving mode. As a result, a decrease in the SOC of the units 12a and 12c is not suppressed. As a result, the distribution range Vdif of the unit voltage V12 decreases, and the SOC variation between the units also decreases.

[0076] Thereafter, when the unit voltage V12c of unit 12c falls below the average value Vave, the power storage device control unit 11 also switches unit 12c from the normal mode to the power saving mode. Furthermore, when the distribution range Vdif of the unit voltage V12 decreases and becomes less than the allowable value ΔV2, the power storage device control unit 11 ends the operation mode control and also switches unit 12a from the normal mode to the power saving mode. With regard to the power storage elements 43 within each unit, the power storage element balancing circuit 50 works to suppress variations in SOC, so variations in SOC between the power storage elements 43 of different units 12 do not increase.

[0077] If there is a bypassed unit 12, that unit 12 is excluded from the operation mode control and is also excluded from the calculation of the maximum value Vmax, minimum value Vmin, and average value Vave. Normally, a bypassed unit is fixed to the power saving mode.

[0078] 6 and 7 illustrate the case where there are two operation modes, the normal mode and the power-saving mode. However, even if there are three or more operation modes, the same approach can be applied by setting the operation mode to one that consumes more power for units with higher unit voltages V12. Also, in FIGS. 6 and 7, operation mode control is performed on units 12 that satisfy V12 > Vave based on a comparison between the unit voltage V12 and the average value Vave. However, the criteria for determining whether to perform operation mode control are not limited to this. For example, operation mode control may be performed on units whose difference between the unit voltage V12 and the minimum value Vmin is greater than a reference value. Any other criteria may be used as long as the variation in the unit voltage V12 can be reduced by performing operation mode control on units whose unit voltage V12 is relatively higher than the other units.

[0079] [Effects of the First Embodiment] As described above, the energy storage device 10 of the first embodiment includes the energy storage element balancing circuit 50 for suppressing variations in the SOC of the energy storage elements 43 in each unit 12, and performs unit voltage balance control (i.e., operation mode control) for suppressing variations in the unit voltage V12 between the units. This makes it possible to suppress variations in the SOC of the energy storage elements 43 even when the number of units 12 connected in series is large and the energy storage device 10 is a high-voltage system. Here, the energy storage element balancing circuit 50 in the unit 12 and its control can be a conventional one for low-voltage systems. Furthermore, the unit voltage balance control balances the voltages of the units 12 using power consumed by the unit control unit 31 and the energy storage module control unit 42, eliminating the need to provide additional discharge resistors for discharging the energy storage elements 43 in each unit.

[0080] Embodiment 2 The power storage device 10 of the second embodiment differs from the power storage device 10 of the first embodiment in the configuration of the power supply portion of the unit control unit 31. Specifically, in the power storage device 10 of the second embodiment, power can also be supplied to the unit control unit 31 from an external power source. Hereinafter, the same parts as those of the first embodiment will be assigned the same reference numerals and their description will be omitted, and only the different parts will be described.

[0081] [Configuration of power supply related to unit control unit 31 according to embodiment 2] Fig. 8 is a diagram showing an example of the power supply related configuration of unit control unit 31 in power storage device 10 of embodiment 2. Unit control unit 31 in Fig. 8 includes unit power supply unit 61, unit control power supply unit 62, diode 63, processing circuit 68, and communication circuit 69, similar to the case of embodiment 1. However, the input side of unit power supply unit 61 of unit control unit 31 is connected between positive side node P2 and negative side node N2 of power storage modules 41a to 41c via diode 63 for preventing backflow, and is also connected to external AC control power supply 2.

[0082] More specifically, the unit power supply unit 61 of the unit control unit 31 further includes a switch 72 and an AC-DC converter 73 in addition to the switch 64, DC-DC converter 65, control power storage device 66, and switch 67 shown in FIG. 5 for the first embodiment.

[0083] 8, a first AC input terminal of AC-DC converter 73 is connected to a first output terminal of AC control power supply 2 via switch 72, and a second AC input terminal of AC-DC converter 73 is connected to a second output terminal of AC control power supply 2. A positive DC output terminal of AC-DC converter 73 is connected to a positive output terminal of DC-DC converter 65, and a negative DC output terminal of AC-DC converter 73 is connected to a negative output terminal of DC-DC converter 65.

[0084] According to the configuration of unit power supply section 61 described above, when switch 64 is opened and switch 72 is closed, power is supplied from AC control power supply 2 to AC-DC converter 73, and the AC voltage of AC control power supply 2 is converted by AC-DC converter 73 into a DC voltage compatible with the input of unit control power supply section 62. As a result, power can be supplied to unit control power supply section 62 from the external AC control power supply 2 instead of from power storage module 41, and power from power storage module 41 is not consumed.

[0085] The switch 72 is composed of a contactor, a relay, etc. In Fig. 8, a single-pole switch 72 is provided and inserted between one of the AC input terminals of the AC-DC converter 73 and one of the output terminals of the AC control power supply 2. Alternatively, a double-pole switch 72 may be inserted between both of the AC input terminals of the AC-DC converter 73 and both of the output terminals of the AC control power supply 2.

[0086] The specifications of the AC-DC converter 73 are not particularly limited. For example, the AC-DC converter 73 may be separated into an AC-DC conversion section and a DC-DC conversion section. Furthermore, it is desirable that the AC-DC converter 73 be an insulated type so that the potential of the output terminal of the AC-DC converter 73 can be adjusted to the potential level of the unit control section 31. In particular, since the potential of the unit 12 becomes increasingly different from the ground potential as the arrangement of the unit 12 approaches the positive electrode P1 of the power storage device 10, it is desirable to insulate the AC control power supply 2 in advance before supplying power from the AC control power supply 2 to the unit control section 31.

[0087] As another modification, DC power may be supplied from a DC control power supply via a DC-DC converter instead of the AC control power supply 2 and AC-DC converter 73. Also, two or more control power supplies for input may be provided.

[0088] Either the power storage module 41 or the AC control power supply 2 may be selected as the power source for the unit power supply unit. If a reverse current is prevented, the unit power supply unit 61 may be powered by both the power storage module 41 and the AC control power supply 2 by closing both switches 64, 72.

[0089] [SOC variation suppression between units using power supply modes] The power storage device control unit 11 in the second embodiment determines the power supply mode to the unit control unit 31. The power supply mode includes at least two modes: a power storage module mode in which power is supplied from the power storage module 41, and an external power supply mode in which power is supplied from the AC control power supply 2. In addition, a dual power supply mode in which power can be supplied from both the power storage module 41 and the AC control power supply 2 may be included. In the present disclosure, the power storage module mode is also referred to as a first power supply mode, and the external power supply mode is also referred to as a second power supply mode.

[0090] The power storage device 10 of the second embodiment performs unit voltage balance control using a power supply mode in addition to unit voltage balance control using operation modes with different power consumption (normal mode, power saving mode).

[0091] In balance control using the power supply mode, the power storage device control unit 11 receives a detected value of the unit voltage V12 between the positive-side node P2 and the negative-side node N2 of each unit from each unit control unit 31 and monitors voltage variations between the units based on the received voltage V12. When the voltage variations reach an upper limit (ΔV3) of voltage variations, at which there is concern about a decrease in the usable SOC range of the power storage device 10 or deviation from the upper or lower limit voltage of the storage element 43, the power storage device control unit 11 performs unit voltage balance control using the power supply mode. The power storage device control unit 11 commands the unit control unit 31 of the unit 12 whose voltage V12 is relatively low to use the external power supply mode, and commands the unit control unit 31 of the unit 12 whose voltage V12 is relatively high to use the power storage module mode, until the voltage variations become less than the allowable value (ΔV4).

[0092] 9 is a flowchart illustrating the process of unit voltage balance control using the power supply mode. Hereinafter, the process of unit voltage balance control using the power supply mode will be described with reference to FIGS.

[0093] In step S132, the power storage device control unit 11 compares the unit voltages V12 received from the units 12 to calculate the maximum value Vmax, the minimum value Vmin, and the distribution range Vdif.

[0094] In the next step S133, the power storage device control unit 11 compares the distribution range Vdif with the upper limit value ΔV3, and if Vdif>ΔV3 (YES in step S133), it determines that the voltage variation between units is large and unit voltage balance control is necessary, and proceeds to step S134.

[0095] After calculating the average value Vave of the unit voltage V12 of each unit in step S134, the power storage device control unit 11 performs a power supply mode control process in the next step S135.

[0096] Fig. 10 is a flowchart illustrating the process of power supply mode control in step S135 of Fig. 9. Note that power supply mode control refers to setting the power supply mode to the external power supply mode or the power storage module mode in accordance with the unit voltage V12. For example, controlling the power supply mode to the external power supply mode refers to changing the power supply mode to the external power supply mode if the power storage module mode or the dual power supply source mode has been selected as the power supply mode, or to maintaining the power supply mode as the external power supply mode if the external power supply mode has been selected as the power supply mode.

[0097] First, in step S141, the power storage device control unit 11 selects a unit to be processed from all the units 12 in order, and performs the processing from step S142 onwards on the selected unit.

[0098] In step S142, the power storage device control unit 11 compares the unit voltage V12 of the selected unit 12 with the average value Vave, and if V12>Vave (YES in step S142), the process proceeds to step S143. In step S143, the power storage device control unit 11 controls the power supply mode of the selected unit to the power storage module mode.

[0099] On the other hand, if V12>Vave is not satisfied (NO in step S142), power storage device control unit 11 advances the process to step S144. In step S144, power storage device control unit 11 controls the power supply mode of the selected unit to the external power supply mode.

[0100] After steps S143 and S144 are completed, the power storage device control unit 11 advances the process to step S145. In step S145, the power storage device control unit 11 determines whether or not there are any unprocessed units. If there are no unprocessed units (YES in step S145), the operation mode control process ends. If there are unprocessed units (NO in step S145), the power storage device control unit 11 returns the process to step S141 and selects a unit to be processed from the unprocessed units. Thereafter, the above process is performed on the selected unit.

[0101] 9, the power storage device control unit 11 controls the power supply mode to the power storage module mode for units 12 whose unit voltage V12 is greater than the average value Vave, and controls the power supply mode to the external power supply mode for units whose unit voltage V12 is equal to or less than the average value Vave. After step S135 in FIG. 9 is completed, the process proceeds to step S136.

[0102] Returning to FIG. 9, in step S133, if Vdif>ΔV3 is not satisfied, that is, if Vdif≦ΔV3 (NO in step S133), power storage device control unit 11 advances the process to step S137.

[0103] In step S137, the power storage device control unit 11 compares the distribution range Vdif with the allowable value ΔV4, and if Vdif<ΔV4 (YES in step S137), it determines that the voltage variation between the units is small and voltage balance control is unnecessary, and proceeds to step S139. Step S139 is a process of not performing power supply mode control. If power supply mode control was performed in the previous process, the power storage device control unit 11 resets it, and then proceeds to step S136.

[0104] On the other hand, if Vdif<ΔV4 is not satisfied, that is, if Vdif≧ΔV4 (NO in step S137), the power storage device control unit 11 proceeds to step S138. In step S138, the power storage device control unit 11 determines whether or not power supply mode control was being performed in the previous process. If power supply mode control is being performed (YES), the power storage device control unit 11 proceeds to step S134 and continues power supply mode control. On the other hand, if power supply mode control is not being performed (NO in step S138), the power storage device control unit 11 proceeds to step S139 and continues not performing power supply mode control.

[0105] Since the power supply mode (power storage module mode or external power supply mode) of each unit has been determined in steps S135 and S139 above, power storage device control unit 11 instructs each unit control unit 31 to set the power supply mode in the next step S136, and the process ends.

[0106] The power supply mode control can also be performed when the operating mode is the normal mode. Below, a specific example of processing when the power supply mode preset in the power storage device control unit 11 is the power storage module mode will be described. In the following description, the power storage device 10 includes three units 12a, 12b, and 12c, and the unit voltages V12 of the units 12a, 12b, and 12c will be referred to as V12a, V12b, and V12c, respectively.

[0107] 9, it is assumed that the power storage device control unit 11 calculates Vmax=V12a, Vmin=V12b, and Vdif=V12a-V12b. Furthermore, it is assumed that the power storage device control unit 11 determines in step S133 that Vdif>ΔV3 (YES in step S133). In this case, the power storage device control unit 11 calculates the average value Vave of the unit voltage V12 in step S134, and then proceeds to power supply mode control in step S135.

[0108] 10, the power storage device control unit 11 compares the unit voltages V12a, V12b, and V12c of the units 12a, 12b, and 12c, respectively, with the average value Vave. As a result, it is determined that the unit voltages V12a and V12c are greater than the average value Vave, and the unit voltage V12b is smaller than the average value Vave. In this case, the power storage device control unit 11 commands the unit control units 31a and 31c of the units 12a and 12c to switch to the power storage module mode, and controls the unit control units 31a and 31c to receive power from the power storage module 41. As a result, the SOC of the units 12a and 12c decreases by the amount of power supplied to the unit control units 31a and 31c.

[0109] Meanwhile, the power storage device control unit 11 commands the unit control unit 31b of the unit 12b to switch to the external power supply mode, and controls the unit control unit 31b to receive power from the AC control power supply 2. As a result, power is not supplied to the unit control unit 31b from the power storage module 41, and a decrease in the SOC of the unit 12b is suppressed. As a result, the distribution range Vdif of the unit voltage V12 decreases, and the variation in SOC between the units also decreases.

[0110] Thereafter, when the unit voltage V12c of the unit 12c becomes equal to or lower than the average value Vave, the power storage device control unit 11 shifts the unit 12c from the power storage module mode to the external power supply mode. Furthermore, when the distribution range Vdif of the unit voltage V12 decreases and becomes less than the allowable value ΔV4, the power storage device control unit 11 ends the power supply mode control and commands the unit control units 31a to 31c of all the units 12a to 12c to switch to the power storage module mode.

[0111] Here, when the operating mode is the normal mode, charging and discharging is performed as the power storage device 10, so the current flowing through each storage element 43 is larger than the current for supplying power to the unit control unit 31, and the magnitude of the current flowing through each storage element 43 changes transiently. Therefore, fluctuations in the unit voltage V12 tend to be large, and the distribution range Vdif of the unit voltage V12 also tends to fluctuate easily. Therefore, it is desirable to set the upper limit value ΔV3 and the allowable value ΔV4 in the power supply mode control to be larger than the upper limit value ΔV1 and the allowable value ΔV2 in the operating mode control, such that ΔV3 > ΔV1 and ΔV4 > ΔV2. However, it goes without saying that the upper limit value ΔV3 may be set to the same value as the upper limit value ΔV1, and the allowable value ΔV4 may be set to the same value as the allowable value ΔV2.

[0112] If there is a bypassed unit 12, that unit 12 is excluded from the targets of power supply mode control, and is also excluded from the targets of calculation of the maximum value Vmax, the minimum value Vmin, and the average value Vave.

[0113] The relationship between the unit voltage balance control process using the operation mode and the power supply mode is explained below. When Vdif > ΔV1 during power saving mode, operation mode control is performed. In this case, for the unit 12 where V12 > Vave, the operation mode is changed from power saving mode to normal mode, and it is expected that more power will be discharged from the power storage module 41. Therefore, for units 12 that are set to normal mode in the operation mode control, the power supply mode must be set to power storage module mode. For units 12 that are set to power saving mode in the operation mode control, setting the power supply mode to external power supply mode will achieve a greater power saving effect, but another mode (power storage module mode or dual power supply source mode) may also be used.

[0114] [Effects of the second embodiment] As described above, according to the power storage device 10 of the second embodiment, in addition to the configuration of the power storage device 10 of the first embodiment, power is supplied to the unit control unit 31 from two or more power supply sources including the power storage module 41 and an external power supply. Then, by performing unit voltage balance control using the power supply modes (power storage module mode and external power supply mode), in addition to the effect of the first embodiment, it is possible to suppress SOC variations between units even in normal mode. Therefore, even in the power conversion device 100 in which the period during which charging and discharging of the power storage device 10 is suspended is short, it is possible to suppress an increase in SOC variations between units.

[0115] Furthermore, unit voltage balance control using the operation mode and power supply mode control may be combined. In this case, by supplying power from the AC control power supply 2 to the unit control unit 31 of the unit 12 with a low SOC during operation mode control, the effect of suppressing SOC variations between units can be improved.

[0116] Embodiment 3 The power storage device 10 of the third embodiment suppresses variations in SOC between units by using SOC instead of the unit voltage V12 of the unit 12. That is, while the first and second embodiments perform unit voltage balance control to suppress SOC variations between units 12, the third embodiment performs unit SOC balance control to suppress SOC variations.

[0117] The following mainly describes the parts that are different from the first and second embodiments, and the parts that are common to the first and second embodiments are given the same reference numerals and the description thereof will not be repeated.

[0118] [SOC variation suppression between units using operation modes] The power storage device control unit 11 acquires information about the state of charge (SOC) of each unit 12 and monitors SOC variations based on the acquired SOC information. The SOC is calculated by the unit control unit 31 or the power storage device control unit 11. The calculation method is not limited. In this embodiment, the range of the SOC distribution (the difference between the maximum and minimum values) of the units 12 is used as an index value indicating the degree of SOC variation, but this is not limiting. For example, the variance of the SOC of the units 12 may be used as an index value for SOC variation.

[0119] Fig. 11 is a flowchart illustrating the process of SOC balance control between units using operation modes in a power storage device according to embodiment 3. In the case of Fig. 6 of embodiment 1, SOC variations are managed based on unit voltage V12, whereas in Fig. 11 of embodiment 3, they are managed based on the SOC of each unit 12. In this respect, embodiment 3 differs from embodiment 1. Below, with reference to the flowcharts of Figs. 11 and 12, steps that differ from the steps in the flowcharts of Figs. 6 and 7 will be mainly described, and equivalent steps will be assigned the same reference numerals and detailed description will not be repeated.

[0120] 11, when the unit control unit operation mode is the power saving mode (YES in step S111), the power storage device control unit 11 advances the process to step S152. In step S152, the power storage device control unit 11 compares the SOC of each unit to calculate a maximum value SOCmax, a minimum value SOCmin, and a distribution range SOCdif. The distribution range SOCdif is SOCdif = SOCmax - SOCmin (2) It is calculated as follows.

[0121] In the next step S153, the power storage device control unit 11 compares the distribution range SOCdif with the upper limit value ΔSOC1 to determine whether SOCdif > ΔSOC1. The upper limit value ΔSOC1 is a value at which the SOC variation is determined to be large enough to raise concerns about a reduction in the usable SOC range of the power storage device 10. Here, the voltage of the power storage elements 43 must be managed so as not to deviate from the upper and lower limit voltages. Therefore, when determining the SOC variation based on the SOC of each unit 12, it is necessary to estimate the terminal voltage from the SOC value of each unit 12, the characteristics of the power storage elements, the current flow, etc., and set the upper limit value ΔSOC1 so that the estimated terminal voltage value does not deviate from the upper and lower limit voltages.

[0122] If SOCdif>ΔSOC1 (YES in step S153), power storage device control unit 11 proceeds to step S154. After calculating the average value SOCave of the SOC of each unit 12 in step S154, power storage device control unit 11 performs operation mode control processing in the next step S155. Details of the operation mode control processing in step S155 will be described later with reference to FIG. 12.

[0123] On the other hand, if SOCdif>ΔSOC1 is not satisfied, that is, if SOCdif≦ΔSOC1 (NO in step S153), power storage device control unit 11 advances the process to step S157.

[0124] In step S157, the power storage device control unit 11 compares the distribution range SOCdif with the allowable value ΔSOC2 to determine whether SOCdif<ΔSOC2. The allowable value ΔSOC2 is a value that can be determined to be an allowable level of SOC variation.

[0125] If SOCdif<ΔSOC2 (YES in step S157), power storage device control unit 11 proceeds to step S119. Step S119 is a process of not implementing operation mode control, and if operation mode control is being implemented, operation mode control is reset. On the other hand, if SOCdif<ΔSOC2 is not true, that is, if SOCdif≧ΔSOC2 (NO in step S157), power storage device control unit 11 proceeds to step S154 to continue implementing operation mode control if operation mode control is being implemented (YES in step S118), and proceeds to step S119 to continue not implementing operation mode control if operation mode control is not being implemented (NO in step S118).

[0126] Figure 12 is a flowchart illustrating the operation mode control process in step S155 of Figure 11. The flowchart of Figure 12 differs from the flowchart of Figure 7 in that step S162 is provided in which the SOC of the processing unit 12 is compared with the SOC average value SOCave, instead of step S122 in which the unit voltage V12 is compared with the average value Vave of the unit voltage V12. Since other points in Figure 12 are the same as those in Figure 7, the same or corresponding steps are designated with the same reference numerals and their description will not be repeated.

[0127] Returning to FIG. 11, since the operation mode (normal mode or power saving mode) of each unit has been determined in the above steps S155 and S119, in the next step S116, the storage device control unit 11 instructs each unit control unit 31 to select the operation mode, and then the processing ends.

[0128] In this way, by performing the SOC balance control process for each unit shown in Figures 11 and 12, it is possible to suppress SOC variations between units by utilizing the operating modes (normal mode and power saving mode) in the same way as the unit voltage balance control process shown in Figures 6 and 7.

[0129] [SOC variation suppression between units using power supply modes] In the flowcharts of unit voltage balance control using the power supply mode shown in Figures 9 and 10, by changing the processing related to the unit voltage V12 to processing related to the SOC of each unit 12, the flowchart can be changed to a flowchart of unit SOC balance control using the power supply mode. As a result, it is possible to suppress SOC variations between units using the power supply mode, as in the case of embodiment 2. Below, differences from Figures 9 and 10 will be mainly described with reference to Figures 13 and 14, and equivalent steps will be assigned the same reference numerals and detailed description will not be repeated.

[0130] 13 is a flowchart illustrating processing for controlling SOC balance between units using power supply modes in the power storage device of Embodiment 3. Referring to Fig. 13, in step S172, power storage device control unit 11 compares the SOC of each unit 12 to calculate maximum value SOCmax, minimum value SOCmin, and distribution range SOCdif.

[0131] In the next step S173, the power storage device control unit 11 compares the distribution range SOCdif with the upper limit value ΔSOC3 to determine whether SOCdif is greater than ΔSOC3. The upper limit value ΔSOC3 is a value at which the SOC variation is determined to be large enough to raise concerns about a reduction in the usable SOC range of the power storage device 10.

[0132] If SOCdif>ΔSOC3 (YES in step S173), the power storage device control unit 11 proceeds to step S174. After calculating the average value SOCave of the SOC of each unit 12 in step S174, the power storage device control unit 11 performs power supply mode control processing in the next step S175. Details of the power supply mode control processing in step S175 will be described later with reference to FIG. 14.

[0133] On the other hand, if SOCdif>ΔSOC3 is not satisfied, that is, if SOCdif≦ΔSOC3 (NO in step S173), power storage device control unit 11 advances the process to step S177.

[0134] In step S177, the power storage device control unit 11 compares the distribution range SOCdif with the allowable value ΔSOC4 to determine whether SOCdif<ΔSOC4. The allowable value ΔSOC4 is a value that can be determined to be an allowable level of SOC variation.

[0135] If SOCdif<ΔSOC4 (YES in step S177), the power storage device control unit 11 proceeds to step S139. Step S139 is a process of not implementing power supply mode control, and if power supply mode control is being implemented, the power supply mode control is reset. On the other hand, if SOCdif<ΔSOC4 is not true, that is, if SOCdif≧ΔSOC4 (NO in step S177), the power storage device control unit 11 proceeds to step S174 to continue implementing power supply mode control if power supply mode control is being implemented (YES in step S138), and proceeds to step S139 to continue not implementing power supply mode control if power supply mode control is not being implemented (NO in step S138).

[0136] Fig. 14 is a flowchart illustrating the processing of power supply mode control in step S175 of Fig. 13. The flowchart of Fig. 14 differs from the flowchart of Fig. 10 in that step S182 is provided in which the SOC of the processing unit 12 is compared with the average SOC value SOCave, instead of step S142 in which the unit voltage V12 is compared with the average Vave of the unit voltage V12. Since other points in Fig. 14 are the same as those in Fig. 10, the same or corresponding steps are designated with the same reference numerals, and their description will not be repeated.

[0137] Returning to FIG. 13, since the power supply mode (power storage module mode or external power supply mode) of each unit has been determined in the above steps S175 and S139, in the next step S136, the power storage device control unit 11 instructs each unit control unit 31 to select the power supply mode, and then ends the processing.

[0138] In this way, by performing the SOC balance control process for each unit shown in Figures 13 and 14, it is possible to suppress SOC variations between units by utilizing the power supply modes (storage module mode and external power supply mode) in the same way as the unit voltage balance control process shown in Figures 11 and 12.

[0139] [Effects of the Third Embodiment] As described above, according to power storage device 10 of embodiment 3, unit SOC balance control based on monitoring of unit SOC variations is performed instead of the unit voltage balance control in power storage device 10 configured as in embodiments 1 and 2, and therefore effects equivalent to those of embodiments 1 and 2 can be obtained. In addition, since the variations are suppressed by directly monitoring the SOC of the units, the effect of suppressing SOC variations is enhanced when the SOC estimation accuracy is high.

[0140] Furthermore, in the case of a storage battery with a small slope of the SOC-OCV curve, or in the case of a storage battery in which the SOC cannot be estimated by measuring the OCV alone and the SOC is determined by other methods, such as by integrating the current alone, the SOC variation can be suppressed even when the degree of SOC variation does not match the degree of variation in the unit voltage V12 between the positive node P2 and the negative node N2 of the unit.

[0141] Embodiment 4 The power storage device 10 of the fourth embodiment differs from the power storage devices 10 of the first to third embodiments in that the configuration of the unit 12 is large-scale. Specifically, the power storage device 10 of the fourth embodiment includes a plurality of banks 34 connected in parallel. The following mainly describes the differences from the power storage devices 10 of the first to third embodiments, and the same reference numerals are used to designate the same or corresponding parts to the power storage devices 10 of the first to third embodiments, and description thereof will not be repeated.

[0142] [Configuration of unit 12 in the fourth embodiment] Fig. 15 is a diagram showing an example of the configuration of unit 12 in the power storage device of embodiment 4. As shown in Fig. 15, unit 12 includes a plurality of banks 34a to 34c (three in Fig. 15) connected in parallel to each other between a positive-side node P2 and a negative-side node N2. In Fig. 1, both ends of series-connected power storage modules 41 are the positive-side node P2 and the negative-side node N2, but in Fig. 15, both ends of the plurality of banks 34a to 34c are the positive-side node P2 and the negative-side node N2. The plurality of banks 34a to 34c will be referred to collectively as bank 34 or any one of them will be referred to as bank 34.

[0143] Furthermore, as in the case of Figure 1, the unit 12 includes a series switch 32 connected in series with the multiple banks 34, a parallel switch 33 connected in parallel with the series switch 32 and the entire multiple banks 34, and a unit control unit 31.

[0144] Each bank 34 includes a plurality of (three in the case of FIG. 15) power storage modules 41a to 41c connected in series. The positive node of the series-connected power storage modules 41 is designated as P3, and the negative node is designated as N3. Each bank 34 further includes a bank control unit 35 (35a, 35b, 35c) that manages and controls the bank 34, a switch 36, and a fuse 37. The plurality of power storage modules 41, the switch 36, and the fuse 37 are connected in series with one another.

[0145] 15, for simplicity, the number of banks 34 connected in parallel is set to three, and the number of power storage modules 41 connected in series in each bank 34 is set to three, but these numbers may be any number equal to or greater than 2. Also, in FIG. 15, for banks 34b and 34c, only bank control units 35b and 35c are shown, respectively, and the power storage modules 41, switches 36, and fuses 37 are not shown.

[0146] The bank control unit 35 has a communication function with each module control unit 42 and the unit control unit 31. When the bank 34 itself detects voltage, current, temperature, etc., the bank control unit 35 monitors these detected values, issues an alarm for abnormalities based on the detected values, and transmits the voltage, temperature, SOC, etc. of the bank 34 to the unit control unit 31. Furthermore, the bank control unit 35 receives an operation command for the switch 36 from the unit control unit 31 and operates the switch 36 in accordance with the operation command.

[0147] Switch 36 is normally closed. Switch 36 may be any of a type that can be opened and closed by an external signal, such as an electromagnetic contactor, a type that can be opened and closed manually, such as a no-fuse breaker, or a type that can only be opened by an external signal, and is selected depending on the required functions of the system. Furthermore, depending on the specifications of switch 36, fuse 37 may be omitted, or a fuse may be added between negative node N2 and negative node N3 in addition to fuse 37 provided between positive node P2 and positive node P3.

[0148] If an overcurrent or a short-circuit current is detected in the bank 34, the switch 36 opens or the fuse 37 blows. In this case, the bank is disconnected and the number of banks connected in parallel to the unit 12 decreases, but the operation of the energy storage device 10 can continue.

[0149] In the fourth embodiment, module control unit 42 communicates with bank control unit 35, rather than with unit control unit 31. Unit control unit 31 collects the state of each storage element 43 via bank control unit 35.

[0150] [Example of power supply configuration of bank control unit 35 and unit control unit 31] Fig. 16 is a diagram showing an example of the power supply configuration of bank control units 35 and unit control unit 31 in the power storage device of embodiment 4. Fig. 16 shows the power supply configuration of bank control units 35a-35c of banks 34a-34c and the power supply configuration of unit control unit 31 inside unit 12 of Fig. 15. Note that each bank control unit 35 has a similar power supply configuration, and therefore Fig. 16 shows the power supply configuration of bank control unit 35a as a representative.

[0151] 16, bank control unit 35a has, as power supply-related components, a bank power supply unit 81 connected to positive node P3 and negative node N3 of bank 34a via diodes 83, and a bank control power supply unit 82. Bank power supply unit 81 of bank control unit 35a is supplied with power from a plurality of power storage modules 41 connected in series between positive node P3 and negative node N3 in the bank.

[0152] Bank power supply unit 81 includes switches 84 and 87, a DC-DC converter 85, and a control power storage device 86. The configuration of bank power supply unit 81 is similar to the configuration of unit power supply unit 61 in FIG. 5, with switches 84 and 87 corresponding to switches 64 and 67 in FIG. 5, DC-DC converter 85 corresponding to DC-DC converter 65 in FIG. 5, and control power storage device 86 corresponding to control power storage device 66 in FIG. 5. Therefore, a detailed description of the configuration of bank power supply unit 81 will be omitted. DC-DC converter 65 of bank power supply unit 81 supplies power to bank control power supply unit 82 and unit power supply unit 61 of unit control unit 31.

[0153] The bank control power supply unit 82 corresponds to the unit control power supply unit 62 in Fig. 5. The bank control power supply unit 82 generates and supplies control power of a value appropriate to a processing circuit 88 for a controller in the bank control unit 35a, a communication circuit 89, a detector (not shown), and the like.

[0154] Unit control unit 31 in Fig. 16 has a unit power supply unit 61 and a unit control power supply unit 62 as power supply-related components, similar to unit control unit 31 in Fig. 5, but the method of feeding power to unit power supply unit 61 differs from that in Fig. 5. Specifically, unit power supply unit 61 in Fig. 16 receives power not directly from power storage module 41, but from bank power supply units 81 of banks 34a to 34c, respectively. Because banks 34a to 34c are connected in parallel, they have roughly the same potential when not disconnected.

[0155] The reference potential for the output of the bank power supply unit 81 of a bank 34 is generally taken at the negative node N3 of that bank 34. On the other hand, the reference potential for the input of the unit power supply unit 61 of a unit 12 is taken at the negative node N2 of that unit 12. The output voltage of each DC-DC converter 85 is input to the unit power supply unit 61 from the high-potential output terminal of the DC-DC converter 85 of each bank power supply unit 81 via the corresponding diode 63 (63a-63c). The unit power supply unit 61 has switches 64a-64c between it and the output terminals of the bank control units 35a-35c, respectively. These switches 64a-64c are normally all closed, but if, for example, bank 34a is disconnected, the corresponding switch 64a is opened.

[0156] Figure 17 is a diagram showing an example of the internal configuration of unit power supply section 61 of Figure 16. Figure 17(A) shows an example of the configuration when DC-DC converter 65 is provided, and Figure 17(B) shows an example of the configuration when DC-DC converter 65 is not provided.

[0157] 17A differs from the unit power supply unit 61 of FIG. 5 in that it includes multiple (three in the illustrated example) switches 64a-64c corresponding to the bank control units 35a-35c, respectively. A high-side input node ND1 of DC-DC converter 65 is connected via switch 64a and diode 63a to a high-side output terminal of DC-DC converter 85 provided in bank power supply unit 81 of bank control unit 35a. Input node ND1 is further connected via switch 64b and diode 63b to a high-side output terminal of DC-DC converter 85 provided in bank power supply unit 81 of bank control unit 35b. Input node ND1 is further connected via switch 64c and diode 63c to a high-side output terminal of DC-DC converter 85 provided in bank power supply unit 81 of bank control unit 35c. Other configurations of unit power feeding section 61 in FIG. 16 are similar to those of unit power feeding section 61 in FIG. 5, and therefore the same or corresponding parts will be given the same reference characters and description thereof will not be repeated.

[0158] Alternatively, a DC-DC converter may be provided for each output voltage of the bank control units 35a to 35c, and the output voltages of these DC-DC converters may be combined.

[0159] 17(B) has a configuration in which DC-DC converter 65 is removed from unit power supply section 61 of FIG. 17(A). Therefore, the combined voltage at input node ND1 in FIG. 17(B) is output as the high-side output voltage of unit power supply section 61. The voltage at negative-side node N2 of unit 12 is output as the low-side output voltage of unit power supply section 61.

[0160] As described above, in power storage device 10 of the fourth embodiment, unit control unit 31 receives power from bank power supply unit 81 of each bank control unit 35, but the specific internal configuration related to the power supply of unit control unit 31 is not particularly limited.

[0161] [SOC variation suppression between units] In the energy storage device 10 of the fourth embodiment, the plurality of banks 34 are connected in parallel with one another, and therefore function to automatically balance the voltages. Therefore, if the SOC can be controlled by controlling the OCV of each energy storage element 43, the SOC variation is unlikely to become large.

[0162] In the energy storage device 10 of embodiment 4, similarly to the energy storage devices 10 of embodiments 1 and 2, when the energy storage device control unit 11 receives the unit voltage V12 between the positive side node P2 and the negative side node N2 of each unit from each unit control unit 31 and monitors the variation in the unit voltage V12, it is possible to perform unit voltage balance control using the operation mode and unit voltage balance control using the power supply mode.

[0163] In unit voltage balance control using the operation mode, power storage device control unit 11 instructs unit control unit 31 to select an operation mode in accordance with the processing described with reference to Figures 6 and 7. Furthermore, when bank control unit 35 receives power from AC control power supply 2, power storage device control unit 11 instructs unit control unit 31 to select a power supply mode in accordance with the processing described with reference to Figures 9 and 10. Unit control unit 31 instructs bank control unit 35 to select the operation mode and / or power supply mode received from power storage device control unit 11. Bank control unit 35 operates in the operation mode and / or power supply mode instructed by power storage device control unit 11 via unit control unit 31. This suppresses variations in voltage and SOC between units.

[0164] Similarly to the power storage device 10 of the third embodiment, the power storage device 10 of the fourth embodiment can also perform unit SOC balance control using the operation mode and unit SOC balance control using the power supply mode when the power storage device control unit 11 monitors variations in SOC between units. In this case as well, the bank control unit 35 operates in the operation mode and / or the power supply mode instructed by the power storage device control unit 11 via the unit control unit 31. This suppresses variations in SOC among the units 12.

[0165] Note that if the SOC cannot be estimated solely by measuring the OCV of the storage elements 43, the SOCs of the parallel-connected banks 34 may vary even if the voltages of the parallel-connected banks 34 are the same. In this case, the unit control unit 31 may change the operating mode and power supply mode received from the power storage device control unit 11 and instruct the bank control unit 35 to do so. For example, if the SOC of bank 34a, of the parallel-connected banks 34a, 34b, and 34c, is lower than the SOCs of banks 34b and 34c, the unit control unit 31 switches bank 34a to the power-saving mode and keeps banks 34b and 34c in the normal mode. This reduces the SOC variation between the banks.

[0166] [Effects of the Fourth Embodiment] As described above, the energy storage device 10 of the fourth embodiment includes a plurality of banks 34 connected in parallel within each unit 12, and a plurality of energy storage modules 41 connected in series within each bank 34. Therefore, the energy storage device 10 has a configuration suitable for increasing capacity. Even with a configuration in which each unit 12 includes a plurality of banks 34 connected in parallel, it is possible to perform unit voltage balance control similar to that of the first and second embodiments, and unit SOC balance control similar to that of the third embodiment, and therefore it is possible to obtain the effect of suppressing SOC variations between units similar to that of the first to third embodiments.

[0167] Embodiment 5. [Configuration of Power Storage Device 10 of Fifth Embodiment] 18 is a diagram showing a configuration example of the energy storage device 10 according to the fifth embodiment. The energy storage device 10 according to the fifth embodiment includes a plurality of strings connected in parallel, and a plurality of units 12 each of which is connected in series, thereby achieving a further increase in capacity.

[0168] Specifically, the energy storage device 10 of Fig. 18 includes a plurality of strings 91 (three in Fig. 18) connected in parallel between the positive electrode P1 and the intermediate electrode C1, and a plurality of strings 94 (three in Fig. 18) connected in parallel between the intermediate electrode C1 and the negative electrode N1. Therefore, each string 91 and each string 94 are connected in series between the positive electrode P1 and the negative electrode N1. The intermediate electrode C1 may be grounded or ungrounded.

[0169] Each positive string 91 includes a plurality of units 12 (three in the case of FIG. 18) connected in series, a string control unit 92, and a switch 93. The positive node of the string 91 is designated as P4, and the negative node is designated as N4. The positive node P4 is connected to the positive electrode P1 via a switch 13p. The negative node N4 is connected to the intermediate electrode C1. The switch 93 is connected in series with the plurality of units 12 between the positive node P4 and the negative node N4, and is connected to the high potential side of the plurality of units 12.

[0170] Each negative string 94 includes a plurality of units 12 (three in the case of FIG. 18) connected in series, a string control unit 95, and a switch 96. The positive node of the string 94 is designated as P5, and the negative node is designated as N5. The positive node P5 is connected to the intermediate electrode C1. The negative node N5 is connected to the negative electrode N1 via a switch 13n. The switch 96 is connected in series with the plurality of units 12 between the positive node P5 and the negative node N5, and is connected to the low potential side of the plurality of units 12.

[0171] As described above, string 91 differs from string 94 in that switch 93 is connected to the high potential side in string 91 and switch 96 is connected to the low potential side in string 94, but the functions of string 91 and string 94 are almost the same.

[0172] The reference potential of the string control unit 92 may be set to a potential near the switch 93, and the reference potential of the string control unit 95 may be set to a potential near the switch 96. However, the present invention is not limited to this, and the potentials of the string control units 92 and 95 may be determined by other methods.

[0173] The string control units 92 and 95 share some of the functions of the power storage device control unit 11 in the first to fourth embodiments. The remaining functions of the power storage device control unit 11 in the fifth embodiment are a function of communicating with the control device 21 that controls the power converter 20, a function of receiving an operation command for the power storage device 10 from the control device 21, and a function of transmitting the state of the power storage device 10 and the occurrence of an abnormality to the control device 21. In the present disclosure, the power storage device control unit 11 and the string control units 92 and 95 are collectively referred to as "one or more control units."

[0174] The switch 93 of each string 91 and the switch 96 of each string 94 are normally closed. When the switch 93 of a certain string 91 is opened, that string 91 can be de-energized, and when the switch 94 of a certain string 94 is opened, that string 94 can be de-energized.

[0175] In the example of Fig. 18, three strings 91 are connected in parallel, and three units 12 are connected in series to each string 91. Similarly, three strings 94 are connected in parallel, and three units 12 are connected in series. The number of parallel connections of the strings 91 and 94 and the number of series connections of the units 12 are merely examples, and the number of parallel connections and the number of series connections are not limited as long as they are two or more. Furthermore, only string 91 may be provided and not string 94, or conversely, only string 94 may be provided and not string 91.

[0176] [SOC variation suppression between units] String control units 92 and 95 perform the same control as the unit voltage balance control and / or unit SOC balance control performed by power storage device control unit 11 in embodiments 1 to 4 on SOC variations between units in their respective strings 91 and 94. This makes it possible to suppress SOC variations between units in strings 91 and 94.

[0177] The SOC variation between the series-connected strings 91 and 94 can be suppressed in the following manner. When unit voltage balance control is being used, the power storage device control unit 11 collects the string voltage from each of the strings 91 and 94 or the average voltage of the units 12 in that string. If the difference between the voltage of string 91 (or the average voltage of the units) and the voltage of string 94 (or the average voltage of the units) and the unit 12 becomes greater than a threshold, the voltage of string 91 (or the average voltage of the units) and the voltage of string 94 (or the average voltage of the units) are changed by using the operating mode and power supply mode. This makes it possible to reduce the difference between the two voltages below the threshold. When unit SOC balance control is being used, the SOC variation can be suppressed in a similar manner.

[0178] Note that the voltages of strings 91 connected in parallel to each other are equal, and the voltages of strings 94 connected in parallel to each other are equal. Therefore, the voltages of the parallel-connected strings are automatically balanced, and no active control is required. If the SOC cannot be estimated by measuring the OCV of the storage element 43 alone, there may be variations in the voltages between the parallel-connected strings. However, even in this case, the SOC variations can be suppressed by using the operating mode and / or the power supply mode.

[0179] [Effects of the fifth embodiment] As described above, the energy storage device 10 of the fifth embodiment has a configuration in which a plurality of strings 91, 94, each of which includes a plurality of units 12 connected in series, are connected in parallel. This allows the energy storage device 10 to be configured to be more suitable for higher voltages and larger capacities. Even with the energy storage device 10 configured in this manner, the unit voltage balance control and / or unit SOC balance control described in the first to fourth embodiments can be performed, thereby achieving the same SOC variation suppression effect as in the first to fourth embodiments. Furthermore, since the difference in average voltage or SOC of the units 12 between the series-connected strings 91 and 94 can be suppressed, the SOC variation of the energy storage elements 43 in the energy storage device 10 can be suppressed.

[0180] Embodiment 6 In the sixth embodiment, an example of a method of supplying power to power storage device control unit 11 and string control units 92 and 95 will be described. The sixth embodiment can be combined with the first to fifth embodiments.

[0181] The method of feeding power to unit power supply unit 61 provided in unit control unit 31 is as described in Figures 8 and 16. Power can be further fed from the output of unit power supply unit 61 to power storage device control unit 11 and string control units 92, 95.

[0182] The following describes the power supply to the string control unit 92 as an example. Assume that the units 12a, 12b, and 12c are connected in this order from the high-potential side to the low-potential side within the string 91. If the reference potential of the string control unit 92 is set to the potential near the switch 93, the potential of the unit 12a will be closest to the potential of the string control unit 92. Therefore, it is advantageous in terms of insulation to supply power to the string control unit 92 from the unit power supply 61 of the unit 12a. In this case, the power consumption of the unit 12a is expected to be greater than the power consumption of the units 12b and 12c. However, SOC variations can be suppressed by using unit voltage balance control and / or unit SOC balance control. Furthermore, if the string control unit 92 is configured to be able to supply power from the unit power supply 61 of the unit 12b or the AC control power supply 2, the power supply source may be switched depending on SOC variations. Furthermore, if the units 12a to 12c are configured so that power can be fed from the unit power feeders 61 to the string control units 92, the power feed to the string control units 92 can be actively used to suppress SOC variations between the units.

[0183] Embodiment 7 In the seventh embodiment, a description will be given of an example of using a control power storage device 66 provided in a unit power supply unit 61 and a control power storage device 86 (typically a control power storage device provided in one or more control units) provided in a bank power supply unit 81. The seventh embodiment can be combined with the first to sixth embodiments.

[0184] An example of the unit power supply unit 61 will be described with reference to Fig. 5. When switch 67 is closed, power can be supplied from the control power storage device 66 to the unit control power supply unit 62 even if switch 64 is opened to stop the power supply from the power storage module 41. Therefore, when the unit control unit operating mode is the normal mode and the voltage or SOC of the units 12 varies greatly, power is supplied from the control power storage device 66 by opening switch 64 of the unit 12 with a relatively low voltage or SOC and closing switch 67. This makes it possible to prevent the voltage or SOC variation between units from increasing.

[0185] As described above, when the energy of the control power storage device 66 is used to suppress SOC variations, it becomes necessary to supplementarily charge the control power storage device 66. As a method for this, for example, unit voltage balance control and / or unit SOC balance control may be performed with the switches 64 and 67 closed during a long period of suspension of charging / discharging from the positive electrode P1 and the negative electrode N1.

[0186] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. For example, it is possible to combine other known technologies with the power storage devices and power conversion devices including the power storage devices shown in Embodiments 1 to 7, and it is also possible to make modifications such as omitting parts without departing from the gist of the present disclosure. The scope of this application is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0187] 1 power system, 2 control power supply, 10 energy storage device, 11 energy storage device control unit, 12 unit, 13, 32, 33, 36, 64, 67, 72, 84, 87, 93, 96, SW switch, 14, 38 communication line, 20 power converter, 21 control device, 22 DC end, 23 AC end, 31 unit control unit, 34 bank, 35 bank control unit, 37 fuse, 41 energy storage module, 42 module control unit, 43 energy storage element, 50 energy storage element balancing circuit, 51 voltage detection circuit, 52 current detector, 53 current detection circuit, 54 temperature detector, 55, 68, 88 processing circuit, 56, 69, 89 communication circuit, 61 unit power supply unit, 62 unit control power supply unit, 63, 83 diode, 65, 85 DC-DC converter, 66, 86 Control storage device, 73 AC-DC converter, 81 bank power supply unit, 82 bank control power supply unit, 91, 94 string, 92, 95 string control unit, 100 power conversion device, C1 intermediate pole, N1 negative pole, N2, N3, N4, N5 negative side node, ND1 input node, P1 positive pole, P2, P3, P4, P5 positive side node, RA resistive element, SOCave, Vave average value, SOCdif, Vdif distribution range, SOCmax, Vmax maximum value, SOCmin, Vmin minimum value, V12 unit voltage.

Claims

1. It is an energy storage device, Positive electrode and negative electrode, A plurality of units connected in series between the positive electrode and the negative electrode, It comprises one or more control units, Each of the aforementioned plurality of units is The positive node and the negative node, A plurality of energy storage modules connected in series between the positive node and the negative node, A switch connected in series with the plurality of energy storage modules is placed between the positive node and the negative node. The unit includes a unit control unit that is powered by the plurality of energy storage modules and has a first operating mode and a second operating mode that consumes less power than the first operating mode, Each of the aforementioned plurality of energy storage modules is Multiple energy storage elements, The system includes a storage element balancing circuit that balances the voltage or charge state of the plurality of storage elements by discharging one or more of the plurality of storage elements, The unit control unit is connected to one or more control units via a communication line. The unit control unit is The unit collects the status of its own unit, including the voltage or charge state of each energy storage element within the unit. Based on the state of the unit and the operation commands from one or more control units, the switches within the unit are operated. Each of the energy storage modules is configured to determine which energy storage element to discharge using the energy storage element balancing circuit and to issue a command to the control circuit of the energy storage element balancing circuit. An energy storage device in which, when an index value representing the degree of variation in voltage or charge state among the plurality of units exceeds an upper limit during a stop in charging and discharging of the energy storage device, the unit control unit of a unit with a relatively high voltage or charge state operates in the first operating mode, and the unit control unit of a unit with a relatively low voltage or charge state operates in the second operating mode.

2. The unit control unit has a first power supply mode in which power is supplied from the plurality of energy storage elements and a second power supply mode in which power is supplied from an external power source. The energy storage device according to claim 1, wherein one or more control units operate the unit control unit of a unit with a relatively high voltage or charge state in the first power supply mode and the unit control unit of a unit with a relatively low voltage or charge state in the second power supply mode when an index value representing the degree of variation in voltage or charge state among the plurality of units exceeds an upper limit.

3. Each of the aforementioned plurality of units comprises a plurality of banks connected in parallel between the positive node and the negative node, Each of the aforementioned banks is The plurality of energy storage elements connected in series, The bank control unit is powered by a plurality of energy storage elements within its own bank and has a first operating mode and a second operating mode as operating modes, The unit control unit is powered by each of the bank control units of the plurality of banks. The energy storage device according to claim 1, wherein if an index value representing the degree of variation in voltage or charge state among the plurality of units exceeds an upper limit during a halt in charging or discharging of the energy storage device, the bank control unit in the unit with a relatively high voltage or charge state operates in the first operating mode, and the bank control unit in the unit with a relatively low voltage or charge state operates in the second operating mode.

4. The bank control unit has a first power supply mode in which power is supplied from the plurality of energy storage elements within its own bank, and a second power supply mode in which power is supplied from an external power source. The energy storage device according to claim 3, wherein one or more control units operate the bank control unit in a unit with a relatively high voltage or charge state in the first power supply mode and the bank control unit in a unit with a relatively low voltage or charge state in the second power supply mode when an index value representing the degree of variation in voltage or charge state among the plurality of units exceeds an upper limit.

5. The energy storage device according to claim 1, wherein the one or more control units are powered by a unit control unit provided in at least one of the plurality of units.

6. The energy storage device according to claim 3, wherein the one or more control units are powered by each of the bank control units of the plurality of banks provided in at least one of the plurality of units.

7. The unit control unit is configured to be able to receive power from a power storage device provided in its unit, The energy storage device according to claim 1, wherein the unit control unit receives power from the energy storage device when an index value representing the degree of variation in voltage or charge state among the plurality of units exceeds an upper limit during operation in the first operating mode.

8. The bank control unit is configured to be able to receive power from a power storage device provided in its own bank. The energy storage device according to claim 3, wherein the bank control unit receives power from the energy storage device when an index value representing the degree of variation in voltage or charge state among the plurality of units exceeds an upper limit during operation in the first operating mode.

9. The energy storage device comprises a plurality of strings connected in parallel between the positive electrode and the negative electrode, The energy storage device according to any one of claims 1 to 8, wherein each of the plurality of strings comprises the plurality of units connected in series.

10. A power storage device according to any one of claims 1 to 8, A power conversion device comprising a power converter connected between the energy storage device and a power grid, configured to discharge energy stored in the energy storage device to the power grid and to charge the energy storage device from the power grid.

Images