Electric power storage system

Abstract

Provided is an electric power storage system comprising: a DC bus; a plurality of batteries that are connected to the DC bus and are connected in parallel with each other; a plurality of diagnostic units that are respectively provided to the plurality of batteries and measure the state of deterioration of the batteries by discharging the batteries at a constant electric current or constant electric power; and a power conditioner that is connected to the DC bus and that performs AC / DC power conversion, wherein at least a portion of the electric power discharged from a test subject battery among the plurality of batteries, the deterioration state of which test subject battery being measured by the diagnostic unit, is charged into at least one of the plurality of batteries or supplied to the power conditioner.

Description

Energy Storage System

[0001] The present invention relates to an energy storage system.

[0002] Conventionally, a power system has been known in which battery units each made of a secondary battery are connected in parallel to a power conversion circuit (see Patent Document 1). [Prior art documents] [Patent Document 1] JP 2013-135482 A General disclosure

[0003] (Problem to be Solved) It is preferable to perform the deterioration diagnosis of each secondary battery at a constant discharge power or a constant discharge current. (Means for Solving the Problem)

[0004] An embodiment of the present invention provides a power storage system. The power storage system may include a DC bus. The power storage system may include a plurality of batteries connected to the DC bus and connected in parallel to each other. Any of the power storage systems may include a plurality of diagnostic units provided in each of the plurality of batteries, the diagnostic units measuring a state of deterioration of the batteries by discharging the batteries at a constant current or a constant power. Any of the power storage systems may include a power conditioner connected to the DC bus and converting DC power to AC power. In any of the power storage systems, at least a portion of power discharged from a battery under test whose state of deterioration is being measured by the diagnostic unit among the plurality of batteries may be charged to at least one other battery among the plurality of batteries or supplied to the power conditioner. In any of the power storage systems, at least a portion of power discharged from a battery under test whose state of deterioration is being measured by the diagnostic unit among the plurality of batteries may be charged to at least one other battery among the plurality of batteries.

[0005] In any of the above power storage systems, the DC bus may supply power to the power conditioner or receive power from the power conditioner while the diagnostic unit is measuring the state of deterioration of the battery under test.

[0006] In any of the above-described power storage systems, the degradation state of the battery under test may be updated based on the measurement result of the degradation state. In any of the above-described power storage systems, the diagnostic unit may update the degradation state based on the amount of drop in the battery voltage and past measurement results of the amount of drop in the battery voltage.

[0007] In any of the above-described power storage systems, the control unit may adjust the number of the batteries under test to be measured simultaneously based on the capacities of the plurality of batteries calculated from the measurement results of the plurality of diagnostic units.

[0008] Any of the above-described power storage systems may further include a control unit capable of communicating with the plurality of diagnostic units and the power conditioner. In any of the above-described power storage systems, the control unit may calculate a total capacity of the plurality of batteries from the measurement results of the degradation state by the diagnostic unit, and control the power conversion amount of the power conditioner based on the total capacity of the plurality of batteries.

[0009] The power storage system may further include a plurality of DC-DC converters provided between the plurality of batteries and the DC bus, and the plurality of DC-DC converters may control charge / discharge amounts of the plurality of batteries based on the measurement results of the deterioration state by the diagnostic unit.

[0010] In any of the above power storage systems, the battery, the diagnostic unit, and the DC-DC converter may be integrated into a single module, and the entire module may be detachable from the DC bus.

[0011] The power storage system may further include a control unit capable of communicating with the plurality of DC-DC converters. In the power storage system, the control unit may control the DC-DC converters in accordance with the measurement result of the degradation state by the diagnostic unit to disconnect the DC-DC converters from the DC bus.

[0012] The above summary of the invention does not list all of the features of the present invention, and subcombinations of these features may also be inventions.

[0013] Fig. 1 is a diagram showing an example of a power storage system 100 according to an embodiment of the present invention. Fig. 2 is a diagram showing an operation example of the power storage system 100 according to an embodiment of the present invention. Fig. 3 is a diagram showing a communication network of the power storage system 100 according to an embodiment of the present invention. Fig. 4 is a diagram showing a modified example of the power storage system 100 according to an embodiment of the present invention.

[0014] The present invention will be described below through embodiments of the invention, but the following embodiments do not limit the scope of the invention. Furthermore, not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention. Furthermore, the same components in each drawing may be designated by the same reference numerals, and their description may be omitted.

[0015] In this specification, the expression "connected" is not limited to a direct connection without an intervening element, but also includes an indirect connection via an intervening element. Furthermore, in this specification, the expressions "connected between... and...," "provided between... and...," or "disposed between... and..." do not limit the physical arrangement, but rather mean "electrically connected between... and...."

[0016] FIG. 1 is a diagram showing an example of a power storage system 100 according to an embodiment of the present invention. The power storage system 100 is connected to a power facility, stores power from the power facility, and supplies power to the power facility. The power facility includes, for example, a power generation facility that uses renewable energy. The power storage system 100 stores surplus power in the power generation facility, and supplies power from the power storage system 100 when there is a power shortage in the power generation facility. The power facility may be a power grid. The power storage system 100 supplies power to the power grid and stores power from the power grid.

[0017] The power storage system 100 includes multiple power storage units 16, a DC bus 30, a power conditioner 40, and a transformer 50. Each power storage unit 16 is composed of a DC-DC converter 10 and a battery 20 and is connected to the DC bus 30. The DC-DC converter 10 is provided between each of the multiple batteries 20 and the DC bus 30. The multiple batteries 20 are connected to the DC bus 30 via the DC-DC converters 10 connected to each of the multiple batteries 20, and are also connected in parallel with each other. The batteries 20 may be secondary batteries such as lithium-ion batteries. The batteries 20 may be, for example, lithium-ion batteries that have been used as EV batteries. Since lithium-ion batteries are generally not easy to recycle, it is preferable to reuse them as much as possible. Using used secondary batteries as the batteries 20 allows the secondary batteries to be reused. At least one of the batteries 20 may be a used battery. Each of the batteries 20 outputs a different predetermined battery voltage.

[0018] The DC-DC converter 10 converts (e.g., boosts) the battery voltage to the voltage of the DC bus 30. The battery voltage is the voltage at the output terminal of the battery 20. The DC-DC converter 10 may convert (e.g., step down) the voltage of the DC bus 30 to the battery voltage and charge the battery 20.

[0019] The DC-DC converter 10-1 of this example includes a switch SW11, a switch SW12, an inductor L1, and a capacitor C11. The DC-DC converter 10-1 of this example converts voltage by operating as a step-up chopper or a step-down chopper. However, the configuration of the DC-DC converter 10-1 is not limited to this. The DC-DC converter 10-1 only needs to be able to convert voltage.

[0020] A plurality of DC-DC converters 10 are connected to the DC bus 30. Although three DC-DC converters 10 and three batteries 20 are shown in FIG. 1 , the power storage system 100 may include more DC-DC converters 10 and batteries 20.

[0021] DC power is applied to the DC bus 30. In this example, multiple batteries 20 are connected to the DC bus 30. Each DC-DC converter 10 may operate so that the voltage of the DC bus 30 is maintained at a predetermined value. In this example, the DC bus 30 includes a high potential line 32 and a reference potential line 24. The high potential line 32 has a higher voltage than the reference potential line 24. The reference potential line 24 is connected to the low-voltage side terminal of each battery 20. The high potential line 32 is connected to the output terminal of each DC-DC converter 10. The voltage of the DC bus 30 is the potential difference between the high potential line 32 and the reference potential line 24.

[0022] The power conditioner 40 converts DC power and AC power. One side of the power conditioner 40 is connected to the DC bus 30, and the other side is connected to the transformer 50. The power conditioner 40 converts the DC power of the DC bus 30 into AC power and supplies it to the transformer 50. The power conditioner 40 also converts the AC power of the transformer 50 into DC power and supplies it to the DC bus 30.

[0023] The power conditioner 40 of this example has a capacitor C1 that is charged by the voltage of the DC bus 30 or the voltage from the transformer 50. The power conditioner 40 of this example includes a three-phase inverter that converts DC power from the capacitor C1 into AC power and converts AC power from the transformer 50 into DC power. The three-phase inverter has switches SW1 to SW6, with switches SW1 and SW2, switches SW3 and SW4, and switches SW5 and SW6 corresponding to each arm of the three-phase inverter. An inductor ALC1 is connected to the connection point of the switches in each arm. A capacitor may be provided between each inductor ALC1 and a reference potential. However, the structure of the power conditioner 40 is not limited to this. It is sufficient for the power conditioner 40 to be able to convert DC power and AC power into each other.

[0024] The transformer 50 converts the voltage of the AC power. The transformer 50 converts the voltage of the AC power output from the power conditioner 40 and outputs it to the power equipment. The transformer 50 also converts the voltage of the AC power of the power equipment and outputs it to the power conditioner 40.

[0025] Note that the power conversion by the power conditioner 40 is not limited to conversion between DC power and AC power, but may be any power that can be converted into power suitable for transmission and reception by the power storage system 100. That is, although a circuit configuration that converts DC power and AC power to each other using the power conditioner 40 and the transformer 50 has been described in Fig. 1, the present invention is not limited to this circuit configuration, and a circuit configuration that converts DC power to DC power may also be used.

[0026] A limit switch SW13 may be provided between the DC-DC converter 10 and the DC bus 30. Furthermore, a free wheel diode Dd11 may be provided between the limit switch SW13 and the reference potential line 24. The limit switch SW13 limits the current flowing through the DC bus 30. The limit switch SW13 may be a semiconductor switch. The free wheel diode Dd11 secures a current path for current flowing while the limit switch SW13 is off. The limit switch SW13 and the free wheel diode Dd11 may be provided for each DC-DC converter 10.

[0027] As described above, the battery 20 includes a used secondary battery. Each battery 20 may have a different type or usage history. Generally, batteries deteriorate due to repeated charging and discharging or charging and discharging in extreme environments. Degradation deteriorates battery characteristics such as capacity and output voltage, as well as charge and discharge characteristics at high current values. Specifically, increasing the C rate during charging and discharging results in a rapid decrease in battery capacity and output voltage. Therefore, when reusing secondary batteries, it is preferable to set an appropriate C rate for each battery 20 depending on its deterioration status. To achieve this, it is preferable to measure the deterioration state of each battery 20 with high accuracy and accurately understand the deterioration state of each battery 20.

[0028] Fig. 2 is a diagram showing an example of the operation of the power storage system 100 according to the embodiment of the present invention. Each of the plurality of batteries 20 is provided with a diagnostic unit shown in Fig. 3. The diagnostic unit may be a battery management system that measures the current, voltage, temperature, etc. of the battery. The battery management system may be a system that has been used for another purpose (for example, for an EV).

[0029] The diagnostic unit may measure the deterioration state of the battery 20 by discharging the battery 20 at a constant current or constant power. The diagnostic unit may measure electrical characteristics of the battery 20, such as the discharge capacity (Ah), output voltage (V), output current (A), output power (W), output energy density (Wh), and internal impedance (Ω). The discharge capacity is the amount of electricity when the battery 20 is discharged from a fully charged state until the output voltage drops to a predetermined value. When measuring the discharge capacity, it is preferable to charge the battery 20 in advance. The diagnostic unit may acquire time waveforms obtained by measuring electrical characteristics such as the output voltage at multiple times. The diagnostic unit may measure the rate of change of electrical characteristics such as the output voltage with respect to the discharge time.

[0030] The diagnostic unit may calculate the degree of deterioration from a predetermined initial state for at least some of these electrical characteristics as the deterioration state. The initial state of each characteristic may use the specification value of the battery 20, or may use the characteristic value that the diagnostic unit initially measured for the battery 20.

[0031] More specifically, the degradation state refers to, for example, the degree of decrease in capacity or output voltage at a high rate in the battery's charge / discharge characteristics (rate characteristics). Measuring the degradation state may involve estimating the degradation state or calculating the rate characteristics from the amount of battery voltage drop when a constant current or constant power is discharged, or directly measuring the rate characteristics. Another measurement method involves estimating the electromotive force and internal resistance during charging or discharging from the relationship between the battery voltage and current during normal operation to determine the degradation state. The degradation state can also be estimated from the battery's usage history. However, the degradation state estimated by these methods is not very accurate. On the other hand, as in this example, the degradation state of the battery 20 can be accurately measured by measuring the amount of battery voltage drop when a constant current or constant power is discharged for discharge measurement. As an example, the diagnostic unit measures the degradation state by discharging the battery 20 at a constant current or power for approximately 5 to 10 seconds.

[0032] The diagnostic unit may update the degradation state based on the amount of drop in the battery voltage and past measurement results of the amount of drop in the battery voltage. The past measurement results may be, for example, an average value of a predetermined number of past battery voltage measurement results. This makes it possible to suppress the effects of measurement errors and temporary fluctuations in the battery degradation state, thereby enabling more accurate measurements. The diagnostic unit may update the degradation state based on past measurement results of the amount of drop in the battery voltage.

[0033] The diagnostic unit may also update the degradation state based on both the amount of battery voltage drop and past measurements of the amount of battery voltage drop. For example, the diagnostic unit may estimate the remaining life of the battery as a degradation state based on relative changes in the degradation state. This allows the timing of battery replacement to be predicted.

[0034] In this specification, among the multiple batteries 20, the battery 20 whose deterioration state is being measured by the diagnostic unit may be referred to as the battery under test. In the example of FIG. 2, battery 20-1 is the battery under test. The battery under test is discharging power. The arrow extending rightward from battery 20-1 in the figure represents this discharging. Also, for example, when measurement of the deterioration state of battery 20-1 is completed and the diagnostic unit next measures the deterioration state of battery 20-2, battery 20-2 becomes the battery under test.

[0035] At least a portion of the power discharged from the battery under test is charged to at least one other battery 20 of the plurality of batteries 20 or supplied to the power conditioner 40. When the power discharged from the battery under test is supplied to the DC bus 30, it may be considered that at least a portion of the power discharged from the battery under test is charged to at least one other battery 20 of the plurality of batteries 20 or supplied to the power conditioner 40. This allows for effective use of the power discharged when measuring the deterioration state. All of the power discharged from the battery under test may be charged to at least one other battery 20 of the plurality of batteries 20 or supplied to the power conditioner 40.

[0036] At least a portion of the power discharged from the battery under test may be charged to at least one other battery 20 among the multiple batteries 20. In this example, the power discharged from the battery under test is charged to battery 20-2 and battery 20-3. The arrows pointing left toward battery 20-2 and battery 20-3 in the figure represent this charging. Some or all of the power discharged from the battery under test during measurement of the state of deterioration is charged to the other batteries 20. The period during which the state of deterioration is being measured may refer to the period during which the diagnostic unit measures the above-mentioned electrical characteristics of the battery under test. In another example, the period during which the battery under test is being measured may refer to the period during which the battery under test discharges a constant current or constant power that is independent of the load's demand power or surplus power (demand power and surplus power are referred to as load power). The amount of charge and discharge power of each battery 20 is controlled according to the load power. The power storage system 100 may have a control unit that controls the amount of charge and discharge power of each battery 20 according to the load power. During the period in which the deterioration state of the battery under test is being measured, the control unit may control the amount of charge / discharge power of the batteries 20 other than the battery under test according to the load power. During the period in which the deterioration state of the battery under test is being measured, the control unit discharges the battery under test at a constant current or constant power regardless of the load power. Because the discharge current or discharge power of the battery under test is a constant value, during the period in which the deterioration state of the battery under test is being measured, an excess or deficiency of power or current occurs relative to the load power, causing fluctuations in the voltage of the DC bus 30. By controlling to suppress voltage fluctuations on the DC bus 30 due to the charging / discharging of the batteries 20 other than the battery under test, it is possible to measure the deterioration state of the battery under test without disconnecting it from the DC bus 30.

[0037] If any of the batteries 20 is charging during a period in which the battery under test is discharging, it may be assumed that at least a portion of the power discharged from the battery under test is being charged to that battery 20. In another example, if the control unit controls the charge amount of any of the batteries 20 to increase in accordance with the discharge amount of the battery under test, it may be assumed that at least a portion of the power discharged from the battery under test is being charged to that battery 20. Furthermore, if the control unit controls the discharge amount of any of the batteries 20 to decrease in accordance with the discharge amount of the battery under test, it may be assumed that at least a portion of the power discharged from the battery under test is being charged to that battery 20.

[0038] In the above example, the power discharged from the battery under test was charged to battery 20-2 and battery 20-3, but part of the power discharged from the battery under test may also charge capacitor C1 of power conditioner 40. As will be described later, each battery 20 operates so that the voltage of the DC bus 30 becomes a predetermined value. Therefore, when power is supplied from the power storage system 100 to the power equipment, each battery 20 discharges power to the DC bus 30. At this time, the power discharged from the battery under test is charged to capacitor C1 of power conditioner 40. Even in this case, power discharged from the battery under test during other time periods may be charged to another battery 20.

[0039] The multiple DC-DC converters 10 may control the charge / discharge rates of the multiple batteries 20 based on the measurement results of the deterioration state by the diagnostic unit. Controlling the charge / discharge rates may involve controlling the C rate during charging / discharging. As an example, the C rate during charging / discharging may be lowered as the deterioration state becomes more severe. The diagnostic unit may set a maximum allowable C rate based on the measurement results of the deterioration state. While the multiple DC-DC converters 10 are controlling the charge / discharge rates, the DC bus 30 supplies power to a load or receives power from a load. That is, during normal power supply or power storage operation of the power storage system 100, the multiple DC-DC converters 10 may control the charge / discharge rates of the multiple batteries 20 based on the measurement results of the deterioration state by the diagnostic unit. The multiple DC-DC converters 10 may be capable of communicating with the diagnostic unit, as described below. Furthermore, each battery 20 may be charged / discharged between approximately 70% and 10% of its capacity.

[0040] As described above, the rate characteristics of a battery deteriorate as it deteriorates. According to this example, even a deteriorated battery can be used as the battery 20. Furthermore, because the battery is used at an appropriate charge / discharge rate, the progression of deterioration during use in the power storage system 100 can be delayed. In this example, multiple batteries 20 are connected in parallel, so even if the charge / discharge rate of each battery 20 is low, a predetermined charge / discharge rate can be ensured by combining it with other batteries 20. Furthermore, the batteries 20 in this example are of various types and have different usage histories, and therefore have different battery voltages. In this example, multiple DC-DC converters 10 are provided for each battery 20, so batteries with different battery voltages can be used as the batteries 20.

[0041] In this example, the discharge amount of constant current or constant power in measuring the deterioration state is constant regardless of the deterioration state, which allows for more accurate measurement of the deterioration state.

[0042] The DC-DC converter 10 may be selected depending on the performance and deterioration state of the battery 20. For example, if a battery with a large charge / discharge capacity is used as the battery 20-1, a DC-DC converter with a large rated current is selected as the DC-DC converter 10-1. Furthermore, if the deterioration of the battery 20-1 progresses and the charge / discharge capacity decreases, the DC-DC converter 10-1 may be replaced with a DC-DC converter with a smaller rated current.

[0043] Fig. 3 is a diagram showing a communication network of the power storage system 100 according to an embodiment of the present invention. In this example, each component of the power storage system 100 is shown schematically. In Fig. 3, wiring to which DC power is applied is shown by a thick line, and wiring to which AC power is applied is shown by a thin line. DC power is applied to the battery 20 side of the power conditioner 40, and AC power is applied to the transformer 50 side of the power conditioner 40.

[0044] As described above, each of the multiple batteries 20 is provided with a diagnostic unit 22. That is, the power storage system 100 includes multiple diagnostic units 22. The power storage system 100 may further include a control unit 42. The control unit 42 may be capable of communicating with the power conditioner 40, multiple DC-DC converters 10, and multiple diagnostic units 22. Furthermore, the DC-DC converter 10 may be capable of communicating directly with the diagnostic unit 22 or may be capable of communicating with the diagnostic unit 22 via the control unit 42. The control unit 42 may indirectly acquire the measurement results of each diagnostic unit 22 by communicating with each DC-DC converter 10. The control unit 42 may indirectly control the DC-DC converter 10 via the diagnostic unit 22. The dashed arrows in the figure indicate an example of communication between each component.

[0045] The control unit 42 controls each of the DC-DC converters 10 in accordance with the voltage of the DC bus 30. The control unit 42 may control each of the DC-DC converters 10 so that the voltage of the DC bus 30 becomes a predetermined value. As an example, the control unit 42 may perform droop control on each of the DC-DC converters 10.

[0046] While the diagnostic unit 22 is measuring the state of deterioration of the battery under test, the DC bus 30 may supply power to a load or receive power from a load. That is, the diagnostic unit 22 measures the state of deterioration of the battery under test during normal power supply or power storage operation of the power storage system 100. While the diagnostic unit 22 is measuring the state of deterioration of the battery under test, at least one other battery 20 of the multiple batteries 20 may be charged or discharged according to the voltage of the DC bus 30, or all other batteries 20 may be charged or discharged according to the voltage of the DC bus 30.

[0047] While the diagnostic unit 22 is measuring the degradation state of the battery under test, the control unit 42 may control at least one or all of the other DC-DC converters 10 to charge and discharge the battery 20. As an example, the control unit 42 may treat the battery under test as a load and perform droop control on at least one or all of the other DC-DC converters 10. This allows the degradation state of the battery under test to be measured without stopping the operation of the power storage system 100.

[0048] The control unit 42 may calculate the total capacity of the plurality of batteries 20 from the measurement results of the deterioration state by the diagnosing unit 22, and control the amount of power conversion of the power conditioner 40 based on the total capacity of the plurality of batteries 20. The calculated total capacity may be in units of W or Wh. As an example, the control unit 42 updates the upper limit of the amount of power that can be converted by the power conditioner 40 based on the calculated total capacity.

[0049] The control unit 42 may control the diagnostic unit 22 to adjust the number of batteries under test to be simultaneously measured based on the capacities of the multiple batteries 20 calculated from the measurement results of the multiple diagnostic units 22. Simultaneous measurement here refers not only to cases where the start and end times of the measurements are completely synchronized, but also to cases where the measurement times overlap. Increasing the number of batteries under test shortens the time required to measure the degradation state of all batteries 20. Meanwhile, the battery 20 being measured no longer contributes to the power supply to or power storage from the DC bus 30, except for discharging during measurement. Therefore, for example, if the capacity of a battery under test is smaller than a predetermined value, the number of batteries under test to be simultaneously measured may be increased by one. The control unit 42 may repeat this procedure until the total capacity of the batteries under test exceeds the predetermined value. The control unit 42 may adjust the number of batteries under test to be simultaneously measured based on the capacities of the multiple batteries 20 corresponding to the most recent measurement results of the multiple diagnostic units 22. The capacities of the multiple batteries 20 may be calculated from past measurement results of the multiple diagnostic units 22.

[0050] When a battery is newly installed in the energy storage system 100 as the battery 20, the diagnostic unit 22 may estimate the state of degradation from the battery specifications or usage history until the initial measurement of the state of degradation is performed. In this case, too, the accuracy of the state of degradation can be improved by later discharging the battery at a constant current or constant power and measuring the state of degradation.

[0051] When a cell is newly attached to the power storage system 100 as the battery 20, the control unit 42 may estimate the capacity of the battery 20 from the specifications or usage history of the battery. The control unit 42 may adjust the number of batteries under test to be measured simultaneously based on the estimated capacity. The control unit 42 may also prioritize measuring the deterioration state of the newly attached battery 20.

[0052] The control unit 42 may sequentially measure the state of deterioration of each battery 20 by controlling the diagnosing unit 22. The control unit 42 may periodically measure the state of deterioration of each battery 20 by controlling the diagnosing unit 22. The state of deterioration of all batteries 20 may be periodically measured. As an example, the state of deterioration may be diagnosed every week, every month, or every year.

[0053] Fig. 4 is a diagram showing a modified example of the power storage system 100 according to the embodiment of the present invention. In Fig. 4, only the configuration from the DC bus 30 to the battery 20 of the power storage system 100 is shown.

[0054] In this example, the battery 20, the diagnostic unit 22, and the DC-DC converter 10 are integrated into one module 52. FIG. 4 illustrates a total of four modules 52, each of which is integrated into one module 52, with each battery 20, each diagnostic unit 22, and each DC-DC converter 10. The module 52 may include a housing that houses the battery 20, the diagnostic unit 22, and the DC-DC converter 10. The housing may be formed of an insulating material such as resin or ceramic. Each module 52 may be connected to the DC bus 30 via a mechanical switch 54. The mechanical switch 54 may be provided between the DC-DC converter 10 and the DC bus 30. As an example, the mechanical switch 54 is a breaker.

[0055] In this example, the battery 20, diagnostic unit 22, and DCDC converter 10 can be attached to and detached from the DC bus 30 together with the module 52. This facilitates replacement of the battery 20. Furthermore, because the DCDC converter 10 makes the voltage of the module 52 equal to the voltage of the DC bus 30, there is no need to match the voltages, and the battery 20 can be replaced easily and safely.

[0056] The energy storage system 100 may include slots that detachably accommodate the modules 52. Each slot has a shape corresponding to the outer shape of the module 52. For example, by installing a module 52 in each slot, the module 52 is connected to the DC bus 30 via a mechanical switch 54. The multiple slots may be arranged side by side in a predetermined direction, or may be arranged two-dimensionally side by side in two directions.

[0057] The control unit 42 may control the DCDC converter 10 in accordance with the measurement result of the deterioration state by the diagnosis unit 22, and may disconnect the DCDC converter 10 from the DC bus 30. As an example, if the above-mentioned maximum allowable C rate falls below a predetermined value, the control unit 42 disconnects the DCDC converter 10 from the DC bus 30. As a result, the battery that has deteriorated and can no longer be used as the battery 20 is disconnected from the energy storage system 100.

[0058] 4 is disconnected from the DC-DC converter 10-1 and the DC bus 30, the control unit 42 first turns off the switches SW11 and SW12 of the DC-DC converter 10. This stops the voltage step-up or step-down operation of the DC-DC converter 10. If the switch SW13 is turned on at this time, the voltage of the capacitor C11 of the DC-DC converter 10 and the voltage of the capacitor C1 of the power conditioner 40 become equal. After the capacitors C1 and C11 have reached the same potential, the switch SW13 is turned off. Finally, the mechanical switch 54 is turned off, and the module 52 is removed from the DC bus 30.

[0059] Although the present invention has been described above using embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It will be apparent to those skilled in the art that various modifications and improvements can be made to the above embodiments. It is clear from the claims that such modifications and improvements can also be included within the technical scope of the present invention.

[0060] 10: DC-DC converter, 16: power storage unit, 20: battery, 22: diagnostic unit, 24: reference potential line, 30: DC bus, 32: high potential line, 40: power conditioner, 42: control unit, 50: transformer, 52: module, 54: mechanical switch, 100: power storage system

Claims

1. A power storage system comprising: a DC bus; a plurality of batteries connected to the DC bus and connected in parallel with each other; a plurality of diagnostic units provided in each of the plurality of batteries, for measuring the state of deterioration of the battery by discharging the battery at a constant current or constant power; and a power conditioner connected to the DC bus and for converting DC power to AC power, wherein at least a portion of the power discharged from a battery under test whose state of deterioration is being measured by the diagnostic unit among the plurality of batteries is charged to at least one other battery among the plurality of batteries or is supplied to the power conditioner.

2. The power storage system according to claim 1, wherein at least a portion of the power discharged from the battery under test among the plurality of batteries is charged into at least one other battery among the plurality of batteries.

3. The energy storage system according to claim 2, wherein the DC bus supplies power to the power conditioner or receives power from the power conditioner while the diagnostic unit is measuring the deterioration state of the battery under test.

4. The power storage system according to claim 2, wherein the diagnostic unit measures the state of deterioration by measuring the amount of drop in battery voltage when measuring the state of deterioration.

5. The power storage system according to claim 4, wherein the diagnostic unit updates the deterioration state based on the amount of drop in the battery voltage and past measurement results of the amount of drop in the battery voltage.

6. The energy storage system according to claim 2, further comprising a control unit capable of communicating with the plurality of diagnostic units, wherein the control unit adjusts the number of the batteries under test to be measured simultaneously based on the capacities of the plurality of batteries calculated from the measurement results of the plurality of diagnostic units.

7. The power storage system according to claim 2, further comprising a control unit capable of communicating with the plurality of diagnostic units and the power conditioner, wherein the control unit calculates a total capacity of the plurality of batteries from the measurement results of the deterioration state of the diagnostic units, and controls the amount of power conversion of the power conditioner based on the total capacity of the plurality of batteries.

8. The power storage system according to any one of claims 1 to 7, further comprising a plurality of DC-DC converters provided between each of the plurality of batteries and the DC bus, wherein the plurality of DC-DC converters control the charge / discharge amounts of the plurality of batteries based on the measurement results of the deterioration state by the diagnostic unit.

9. The power storage system according to claim 2, further comprising a plurality of DC-DC converters provided between each of the plurality of batteries and the DC bus, wherein the battery, the diagnostic unit and the DC-DC converter are integrated into a single module, and the entire module is detachable from the DC bus.

10. The power storage system according to claim 9, further comprising a control unit capable of communicating with the plurality of DC-DC converters, wherein the control unit controls the DC-DC converters in accordance with the measurement results of the deterioration state by the diagnostic unit, and disconnects the DC-DC converters from the DC bus.

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