Control device for secondary battery system

Abstract

A control device (4) for a secondary battery system (1) comprises: an operation control unit (40) that controls the operation of a power conversion device (3) so that the output power from a secondary battery (2) is equal to or less than a first power limiter (L1); a current monitoring unit (41) that monitors the output current (Iout) of the secondary battery (2); a determination unit (42) that determines whether or not the output current (Iout) exceeds a current limiter; a current excess amount calculation unit (43) that calculates an excess amount (EA) of the output current (Iout) with respect to the current limiter; and a power limiter calculation unit (44) that inputs, to the operation control unit (40), a second power limiter (L2) for setting the excess amount (EA) calculated by the current excess amount calculation unit (43) to 0 or less. When receiving the input of the second power limiter (L2) from the power limiter calculation unit (44), the operation control unit (40) controls the operation of the power conversion device (3) so that the output power from the secondary battery (2) is equal to or less than the second power limiter (L2).

Description

Control device for a secondary battery system

[0001] The present invention relates to a control device for a secondary battery system.

[0002] As this type of secondary battery system that has been conventionally used, for example, the configurations shown in Patent Document 1 below can be cited. Patent Document 1 discloses a secondary battery system (a linked system equipped with a power storage device) including a secondary battery, a power conversion device (such as a bidirectional converter) that converts the DC power of the secondary battery into AC power, and a control device (control unit).

[0003] International Publication No. 2011 / 052314

[0004] In the secondary battery system as described above, a power limiter corresponding to the depth of the secondary battery is input to the power conversion device, and the operation of the power conversion device is controlled so that the output power from the secondary battery becomes equal to or less than the power limiter. As the power limiter, a general-purpose one that can cope with many combinations of secondary batteries and power conversion devices is used. If power is output within the range of the power limiter during discharge, an excessive current is less likely to flow from the secondary battery. However, depending on the individual differences between the secondary battery and the power conversion device and the deterioration of the secondary battery, an excessive current may flow from the secondary battery even when power is output within the range of the power limiter. When an excessive current flows from the secondary battery, there is a risk of shortening the life of the secondary battery.

[0005] The present invention has been made to solve the above problems, and one of its purposes is to provide a control device for a secondary battery system that can reduce the risk of an excessive current flowing from the secondary battery.

[0006] [1] In one embodiment, the present invention is a control device for a secondary battery system, the secondary battery system comprising a secondary battery, a power converter that converts the DC power of the secondary battery into AC power and outputs it, and the control device, the control device inputs a first power limiter corresponding to the depth of the secondary battery to the power converter and controls the operation of the power converter so that the output power from the secondary battery is less than or equal to the first power limiter, the control device includes an operation control unit that monitors the output current of the secondary battery when the operation control unit is controlling the operation of the power converter, and compares the output current monitored by the current monitoring unit with the current limiter corresponding to the depth of the secondary battery, and the output current is less than or equal to the The present invention relates to a control device for a secondary battery system, comprising: a determination unit that determines whether or not the output current exceeds a current limiter; a current excess amount calculation unit that calculates the amount of the output current exceeding the current limiter when the determination unit determines that the output current exceeds the current limiter; and a power limiter calculation unit that calculates a second power limiter to make the excess amount calculated by the current excess amount calculation unit zero or less, and inputs the second power limiter to the operation control unit, wherein the operation control unit, upon receiving the input of the second power limiter from the power limiter calculation unit, inputs the second power limiter to the power converter and controls the operation of the power converter so that the output power from the secondary battery is less than or equal to the second power limiter.

[0007] [2] The present invention may also relate to a control device for a secondary battery system as described in paragraph 1, wherein when the operation control unit receives an input for the second power limiter from the power limiter calculation unit, it updates and holds the value of the first power limiter corresponding to the depth of the secondary battery when the determination unit determines that the output current exceeds the current limiter, to the value of the second power limiter.

[0008] [3] The present invention may relate to a control device for a secondary battery system as described in paragraph 2, wherein the value of the first power limiter is updated to the value of the second power limiter for each 1 Ah depth of the secondary battery.

[0009] [4] The present invention may also relate to a control device for a secondary battery system according to any one of the first to third claims, wherein the second power limiter is obtained by subtracting a value obtained by multiplying the excess amount by a predetermined gain from the first power limiter corresponding to the depth of the secondary battery when the determination unit determines that the output current exceeds the current limiter.

[0010] [5] The present invention may relate to a control device for a secondary battery system as described in paragraph 4, wherein the gain is 1%.

[0011] According to one embodiment of the control device for a secondary battery system of the present invention, when the operation control unit receives input of a second power limiter from the power limiter calculation unit, it inputs the second power limiter to the power converter and controls the operation of the power converter so that the output power from the secondary battery is less than or equal to the second power limiter, thereby reducing the risk of excessive current flowing from the secondary battery.

[0012] This is a schematic block diagram showing a secondary battery system according to an embodiment of the present invention. This is a block diagram of the control device shown in Figure 1. This is a graph showing an example of the change in the output current of the secondary battery when a general-purpose value (initial value) is used as the first power limiter. This is a graph showing an example of the change in the output current of the secondary battery when the value of the first power limiter is updated to and held as the value of the second power limiter.

[0013] Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. The present invention is not limited to each embodiment, and can be materialized by modifying the components without departing from the spirit of the invention. Furthermore, various inventions can be formed by appropriately combining the multiple components disclosed in each embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, components from different embodiments may be appropriately combined.

[0014] Figure 1 is a schematic block diagram showing a secondary battery system 1 according to an embodiment of the present invention. As shown in Figure 1, the secondary battery system 1 includes a secondary battery 2, a power conversion device 3, and a control device 4.

[0015] The secondary battery 2 is electrically connected to the power converter 3 and the control device 4. The secondary battery 2 may be a module battery including a collection of multiple single sodium-sulfur cells connected in series and / or parallel.

[0016] The power converter 3 is a device that converts the DC power from the secondary battery 2 into AC power and outputs it. The AC power output from the power converter 3 is supplied to the loads of the power system connected to the secondary battery system 1. The power converter 3 may convert the AC power from the power system into DC power and input it to the secondary battery 2.

[0017] The power conversion device 3 may include a converter 30, a transformer 31, and a conversion control unit 32. The converter 30 is composed of, for example, an inverter and a converter, and is connected to the secondary battery 2. The converter 30 performs DC-AC power conversion. The transformer 31 is placed between the converter 30 and the power system and adjusts the voltage of the AC power from and to the converter 30. The conversion control unit 32 is connected to the converter 30 and the transformer 31 and controls the operation of the converter 30 and the transformer 31. The conversion control unit 32 may be composed of a computing device such as a computer that operates based on a program.

[0018] The control device 4 is connected to the secondary battery 2 and the power converter 3. The control device 4 may be composed of a computing device such as a computer that operates based on a program. The control device 4 may be housed together with the secondary battery 2 and the power converter 3 in a container (not shown), for example.

[0019] Next, Figure 2 is a block diagram of the control device 4 in Figure 1. As shown in Figure 2, the control device 4 includes an operation control unit 40, a current monitoring unit 41, a determination unit 42, a current excess amount calculation unit 43, and a power limiter calculation unit 44. Each of these units may be implemented in hardware and / or software within the control device 4.

[0020] The operation control unit 40 inputs a first power limiter L1 corresponding to the depth of the secondary battery 2 to the power converter 3 and controls the operation of the power converter 3 so that the output power (DC power) from the secondary battery 2 is less than or equal to the first power limiter L1.

[0021] The depth of the secondary battery 2 is the remaining capacity (Ah) relative to the discharge capacity (Ah) of the secondary battery 2. As the secondary battery 2 discharges, its depth increases. The operation control unit 40 maintains a value for the first power limiter L1 for each depth of the secondary battery 2. The output power of the secondary battery 2 is controlled by the power setting of the power converter 3, and the value of this power setting is set in the first power limiter L1, which is input from the operation control unit 40 to the power converter 3 (more specifically, the conversion control unit 32). In other words, the first power limiter L1 defines the maximum power that can be output from the secondary battery 2 for each depth of the secondary battery 2.

[0022] The current monitoring unit 41 monitors the output current Iout of the secondary battery 2 when the operation control unit 40 is controlling the operation of the power converter 3. The current monitoring unit 41 inputs the output current Iout to the determination unit 42.

[0023] The determination unit 42 compares the output current Iout, monitored by the current monitoring unit 41, with a current limiter corresponding to the depth of the secondary battery 2, and determines whether the output current Iout exceeds the current limiter. The current limiter defines the maximum current that can be output from the secondary battery 2 for each depth of the secondary battery 2. The maximum current is set to prevent excessive current from flowing from the secondary battery 2, which would shorten the lifespan of the secondary battery 2. The determination unit 42 inputs the determination result JR to the current excess amount calculation unit 43. The determination result JR may include whether the output current Iout exceeds the current limiter, the value of the output current Iout, and the value of the current limiter.

[0024] The current excess amount calculation unit 43 calculates the excess amount EA of the output current Iout relative to the current limiter when the determination unit 42 determines that the output current Iout exceeds the current limiter. The current excess amount calculation unit 43 inputs the excess amount EA to the power limiter calculation unit 44.

[0025] The power limiter calculation unit 44 calculates a second power limiter L2 to make the excess amount EA calculated by the current excess amount calculation unit 43 0 or less, and inputs the second power limiter L2 to the operation control unit 40.

[0026] When the operation control unit 40 receives input from the power limiter calculation unit 44 for the second power limiter L2, it inputs the second power limiter L2 to the power converter 3 and controls the operation of the power converter 3 so that the output power from the secondary battery 2 is less than or equal to the second power limiter L2.

[0027] Here, current is output from the secondary battery 2 according to the power setting of the power converter 3. The first power limiter L1 is a general-purpose type that can accommodate many combinations of secondary battery 2 and power converter 3, and if the power output during discharge is within the range of the first power limiter L1, excessive current will not flow from the secondary battery 2. However, due to individual differences in the secondary battery 2 and power converter 3, or deterioration of the secondary battery 2, excessive current may flow from the secondary battery 2 even if the power output is within the range of the first power limiter L1. If excessive current flows from the secondary battery 2, it may shorten the lifespan of the secondary battery 2. As in the control device 4 of this embodiment, when the operation control unit 40 receives input of the second power limiter L2 from the power limiter calculation unit 44, it inputs the second power limiter L2 to the power converter 3 and controls the operation of the power converter 3 so that the output power from the secondary battery 2 is less than or equal to the second power limiter L2, thereby reducing the risk of excessive current flowing from the secondary battery 2. More specifically, this reduces the risk of excessive current continuing to flow from the secondary battery 2.

[0028] When the operation control unit 40 receives input from the power limiter calculation unit 44 to the second power limiter L2, it updates and holds the value of the first power limiter L1 corresponding to the depth of the secondary battery 2 at the time the determination unit 42 determines that the output current Iout exceeds the current limiter, and sets it to the value of the second power limiter L2. That is, the value of the first power limiter L1 is updated to a value that takes into account individual differences in the secondary battery 2 and the power converter 3, as well as the degradation of the secondary battery 2, and the first power limiter L1 with the updated value is used the next time. By updating the value of the first power limiter L1, the excess amount EA of the output current Iout of the secondary battery 2 relative to the current limiter can be suppressed. In addition, the period during which excessive current flows from the secondary battery 2 can be reduced.

[0029] The value of the first power limiter L1 may be updated arbitrarily, but it is preferable that it be updated to the value of the second power limiter L2 for each 1Ah depth of the secondary battery 2 (in 1Ah increments). In other words, it is preferable that the second power limiter L2 is calculated each time the depth of the secondary battery 2 changes by 1Ah and input to the operation control unit 40. With this configuration, even if the secondary battery 2 deteriorates, the excess amount EA of the output current Iout of the secondary battery 2 relative to the current limiter can be suppressed. As the discharge depth progresses towards the end of discharge, the corresponding current limiter decreases. In this context, updating the current limiter at a finer granularity leads to better suppression of the excess amount EA.

[0030] The second power limiter L2 may be calculated based on various formulas, but it is preferable to subtract the value obtained by multiplying the excess amount EA by a predetermined gain G from the first power limiter L1, which corresponds to the depth of the secondary battery 2 when the determination unit 42 determines that the output current Iout exceeds the current limiter. By calculating the second power limiter L2 from the current excess amount with the first power limiter L1 as a reference in this way, the power limiter can be lowered by the amount that exceeds the limit. This avoids excessive output suppression and allows for maximum discharge.

[0031] The gain G obtained when acquiring the second power limiter L2 can be changed arbitrarily, but it is preferable to set it to 1%. By setting the gain G to 1%, excessive current suppression can be avoided while protecting the current limiter, and maximum discharge can be achieved. For example, if the gain G is set to a larger value such as 5%, the response to suppression will be faster, but the output current may be excessively suppressed.

[0032] Next, Figure 3 is a graph showing an example of the change in the output current Iout of the secondary battery 2 when a general-purpose value (initial value) is used as the first power limiter L1. The upper graph in Figure 3 shows the relationship between the output power from the secondary battery 2 and the power limiters (first power limiter L1 and second power limiter L2), and the lower graph shows the relationship between the output current Iout from the secondary battery 2 and the current limiter. The horizontal axis of both graphs is the depth of the secondary battery 2.

[0033] As schematically shown in the upper graph of Figure 3, power is output from the secondary battery 2 according to the power setting of the power converter 3. For example, when a large piece of equipment in a factory is operated, the power consumption in the factory increases sharply. Such a sharp increase in power consumption may be covered by the power of the secondary battery 2 installed in the factory. In such cases, the output power from the secondary battery 2 increases. When the output power from the secondary battery 2 reaches the first power limiter L1, as shown in (1), the output current Iout of the secondary battery 2 may exceed the current limiter, as shown in (2). This is due to individual differences in the secondary battery 2 and the power converter 3, or deterioration of the secondary battery 2. When the output current Iout of the secondary battery 2 exceeds the current limiter in this way, a second power limiter L2 is calculated to keep the excess amount EA of the output current Iout relative to the current limiter at 0 or less. At this time, as shown in (3), the second power limiter L2 is input to the power converter 3, and the operation of the power converter 3 is controlled so that the output power from the secondary battery 2 is less than or equal to the second power limiter L2. This reduces the risk of excessive current flowing from the secondary battery 2 (it reduces the risk of excessive current continuing to flow from the secondary battery 2).

[0034] Next, Figure 4 is a graph showing an example of the change in the output current Iout of the secondary battery 2 when the value of the first power limiter L1 is updated to and held at the value of the second power limiter L2. Similar to Figure 3, the upper graph in Figure 4 shows the relationship between the output power from the secondary battery 2 and the power limiters (first power limiter L1 and second power limiter L2), and the lower graph shows the relationship between the output current Iout from the secondary battery 2 and the current limiter. The horizontal axis of both graphs represents the depth of the secondary battery 2.

[0035] In the example shown in Figure 4, the value of the first power limiter L1 is updated and held by the operation control unit 40 to the value of the second power limiter L2. When the output power from the secondary battery 2 reaches the first power limiter L1, as shown in (1), even if the output current Iout of the secondary battery 2 exceeds the current limiter, as shown in (2), the excess amount EA of the output current Iout relative to the current limiter is smaller compared to the case in Figure 3. This is because the value of the first power limiter L1 is updated to a value that takes into account individual differences in the secondary battery 2 and the power converter 3, as well as the degradation of the secondary battery 2. From this, it can be seen that the excess amount EA can be suppressed by updating and holding the value of the first power limiter L1 to the value of the second power limiter L2. Note that even when the value of the first power limiter L1 is updated, the output current Iout of the secondary battery 2 will exceed the current limiter when the secondary battery 2 deteriorates.

[0036] When the output current Iout of the secondary battery 2 exceeds the current limiter, a second power limiter L2 is calculated to keep the excess amount EA below zero. As shown in (3), the second power limiter L2 is input to the power converter 3, and the operation of the power converter 3 is controlled so that the output power from the secondary battery 2 is less than or equal to the second power limiter L2. In this case, because the excess amount EA is small, the difference between the value of the second power limiter L2 and the value of the first power limiter L1 is small, and the time until the output current Iout of the secondary battery 2 falls below the current limiter is shorter compared to the case in Figure 3. From this, it can be seen that the period during which excess current flows from the secondary battery 2 can be shortened.

[0037] Although preferred embodiments of the present invention have been described in detail above with reference to the attached drawings, the present invention is not limited to these examples. It is clear to any person with ordinary skill in the art to which the present invention belongs that various modifications or alterations can be conceived within the scope of the technical idea described in the claims, and these are also understood to fall within the technical scope of the present invention.

[0038] 1: Secondary battery system 2: Secondary battery 3: Power conversion device 4: Control device 40: Operation control unit 41: Current monitoring unit 42: Determination unit 43: Current excess amount calculation unit 44: Power limiter calculation unit EA: Excess amount G: Gain Iout: Output current L1: First power limiter L2: Second power limiter

Claims

1. A control device for a secondary battery system, wherein the secondary battery system comprises a secondary battery, a power converter that converts the DC power of the secondary battery into AC power and outputs it, and the control device, wherein the control device includes: an operation control unit that inputs a first power limiter corresponding to the depth of the secondary battery to the power converter and controls the operation of the power converter so that the output power from the secondary battery is less than or equal to the first power limiter; a current monitoring unit that monitors the output current of the secondary battery when the operation control unit is controlling the operation of the power converter; a determination unit that compares the output current monitored by the current monitoring unit with the current limiter corresponding to the depth of the secondary battery and determines whether the output current exceeds the current limiter; and a current excess amount calculation unit that calculates the excess amount of the output current relative to the current limiter when the determination unit determines that the output current exceeds the current limiter. A control device for a secondary battery system, comprising: a power limiter calculation unit that calculates a second power limiter to make the excess amount calculated by the current excess amount calculation unit zero or less, and inputs the second power limiter to the operation control unit, wherein the operation control unit, upon receiving input of the second power limiter from the power limiter calculation unit, inputs the second power limiter to the power converter and controls the operation of the power converter so that the output power from the secondary battery is less than or equal to the second power limiter.

2. The control device for a secondary battery system according to claim 1, wherein when the operation control unit receives an input for the second power limiter from the power limiter calculation unit, it updates and holds the value of the first power limiter corresponding to the depth of the secondary battery when the determination unit determines that the output current exceeds the current limiter, to the value of the second power limiter.

3. The control device for a secondary battery system according to claim 2, wherein the value of the first power limiter is updated to the value of the second power limiter for each 1 Ah depth of the secondary battery.

4. The control device for a secondary battery system according to any one of claims 1 to 3, wherein the second power limiter is obtained by subtracting a value obtained by multiplying the excess amount by a predetermined gain from the first power limiter corresponding to the depth of the secondary battery when the determination unit determines that the output current exceeds the current limiter.

5. The control device for a secondary battery system according to claim 4, wherein the gain is 1%.

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