JP7720280B2 - Input/output upper and lower limit value determination method, power supply control device, and power storage system - Google Patents

Description

The present invention relates to a method for determining upper and lower input/output limits, a power supply control device, and a power storage system.

In the power supply system described in Patent Document 1, due to the demand for high capacity and high output, a high-capacity power supply and a high-output power supply are connected in parallel via a power conversion circuit or the like. This power supply system is installed in a vehicle, and the method of power distribution between the two types of power supplies is changed depending on the driving mode.

JP 2014-187756 A

The power supply system described in Patent Document 1 is installed in a vehicle, but there are also energy storage systems that charge and discharge to and from the power grid. In such energy storage systems, the SOC, which indicates the state of charge of high-output power supplies, can fluctuate significantly when power is distributed by the power company depending on its intended use. For this reason, there is a need to suppress fluctuations in the SOC of high-output power supplies.

A method for determining upper and lower input/output limits that solves the above problem is a method for determining upper and lower input/output limits for a second power source in a power storage system including a first power source and a second power source that has a smaller capacity but a larger output than the first power source. The method includes: a maximum input/output value acquisition step for acquiring the maximum input/output value that can be input/output for each continuous input/output time period at an SOC that indicates the state of charge of the second power source; an input/output requirement value acquisition step for acquiring an input/output requirement value that is the input/output value required to return the SOC to a center SOC that serves as the control center when the second power source performs input/output control for each continuous input/output time period; and a determination step for determining the upper and lower input/output limits for the second power source from the intersection of the maximum input/output value and the input/output requirement value for the same continuous input/output time period on a graph whose first axis is the SOC and whose second axis is the input/output requirement value for each continuous input/output time period.

According to the above method, the upper and lower input/output limits for the SOC of the second power source are determined from the intersection of the maximum input/output values and the input/output requirement values for the same continuous input/output time on a graph showing the maximum input/output values for each continuous input/output time at the SOC of the second power source and a graph showing the input/output requirement values for each continuous input/output time at the SOC of the second power source. This makes it possible to determine the upper and lower input/output limits taking the maximum input/output values into account, allowing the input/output to be set high without causing battery degradation. This makes it possible to suppress fluctuations in the SOC of the second power source.

In the above method for determining upper and lower input/output limits, the absolute values of the determined upper and lower input/output limits peak near the SOC where the maximum input/output value is at its maximum, and decrease as they move away from the peak.

In the above-mentioned method for determining upper and lower input/output limits, since the second power supply functions to back up the first power supply, it is preferable that when there is no external output request, the second power supply inputs power from the first power supply to return the SOC to the center SOC and waits in that state.

According to the above method, the second power supply outputs high power when there is an external output request, and power is input from the first power supply to back up the first power supply. Therefore, upper and lower limits for this power input and output can be determined taking into account the maximum input and output values, allowing the input and output to be set at a large value. This makes it possible to suppress fluctuations in the SOC of the second power supply.

A power supply control device that solves the above problem controls a power storage system including a first power supply and a second power supply that has a smaller capacity but a higher output than the first power supply. The power supply control device obtains the maximum input/output value that can be input/output for each continuous input/output time period for the SOC that indicates the state of charge of the second power supply, obtains input/output requirement values that are the input/output values required to return the SOC to a center SOC that serves as the control center when the second power supply performs input/output control for each continuous input/output time period, and controls the input/output of the second power supply using upper and lower limit values determined from the intersection of the maximum input/output value and the input/output requirement value for the same continuous input/output time period on a graph where the first axis is the SOC and the second axis orthogonal to the first axis is the maximum input/output value for each continuous input/output time period.

With the above configuration, upper and lower limits for input/output at the SOC of the second power source are controlled from the intersection of the maximum input/output value and the input/output requirement value for the same continuous input/output time on a graph showing the maximum input/output value for each continuous input/output time at the SOC of the second power source and a graph showing the input/output requirement value for each continuous input/output time at the SOC of the second power source. This makes it possible to determine the upper and lower limits for input/output taking the maximum input/output value into account, and to set the input/output high within a range that does not cause battery degradation. This makes it possible to suppress fluctuations in the SOC of the second power source.

In the power supply control device, the absolute values of the determined upper and lower limit values of the input and output have a peak near the SOC at which the maximum input and output value is maximized, and decrease as they move away from the peak.
In the above power supply control device, it is preferable that the second power supply inputs the SOC from the first power supply so as to return the SOC to the center SOC when there is no external output request.

With the above configuration, the second power supply provides high output when there is an external output request, and receives input from the first power supply when there is no external output request. This allows the upper and lower limits of input and output to be determined taking into account the maximum input and output values, allowing the input and output to be set at a large value. This makes it possible to suppress fluctuations in the SOC of the second power supply.

The power storage system that solves the above problem includes a first power source, a second power source that has a smaller capacity but a larger output than the first power source, and the above power source control device.
According to the above configuration, upper and lower limit values of input/output at the SOC of the second power source are controlled from the intersection of the maximum input/output value and the input/output requirement value for the same continuous input/output time in a graph showing the maximum input/output value for each continuous input/output time at the SOC of the second power source and a graph showing the input/output requirement value for each continuous input/output time at the SOC of the second power source. This makes it possible to determine the upper and lower limit values of input/output taking the maximum input/output value into consideration, allowing the input/output to be set at a large value. This makes it possible to suppress fluctuations in the SOC of the second power source.

This invention makes it possible to suppress fluctuations in the SOC of high-output power supplies.

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of a power storage system. 3 is a diagram showing a calculation process of an output value performed by the power supply control device of the embodiment. 6 is a graph showing maximum input/output values and input/output requirement values of a second power source of the power supply control device of the embodiment; 6 is a graph showing upper and lower limit values of input and output of a second power source of the power storage system of the embodiment;

Below, one embodiment of a power supply control device and a power storage system will be described with reference to Figures 1 to 4. In the power storage system, the power supply control device controls the output from and input to the power supply.

(Electricity storage system 10)
As shown in FIG. 1 , a power storage system 10 is connected to a commercial power grid 1 and inputs and outputs power to and from the commercial power grid 1. The power storage system 10 includes a capacity battery 11, an output battery 12, and a power supply control device 20. The capacity battery 11 corresponds to a first power source and has a larger capacity than the output battery 12. The capacity battery 11 is, for example, a lithium-ion secondary battery. The output battery 12 corresponds to a second power source and has a larger output than the capacity battery 11. The output battery 12 is, for example, a nickel-metal hydride secondary battery. The output battery 12 functions to back up the capacity battery 11 when output is required. For this reason, the power supply control device 20 waits with its SOC, which indicates the state of charge, returned to a center SOC to respond to sudden requests. When there is no output request from the external commercial power grid 1, the power supply control device 20 inputs power from the capacity battery 11 to the output battery 12. For this reason, the output battery 12 inputs and outputs power so as to return its SOC to the center SOC. The central SOC is an SOC that is the control center when input/output control is performed, and can be set arbitrarily.

A first measuring instrument 11A is provided on the connection line between the capacity battery 11 and the commercial power grid 1, measuring the voltage, current, etc. of the capacity battery 11. The first measuring instrument 11A outputs the measurement results to the power supply control device 20. A second measuring instrument 12A is provided on the connection line between the output battery 12 and the commercial power grid 1, measuring the voltage, current, etc. of the output battery 12. The second measuring instrument 12A outputs the measurement results to the power supply control device 20. The power supply control device 20 calculates the SOC of the capacity battery 11 from the measurement results of the first measuring instrument 11A. The power supply control device 20 also calculates the SOC of the output battery 12 from the measurement results of the second measuring instrument 12A.

(Power supply control device 20)
The Power Control Unit 20 may be configured as one or more processors that execute various processes according to a computer program (software). The processes executed by the Power Control Unit 20, i.e., the processor, include a method for determining upper and lower input/output limits. The method for determining upper and lower input/output limits includes a maximum input/output value acquisition step, an input/output request value acquisition step, and a determination step, as described below. The Power Control Unit 20 may also be configured as a circuitry including one or more dedicated hardware circuits, such as an application-specific integrated circuit (ASIC), or a combination thereof, that executes at least some of the various processes. The processor includes a CPU and memory, such as RAM and ROM. The memory stores program code or instructions configured to cause the CPU to execute the processes. The memory, i.e., computer-readable medium, includes any available medium accessible by a general-purpose or dedicated computer. The programs stored on the computer-readable medium include an input/output determination program. The input/output determination program causes the Power Control Unit 20 to execute the maximum input/output value acquisition step, the input/output request value acquisition step, and the determination step.

The power supply control device 20 includes an acquisition unit 21 and a determination unit 22. The acquisition unit 21 acquires the maximum input/output values that can be input/output during each continuous input/output time at the SOC of the output-type battery 12. The acquisition unit 21 corresponds to a maximum input/output value acquisition unit. The acquisition unit 21 also acquires input/output requirement values, which are the input/output values required for the output-type battery 12 to return its SOC to the center SOC during each continuous input/output time. The acquisition unit 21 corresponds to an input/output requirement value acquisition unit. The determination unit 22 determines the upper and lower limit values for the input/output of the output-type battery 12 based on the maximum input/output values and input/output requirement values for each continuous input/output time.

(Output value calculation process)
Next, the calculation process of the output value of the power supply control device 20 will be described with reference to Fig. 2. When there is an output request from the commercial power grid 1, the power supply control device 20 calculates an output value in accordance with the requested power.

First, the power supply control device 20 acquires the SOC of the output-type battery 12 and calculates the input/output command values for the output-type battery 12 (step S1). That is, the power supply control device 20 calculates the input/output command values for the output-type battery 12 so that the SOC of the output-type battery 12 returns to the center SOC. The power supply control device 20 calculates the input/output command values based on the upper and lower input/output limit values for the output request.

Next, the power supply control device 20 calculates the power requirement of the capacity battery 11 (step S2). That is, the power requirement of the capacity battery 11 is calculated by subtracting the input/output instruction value of the output battery 12 calculated in step S1 from the output requirement of the commercial power grid 1.

Next, the power supply control device 20 calculates the power requirement of the output-type battery 12 (step S3). That is, the power requirement of the output-type battery 12 is calculated by subtracting the power requirement of the capacity-type battery 11 calculated in step S2 from the output requirement of the commercial power grid 1.

Next, the power supply control device 20 can obtain the output of the capacity-type battery 11 calculated in step S1 and the output of the output-type battery 12 calculated in step S2 as output values.

(Calculation of upper and lower limits of input and output)
Next, with reference to Figures 3 and 4, the calculation of the upper and lower limit values of the input and output of the output-type battery 12 by the power supply control device 20 will be described. The upper and lower limit values of the input and output are calculated and set in advance. The power supply control device 20 may calculate and update the upper and lower limit values of the input and output at any timing. In this embodiment, the central SOC of the output-type battery 12 is set to 60%. In Figures 3 and 4, the first horizontal axis represents the SOC, and the second vertical axis, which is perpendicular to the first axis, represents the input and output value.

The power supply control device 20 acquires the maximum input/output value graphs A1, A2, A3, ... and the input/output requirement value graphs B1, B2, B3, ... in advance when the output-type battery 12 is installed in the energy storage system 10. This process corresponds to the maximum input/output value acquisition step and the input/output requirement value acquisition step.

As shown in FIG. 3, the mountain-shaped graphs A1, A2, A3, etc. indicate the maximum input/output values that can be input/output at each continuous input/output time at the SOC of the output-type battery 12. The peak is at the SOC at which the maximum input/output value is greatest. For graphs A1, A2, A3, etc., the maximum input/output value decreases as the continuous input/output time increases. While the graphs show continuous input/output times up to 3 seconds, the graphs remain similar even after 4 seconds. Furthermore, graphs B1, B2, B3, etc., in which the input/output value passes through zero at a center SOC of 60%, indicate the input/output requirement value, which is the input/output value required for the output-type battery 12 to return its SOC to the center SOC during each continuous input/output time. For graphs B1, B2, B3, etc., the maximum input/output value decreases and the slope becomes shallower as the continuous input/output time increases. While the graphs show continuous input/output times up to 3 seconds, the graphs remain similar even after 4 seconds.

Note that Figure 3 only shows maximum input/output values and input/output demand values on the discharge side where the SOC is 60% or above. Maximum input/output values and input/output demand values also exist on the charge side where the SOC is below 60%, and the graph is point-symmetrical with respect to the discharge side and the center SOC, but these are omitted here. The graph of maximum input/output values on the charge side is a downward-convex mountain shape. The graph of input/output demand values on the charge side shows that the input demand value increases as the SOC decreases from the center SOC. Therefore, on the discharge side as well, the upper and lower input/output limit values can be obtained by connecting the intersections of the maximum input/output values and input/output demand values for each continuous input/output time.

Note that in Figure 3, the SOC at which the maximum input/output values are greatest and the center SOC coincide, but they do not have to coincide. In other words, the SOC at which the maximum input/output values are greatest is determined by the battery, and the center SOC is set by the user. In particular, graphs A1, A2, A3, etc. have peaks near the SOC at which the maximum input/output values are greatest, and decrease the further away from the peak. The graph in Figure 4 is an example; if the center SOC setting is changed, the shape of the graph will also change.

The determination unit 22 calculates the intersections between the graphs A1, A2, A3, ... of maximum input/output values and the graphs B1, B2, B3, ... of input/output demand values, which have the same continuous input/output time. The determination unit 22 can then determine the upper and lower limit values of the input/output by connecting these calculated intersections. This process corresponds to the determination step.

As shown in Figure 4, the absolute values of the determined upper and lower input/output limits peak on both the charge and discharge sides near the SOC where the maximum input/output values are at their maximum, and decrease as they move away from the peaks.

The power supply control device 20 determines the input/output instruction value based on the determined input/output upper and lower limit values and the output request. If the input/output value of the output request is smaller than the upper or lower limit values, the power supply control device 20 sets the output request as the input/output instruction value; if the input/output value of the output request is larger than the upper or lower limit values, the power supply control device 20 sets the upper or lower limit values as the input/output instruction value.

According to the above, the upper and lower limit values of the input and output can be determined taking into consideration the maximum input and output values, and the input and output can be set to large values.
Next, the effects of this embodiment will be described.

(1) The upper and lower limit values of input and output at the SOC of the output-type battery 12 are determined from the intersection of the maximum input and output values and the input and output requirement values for the same continuous input and output time on graphs A1, A2, A3, ... showing the maximum input and output values for each continuous input and output time at the SOC of the output-type battery 12 and graphs B1, B2, B3, ... showing the input and output requirement values for each continuous input and output time at the SOC of the output-type battery 12. This makes it possible to determine the upper and lower limit values of input and output taking the maximum input and output values into consideration, and to set the input and output to a large value within a range that does not cause battery degradation. This makes it possible to suppress fluctuations in the SOC of the output-type battery 12.

(2) When there is an external output request, the output-type battery 12 backs up the capacity-type battery 11 by providing high output, and when there is no external output request, power is input from the capacity-type battery 11. Therefore, it is possible to determine upper and lower limits for input and output that take into account the maximum input and output values of this power, allowing the input and output to be set at a large value. This makes it possible to suppress fluctuations in the SOC of the output-type battery 12.

(Other embodiments)
The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

In the above embodiment, the absolute values of the determined upper and lower input/output limits peak near the center SOC and decrease as they move away from the peak because the SOC at which the maximum input/output value is greatest coincides with the center SOC. However, for example, if the SOC at which the maximum input/output value is greatest does not coincide with the center SOC, the absolute values of the determined upper and lower input/output limits will be zero at the center SOC, peak near the center SOC, and will not decrease as they move away from the peak; however, such upper and lower input/output limits are acceptable. Even with such upper and lower input/output limits, the input and output can be set large, thereby suppressing fluctuations in the SOC of the output-type battery 12.

In the above embodiment, the first axis of the SOC is the horizontal axis and the second axis of the input/output value is the vertical axis. However, the first axis of the SOC may be the vertical axis and the second axis of the input/output value may be the horizontal axis.
In the above embodiment, the upper and lower limit values of input and output are determined by the power supply control device 20. However, the power supply control device 20 may not include the acquisition unit 21 and the determination unit 22, and may control the upper and lower limit values of input and output based on values that have been similarly determined in advance by another device.

- In the above embodiment, the capacity-type battery 11, which is the first power source, is a lithium-ion secondary battery, and the output-type battery 12, which is the second power source, is a nickel-metal hydride secondary battery. However, the first power source and the second power source may be combined in other ways, as long as the second power source has a smaller capacity but a larger output than the first power source.

- In the above embodiment, the power storage system 10 is connected to the commercial power grid 1. However, the connection of the power storage system 10 is not limited to the commercial power grid 1, and it may also be to other devices that require a power source.

REFERENCE SIGNS LIST 1 Commercial power grid 10 Energy storage system 11 Capacitive battery as first power source 11A First measuring instrument 12 Output battery as second power source 12A Second measuring instrument 20 Power supply control device 21 Acquisition unit 22 Determination unit

Claims (7)

1. A method for determining upper and lower input/output limit values for a power storage system including a first power source and a second power source having a smaller capacity but a larger output than the first power source, the method comprising:
a maximum input/output value acquisition step of acquiring a maximum input/output value that can be input/output during each continuous input/output time in an SOC that indicates a state of charge of the second power source;
an input/output requirement value acquisition step of acquiring an input/output requirement value that is an input/output value required to return the SOC to a center SOC that serves as a control center when the second power source performs input/output control during each of the continuous input/output times;
a determination step of determining upper and lower input/output limit values of the second power source from an intersection of the maximum input/output value and the input/output required value for the same continuous input/output time on a graph having a first axis representing the SOC and a second axis perpendicular to the first axis representing the maximum input/output value for each continuous input/output time, and a graph having the first axis representing the SOC and the second axis representing the input/output required value for each continuous input/output time. The method for determining upper and lower input/output limits according to claim 1 , wherein the absolute values of the determined upper and lower input/output limits have a peak near an SOC at which the maximum input/output value is maximized, and decrease as the value moves away from the peak. 3. The method for determining input/output upper and lower limit values according to claim 1 or 2, wherein the second power supply functions to back up the first power supply, and when there is no external output request, the second power supply inputs the SOC from the first power supply so as to return the SOC to the center SOC and waits while returning the SOC to the center SOC. A power supply control device that controls a power storage system including a first power supply and a second power supply that has a smaller capacity but a larger output than the first power supply,
obtaining a maximum input/output value that can be input/output during each continuous input/output time in an SOC that indicates the state of charge of the second power source;
acquire an input/output requirement value that is an input/output value required to return the SOC to a center SOC that serves as a control center when the second power source performs input/output control during each of the continuous input/output times;
A power supply control device that controls the input/output of the second power supply using upper and lower limit values determined from the intersection of the maximum input/output value and the input/output required value for the same continuous input/output time on a graph in which a first axis is the SOC and a second axis perpendicular to the first axis is the maximum input/output value for each continuous input/output time, and a graph in which the first axis is the SOC and the second axis is the input/output required value for each continuous input/output time. The power supply control device according to claim 4 , wherein the absolute values of the determined upper and lower limit values of the input and output have a peak near the SOC at which the maximum input and output value is maximized, and decrease as the value moves away from the peak. The power supply control device according to claim 4 , wherein the second power supply inputs the SOC from the first power supply so as to return the SOC to the center SOC when there is no external output request. a first power source;
a second power source having a smaller capacity but a larger output than the first power source;
A power storage system comprising: the power supply control device according to any one of claims 4 to 6.