JP2020085561A - Method for determining degradation of zinc - Google Patents

Abstract

To detect the situation of generation of abnormal insulation between electrodes during float charging and precisely determine degradation in a zinc battery.SOLUTION: The method for determining degradation in a zinc battery according to an embodiment includes: an acquisition step of acquiring a transition of the amount of a current flowing to a zinc battery while the zinc battery is being float-charged; a calculation step of calculating a current increase rate from a reference value in the transition of the current amount; and a determination step of determining degradation in the zinc battery on the basis of the current increase rate.SELECTED DRAWING: Figure 4

Description

The present invention relates to a method for determining deterioration of a zinc battery.

Conventionally, a method of determining deterioration of a storage battery is known. For example, Patent Document 1 describes a method of estimating the deterioration state of a rechargeable battery. This method includes the steps of generating a coulomb count value by integrating the charge/discharge current of the battery, monitoring the state of the battery, and confirming that the battery has been charged/discharged by a predetermined charge amount based on the coulomb count value. And a change amount ΔX according to the state of the battery measured during the period in which the predetermined charge amount is charged/discharged. And changing only.

JP, 2017-116522, A

There are various phenomena in deterioration of a storage battery, but in a zinc battery, an insulation abnormality such as a short circuit between electrodes or a reduction in resistance occurs due to a phenomenon such as dendrite. If insulation abnormality occurs between the electrodes, excessive current continues to flow to the zinc battery, which may cause heat generation in the battery and lead to thermal runaway of the zinc battery. It is desirable to detect in advance and prevent thermal runaway (thermal runaway). However, since the constant voltage is applied during the float charging, the information obtained from the zinc battery is limited. An object of the present invention is to provide a method of determining deterioration of a zinc battery, which can detect the occurrence of insulation abnormality between electrodes in advance during float charging and accurately determine deterioration of the zinc battery.

A determination method of deterioration of a zinc battery according to one aspect of the present invention includes an acquisition step of acquiring a transition of a current amount flowing to the zinc battery during float charging of the zinc battery, and an increase in current from a reference value in the transition of the current amount. And a determination step of determining deterioration of the zinc battery based on the current increase degree. During float charging, the amount of current flowing to the zinc battery is approximately constant or changes slightly. However, when insulation abnormality such as short circuit between electrodes or reduction in resistance occurs, the amount of current increases extremely. In this determination method, since the deterioration of the zinc battery is judged based on the current increase degree from the reference value, the insulation abnormality between the electrodes can be detected well even during the float charging, and the deterioration of the zinc battery can be accurately performed. Can be determined.

In the above determination method, in the determination step, it may be determined that the zinc battery is in a deteriorated state when the current increase degree is equal to or more than the threshold value. For example, with such a method, it is possible to detect the insulation abnormality between the electrodes more accurately.

In the above determination method, in the determination step, the zinc battery is determined to be in the first deterioration state when the current increase degree is the first threshold value or more, and the current increase degree is the second threshold value or more and less than the first threshold value. In some cases, it may be determined that the zinc battery is in the second deterioration state in which the degree of deterioration is smaller than that in the first deterioration state. For example, by determining the deterioration state of the zinc battery stepwise in this manner, it is possible to easily determine the replacement of the zinc battery or the like.

In the above determination method, in the calculation step, the current amount at the time when the fluctuation of the current amount converges within a predetermined range may be used as a reference value, or the discharge process performed immediately before the float charging may be performed. Alternatively, the amount of current acquired at the time when a predetermined time has elapsed from the start of charging may be used as the reference value. For example, one of these methods can set a more appropriate reference value in the determination of deterioration of the zinc battery.

In the above determination method, in the determination step, the deterioration of the zinc battery may be determined based on the number of times a monitoring event that the current increase degree is equal to or higher than the threshold value has occurred. The insulation abnormality due to the dendrite does not continue to occur, and the zinc battery reaches the end of its life by repeatedly generating and recovering the insulation abnormality. Therefore, it may be difficult to determine the deterioration of the zinc battery if the insulation abnormality occurs only once. Even in such a case, the deterioration of the zinc battery can be determined more accurately by determining the deterioration of the zinc battery based on the number of times that the abnormality in the current increase degree (monitoring event) has occurred. In this case, in the determination step, the zinc battery may be determined to be in a deteriorated state when the number of consecutive monitoring events is equal to or greater than a predetermined threshold value, or a monitoring event has occurred. It may be determined that the zinc battery is in a deteriorated state when the number of times of accumulation is equal to or more than a predetermined threshold value.

In the above determination method, the zinc battery may be a nickel zinc battery. In this case, the above determination method is particularly effective.

According to the method for determining deterioration of a zinc battery according to one aspect of the present invention, it is possible to detect the occurrence of insulation abnormality between electrodes in advance during float charging and accurately determine the deterioration of the zinc battery.

FIG. 1 schematically shows an example of the configuration of the power storage system 1 and its surroundings. FIG. 2 shows a functional configuration of the overall controller 30. FIG. 3 is a graph showing an outline of float charging. FIG. 4 is a flowchart showing an example of the operation of the overall controller 30, and specifically shows processing for one power storage device 10. 5A to 5C show various methods of determining the reference value. FIG. 6 shows an example of the determination process (determination step). FIG. 7 is a graph showing changes in the discharge capacity retention rate of five nickel-zinc batteries that underwent the float charge life test under condition 4 (temperature 40° C.). FIG. 8A is a chart showing the measured discharge capacity, and FIG. 8B is a chart showing the discharge capacity retention rate calculated from FIG. 8A (based on FIG. 7). .. FIG. 9 is a graph showing changes in the amount of charging current in five nickel-zinc batteries that underwent the float charging life test under condition 4. FIG. 10 is a graph showing changes in the discharge capacity retention rate of five nickel-zinc batteries that underwent the float charge life test under condition 5 (temperature 55° C.). 11(a) is a chart showing the measured discharge capacity, and FIG. 11(b) is a chart showing the discharge capacity retention rate calculated from FIG. 11(a) (based on FIG. 10). .. FIG. 12 is a graph showing changes in the amount of charging current in five nickel-zinc batteries that underwent the float charging life test under condition 5. FIG. 13 shows another example of the determination process (determination step). FIG. 14 shows another example of the determination process (determination step).

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same or equivalent elements will be denoted by the same reference symbols, without redundant description.

[Overall configuration of power storage system]
The power storage system 1 is a system that stores generated electricity and supplies the stored electricity as needed. The scene to which the power storage system 1 is applied is not limited, and for example, the power storage system 1 can be applied to real estate and movables. As an example of application to a real estate, the power storage system 1 may manage electricity generated using renewable energy, and can be used in various places such as a home, an office, a factory, and a farm. As an example of application to movables, the power storage system 1 may be mounted as a power source on a moving body such as an automobile.

An overview of an electric power system including a power storage system 1 will be described with reference to FIG. 1. FIG. 1 is a diagram schematically showing an example of the configuration of the power storage system 1 and its surroundings. The power storage system 1 is provided between a supply element 2 capable of supplying power to the power storage system 1 and a demand element 4 capable of receiving power from the power storage system 1. A DC system including the power storage system 1 and the supply element 2 and an AC system including the demand element 4 are electrically connected via a PCS (power conditioning system) 3. The power storage system 1, the supply element 2, and the PCS 3 are electrically connected via a DC (Direct Current) bus 6 in which a direct current flows. The demand element 4 and the PCS 3 are electrically connected via an AC (Alternating Current) bus 7 in which an alternating current flows. The electricity generated by the supply element 2 or the electricity stored in the power storage system 1 is supplied to the demand element 4. The power storage system 1 may play a role of mitigating fluctuations in the power supply from the supply element 2 to the demand element 4 by using the storage battery as a cushion.

The supply element 2 is a device or equipment capable of supplying electric power to the power storage system 1. The type of supply element 2 is not limited in any way. For example, the supply element 2 may be a power generation device that generates electricity using renewable energy. The power generation method and the type of power generation device are not limited at all, and for example, the power generation device may be a solar power generation device or a wind power generator. Alternatively, the supply element 2 may be a motor mounted on a mobile.

The demand element 4 is a device or equipment that can receive electric power from the power storage system 1. The type of demand element 4 is not limited at all. For example, the supply element may be an external power system which is a facility of a commercial power source that integrates power generation, substation, power transmission, and power distribution. For example, the external power grid is provided by a power company. Alternatively, the demand element 4 may be a load that is a collection of one or more devices or devices that consume power. Examples of loads include a collection of one or more various household or business electrical appliances and any component of any device.

The PCS 3 is a device that converts direct current electricity into alternating current, and is a type of power converter. The PCS 3 has a DC terminal connected to the DC bus 6 and an AC terminal connected to the AC bus 7.

The power storage system 1 includes a power storage device 10, a power converter 20, and a general controller 30. One power converter 20 corresponds to one power storage device 10, and these two devices are electrically connected via a DC bus. A set of the power storage device 10 and the power converter 20 that correspond to each other can be called a power storage unit. In the example of FIG. 1, the power storage system 1 includes three sets of power storage devices 10 and power converters 20 (three power storage units), but the number of sets is not limited and may be one, two, or four or more. When there are a plurality of power storage units, the performance of the power storage device 10 (eg, rated capacity, response speed, etc.) and the performance of the power converter 20 (eg, rated output, response speed, etc.) may be unified, It does not have to be unified. The general controller 30 is communicatively connected to each power storage device 10 and each power converter 20 via a communication line 40.

The power storage device 10 is a device that converts electricity provided from the supply element 2 into chemical energy and stores the chemical energy, and can be charged and discharged. Power storage device 10 can also be used to mitigate (level) the fluctuation of the DC power provided from supply element 2. Power storage device 10 includes a zinc battery (zinc secondary battery) 11 including a plurality of cells connected in series. Examples of the zinc battery 11 include, but are not limited to, nickel zinc batteries and silver oxide/zinc batteries. The number of cells forming the zinc battery 11 is not limited and may be, for example, 7 or 8. Power storage device 10 further includes a control function such as a battery control unit (BCU), and with this control function, data regarding power storage device 10 can be transmitted to general controller 30.

The power converter 20 is a device that controls charging and discharging of the power storage device 10. Power converter 20 receives an instruction signal (data signal) from general controller 30 and controls charging/discharging of power storage device 10 based on the instruction signal. The power converter 20 stores the electricity flowing from the supply element 2 in the power storage device 10 in the charging mode, discharges the power storage device 10 to supply power to the outside in the discharging mode, and performs charging/discharging in the stopped state. Absent. The power converter 20 may be, for example, a DC/DC converter.

The overall controller 30 is a computer (for example, a microcomputer) that controls the power storage device 10 and the power converter 20. FIG. 2 is a diagram showing a functional configuration of the overall controller 30. As shown in this figure, the overall controller 30 includes a processor 101, a memory 102, and a communication interface 103 as hardware devices. The processor 101 is, for example, a CPU, and the memory 102 is, for example, a flash memory, but the type of the hardware device configuring the overall controller 30 is not limited to these, and may be arbitrarily selected. Each function of the overall controller 30 is realized by the processor 101 executing a program stored in the memory 102. For example, the processor 101 executes a predetermined arithmetic operation on the data read from the memory 102 or the data received via the communication interface 103, and outputs the arithmetic operation result to the other apparatus, so that the other apparatus is controlled. Control. Alternatively, the processor 101 stores the received data or calculation result in the memory 102. The overall controller 30 may be composed of one computer or a set of a plurality of computers (that is, a distributed system).

The general controller 30 may be connected to the monitoring computer 8 via the communication network 41. The configuration of the communication network 41 is not limited, and may be constructed using, for example, at least one of the Internet and the intranet. The monitoring computer 8 is a computer that monitors the status of the power storage system 1. The type of monitoring computer 8 is not limited. For example, the monitoring computer 8 may be a portable or stationary personal computer. Alternatively, the monitoring computer 8 may be a mobile terminal such as a high-performance mobile phone (smartphone), a mobile phone, a personal digital assistant (PDA), or a tablet. The monitoring computer 8 may be a part of the power storage system 1 or may be provided in a computer system different from the power storage system 1.

Here, the float charging will be described. FIG. 3 is a graph showing an outline of float charging. 3, the horizontal axis represents time and the vertical axis represents SOC (State Of Charge). For example, when the power storage system 1 is used as a backup power source or the like, the plurality of power storage devices 10 included in the power storage system 1 are set to a certain voltage (for example, SOC=80 to 100%) at a constant voltage (hereinafter, float charging). The voltage for the self-discharge is constantly charged while being supplied with the voltage. A certain state of charge refers to a state in which electricity is sufficiently stored in the zinc battery 11, for example, a state in which electricity is stored to the maximum extent determined by the capacity or specifications of the zinc battery 11. Say. A period P1 in FIG. 3 is a period in which each power storage device 10 is in such a fully charged state, that is, a float charged state, and for one float charge, for a long period such as several months (three months in the example in the figure). Will continue. Float charging is controlled by, for example, the overall controller 30. Then, the discharge process is periodically performed between the float charging periods P1 (period P2). The discharging process is a process of setting the SOC of each power storage device 10 to 0% (or any size less than 100%). The SOC of each power storage device 10 set to 0% (or an arbitrary size less than 100%) is brought to a certain state of charge (SOC=80 to 100%) by float charging again. Such discharge processing is controlled by the general controller 30, for example. After the discharging process in each period P2, the float charging voltage is applied to each power storage device 10 again in period P1. In this way, the period P1 and the period P2 are alternately repeated until each power storage device 10 reaches the end of its life.

One of the features of the power storage system 1 is the method of determining the deterioration of the zinc battery 11 during the float charging in the period P1 described above, and this feature is realized by, for example, the overall controller 30. Hereinafter, the function and configuration of the overall controller 30 regarding the determination processing will be described.

As shown in FIG. 2, the processor 101 of the overall controller 30 functions as an acquisition unit 31, a calculation unit 32, a determination unit 33, and an output unit 34. The acquisition unit 31 acquires the transition of the magnitude (current amount) of the current flowing to the zinc battery 11 during float charging. The calculation unit 32 calculates the current increase degree from the reference value based on the transition of the acquired current amount. The current increase degree is an index indicating how much the current amount of the zinc battery 11 has increased with respect to the reference value. The determination unit 33 determines the deterioration state of the zinc battery 11 based on the current increase degree. The output unit 34 outputs data based on the determination. The deteriorated state is a concept indicating how much the performance of the zinc battery 11 deteriorates from the initial state (state during manufacturing). A typical example of deterioration of the zinc battery 11 is an insulation abnormality such as a short circuit or a reduction in resistance that occurs when dendrites (needle-shaped or dendrite crystals) growing from the surface of the negative electrode (zinc electrode) penetrate the separator and reach the positive electrode. Is. The degree of deterioration of the zinc battery 11 may depend on the degree of dendrite growth.

The memory 102 stores information necessary for the operation of the processor 101. For example, the memory 102 stores the determination rule 35. The determination rule 35 is information used to determine the deterioration state. The description method of the determination rule 35 is not limited. For example, the determination rule 35 may be represented by any one of a mathematical formula, a threshold value, an algorithm, and a correspondence table, or may be represented by a combination of any two or more of the mathematical formula, the threshold value, the algorithm, and the correspondence table. .. Alternatively, the determination rule 35 may be a part of the program executed by the processor 101.

The determination rule 35 may be rewritable. For example, when the power storage device 10 or the zinc battery 11 is replaced with another type or a new type of the power storage device 10 or the zinc battery 11 is added, the administrator changes the configuration of the memory 102. The judgment rule 35 in is rewritten. In this case, the administrator accesses the overall controller 30 via a management computer (not shown) via a predetermined communication network (not shown), and sets a new determination rule 35 reflecting the change in the configuration to the overall controller 30. May be forwarded to. By this transfer, the determination rule 35 in the memory 102 is rewritten.

The communication interface 103 cooperates with the processor 101 to send and receive data. For example, the communication interface 103 cooperates with the acquisition unit 31 to receive data regarding the zinc battery 11. In addition, the communication interface 103 cooperates with the output unit 34 to transmit data based on the determination.

[Operation of integrated controller]
Here, the operation of the overall controller 30 will be described, and the method for determining the deterioration of the zinc battery according to the present embodiment will be described. FIG. 4 is a flowchart showing an example of the operation of the overall controller 30, and specifically shows processing for one power storage device 10.

In step S11, the acquisition unit 31 acquires the transition of the amount of current flowing through the zinc battery 11 during the float charging of the zinc battery 11 (acquisition step). The change in the amount of current means a change in the current supplied to the zinc battery 11 over time. Further, this current is a charging current mainly for compensating for the self-discharge of the zinc battery 11. When the zinc battery 11 is normal, there is almost no change in the self-discharge amount with the passage of time, and therefore the current amount changes substantially constant. In this acquisition step S11, the current amount may be acquired continuously or intermittently (for example, periodically). For example, the current amount may be acquired once a day at a predetermined time, or may be acquired only once in several days. The amount of current is acquired by connecting a current detector between the power converter 20 (see FIG. 1) and the zinc battery 11, for example.

In step S12, the calculation unit 32 calculates the current increase degree of the zinc battery 11 from the reference value based on the transition of the current amount (calculation step). The calculation method of the current increase degree is not limited as long as it indicates how much the current amount has increased from the reference value. For example, the calculation unit 32 may obtain the difference between the current amount and the reference value (that is, the current increase amount) as the current increase degree. Alternatively, the calculation unit 32 may obtain a value obtained by dividing the difference between the current amount and the reference value by the reference value (that is, the current increase rate) as the current increase degree. Further, various values can be used as the reference value. For example, as shown in FIG. 5A, the current amount at a certain time point t ₁ when the current amount is attenuated is used as a reference value, and the current amount obtained at a time point t ₂ after a time Δta from the time point t ₁ is a reference value. If it increases with respect to the value, it may be determined as deterioration. The time Δta has a length of 1 day, 30 days, or 90 days, for example. Alternatively, as shown in FIG. 5(b), the fluctuation of the current amount, for example, the current amount at the time when the fluctuation rate (ΔI/Δtb) of the current amount within the unit time Δtb converges within a predetermined range is used as a reference. It may be a value. Alternatively, as shown in FIG. 5C, the amount of current obtained when a predetermined time Δtc has elapsed from the start of charging after the discharging process performed immediately before the float charging is used as a reference value. Good. The time Δtc has a length of, for example, 1 day, 30 days, or 90 days.

In step S13, the determination unit 33 determines the deterioration state of the zinc battery 11 based on the current increase degree (determination step). The specific method for determining the deterioration state is not limited to one, and the determination unit 33 may determine the deterioration state using various methods.

FIG. 6 shows an example of the determination process (determination step). In step S111, the determination unit 33 compares the current increase degree with the threshold value Ta (second threshold value). If the degree of increase in current is less than Ta (NO in step S111), the process proceeds to step S112, and determination unit 33 determines that zinc battery 11 is in a normal state. The normal state means that the zinc battery 11 is not deteriorated or the degree of deterioration is negligibly small. On the other hand, if the current increase degree is equal to or higher than Ta (YES in step S111), the process proceeds to step S113, and determination unit 33 further compares the current increase degree with threshold value Tb (first threshold value). This threshold Tb is a value larger than the threshold Ta.

Specific values of the threshold value Ta and the threshold value Tb are not limited. The threshold value Ta and the threshold value Tb can also be changed depending on the operating temperature (or ambient temperature) of the zinc battery 11. The inventor of the present invention has found that the threshold values can be set as follows in consideration of the characteristics of the zinc battery 11. That is, it can be said that the zinc battery 11 is normal when the current increase rate from the reference value is 300% or less. If the rate of increase in current exceeds a value higher than that (for example, 400% or more), there is a possibility that dendrites are growing in the zinc battery 11, and it becomes necessary to start to be aware of the possibility of internal short circuit. If the current increase rate is higher (eg, 500% or more), the dendrites may have grown considerably, and it is highly likely that an internal short circuit will occur in the relatively near future.

Actual test results regarding such a change in current will be described. In the test, a nickel-zinc battery having a nominal voltage of 1.65 V and a rated capacity of 8 Ah, which is an example of a zinc battery, was operated. First, the nickel-zinc battery was brought into a fully charged state (SOC=100%) under the following condition 1 (step S1).

[Condition 1]
・Constant Current-Constant Voltage (CC-CV)
・Temperature: 25℃
・Current: 8A (cutoff current: 0.4A)
・Voltage: 1.9V

Next, in order to confirm the rated capacity, the initial discharge capacity at a current of 8 A was confirmed under the following condition 2 (step S2).
[Condition 2]
・Discharge to DC bus ・Temperature: 25℃
・Current: 8A
-End voltage: 1.1V

Then, after the nickel-zinc battery was fully charged again under the above condition 1 (step S3), the initial discharge capacity at a current of 32 A was confirmed under the following condition 3 (step S4).
[Condition 3]
・Discharge to DC bus ・Temperature: 25℃
・Current: 32A
-End voltage: 1.1V

Then, the float charge life test was started from the state of SOC=0% (step S5). At that time, five nickel zinc batteries were tested under the following condition 4, and another five nickel zinc batteries were tested under the following condition 5.
[Condition 4]
・Constant current constant voltage (CC-CV)
・Temperature: 40℃
・Upper limit of current: 1.6A
Float charge voltage: 5 batteries, 1.825V, 1.83V, 1.84V, 1.85V, and 1.87V, respectively.
・Float charging period: 120 days [Condition 5]
・Constant current constant voltage (CC-CV)
・Temperature: 55℃
・Upper limit of current: 1.6A
Float charge voltage: 5 batteries, 1.825V, 1.83V, 1.84V, 1.85V, and 1.87V, respectively.
・Float charging period: 42 days

Then, the battery temperature was adjusted to approach 25° C. for a predetermined period (12 hours) after the float charging was performed (step S6). After that, the discharge capacity after the float charging was confirmed under the above condition 3 (step S7). If the discharge capacity after the float charging is equal to or less than the threshold value (60%) with respect to the initial discharge capacity, it is determined to be the life, and if it is larger than the threshold value, the process returns to step S5 (step S8). Such steps S5 to S8 were repeated until it was determined that all the nickel-zinc batteries had reached the end of their lives. In this test, the threshold value of the discharge capacity determined to be the life is set to 60%, but the threshold value may be set to any value within the range of 50% to 80%.

FIG. 7 is a graph showing changes in the discharge capacity retention rate of five nickel-zinc batteries that underwent the float charge life test under condition 4 (temperature 40° C.). FIG. 8A is a chart showing the measured discharge capacity, and FIG. 8B is a chart showing the discharge capacity retention rate calculated from FIG. 8A (based on FIG. 7). .. FIG. 9 is a graph showing changes in the amount of charging current in the five nickel-zinc batteries that underwent the float charging life test under condition 4. It should be noted that the reason why the charging current amount drops regularly in FIG. 9 is due to the discharging process (period P2 in FIG. 3). In this test, discharge treatment was performed every 120 days.

Referring to FIG. 9, regarding each nickel-zinc battery in which the float charging voltage was 1.825V, 1.83V, 1.84V, and 1.87V, the charging current amount during the float charging changed gently after the discharge treatment. There is no sharp increase. This indicates that the nickel-zinc battery is normal and there is no insulation abnormality due to dendrite or the like. On the other hand, regarding the nickel-zinc battery with the voltage of 1.85 V, the charging current amount during the float charging increases rapidly during the period of 330 days to 344 days and the period of 351 days to 358 days. This indicates that an insulation abnormality due to dendrite or the like has occurred in the nickel-zinc battery. In this example, the insulation abnormality first occurred in the nickel-zinc battery having a voltage of 1.85V, but the insulation abnormality may occur first in the nickel-zinc battery having another voltage. Usually, the higher the float charging voltage, the earlier the insulation abnormality due to dendrites tends to occur.

FIG. 10 is a graph showing changes in the discharge capacity retention rate of five nickel-zinc batteries that underwent the float charge life test under condition 5 (temperature 55° C.). 11(a) is a chart showing the measured discharge capacity, and FIG. 11(b) is a chart showing the discharge capacity retention rate calculated from FIG. 11(a) (based on FIG. 10). .. In addition, FIG. 12 is a graph showing changes in the amount of charging current in the five nickel-zinc batteries that underwent the float charging life test under condition 5.

Referring to FIG. 12, for each nickel-zinc battery in which the float charging voltage was 1.825V, 1.83V, 1.84V, and 1.85V, the charging current amount during the float charging changed gently after the discharge treatment. There is no sharp increase. On the other hand, regarding the nickel-zinc battery with the voltage of 1.87 V, the charging current amount during the float charging rapidly increases during the period of 35 days to 42 days and the period of 77 days to 84 days.

Referring back to FIG. If the degree of increase in current is Tb or more (YES in step S113), the process proceeds to step S114, and determination unit 33 determines that zinc battery 11 is in the first deterioration state. The first deterioration state refers to a state in which the degree of deterioration of the zinc battery 11 is relatively large. On the other hand, if the current increase is less than Tb (NO in step S113), that is, if the current increase is Ta or more and less than Tb, the process proceeds to step S115, and the determination unit 33 determines that the zinc battery 11 is the second battery. It is determined to be in a deteriorated state. The second deterioration state is a state in which the degree of deterioration of the zinc battery 11 is smaller than that in the first deterioration state. As long as this relationship is maintained, the specific meanings of the first deteriorated state and the second deteriorated state are not limited. For example, the first deterioration state may correspond to a state in which the dendrite is expected to grow to such an extent that an internal short circuit is more likely to occur in the relatively near future. The second deterioration state may correspond to a state in which the performance of the zinc battery 11 may be improved by the dissolution of the dendrite due to the discharge of the zinc electrode, although the dendrite is present.

In the example shown in FIG. 6, the determination unit 33 determines the deterioration of the zinc battery 11 in two stages of the first deterioration state and the second deterioration state, but the determination unit 33 determines the first deterioration state and the second deterioration state. The deterioration of the zinc battery may be determined in three or more stages including the above.

FIG. 13 shows another example of the determination process (determination step). In step S121, the determination unit 33 compares the current increase degree with the threshold value Ta. If the degree of current increase is less than Ta (NO in step S121), the process proceeds to step S122, and determination unit 33 determines that zinc battery 11 is in a normal state.

On the other hand, if the current increase rate is equal to or higher than Ta (YES in step S121), the process proceeds to step S123, and the determination unit 33 continues the state (monitoring event) that the current increase degree is equal to or higher than the threshold value Ta. The number of occurrences n is acquired. Each time the determination unit 33 determines the state of the zinc battery 11, the determination result is recorded in the memory 102 as a history, and the number of times n can be obtained by referring to the history in step S123.

If the number of times n is less than the threshold value Tc (NO in step S124), the process proceeds to step S122, and determination unit 33 determines that zinc battery 11 is in a normal state. On the other hand, if the number of times n is equal to or greater than the threshold value Tc (YES in step S124), the process proceeds to step S125, and the determination unit 33 determines that the zinc battery 11 is in the first deterioration state. The specific value of the threshold value Tc is not limited and may be set based on any reference. For example, the threshold Tc may be set in consideration of various factors such as the characteristics of the zinc battery 11.

Since the zinc that constitutes the negative electrode is repeatedly deposited and dissolved, the dendrite does not always grow monotonically with the passage of time, and the dendrite temporarily disappears (the amount of dendrite protruding from the negative electrode surface is temporarily reduced. Lower). Therefore, in consideration of such characteristics of the dendrite, the determination unit 33 may determine the deterioration state of the zinc battery 11 on the basis of the plurality of successively increased current increases. When the current increase rate continues to be relatively high, the dendrites are expected to grow to some extent, and it can be determined that the zinc battery 11 has deteriorated to some extent. ..

FIG. 14 shows still another example of the determination process (determination step). In step S131, the determination unit 33 compares the current increase degree with the threshold value Ta. If the degree of increase in current is less than Ta (NO in step S131), the process proceeds to step S132, and determination unit 33 determines that zinc battery 11 is in a normal state. On the other hand, if the current increase degree is equal to or higher than Ta (YES in step S131), the process proceeds to step S133, and determination unit 33 further compares the current increase degree with threshold value Tb (Tb>Ta). Specific values of the threshold value Ta and the threshold value Tb may be set similarly to the example of FIG.

If the degree of increase in current is Tb or more (YES in step S133), the process proceeds to step S134, and determination unit 33 determines that zinc battery 11 is in the first deterioration state. On the other hand, if the degree of current increase is less than Tb (NO in step S133), the process proceeds to step S135, and the determination unit 33 continues the state (monitoring event) that the degree of current increase is equal to or greater than the threshold Ta. The number of occurrences n is acquired. If the number of times n is less than the threshold value Tc (NO in step S136), the process proceeds to step S132, and the determination unit 33 determines that the zinc battery 11 is in the normal state. On the other hand, if the number of times n is equal to or greater than the threshold value Tc (YES in step S136), the process proceeds to step S134, and the determination unit 33 determines that the zinc battery is in the first deterioration state. It can be said that the example shown in FIG. 14 is a combination of the two methods shown in FIGS. 6 and 13.

13 and 14 include a process of determining deterioration of the zinc battery 11 based on the number of times a monitoring event has occurred. As a modification of this process, the determination unit 33 replaces the number of times n in which the state (monitoring event) that the current increase degree is equal to or higher than the threshold value Ta occurs consecutively, “the current increase degree is equal to or higher than the threshold value Ta. The deterioration state may be determined based on the cumulative number m of times that the state (monitoring event) has occurred. That is, the determination unit 33 determines that the zinc battery 11 is in the normal state when the cumulative number of occurrences m is less than the threshold Td, and the zinc battery 11 is in the first deterioration state when the cumulative number of occurrences m is equal to or greater than the threshold Td. It may be determined that there is. As mentioned above, dendrites may be temporarily eliminated. However, dendrites are expected to grow to a certain degree when many conditions are detected regardless of whether the conditions with relatively high current increase occur continuously or discontinuously. To be done. Therefore, the determination unit 33 may determine that the zinc battery 11 has deteriorated to some extent in such a case. The specific value of the threshold value Td is not limited and may be set based on an arbitrary criterion. For example, the threshold Td may be set in consideration of various factors such as the characteristics of the zinc battery 11.

Alternatively, the determination unit 33 may determine the deterioration state using both the continuous occurrence count and the cumulative occurrence count. For example, the determination unit 33 counts both the continuous occurrence number n and the cumulative occurrence number m. Then, the determination unit 33 determines that the zinc battery 11 is in the first deterioration state when the continuous occurrence number n is equal to or greater than the threshold value Tc or the cumulative occurrence number m is equal to or greater than the threshold value Td, and otherwise. In this case, it may be determined that the zinc battery 11 is in a normal state.

When using at least one of the continuous occurrence count and the cumulative occurrence count, the determination unit 33 may determine not only the first deterioration state but also the second deterioration state. For the number of consecutive occurrences n, the determination unit 33 uses two threshold values Tc _low and Tc _high (where Tc _low <Tc _high ). Then, the determination unit 33 determines that the zinc battery 11 is in the normal state when n<Tc _low , and determines that the zinc battery 11 is in the second deterioration state when Tc _low ≦n<Tc _high , and Tc _high ≦ In the case of n, the zinc battery 11 may be determined to be in the first deterioration state. For the cumulative number of occurrences m, the determination unit 33 uses two thresholds Td _low and Td _high (where Td _low <Td _high ). Then, the determination unit 33 determines that the zinc battery 11 is in the normal state when m<Td _low , determines that the zinc battery 11 is in the second deterioration state when Td _low ≦m<Td _high , and Td _high ≦ In the case of m, the zinc battery 11 may be determined to be in the first deterioration state. Even when using at least one of the continuous occurrence count and the cumulative occurrence count, the determination unit 33 may determine the deterioration of the zinc battery in three or more stages including the first deterioration state and the second deterioration state.

As described above, various methods can be adopted for the determination of the deterioration state. In any case, the determination unit 33 can determine the deterioration state of the zinc battery 11 using a predetermined determination rule 35 (for example, the determination rule 35 including the above threshold).

Referring back to FIG. In step S14, the output unit 34 outputs the data based on the determination made by the determination unit 33. The content of the data is not limited. For example, the output unit 34 may transmit the determination result (for example, one of the normal state, the first deteriorated state, or the second deteriorated state) to the monitoring computer 8 via the communication network 41. The monitoring computer 8 may execute an arbitrary process such as displaying the determination result on a monitor or storing it in a database. Alternatively, output unit 34 may generate a stop instruction when the determination result is the first deterioration state and transmit the stop instruction to corresponding power storage device 10. “Sending a stop instruction to the power storage device” means sending a stop instruction to the power storage device 10 or to another device corresponding to the power storage device 10 in order to prevent the zinc battery 11 from being charged and discharged. Say that. For example, the output unit 34 may transmit the stop instruction to the power converter 20 corresponding to the power storage device 10 via the communication line 40. The zinc battery 11 of the stopped power storage device 10 is replaced with a new one, for example, manually.

When the power storage system 1 includes a plurality of power storage devices 10, the overall controller 30 executes the processes of steps S11 to S14 for all the power storage devices 10. The processes of steps S11 to S14 are repeatedly executed for one power storage device 10.

[program]
The determination program for causing the computer to function as the overall controller 30 includes a program code for causing the computer to function as the acquisition unit 31, the calculation unit 32, the determination unit 33, and the output unit 34. The determination program may be provided after being fixedly recorded in a tangible recording medium such as a CD-ROM, a DVD-ROM, or a semiconductor memory. Alternatively, the determination program may be provided as a data signal superimposed on a carrier wave via a communication network. The provided determination program is stored in the memory 102, for example. The processor 101 cooperates with the memory 102 to execute the determination program, so that the above functional elements are realized.

[effect]
As described above, the determination method of the deterioration of the zinc battery according to the present embodiment is the acquisition step S11 for acquiring the transition of the current amount flowing to the zinc battery 11 during the float charging of the zinc battery 11, and the transition of the current amount. The calculation step S12 of calculating the current increase degree from the reference value in step S13 and the determination step S13 of determining the deterioration of the zinc battery 11 based on the current increase degree are included. During float charging, the amount of current flowing to the zinc battery 11 is approximately constant or changes slightly. However, when an insulation abnormality such as a short circuit between electrodes due to a Tado light or a decrease in resistance occurs, the amount of current is extremely high. (See FIGS. 9 and 12). In this determination method, since the deterioration of the zinc battery 11 is determined based on the current increase degree from the reference value, the insulation abnormality between the electrodes is well detected and the deterioration of the zinc battery 11 is detected even during the float charging. It can be accurately determined.

As in the present embodiment, in the determination step S13, it may be determined that the zinc battery 11 is in a deteriorated state when the current increase degree is equal to or more than the threshold value. For example, with such a method, it is possible to detect the insulation abnormality between the electrodes more accurately.

As shown in FIG. 6, in the determination step S13, when the current increase degree is the threshold value Tb or more, it is determined that the zinc battery 11 is in the first deterioration state, and the current increase degree is the threshold value Ta or more and the threshold value Tb. When it is less than, it may be determined that the zinc battery 11 is in the second deterioration state in which the degree of deterioration is smaller than that in the first deterioration state. For example, by determining the deterioration state of the zinc battery 11 stepwise in this way, it is possible to easily determine the replacement of the zinc battery 11 or the like.

In the calculation step S12, as shown in FIG. 5A, the current amount at a certain time point t ₁ at which the current amount is attenuated is used as a reference value, and is acquired at a time point t ₂ after a time Δta from the time point t ₁ . When the current amount increases with respect to the reference value, it may be determined that the deterioration has occurred, and as shown in FIG. 5B, the current amount at the time when the variation of the current amount converges within a predetermined range. May be used as a reference value, or, as shown in FIG. 5(c), it is obtained when a predetermined time Δtc has elapsed from the start of charging after the discharging process performed immediately before the float charging. The amount of current thus generated may be used as a reference value. For example, any one of these methods can set a more appropriate reference value in the determination of deterioration of the zinc battery 11.

As shown in FIGS. 13 and 14, in the determination step S13, the deterioration of the zinc battery 11 may be determined based on the number of times n that a monitoring event that the current increase degree is equal to or higher than the threshold value Ta occurs. As described above, the insulation abnormality due to the dendrite does not continue to occur, and the zinc battery 11 reaches the end of its life while repeating the occurrence and recovery of the insulation abnormality. Therefore, it may be difficult to determine the deterioration of the zinc battery 11 if the insulation abnormality occurs only once. Even in such a case, the deterioration of the zinc battery 11 can be determined more accurately by determining the deterioration of the zinc battery 11 based on the number n of times of occurrence of abnormality (monitoring event) in the current increase degree. it can. In this case, in the determination step S13, the zinc battery 11 may be determined to be in a deteriorated state when the number n of consecutive monitoring events is equal to or greater than a predetermined threshold Tc (FIG. 14). Alternatively, it may be determined that the zinc battery 11 is in a deteriorated state when the cumulative number n of times the monitoring event has occurred is equal to or greater than a predetermined threshold value Tc (FIG. 13).

As in the present embodiment, the zinc battery 11 may be a nickel zinc battery. In this case, the determination method of this embodiment is particularly effective, and the above-mentioned effects can be remarkably exhibited.

[Modification]
The present invention has been described in detail above based on the embodiments. However, the present invention is not limited to the above embodiment. The present invention can be variously modified without departing from the gist thereof. For example, the processing procedure of the method for determining deterioration of a zinc battery, which is executed by at least one processor, is not limited to the example in the above embodiment. For example, some of the steps (processes) described above may be omitted, or each step may be executed in a different order. Further, any two or more of the steps described above may be combined, or some of the steps may be modified or deleted. Alternatively, other steps may be executed in addition to the above steps.

When comparing the magnitude relationship of two numerical values in the power storage system 1, either of two criteria of “greater than or equal to” and “greater than” may be used, and two criteria of “less than or equal to” and “less than” may be used. Either of these may be used. The selection of such a criterion does not change the technical significance of the process of comparing the magnitude relationship of two numerical values.

Although the overall controller 30 executes the method for determining the deterioration of the zinc battery in the above embodiment, part or all of this method may be performed manually.

1... Power storage system, 2... Supply element, 3... PCS, 4... Demand element, 6... DC bus, 7... AC bus, 8... Monitoring computer, 10... Power storage device, 11... Zinc battery, 20... Power converter, 30... Overall controller, 31... Acquisition part, 32... Calculation part, 33... Judgment part, 34... Output part, 35... Judgment rule, 40... Communication line, 41... Communication network.

Claims (9)

An acquisition step of acquiring the transition of the amount of current flowing to the zinc battery during float charging of the zinc battery,
A calculation step of calculating a current increase degree from a reference value in the transition of the current amount,
A determination step of determining deterioration of the zinc battery based on the current increase degree;
A method for determining deterioration of a zinc battery, including: The method for determining deterioration of a zinc battery according to claim 1, wherein the determination step determines that the zinc battery is in a deteriorated state when the current increase degree is equal to or more than a threshold value. In the determining step, the zinc battery is determined to be in a first deterioration state when the current increase degree is a first threshold value or more, and the current increase degree is a second threshold value or more and less than the first threshold value. In this case, the zinc battery determination method according to claim 2, wherein the zinc battery is determined to be in a second deterioration state in which the degree of deterioration is smaller than that in the first deterioration state. The said calculation step WHEREIN: The said amount of electric currents at the time when the fluctuation|variation of the said amount of electric currents converged within the predetermined range is made into the said reference value, The deterioration of the zinc battery as described in any one of Claims 1-3. Judgment method. In the calculation step, the current amount acquired at a time point when a predetermined time has elapsed from the start of charging after the discharging process performed immediately before the float charging is set as the reference value. The method for determining deterioration of a zinc battery according to any one of 1. Deterioration of the zinc battery according to any one of claims 1 to 5, wherein in the determination step, the deterioration of the zinc battery is determined based on the number of times a monitoring event that the current increase degree is equal to or greater than a threshold value has occurred. Judgment method. The deterioration of the zinc battery according to claim 6, wherein in the determining step, the zinc battery is determined to be in a deteriorated state when the number of times the monitoring event has occurred consecutively is equal to or greater than a predetermined threshold value. Judgment method. The zinc battery according to claim 6 or 7, wherein in the determining step, the zinc battery is determined to be in a deteriorated state when the cumulative number of occurrences of the monitoring event is equal to or greater than a predetermined threshold value. Deterioration judgment method. The method for determining deterioration of a zinc battery according to claim 1, wherein the zinc battery is a nickel zinc battery.

Images