Patent Description:
An unmanned carrier includes an energy storage apparatus configured as a power supply including a plurality of energy storage devices connected in series. Such an energy storage apparatus is configured to, for security purposes, monitor voltage of each of the energy storage devices, determine as being abnormal if minimum cell voltage becomes less than a lower limit value, and actuate a protective apparatus such as a current breaker.

<CIT> describes a battery pack capacity adjustment apparatus, which is installed in a vehicle, executes capacity adjustment for a plurality of cells constituting a battery pack by raising the target charging rate for the battery pack from a first target charging rate to a second target charging rate when a voltage variance abnormality among the plurality of cells is detected and the currently traveling vehicle is predicted to stop.

<CIT> describes a battery controller for controlling an assembled battery configured by connecting battery groups each including battery cells. The battery controller includes: voltage measuring units that are provided respectively for the battery groups each to measure a voltage of each of the battery cells included in a corresponding battery group; a minimum value detecting unit that detects a minimum value of the battery cells for each of the battery groups based upon the measured voltage of each of the battery cells; a reference value setting unit that sets a reference value used to determine an abnormal voltage drop for each of the battery groups based upon the measured voltage of each of the battery cells; and an abnormality determining unit that makes a determination that an abnormal voltage drop is present, if a difference between the reference value and the minimum value exceeds a predetermined value, for each of the battery groups.

<CIT> describes a capacity adjusting method for a battery pack.

<CIT> describes a method for diagnosing a battery of a vehicle and a system thereof. When charging of a battery is started, a voltage of each module being charged is detected, and then an average voltage and at least one of a maximum voltage and a minimum voltage of the modules are calculated. Subsequently, if an absolute value of a difference between the average voltage and at least one of the maximum and the minimum voltages is greater than a predetermined reference value, it is determined that the battery may be malfunctioning. If it is determined that the battery may be malfunctioning, a charging mode is changed to a safer mode and a warning of the possible malfunction is given.

<CIT> describes a method to reliably detect an abnormal cell having an abnormal voltage. A battery controller detects the abnormal cell based on the voltage of each cell measured by a cell controller, the average voltage of all cells computed by the battery controller, an abnormality determining threshold value, and a correction value to correct the average voltage or the abnormality determining threshold value. This correction value is a value based on the characteristics of a battery assembly formed by plural cells.

The energy storage apparatus configured as described above determines a state of the energy storage apparatus, such as whether or not the energy storage apparatus has abnormality, in accordance with the minimum cell voltage. The energy storage devices, however, have decrease in voltage due to internal resistance. There has been a demand for a measure, because such a method of determining the state of the energy storage apparatus only in accordance with the minimum cell voltage may fail to achieve accurate determination on the state of the energy storage apparatus.

The present invention has been made in view of the above circumstance, and achieves improvement in accuracy of determination on a state of an energy storage apparatus.

This object is solved by the claimed invention as claimed in the appended independent claims. Particular embodiments of the present invention are defined by the appended dependent claims.

The present application discloses an energy storage apparatus including: a plurality of energy storage devices connected in series; a voltage detection unit configured to detect voltage of each of the energy storage devices; and a monitoring unit configured to monitor the plurality of energy storage devices. The monitoring unit determines a state of the energy storage apparatus during discharge in accordance with: minimum cell voltage of the plurality of energy storage devices and one of average cell voltage and average SOC of the plurality of energy storage devices; and the monitoring unit is further configured to determine whether or not to limit discharge current of the energy storage apparatus in accordance with the minimum cell voltage of the plurality of energy storage devices when the average cell voltage or the average SOC of the plurality of energy storage devices is less than a threshold.

The present application discloses an energy storage apparatus including: a plurality of energy storage devices connected in series; a voltage detection unit configured to detect voltage of each of the energy storage devices; and a monitoring unit configured to monitor the plurality of energy storage devices. The monitoring unit determines a state of the energy storage apparatus in accordance with average cell voltage or an average SOC of the plurality of energy storage devices and minimum cell voltage of the plurality of energy storage devices.

The present application further discloses a multibank energy storage system including a plurality of energy storage apparatuses connected parallelly (in parallel). The energy storage system includes: the plurality of energy storage apparatuses connected parallelly; and an integrated monitoring unit configured to monitor the plurality of energy storage apparatuses. The integrated monitoring unit determines a state of the energy storage system in accordance with the average cell voltage or the average SOC of the energy storage devices of the energy storage system and the minimum cell voltage of the energy storage devices of the energy storage system.

The present application also discloses a method of determining a state of an energy storage apparatus. The energy storage apparatus includes a plurality of energy storage devices connected in series. The method includes determining the state of the energy storage apparatus in accordance with average cell voltage or an average SOC of the plurality of energy storage devices and minimum cell voltage of the plurality of energy storage devices.

The energy storage apparatus disclosed in the present application achieves more accurate determination on the state of the energy storage apparatus in comparison to determination on the state of the energy storage apparatus only in accordance with the minimum cell voltage. The energy storage system and the method of determining the state of the energy storage apparatus disclosed in the present application achieve the same effect.

An energy storage apparatus disclosed in the present embodiment will be summarized initially.

The energy storage apparatus includes: a plurality of energy storage devices connected in series; a voltage detection unit configured to detect voltage of each of the energy storage devices; and a monitoring unit configured to monitor the plurality of energy storage devices. The monitoring unit determines a state of the energy storage apparatus in accordance with average cell voltage or an average SOC of the plurality of energy storage devices and minimum cell voltage of the plurality of energy storage devices.

This configuration achieves more accurate determination on the state of the energy storage apparatus in comparison to determination on the state of the energy storage apparatus only in accordance with the minimum cell voltage of the plurality of energy storage devices.

The monitoring unit may determine whether or not the energy storage apparatus has abnormality in accordance with the minimum cell voltage of the plurality of energy storage devices when the average cell voltage or the average SOC of the plurality of energy storage devices is not less than a threshold.

When an average cell voltage or an average SOC is not less than the threshold and minimum cell voltage is less than an ordinary value, that particular cell is likely to be abnormal. This configuration achieves accurate determination on whether or not the energy storage apparatus has abnormality.

The monitoring unit may compare the minimum cell voltage of the plurality of energy storage devices with a determination value smaller than the threshold when the average cell voltage or the average SOC of the plurality of energy storage devices is not less than the threshold, and may determine that the energy storage apparatus has abnormality when the minimum cell voltage is less than the determination value. With this configuration, the energy storage apparatus is determined as being abnormal if the minimum cell voltage becomes less than the determination value with the average cell voltage or the average SOC being not less than the threshold.

The threshold and the determination value may have a difference therebetween set in accordance with a permissible range of voltage variation of the energy storage device. This configuration achieves higher determination accuracy because the energy storage apparatus is not determined as being abnormal with the voltage variation of the energy storage devices being within the permissible range.

The determination value may be obtained by adding a predetermined margin to a lower limit value of cell voltage of the energy storage device. This configuration enables abnormality determination on the energy storage apparatus before the minimum cell voltage reaches the lower limit value.

The energy storage apparatus may further include: a current breaker configured to break current flowing through the plurality of energy storage devices. The monitoring unit may break the current breaker when the monitoring unit determines that the energy storage apparatus has abnormality. This configuration enables the abnormal energy storage apparatus to be disconnected from the power supply target instrument.

The monitoring unit may determine whether or not to limit discharge current of the energy storage apparatus in accordance with the minimum cell voltage of the plurality of energy storage devices when the average cell voltage or the average SOC of the plurality of energy storage devices is less than the threshold.

When the plurality of energy storage devices has decreased minimum cell voltage with the average cell voltage or the average SOC being less than the threshold, the energy storage apparatus is less likely to be abnormal but the flowing discharge current is likely to exceed an appropriate value. This configuration thus achieves accurate determination on whether or not the discharge current needs to be limited.

The monitoring unit may compare the minimum cell voltage of the plurality of energy storage devices with switching voltage higher than the lower limit value when the average cell voltage or the average SOC of the plurality of energy storage devices is less than the threshold, and may determine that the discharge current of the energy storage apparatus needs to be limited when the minimum cell voltage is not more than the switching voltage and may notify to request a power supply target instrument to execute current limitation processing of limiting the discharge current.

This configuration achieves request for execution of the current limitation processing to reduce the discharge current when the minimum cell voltage reaches the switching voltage, so as to suppress decrease in voltage of the energy storage devices. The minimum cell voltage of the plurality of energy storage devices can thus be kept not less than the lower limit value to allow continuous use of the energy storage apparatus.

The same applies to a multibank energy storage system including the energy storage apparatuses connected parallelly.

The first embodiment of the present invention will now be described with reference to <FIG>.

<FIG> is a block diagram of a power supply system. The power supply system U is applied as a power supply of an unmanned carrier <NUM> or the like, and includes an integrated monitoring unit <NUM> and a plurality of battery banks B1 to B10. The power supply system U corresponds to a "multibank power supply system", and the battery banks B1 to B10 each correspond to an "energy storage apparatus".

As depicted in <FIG>, the plurality of battery banks B1 to B10 is connected parallelly, and is connected to a driving unit (specifically, a motor) <NUM> of the unmanned carrier <NUM> via a common current path Lo. The number of the battery banks B connected parallelly is "ten" in the present example.

The battery banks B1 to B10 are structured identically, and each include a plurality of battery modules <NUM> connected in series, a plurality of module sensors <NUM>, a current sensor <NUM>, a current breaker <NUM>, and an individual monitoring unit <NUM>.

As depicted in <FIG>, the battery modules <NUM> each include a plurality of secondary batteries (exemplified by lithium ion secondary batteries) <NUM> connected in series. The battery modules <NUM> according to the present example each include twelve secondary batteries <NUM>. There are fifteen battery modules <NUM> connected in series. Each of the battery banks B thus includes <NUM> secondary batteries <NUM> connected in series. The following description will refer to a "cell" indicating a constituent unit of the battery module <NUM>, and a single cell corresponds to a single secondary battery <NUM>.

Each of the module sensors <NUM> is provided for corresponding one of the battery modules <NUM>, and detects cell voltage V of each of the secondary batteries <NUM> of the battery module <NUM>. The module sensors <NUM> further detects temperature of the battery module <NUM>. The module sensors <NUM> is connected with the individual monitoring unit <NUM> via a signal line. Cell voltage data on each of the secondary batteries <NUM> and temperature data on the battery module <NUM> detected by the module sensor <NUM> is transmitted to the individual monitoring unit <NUM>. The module sensor <NUM> corresponds to a "voltage detection unit".

The current sensor <NUM> is exemplified by a hall sensor. The current sensor <NUM> is provided on a current path Lm of the battery modules <NUM> and detects current flowing to/from the battery modules <NUM>. The current sensor <NUM> is connected to the individual monitoring unit <NUM> via a signal line. Current data detected by the current sensor <NUM> is transmitted to the individual monitoring unit <NUM>.

The current breaker <NUM> is exemplified by a molded case circuit breaker provided on the current path Lm of the battery modules <NUM>. The current breaker <NUM> opens the current path Lm of the battery modules <NUM> to break current in response to a command from the individual monitoring unit <NUM>. Actuating the current breaker <NUM> to break current will hereinafter be expressed as tripping.

The individual monitoring unit <NUM> includes a central processing unit (CPU) (not depicted) and a memory (not depicted) configured to store various types of information. The individual monitoring unit <NUM> monitors the state of the battery bank B in accordance with data received from the module sensors <NUM> and the current sensor <NUM>. The individual monitoring unit <NUM> monitors the following data items.

The integrated monitoring unit <NUM> is connected with the individual monitoring units <NUM> of the battery banks B1 to B10 via signal lines, and is configured to receive, from the individual monitoring units <NUM> of the battery banks B1 to B10, data on the states of the battery banks B, that is, data on the items (<NUM>) to (<NUM>) described above.

The integrated monitoring unit <NUM> monitors the states of the battery banks B1 to B10 in accordance with the data on the items (<NUM>) to (<NUM>) received from the individual monitoring units <NUM> of the battery banks B1 to B10. The integrated monitoring unit <NUM> is also connected with a control unit <NUM> of the unmanned carrier <NUM> so as to be communicable with the control unit <NUM> of the unmanned carrier <NUM>.

In a case where part of the secondary batteries <NUM> of the battery bank B has abnormality such as an internal short-circuit or voltage variation outside a permissible range, the battery bank B needs to be disconnected from the power supply system U for security of the power supply system U.

The secondary battery <NUM> having an internal short-circuit or voltage variation outside the permissible range has decrease in voltage. The secondary battery <NUM> can be determined as being "abnormal" if minimum cell voltage Vmi of the secondary battery <NUM> of the battery bank B compared with a lower limit value X1 (at an application limit) becomes lower than the lower limit value X1, and the battery bank B including the secondary battery <NUM> determined as being abnormal is to be disconnected from the power supply system U.

The secondary batteries <NUM>, however, have decrease in voltage (hereinafter, referred to as drop) due to internal resistance. Even in a case where the cell itself has no actual abnormality, the secondary batteries <NUM> of the battery bank B can entirely be decreased in cell voltage V by drop due to internal resistance during discharge and part of the secondary batteries <NUM> can have cell voltage lower than the lower limit value X1.

In view of this, the present embodiment includes determination on whether or not the battery bank B has abnormality according to average cell voltage Vav of all the secondary batteries <NUM> of the operating bank B and the minimum cell voltage Vmi of the secondary batteries <NUM> of the operating bank B.

Specifically, if the average cell voltage Vav of the secondary batteries <NUM> of all the operating banks B is not less than a threshold X3 (YES in S20 in <FIG>) and the minimum cell voltage Vmi of the secondary batteries <NUM> of all the operating banks B is less than a determination value X2 that is smaller than the threshold X3 (S30 in <FIG>), the integrated monitoring unit <NUM> determines that the operating banks B have abnormality (S40 in <FIG>). In other words, the integrated monitoring unit <NUM> determines that part of the secondary batteries <NUM> of the operating banks B has abnormality. The words "operating bank" indicate the battery bank B including the current breaker <NUM> not being tripped and being capable of supplying power to the unmanned carrier <NUM> serving as a load.

As indicated in <FIG>, the determination value X2 is obtained by adding a predetermined margin (allowance) a to the lower limit value (an application limit value on a discharge side) X1 of the voltage of the secondary battery <NUM>. The lower limit value X1 is <NUM> [V] and the margin is <NUM> [V] in the present example, so that the determination value X2 is <NUM> [V]. The threshold X3 is <NUM> [V] or the like, which is set to a numerical value obtained by adding permissible variation β of the voltage of the secondary battery <NUM> to the determination value X2.

The permissible range β of the voltage variation according to the present example is calculated in accordance with a permissible range of initial capacity variation of the secondary battery <NUM>. Specifically, the initial capacity [Ah] of a predetermined number of secondary batteries <NUM> is actually measured to preliminarily calculate distribution of the initial capacity, and the permissible range of the initial capacity variation is set to 3σ thereof. <FIG> includes a curved line G indicating the initial capacity variation, and the symbol "σ" indicates a standard deviation. The value 3σ is merely exemplary, and can be different depending on variation in production of the adopted energy storage devices (the secondary batteries <NUM>). An appropriate permissible range of the voltage variation is determined in accordance with the permissible range of capacity variation of the adopted energy storage devices.

The initial capacity variation is converted to a state of charge (SOC), and a permissible range Y (e.g. <NUM>%) of SOC variation of the secondary battery <NUM>. Further conversion is made in accordance with correlation between the SOC and the voltage (curved line L2 indicated in <FIG>), to calculate the permissible range β of the voltage variation. The permissible range of the SOC variation is <NUM>% and the permissible range β of the voltage variation is <NUM> V in the present example.

<FIG> includes a solid curved line L1 indicating correlation between open circuit voltage and the SOC of the secondary battery <NUM>, and the broken curved line L2 indicating correlation between the cell voltage V and the SOC of the secondary battery <NUM> discharging at a predetermined rate.

The threshold X3 is set to the numerical value obtained by adding the permissible range β of the voltage variation to the determination value X2. In a case where the operating bank B does not include the secondary battery <NUM> having voltage decreased to be out of the permissible range β, if the average cell voltage Vav of all the secondary batteries <NUM> in the operating bank B is higher than the threshold X3, the minimum cell voltage Vmi is higher than the determination value X2, as indicated by a line (a) in <FIG>. The operating bank B can thus be determined as normal, in other words, not including any abnormal secondary battery <NUM>.

In another case where the operating bank B includes the secondary battery <NUM> having voltage decreased to be out of the permissible range β or the secondary battery <NUM> having an internal short-circuit, as indicated by a line (d) in <FIG>, the minimum cell voltage Vmi is lower than the determination value X2 even if the average cell voltage Vav of the secondary batteries <NUM> of all the operating banks B is higher than the threshold X3. The operating bank B is thus determined as having abnormality, in other words, including the abnormal secondary battery <NUM>.

As indicated by lines (b) and (c) in <FIG>, if the average cell voltage Vav of all the secondary batteries <NUM> of the operating bank B is lower than the threshold X3, whether or not the operating bank B has abnormality is not determined regardless of whether or not the minimum cell voltage Vmi is lower than the determination value X2.

Accordingly, abnormality determination is not made when all the secondary batteries <NUM> of the operating bank B have the cell voltage V entirely decreased by drop due to internal resistance. The operating bank B is thus not erroneously determined as being abnormal when all the secondary batteries <NUM> of the operating bank B have the cell voltage V entirely decreased to partially reach the determination value X2. This improves accuracy of abnormality determination on the operating bank B.

In the present embodiment, if the average cell voltage Vav of all the secondary batteries <NUM> of the operating bank B is less than the threshold X3 (No in S20 in <FIG>) and the minimum cell voltage Vmi of the secondary batteries <NUM> of the operating bank B is less than the determination value X2 (YES in S90 in <FIG>), the integrated monitoring unit <NUM> notifies to request the control unit <NUM> of the unmanned carrier <NUM> to execute current limitation processing of reducing current of the power supply system U (S100 in <FIG>).

Specifically, the integrated monitoring unit <NUM> notifies to request the control unit <NUM> to slow down the driving unit <NUM>. Upon receipt of the notification, the control unit <NUM> slows down the driving unit <NUM> to decrease discharge current Ib flowing from the power supply system U to the driving unit <NUM>.

In this configuration, when the secondary batteries <NUM> of the battery bank B have voltage entirely decreased by drop due to internal resistance to partially reach the determination value X2, the discharge current Ib is reduced to decrease the drop of the secondary batteries <NUM> due to internal resistance. The minimum voltage Vmi of the secondary batteries <NUM> can thus be inhibited from becoming less than the determination value X2 as well as the lower limit value X1. The determination value X2 exemplifies the "switching voltage".

<FIG> is a flowchart depicting an abnormality determination flow of the power supply system U, and the abnormality determination flow is started after the power supply system U is activated. After the activation, each of the module sensors <NUM> in each of the battery banks B1 to B10 executes, periodically at a constant cycle, processing of detecting the cell voltage V of the secondary batteries <NUM> of the corresponding battery module <NUM>, and processing of detecting the temperature T of the battery module <NUM>. The current sensor <NUM> executes, periodically at a constant cycle, processing of detecting the current Ib flowing to/from the battery modules <NUM>.

The individual monitoring unit <NUM> monitors the data on the items (<NUM>) to (<NUM>), namely, the cell voltage V of the secondary batteries <NUM> of the battery modules <NUM>, the total voltage Vb of the battery bank B, the temperature T of the battery modules <NUM>, and the current Ib of the battery bank B, in accordance with the data received from the module sensors <NUM> and the current sensor <NUM>.

The data on the items (<NUM>) to (<NUM>) and the data on the item (<NUM>) of the operating condition of the current breaker <NUM> are periodically transmitted from the individual monitoring unit <NUM> of each of the battery banks B1 to B10 to the integrated monitoring unit <NUM>, which also stores the data on the items (<NUM>) to (<NUM>).

The integrated monitoring unit <NUM> calculates the average cell voltage Vav of the secondary batteries <NUM> of all the operating banks B in accordance with the data on the cell voltage V of the secondary batteries <NUM> of the operating banks B. In a case where there are nine operating banks B1 to B9, the integrated monitoring unit <NUM> calculates the average cell voltage Vav of all the secondary batteries <NUM> of the nine operating banks B1 to B9. The integrated monitoring unit <NUM> then compares the average cell voltage Vav of the operating banks B1 to B9 with the threshold X3 (S20).

If the average cell voltage Vav of the operating banks B1 to B9 is not less than the threshold X3 (YES in S20), the integrated monitoring unit <NUM> calculates the minimum cell voltage Vmi or the lowest voltage of all the secondary batteries <NUM> of the operating banks B1 to B9.

The integrated monitoring unit <NUM> then compares the calculated minimum cell voltage Vmi with the determination value X2 (S30). In a case where the minimum cell voltage Vmi is not less than the determination value X2 (NO in S30), the integrated monitoring unit <NUM> determines that the operating banks B1 to B9 are normal, in other words, that the secondary batteries <NUM> of the operating banks B1 to B9 have no abnormality. In this case, the process flow returns to step S10.

In another case where the minimum cell voltage Vmi is less than the determination value X2 (YES in S30), the integrated monitoring unit <NUM> determines that the operating banks B1 to B9 have abnormality (S40). In other words, the integrated monitoring unit <NUM> determines that part of the operating banks B1 to B9 includes an abnormal secondary battery <NUM>. The integrated monitoring unit <NUM> then notifies the applicable operating bank B of abnormality. The applicable operating bank B includes the secondary battery <NUM> having the minimum cell voltage Vmi less than the determination value X2 (the operating bank B1 in this case).

The individual monitoring unit <NUM> of the applicable operating bank B1 then compares the minimum cell voltage Vmi with the lower limit value X1 (S50).

The minimum cell voltage Vmi is kept monitored while the minimum cell voltage Vmi is larger than the lower limit value X1. If the minimum cell voltage Vmi becomes less than the lower limit value X1 (YES in S50), the individual monitoring unit <NUM> transmits a command to the current breaker <NUM> to trip the current breaker <NUM> (S60).

The operating bank B1 including the abnormal secondary battery <NUM> is accordingly disconnected from the power supply system U. After the operating bank B1 is disconnected, only the operating banks B2 to B9 determined as being normal continuously supply power to the unmanned carrier <NUM>.

The integrated monitoring unit <NUM> constantly determines whether or not the number N of the currently operating banks is sufficient (S70). Specifically, the number N of the currently operating banks is more than "the minimum number of banks necessary for driving the unmanned carrier <NUM>", the integrated monitoring unit <NUM> determines that the number of the operating banks is sufficient. In a case where the number N of the currently operating banks is "nine" and the minimum number of banks necessary for driving is "seven", the number N of the operating banks is larger than the minimum number of banks by two and the number N of the operating banks is determined as being sufficient.

In a case where the number N of the operating banks is determined as being sufficient (YES in S70), the process flow returns to step S10.

In the case where the number of the operating banks B is larger than the minimum number of banks (YES in S70), if part of the secondary batteries <NUM> has abnormality, the operating banks B2 to B9 including the abnormal secondary batteries <NUM> are to sequentially be disconnected from the power supply system U when the minimum cell voltage Vmi reaches the lower limit value X1. Alternatively, the operating bank B can be immediately disconnected when the minimum cell voltage Vmi becomes less than the determination value X2.

In another case where the number of the operating banks is not more than the minimum number of banks (NO in S70), disconnecting any additional operating bank B causes the number of the operating banks to be less than the minimum number of banks and power cannot continuously be supplied to the unmanned carrier <NUM>.

In this case, the integrated monitoring unit <NUM> determines that discharge cannot be continuously executed, and notifies to request the control unit <NUM> of the unmanned carrier <NUM> to stop discharge, in other words, to stop the driving unit <NUM> (S80).

Described next is a case where the average cell voltage Vav of all the operating banks B is less than the threshold X3 (NO in S20). Assume that there are nine operating banks B1 to B9.

If the average cell voltage Vav of all the operating banks B1 to B9 is less than the threshold X3, the integrated monitoring unit <NUM> calculates the minimum cell voltage Vmi or the lowest voltage of all the secondary batteries <NUM> of all the operating banks B1 to B9, as in step S30. The integrated monitoring unit <NUM> then compares the calculated minimum cell voltage Vmi with the determination value X2 (S90).

In a case where the minimum cell voltage Vmi is not less than the determination value X2 (NO in S90), the process flow returns to step S10.

In another case where the minimum cell voltage Vmi of the operating banks B1 to B9 is less than the determination value X2 (YES in S90), the integrated monitoring unit <NUM> determines that the discharge current of the operating banks B1 to B9 needs to be limited, and notifies to request the control unit <NUM> of the unmanned carrier <NUM> to execute the current limitation processing. Specifically, the integrated monitoring unit <NUM> notifies to request the control unit <NUM> to slow down the driving unit <NUM> (S100).

The control unit <NUM> accordingly slows down the driving unit <NUM> so as to decrease the discharge current Ib flowing from the operating banks B1 to B9 to the driving unit <NUM>. The secondary batteries <NUM> of the operating banks B1 to B9 thus have smaller drop (decrease in voltage) due to internal resistance. This inhibits the minimum cell voltage Vmi from becoming less than the determination value X2, in other words, reaching the lower limit value X1 at the application limit. The operating banks B1 to B9 can thus continuously supply power to the unmanned carrier <NUM> while tripping the current breakers <NUM> being inhibited.

In the power supply system U according to the present embodiment, whether or not the operating banks B1 to B9 have abnormality is determined in accordance with the two determination criteria of "the average cell voltage Vav of the secondary batteries <NUM>" and the "minimum cell voltage Vmi of the secondary batteries <NUM>". This improves determination accuracy in comparison to the case where determination is made only in accordance with the determination criterion of "the minimum cell voltage Vmi".

Specifically, the integrated monitoring unit <NUM> determines whether or not the operating bank B has abnormality in accordance with the minimum cell voltage Vmi of all the secondary batteries <NUM> of the operating bank B when the average cell voltage Vav of all the secondary batteries <NUM> of the operating bank B is not less than the threshold X3 (YES in S20).

If the average cell voltage Vav is not less than the threshold X3 and the minimum cell voltage Vmi is lower than an ordinary value, the operating bank B is likely to include an abnormal secondary battery <NUM>. This enables accurate determination on whether or not the operating bank B has abnormality.

In the power supply system U according to the present embodiment, the operating bank B is determined as being abnormal if the minimum cell voltage Vmi is less than the determination value X2 (YES in S30). The determination value X2 is obtained by adding the predetermined margin to the lower limit value X1 of the secondary battery <NUM>. This configuration thus achieves determination that the operating bank B has abnormality before the minimum cell voltage Vmi reaches the lower limit value X1.

In the power supply system U according to the present embodiment, whether or not the operating banks B1 to B9 need current limitation is determined in accordance with the two determination criteria of "the average cell voltage Vav of the secondary batteries <NUM>" and the "minimum cell voltage Vmi of the secondary batteries <NUM>". This improves determination accuracy in comparison to the case where determination is made only in accordance with the determination criterion of "the minimum cell voltage Vmi".

Specifically, whether or not current limitation is needed is determined in accordance with the minimum cell voltage Vmi of all the secondary batteries <NUM> of the operating bank B in the case where the average cell voltage Vav of all the secondary batteries <NUM> of the operating bank B is less than the threshold X3 (NO in S20).

When average cell voltage Vav is less than the threshold X3 and the minimum cell voltage Vmi is decreased (NO in S20), the operating bank B is less likely to be abnormal but the flowing discharge current is likely to exceed an appropriate value. This configuration thus achieves accurate determination on whether or not the discharge current needs to be limited.

When the minimum cell voltage Vmi is less than the determination value X2, the integrated monitoring unit <NUM> determines that the current needs to be limited and notifies to request the control unit <NUM> of the unmanned carrier <NUM> to slow down the driving unit <NUM>. The control unit <NUM> then slows down the driving unit <NUM>, and the secondary batteries <NUM> of the operating banks B1 to B9 thus have smaller drop (decrease in voltage) due to internal resistance. This inhibits the minimum cell voltage Vmi from becoming less than the determination value X2, in other words, reaching the lower limit value X1 at the application limit. The operating banks B1 to B9 can thus continuously supply power to the unmanned carrier <NUM> while tripping the current breakers <NUM> being inhibited.

The second embodiment of the present invention will now be described with reference to <FIG> and <FIG>.

In the first embodiment, the operating banks B are determined as having abnormality in the case where the average cell voltage Vav of all the secondary batteries <NUM> of the operating banks B1 to B9 is not less than the threshold X3 (YES in S20 in <FIG>) and the minimum cell voltage Vmi of the secondary batteries <NUM> of the operating banks B1 to B9 is less than the determination value X2 (YES in S30 in <FIG>). In other words, part of the operating banks B includes an abnormal secondary battery <NUM>.

Furthermore, the operating banks B1 to B9 are determined as needing current limitation in the case where the average cell voltage Vav of all the secondary batteries <NUM> of the operating banks B1 to B9 is less than the threshold X3 (NO in S20 in <FIG>) and the minimum cell voltage Vmi of the secondary batteries <NUM> of the operating banks B1 to B9 is less than the determination value X2 (YES in S90 in <FIG>).

The voltage V and the SOC of the secondary battery <NUM> has a unique correspondence relation, and certain voltage V corresponds to a single SOC value.

Determination similar to that in step S20 can be executed in accordance with an average SOC of the secondary batteries <NUM> in place of the average cell voltage Vav of the secondary batteries <NUM>.

Specifically, the individual monitoring unit <NUM> of each of the operating banks B1 to B9 according to the second embodiment calculates, after the start of monitoring the state of the battery bank B (from S10), the SOC of each of the secondary batteries <NUM> in accordance with the current integration method or the like and further calculates the average SOC of the secondary batteries <NUM>. The average SOC is calculated at a predetermined cycle and is updated to the latest value.

The individual monitoring unit <NUM> of each of the operating banks B1 to B9 periodically transmits, to the integrated monitoring unit <NUM>, data on the SOC of each of the secondary batteries <NUM> and the average SOC of the secondary batteries <NUM>. The integrated monitoring unit <NUM> periodically calculates the average SOC of the secondary batteries <NUM> of all the operating banks B1 to B9.

The integrated monitoring unit <NUM> then compares the average SOC of the secondary batteries <NUM> of all the operating banks B1 to B9 with the threshold X3 (S25 in <FIG>).

As indicated in <FIG>, the determination value X2 is <NUM> [V] and the SOC corresponding thereto is <NUM> [%]. The threshold X3 of the average SOC is <NUM> [%] in the present example, because the permissible variation 3σ in initial capacity of the adopted energy storage device (secondary battery <NUM>) is exemplarily converted to SOC permissible variation of about <NUM>%.

If the average SOC is larger than <NUM> [%] as the threshold X3, the integrated monitoring unit <NUM> compares the minimum voltage Vmi of the secondary batteries <NUM> of all the operating banks B1 to B9 with the determination value X2.

In the case where the minimum voltage Vmi is less than the determination value X2 (YES in S30 in <FIG>), the integrated monitoring unit <NUM> determines that the operating banks B1 to B9 have abnormality (S40 in <FIG>). In other words, the integrated monitoring unit <NUM> determines that part of the operating banks B1 to B9 includes an abnormal secondary battery <NUM>.

In the second embodiment, whether or not the battery banks B1 to B9 have abnormality is determined in accordance with the average SOC of the secondary batteries <NUM> of all the operating banks B1 to B9 and the minimum cell voltage Vmi of the secondary batteries <NUM> of all the operating banks B1 to B9.

Similarly to the first embodiment, whether or not the operating banks B have abnormality can be determined more accurately in comparison to the case of determining whether or not the operating banks B have abnormality only in accordance with the determination criterion of the minimum voltage Vmi of the secondary batteries <NUM>.

Although not described in detail, the second embodiment also includes processing of transmitting a command to the current breaker <NUM> to trip the current breaker <NUM> if the operating banks B are determined as having abnormality and the applicable operating bank B has the minimum cell voltage Vmi reaching the lower limit value X1. The operating bank B determined as having abnormality is then disconnected from the power supply system U.

When the average SOC of all the operating banks B1 to B9 is less than the threshold X3 (NO in S25 in <FIG>) and the minimum cell voltage Vmi of the secondary batteries <NUM> of all the operating banks B1 to B9 is less than the determination value X2 (YES in S90 in <FIG>), the integrated monitoring unit <NUM> notifies to request the control unit <NUM> of the unmanned carrier <NUM> to slow down the driving unit <NUM>.

Similarly to the first embodiment, the control unit <NUM> then controls to slow down the driving unit <NUM>. This inhibits the voltage of the secondary batteries <NUM> of the operating banks B1 to B9 from becoming lower than the determination value X2.

The scope of the present invention is defined by the appended independent claims. Embodiments of the present invention are defined by the appended dependent claims.

In the following are set out additional aspects and variants - which are not necessarily encompassed by the claims - but helpful to fully comprehend the invention and therefore included for explanatory purposes only.

If the battery bank B is determined as having abnormality (S40), the processing of determining the minimum cell voltage Vmi is executed (S50). When the minimum cell voltage Vmi becomes lower than the lower limit value X1, the monitoring unit <NUM> executes the processing of tripping the current breaker <NUM> (S60).

In the case where the average cell voltage Vav of the secondary batteries <NUM> of the single battery bank B is less than the threshold X3 (NO in S20) and the minimum cell voltage Vmi of the secondary batteries <NUM> of the single battery bank B is less than the determination value X2 (YES in S90), the battery bank B is determined as needing current limitation and the monitoring unit <NUM> notifies to request the control unit <NUM> of the unmanned carrier <NUM> to execute the current limitation processing. The power supply system U configured by the single battery bank B, needs neither the processing of determining the number of the operating banks (S70 in <FIG>) nor the processing of requesting execution of discharge stop (S80 in <FIG>).

The integrated monitoring unit <NUM> according to the first embodiment executes determination according to the average cell voltage or the average SOC of all the operating banks and the minimum cell voltage Vmi, and notifies to request execution of the current limitation processing or discharge stop. The control unit <NUM> can alternatively execute similar processing in accordance with the parameters externally transmitted from the integrated monitoring unit <NUM>. The individual monitoring unit trips the current breaker also in this case.

The first embodiment includes two cases (a) and (b) of determination on the power supply system U according to "the average cell voltage Vav of all the secondary batteries <NUM> of the operating banks B1 to B9" and "the minimum cell voltage Vmi of all the secondary batteries <NUM> of the operating banks B1 to B9".

The present technique is widely applicable to determination on the state of the power supply system U in accordance with "the average cell voltage (or the average SOC) of the secondary batteries <NUM>" and "the minimum cell voltage of the secondary batteries <NUM>". The present technique is alternatively applied to determination on a state other than the cases (a) and (b). The same applies to the power supply system U of the standalone type including the single battery bank B.

Claim 1:
An energy storage apparatus comprising:
a plurality of energy storage devices (<NUM>) connected in series;
a voltage detection unit (<NUM>) configured to detect cell voltage of each of the energy storage devices (<NUM>); and
a monitoring unit (<NUM>) configured to monitor the plurality of energy storage devices (<NUM>),
characterized in that
the monitoring unit (<NUM>) is further configured to determine a state of the energy storage apparatus during discharge in accordance with: minimum cell voltage of the plurality of energy storage devices (<NUM>) and one of average cell voltage and average SOC of the plurality of energy storage devices (<NUM>); and
the monitoring unit (<NUM>) is further configured to determine whether or not to limit discharge current of the energy storage apparatus in accordance with the minimum cell voltage of the plurality of energy storage devices (<NUM>) when the average cell voltage or the average SOC of the plurality of energy storage devices (<NUM>) is less than a threshold.