Management device, and power storage system

1. A management device configured to manage a power storage module including n power storage blocks series-connected, where n is an integer greater than or equal to 2, each of the power storage blocks containing m power storage cells parallel-connected, where m is an integer greater than or equal to 1, the management device comprising:

a voltage measuring unit to measure n pieces of voltages across the n power storage blocks; and

a controller including a processor and a memory storing a program,

wherein the program, when executed by the processor, causes the controller to:

assign ranks to the voltages measured across the n power storage blocks in descending order from high to low or in ascending order from low to high; and

detect an abnormality when information about the ranks differs from information about ranks for the power storage blocks in a normal state.

2. The management device according to claim 1 , wherein the information about the ranks is any one of a distribution of frequency of the ranks assigned to the voltages in descending or ascending order and a statistical indicator associated with the distribution of frequency.

3. The management device according to claim 1 , wherein the program, when executed by the processor, causes the controller to verify whether or not a significant difference exists between pieces of the information about the ranks.

4. The management device according to claim 1 , wherein the program, when executed by the processor, causes the controller to:

compile ranks assigned to voltages measured across the respective n power storage blocks during a set period and generate frequency distribution data of the ranks for the measured voltages;

hold the frequency distribution data of the ranks assigned to the voltages of the respective n power storage blocks in the normal state as reference frequency distribution data;

compare the frequency distribution data for the respective power storage blocks with reference frequency distribution data for the respective power storage blocks; and

in response to a result of comparison, determine that any one of the power storage blocks is abnormal on condition that a simple or significant difference exists between frequency distribution data and reference frequency distribution data for the power storage block in question.

5. The management device according to claim 4 , wherein the program, when executed by the processor, causes the controller to:

assign ranks to voltages of the n power storage blocks in descending order, and

estimate occurrence of an abnormality of decreased battery capacity or increased internal resistance in any of the power storage blocks when the rank in voltage shown in frequency distribution data for the abnormal power storage block changes upward during charging, and when the rank in voltage shown in frequency distribution data for the abnormal power storage block changes downward during charging, estimate formation of an abnormal route of a short circuit inside or outside the power storage block.

6. The management device according to claim 4 , wherein the program, when executed by the processor, causes the controller to:

assign ranks to voltages of the n power storage blocks in descending order, and

estimate occurrence of an abnormality of decreased battery capacity or increased internal resistance in any of the power storage blocks when the rank in voltage shown in frequency distribution data for the abnormal power storage block changes upward during charging and downward during discharging, and when the rank in voltage shown in frequency distribution data for the abnormal power storage block changes downward during charging and discharging, estimate formation of an abnormal route of a short circuit inside or outside the power storage block.

7. The management device according to claim 4 , wherein the program, when executed by the processor, causes the controller to:

hold a plurality of pieces of data about reference frequency distribution generated for a plurality of states categorized for each of the power storage blocks, and

compare frequency distribution data for any one of the power storage blocks with reference frequency distribution data for the power storage block in one of the categorized states corresponding to the state of the power storage block categorized at a voltage measurement time.

8. The management device according to claim 7 , wherein the plurality of states categorized for each of the power storage blocks are states categorized according to at least one item of state-of-charge (SOC) of the power storage block, temperature of the power storage block, direction of electric current flowing through the power storage block, or value of electric current flowing through the power storage block.

9. The management device according to claim 8 , wherein the program, when executed by the processor, causes the controller to:

temporarily hold pieces of data about frequency distribution for the respective power storage blocks and the states categorized for the respective power storage blocks at a voltage measurement time; and

a update updatable data about reference frequency distribution out of reference frequency distribution data for the respective power storage blocks by categorized state every time a predetermined updating period elapses, with use of frequency distribution data.

10. The management device according to claim 9 , wherein the program, when executed by the processor, causes the controller to, when control for equalizing the n power storage blocks is completed, further update updatable data about reference frequency distribution out of reference frequency distribution data for the respective power storage blocks by categorized state, with use of frequency distribution data held.

11. A power storage system comprising:

a power storage module; and

the management device according to claim 1 to manage the power storage module.