Device and method for determining state of battery pack

A device that determines a state of a battery pack comprising three or more series-connected parallel-cell blocks each including a plurality of cells connected in parallel, comprising:

• a voltage sensor that detects an inter-terminal voltage of the parallel-cell block;
• a current sensor that detects that detects amount of the current flowing through the parallel-cell block;
• a processor configured to execute machine readable instructions to:
• obtain a parameter indicating a state of the parallel-cell block;
• calculate a parameter ratio that is a ratio of a parameter of a parallel-cell block to be determined to an average value of parameters of a plurality of parallel-cell blocks;
• calculate a moving-average value of the parameter ratio;
• obtain an index value that is a difference between the parameter ratio of the parallel-cell block to be determined and the moving-average value of the parameter ratio;
• determine a state of the parallel-cell block to be determined, based on the index value;
• and
• provide warning information indicating that abnormal degradation is caused when it is determined that the index value exceeds a threshold value;
• wherein
• the parameter indicating a state of the parallel-cell block includes the inter-terminal voltage detected by the voltage sensor and the amount of the current flowing detected by the current sensor,
• the processor obtains the parameter of the parallel-cell block to be determined whenever a predetermined time arrives,
• calculates the index value based on a moving-average value of the parameter ratio calculated using a parameter of the parallel-cell block to be determined obtained when the predetermined time immediately previously arrives and a parameter of the parallel-cell block to be determined obtained when the predetermined time currently arrives;
• as the plurality of parallel-cell blocks subject to calculation of the average value, parallel-cell blocks close in temperature to the parallel-cell block to be determined are selected;
• the processor obtains the parameter of the parallel-cell block to be determined whenever a predetermined time arrives;
• the temperature of the parallel-cell block to be determined is that of the parallel-cell block to be determined at the predetermined time;
• the battery pack is a battery pack mounted in a vehicle;
• the predetermined time is any one of:
• when the battery pack is externally charged;
• when an amount of power stored in the battery pack reaches a predetermined value while the vehicle is traveling;
• when the vehicle starts traveling;
• and when the vehicle ends traveling;
• and
• an inlet is connected to the battery pack, and the battery pack is charged by electric power supplied from the inlet.