Power storage system

1 . A power storage system comprising:

a battery;

a voltmeter configured to measure voltage of the battery;

an ammeter configured to measure current of the battery;

a temperature sensor configured to measure temperature of the battery; and

processing circuitry configured to:

calculate internal resistance of the battery, based on the voltage and the current;

obtain a reference value for the internal resistance of the battery corresponding to a present state of charge and a present temperature of the battery from a map of the state of charge and the temperature to the reference value;

calculate a correction coefficient indicating a difference between the internal resistance and the reference value;

calculate a correction value by correcting the reference value using the correction coefficient;

calculate estimated internal resistance, which is an estimated present value of the internal resistance, based on the correction value and a present voltage;

control charge and/or discharge of the battery, based on the internal resistance or the estimated internal resistance; and

calculate the correction value by correcting the reference value using the correction coefficient calculated in the past when a voltage fluctuation ΔV or a current fluctuation ΔI is 0 (zero), and the processing circuitry is unable to calculate the internal resistance.

2 . The power storage system according to claim 1 , wherein

the processing circuitry is further configured to:

learn from the correction coefficient; and

calculate the correction value by correcting the reference value using training results by the processing circuitry when the processing circuitry is unable to calculate the internal resistance, and

the training results are an average or a median of the correction coefficient calculated in a past period.

3 . The power storage system according to claim 2 , wherein

the processing circuitry is further configured to start learning when a predetermined period has passed since the processing circuitry is ready to calculate the internal resistance.

4 . The power storage system according to claim 2 , wherein

the processing circuitry is further configured to stop learning when the processing circuitry has been unable to calculate the internal resistance for a predetermined period.

5 . The power storage system according to claim 2 , wherein

the processing circuitry stops learning when at least the state of charge, the temperature, or the reference value corresponding to the state of charge and the temperature fluctuates more than a predetermined value from a value when the processing circuitry calculated the internal resistance most recently.

6 . The power storage system according to claim 1 , wherein

the internal resistance includes an R component and a parallel-RC component connected in series, and

the processing circuitry is further configured to:

calculate first internal resistance, which reflects a characteristic of the R component, and a second internal resistance, which reflects a characteristic of the parallel-RC component;

obtain a first reference value corresponding to the present state of charge and the present temperature from a first map of the state of charge and the temperature of the battery to the first reference value;

obtain a second reference value corresponding to the present state of charge and the present temperature from a second map of the state of charge and the present temperature to the second reference value;

calculate a first correction coefficient, which indicates a difference between the first internal resistance and the first reference value;

calculate a second correction coefficient, which indicates a difference between the second internal resistance and the second reference value;

calculate a first correction value by correcting the first reference value using the first correction coefficient;

calculate a second correction value by correcting the second reference value using the second correction coefficient; and

calculate the estimated internal resistance, based on the first and the second correction values.