Battery pack and method for calculating electric energy of battery pack

1. A battery pack comprising:

a plurality of battery units which are connected in series to each other;

a voltage and current measurement unit configured to measure voltages and currents of the battery units;

a temperature measurement unit configured to measure temperatures of the battery units;

a calculation unit configured to calculate a power variation which is a variation of electric energy remaining in the battery units on the basis of the voltages, the currents, and the temperatures of the battery units;

a storage unit configured to store internal resistance data which is data for calculating internal resistances of the battery units from the temperatures of the battery units; and

a communication unit configured to transmit a predictive signal, based on a substantial electric energy, to an external device,

wherein the calculation unit is further configured to refer to the internal resistance data to determine the internal resistances of the battery units at a present temperature, and calculate, when a power variation of all the battery units from reference time 0 to current time t is set to ΔE(t) and a total internal resistance which is a total sum of the internal resistances of the battery units is set to R temp (t), the power variation ΔE(t) from an expression defined as

Δ E ( t )=∫ 0 t {V ( t ) I ( t )− I 2 ( t ) R temp ( t )} dt

wherein V(t) is a total voltage of all the battery units, and I(t) is a current of the battery units,

wherein the calculation unit is further configured to calculate an accumulated electric energy balance which is accumulated in the battery units on the basis of a stored initial electric energy of the battery pack and the calculated power variation ΔE(t),

wherein in a state where a time of initial full charge is set to reference time 0, the storage unit is further configured to store the initial electric energy which is an electric energy measured at the reference time, and the calculation unit is further configured to calculate a present electric energy by a sum of the initial electric energy and the power variation,

wherein the calculation unit is further configured to calculate a deterioration ratio obtained by comparing an electric energy at a time immediately preceding full charge with the initial electric energy, and correct the total internal resistance on the basis of the deterioration ratio, and

wherein the calculation unit is further configured to calculate an electric quantity of the battery units on the basis of the currents, and calculate the substantial electric energy capable of being output by the battery units on the basis of the accumulated electric energy balance and the electric quantity.

2. The battery pack according to claim 1 , wherein the temperature measurement unit is further configured to measure a temperature of a first battery unit which is one of the battery units, and

the calculation unit is further configured to refer to the internal resistance data from the temperature of the first battery unit to specify an internal resistance of the first battery unit, calculate a total sum R temp (t) of the internal resistances of the battery units from an expression defined as R temp (t)=Nr s (t), and calculate, the power variation,

wherein N is a total number of the battery units, and r s (t) is the internal resistance of the first battery unit

R temp ( t )= Nr s ( t )  (3).

3. The battery pack according to claim 1 , wherein the calculation unit is further configured to multiple the immediately preceding total internal resistance by a reciprocal number of the deterioration ratio, and corrects the total internal resistance.

4. A method for calculating electric energy of a battery pack, the method comprising:

measuring voltages and currents of a plurality of battery units which are connected in series to each other, and measuring temperatures of the battery units;

calculating a power variation which is a variation of electric remaining in the battery units on the basis of the voltages, the currents, and the temperatures of the battery units;

storing internal resistance data which is data for calculating internal resistances of the battery units from the temperatures of the battery units;

referring to the internal resistance data to determine the internal resistances of the battery units at the present temperature,

calculating, when a power variation of all the battery units from reference time 0 to current time t is set to ΔE(t) and a total internal resistance which is a total sum of the internal resistances of the battery units is set to R temp (t), the power variation ΔE(t) from an expression defined as ΔE(t)=∫ 0 t {V(t)I(t)−I 2 (t)R temp (t)} dt, V(t) being a total voltage of all the battery units and I(t) being a current of the battery units;

calculating an accumulated electric energy balance which is accumulated in the battery units on the basis of a stored initial electric energy of the battery pack and the calculated power variation ΔE(t);

storing, in a state where a time of initial full charge is set to reference time 0,

the intitial electric entergy which is an electric energy measured at the reference time,

calculating a present electric energy by a sum of the initial electric energy and the power variation;

calculating a deterioration ratio obtained by comparing an electric energy at a time immediately preceding full charge with the initial electric energy;

correcting the total internal resistance on the basis of the deterioration ratio;

calculating an electric quantity of the battery units on the basis of the currents;

calculation a substantial electric energy capable of being output by the battery units on the basis of the accumulated electric energy balance and the electric quantity; and

transmitting a predictive signal, based on the substantial electric energy, to an external device.