FORM 2
THE PATENTS ACT 1970
(39 of 1970)
AND
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10 and rulel3)
1. TITLE OF THE INVENTION:
"SYSTEM AND METHOD FOR BATTERY MONITORING"
2. APPLICANT:
(a) NAME: KPIT Cummins Infosystems Limited
(b) NATIONALITY: Indian Company incorporated under the
Companies Act, 1956
(c) ADDRESS: 35 & 36 Rajiv Gandhi Infotech Park, Phase 1, MIDC,
Hinjewadi, Pune 411057, Maharashtra, India.
3. PREAMBLE TO THE DESCRITION:
The following specification particularly describes the invention and the manner in which it is to be formed.

FIELD OF INVENTION:
The field of invention generally relates to determining the health of a battery and more specifically relates to determining state of charge of a battery and battery degradation.
BACKGROUND OF INVENTION:
A battery management system is used to determine State of Charge (SOC) and State of Health (SOH) of a battery. SOH of the battery gives the percentage degradation of the battery. SOC of a battery is the equivalent of a fuel gauge for a battery or a battery pack and provides the battery capacity. In other words, SOC is the ratio of the charge stored in the battery to the maximum charge that the battery can hold. SOC is usually expressed in terms of percentage. It is quite useful to determine the battery SOC for various applications. Battery SOC when estimated provides an indication of how much charge is remaining in the battery and how long it can be used for a particular application.
SOC of a battery is directly related to charge (Q) of the battery.' As per the fundamental equations of Physics that are known in art, an electric current is flow of charge, given by I = dQ/dt
Total charge built up for a given time, taking the time integral over a period, is given by Q = ∫ I dt
Thus, theoretically, change in the state-of-charge (SOC) of the battery is proportional to the current that is drawn out of the battery or is put in to the battery over a time period 't'. However, batteries are of various types and characteristics of the battery depend on its type. The battery characteristics like internal resistance, discharge curve, capacity, etc. depend on various parameters like age of battery, battery usage, temperature, etc. The battery characteristics change with a change in battery parameters as well as external conditions.
The existing methods do not provide an accurate SOC estimation as they are dependent on parameters of the battery which change with age, usage, etc. Further, the constants and errors in the equations used for SOC estimation are not accounted and compensated for leading to an inaccurate SOC estimation. The existing methods for battery SOH

estimation do not provide for determining age of the battery or battery degradation. Therefore, there is a need for a method that can correct for errors in the SOC estimation.
SUMMARY OF INVENTION:
The present invention discloses a method and system for estimating accurate State of Charge (SOC) and State of Health (SOH) of a battery comprising alternate use of a correction mechanism utilizing a function dependent on temperature of the battery and degradation of the battery and an exponential factor which is dependent on the battery current and the battery temperature and a correction loop, during charging-discharging cycle of the battery, wherein said method and system involves correction loop to correct/compensate any accumulation errors, caused due to battery parameters and determining age of the battery.
An object of the invention is to provide a system and method for determining the state-of-charge of a battery and battery degradation accurately over a period of time. The system and method of the invention may be used to determine the SOC of a battery and battery degradation either runtime, while the battery is being used or offline, while the battery is resting.
Another object of the invention is to provide a system and method for determining the state-of-charge of a battery which considers the battery characteristics that change over time and usage and hence provide for an accurate SOC estimation. The method of the invention compensates for the errors caused due to the parameters that change with a change in age, change in internal resistance, change in external temperature etc. and hence, affect the estimated SOC. With the method of the invention, SOC can be determined for all types of batteries.
A further object of the invention is to provide a method for estimating the battery degradation.
BRIEF DESCRIPTION OF DRAWINGS:
Fig. 1 illustrates a method for SOC estimation. Fig. 2 illustrates a method for SOH estimation.

Fig. 3 illustrates a block diagram for the system of the invention.
Fig. 4 illustrates typical relation between Open Circuit Voltage (OCV) and State of
Charge (SOC) of a battery.
Fig. 5 illustrates impedance model representation of a battery.
DETAILED DESCRIPTION;
The present invention uses a combination of a correction mechanism and a correction loop, accommodating for any differences in the voltage and current measurements. The present invention uses a correction mechanism method for calculating the SOC values. However, it accumulates error over time and hence a cumulative correction loop is used, which corrects for any errors in SOC estimation and which is based on the battery characteristics. It should be noted that both the approaches are not used simultaneously or at a given time instant, but either the correction mechanism or the correction loop is used.
SOC of a battery is directly related to charge (Q) of the battery. As per the fundamental equations of Physics that are known in art, an electric current is flow of charge, given by I = dQ/dt.
Total charge built up for a given time, taking the time integral over a period, is given by Q = ∫ I dt.
Thus, theoretically, change in the state-of-charge (SOC) of the battery is proportional to the current that is drawn out of the battery or is drawn in to the battery over a time period 't' However, batteries are of various types and characteristics of the battery depend on its type. The battery characteristics like internal resistance, discharge curve, capacity, etc. depend on various parameters like age of battery, battery usage, etc. The battery characteristics change with a change in battery parameters.
Based on the fundamental charge and current equation, the method of the present invention uses a correction mechanism to estimate SOC, which accommodates various errors by taking into account the battery characteristics like the battery current, the battery temperature and the battery degradation.

According to the method of the invention, SOC estimation is given by,
SOC (t) = SOC (t-1) + I (t)*∆t*k*exp (-λ*1 (t)) — Eq. 1
Where SOC(t) and SOC(t-l) are the SOC at time instants t and t-1, l(t) is the current at tth time instant, At is the time interval between the time instants, k = f(θ, %degradation), l=f(θ) which are as defined below, θ is the temperature and %degradation is given by the SOH of the battery

Where b1, b2, b3, b4 constants and c1, c2, c3, c4 proportionality constants. The values of these constants are determined by experimentation and vary from battery to battery. For example, for the battery under experimentation (12 V 5.3Ah lithium ion), the constants obtained are as listed below.

The values for different constants are obtained by minimizing the error between SOC obtained and reference SOC during experimentation stages. Any of the standard optimization techniques can be used to obtain the constants.
Whenever the current is very low, usually at rest time or at the ending of a charge or discharge cycle, cumulative correction loop is employed to correct for any accumulation error.
The correction loop is used during the following conditions when:

• There is a sudden drop or rise in voltage. It happens when the current suddenly goes to zero or when the current shoots up from zero. At these time instants, resistance is estimated and OCV is calculated from SOC = f (OCV) can be estimated.
• AV and AI for consecutive time instants are both close to zero then the battery is considered as being rested
SOC estimation:
The following steps describe the method of estimation of SOC:
Step 1: Initially, voltage, current and temperature at an instant't' is obtained i.e. V (t), I
(t) and 9 (t) readings are obtained.
Step 2: The initial SOC from the previous recording is obtained, if it is the first time, and the SOC from SOC vs OCV characteristics is calculated as SOC(t)= f(OCV(t)) [OCV (t) = V (t) at t=0]
Step 3: If the change in the voltage and current measurements is approximately 0 i.e., |V(t) - V(t-1)|40 or otherwise stepl repeated.
Step 5: % degradation of the battery is computed as




Step 6: The average of % degradation over multiple cycles (say n cycles) is calculated as
Step 7: SOH is calculated as
Accordingly, a method and system for estimating accurate State of Charge (SOC) and State of Health (SOH) of a battery comprises alternate use of a correction mechanism utilizing a function dependent on temperature of the battery and degradation of the battery and an exponential factor which is dependent on the battery current and the battery temperature and a cumulative correction loop, during charging-discharging cycle of the battery, wherein said method and system involves correction loop to correct/compensate any accumulation errors, caused due to battery parameters and determining age of the battery.
The said correction loop, called in the method and system, is employed while battery current at consecutive time instants being close to zero while voltage remains constant or, when current suddenly drops to zero or rises from zero. The correction loop employed computes the resistance of the battery.
During the estimation of SOC of the battery, while the correction loop is not being used, the method utilizes a function (k) dependent on temperature of the battery and degradation of the battery and a correction exponential factor which is dependent on the battery current and the battery temperature.
In a preferred embodiment, as illustrated in Fig. 1, the method consists of measuring initial values of battery current, voltage and temperature; determining initial value of battery SOC from previous recording or alternately calculating SOC from known corresponding OCV values if there is no previous record; determining SOC at an instant 't' by employing correction loop if battery current at consecutive instants is less than a threshold TH1, which is close to zero; determining SOC at an instant 't' by employing

correction loop if there is a sudden drop in or rise in voltage during start or end of charging-discharging cycle, thus computing resistance and assuming OCV remains constant thereby change in battery current is infinitesimal; updating SOC employing correction loop if the stated conditions are not satisfied; computing State of Health (SOH) of the battery thereby periodically updating value of the function dependent on temperature of the battery and degradation of the battery k. This procedure is repeated for new samples obtained.
As illustrated in Fig. 3, the system disclosed in the present invention consists of a first input device (1), a second input device (2), a processor (3) and an output device (4). The processor (4) computes battery SOC based on the provided input values.
As illustrated in Fig. 2, the steps for calculating SOH consists of computing kest when battery properly rested; computing percentage degradation of the battery; calculating average of percentage degradation over multiple cycles; calculating SOH using values which are calculated previously.
The steps for computing keSt during calculation of said SOH consists of calculating initial battery SOC using known corresponding OCV values at an instant tl when battery is properly rested; computing accumulation sum; calculate final battery SOC at another instant t2; compute kest if difference between initial and final battery SOC being greater than 40, otherwise repeating previous steps. The relation between SOC and OCV to calculate initial SOC is shown in FIG. 4, whereas FIG. 5 illustrates the impedance model representation of a battery.
The method and system of the invention maybe utilized to determine SOC for various types of batteries and various applications. SOC maybe determined for batteries used in various applications, like hybrid vehicle battery, electric vehicle battery, an inverter battery, etc. Additionally, the battery SOC maybe determined either online, while the battery is in use or offline, while the battery is resting. The above examples, will serve to illustrate the practice of this invention being understood that the particular shown by way of example, for purpose of illustrative discussion of preferred embodiment of the invention and are not limiting the scope of the invention.

WE CLAIM,
1. A method and system for estimating accurate State of Charge (SOC) and State of Health (SOH) of a battery comprising alternate use of a correction mechanism utilizing a function dependent on temperature of the battery and degradation of the battery and an exponential factor dependent on the battery current and the battery temperature and a cumulative correction loop, wherein said method and system involves the cumulative correction loop to correct/compensate any accumulation errors, caused due to battery parameters and determining age of the battery.
2. The method and system for estimating SOC and SOH of a battery according to claim 1, wherein said cumulative correction loop being employed while battery current at consecutive time instants being close to zero while voltage remaining constant or, current suddenly dropping to zero or rising from zero.
3. The method and system for estimating SOC and SOH of a battery according to claim 1, wherein said cumulative correction loop employed while current suddenly dropping to zero or is rising from zero, comprises computing the resistance of the battery.
4. The method and system for estimating SOC and SOH of a battery according to claim 1, wherein while the cumulative correction loop is not being used, the SOC estimation comprises utilizing a function (k) dependent on temperature of the battery and degradation of the battery and a correction exponential factor which is dependent on the battery current and the battery temperature.
5. The method and system for estimating SOC and SOH of a battery according to claim 1, wherein the SOC of a battery is determined either online, while the battery is being used or offline, while the battery is being rested.
6. The method and system for estimating SOC and SOH of a battery according to claim 1, wherein said method further comprising:
(i) Measuring initial values of battery current, voltage and temperature;

(ii) Determining initial value of battery SOC from previous recording or
alternately calculating SOC from known corresponding OCV values if
there is no previous record; (iii) Determining SOC at an instant 't' by employing correction loop if
battery current at consecutive instants is less than a threshold TH_1,
which being close to zero. (iv) Determining SOC at an instant 't' by employing correction loop if
there is a sudden drop in or rise in voltage during start or end of
charging-discharging cycle, thus computing resistance and assuming
OCV remains constant thereby change in battery current is
infinitesimal; (v) Updating SOC employing correction loop if conditions in steps (iii)
and (iv) are not satisfied; (vi) Computing State of Health (SOH) of the battery thereby periodically
updating value of the function dependent on temperature of the battery
and degradation of the battery k; (vii) Repeating steps (ii) to (vi) for new samples obtained.
7. The method and system for estimating SOC and SOH of a battery according to claim 1, wherein said system comprising a first input device (1), a second input device (2), a processor (3) and an output device (4).
8. The method and system for estimating SOC and SOH of a battery according to claim 4, wherein said processor computes battery SOC based on the provided input values.
9. The method and system for estimating SOC and SOH of a battery according to claim 3, wherein calculating said SOH comprising:
(viii) Computing the estimated 'k' when battery properly rested;
(ix) Computing percentage degradation of the battery;
(x) Calculating average of percentage degradation over multiple cycles;
(xi) Calculating SOH using values calculated during steps (i) to (iii).

10. The method and system for estimating SOC and SOH of a battery according to claim 8, wherein computing kest during calculation of said SOH further comprising:
(xii) Calculating initial battery SOC using known corresponding OCV
values at an instant tl when battery is properly rested; (xiii) Computing accumulation sum; (xiv) Calculate final battery SOC at another instant t2; (xv) Compute kest if difference between initial and final battery SOC being greater than 40 or else repeating steps (i) to (iii).