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:
"BATTERY STATE OF CHARGE ESTIMATION"
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 DESCRIPTION:
The following specification particularly describes the invention and the manner in which it is to be formed

FIELD OF INVENTION:
The present invention relates to the estimating battery state of charge (SOC) in a dynamic current application for batteries and more specifically for electric and hybrid vehicle batteries. The SOC according to the method of the invention is estimated by dynamically generating acid diffusion rate factor and multiplying with instantaneous ampere hour.
BACKGROUND & PRIOR ART:
Rechargeable battery is one of the critical components in electric and hybrid electric vehicles due to the fact that these vehicles are run by electrical energy provided by the batteries. Hence, it is important to accurately estimate battery state of charge. Furthermore, it is more important to accurately estimate battery state of charge in dynamic current application to control depth of discharge to enhance the battery cyclic life.
The efficiency factors of rechargeable batteries are different for different rate of discharges. The main reason behind this fact is that in low rate of discharge, the active material conversion is as high as possible, since acid availability throughout the plate is high. In high rate of discharge, the active material conversion does not take place throughout the plate. The interior part of active material does not participate in electro chemical reactions and remains in-active which results to the lower efficiency factor. For example, a battery with rating of 300Ah capacity when discharged with 30A gives the complete back up of rated lOhrs; however, it is delivering only 250Ah capacity when discharged at the 5 hour rate. Thus, estimation of correct battery SOC in dynamic current application is challenging with simple Amps x time (Ah) calculations on lead acid batteries in dynamic discharge currents.
US6160380 provides a method and apparatus for correcting battery characteristics and for estimating a residual energy of a battery. The method for correcting battery characteristics comprises detecting temperature of a battery; calculating temperature correction factors on the basis of detected battery temperature; detecting discharge characteristics of a battery; calculating a deterioration correction factor on the basis of detected battery discharge characteristics; and then correcting battery on the basis of calculated

temperature correction factors and calculated deterioration correction factor. It further estimates battery residual energy by subtracting battery power discharged amount from battery power dischargeable amount.
US6300763 discloses an apparatus and methods to estimate dynamic state of charge of a battery that is subject to periodic charging and discharging within a system. The method comprises empirically deriving a correction factor under various operational conditions; measuring charge currents and discharge currents; establishing a time interval relating to the charge and discharge current such that associated ampere-hour is calculated; calculating a dynamic state of charge value for the battery by incrementally applying said correction factor to each to each ampere-hour increment to update an existing state of charge value.
However, the existing solutions do not provide an accurate battery state of charge estimation in a dynamic environment. The existing solutions do not consider the instantaneous ampere and are not based on the rated capacity to provide an accurate battery state of charge estimation. Hence, there is a need to provide a method for accurate battery state of charge estimation and, in particular, for electric and hybrid vehicles in a dynamic environment.
SUMMARY OF INVENTION:
The present invention discloses a system and method to estimate State of Charge (SOC) of a rechargeable battery in a dynamic current application to accurately determine SOC. The SOC is estimated by dynamically generating acid diffusion rate factor and multiplying with instantaneous ampere hour. The method provides for true SOC indication which is independent of any lead acid battery technology, capacity & system voltage.
In an aspect, the present invention enhances the battery life by operating at a specified battery depth of discharge. The control of battery depth of discharge is independent of system operation. Another aspect of the invention is to eliminate the fixed Ampere hour to control the battery depth of discharge.

BRIEF DESCRIPTION OF DRAWINGS:
FIG. 1 illustrates a system of the present invention.
FIG. 2 illustrates a flowchart according to the method of the present invention.
FIG. 3 illustrates a graph of dynamically generated acid diffusion rate factor based on
dynamic current according to the method of the present invention.
FIG. 4 illustrates a graph of dynamically generated temperature factor based on
dynamically generated acid diffusion rate factor according to the method of the present
invention.
FIG. 5 illustrates a graph of battery SOC based on the dynamic current as final output
according to the method of the present invention.
FIG. 6 illustrates a graph of battery capacity v/s battery no load voltage.
FIG. 7 illustrates graph of ageing factor of a battery v/s number of cycles in the battery.
FIG. 8 illustrates graph of acid diffusion factor v/s battery recharge current.
FIG. 9 illustrates graph of temperature correction factor v/s acid diffusion rate factor.
DETAILED DESCRIPTION:
The present invention discloses a system and method to estimate State of Charge (SOC) of a rechargeable battery in a dynamic current application to accurately determine SOC; wherein the SOC being estimated by dynamically generating acid diffusion rate factor and multiplying with instantaneous ampere hour.
The method consists of calculating battery initial SOC based on key switch voltage; generating battery ageing factor based on number of cycles; generating acid diffusion rate factor based on dynamic current; generating temperature correction factors based on generated acid diffusion rate factor; calculating instantaneous ampere hours at operating temperature; calculating instantaneous ampere hours at room temperature; calculating recharge SOC; calculating instantaneous battery SOC using generated battery ageing factor, generated acid diffusion rate factor, generated temperature correction factors; and calculating and displaying cumulative battery SOC at any point of time during operation Referring to FIG. 1, which is a preferred embodiment, the system consists of an input device(l), and a processing unit(2) and an output device(3). The input parameters are fed to the system through the input device(l). The various parameters required to calculate

battery SOC as well as final battery SOC is calculated by the processing unit(2). The output device(3) can be a display which flashes calculated parameters.
The method of performance can be understood by referring to FIG. 2. The initial SOC is calculated by the processing unit(2) based on initial battery voltage. The average cell voltage in a battery system is taken into consideration to calculate the initial battery SOC. Then, the battery ageing factor is generated using number of cycles. The number of cycles is determined based on the cumulative ampere hour consumed per day. The instantaneous battery current is read and fed to the processing unit(2) by the input device(l). Then the acid diffusion factor is generated using dynamic current. FIG. 3 illustrates a graph of dynamically generated acid diffusion rate factor based on dynamic current according to the method of the present invention. It shows the relation between battery discharge, acid diffusion rate factors and discharge duration. Again referring to FIG. 2, based on the acid diffusion factor, the temperature correction factor is generated by the processing unit(2). FIG. 4 illustrates a graph of dynamically generated temperature factors based on dynamically generated acid diffusion rate factor according to the method of the present invention. It shows the relation between acid diffusion rate factor, temperature correction factors and discharge duration. Once again referring to FIG. 2, the next step is to calculate instantaneous ampere-hour at operating temperature. This value is useful for calculating recharge SOC. Then, the instantaneous ampere-hour at room temperature is calculated by the processing unit(2). In the preferred embodiment, the room temperature is 27° C. The value of the instantaneous ampere-hour at room temperature is useful for calculating instantaneous battery SOC which is calculated by the processing unit(2). The recharge SOC is calculated by the processing unit(2) hereafter. The cumulative battery SOC at any point of time during operation is calculated by the processing unit(2) and then displayed on the output device(3). FIG. 5 illustrates a graph of battery SOC based on the dynamic current as final output according to the method of the present invention. It shows the relation between battery dynamic current, battery SOC and discharge duration.
At the end of the day, the number of cycles based on ampere-hour consumed per day is fed by the input unit(l) and stored in the processing unit(2) for continued calculations.

The steps of the method as described before to estimate SOC of a rechargeable battery in a dynamic current application are as follows:
Step 1: Calculation of initial battery SOC
The initial battery SOC is calculated using average cell voltage in a battery system. To
consider battery self-discharge effect on SOC calculation, initial SOC calculated by
solving polynomial equation based on battery no load voltage.
Initial SOC (in percentage) = (A X - B)
X is average cell voltage in a battery system
The constants A, B are derived from OCV v/s SOC information provided by battery
supplier. The relation between capacity and battery no load voltage is shown in FIG. 6.
Step 2: Generation of battery ageing factors:
Ageing factor is defined as capacity reduction factor due to cycle life to ensure correct
battery state of health in cyclic application The battery ageing factor is generated using
number of battery life cycle count.
Aging factor = (-DY2-EY + F)
Y is number of battery life cycle count. The battery cycle count measured based on the
cumulative ampere hours consumed per day.
The constants D,E,F are derived from cycle life trend information provided by battery
supplier. FIG. 7 shows the relation between number of cycles in the battery and it's
ageing factor.
Step 3: Generating acid diffusion rate factor
Acid diffusion rate factor is the degradation of acid battery. It is generated using dynamic
battery current.
Battery acid diffusion rate = (G / (Z°3))
Z is the dynamic battery current.
D is a constant derived from battery supplier published rate of discharge, discharge
current data.
FIG. 8 refers to the relation between battery discharge current and acid diffusion rate
factor.

Step 4: Generation of temperature correction factor
The battery temperature correction' factor is generated/calculated by utilising acid
diffusion rate factor.
Battery temperature factor = Tx = (-H w2 + 1 w + J)
w is acid diffusion rate factor
H, I, J are constants derived from the relation between temperature correction factors,
discharge current and discharge current, acid diffusion rate factor. FIG. 9 refers to the
relation between temperature correction factor and acid diffusion rate factor.
Step 5: Calculation of instantaneous ampere-hour at operating temperature
The battery instantaneous ampere hour at operating temperature is calculated by
multiplying battery dynamic discharge and discharge duration.
Battery instantaneous Ah at operating =InstAhtx = Battery dynamic discharge x
Discharge duration
Step 6; Calculation of instantaneous ampere-hour at room temperature (27°C)
The instantaneous ampere hour at room temperature is calculated using said instantaneous
ampere hour at operating temperature, the auto generated temperature correction factor
and operating temperature.
The conversion of battery instantaneous ampere hours at operating temperature in to room
temperature as follows:
Battery instantaneous Ah at 27°C = Inst_Ah27 = (InstAhJx + (InstAhJx * (Tx/100) x
(27-t))
The constants in this equations are defined as:
InstAhJx = Instantaneous Ah at operating temperature
Tx = auto generated temperature correction factor
t= Operating temperature
Step 7: Calculation of recharge SOC
The recharge SOC is calculated using previous SOC, net cumulative ampere hours from the battery at any point of time and instantaneous ampere hour and battery rated capacity If (0.15<(Previous net Ah /battery rated capacity)>0.98) then

Recharge SOC =

Else
Recharge SOC = (Instantaneous charging Ah / Battery rated capacity)* 100
Step 8: Calculating instantaneous battery SOC
The battery instantaneous SOC is calculated using said battery acid diffusion rate factor,
said ageing factor, battery rated capacity and recharge factor.
Battery SOC inst =

Where Previous %SOC = Initial %SOC at power ON
The battery SOC at any point of time during operation is the cumulative instantaneous
battery SOC.
Battery %SOC = Cumulative Battery SOC inst
The method described before in detail is implemented to enhance battery life by operating at a specified depth of discharge and to eliminate fixed ampere hour to control battery depth of discharge.
The system and method of the present invention may be used to estimate State of Charge (SOC) of a various types of batteries in a dynamic current application. SOC maybe determined for batteries used in various applications, hybrid vehicle battery, electric vehicle battery, an inverter battery, etc. In effect, the system and method of the present invention may be used to estimate SOC of any rechargeable battery in a dynamic current application. Additionally, the battery SOC maybe determined either online, while the battery is in use or offline, while the battery is resting. The present invention is described in scientific terms using the mathematical formulae and certain examples as stated herein. 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 system and method to estimate State of Charge (SOC) of a rechargeable battery in a dynamic current application to accurately determine SOC; wherein the SOC being estimated by dynamically generating acid diffusion rate factor and multiplying with instantaneous ampere hour.
2. The system and method to estimate SOC of a rechargeable battery in a dynamic current application according to claim 1; wherein said method comprises:
(i) calculation of battery initial SOC based on key switch voltage;
(ii) generating battery ageing factor based on number of cycles;
(iii) generating acid diffusion rate factor based on dynamic current;
(iv) generating temperature correction factors based on generated acid
diffusion rate factor; (v) calculating instantaneous ampere hours at operating temperature; (vi) calculating instantaneous ampere hours at room temperature; (vii) calculating recharge SOC; (viii) calculating instantaneous battery SOC by considering steps (ii), (iii),
(iv); and (ix) calculating and displaying cumulative battery SOC at any point of time
during operation.
3. The system and method to estimate SOC of a rechargeable battery in a dynamic current application according to claim 1; wherein said system comprises an input device, a processing unit and an output device.
4. The system and method to estimate SOC of a rechargeable battery in a dynamic current application according to claim 2; wherein said initial battery SOC is calculated using average cell voltage in a battery system.
5. The system and method to estimate SOC of a rechargeable battery in a dynamic current application according to claim 2; wherein said battery ageing factor is generated using number of battery life cycle count.

6. The system and method to estimate SOC of a rechargeable battery in a dynamic current application according to claim 2; wherein said battery ageing factor is calculated for battery current greater than zero.
7. The system and method to estimate SOC of a rechargeable battery in a dynamic current application according to claim 2; wherein said battery acid diffusion rate factor is calculated using dynamic battery current greater than zero.
8. The system and method to estimate SOC of a rechargeable battery in a dynamic current application according to claim 2 and 6; wherein said temperature correction factor is calculated using said acid diffusion rate factor.
9. The system and method to estimate SOC of a rechargeable battery in a dynamic current application according to claim 2; wherein said instantaneous ampere hour at operating temperature is calculated by multiplying battery dynamic discharge and discharge duration.
10. The system and method to estimate SOC of a rechargeable battery in a dynamic current application according to claim 2; wherein said instantaneous ampere hours at room temperature is calculated using said instantaneous ampere hours at operating temperature, said auto generated temperature correction factors and operating temperature.
11. The system and method to estimate SOC of a rechargeable battery in a dynamic current application according to claim 2; wherein said recharge SOC is calculated using previous SOC, net cumulative ampere hours from the battery at any point of time, instantaneous ampere hours and battery rated capacity.
12. The system and method to estimate SOC of a rechargeable battery in a dynamic current application according to claim 2; wherein said battery instantaneous SOC is calculated using said battery acid diffusion rate factor, said ageing factor, battery rated capacity and recharge factor.

13. The system and method to estimate SOC of a rechargeable battery in a dynamic current application according to any of the preceding claim; wherein said method is implemented to enhance battery life by operating at a specified depth of discharge and to eliminate fixed ampere hour to control battery depth of discharge.