Estimating real-time state of charge to determine runtime of secondary batteries using microcontroller

FIELD OF INVENTION
[001] The embodiments herein generally relate to batteries, and, more particularly, to estimating the state of charge and runtime of the battery.

BACKGROUND AND PRIOR ART
[002] In a UPS system, a rechargeable battery is used to supply power to a variety of loads, in both commercial and residential scenarios. However, there is no inline method to predict the remaining charge in the battery and hence the time for which the battery can supply power to the load and display the same.

SUMMARY OF INVENTION
[003] In view of the foregoing, an embodiment herein provides a system and method to determine the capacity and runtime of a battery when connected to a load in a UPS type of system using microcontroller. The embodiments describe an inline monitoring technique to establish real-time battery capacity and display the remaining run time of the battery.
[004] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.

BRIEF DESCRIPTION OF DRAWINGS
[005] The embodiments herein will be better understood from the following description with reference to the drawings, in which:
FIG. 1 shows the system diagram, according to embodiments disclosed herein;
FIG. 2 shows a flow diagram of the process, according to embodiments disclosed herein;
FIG. 3 shows a graph between state of charge and internal resistance of the battery;
FIG. 4 shows a graph between K1, K2 coefficients of SOC equation and battery current; and
FIG. 5 shows a graph between K3 coefficient of SOC equation and battery current.

DESCRIPTION OF EMBODIMENTS
[006] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
[007] As mentioned, there remains a need for a system to determine system backup time of a battery. The embodiments herein achieve this by providing a microcontroller to determine the runtime of the battery. Referring now to the drawings, and more particularly to FIGS. 1 through 5, where similar reference characters denote corresponding features consistently throughout the figures, there are shown preferred embodiments.
[008] A model has been created to determine the capacity and runtime of a battery when connected to a load in a UPS type of system using microcontroller. Embodiments herein describe an inline monitoring technique to establish real-time battery capacity and display the remaining run time of the battery. A microcontroller is connected to the battery to do inline sensing, calculations and display the run-times of the battery based on connected load.
[009] A battery is connected to a load. The voltage and current patterns for different loads, temperatures are obtained. Internal resistance of said battery, Ri is calculated. A graph is drawn between the capacity of the battery, SOC and internal resistance, Ri of the battery, as shown in FIG. 3. From said graph a second order equation for state of charge of battery is developed with internal resistance as the variable. The constants in the equation are again function of battery current.
[0010] Said equation is,
SOC = K1Ri2 – K2Ri + K3 (1)
K1 = C1I2 + C2I – C3 (2)
K2 = D1I – D2 (3)
K3 = E1I + E2 (4)
where,
SOC = State of charge (Remaining Capacity)
Ri = Internal Resistance
I = Battery current.
K1, K2, K3 in equation (1) are derived from equations (2), (3) and (4) respectively.
C1, C2, C3, D1, D2 are constants derived from FIG. 4
E1, E2 are constants derived from FIG.5
[0011] As shown in FIG. 1, a battery (101) is connected to a load (104). The battery terminal voltage and the current are sensed and given as inputs to a microcontroller (102). Said microcontroller (102) is programmed with equation (1). The voltage across the battery and the current drawn from the battery when it is supplying a load is sensed at regular intervals using ADC of said microcontroller (102). Then internal resistance of said battery (101) is calculated. The state of charge of battery is estimated using equation (1) with battery current and internal resistance as parameters and runtimes of said battery are shown on a display (103), where said runtimes are the time said battery has been in discharging mode and time for which said battery can supply power to said load.
[0012] FIG. 2 shows a flow chart, according to embodiments described herein. Said microcontroller (102) measures battery terminal voltage and current (201). On detecting the condition of the battery (202) i.e. the battery is in charging mode or discharging mode, if said battery is in charging mode, said microcontroller continues to measure battery terminal voltage and current. If said battery has been detected in discharging mode, total usage time of said battery is calculated (203). Coefficient K1 is calculated using equation (2) (204), with constants C1, C2 and C3 being derived from FIG. 4. Coefficient K2 is calculated using equation (3) (205), with constants D1 and D2 being derived from FIG. 4. Coefficient K3 is calculated using equation (4) (206), with constants E1 and E2 being derived from FIG. 5. Remaining capacity of battery is calculated using equation (1) (207), using which remaining runtime of battery is calculated (208) and runtimes are displayed (209) on said display. Said displayed runtimes are the time said battery has been in discharging mode and time for which said battery can further supply power to said load. Flow mentioned above is repeated.
[0013] Embodiments disclosed herein allow consumers to do load management by optimizing use of battery in their systems. If multiple loads are connected to the battery, the user can turn off any load by monitoring the remaining runtime display and thereby increase the runtime on other loads.
[0014] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the appended claims.
ABSTRACT
A system and method has been described herein to determine the capacity and runtime of a battery when connected to a load in a UPS type of system using microcontroller. The embodiments use an inline monitoring technique to establish real-time battery capacity and display the run times of the battery, where the runtimes are the time the battery has been in discharging mode and time for which the battery can further supply power to the load.