W. Peng, Student Member, IEEEY. Baghzouz, Senior Member, IEEE

Department of electrical & Computer engineeringUniversity of Nevada, Las Vegas (USA)

THE INTERNATIONAL CONFERENCE & UTILITY EXHIBITION 201128-30 September 2011 Pattaya City, Thailand

*Need for battery models

*Typical battery discharge curves

*Derivation of Steady-State Circuit Model from Manufacturer Data

*Steady-State Model verification

*Derivation of Dynamic Circuit Model from Laboratory Tests Data and Verification.

*Conclusion

*Energy storage on the electric power system is becoming an increasingly important tool in *Managing the integration of large-scale, intermittent solar

and wind generation.

*Shaping the load curve (Peak shaving and valley filling)

*Smart Grid designs that call for additional distribution automation and sophistication such as islanding.

*Energy storage in the automotive industry is also becoming important due to the proliferation of Hybrid-Electric and Pure-Electric Vehicles.

*There are many types of batteries, each of which has advantages and disadvantages:*the Absorbed-Glass-Mat (AGM) battery - a type of Valve-

Regulated-Lead-Acid (VRLA) battery that is widely popular in renewable energy storage systems due to its high performance and maintenance-free requirement – is analyzed in this study.

3.7 A 0.75 A89 A

*Rs: total resistance (copper and electrolytic) – dependent on rate of discharge.

*Vs: equivalent voltage source –dependent on rate of discharge and DOD (or SOC).

*Vs can be replaced by an equivalent capacitance Cs. The relation between these two is:

I

soss CItVV /,

*Best curve fit: 21

as IaR

*Best curve fit:

543 ))((

)()(

aDODIfaIf

Ifa

NCCs

IaaIf 76)(

8HR – 9.8 A

4HR – 18.25 A

*Equivalent resistance split into parts:

*Total voltage drop due to sudden draw of current i (starting from rest):

ttont

tsdrop CReiRiRV on ),1( /'

tss RRR '

Sudden voltage drop

Exponential Voltage drop

Static componentDynamic component

The time constants at turn-on and turn-off are different.

Current Pulse (A)

20 15 10 5

(1-k)Rs (Ω) 0.022 0.023 0.023 0.024

kRs (Ω) 0.012 0.013 0.014 0.015

Rs (Ω) 0.033 0.036 0.037 0.039

τon (sec) 14 15 17 20

τoff (sec) 96 98 100 101

*A circuit model for an AGM Lead-acid battery was developed for steady-state and transient conditions: *The steady-state model (which consists of two dependent circuit parameters) was derived from the discharge curves provided by the manufacturer. *The dynamic model was obtained by adding a capacitive element across a portion of the series resistance, and the parameter values were obtained from laboratory tests.

*The resulting circuit model is found to predict battery performance under both constant as well as variable current discharge with sufficient accuracy.*The tests in this study were conducted indoors at room temperature. Future work consists of upgrading the circuit model by taking into account battery temperature when operating outdoors.