W. Peng, Student Member, IEEE Y. Baghzouz, Senior Member, IEEE Department of electrical & Computer engineering University of Nevada, Las Vegas (USA) THE INTERNATIONAL CONFERENCE & UTILITY EXHIBITION 2011 28-30 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 PureElectric 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. * 89 A 3.7 A 0.75 A * I * 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: Vs Vs,o It / Cs * * Best curve fit: Rs a1I a2 * *Best curve fit: Cs NC a3 f ( I ) f (I ) a4 f ( I )(DOD) a5 f ( I ) a6 a7 I * * * * 8HR – 9.8 A 4HR – 18.25 A * *Equivalent resistance split into parts: Rs Rs' Rt *Total voltage drop due to sudden draw of current i (starting from rest): Vdrop Rs' i Rt i(1 et / o n ), on Rt Ct Sudden voltage drop Exponential Voltage drop * ►The time constants at turn-on and turn-off are different. Static component Dynamic component * 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.