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Accurate Circuit Model for Steady-State and Dynamic Performance of Lead-Acid AGM Batteries. W. Peng , Student Member, IEEE Y . Baghzouz , Senior Member, IEEE Department of electrical & Computer engineering University of Nevada, Las Vegas (USA). Need for battery models
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Accurate Circuit Model for Steady-State and Dynamic Performance of Lead-Acid AGM Batteries W. Peng, Student Member, IEEE Y. Baghzouz, Senior Member, IEEE Department of electrical & Computer engineering University of Nevada, Las Vegas (USA)
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 Overview
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. Need for Accurate Battery Models
Discharge Curves of 89 Ah, 12V AGM Battery(Source: Manufacturer Technical Manual) 3.7 A 0.75 A 89 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 Simplified Steady-State Equivalent Circuit
Best curve fit: Equivalent Series Resistance
Best curve fit: Equivalent Capacitance
Discharge Curves at Various Rates(obtained from analytical model)
8HR – 9.8 A 4HR – 18.25 A Comparison Between Measured and Calculated Discharge Characteristics
Equivalent resistance split into parts: • Total voltage drop due to sudden draw of current i (starting from rest): Equivalent Dynamic Circuit Model Exponential Voltage drop Sudden voltage drop
►The time constants at turn-on and turn-off are different. Static component Dynamic component Derivation of dynamic circuit parameters through measurements
Derivation of dynamic circuit parameters through measurements
Comparison Between Measured and Calculated Terminal Voltage under Non-uniform Current Discharge
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. Conclusion