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Accurate Circuit Model for Steady-State and Dynamic Performance of Lead-Acid AGM Batteries

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

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  1. 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)

  2. 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

  3. 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

  4. Discharge Curves of 89 Ah, 12V AGM Battery(Source: Manufacturer Technical Manual) 3.7 A 0.75 A 89 A

  5. 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

  6. Best curve fit: Equivalent Series Resistance

  7. Best curve fit: Equivalent Capacitance

  8. Discharge Curves at Various Rates(obtained from analytical model)

  9. Laboratory Experiment setting

  10. Three-Step Battery Charging

  11. 8HR – 9.8 A 4HR – 18.25 A Comparison Between Measured and Calculated Discharge Characteristics

  12. 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

  13. ►The time constants at turn-on and turn-off are different. Static component Dynamic component Derivation of dynamic circuit parameters through measurements

  14. Derivation of dynamic circuit parameters through measurements

  15. Comparison Between Measured and Calculated Terminal Voltage under Non-uniform Current Discharge

  16. 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

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