Accurate Circuit Model for Steady-State and Dynamic Performance

Report
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  et / 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.

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