Page 40 - ASME DSCC 2015 Program

Technical Program

Thermal Management and Voltage Stabilization in Air-forced open- Multi-objective optimization to Minimize Battery Degradation and
Cathode fuel Cells Electricity Cost for Demand Response in Datacenters
Contributed regular paper. DSCC2015-9920 Contributed regular paper. DSCC2015-9812
Nima Lotfi, hesam Zomorodi, robert Landers, Missouri University of Abdullah-Al Mamun, Iyswarya narayanan, Anand Sivasubramaniam,
Science and Technology, Rolla, MO, United States Hosam K. fathy, The Pennsylvania State University, University Park, PA,
United States, Di Wang, Microsoft Research, Redmond, WA, United States
Temperature control is undoubtedly one of the important challenges in
open-cathode fuel cell systems. Due to cost considerations, it is traditionally This paper presents a Lithium-ion battery control framework to achieve
achieved by constant-speed operation of the fans. In this paper, a state minimum health degradation and electricity cost when batteries are used
feedback temperature controller, combined with a Kalman filter to mitigate for datacenter demand response. Demand response in datacenters refers
the noisy temperature measurements is designed and implemented. The to the adjustment of demand for grid electricity to minimize electricity cost.
controller-filter set facilitates robust thermal management with respect to Utilizing batteries for demand response will reduce the electricity cost but
model uncertainties and measurement noise. The proposed temperature might accelerate health degradation. This tradeoff makes battery control for
control not only manages to track the fuel cell temperature reference, it can demand response a multi-objective optimization problem. Current research
also be used to stabilize the output voltage. Voltage regulation is of great focuses only on minimizing the cost of demand response and does not cap-
importance for open-cathode fuel cells as it guarantees a predictable and ture battery transient and degradation dynamics. We address this multi-ob-
fixed fuel cell output voltage for given current values in spite of internal and jective optimization problem using a second-order equivalent circuit model
external disturbances. The controllers were implemented experimentally and an empirical capacity fade model of Lithium-ion batteries.
and the results show promising performances in regulating the reference Estimation of lithium-Ion Concentrations in Both Electrodes of a
temperature and voltage despite model uncertainties and disturbances. lithium-Ion Battery Cell
Elevated Temperatures Can Extend the life of lithium Iron Phosphate Contributed regular paper. DSCC2015-9693
Cells in Hybrid Electric Vehicles Satadru Dey, Beshah Ayalew, Pierluigi Pisu, Clemson University,
Contributed regular paper. DSCC2015-9763 Greenville, SC, United States
Tanvir R. Tanim, Christopher D. Rahn, The Pennsylvania State University, For control and estimation tasks in battery management systems, the bench-
State College, PA, United States, niklas legnedahl, Volvo Group Trucks mark Li-ion cell electrochemical pseudo-two-dimensional (P2D) model is
Technology, Gothenburg, Gothenburg, Sweden
often reduced to the Single Particle Model (SPM). The original SPM consists
This study investigates the effects of elevated temperature on commercially of two electrodes approximated as spherical particles with spatially distrib-
available high power graphite/LiFePO4 cells using a temperature depen- uted Li-ion concentration. However, the Li-ion concentration states in these
dent, electrolyte enhanced, single particle model (ESPM-T) coupled with a two-electrode models are known to be weakly observable from the voltage
Solid Electrolyte Interphase (SEI) layer growth aging model. The ESPM-T is output. This has led to the prevalent use of reduced models in literature that
capable of simulating up to 25C and 10 sec charge-discharge pulses within generally approximate Li-ion concentration states in one electrode as an al-
a 35-65% SOC window and 25degC to 40degC temperature range with less gebraic function of that in the other electrode. In this paper, we remove such
than 1% voltage error, so it is suitable for hybrid electric vehicle (HEV) ap- approximations and show that the addition of the thermal model to the elec-
plications. The aging model is experimentally validated with an aggressive trochemical SPM essentially leads to observability of the Li-ion concentration
HEV cycle running for 4 months with less than 1% error. Instead of defining states in both electrodes from voltage and temperature measurements.
battery End of Life (EOL) as an arbitrary percent of capacity loss, we use the Then, we propose an estimation scheme based on this SPM coupled with
cycle number when the battery voltage hits 3.6V/2V (maximum/minimum) lumped thermal dynamics that estimates the Li-ion concentrations in both
voltage limits. This is the practical limit of operation without reduced perfor- electrodes. Moreover, these Li-ion concentration estimates also enable the
mance. Simulations show that operating cells at 35degC increases their life estimation of the cell capacity. The estimation scheme consists of a sliding
by 45% compared to room temperature operation. If the cell temperature is mode observer cascaded with an Unscented Kalman filter (UKF). Simulation
increased stepwise, then battery life is increased 85% more with a 50degC studies are included to show the effectiveness of the proposed scheme.
cell temperature at EOL. Battery initial size can be reduced by 24% using
this temperature set-point strategy.

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