Electrochemical cells are complicated energy storage systems with nonlinear voltage dynamics.There is a need for accurate dynamic modeling of the battery system to predict its behavior over time when discharging. The study conducted in this paper developed an intuitive model for electrochemical cells based on a simple mechanical analogy. A three-degree-of-freedom, spring-mass-damper system is decomposed into modal coordinates that represent the overall discharge, mass transport, and double-layer effect of the electrochemical cell. The developed model was experimentally demonstrated through pulsed discharge tests of commercially available lithium-ion and nickel metal hydride cells. The modal parameters of the natural frequency and damping ratio for each mode were determined by numerically minimizing the error in the time responses. Additionally, the mechanical analog was applied to two datasets [23,24]. The first dataset was used to optimize the modal parameters whereas the second dataset was utilized to validate the tuned parameters. It was found that the modal representation of the mechanical analog could accurately predict the time-response dynamics of all the cells considered. Additionally, by considering the discharge modal coordinate, the open-circuit voltage was determined and validated to that measured experimentally from the voltage relaxation peaks.
This study examines the discharge behaviour of a cylindrical LiFeS 2 cell to evaluate the parameters that can be used to predict and estimate the nonlinear dynamic response of a battery. A linear model is developed to simulate the discharge behaviour and examine the thermal behaviour. In particular, a commercial-grade battery is discharged with the industry-standard hybrid power pulsing characterization (HPPC) test and the current and voltage responses are recorded. The dynamic system is modelled with the equivalent circuit model (ECM) through MATLAB Simulink. A block diagram representation of the equivalent circuit model governing equations was developed. The parameter estimation tool was utilized to reduce the error and fit the simulation results to the experimental voltage responses, in order to obtain state of charge dependent dynamic parameters. Those parameters were then used in a Dual-Potential Multi-Scale Multi-Domain (MSMD) Battery Model solved in ANSYS Fluent to analyze the thermal behaviour by acquiring the temperature profiles and the temperature distribution within the cell. The nonlinear behaviour of the battery was characterized and the equivalent circuit model parameters were identified and are shown to agree with the experimental voltage responses. Furthermore, it is found that the battery temperature increased by 7.35℃ and was distributed uniformly within the cell.
Simulation and experimental studies were conducted to investigate energy consumption, develop ECMs (Energy Conservation Measures), and analyze temperature increase under a power failure scenario for a research data center at Youngstown State University. Two ECMs were developed to improve energy consumption by analyzing the thermal performance of the data center: (1) increase the return temperature in air conditioning vents; (2) provide cold aisle containment with the set point temperature increase. A transient analysis was conducted under a cooling system failure scenario to predict the temperature variation over time. The results suggest that it takes 600 s to increase the server inlet temperature by 16.1 °C for the baseline model. In addition, in the ECM #2, the maximum temperature at the server inlet did not reach 40 C under the air conditioning system failure scenario, which is the maximum operating temperature of the ASHRAE A3 envelop.
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