Battery Emulator for Coupled Electro-Thermo Powertrain Testing

Abstract

Approved, DCN# 543-443-23Battery emulation systems are useful for testing and evaluating powertrain systems; but typically,only consider the electrical characteristics of a battery. Powertrains with shared cooling components/systems between batteries and power electronics would benefit from hardware-in-the-loop testing facilities that consider both the electrical and thermal aspects of energy storage. In this work a battery emulator that physically emulates both the electrical and thermal characteristics with a coupled electro-thermal powertrain testbed is demonstrated. The coupled electro-thermo model links the electrical and thermal outputs together and calculates them in real-time. The electrical model is an equivalent circuit representation of a battery making use of experimental data from tested cells. The electrical model is coupled to the thermal model through temperature-dependent parameters of the cell resistance and open circuit voltages. The thermal model is a lumped isothermal reduced order heat generation model. This model will calculate the net heat generated from the ohmic losses, entropic losses, and losses to cooling (liquid and ambient). The thermal model is coupled to the electrical model by being dependent on the cell’s state of charge and using the cell’s current and voltage outputs for its governing equations. Models are parameterized on experimental data acquired through pulsed hybrid testing. In this work, a 3.5 kWh battery pack with a discharge of 40 amps at 48 volts generating 38.4 Watts of heat is emulated in an electro-thermo powertrain testbed configured to represent an electric naval platform such as a small autonomous boat subjected to both baseline and pulsed loading. The electrical emulation is performed through a bidirectional power supply and thermal emulation through a resistive heater. The electro-thermo powertrain testbed then dissipates the emulated electrical energy through power convertors and electronic loads while the thermal energy is dissipated through a heat exchanger that also cools the power convertors. Numerical and experimental validation demonstrate that the coupled electro-thermo battery emulator is capable of accurately representing the electrical and thermal aspects of a 3.5 kWh battery. Limitations in terms ofemulating batteries at higher temperatures and current draws are discussed. Effects of scaling the coupled electro-thermo battery emulator are also presented.Acknowledgment: This work was supported in part by the Office of Naval Research under contract NO.N00014-22-C-1003DISTRIBUTION STATEMENT A. Approved for public release: distribution unlimited