A battery pack is critical in electric vehicle (EV) performance, lifetime, and cost. It experiences high currents during charging and discharging that can damage the cells if not properly managed. During vehicle operation, it can also generate large amounts of heat that must be dissipated and is subjected to mechanical shock and vibration.
This article reviews some of the benefits of EV battery simulation, the results of a battery charging simulation, and the use of battery simulator emulators in electric powertrain development.
3D simulation software can combine disciplines like structural mechanics, computational fluid dynamics, multibody dynamics, and electromagnetic field simulation — supporting a multiphysics simulation approach for EV battery packs. For example, fluid dynamics can be used to analyze liquid and air-cooling approaches. Temperature changes can be predicted over time, incorporating weather and driving conditions into the simulation. Cooling fan designs in an air-cooled system can be optimized to maximize cooling and minimize noise.
That same simulation software suite can model structural factors like the impact of vibration during driving and how much deformation the pack can withstand without rupturing. Impact simulations can virtual test the crashworthiness of battery modules and the entire pack. Impact simulations can speed the design of the battery and ensure structural integrity while minimizing weight.
Electromagnetic simulation models of the currents and fields in the power electronics circuitry can be crucial in identifying potential sources of electromagnetic interference (EMI) from the battery charger and traction inverter to ensure proper operation of the overall system. The same software can simulate the heating of connectors and cables. Considering all the system elements can produce an accurate thermal map of the battery pack during various operating conditions (Figure 1).
Figure 1. EV battery pack simulation can produce a thermal map of the pack under a range of operating conditions. (Image: Dassault Systèmes)
Battery charging simulation
A battery charging simulation can be implemented using an equivalent circuit model (ECM) of the battery. An ECM with two resistor-capacitor (RC) elements can accurately capture the diffusion effects and predict Li-ion cell behavior. The simulation model includes eight temperature levels between -10° and 60° C for temperature dependency estimations. Outputs include the cell’s heat generation rate, current, voltage, and state of charge (SOC).
In one case, an 80-kWh battery pack with 456 prismatic Li-ion cells on a liquid-cooling plate has been simulated using these techniques. The ECM was assigned to the cells using a configurator that produced a mesh of 6.6 million finite-volume elements (Figure 2). A simulation was performed of 150 kW fast charging for 20 minutes. In that scenario, inefficiencies in the cooling plate combined with the high current flow resulted in nonuniform heating of the pack. The highest temperature spots remained under 45° C — the typical maximum value required to ensure safe operation.
Figure 2. Finite volume mesh for the battery pack thermal simulation with 6.6M finite volume elements. (Image: Siemens)
Battery simulator-emulator
Even before the final battery pack design is available, it’s usually necessary to begin developing the rest of the EV propulsion system. Battery simulator-emulators are available to test traction inverters and motors. These simulator-emulators have programmable slew rates, enabling designers to precisely control the response to a change in the desired output or changes in the load.
With output current and voltage ripple under 1%, they can accurately mimic the dc power flow from a battery pack. Large numbers of potential battery pack designs can be tested quickly.
The voltage can be controlled to be constant or dynamic. For example, the voltage can be programmed to decrease as the current increases to simulate the impedance of a high-voltage EV battery pack. Multiple simulator-emulators can be connected to support higher loads. In addition, these systems can recycle regenerated power back to the power grid, eliminating the need to dissipate power through resistors and reducing operating costs.
Summary
Simulation can speed the development of robust and long-life EV battery packs. It can model various chemical, thermal, electrical, and mechanical operating conditions and accurately predict pack performance. Before the pack is available, a battery simulator-emulator can be used to develop other components in the EV propulsion system, including the traction motor and inverter.
References
- Battery engineering from chemistry to systems, Dassault Systèmes
- Battery Simulator / Emulator, Unico
- The fast and the obvious – battery pack thermal simulation, Siemens
Images
Filed Under: Batteries, FAQs