Simulating an electric motor system becomes increasingly complex and time-consuming when additional components, such as the battery and inverter, are included at the system level.
To model the electric motor, tools like Ansys Maxwell or Motor-CAD can be used, while Ansys TwinBuilder is ideal for simulating the inverter and battery. Their individual thermal behaviours can be analyzed using Ansys Icepak or Fluent. However, evaluating all these results together at the system level—and doing so much faster than with full CFD or FEA simulations—is made possible by Ansys Twin Builder, which uses Reduced Order Models (ROMs).A ROM is generated from an existing FEA or CFD dataset and can be reused for multiple design iterations with varying input parameters. This enables fast, coupled system-level simulations without re-running detailed 3D analyses.
The first part of this blog series will discuss how to create the Dynamic ROM of the electric motor.
To begin, create a Dynamic ROM for the electric motor using the model previously published in the Ozen Engineering blog (Reference Electric Motor).
Before using the Dynamic ROM feature in Ansys Icepak, ensure that your base model runs successfully with no setup errors. Then, proceed with the steps shown below to export and link the ROM for system-level analysis.
Go to Icepak/Toolkit/Modeling/LTI_ROM_Parametric_Setup and make sure you are in the Transient solution type.
From the pop-up window, the input sources are automatically selected. If no sources appear, you need to assign block heat flux or heat sources to the stator windings.
The Input Object Power should represent the maximum power of any component in the system. For example, if the DC winding loss is 10 W and the magnet loss is 2 W, you should enter 10 W here. Even though the simulation may temporarily apply 10 W to another component during database generation, this does not affect accuracy—it’s simply used to build the ROM database.
Finally, check the “Create steady-state design and link with transient setup” option. This ensures that the system first runs a steady-state simulation (with no losses) and then performs the transient simulation on top of it. Then you can click "create and run setup," and it will create the flow for you and run the simulation.
After the simulation is complete, Icepak displays a message in the Message Manager showing the location of the generated LTI file. This file contains the thermal response data that will be used in Twin Builder for creating the Reduced Order Model (ROM).
Open Ansys Twin Builder and create a new blank project.
From the top ribbon, navigate to Twin Builder → Toolkit → Thermal Model Identification.
In the pop-up window, select the same input and output points defined in your Icepak model.
In this example, there are four inputs (Phases A, B, and C currents) and six outputs (Phases A, B, C, Magnet Monitor, and Housing Monitor).
Keep the default settings, browse to the LTI file location generated by Icepak, and click Generate.
Once successfully created, the ROM can be inserted into your system-level simulation in Twin Builder.
To validate the ROM:
Couple the ROM block with a STEP function as an excitation source.
Assume a current input of 5 A (peak) applied for 500 seconds, which then drops to 1 A until 1000 seconds.
The expected behaviour is a temperature rise to 500 seconds, followed by a gradual cooldown.
Connect three STEP blocks (for Phases A, B, and C) to the ROM inputs.
Before running the model, ensure that the ROM outputs are included in the results. Go to Twin Builder → Output Dialogue and enable all ROM outputs.
For visualization, create a plot by selecting Draw → Report → Rectangular Plot, and add the desired traces.
Run the simulation and observe the results within seconds. The ROM model predicts a realistic thermal response:
Phases A, B, and C reach approximately 140°C,
Magnets reach 80°C,
Housing stabilizes near 120°C, then cools gradually after 500 seconds.
Alternatively, the current input with and without temperature feedback can be used to evaluate the temperatures more accurately at the system level design, which will be used in the next parts of the blog.
Winding resistance temperature feedback is enabled. The top right plot shows the winding resistance comparison with and without feedback. The bottom right plots show the temperature results with and without the resistance feedback. The results can be observed in more detail from the provided downloadable content.
The electric motor ROM model for temperature simulation, derived from the CFD results, is now complete. We will use this model in the next steps to build a system-level electric motor simulation.
Downloadable content:
The dynamic Reduced Order Model created from the Icepak CFD results provides an efficient and accurate way to predict the thermal behaviour of the electric motor under various operating conditions. By capturing the essential physics in a compact form, the ROM enables rapid simulations in Twin Builder that would otherwise require heavy full-scale CFD or FEA analyses.
With the ROM successfully validated, it is now ready to be integrated into the broader system-level workflow, where the motor can be coupled with the inverter, battery, and control logic. This approach allows reliable multiphysics evaluation at a fraction of the computational cost, making it a powerful method for design exploration, optimization, and real-time performance assessment.
Ozen Engineering Inc. leverages its extensive consulting expertise in CFD, FEA, optics, photonics, and electromagnetic simulations to achieve exceptional results across various engineering projects, addressing complex challenges such as antenna design, signal integrity, electromagnetic interference (EMI), and electric motor analysis using Ansys software.
We offer support, mentoring, and consulting services to enhance the performance and reliability of your electronics systems. Trust our proven track record to accelerate projects, optimize performance, and deliver high-quality, cost-effective results. For more information, please visit https://ozeninc.com.
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FEA: https://www.ozeninc.com/consulting/fea-consulting/
Optics: https://www.ozeninc.com/consulting/optics-photonics/
Photonics: https://www.ozeninc.com/consulting/optics-photonics/
Electromagnetic Simulations: https://www.ozeninc.com/consulting/electromagnetic-consulting/
Thermal Analysis & Electronics Cooling: https://www.ozeninc.com/consulting/thermal-engineering-electronics-cooling/