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Contract No. DE-AC36-08GO28308

Electric Drive Dynamic Thermal 

System Model for Advanced 

Vehicle Propulsion Technologies

Cooperative Research and Development 

Final Report

CRADA Number: CRD-09-360

NREL Technical Contact: Kevin Bennion

CRADA Report

NREL/TP-7A10-59230

October 2013
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Cover Photos: (left to right) photo by Pat Corkery, NREL 16416, photo from SunEdison, NREL 17423, photo by Pat Corkery, NREL 

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This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.

Cooperative Research and Development Final Report

In accordance with Requirements set forth in Article XI.A(3) of the CRADA document, this document is 

the final CRADA report, including a list of Subject Inventions, to be forwarded to the Office of Science 

and Technical Information as part of the commitment to the public to demonstrate results of federally 

funded research.

CRADA Number: CRD-09-360

CRADA Title: Electric Drive Dynamic Thermal System Model for Advanced Vehicle 

Propulsion Technologies

Parties to the Agreement: Ford Motor Company

Joint Work Statement Funding Table Showing DOE Commitment:

Estimated Costs NREL Shared Resources

Year 1 $ 100,000.00

Year 2 $ 50,00.00

Year 3 $ 00.00

TOTALS $ 150,000.00

Abstract of CRADA Work:

Electric drive systems, which include electric machines and power electronics, are a key enabling 

technology for advanced vehicle propulsion systems that reduce the dependence of the U.S. transportation 

sector on petroleum. However, to penetrate the market, these electric drive technologies must enable 

vehicle solutions that are economically viable. The push to make critical electric drive systems smaller, 

lighter, and more cost-effective brings respective challenges associated with heat removal and system 

efficiency. In addition, the wide application of electric drive systems to alternative propulsion 

technologies ranging from integrated starter generators, to hybrid electric vehicles, to full electric vehicles 

presents challenges in terms of sizing critical components and thermal management systems over a range 

of in-use operating conditions.

This effort focused on developing a modular modeling methodology to enable multi-scale and multiphysics simulation capabilities leading to generic electric drive system models applicable to alternative 

vehicle propulsion configurations. The primary benefit for the National Renewable Energy Laboratory 

(NREL) is the ability to define operating losses with the respective impact on component sizing, 

temperature, and thermal management at the component, subsystem, and system level. However, the 

flexible nature of the model also allows other uses related to evaluating the impacts of alternative 

component designs or control schemes depending on the interests of other parties.
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This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.

Summary of Research Results:

The CRADA between Ford Motor Company and NREL produced a modular modeling methodology to 

support collaborative design of electric drive systems incorporating complex system interactions, multiple 

physical domains, and multiple simulation scales.

Electric drive systems for vehicle propulsion involve the interactions of multiple components over 

multiple physical domains. The complex interactions require simulation tools that support the design and 

testing of electric drive systems and components. Simulation tools support designers on multiple levels 

including activities such as component design, system interactions, system optimization, efficiency 

analysis, thermal design, and controls development. 

However, developing a model to simulate a specific component's physical characteristics for a single 

application is not the final goal. The wide use of simulation or computer aided engineering (CAE) tools 

for electric drive systems presents challenges that include enabling reuse of validated models, managing 

and communicating model updates, applying appropriate interfaces or boundary conditions, supporting 

communication between different engineering disciplines to cover the multiple physical domains, and 

enabling a flexible model framework that captures the appropriate detail for the intended application. The 

scope of the project emphasized a multi-scale, multi-physics modular modeling methodology compatible 

with commonly used commercial codes that enabled cross discipline or organization collaboration. The

scope focused on an electric drive system as shown in Figure 1, which highlights an example application 

using two electric machines and inverters that represent a dual electric drive system The model also has 

the flexibility to configure itself as a single electric drive system depending on the model configuration 

settings defined by the user, as shown in Figure 2.

Figure 1. Electric drive system model scope (dual electric drive example)
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Figure 2. Single electric drive configuration example

The model was also required to run as a stand-alone model or be integrated into a larger vehicle system 

level model. This flexibility was provided through the external interface definitions. The external 

interfaces were the electrical energy storage system, such as a battery, and the electric machine shafts that 

were connected to the vehicle mechanical powertrain as shown in Figure 1.

Another requirement of the electric drive system model was that it needed to have the ability to swap 

component models based on the desired modeling scale. The ability to swap component models was 

created by breaking up the electric drive system model into modular component definitions, which are

listed in Table 1. The user is able to select component models within each category for their specific 

application.

Table 1: Scope of Model Components

Model Components Definitions

Electric Machine Power Conversion and Loss Model

Inverter Power Conversion and Loss Model

DC/DC Converter Power Conversion and Loss Model

Electric Machine Thermal and Cooling Model

Inverter Thermal and Cooling Model

DC/DC Converter Thermal and Cooling Model 

Vehicle Thermal Management System Model

Electric Drive Control Systems for the Electric Machine, Inverter, and DC/DC Converter

External Interface Definitions: Energy Storage System (such as a battery), Powertrain System (such as 

motor shaft)

Multi-Scale Flexible Modular Modeling Methodology

We developed a modular modeling methodology—built around MATLAB and Simulink because it is a 

commonly used program for modeling and simulation of physical systems and controls—leading to a 

generic electric drive system modeling framework applicable to alternative vehicle propulsion 

configurations. Supported applications include single and dual electric drive systems. Examples include 

electric drive systems relevant to hybrid electric vehicles, plug-in hybrid electric vehicles, battery electric 

vehicles, fuel cell vehicles, and integrated starter generator systems. A key feature of the model is the 

flexibility to simulate alternative electric drive configurations while easily swapping component models 
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at www.nrel.gov/publications.

depending on the user requirements. The modular modeling approach enables users to swap or exchange 

component models for the components in Table 1, resulting in a generic model not tied to a specific 

technology or company. For example a detailed model of the inverter switches can be selected to capture 

the switching characteristics, or a less-detailed model can be chosen for applications focused on longer 

time scales. Similarly, a detailed thermal model of the inverter could be selected to capture the transient 

temperature responses or a less detailed model could be selected that fixes the component temperatures to 

a specified value.

In addition to simulating a full electric drive system over a range of applications, the developed model 

framework also allows a designer to focus on a specific component or subsystem. For example it is 

possible to focus on a single component such as the inverter or electric machine as shown in Figure 3 and 

Figure 4. It is also possible to focus on specific subsystems, such as the combined inverter and electric 

machine subsystem, as shown in Figure 5.

Figure 3. Model configured for inverter component focus

Figure 4. Model configured for electric machine component focus
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Figure 5. Model configured for inverter and electric machine subsystem focus

The model framework was designed to run in a stand-alone mode with an emphasis on the electric drive 

system. It is also possible to integrate the model into a larger vehicle system model by applying the 

necessary external interface definitions for the input DC bus voltage, motor shaft speed, and commanded 

motor torque. The listed examples of the multi-scale modeling methodology are included to demonstrate 

the flexibility of the model framework; users can develop custom models based on their simulation needs.

Multi-Physics Capability

The model includes a multi-physics domain capability incorporating electrical, mechanical, thermal, fluid, 

electromagnetic, and control elements. The project focused on the model framework and methodology

with some sample component models. The model includes sample component models as illustrative 

examples, which can be adjusted or modified as needed based on the user’s needs. It is expected that users 

would develop custom models based on their own needs.

The model framework includes elements for control logic related to specific components, physical plant 

models representing the physical component, loss models for heat load prediction, thermal models for 

component temperatures, and a vehicle thermal management system model.

Each of the physical domain models assumes a standard interface definition to ensure compatibility with 

linked physical domains, which enables the ability to develop models at different scales for the intended 

application.

Enable Cross Discipline or Organization Collaborations

In addition, the structured modeling approach improves the ability to share models or integrate new 

component models. The model framework was developed with the need of cross group or company 

collaboration in mind, allowing users to share relevant models at a component, subsystem, or system 

level. The structure of the model framework allows engineers or designers to work on specific 

components related to their area of expertise. For example the power electronics electrical engineer can 

work on the inverter electrical models, the electric machine designer can support the motor 

electromagnetic models, the controls engineer can develop the necessary control methods, and the thermal 

engineer can work on the relevant thermal models. Once the models are validated, the developed models 

are placed in an established library or model repository to share across the relevant organization. The 

structured component model interface definitions enable easier integration of new component models 
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developed within or outside of the organization. In addition to supporting collaboration within an 

organization, the model framework also supports outside collaboration with organizations that do not 

have access to the full model libraries or repositories; stand-alone electric drive system models can be 

shared with groups without access to the model libraries.

Conclusions

The CRADA between Ford Motor Company and NREL produced a modular modeling methodology for 

electric drive systems, subsystems, and components. A key feature of the model is the flexibility to 

simulate alternative electric drive configurations incorporating single or dual electric drive systems. The 

modular modeling approach enables users to swap or exchange component models and includes a multiphysics domain capability incorporating mechanical, electromagnetic, electrical, thermal, fluid, and 

control elements.

The primary benefit for NREL, as the lead U.S. Department of Energy (DOE) laboratory for electric drive 

thermal management, is the ability to define operating losses with the respective impact on component 

sizing, temperature, and thermal management at the component, subsystem, and system level. The 

flexible nature of the model also allows for other uses related to evaluating the impacts of alternative 

component designs or control schemes depending on the interests of other parties. The modeling 

methodology can be shared with other interested partners, and through additional DOE and industry 

collaborations, improved component models can be developed to support the improvement of CAE tools 

for power electronics and electric machines.

Subject Inventions Listing: None

Report Date: 9/9/2013

Responsible Technical Contact at Alliance/NREL: Kevin Bennion

This document contains NO confidential, protectable, or proprietary information.