ARC Collaborative Research Seminar Series
Fall 2012

ARC members can download the presentation files on our password-access online portal iARC.
Non-ARC members please email arcweb-info@umich.edu with your requests.

If you wish to attend the seminar remotely, please contact William Lim (williamlim@umich.edu) for teleconference details.


October 5th, Friday (9:15 - 11:00am)
University of Michigan, UM North Campus, Duderstadt 1180

On Ground Vehicle Electric Components

Computationally-Efficient Finite-Element-Based Thermal Models of Electric Machines
Dr. Heath Hofmann, Electrical Engineering and Computer Science, U. of Michigan

        Knowledge of the internal temperatures of an electric machine under real-time operating conditions would be extremely useful in order to determine its torque capabilities in real time. This knowledge is also useful for full-scale electric vehicle simulation and optimization.
        In this seminar, we present a technique for developing computationally-efficient thermal models for electric machines that can be used for real-time thermal observers and vehicle-level simulation and optimization. The technique is based upon simulating the eigenmodes of the thermal dynamics, as determined by 3D finite element analysis. The order of the model is then dramatically reduced in two ways. First, the system is decomposed into two subsystems, dynamic and static, by using the orthogonal property of the eigenvectors. The extent of excitation of each eigenmode is calculated, and only eigenmodes that are significantly excited are included in the dynamic model; other eigenmodes are treated as static. Second, only a few "hot spot" temperatures in various regions of the machine are chosen.
        The result is a thermal model that can accurately model internal temperatures of the machine while requiring the modeling of only a handful of states.To verify the proposed model, a test-bed has been built, and thermal experiments have been conducted on an AC stator. In the experiments the stator is excited with current corresponding to a driving cycle. Results show that the proposed model can capture the thermal behavior of the stator with acceptable accuracy.

Improved Density and Temperature Range of In-vehicle Power Converters: High Frequency Power Supplies for High Temperature Environments
Dr. Juan Rivas, Electrical Engineering and Computer Science, U. of Michigan

        Modern applications are driving demand for power systems with capabilities beyond what is presently achievable. High performance systems, like radars, medical imaging systems and military applications impose challenging specifications on power density and bandwidth that are difficult to achieve with current circuit topologies. Power density can be improved with better semiconductor components and passive elements, and by reducing the energy storage requirements of the system. By dramatically increasing the switching frequency, it is possible to reduce the energy storage requirements and improve bandwidth. I will describe the development of system architectures and circuit topologies for dc-dc power conversion at very high frequencies (>10MHz). The systems architectures are structured to overcome limitations associated with conventional designs. At the proposed switching frequencies, all inductors can be air-cored, eliminating core losses, saturation, and extending their operating temperature range. Very high frequency designs need efficient gate drive circuitry.
        We will discuss some fabrication techniques that simplify (and can potentially eliminate) tuning of resonant components while maintaining manufacturing cost low. It is expected that the architectures and circuit designs discussed here will lead to power converters having greatly reduced size and will be able to operate with an extended temperature range.


November 2nd, Friday (9:15 - 11:00am)
University of Michigan, UM North Campus, Duderstadt 1180

On Robotics Control

Integrated Power Systems for Improved Mobility of Ground Robots
Dr. Huei Peng, Department of Mechanical Engineering, U. of Michigan

        Unmanned Ground Vehicles can perform many surveillance, scouting, detection and rescue missions and keep soldiers out of harms’ way in the battlefield. Literature review and analysis indicates that existing SUGVs have short mission duration, lasting for less than 1-2 hours due to the limitation of their on-board power systems. The long-term goal of this project is to make significant progress toward the goal of reaching 10-hour mission duration without compromising the mission quality. This vision, we believe, we can achieved by working on research tasks in three directions: (1) load characterization, (2) sizing and configuration and (3) control including possibly path planning.
        For load characterization, the main focus over the last two year has been on building the terrain-wheel and terrain-track models. Experiments have been (and will continue to be) conducted, and experimental data have been collected from publications from other research groups. The experimental data are used to verify the models we have developed. IN this talk, we will provide update on our recent results for both wheel-terrain and track-terrain models.

Energy and Thermal Considerations in Small Ground Robots
Dr. Dawn Tilbury, Mr. John Broderick, Department of Mechanical Engineering, U. of Michigan

        Many reliability challenges in ground robots arise due to overheating and limited battery power. Small ground robots that were designed to be airtight may not have adequate cooling, particularly in hot environments. We have performed a number of experiments to characterize the thermal behavior of a Packbot using dynamic systems models. Our results show that these models can be used to predict the temperature of a Packbot reasonably accurately over a short time horizon. This predicted temperature information can be used to either inform the operator to slow down the operation, or to directly modify operator commands that may lead to a thermal overload and shutdown.
        We will also present experimental results on energy usage of a Packbot, at different velocities and on different terrains. We will characterize the overall energy usage from both mechanical and electrical perspectives, using data taken from the Packbot and our external measurements (e.g., GPS). We will present the somewhat surprising finding that the Packbot uses less energy (per kilometer) to drive at faster speeds, and discuss potential underlying causes (e.g., motor efficiencies).


December 7th, Friday (9:15 - 11:00am)
University of Michigan, UM North Campus, Duderstadt 1180

On Ground Vehicle Cooling.

Thermal management of battery modules investigated using experimental and computational techniques
Xuesong Li, Frank He, Dr. Lin Ma, Virginia Tech

        Thermal management is a critical for the reliable and efficient operation of vehicles. However, existing thermal management technologies have been shown to be inappropriate under many circumstances, including extreme ambient conditions and hybrid power schemes. Furthermore, existing controlled and well-documented experimental data are sparse. Such data are solely needed to validate and develop computational models for the exploration of innovative designs and optimization. Therefore, this work takes a holistic approach to address thermal management of batteries. We will combine high-fidelity simulation, controlled experiments (e.g., in wind tunnels), battery modeling in collaboration with other ARC partner universities, and the integration of these techniques for a system-level demonstration in collaboration with Michigan and TARDEC. This presentation will report the progress, both experimental and computational, in these areas and also outline future research directions.

Powertrain Thermal Management: Integration & Control of a Hybrid Electric Vehicle Battery Pack
Xin (William) Tao and Dr. John Wagner, Clemson University

        The operation of military vehicles in harsh environments requires robust thermal management systems to effectively remove heat from the powertrain components and occupant spaces. For hybrid electrical vehicles, the battery pack undergoes repeated charging and discharging cycles which generate heat that must be effectively managed for system reliability. In this project, smart cooling system designs and accompanying control strategies are under investigation for hybrid electric battery pack modules. An integrated AMESim-Matlab simulation has been created for a vapor compression system (loop 1) with two evaporators generating conditioned air for the passenger compartment thermal load (loop 2) and cooling air dedicated to the battery thermal load (loop 3). The mathematical model simulates the batteries’ electrical behavior and temperatures, as well as the temperature of the cooling fluids. Next, the electric compressor, fans, and a series of actuated controlled valves can be adjusted to offer temperature tracking while reducing cooling system power usage. An initial controller was implemented to minimize power consumption while maintaining the prescribed battery module temperature(s) for different operating conditions. The simulation results show that the battery core temperature can be stabilized within a small error region; the power consumption for loop 1 has been analyzed for two different cooling system configurations and ambient temperatures.


ARC members can download the presentation files on our password-access online portal iARC.
Non-ARC members please email arcweb-info@umich.edu with your requests.