Geometry Optimization of an Interior Permanent Magnet Machine for Electric Vehicles - Life Cycle Cost Minimization for City, Rural and Highway Driving
Doctoral thesis, 2023
This thesis investigates the benefits of customizing an Interior Permanent magnet Machine (IPM) for a specific combination of city, rural and highway driving. Focus lies on the potential to reduce the Life Cycle Cost (LCC) of the IPM and power electronic converter, for an example Battery Electric Vehicle (BEV), by custom-making the IPM.
The IPM customization is done with an optimization work-flow where both the size and shape of the IPM geometry is varied to minimize the LCC for a given driving scenario. The driving is represented with a distribution of energy and time over the entire torque versus speed plane of the IPM, which allows a large number of drive cycles to be aggregated and included without affecting the computational time. The optimization work-flow includes scaling of electromagnetic finite element results, to automatically select the best feasible version of each IPM geometry, considering performance requirements as well as thermal and mechanical constraints. Customized IPM designs are created for city, rural and highway driving and compared with an IPM optimized for mixed driving. The city, rural and highway driving types are represented both with single drive cycles and with large amounts of measured driving.
Customizing the IPM geometry was found to give significant LCC reduction in cases with pronounced city or highway driving. The LCC was found to be 7% lower for a city driving cycle and 1% lower for a highway driving cycle, for the customized IPM compared to the IPM optimized for mixed driving. For the city driving cycle, the optimization results in an IPM design with large slots, high amount of copper and relatively shallow flux barriers which are well filled with magnets. Comparatively, the IPM custom-made for the highway cycle has smaller slots and lower copper and magnet amounts.
Still, the IPM optimized for mixed driving has a large and well-placed operating region with high efficiency and has a low LCC for most of the included driving scenarios. None of the included driving distributions based on large amounts of measured driving were specialized enough to benefit significantly from customization of the IPM. Overall, the results indicate that the usage that is currently typical for passenger cars can be well met with an IPM optimized for general driving and the potential for further improvement by custom-making the IPM is rather limited. However, the benefit of custom-making the IPM design is likely higher for BEV applications with more specialized driving type and larger amounts of driving.
The IPM customization is done with an optimization work-flow where both the size and shape of the IPM geometry is varied to minimize the LCC for a given driving scenario. The driving is represented with a distribution of energy and time over the entire torque versus speed plane of the IPM, which allows a large number of drive cycles to be aggregated and included without affecting the computational time. The optimization work-flow includes scaling of electromagnetic finite element results, to automatically select the best feasible version of each IPM geometry, considering performance requirements as well as thermal and mechanical constraints. Customized IPM designs are created for city, rural and highway driving and compared with an IPM optimized for mixed driving. The city, rural and highway driving types are represented both with single drive cycles and with large amounts of measured driving.
Customizing the IPM geometry was found to give significant LCC reduction in cases with pronounced city or highway driving. The LCC was found to be 7% lower for a city driving cycle and 1% lower for a highway driving cycle, for the customized IPM compared to the IPM optimized for mixed driving. For the city driving cycle, the optimization results in an IPM design with large slots, high amount of copper and relatively shallow flux barriers which are well filled with magnets. Comparatively, the IPM custom-made for the highway cycle has smaller slots and lower copper and magnet amounts.
Still, the IPM optimized for mixed driving has a large and well-placed operating region with high efficiency and has a low LCC for most of the included driving scenarios. None of the included driving distributions based on large amounts of measured driving were specialized enough to benefit significantly from customization of the IPM. Overall, the results indicate that the usage that is currently typical for passenger cars can be well met with an IPM optimized for general driving and the potential for further improvement by custom-making the IPM is rather limited. However, the benefit of custom-making the IPM design is likely higher for BEV applications with more specialized driving type and larger amounts of driving.
Optimization
Finite Element Analysis
Interior Permanent Magnet Machine
Drive Cycles
Life Cycle Cost
Battery Electric Vehicle
Electric Machine Design
EC, Hörsalsvägen 11, Göteborg
Opponent: Dr. Mircea Popescu, Principal Product Specialist, Ansys Corporation, UK.
Author
Elisabet Jansson
Chalmers, Electrical Engineering, Electric Power Engineering
Convergence of Core Losses in a Permanent Magnet Machine, as Function of Mesh Density Distribution, a Case-Study Using Finite-Element Analysis
IEEE Transactions on Energy Conversion,;Vol. 35(2020)p. 1667-1675
Journal article
Time Resolution Dependency of Core Loss Accuracy in Finite Element Analysis of a Permanent Magnet Synchronous Machine
Proceedings - 2020 International Conference on Electrical Machines, ICEM 2020,;(2020)p. 1011-1017
Paper in proceeding
E. Jansson, E. Grunditz, T. Thiringer, "Impact of Saturation and Scaling on the Field Weakening Performance of an Interior PM Machine.", 2020 International Conference on Electrical Machines (ICEM), IEEE, 2020.
E. Jansson, T. Thiringer, E. Grunditz, "Influence of Flux Barrier Shape and Mechanical Constraints on Field-Weakening Performance in Double-Layer Interior Permanent Magnet Machines."
The interest in electric cars is rising rapidly and even though electric motors have a long history, using them in electric cars leads to new challenges. Therefore, research efforts aim to improve electric motors specifically for electric car applications. To reduce losses and improve the driving range of the electric car, the electric motor needs to have high efficiency. An electric car motor also needs to be able to accelerate the car fast enough and should not be too costly.
The electric motor needs to run differently depending on whether you are driving through the city center, along a winding rural road or cruising on the highway. These driving types differ in both speed and acceleration of the car, which means that they also differ in the rotational speed and torque that the electric motor needs to deliver. Additionally, the efficiency of the electric motor changes with rotational speed and torque as well as the design of the motor. Therefore, the best electric motor design can be different depending on the type of driving it will be used for.
This thesis presents a method to optimize the design of the most common type of electric car motor, the Interior Permanent magnet Machine (IPM). The optimization method is used to minimize the life-cycle cost, including both the initial investment and the cost of losses for both the IPM and the converter that powers it. Focus lies on comparing the results of the optimization for different combinations of city, rural and highway driving. The results show that the same well-balanced IPM design is the best option for a wide range of mixed driving. However, custom-making the IPM design is found to offer a life-cycle cost reduction of 7% for pronounced city driving and 1% for pronounced highway driving.
The electric motor needs to run differently depending on whether you are driving through the city center, along a winding rural road or cruising on the highway. These driving types differ in both speed and acceleration of the car, which means that they also differ in the rotational speed and torque that the electric motor needs to deliver. Additionally, the efficiency of the electric motor changes with rotational speed and torque as well as the design of the motor. Therefore, the best electric motor design can be different depending on the type of driving it will be used for.
This thesis presents a method to optimize the design of the most common type of electric car motor, the Interior Permanent magnet Machine (IPM). The optimization method is used to minimize the life-cycle cost, including both the initial investment and the cost of losses for both the IPM and the converter that powers it. Focus lies on comparing the results of the optimization for different combinations of city, rural and highway driving. The results show that the same well-balanced IPM design is the best option for a wide range of mixed driving. However, custom-making the IPM design is found to offer a life-cycle cost reduction of 7% for pronounced city driving and 1% for pronounced highway driving.
Electric Machine concept for next generation electrical vehicles (ELMA)
Swedish Energy Agency (42818-1), 2017-01-01 -- 2021-09-30.
Driving Forces
Sustainable development
Areas of Advance
Transport
Energy
Subject Categories
Electrical Engineering, Electronic Engineering, Information Engineering
Energy Systems
ISBN
978-91-7905-937-8
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5403
Publisher
Chalmers
EC, Hörsalsvägen 11, Göteborg
Opponent: Dr. Mircea Popescu, Principal Product Specialist, Ansys Corporation, UK.