Peter J. Savagian

Design and Performance of Electrical Propulsion System of Extended Range Electric Vehicle (EREV) Chevrolet Volt

This paper presents the design and performance details of the Chevrolet Volt electric propulsion system. The propulsion system has two machines: One machine is operating mostly as a motor while the other machine is operating mostly as a generator. Both machines of the Volt electric drive system are permanent-magnet ac synchronous machine types with the magnets buried inside the rotor. The motor has distributed windings. However, as opposed to a conventional stranded winding, the Chevrolet Volt motor has bar-wound construction to improve the motor performance, particularly in the low to medium speed range. At higher speed, the skin and proximity effects in the stator bars lead to increased stator winding losses but are addressed in the design. The bar-wound construction also has excellent thermal performance, in both the steady-state and transient conditions, necessary for full electric vehicle (EV) driving. The generator uses concentrated windings. The concentrated winding construction has good slot fill and short end-turn length. These features resulted in good performance in the intended operational region and were an enabler for machine packaging inside the transmission. Both the machines exhibit excellent efficiency and exceptionally smooth and quiet operation. The machine design and construction details, as well as the measured thermal, electromagnetic, and acoustic noise performances, are presented in this paper.

Induction Machine Design and Analysis for General Motors e-Assist Electrification Technology

The integrated starter generator replaces the conventional starter and alternator with one electrical machine handling both functions. Start/Stop functionality, vehicle launch assistance, and higher speed transient power supplementing enhance the vehicle performance at the lower fuel consumption rate. This functionality requires the electrical machine to provide high starting and launch assistant torque in motoring mode and relatively high power capability over the wide speed range for battery charging. The overall cost of the system is the underlining concern and crucial part of the design optimization. This paper focuses on advantages of induction machines (IMs) in automotive industry and an approach to design a cost-effective electrical machine for belted starter-alternator applications. Design optimization of the IM is described to achieve desired performance, including rotor bar count, solid conductor (bar winding) versus stranded winding design, rotor bar shape optimization, and finally performance maps for the electrical machine, including both predicted and measured results. A thermal study of the machine is also presented, as well as the noise, vibration, and harshness (NVH) consideration in the design selection.

Separately excited synchronous motor with rotary transformer for hybrid vehicle application

The cost of rare earth (RE) permanent magnet along with the associated supply volatility have intensified the interests for machine topologies which eliminate or reduce the RE magnets usage. This paper presents one such design solution, the separately excited synchronous motor (SESM) which eliminates RE magnets, however, but does not sacrifice the peak torque and power of the motor. The major drawback of such motors is the necessity of brushes to supply the field current. This is especially a challenge for hybrid or electric vehicle applications where the machine is actively cooled with oil inside the transmission. Sealing the brushes from the oil is challenging and would limit the application of such motor inside a transmission. To overcome this problem, a contactless rotary transformer is designed and implemented for the rotor field excitation. The designed motor is built and tested. The test data show that the designed motor outperforms an equivalent interior permanent magnet (IPM) motor, which is optimized for a hybrid application, for both peak torque and power. Better drive system efficiency is measured at high speed compared to the IPM machine, while the later outperforms (for efficiency) the SESM at low and medium speed range.

Design and performance of electrical propulsion system of extended range electric vehicle (EREV) Chevrolet Voltec

This paper presents the design and performance details of the Chevrolet Voltec electric propulsion system. The propulsion system has two machines, one machine is operating mostly as a motor while the other machine is operating mostly as a generator. Both machines of the Voltec electric drive system are permanent magnet AC synchronous machine types with the magnets buried inside the rotor. The motor has distributed windings. However, as opposed to a conventional stranded winding the Chevrolet Volt motor has bar-wound construction to improve the motor performance, especially in the low to medium speed range. At higher speed the skin and proximity effects in the stator bars lead to increased stator winding losses but are addressed in the design. The bar-wound construction also has excellent thermal performance, in both the steady-state and the transient conditions, necessary for full EV driving. The generator uses concentrated windings. The concentrated winding construction has good slot fill and short end-turn length. These features resulted in good performance in the intended operational region and were an enabler for machine packaging inside the transmission. Both the machines exhibit excellent efficiency and exceptionally smooth and quiet operation. Machine design and construction details as well as the measured thermal, electromagnetic and acoustic noise performances are presented in the paper.

Next generation chevy volt electric machines; design, optimization and control for performance and rare-earth mitigation

This paper presents the design, performance and control details of traction electric machines for GMs second generation Extended Range Electric Vehicle (EREV). Chevy Volt was the first personal vehicle in the industry with EREV power flow configuration which is carried over to the second generation. Since its introduction in 2011 Chevy Volts have been driven over half a billion miles, 67% of which in EV mode. The second generation of Volt brings a significant mass reduction and increased performance, EV driving range and fuel economy while simultaneously reducing rare earth content in its traction electric motors. The electric propulsion system is built on two electric machines; both PMAC topology. While hybrid-electric vehicles are gaining in popularity in hopes of addressing cleaner, energy sustainable technology in transportation, materials sustainability and rare earth dependence mitigation has not been the first priority in the hybrids available on the market today. However, design robustness to material cost volatility is crucial in automotive industry success and therefore designing electric propulsion to minimize or eliminate rare earth usage plays a major role in HEVs success. The objective of this paper is to present the newly redesigned electric traction machines for added performance while simultaneously reducing the rare earth and heavy rare earth content by over 80% and 50% respectively and in turn the cost of the system and yielding all around “cleaner” and more sustainable vehicle. A tall order by any measure; so various technologies were utilized to achieve this goal. The paper discusses grain boundary dysprosium diffusion process in permanent magnets as means to rare earth reduction in PMAC machines and design challenges surrounding such material use. We also discuss innovative PMAC topologies employing ferrite magnets to completely eliminate rare earth usage while maintaining the electric drive unit performance. The design of electric machines is presented in detail along with performance measurement results as well as thermal and NVH aspects. It is absolutely crucial that high performance electric machines are coupled with high performance control algorithms to enable maximum system efficiency and performance. Specifically, key challenges toward that goal are inverter voltage utilization, for maximum power capability and switching loss minimization. In order to address those, six-step mode of inverter control is a must. We focus on a specific challenge associated with this operation mode to keep the closed-loop current control regulation in the full six-step mode while losing a degree of freedom in the controls scheme. We present a novel PMSM control algorithm with a closed-loop current control regulation that can be used in both the SVPWM and full six-step mode.

Electric machine design and selection for General Motors e-Assist Light Electrification Technology

The integrated starter generator replaces conventional starter and alternator with one electrical machine handling both functions. Start/Stop functionality, vehicle launch assistance and higher speed transient power supplementing enhances the vehicle performance at the lower fuel consumption rate. This functionality requires the electrical machine to provide high starting and launch assistant torque in motoring mode and relatively high power capability over the wide speed range for battery charging. The overall cost of the system is the underlining concern and crucial part of the design optimization. This paper focuses on advantages of induction machines in automotive industry and an approach to design a cost effective electrical machine for belted starter-alternator application. Design optimization of the induction machine is described to achieve desired performance including; rotor bar count, solid conductor (bar winding) vs. stranded winding design, rotor bar shape optimization and finally performance maps for the electrical machine including both, predicted and measured results. Thermal study of the machine is also presented as well as the NVH consideration in the design selection.

Propulsion System Design of a Battery Electric Vehicle

Governments all around the world are mandating a greater level of vehicle electrification due to environmental and energy concerns. There are different levels of electrification in vehicles starting from mild hybrid to full battery electric vehicle (EV). These increasing levels of electrification result in rising levels of gasoline displacement with electricity and a subsequent improvement of fuel economy and reduction in emissions. Hybrids and their variants are being introduced. However, a full electrification of the vehicle is widely believed to be the future in addressing the above issues. General Motors (GM) has its own strategy for powertrain electrification, which includes a wide range of propulsion architectures from light hybrid systems, such as the eAssist, to fully electric systems, such as the Chevrolet Spark EV. The Spark EV has been introduced as a key part of GM?s overall strategy for powertrain electrification.

Evaluation of torque compensation control algorithm of IPM machines considering the effects of temperature variations

For automotive applications, accurate torque production capability and high efficiency of the traction motor is very important. However, the performance of widely used interior permanent magnet (IPM) machines is influenced by temperature variations, and temperature variations of the magnets in automotive applications can be profound. In this paper, the state-of-the-art torque compensation control methods of IPM machines in the literature are reviewed. The methods for torque error estimation due to temperature variation are classified. In addition, the methods for adjusting the operating points of IPM machines to maintain torque production accuracy and high-efficiency operation are also overviewed. The advantages and disadvantages of each algorithm are described and compared in detail. This paper facilitates the development of high performance and robust IPM machine drive systems for the automotive industry.

Analysis of temperature effects on performance of interior permanent magnet machines

The purpose of this paper is to analyze and investigate the influence of temperature variation on the characteristics and performance of interior permanent magnet (IPM) machines. The impact of temperature variation on the materials of IPM machines is discussed to show the sources of performance variation. The flux linkages and torque output capability variation as functions of the temperature of are analyzed and discussed. The paper also shows the influence of temperature variation on key IPM machines performance including constant torque curves, voltage limit ellipses, maximum torque per ampere and maximum torque per volt trajectories and torque-speed curves. The results and trends shown in this paper set a foundation for developing control algorithm which takes the temperature effects into consideration, especially in the applications where operating temperature varies significantly.

Design, optimization and development of electric machine for traction application in GM battery electric vehicle

This paper presents the design optimization, development and performance details of the Chevrolet Spark battery electric vehicle (BEV) traction electric machine. The propulsion system has one electric machine inside an oild cooled drive unit operating as a motor or generator depending on the drive cycle demand. The machine is permanent magnet AC synchronous machine type with the magnets buried inside the rotor. Details of the motor design, such as; winding selection, efficiency optimization for given drive cycles and rotor geometry optimization are discussed. Absence of an engine and sound it brings to a conventional vehicle can underscore any noise from the drive unit in the battery electric vehicles. Hence, particular attention is given to the NVH performance and torque ripple optimization in this machine. A novel approach to torque ripple minimization, by shaping the rotor surface is presented and its contribution to the NVH characteristics of the motor are discussed in detail. Finally, measurement results of machine efficiency, thermal and NVH performance are presented in the context of the vehicle performance.