Khwaja M. Troy Rahman

Application of direct drive wheel motor for fuel cell electric and hybrid electric vehicle propulsion system

This work presents a gearless wheel motor drive system specifically designed for fuel cell electric and hybrid electric vehicle propulsion application. The system includes a liquid-cooled axial flux permanent magnet machine designed to meet the direct drive requirements. Machine design implements techniques to increase machine inductance in order to improve machine constant power range and high-speed efficiency. The implemented technique reduces machine spin loss to further improve efficiency. Machine design also optimizes the placement of the magnets in the rotor to reduce cogging and ripple torque. An original cooling system arrangement based on the use of high thermal conductivity epoxy joining machine stator and liquid-cooled aluminum casing allows very effective removal of machine power loss. Design details and experimental results are presented.

Design of high-efficiency and high-torque-density switched reluctance motor for vehicle propulsion

A high density and high efficiency switched reluctance (SR) motor has been designed and built for vehicle propulsion. Extensive finite element (FE) analyses have been carried out to optimize the geometry for high density. Steady state performance of the drive has been simulated to ensure good efficiency at all speeds. Special attention has been given during machine design to lower the acoustic noise. Direct liquid cooling of the winding has been designed to improve the machine overload capability. Dyne test results are presented which show good overall performance of the SR drive for vehicle propulsion.

High-performance fully digital switched reluctance motor controller for vehicle propulsion

A high-performance fully digital controller has been designed for the control of a switched reluctance motor (SRM) built for vehicle propulsion. The SRM is specifically designed and built to have high density and low noise. The controller is designed to maximize the machine efficiency, the peak overload capability, and to minimize torque ripple at low speed. Lookup tables are stored in a DSP based controller to calculate the control parameters online. Three interpolations, between torque command, motor speed and battery voltage, are performed to obtain the control parameters. Difficulty associated with the interpolation scheme is addressed. A high bandwidth fully digital PI current regulator has been designed for the control of the phase current. Advantages as well as the difficulties with the operation of the SRM and its control have been addressed. A complete characterization of the controller for the entire torque-speed plane has been made through extensive dyno testing. Simulation and dyno test results have been presented to demonstrate the performance of this controller.

High-performance digital PI current regulator for EV switched reluctance motor drives

This paper presents a design methodology for digital proportional-integral current regulators that may be used for the highly nonlinear switched reluctance motor control. The important nonlinear behavior of saturation, back electromotive force (EMF), and mutual coupling are accounted for to achieve consistent current regulator performance over the entire operating regime. Gain adaptation is used with respect to both position and current to insure stability. An improved back-EMF decoupling scheme is implemented to reduce bandwidth requirements. The proposed control is implemented on a high-torque traction drive for electric vehicle applications. Simulation and experimental results demonstrate excellent performance over the entire operating regime.

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.

On-line minimum-copper-loss control of an interior permanent-magnet synchronous machine for automotive applications

This paper presents an algorithm to calculate the current references on line considering the inherent nonlinear nature of the saturation effect in an interior permanent magnet synchronous machine for the maximum-torque-per-ampere control under the current and voltage limit of the drive system. This work basically approaches this issue as a nonlinearly constrained optimization problem where the torque command acts the nonlinear equality constraint and the voltage condition acts the nonlinear inequality constraint. Depending on the operating region, it solves the corresponding set of nonlinear equations in real time derived from the Lagrange multiplier method. Newtons method among various techniques is selected to obtain the numerical solution. This scheme gives accurate results not only in motoring but also in generating operation of the machine because the voltage drop of the stator resistance is considered, which is not the case using a two-dimensional look-up table where the inputs are the torque command and the maximum flux amplitude and the output is each axis current reference in the rotor reference frame. The simulation and experimental results show the feasibility and performance of the proposed technique.

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.