Sinisa Jurkovic

Speed Observer and Reduced Nonlinear Model for Sensorless Control of Induction Motors

We consider field-oriented speed control of induction motors without mechanical sensors. We augment the traditional approach with a flux observer and derive a sixth-order nonlinear model that takes into consideration the error in flux estimation. A high-gain speed observer is included to estimate the speed from field-oriented currents and voltages. The observer design is independent of the feedback controller design. By high-gain-observer theory, we define a virtual speed output for the sixth-order nonlinear model, which can now be used to design a feedback controller whose performance is recovered by the speed observer when the observer gain is chosen high enough. We then focus on the traditional field oriented control (FOC) approach where the flux is regulated to a constant reference and high-gain current controllers are used. By designing a flux regulator to maintain the flux at a constant reference, and a current regulator to regulate the q-axis current to its command, we derive a third-order nonlinear model that captures the essence of the speed regulation problem. The model has the speed and two flux estimation errors as the state variables, the q -axis current as the control input, and the virtual speed as the measured output. It enables us to perform rigorous analysis of the closed-loop system under different controllers, and under uncertainties in the rotor and stator resistances and the load torque. In this paper, we emphasize the design of feedback controllers that include integral action. The analysis reveals an important role played by the steady-state product of the flux frequency and the q-axis current in determining the control properties of the system. The conclusions arrived at by using the reduced-order model are collaborated by simulation and experimental results.

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.

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.

Design and Analysis of a High-Gain Observer for the Operation of SPM Machines Under Saturation

This paper presents a high-gain observer of the rotor position for the control of surface permanent magnet synchronous machines under loaded conditions, e.g., saturation. Determining the rotor flux position of permanent magnet AC machines under no load is simpler, since its flux and rotor position coincide. However under load and in the presence of saturation in particular, the flux is comprised of two components: one due to the rotor magnets and the other due to the stator current. This causes the magnetic axis to shift from the rotor position, which in turn causes an error in a control algorithm that uses conventional rotor position estimation. This paper characterizes this error through a nonlinear model of the machine and finite element analysis. Design and analysis of a general position observer algorithm for PMAC machines accounting for saturation is presented, along with its implementation for a control methods using back EMF measurement and high-frequency Injection. Experimental results validating the nonlinear model of the machine, existence of the saturation-induced error, and performance of the proposed observer are also given.

Optimal speed control of an Interior Permanent Magnet Synchronous Motor including cross saturation

This paper presents the methodology to design an optimal speed controller (total losses minimization) of an IPMSM for traction applications. IPMSMs have high efficiency, however to exploit that efficiency it is required to design an optimal control, with the capability to accurately calculate and command the current components for the whole range. The speed controller is optimized by calculating the optimal trajectory between two points, defined by their torque and speed. The trajectory calculation is made in two stages: current space vector calculation based on the concept of maximum torque per ampere and optimal trajectory calculation. The first stage corresponds to the calculation of the optimal magnitude and angle of the current space vector for any given torque and speed point, maximum torque per ampere is the control technique selected for the IPMSM model inversion. The second stage involves calculating the currents that define the trajectory from one point to another, with minimal copper losses. The proposed optimization is numerical, constrained, based on the steepest descent method. Simulation and experimental results are presented to validate the proposed methodology.

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.