Tomy Sebastian

Issues in reducing the cogging torque of mass-produced permanent-magnet brushless DC motor

A variety of techniques are available to reduce cogging torque in permanent-magnet brushless DC motors. Theoretically, all the techniques are quite effective for minimizing the cogging torque. This paper presents the efficacy of these methods in mass production subject to manufacturing tolerances/variations. The cogging torque minimization becomes a challenging task when the requirement is very stringent in applications such as electric power steering and robotics. Some of the known techniques for reducing the cogging torque are the magnet pole design, skewing, step skewing, and dummy slots in the stator lamination. They will be discussed in this paper considering manufacturing tolerances/variations when used in mass production. Finite-element analysis is carried out to determine the worst case scenarios. The research demonstrates that the cogging torque amplitude and frequency are highly sensitive to magnet shapes, dimensions, locations and magnetization pattern, as well as slot/pole combination. In reality, the cogging torque may not be eliminated completely but minimized to a satisfactory level depending on the application requirements.

Analysis of induced EMF waveforms and torque ripple in a brushless permanent magnet machine

Permanent magnet machines with trapezoidal back EMF waveform have been the subject of several papers in the past. The simplicity in control and the absence of an absolute position sensor makes this type of motor very attractive. Idealized analysis of such a machine is simple and will result in trapezoidal or square wave back EMF waveforms depending on the assumptions made. In the case of an idealized quasi-square wave current excitation, a ripple-free torque will be obtained. The actual back EMF waveform of these machines depends on the flux density and the conductor distributions. This in turn is a function of the magnet magnetization and the stator tooth and slot structure. In applications where a fairly smooth torque is needed, these machines are made with either the stator slots or the rotor magnets skewed by one slot. This paper deals with the analysis of the back EMF waveform and of the torque ripple waveform of such a machine when the stator slots or rotor magnets are skewed by one slot. The analysis takes into consideration the actual stator conductor distribution and the effect of magnet magnetization on the back EMF waveform. An empirical formula is developed for the magnet flux density distribution which could be used for various magnetization conditions of the magnet. Experimental results are included to confirm the analytical results.

Design considerations of sinusoidally excited permanent magnet machines for low torque ripple applications

Several high performance applications such as electric power steering require, the motor drive to produce smooth torque with very stringent torque ripple requirement. This paper is focused on various machine design considerations that can be used in reducing the torque ripple of a sinusoidally excited permanent magnet (PM) brushless DC (BLDC) motor. The paper quantifies the various sources of torque ripple, which may be minimized by appropriate design considerations. The paper discusses the factors influencing the harmonic content of the induced voltage, effect of slot/pole combination, winding distribution and magnetic saturation. Design optimization is directed to minimize cogging torque and the harmonic contents in the back-emf, thus reducing the overall torque ripple. Comprehensive finite element analysis along with experimental data is provided to validate the theory. The research demonstrates that saturation in the magnetic circuit is another major contributor to the torque ripple and torque nonlinearity as the current increases. A model is developed to study the saturation effect on torque linearity and is verified by FE simulation. Design techniques have been provided to minimize the overall torque ripple and increase the torque linearity.

Issues in reducing the cogging torque of mass-produced permanent magnet brushless DC motor

A variety of techniques are available to reduce cogging torque in permanent magnet brushless DC motors. Theoretically, all the techniques are quite effective for minimizing the cogging torque. This research presents the efficacy of these methods in mass production subject to manufacturing tolerances/variations. The cogging torque minimization becomes a challenging task when the requirement is very stringent in applications such as electric power steering and robotics. Some of the known techniques for reducing the cogging torque are the magnet pole arc design, skewing, step skewing, and dummy slots in the stator lamination. They are discussed in this paper considering manufacturing tolerances/variations when used in mass production. Finite element analysis is carried out to determine the worst-case scenarios. The research demonstrates that the cogging torque-amplitude and -frequency are highly sensitive to magnet shapes, dimensions, locations and magnetization pattern as well as slot/pole combination. In reality, the cogging torque may not be eliminated completely but minimized to a satisfactory level depending on the application requirements.A variety of techniques are available to reduce cogging torque in permanent-magnet brushless DC motors. Theoretically, all the techniques are quite effective for minimizing the cogging torque. This paper presents the efficacy of these methods in mass production subject to manufacturing tolerances/variations. The cogging torque minimization becomes a challenging task when the requirement is very stringent in applications such as electric power steering and robotics. Some of the known techniques for reducing the cogging torque are the magnet pole design, skewing, step skewing, and dummy slots in the stator lamination. They will be discussed in this paper considering manufacturing tolerances/variations when used in mass production. Finite-element analysis is carried out to determine the worst case scenarios. The research demonstrates that the cogging torque amplitude and frequency are highly sensitive to magnet shapes, dimensions, locations and magnetization pattern, as well as slot/pole combination. In reality, the cogging torque may not be eliminated completely but minimized to a satisfactory level depending on the application requirements.

Role of electronics and controls in steering systems

Automotive steering systems have gone through several changes over the years since its first introduction in early 1900s. The advances in electronics, controls, and electrical machines are enabling the replacement of hydraulically assisted steering to electromechanically assisted steering. These also enabled the introduction of four-wheel steering, which gives the driver much more vehicle maneuverability and safer operation. Integration of steering and other chassis functions provides improved vehicle stability under various driving conditions. This paper discusses the role of electronics in the present and future steering systems.

Fault-tolerant switched reluctance motor drive using adaptive fuzzy logic controller

An adaptive fuzzy controller has been designed to develop a high-performance fault-tolerant switched reluctance motor (SRM) drive. The fuzzy controller continuously adapts its properties to regulate the machine torque as desired by the drive system even under fault conditions. The adaptation of the fuzzy membership functions results in extended conduction period and increased peak current of the healthy phases to deliver the commanded torque, as much as possible. The adaptive fuzzy controller provides smooth torque output with minimum ripple, even under fault conditions, yielding a high-performance SRM drive with fault-tolerant capability.An adaptive fuzzy controller has been designed to develop a high-performance fault-tolerant SRM drive. The fuzzy controller continuously adapts its properties to regulate the machine torque as desired by the drive system even under fault conditions. The adaptation of the fuzzy membership functions results in extended conduction period and increased peak current of the healthy phases to deliver the commanded torque, as much as possible. The adaptive fuzzy controller provides smooth torque output with minimum ripple, even under fault conditions, yielding a high-performance SRM drive with fault-tolerant capability.

Minimization of torque pulsations in a trapezoidal back-EMF permanent magnet brushless DC motor

This paper discusses the different methods used to reduce the torque pulsations (i.e. cogging torque and torque ripple) in a trapezoidal back-EMF permanent magnet (PM) brushless DC motor. The paper covers the design options to reduce both cogging torque and torque ripple. The effect of stator ampere-turns, the influence of rotor magnetization and the effect of the processing of electrical steel used in the fabrication of the stator on the motor torque ripple are discussed. The conclusions in the paper are supported by experimental results. A 3-phase, 18-slot, 6-pole brushless DC motor using high energy NdFeB magnets is used to illustrate the findings.

Real time estimation of parameters for controlling and monitoring permanent magnet synchronous motors

In permanent magnet synchronous motor (PMSM) drives, accurate knowledge of machine parameters has advantage in its control and/or monitoring its condition. This paper provides an adaptation method to determine the machine parameters. The machines phase resistance, phase inductance and back-emf constant are updated continuously. The online adaptation helps tracking any dynamic change in the motor parameters due to environmental, aging and loading condition. The motor parameters used in the controller can be updated to enhance the performance. This method can also be used for end of line motor parameter calibration in mass production and condition monitoring of drive systems. The method eliminates the need for a priori knowledge of the machine parameters making the controller robust for high performance operation. Simulation and experiment demonstrate the validity and usefulness of the proposed algorithm for PMSM drive.

Electric Motors for Automotive Applications

Abstract The use of electric motors in automobiles has been steadily increasing since the mid 1900’s. The application of speed or torque controlled motors in automobiles is fueled by the need for improved fuel economy, and the demand for vehicles with more comfort and convenience. Though the advances in power and control electronics and the developments in high-energy magnets have enhanced the cost effectiveness of such systems, many more advances will be required before large scale use of such machines in automobiles is achieved. This paper discusses the trends and challenges in introducing these motors into automotive applications. The paper also discusses the potential motor technologies and the key developments that are needed for these motors to be acceptable for automotive applications

Special Section on Automotive Electromechanical Converters

The 11 papers in this special section focus on automotive electromechanical converters. The special section addresses design, advanced control, integration of drive electronics, and application of adjustable-speed motor drives in automotive subsystems.