Sensorless Commutation Method for Low-Voltage BLDC Motors Based on Unfiltered Line Voltage

This study presents a filterless and sensorless commutation method for low-voltage brushless DC motors. The proposed method utilizes controlled DC-link inverter instead of the Pulse-Width Modulation (PWM) scheme. Therefore, motor voltages and currents become free from the high-frequency noise of PWM switching, thereby decreasing motor losses. Consequently, the method does not require any Low-Pass Filter (LPF) and it does not involve speed-dependent phase delay caused by the LPF. However, current commutation deteriorates waveform of line voltages. Thus, specific functions are defined to compensate for the current commutation spikes and remove false zero-crossing points of line voltages. Furthermore, the use of unfiltered line voltages eliminates the requirement of any phase shifter. Hence, the main superiority of the proposed method over preceding sensorless commutation methods is the simultaneous elimination of the phase shifter and LPF, which makes the method simple and cost-effective. The simulation and experimental results show the effectiveness and validity of the method

Direct torque control of permanent magnet synchronous motors with non-sinusoidal back-EMF

This work presents the direct torque control (DTC) techniques, implemented in four- and six-switch inverter, for brushless dc (BLDC) motors with non-sinusoidal back- EMF using two and three-phase conduction modes. First of all, the classical direct torque control of permanent magnet synchronous motor (PMSM) with sinusoidal back-EMF is discussed in detail. Secondly, the proposed two-phase conduction mode for DTC of BLDC motors is introduced in the constant torque region. In this control scheme, only two phases conduct at any instant of time using a six-switch inverter. By properly selecting the inverter voltage space vectors of the two-phase conduction mode from a simple look-up table the desired quasi-square wave current is obtained. Therefore, it is possible to achieve DTC of a BLDC motor drive with faster torque response while the stator flux linkage amplitude is deliberately kept almost constant by ignoring the flux control in the constant torque region. Third, the avarege current controlled boost power factor correction (PFC) method is applied to the previously discussed proposed DTC of BLDC motor drive in the constant torque region. The test results verify that the proposed PFC for DTC of BLDC motor drive improves the power factor from 0.77 to about 0.9997 irrespective of the load. Fourth, the DTC technique for BLDC motor using four-switch inverter in the constant torque region is studied. For effective torque control in two phase conduction mode, a novel switching pattern incorporating the voltage vector look-up table is designed and implemented for four-switch inverter to produce the desired torque characteristics. As a result, it is possible to achieve two-phase conduction DTC of a BLDC motor drive using four-switch inverter with faster torque response due to the fact that the voltage space vectors are directly controlled.. Finally, the position sensorless direct torque and indirect flux control (DTIFC) of BLDC motor with non-sinusoidal back-EMF has been extensively investigated using three-phase conduction scheme with six-switch inverter. In this work, a novel and simple approach to achieve a low-frequency torque ripple-free direct torque control with maximum efficiency based on dq reference frame similar to permanent magnet synchronous motor (PMSM) drives is presented

Sensorless drives for aerospace applications

This Engineering Doctorate thesis investigates the different implementations and theories allowing drives to control motors using sensorless techniques that could be used in an aerospace environment. A range of converter topologies and their control will be examined to evaluate the possible techniques that will allow a robust and reliable drive algorithm to be implemented. The focus of the research is around sensorless drives for fuel pump applications, with the potential to replace an existing analogue implementation that is embedded in a fuel pump, contained within the fuel tank. The motor choice (Brushless DC) reflects the requirement for endurance and tight speed control over the life of the aircraft. The study of currently understood sensorless control will allow a critical analysis over the best and most robust sensorless control technique for a controller of this nature, where reliability is a fundamental requirement.EThOS - Electronic Theses Online ServiceEaton AerospaceTitchfieldGBUnited Kingdo

Improved transistor-controlled and commutated brushless DC motors for electric vehicle propulsion

The development, design, construction, and testing processes of two electronically (transistor) controlled and commutated permanent magnet brushless dc machine systems, for propulsion of electric vehicles are detailed. One machine system was designed and constructed using samarium cobalt for permanent magnets, which supply the rotor (field) excitation. Meanwhile, the other machine system was designed and constructed with strontium ferrite permanent magnets as the source of rotor (field) excitation. These machine systems were designed for continuous rated power output of 15 hp (11.2 kw), and a peak one minute rated power output of 35 hp (26.1 kw). Both power ratings are for a rated voltage of 115 volts dc, assuming a voltage drop in the source (battery) of about 5 volts. That is, an internal source voltage of 120 volts dc. Machine-power conditioner system computer-aided simulations were used extensively in the design process. These simulations relied heavily on the magnetic field analysis in these machines using the method of finite elements, as well as methods of modeling of the machine power conditioner system dynamic interaction. These simulation processes are detailed. Testing revealed that typical machine system efficiencies at 15 hp (11.2 kw) were about 88% and 84% for the samarium cobalt and strontium ferrite based machine systems, respectively. Both systems met the peak one minute rating of 35 hp

Mathematical Approaches to Modeling, Optimally Designing, and Controlling Electric Machine

Optimal performance of the electric machine/drive system is mandatory to improve the energy consumption and reliability. To achieve this goal, mathematical models of the electric machine/drive system are necessary. Hence, this motivated the editors to instigate the Special Issue “Mathematical Approaches to Modeling, Optimally Designing, and Controlling Electric Machine”, aiming to collect novel publications that push the state-of-the art towards optimal performance for the electric machine/drive system. Seventeen papers have been published in this Special Issue. The published papers focus on several aspects of the electric machine/drive system with respect to the mathematical modelling. Novel optimization methods, control approaches, and comparative analysis for electric drive system based on various electric machines were discussed in the published papers

Advances in Rotating Electric Machines

It is difficult to imagine a modern society without rotating electric machines. Their use has been increasing not only in the traditional fields of application but also in more contemporary fields, including renewable energy conversion systems, electric aircraft, aerospace, electric vehicles, unmanned propulsion systems, robotics, etc. This has contributed to advances in the materials, design methodologies, modeling tools, and manufacturing processes of current electric machines, which are characterized by high compactness, low weight, high power density, high torque density, and high reliability. On the other hand, the growing use of electric machines and drives in more critical applications has pushed forward the research in the area of condition monitoring and fault tolerance, leading to the development of more reliable diagnostic techniques and more fault-tolerant machines. This book presents and disseminates the most recent advances related to the theory, design, modeling, application, control, and condition monitoring of all types of rotating electric machines

Design and Control of Electrically Excited Synchronous Machines for Vehicle Applications

Electrically excited synchronous machines (EESMs) are becoming an alternative to permanent magnet synchronous machines (PMSMs) in electric vehicles (EVs). This mainly attributes to the zero usage of rare-earth materials, as well as the ability to achieve high starting torque, the effectiveness to do field weakening and the flexibility to adjust power factor provided by EESMs. Furthermore, in case of converter failure at high speed, safety can be improved by shutting down the field current in EESMs. The purpose of this study is to investigate the potential application of EESMs in EVs. To achieve this aim, several topics are covered in this study. These topics are studied to confront the challenges before EESMs could become prevalent and to maximumly use the advantages of EESMs for EV applications. In control strategies, the challenge is to properly adjust the combination of stator and field currents so that high power factor and minimum copper losses can be achieved. To tackle this, control strategies are proposed so that reactive power consumption and total copper losses are minimized. With the proposed strategies, the output power is maximized along the torque-speed envelope and high efficiency in field-weakening is achieved. In dynamic current control, due to the magnetic couplings between field winding and stator winding, a current rise in one winding would induce an electromagnetic force (EMF) in the other. This introduces disturbances in dynamic current control. In this study, a current control algorithm is proposed to cancel the induced EMF and the disturbances are mitigated. In machine design, high starting torque and effective field weakening are expected to be achieved in the same EESM design. To realize this, some criteria need to be satisfied. These criteria are derived and integrated into the design procedure including multi-objective optimizations. A 48\ua0V EESM is prototyped during the study. In experimental verification, a torque density of 10 N\ub7m/L is achieved including cooling jacket. In field excitation, a contactless excitation technology is adopted, which leads to inaccessibility of the field winding. To realize precise control of field current in a closed loop, an estimation method of field current is proposed. Based on the estimation, closed-loop field current control is established. The field current reference is tracked within an error of 2% in experimental verifications. The cost of an EESM drive increases because of the additional converter used for field excitation. A technique is proposed in which the switching harmonics are extracted for field excitation. With this technique, both stator and field windings can be powered using only one inverter. From all the challenges tackled in this study, it can be concluded that the application of EESMs in EVs is feasible

Design and prototyping methods for brushless motors and motor control

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010."June 2010." Cataloged from PDF version of thesis.Includes bibliographical references (p. 109).In this report, simple, low-cost design and prototyping methods for custom brushless permanent magnet synchronous motors are explored. Three case-study motors are used to develop, illustrate and validate the methods. Two 500W hub motors are implemented in a direct-drive electric scooter. The third case study, a 10kW axial flux motor, is used to demonstrate the flexibility of the design methods. A variety of ways to predict the motor constant, which relates torque to current and speed to voltage, are presented. The predictions range from first-order DC estimates to full dynamic simulations, yielding increasingly accurate results. Ways to predict winding resistance, as well as other sources of loss in motors, are discussed in the context of the motor's overall power rating. Rapid prototyping methods for brushless motors prove to be useful in the fabrication of the case study motors. Simple no-load evaluation techniques confirm the predicted motor constants without large, expensive test equipment. Methods for brushless motor controller design and prototyping are also presented. The case study, a two channel, 1kW per channel brushless motor controller, is fully developed and used to illustrate these methods. The electrical requirements of the controller (voltage, current, frequency) influence the selection of components, such as power transistors and bus capacitors. Mechanical requirements, such as overall dimensions, heat transfer, and vibration tolerance, also play a large role in the design. With full-system prototyping in mind, the controller integrates wireless data acquisition for debugging. Field-oriented AC control is implemented on low-cost hardware using a novel modification of the standard synchronous current regulator. The controller performance is evaluated under load on two case study systems: On the direct-drive electric scooter, it simultaneously and independently controls the two motors. On a high-performance remote-control car, a more extreme operating point is tested with one motor.by Shane W. Colton.S.M

Milestones, hotspots and trends in the development of electric machines

As one of the greatest inventions of human beings, the electric machine (EM) has realized the mutual conversion between electrical energy and mechanical energy, which has essentially led humanity into the age of electrification and greatly promoted the progress and development of human society. This paper will briefly review the development of EMs in the past two centuries, highlighting the historical milestones and investigating the driving force behind it. With the innovation of theory, the progress of materials and the breakthrough of computer science and power electronic devices, the mainstream EM types has been continuously changing since its appearance. This paper will not only summarize the basic operation principle and performance characteristics of traditional EMs, but also that of the emerging types of EMs. Meanwhile, control and drive system, as a non-negligible part of EM system, will be complementarily introduced. Finally, due to the background of global emission reduction, industrial intelligentization and transportation electrification, EM industry will usher again in a golden period of development. Accordingly, several foreseeable future developing trends will be analyzed and summarized