A Hybrid Observer for High Performance Brushless DC Motor Drives

Brushless DC motor drive systems are used in a wide variety of applications. These drives may be classified as being one of two types: sinusoidal drives in which there are no low-frequency harmonics in the current waveforms and no low-frequency torque ripple; and nonsinusoidal drives in which there is considerable low-frequency harmonic content, both in the current and torque waveforms. Although sinusoidal drives feature superior performance, they are generally more expensive since rotor position must be sensed on a continuous basis, thus requiring an optical encoder or a resolver, whereas relatively inexpensive Hall-effect sensors may be used for nonsinusoidal drives. In this paper, a straightforward hybrid observer is set forth which enables rotor position to be estimated on a continuous basis using information available from the Hall-effect sensors. The proposed observer is experimentally shown to perform just as well as an optical encoder for steady-state conditions and nearly as well as the optical encoder during transient conditions. The proposed scheme provides designers with a new option for rotor position sensing, one which offers an excellent compromise between accuracy and expense

Multilevel Converter-Based Dual-Frequency Induction Heating Power Supply

Most existing power supplies for induction heating equipment produce voltage at a single (adjustable) frequency. Recently, however, induction heating power supplies that produce voltage at two (adjustable) frequencies have been researched and even commercialized. Dual-frequency power supplies are a significant development for heat-treating workpieces with uneven geometries, such as gears, since different portions of such workpieces are heated dissimilarly at a single frequency and so require a two step process using a single-frequency power supply. On the other hand, a dual-frequency power supply can achieve the desired result for such workpieces in a one step process. However, the existing approaches to dual-frequency voltage generation could be improved to achieve higher efficiency, improved control, reduced electromagnetic interference and greater reliability. This paper proposes the use of multilevel converters for providing induction heating power at two frequencies simultaneously. It also describes how the stepping angles for the desired output from this converter were determined. Furthermore, experimental results are presented as a verification of the analysis

Multilevel Inverter-Based Dual-Frequency Power Supply

Most existing power supplies for induction heating equipment produce voltage at a single (adjustable) frequency. Recently, however, induction heating power supplies that produce voltage at two (adjustable) frequencies simultaneously have been introduced and commercialized. These represent a significant development particularly for heat-treating workpieces with uneven geometries, such as gears. Still, the existing approaches to dual-frequency voltage generation could be improved upon to achieve better control, higher efficiency, and reduced electromagnetic interference. This letter proposes the use of multilevel inverters for providing power at two frequencies simultaneously. It describes how the stepping angles for the desired output from such inverters can be determined. Furthermore, experimental results are presented as verification of the concept and to demonstrate the achievement of improved harmonic level control and reduced device switching frequency

A Flux-weakening Strategy for Current-Regulated Surface-mounted Permanent-magnet Machine Drives

Permanent-magnet synchronous machines fed from current-regulated converters feature nearly ideal performance at low-to-moderate speeds. However, as rotor speed increases the back emf rises which results in loss of current regulation and decreased torque. In buried-magnet machine drives, flux weakening is often used to extend the speed range. This paper sets forth a flux-weakening control specifically designed for surface-mounted permanent-magnet machines which is simple and does not require knowledge of the machine or system parameters. The proposed method is demonstrated both experimentally and through the use of computer simulatio

Analysis of a Current-Regulated Brushless DC Drive

Current-regulated brushless DC machines are used in a wide variety of applications including robotics, actuators, electric vehicles, and ship propulsion systems. When conducting system analysis of this or any other type of drive, average-value reduced-order models are invaluable since they provide a means of rapidly predicting the electromechanical dynamics and are readily linearized for control system synthesis. In this paper, a highly accurate average-value reduced-order model of a hysteresis current-regulated brushless DC drive is set forth. In so doing it is demonstrated that the drive exhibits five distinct operating modes. The physical cause of each of these modes is explained and a mathematical model for each mode is set forth. The mathematical models are verified both experimentally and through the use of computer simulation. It has been found that the model set fourth herein is on the order of 300 times faster than a detailed computer simulation in calculating electromechanical transient

Performance Characteristics of a Cascaded Two-level Converter

A cascaded two-level power converter is proposed which utilizes two six-transistor inverters and is capable of producing voltages which are identical to those of three-level and four-level converters. Since the machine voltages are the same, the converter performance is the same as is verified through laboratory tests. The advantages and disadvantages of the proposed cascaded converter are explored. The proposed converter is simpler to construct and offers more nonredundant switching states per number of active semiconductors than standard multi-level converter

Multilevel Inverters with Equal or Unequal Sources for Dual-Frequency Induction Heating

Most existing power supplies for induction heating equipment produce voltage at a single (adjustable) frequency. Recently, however, induction heating power supplies that produce voltage at two (adjustable) frequencies have been researched and even commercialized. Dual-frequency power supplies are a significant development for heat-treating workpieces with uneven geometries, such as gears, since different portions of such workpieces are heated dissimilarly at a single frequency and so require a two step process using a single-frequency power supply. On the other hand, a dual-frequency power supply can achieve the desired result for such workpieces in a one step process. This paper proposes the use of multilevel converters for providing induction heating power at two frequencies simultaneously, which may achieve higher efficiency, improved control, reduced electromagnetic interference and greater reliability than existing dual-frequency power supplies. It also describes how the stepping angles for the desired output from such converters can be determined for both the equal and unequal source cases. Furthermore, experimental results are presented as a verification of the analysis

Self-Healing Control with Multifunctional Gate Drive Circuits for Power Converters

Many commercial and military transport systems have fault diagnostic functions implemented to help protect the device when a severe fault occurs. However, most present systems do not contain prognostics capability which would allow operators to observe an unhealthy system component in its pre- fault condition. In industry applications, scheduled downtime can result in considerable cost avoidance. The next technology step is self-healing system components which observe not only potential problems, but can also take steps to continue operation under abnormal conditions - whether due to long-term normal wear-and-tear or sudden combat damage. In this paper, current and voltage information using the double-layer gate drive concept is fed to intelligent networks to identify the type of fault and its location. These intelligent networks are based on unsupervised and supervised learning networks (self-organizing maps and learning vector quantization networks respectively). The proposed concept allows the reconfiguration of the electric machinery system for continued normal operation of the machine. This paper presents an intelligent health monitoring and self-healing control strategy for a multi-phase multilevel motor drive under various types of faults