Showing papers in "IEEE Transactions on Industry Applications in 1993"

Permanent-magnet synchronous motors: a comprehensive approach to cogging torque suppression

Abstract: Torque ripple minimization in permanent-magnet synchronous motors is traditionally achieved either by special motor design or by an adequate control of the driver. Due to motor-driver interactions, the choice of driver or motor design must consider the respective performance of each. The approach presented provides appropriate current shapes for driving a given motor without torque ripple and/or appropriate back-EMF shapes for a given current or voltage supply. Reluctance torque, due to the interaction between the rotor magnets and the stator slots, is also taken into consideration. >

Power electronics and motion control-technology status and recent trends

Abstract: Power electronics and motion control have emerged as very important technologies in the recent trend of industrial automation. This work reviews the technology status and trends in power electronics and motion control with emphasis on AC machine drives. A comprehensive review of power semiconductor devices, power converter circuits, machine drives, and various motion control techniques is included. The effect of expert systems, fuzzy logic, and neural networks on intelligent motion control is also discussed. >

Voltage sag analysis case studies

Abstract: This paper summarizes the results from a number of different voltage sag investigations. These investigations involve characterizing the voltage sag performance at a customer facility and evaluating equipment sensitivity to different voltage sag magnitudes and durations. Possible solutions to voltage sag sensitivity problems are also described. >

Servo drive system and control characteristics of salient pole permanent magnet synchronous motor

Abstract: Permanent magnet (PM) synchronous motors fed by PWM inverters are considered. PM motors sometimes have a saliency, in which the q-axis inductance is larger than the d-axis inductance. A high-performance servomotor drive system for a salient-pole PM motor is described. An armature current vector is actively controlled according to load conditions in order to use a reluctance torque effectively, and, as a result, a large torque can be produced. The control algorithm for the armature current vector is described, taking the demagnetization of the PM and the magnetic saturation into account. Characteristics such as torque, power factor, efficiency, power capability, transient responses, etc. are examined in detail by computer simulations and experimentally. >

Autocompensation of torque ripple of direct drive motor by torque observer

Abstract: Since a direct drive motor (DDM) does not require a reduction gear, the drive system can be made simple, and therefore it is used in high-precision robot and machine tool applications. However, without reduction gear, a disturbance torque is directly reflected to the motor shaft, and a torque ripple generated by the motor is directly transmitted to the load, causing poor speed control characteristics. An improved torque control system for DDM with a permanent magnet rotor, equipped with a torque observer implemented by digital signal software, is proposed. The speed fluctuation can be fully removed with a torque feedforward loop. >

Proposed chapter 9 for predicting voltage sags (dips) in revision to IEEE Std 493, the Gold Book

Abstract: Voltage sags, also known as dips, are increasingly important to industrial reliability. Modern process controls are often sensitive to voltage sags. The combination of a voltage sag and sensitive equipment may cause significant production outages. Less sensitive equipment may be available at a premium price, but the designer must know the sag characteristics of the electric system to make the best choices between reliability and cost. This proposed chapter offers a way to predict voltage sag performance without long term monitoring and before plants are constructed. The analysis technique proposed for a new chapter 9 in the next revision of IEEE std 493 is shown. >

Comparison of standards and power supply design options for limiting harmonic distortion in power systems

Abstract: Harmonic distortion in power systems is growing due to the popularity of switch-mode power electronic equipment. This equipment has recognized advantages, such as reducing weight and improving control and efficiency in power converters and supplies. A disadvantage of switch-mode power converters is that their lowest-cost circuit may burden the power system with harmonic loading. Methods to reduce this distortion are recognized, but economic incentives are yet to be realized. Standardization is the most effective means to influence equipment design and to control distortion in power systems. The authors compare the major European and American standards, as well as some of the electronic equipment design changes that are supposed to limit harmonics. >

Dynamic equalization during charging of serial energy storage elements

Abstract: A technique is described that equalizes the amount of charge in a serial string of energy-storage cells during charging by using DC-to-DC converters to divert portions of the charging current past selected cells (or groups of cells). When no converters are operating, the charging current through the string is equal to that of the charging source. As the string charges, one cell eventually reaches a threshold voltage V/sub A/. At threshold, a shunt converter is activated to divert current around the cell, thus maintaining it at V/sub A/. The diverted current extracts energy, which is returned to the charging bus and appears as an additional charging current to the source. This positive feedback increases the current available for charging the string and allows the least charged cells, or cells of larger capacity, to be charged at higher rates than available directly from the source. During discharging, the converters across the remaining cells supply energy to the bus, while the converter across the open cell maintains a constant terminal voltage. The maximum current gain of the system is equal to the number of converters used in the system. >

Fifty percent energy savings with automatic lighting controls

Abstract: An electronically ballasted lighting control system was demonstrated at an office building in the San Francisco Bay Area. The system was used to demonstrate the energy savings and demand-reduction capabilities of a lighting control system designed to exploit all major control strategies, including scheduling, daylighting, and lumen maintenance. After 9 months of operation, lighting energy savings of approximately 50% relative to previous usage have been consistently achieved. A novel, two-part control photocell that permits successful implementation of daylighting and lumen maintenance strategies was demonstrated. >

The control of high-speed variable-reluctance generators in electric power systems

Abstract: This work studies the control of a direct-current (DC) electric power system that is sourced by a variable-reluctance generator. The power system includes the generator and its switching inverter, a filtering capacitor, a distribution network and an electrical load. The network comprises a series resistor and inductor, while the load comprises a parallel resistor, capacitor and power sink. The voltage at the load is regulated by adjusting the rotor angles at which the inverter switches. Both steady-state and transient performance are considered. Simulations are provided to illustrate performance. >

Design considerations for high-frequency coaxial winding power transformers

Abstract: The use of coaxial windings to create low-loss, low-leakage-reactance, power transformers for use in high-frequency soft-switched DC/DC and resonant converters has been demonstrated by M.H. Kheraluwalest al. (1990). Some of the important loss aspects of the design of coaxial winding transformers are examined, including the influence of the skin effect on winding resistance, the variation of core loss caused by nonuniform core flux density, and the choice of the principle dimensions and aspect ratios for maximum efficiency. Experimental measurements on a 50 kVA, 50 kHz unit are included to confirm portions of the analytical results and suggested design procedures. >

Trouble shooting motor problems

Abstract: Motor problems usually cause a crisis, and are quite annoying, especially if the problem could have been prevented. The keys to successful motor operation include; a quality motor; understanding of the application; choice of the proper type of motor for the application; proper installation-mounting, coupling, surroundings-for the motor; and proper maintenance of the motor. Many problems could be avoided if the application and environment were understood, while others may be caused by a changing environment in which the motor operates, and, of course, some are due to the motor itself. This paper examines common motor problems and their preventative action. >

An update on AC induction motor efficiency

Abstract: The need for higher levels of motor efficiency is increasing significantly. Numerous opportunities are available to reach these levels, many of which are being influenced by changes in government regulations, rebate programs, industry standards, and the cost of energy. The purpose of this paper is to update users on the opportunities available to achieve higher performance levels and to summarize those activities that are driving these higher levels. The impact of adjustable frequency drives is included. A summary is provided forecasting the future required levels and the method of demonstrating compliances. The relationship and trade-offs between efficiency and power factor is also addressed. >

Calculation of corona onset voltage for duct-type precipitators

Abstract: A pure theoretical method for calculating the onset voltage of corona in duct-type electrostatic precipitators that is independent of the arrangement of discharge wires relative to the collecting plates is described. This method is based on a criterion for self-recurring single electron avalanches in a known electric field distribution in the ionization zone surrounding the discharge wire. The results computed by this method are in reasonable agreement with those measured experimentally. >

Electronically enhanced low voltage motor protection and control

Abstract: The major advances in motor protection and control today and in the future will be based on electronic enhancements. Electromechanical-based systems are limited to simple protection modes and typically have a one-to-one relationship between input (e.g., current) and reaction (e.g., deflection). Microcomputer chips, with their ever increasing processing speeds and program instruction sets, have given designers the tools and the freedom to package multiple protection modes as well as customized protection. This computing power allows designers to develop modern multi-function motor protection systems that include control functions previously achieved only through complex hard-wired control circuits. The designer can now re-examine motor protection requirements and provide unique solutions. It is also possible to replace some high level programmable controller solutions with a dedicated controller built into a more user friendly, individual motor protection package. This same package may provide data communication links for factory-wide management systems. Such a motor protection and control system addresses motor application needs that, in the past, were often beyond the range of practicality. >

Basics and advances in battery systems

Abstract: One of the most common components in both the utility and industrial/commercial power system is the stationary battery. In many cases, the original design is marginal or inadequate; the maintenance and testing is practically nonexistent; but the system is called upon during emergency conditions and is expected to perform flawlessly. This paper begins with basic battery theory starting with the electrochemical cell. A working knowledge of the battery cell is important to understand typical problems such as hydrogen production, sulfating, and battery charging. The paper then discusses some of the common batteries and battery chargers. While this paper concentrates primarily on the lead acid type of battery, the theory can be utilized on other types such as the nickel-cadmium. Reference is made to industry standards and codes which are used for the design, installation, and maintenance of battery systems. Along with these standards is a discussion of the design considerations, maintenance and testing, and, finally, some advanced battery system topics such as individual battery cell voltage equalizers and battery pulsing units. The goal of this paper is to provide the reader with a basic working understanding of a battery system. Only with that knowledge can a person be expected to design and/or properly maintain a battery system which may be called upon during an emergency to minimize the effects of a normal power outage, to minimize personnel hazards and to reduce property damage. >

Analysis of field oriented control for permanent magnet hysteresis synchronous motors

Abstract: A microprocessor implementation of the field-oriented control scheme for the permanent magnet (PM) hysteresis synchronous motor is reported. The basic principle is to decouple the torque-current component from the flux-current component so that these two components can be independently controlled. A d-q axis model of the PM hysteresis synchronous motor is presented, and the field-oriented control obtained from the basic machine model. A control scheme that decouples the stator current components and orients it to the rotor frame is described. A scheme for detecting the rotor position is proposed. A software package based on the Intel 8086 microprocessor has been developed. A sine PWM voltage source inverter is used in the experimental work. The test results validate the theoretical steady state and dynamic performances of the laboratory prototype motor. >

Relay performance considerations with low ratio CTS and high fault currents

Abstract: Low-ratio toroidal current transformers (CTs) are in existence in many locations on power systems. The majority of these CTs are in the auxiliary switchgear at generating stations, but are not limited to this application. The ratio of the CTs used in this application is usually selected to accommodate metering and overload protection. The problem addressed is the absence of consideration in this ratio selection for fault protection. In many cases the fault duty of this switchgear is very high and, because the low-ratio CTs also are of low accuracy classes, the CTs will saturate during a fault. The analysis of some fault cases shows that the protective relaying will not operate, or will not operate properly, due to the saturated CTs. The significance and consequences of the use of these CTs and the accompanying saturation during high-fault currents are discussed. Considerations when testing low-ratio CT applications for saturation are presented as well as a computer program to demonstrate the volt-time concept of CT saturation. Alternate CT connections and corrective alternatives are given along with conclusions to aid in resolving low-ratio/high-fault current situations. >

Optimal synchronous pulsewidth modulation with a trajectory-tracking scheme for high-dynamic performance

Abstract: Synchronous pulse-width modulation (PWM) based on precalculated and stored optimal pulse patterns could be a superior method for the control of high-power inverters operated at low switching frequency. The technique has rarely been applied in practice owing to its poor dynamic performance. A novel feedforward control technique eliminates this decisive drawback: the space vector of the machine currents is forced to track a precalculated optimal trajectory in the steady-state and under the transient operating conditions commanded by the drive control system. Undesired transients caused by the pulse-width modulator are avoided. Experimental results obtained from a 30 kW AC drive are presented. >

Remnant roof coal thickness measurement with passive gamma ray instruments in coal mines

Abstract: The need to leave coal on the roof of a mined-out area occurs on both continuous miner and longwall sections and is derived from considerations of ground control, quality control, machine guidance, or simply good operating practice. Efforts at measuring boundary coal thickness using the nucleonic method is described. Natural gamma devices are the instruments of choice, and the use of gamma-ray backscatter sensing is discussed. The calibration of natural gamma background (NGB) instruments is described, and it is concluded that they cannot be used in areas where NGB radiation is not present. This radiation is ordinarily present in the fine-grained sedimentary rocks that bound many coal seams. >

Design and control system of inverter-driven permanent magnet synchronous motors for high torque operation

Abstract: This work describes a current vector control method for permanent magnet (PM) synchronous motors suitable for high-torque operation. The current phase angle is controlled according to load conditions in order to use the reluctance torque effectively. Characteristics such as torque, efficiency, power capability and so on are greatly improved by this control method in comparison with the conventional control method. The performance characteristics are greatly affected by the motor parameters, which depend on the rotor configurations and permanent magnet geometries. The available maximum torque and power capability are also examined for the several types of PM motor, taking into consideration the inverter capacity. The tendency toward magnetic saturation and demagnetization of the permanent magnet is also examined. >

Lightning protection systems: advantages and disadvantages

Abstract: The successful 200-year-old method of using a (Franklin) rod to collect, control, and convey to earth the awesome and destructive power of lightning has produced other controversial, potential alternate methods. The mechanics and interaction of lightning-producing thunderclouds and earth are discussed. Compared to the Franklin air terminal (rod) and Faraday cage method, the debatable advantages and disadvantages of the early streamer emission-enhanced ionizing air terminal and multipoint discharge systems are examined, along with conceptual future methods of lightning protection. >

Thermal considerations in specifying dry type transformers

Abstract: In 1944, the hottest spot temperature allowance for ventilated dry-type transformers was established as 30/spl deg/C for 80/spl deg/C average winding temperature rise and IEEE standards use a constant 30/spl deg/C hottest spot temperature allowance for all insulation temperature classes and all transformer ratings. Thermal tests under different loading conditions were performed on a prototype 2500 kVA ventilated dry-type transformer and six full-size test coils with imbedded thermocouples in the windings. The test data indicated that the hottest spot temperature allowance used in IEEE and IEC standards is too low for ventilated dry-type transformers above 500 kVA. It is impossible to design ventilated dry-type transformers above 500 kVA with an average temperature rise of 150/spl deg/C exceeding the permissible hottest spot temperature rise of 180/spl deg/C due to large thermal gradients. The average temperature rise for ventilated dry-type transformers above 500 kVA with 220/spl deg/C insulation temperature class should be 120/spl deg/C. IEEE standards should require measurement of hottest spot temperature rise on prototype transformers or windings as a design test to qualify a design family and the manufacturer's mathematical models. This is especially important for ventilated dry-type transformers rated for nonsinusoidal load currents. The specification suggested in the paper should be used until IEEE standards are revised. >

A solid-state high-performance reactive-power compensator

Abstract: A high-performance reactive-power compensator is presented and analyzed. The VAR compensator consists of a three-phase current-regulated pulse width modulated voltage-source inverter connected to a self-controlled DC bus. Reactive-power compensation is achieved by forcing the inverter output current to follow a reactive sinusoidal reference waveform at a constant switching frequency. The main advantages of this scheme are that it reduces the stresses on the switching devices (as compared with other current regulated techniques), and it has a fast response time, which allows almost instantaneous reactive current control, and low harmonic distortion in the line currents. In particular, the authors discuss the proposed scheme in terms of principles of operation, power and control system design, and the analysis under transient operating conditions. Simulated results obtained with the Spice simulating package for steady-state and transient operating conditions are presented and validated on an experimental unit. >

High-power drive system with advanced power circuitry and improved digital control

Abstract: A drive system featuring a three-level inverter (which is also known as a neutral-point-clamped inverter) and offering new features is introduced. The circuit concept not only makes it possible to expand the power range without connecting GTOs directly in series or parallel, but it also greatly improves the voltage and current waveforms, enhances control properties, and reduces losses. In addition, this drive system features a self-commutated GTO converter on the line side. It permits free energy exchange in both directions without reactive power and with a low harmonic content of the line current. Digital, signal-processor-based vector control and new PWM methods for both convertors are ideally suited for steady-state operation as well as for conditions demanding high dynamic performance. The results of a system test in the megawatt range underscore the qualities of this drive system. >

The performance of an integrated air purifier for control of aerosol, microbial, and odor

Abstract: A new type of an air purifier has been developed for a simultaneous control of aerosol, microbial, and odor in living environments using ozone, corona precharger, an electrified minipleats filter, and an ozone-decomposing catalyzer as well as a semiconductor ozone sensor for safety control. Ozone is generated in the corona precharger by enhancing negative corona with the application of a higher-than-ordinary voltage. This device, which is named AIP, indicates 85% one-through number collection efficiency for aerosol particles in the size range of 0.1-1.0 mm. AIP shows a very satisfactory deodorizing performance for man-originated and living environment-originated odors, such as ammonia, hydrogen sulfide,methylmercaptane, etc. The AIP also effectively kills, through long exposure to low-concentration ozone, most bacteria, fungi, viruses, and other microbials and small insects collected in its filter. >

Latent effects due to ESD in CMOS integrated circuits: review and experiments

Abstract: A review of the current information published on the subject of EOS/ESD latent failures is presented. In order to gain a better understanding of the phenomena involved in the input protection networks of CMOS integrated circuits, measurements were performed on both commercially available integrated circuits and a set of custom designed and fabricated devices. The tests investigated the effects of electrical stress, thermal shock, exposure to ultraviolet light, and thermal annealing. The results demonstrate the presence of latent failures in CMOS integrated circuits following exposure to ESD. The cumulative effect of repeated discharge can be partially alleviated using thermal annealing or exposure to light. A charge injection model is proposed to interpret the results. >

FCBM-a field-induced charged-board model for electrostatic discharges

Abstract: This work addresses a test method for the evaluation of electronic subassemblies against the threat of electrostatic discharges (ESD) It describes a field-induced charged board model (FCBM) for the simulation of real world ESD An experiment is designed to observe and measure ESD current waveforms An analytic theory is developed to describe important fundamental processes of the ESD phenomenon The application of the theory to the FCBM ESD predicts waveform characteristics in excellent agreement with the experiment A recommendation for the specification of the ESD waveform is offered for inclusion in future ESD test standards for electronic subassemblies >

Quasi-dual modulation of three-phase PWM converters

Abstract: The possibility of transferring the modulation method developed for a pulse width modulated (PWM) power converter with a DC voltage link (VLC) to a PWM converter with a DC current link (CLC) based on the inverse current and voltage behavior of these two systems is evaluated. The duality between VLC and CLC, which has been intuitively clear, is treated here in a scientific approach. It is shown that the nonplanar property of three-phase bridge circuits leads to a quasi-dual relation of the switching states of the VLC and CLC systems. The code conversion of the binary switching functions of a VLC into control signals of the power electronic devices of a CLC is given. The remaining degree of freedom of the correspondence is set by the requirement of minimum switching frequency of the converter. >

The value of controls and monitoring for electrical heating tracing

Abstract: In this paper the variety of controls and monitoring methods in use today are explored to develop an understanding of the advanced technologies available. Mechanical, solid-state and microprocessor-based packages are reviewed with particular attention given to multi-circuit centralized systems. As the costs of many systems continue to rise, questions regarding the value from the users' perspectives are also explored. >