High-Performance Vector-Controlled AC Motor Drives: Applications and New Technologies

A high-performance ac motor control has been developed by employing the vector control concept. Its versatility has been proven through the six years of experience in applications to pinch roll drives of continuous casting plants, machine tool spindle drives, and other drive systems in industry. Equivalent torque characteristics are achieved with ac motors compared to dc motors without direct detection of the magnetic flux. The effect of rotor temperature on the torque characteristics has been compensated to a satisfactory level in actual industrial use by various means. Servo drives, both synchronous motor and induction motor types, have been introduced. The test results show that the performance of ac servo drives is equivalent or superior to that of the PWM-controlled dc servo drives. Furthermore, an example of the direct-drive servo is described, where an ultra-low speed high-torque motor and an ultra-high resolution position sensor play key roles. In addition, the possibility of a more sophisticated servo drive exploiting modern control theory is suggested.     

Electric Drives (Boldea, I and Nasar, S.A.; 2006) [Book Review]

The new enlarged second edition of this excellent textbook presents the latest concepts and basic electrical drive technology including vector and direct torque control of ac motors and generators. Some of the topics covered in the book's 15 chapters include: energy conversion in electric drives; electric motors for drives; power electronic converters for drives; dc brush motor drives; controlled rectifier dc brush motor drives; synchronous motor for drives; PM and reluctance synchronous motor drives; switched reluctance motor (SRM) drives; practical issues with PWM converter motor drives, large power drives, and an entirely new chapter on control of electric generators. Each chapter is supplemented with adequate, well-selected examples, summary, problems, and selected references at the end. An important advantage is an attached CD that includes test browsing, PowerPoint slides, and Matlab-Simulink programs with eight selected dc and ac closed-loop drives. The book is recommended as a basic text to a wide audience of engineering educators, students, and engineers in industry.     

DC Kiln Drive Motors

The most important considerations in applying dc drive motors and thyristor power supplies to a cement kiln are their procurement, maintenance, and operating costs; and equipment reliability in the cement plant environment. Drive requirements and their effect on motor size are discussed. Efficiency comparisons at several speeds for three different designs of dc drive motors are made. Two motor kiln drives with motors connected in series and also in parallel are discussed. Recommendations for applying each connection with regard to drive horsepower and voltage are made. Included is a brief discussion on applying dc motors by taking a part of the total speed range as constant horsepower rather than taking the entire speed range as constant torque.     

A traction electric drive for electric cars

It is advisable to use a controlled electric drive in electric drives of electric off-road vehicles due to its significant multiplicity of the supported torque (5: 1 and higher) in a low-power mode. Such overloads can be achieved, for example, in electric drives with a field-regulated reluctance machine, not only because of the capacity of the electric machines, but also due to the choice of the drive control system. Analysis of requirements for the electric drive of an electric vehicle is performed, and the influence of the control method on the specific parameters is considered. Analysis of the number of independent control actions in synchronous reluctance electric drives is provided. The possibility of increasing the overload multiplicity of the torque by abandoning the vector control in favor of structures similar to dc drive systems is shown.     

Current Control of Voltage-Source Inverters for Fast Four-Quadrant Drive Performance

A rotating reference frame controller for ac machines which enables smooth four-quadrant drive operation with good torgue control bandwidth is described. The advantages which result from the control of stator magnetomotive force (MMF) in a rotor reference frame are illustrated with regard to synchronous and induction motors. The application of this method to a cycloconverter synchronous motor drive is outlined.     

Designing and modeling a linear electric motor for vibration-technology machines

One industrial application of linear motors is as working-body drives of vibration-technology machines. Such drives allow manufacturing of equipment with very low energy consumption and material costs. This paper presents the results of research on substantiation of the prospects of application of linear electric motors as drive vibration-technology machines. The results of designing a linear dc motor are presented. This paper describes the design of the electric motor and its operation in the hold-down and vibrating modes. The main technical characteristics of the motor are given. Simulation of the electric-motor electromagnetic field based on symmetrical setting of the task for the Poisson equation was performed with a view to specifying and verifying the preliminary calculation data. The results of the calculations and simulations show that it is possible to create low-cost, manufacturable, and reliable electrical motors for a linear vibratory actuator.     

Synchronous and Reluctance Motors in Position Servo Loops

At the present state of the control art, it is economical to replace dc motors in servo systems with ac synchronous and induction motors, in spite of the generally more complex circuitry induction motors, in spite of the generally more complex circuitry required by the ac principle. This report deals with synchronous motors that rely on shaft position reference to fit them into high-performance position feedback systems. It is shown analytically that any synchronous motor, including the reluctance motor, becomes a direct replacement for a converter driven dc motor if the phase voltages are the result of properly modulated shaft resolver outputs.     

Electric drives of mining installations

Ventilation systems are one of the most important and energy-consuming systems in the manufacturing process of modern mining enterprises. Variable-frequency asynchronous and synchronous electric drives with frequency converters based on self-commutated inverters or variable-frequency synchronous electric drives based on the LCI scheme are considered as advanced drives for ventilation units. When upgrading electric centrifugal fans with slip-ring asynchronous motors and unexhausted performance potential, it is effective to apply a wound-rotor slip-recovery system. A converter with natural commutation with an intermediate dc link is used in the LCI scheme. Robicon frequency converters are used for variable-frequency high-voltage electric motors. An important advantage of these converters is that they can be used for standard 6- and 10-kV motors.     

Motor soft starters in electric drives used in mining machinery

This paper analyzes the selection of the type of a starter for electric drives with high-voltage synchronous motors depending on the nature of the change in the load torque of the mechanism, the amount of driving synchronous motors to be started up (single motor or successive start of several motors), and the technological regime requirements, as well as the parameters of the synchronous motor. Single-line schemes of implementing the soft starters of driving high-voltage synchronous motors of large grinding machines and axial mine fans for main and auxiliary ventilation are given.     

Power Transmission to Synchronous Machines for Adjustable-Speed Pump and Compressor Drive Systems

The adjustable-speed synchronous motor drive system uses static power conversion technology and hardware which has been proven by millions of kilowatts of installed capacity in dc motor drives and dc transmission systems. The application of dc power conversion technology to transmit power to a synchronous machine provides unique operating characteristics of the drive system with respect to pump and compressor applications. Alternative drive system configurations are presented with the benefits relative to performance and reliability.     

Microprocessor-Controlled AC-Servo Drives with Synchronous or Induction Motors: Which is Preferable?

With the recent advances of power transistors and microprocessors it has become possible to design high-dynamic-performance ac-servo drives free of moving contacts using synchronous or asynchronous motors. Both schemes have their particular strengths. A general control principle, based on field or rotor orientation, is described which has been realized with a state-of-the-art microcomputer, where all the signal processing, including modulation of the inverter, is performed by software. Extensive tests have been carried out with different motors to compare the characteristics of the various types of drives.     

Field-Oriented Control of a Standard AC Motor Using Microprocessors

Field orientation has emerged as a powerful tool for controlling ac machines such as inverter-supplied induction motors. The dynamic performance of such a drive is comparable to that of a converterfed four quadrant dc drive. The complex functions required by filed-oriented control may be executed by microprocessors on line, thus greatly reducing the necessary control hardware. It is shown that the flux signals may be derived from sensing coils or, with some compromise in performance, from the stator voltages and currents. The speed signal is obtained from a digital tachometer. Results from a 2-kW experimental drive are given.     

Application of Gate Turn-Off Thyristors in 460-V 7.5-250-hp AC Motor Drives

A 7.5-250-hp range of variable-frequency ac motor drives has been under development at the Westinghouse R & D Center since early in 1981. Design and performance details for prototype equipment rated for 10, 20, and 50 hp will be discussed. The drive system comprises a three-phase thyristor controlled ac/dc converter in conjunction with a dc/ac adjustable-frequency inverter using gate turn-off thyristors (GTO's). The output of the inverter is a six-step voltage wave in the range of 6-120 Hz, suitable for driving three-phase ac induction or synchronous motors. Details of the inverter design, including means to protect the gate turn-off thyristors from output line-to-line or line-to-ground short circuits, will be given special attention.     

Characteristics of a permanent magnet type bearingless motor

Super high-speed and high-power electric machines are required for turbomolecular pumps and spindle drives. High rotational speed and high power drives can be achieved with bearingless motors. In this paper, a bearingless motor with the principles of permanent magnet type synchronous motors is proposed. High power factor and high efficiency can be expected in permanent magnet type bearingless motors. The proposed bearingless motor is a 4 pole permanent magnet synchronous motor, in which additional 2-pole windings are wound together with 4-pole motor windings in stator slots. With currents of 2-pole windings, radial magnetic forces are produced to support a rotor shaft. Principles of radial force production of surface-mounted permanent magnet bearingless motors are analyzed mathematically. It was found that radial forces are efficiently produced by employing thin permanent magnets on the surface of rotor iron core. A test machine was built in order to measure inductance functions as well as relationships between voltages and currents     

High-speed electric drives: technology and opportunity

This article provides background on the development and installation of high-speed electric motors (induction and synchronous) and controllers. There are compelling reasons for electric drives to be considered for applications that would conventionally be driven by steam turbines, gas turbines, and engines or motors with speed-increasing gearboxes. Electric drives offer an opportunity for efficient use of natural resources, clean and (comparatively) quiet power conversion, improved process control, and very attractive life-cycle cost. High-speed electric drives utilize technology (including variable speed control) to meet the needs of a rapidly changing industrial world. The high-speed electric drive provides another valuable option for consideration by the gas pipeline owner. This option needs to be considered as part of initial strategic planning. The electric option offers many “system” benefits for pipeline owners. It represents proven technology, and significant potential opportunity     

Analysis and characteristics of a permanent magnet-type bearingless motor

Super-high-speed and high-power electric machines are required for turbomolecular pumps and spindle drives. High rotational speed and high-power drives can be achieved with bearingless motors. In this paper, a bearingless motor with principles of permanent magnet-type synchronous motors is proposed. High-power factor and high efficiency can be expected in permanent magnet-type bearingless motors. The proposed bearingless motor is a 4-pole permanent magnet synchronous motor, in which additional 2-pole windings are wound together with 4-pole motor windings in stator slots. With currents of 2-pole windings, radial magnetic forces are produced to support a rotor shaft. Principles of radial force production of surface-mounted permanent magnet bearingless motors are analyzed mathematically. The relationships between radial forces and the permanent magnet thickness were derived. From these relationships, the optimal permanent magnet thickness to produce radial forces efficiently is found. A test machine was built to confirm the relationships of radial forces, currents and voltages.     

Selection Criteria for Servo Motor Drives

The power density and acceleration characteristics of the ac servo drive are being recognized as being superior to those of the dc counterpart. The ac servo family consists of permanent-magnet synchronous, dc brushless, induction, and switched reluctance motor drives. This ac servo family is comprised of radial (also known as the sausage type) and axial (also known as the pancake type) field motors, thus enlarging the spectrum of ac servo motors to the users. Realizing that the ac servos are of recent development, it is obvious that their potentials and pitfalls have not been published, thus making it difficult for the user and application engineer to choose one servo from the family of ac servos for a particular application. In this regard, an attempt is made here to develop a set of selection criteria to differentiate the various servo drives of the ac family. The factors proposed to do that are cost, power density, acceleration rates, peak torque capability, speed range, torque per unit ampere, thermal capability, parameter sensitivity, cogging torque, ripple torque, braking, rotor position feedback device, etc. Application of these criteria would promote appreciation for the various facets of ac servos through their comparison with other drive types.     

A Cycloconverter?Synchronous Motor Drive for Traction Applications

An electric drive suitable for traction is described consisting of a cycloconverter and a synchronous motor. Essentially, the same system can be used with either single-phase or three-phase input with frequencies around 50-100 Hz. The motor speed range is not limited by the input frequency. The cycloconverter thyristors are commutated by the source voltage at low motor speed and by the motor electromotive force (EMF) at higher speed. The transition between the two regions is smooth and automatic. Only 16 low- switching speed thyristors are required for the single-phase input system. The short time overload capability of this drive at low speed is excellent, and full range regenerative, as well as dynamic braking, is readily accomplished. Compared to dc motors occupying the same space, three-phase ac motors, both synchronous and induction, offer higher output power, higher efficiency, and the elimination of brush and commutator maintenance. Compared to inverters, cycloconverters have higher efficiency and lower cost and weight.     

AC Drive System for Tension Reel Control

Recently, adjustable-speed ac drive systems have been employed successfully for blowers, pumps, table rollers, etc., in steel plants instead of the more conventional dc drives. In processing lines many drives require speed and tension control. To confirm the suitability of an ac drive for tension control, the tension reel of an existing pilot processing line has been equipped with an adjustable-speed ac drive. An ac drive system for tension reel control, its characteristics, and performance are described and compared with a dc tension control.     

A unique desk-top electrical machinery laboratory for themechatronics age

This paper describes an electrical machinery laboratory, named MECHATRO LAB 2PLUS, designed to cope with modern realities in which engineering graduates encounter various kinds of servomotors and actuators much more frequently than conventional power electric machines. The set-up can demonstrate the principles of some 20 different kinds of electric machines ranging from conventional rotary machines to modern control-use motors such as stepping motors, brushless motors and switched-reluctance drives. The experimental themes number more than 100, including elementary subjects, microprocessor-controlled power electronic drives and control/drive programming using various computer languages. Unlike conventional motor-generator workshop equipment, a remarkable feature of this desk-top bench is that it does not occupy much space on a permanent basis. Along with the background of its design history, which covers more than 20 years, the uniqueness and advantages of the new experimental set-up are presented in detail, citing some sample experiments and reactions of Japanese students and overseas instructors