Gordon R. Slemon

A permanent magnet motor drive without a shaft sensor

A simple control for a permanent motor drive is described which provides a wide speed range without the use of a shaft sensor. Two line-to-line voltages and two stator currents are sensed and processed in analog form to produce the stator flux linkage space vector. The angle of this vector is then used in a microcontroller to produce the appropriate stator current command signals for the hysteresis current controller of the inverter so that near unity power factor can be achieved over a wide range of torque and speed. A speed signal is derived from the rate of change of angle of the flux linkage. A drift compensation program is proposed to avoid calculation errors in the determination of angle position and speed. The control system has been implemented on a 5 kW motor using Nd-Fe-B magnets. The closed loop speed control has been shown to be effective down to a frequency of less than 1 Hz, thus providing a wide range of speed control. An open loop starting program is used to accelerate the motor up to this limit frequency with minimum speed oscillation.<<ETX>>

A PWM AC to DC converter with fixed switching frequency

For a PWM (pulsewidth-modulated) AC-to-DC converter, a predicted current control strategy with fixed switching frequency (PCFF control) is proposed. Its principle and implementation are described, and experimental results are provided which show that the converter under PCFF control has bidirectional power transmission ability with high dynamic performance. The line currents are close to sinusoidal with unit power factor. The PCFF control produces a better switching pattern than hysteresis current control. This results in a reduction of harmonics in the line currents and lower stress on the switching devices.<<ETX>>

Analysis of an AC-to-DC voltage source converter using PWM with phase and amplitude control

A comprehensive analysis is presented of a pulse-width modulated AC-to-DC voltage source converter under phase and amplitude control. A general mathematical model of the converter, which is discontinuous, time-variant, and nonlinear, is first established. To obtain closed-form solutions, the following three techniques are used: Fourier analysis; transformation of reference frame; and small-signal linearization. Three models, namely, a steady-state DC model, a low-frequency small-signal AC model, and a high-frequency model, are consequently developed. Finally, three solution sets, namely, the steady-state solution, various dynamic transfer functions, and the high-frequency harmonic components, are obtained from the three models. The theoretical results were verified experimentally.<<ETX>>

Modelling of inductance machines for electric drives

Most analyses of inductance machine drives make use of a conventional linear machine model, either in the form of self and mutual inductances or the familiar T-form of equivalent circuits. This model is actually more complex than necessary for analysis in the linear regime. On the other hand, it is inadequate for use when the machine is saturated. The author presents several linear and nonlinear models suitable for transient and steady-state analysis. The models are presented in equivalent-circuit form to preserve the identity of nonlinear parameters. A note on modeling of time harmonics is included.<<ETX>>

Modeling of iron losses of permanent-magnet synchronous motors

Permanent-magnet (PM) motors offer potential energy savings as compared with induction motors because of the virtual elimination of rotor loss and the reduction of stator loss from operation near unity power factor. In PM machines, iron losses form a significant fraction of the total loss partly due to the nonsinusoidal flux density distribution. Design optimization therefore requires good means of predicting these iron losses. Finite-element analysis can be employed but this approach is cumbersome and costly when used in the many iterations needed in optimizing the design. This paper presents a set of improved approximate models for the prediction of iron loss. They can be used in design optimization programs and, since they are directly related to machine dimensions and material properties, they also provide quick insight into the effects of design changes. A time-stepped finite-element method is employed to evaluate the iron losses in a range of typical PM machines and the results are used to evaluate the adequacy of the models. The predictions of overall iron losses are then compared with measurements made on two PM motors.

Operating Limits of Inverter-Driven Permanent Magnet Motor Drives

Recent developments of high-energy permanent magnet (PM) materials such as neodymium-iron-boron have focused attention on the use of PM synchronous motors supplied from inverters for a wide variety of speed control applications. PM motor drives are readily applicable where full torque is required up to full or base speed. They are, however, limited in their ability to operate in the power-limited regime where the available torque is reduced as the speed is increased above its base value. In contrast with the field weakening approach used in dc drives, the magnet is permanent. The torque-speed operating limits of PM motor drives, of conventional design are explored, and then design measures which can substantially extend operation into the power-limited regime are proposed. A trade-off between the low speed-torque limit and the extent of the speed range above base speed is achieved by variations in magnet dimensions and the depth of inset of the magnets in the rotor iron. Experimental results are presented for two motors of different design, each using neodymium magnets and each supplied from a current-controlled inverter with hysteresis control of current waveshape.

Analysis of a PWM AC to DC voltage source converter under the predicted current control with a fixed switching frequency

A detailed analysis of a pulse-width modulated AC to DC voltage source converter under the proposed predicted current control with a fixed switching frequency (PCFF) is presented. A steady-state analysis, a dynamic response analysis, a high-frequency component analysis, and their solutions are also provided. The results show that the converter under the PCFF control has a fast dynamic response, ease of control, and a good switching pattern. The theoretical derivation is experimentally verified. >

PWM-CSI inverter for induction motor drives

A number of issues involved in designing a current source inverter system for a large induction motor drive are discussed. Using two modulation techniques-selective harmonic elimination in the upper frequency range and trapezoidal modulation in the lower frequency range-control of voltage, current, and torque harmonics is achieved while limiting the gate turn-off switching frequency to 180 Hz. Each modulation range is divided into a number of subranges to exploit the available switching capacity and to avoid harmonic resonances involving the capacitor and the motor inductance. In addition to basic principles, simulation waveforms and test results are included from a laboratory experimental system.<<ETX>>

Modeling and Design Optimization Of Permanent Magnet Motors

ABSTRACT Variable-speed permanent (PM) magnet motors are being used in an ever-increasing range of industrial and commercial applications. The objective of this paper is to provide a basis for optimizing the design of such permanent magnet motors and, through this, to provide insight into a comparison of PM motors with other types of drive motor. First, design models are presented for the approximate analysis of torque capability, losses, thermal characteristics, magnet protection and power factor control. These models are then used in an optimization program using sequential unconstrained minimization techniques to produce designs for a wide range of motor torque ratings. In order to examine the potential for large PM motor drives, the design criterion chosen for emphasis in optimization is the minimum total lifetime cost, including the cost of losses. The high efficiency and good power-to-weight ratio of the optimized PM motors leads to a total present value cost which is expected to be significantly lo...

Minimization of iron losses of permanent magnet synchronous machines

In permanent magnet (PM) synchronous machines, iron losses form a larger portion of the total losses than in induction machines. This is partly due to the elimination of significant rotor loss in PM machines and partly due to the nonsinusoidal flux density waveforms in the stator core of PM machines. Therefore, minimization of iron losses is of particular importance in PM motor design. This paper considers the minimizing of iron losses of PM synchronous machines through the proper design of magnets and slots, and through the choice of the number of poles. Both time-stepped finite element method (FEM) and the iron loss model from a previous study are used in this paper to draw the conclusions.