Stephen Richard Macminn

Instantaneous Torque Control of Electric Motor Drives

In the control of adjustable speed drives, the performance of inexpensive digital integrated circuits is approaching the stage where traditional control algorithms may be displaced by newer algorithms that better exploit their speed and the functional capabilities of their software. This paper introduces the concept of “instantaneous torque control” as an objective worth pursuing in the application of such digital ICs to drive systems. Instantaneous torque control would in principle permit the fastest possible response and the elimination of torque ripple, along with many other advantages not possible with conventional control algorithms, most of which are set up to control a time-averaged torque. This paper develops some of the fundamental principles of instantaneous torque control for the switched reluctance motor, which is used as an example because, like the brushless dc permanent-magnet motor with concentrated windings, it has the potential for rapid response but it can have appreciable torque ripple with unfavorable firing angles. Neither of these machines satisfies the conditions for the existence of a reference-frame transformation that will eliminate the rotor position from the voltage and torque equations, and this opens up a number of interesting questions as to the generality of instantaneous torque control algorithms, and whether they can be incorporated into the general or unified theory of electrical machines.

Control techniques for improved high-speed performance of interior PM synchronous motor drives

A description is given of two control techniques to enhance the performance of the interior permanent magnet (IPM) drive over an extended speed range. The first technique is a feedforward compensation algorithm that improves the performance of current regulators operating in the stationary reference frame. Speed-dependent back-EMF (electromotive force) and inductive voltage drops are compensated, so that steady-state current errors are nulled at all speeds until current regulator saturation limits are encountered. The second technique is a flux-weakening control algorithm which uses stator current components to prevent premature current regulator saturation, thereby improving the machines torque production capabilities at high speeds. Neither algorithms requires additional feedback signals from the motor beyond those already used in the preexisting controls, and they are relatively insensitive to variations in the machine parameters, despite their feedforward characteristics.<<ETX>>

A very high speed switched-reluctance starter-generator for aircraft engine applications

An electric direct-drive gearless starter-generator has been designed and built for an aircraft engine application. The system is based on a switched-reluctance motor, which was chosen for its simplicity, robustness, high-speed capability, and efficiency. The overall system configuration and the design of the switched-reluctance motor and its solid-state power converter are described. When operating as engine starter, the motor produces torque to spin the engine up to its light-off speed. Following light-off, the motor continues to produce torque to assist the engine in accelerating to idle speed. When the engine is running, the machine generates electrical power to supply engine and vehicle loads up to a peak operating speed of 50000 r/min. Key issues in the machine design are reliability, high speed, power density, and cost. Test results have verified that the system can meet the torque and generated-power requirements over its entire operating range.<<ETX>>

Microprocessor Simulation of Synchronous Machine Dynamics in Real-Time

A major shortcoming of real-time analog power system simulators has been the lack of an inexpensive and flexible dynamic generator model. This paper describes such a model, implemented using digital hardware. Issues which are addressed in the design include model-to-network interfacing, stability, accuracy, and processor architecture. Simulation results of the resulting model generator are presented. Real-time power system simulation is typically carried out on a scale model of the power system known as a Transient Network Analyzer (TNA), which consists primarily of passive component models of power system elements such as transmission lines and transformers. Several dynamic generator models have been constructed for use with TNAs with varying degrees of success. [1,2] The primary shortcomings of these implementations have been high cost and lack of flexibility. This paper describes a new model generator implementation in which a microprocessor solves the discretized generator dynamic equations. Interface to the TNA is via analog-to-digital and digital-to-analog converters. A few of the advantages to this approach are: the parameter values are easy to change, the mathematical model itself is easily modified, and the hardware is inexpensive.