Speed Control of AC Machines in Power Systems: A Review of Classical and Modern Techniques

Abstract

Speed control of AC machines has attracted extensive research attention due to the increasing demand for efficient, reliable, and flexible electric drive systems in industrial, commercial, and utility applications. Unlike DC machines, whose speed control is relatively straightforward, AC machines require specialized techniques owing to their dependence on supply frequency and machine parameters. This paper presents a comprehensive review of speed control methods for induction machines, AC commutator machines, and synchronous machines. For induction machines, control techniques such as variation of supply frequency, pole changing, slip control, stator voltage control, rotor voltage control, slip power recovery, and variable frequency control are discussed. Slip control using AC commutator machines including rotor-fed brush-shift machines and stator-fed induction regulator types is also examined. Furthermore, speed control of synchronous machines using inverter-fed and cycloconverter-based drives is reviewed. The operating principles, advantages, limitations, and application domains of each method are critically analyzed. The paper highlights the technological evolution from electromechanical and resistive methods to advanced power-electronic-based variable frequency drives and outlines current research trends in AC machine speed control.

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