Control of Synchronous Motors

Introduction ¹

For the countless operations of its machine tools, its robots and its “special machines”, modern industrial production has a tremendous need for elements called “motors”: these machines must impose on tools in motion (generally in rotation) a torque, a speed or a position, all determined by a high level decisional element. Execution rapidity and precision are necessary for a high productivity of quality. Electric motors have thus taken a predominant position in the “drive control”. Consequently, they are found in modern industrial production – but also in many “general public” applications, even if in this book we will mainly discuss the professional applications. Indeed, they have a predominant position because of their maneuverability and their (relative but effective) ease of use. Hydraulic motors (for example) have much better performances in terms of “torque-mass ratio”, but they are much trickier to control.

Historically, direct current motors were the first to be used because – in some aspects – they were ideal: excellent performances in terms of speed and of implementation ease, on the converter level (a thyristor rectifier or a transistorized chopper are sufficient), as well as on the controls level. Indeed, the “electromagnetic torque” is proportional to the “armature current”. Therefore, a simple “current loop” imposes the torque, and then a “speed loop” is sufficient to produce a electronic “speed variator” (see on these topics Chapter 1 of [LOU 04b] ...