Synchronous Machines and Drives

The synchronous machine is a three-phase machine, able to exchange power with a three-phase network. Although it can also operate as a motor (absorbing electric energy) in the majority of applications, it is used as a generator (delivering electric energy). The vast majority of power stations generate electricity in three-phase form, using synchronous machines. Synchronous machines used in power stations, therefore, not only generate active power for the loads, but also contribute to supplying the loads with the needed reactive power. In a synchronous machine rotor, therefore, the insertion of permanent magnets (PMs) can have the same effect as a DC-fed coil with a fixed current flowing in it. In recent years, electronic devices have appeared that are able to convert constant frequency sources into variable frequency, thus allowing modification of voltage and frequency characteristics of a three-phase source.