Synchronous AC machines

Synchronous AC machines have a stator similar to the asynchronous machines, which has usually a three-phase stator winding. Whereas there are two types of rotor structures round cylindrical rotor and salient pole rotor as illustrated schematically in Fig. 5.6. The rotor field is generated by permanent magnets or a DC current winding, as reported in the same figure. In the first case they are called permanent-magnet synchronous AC machines. 

In synchronous AC machines the synchronization between the stator and rotor magnetic fields is achieved since the rotor magnetic field is fixed with respect to a rotor observer and thus it operates at the same speed as the rotor, which is the same speed of the stator magnetic field. 

Variable reluctance synchronous AC machines represent other types of synchronous machines which do not require any excitation system on the rotor [3]. 

During the 1980 s attention turned to AC machines technology with both synchronous and induction being successfully applied. Variable speed and torque control was made possible by variable rotor resistance in the form of Wound Rotor Induction Motors and then the Cyclo Convertor which applied thyristor technology to produce low frequency ac output suitable for the driving large AC machines. 

Keywords Bond graphs Rotary electric machines DC and AC Machines Synchronous machines Induction machines Permanent magnet machines Reluctance machines Electrical drives... 

In the sequel, some general issues concerning AC-machines modeling, mainly change of variables through coordinate transformation (reference-frame theory, see [8]) are discussed. This is followed by the presentation of machine schematics in machine variables and equivalent circuits in transformed variables of both the synchronous and the induction machines, under detailed modeling assumptions. This is accompanied by the corresponding BG models of both machines in transformed variables. Finally, simplified models of the induction motor usually encountered in control system applications are addressed. 

This ability of a bi-directional power transfer makes the controlled ac-dc converter suitable for a use between a synchronous machine driven by the combustion engine and the battery-bus in hybrid vehicles [36]. 

Transient stability is a term applied to alternating current (ac) electric power systems, denoting a condition in which the various synchronous machines of the system remain in synchronism, or in step each other. Conversely, instability denotes a condition involving loss of synchronism, or falling out of step (Kimbark, 1995). 

Section 8.2.1 immediately following this short introduction presents more models of DC-machines while Section 8.2.2 deals with AC synchronous and induction machines, the latter being discussed in more detail. Both are the kind of machines most likely to be encountered in industrial systems converting power in the range... 

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