Design concepts and force generation in inverter-fed synchronous machines with permanent magnet excitation

Synchronous machines with permanent magnet excitation can be designed for high power densities and low losses. This paper initially provides an overview of various machine concepts. Constructions with flux concentration and others with air gap oriented magnets are described. A comparison provides dimensioning rules for designs with minimal amounts of permanent magnetic material. On the basis of this, measures are outlined which improve the thrust density and further reduce the losses. These are: 1. design of machine and current inverter with more than three independent phases to achieve a square wave shape for the field and current; 2. employment of appropriately laminated poles to reduce the armature reaction in conjunction with measures which increase flux concentration. The effectiveness of these measures is demonstrated with the use of an example. For a current loading of 100 kA/m, a mean force density of 100 kN/m²is attainable. In conclusion, a machine concept is described which allows control of the exciter field from the armature, thus enabling a more flexible adaptation to the drive requirements.