Influence of some design parameters on the peak torque of current inverter fed synchronous machines with high phase number

The present paper analyses the influence of the phase number, winding distribution and pole pitch factor on the peak torque capability of inverter fed high phase synchronous machines as compared to classical machines. In order to establish a meaningful comparison, the torque capability of the classical DC machine and the classical triphase synchronous machine are firstly presented, followed by a discussion about the design factors, which influence their torque capability. The peak torque of the synchronous machine is chosen as the base value for comparisons. In the sequence is determined the torque capability of the star-connected high phase synchronous machine fed by a converter with quasiretangular phase current. This kind of current waveform can be nowadays easily produced by a current source inverter (CSI) or by a PWM-inverter with current control. The phase number and the winding distribution are considered as design variables which can be optimized in order to adequate the machine design to the converter. The influence of sinusoidal and quasiretangular rotor field distribution are analysed and discussed. Simple and ready-to-use torque equations as a function of phase number are obtained for the considered windings and rotor Held distribution. These expressions show that a considerable improvement on the torque capability can be obtained by choosing an appropriated combination of the machine design parameters. The main results are illustrated by curves and a table comparing the peak torque capability for synchronous machines with phase number ranging from 3 to 15.