Concerning the design of inductor synchronous motors fed by current source inverters

An approach to the design of the inductor synchronous motor is presented based on two assumptions: The first is that iron saturation, rather than thermal stress, is the basic limitation on this machine. The second is that when fed by a current-source inverter, and under closed loop operation, selection of the operating angle ψ (between the direct axis and the armature current maximum) is feasible. Under these conditions, it is shown that the near-equality of the direct and quadrature axis reactances, a special property of this machine despite its variable reluctance construction, makes it a simple matter to select an optimum value for ψ for unity power factor designs. This choice is characterized by a sizeable reduction of the additive effects of the armature reaction on the air-gap flux density under the pole faces. In turn, this reduces saturation in the armature teeth, the most stressed part of the iron. In addition, at the same time, this choice of ψ maximizes the thrust-per-unit-area, and hence, for a specified power output, tends to lead to a machine of minimum size.