Induction Motor Design Strategy for Wide Constant Power Speed Range

This paper presents a design strategy of an induction motor (IM) for a wide constant power speed range (CPSR). The stator inductance is a key parameter that determines a CPSR, because it affects the voltage limit and the torque simultaneously. Low inductance allows a wide CPSR under a voltage limit. However, it results in torque reduction. On the other hand, if inductance is high, the opposite results take place; high torque and narrow CPSR. Therefore, there is a tradeoff between the power level and the speed range. The classical design process does not consider the CPSR, but provides a guideline to calculate core dimensions and the winding number for a nominal operation point. Thereby, the machine inductance is determined passively. This classical procedure is not appropriate for widening the CPSR. To extend the speed range under a voltage limit, a proper inductance must be chosen in the first place. In this work, a different IM design process is pursued with the objective of widening CPSR: An optimal inductance is obtained that minimizes the maximum current under a constant power condition. In the secondary part, an IM design method is proposed, which determines the winding number and the core dimension under a given inductance. Finally, the proposed analytic design is compared with the design optimized by finite-element-analysis. Based on the design results, a real IM (130 kW, 14 000 r/min) is constructed and tested. The experimental results are in good agreement with the design data.