An investigation of electronic pole changing in high inverter count induction machines

The design of powerful and compact electric machines in highly dynamic applications such as electric traction and integrated starter/generators is an extremely difficult engineering challenge. Use of conventional machine designs with components designed for fixed voltage and frequency operation, unfortunately, do not make things any easier. By embracing recent advancements in the cost, performance, and reliability of power electronics and utilizing machine designs that are able to fully utilize the flexibility available from power electronics-based sources, interesting and potentially superior machine design solutions become available. This dissertation examines the feasibility and advantages of one such solution: electronic pole-changing by means of pole-phase modulation. The implementation and operation of pole-phase modulation is introduced using a 36-slot stator lamination example. The effect of stator lamination, winding, and inverter design decisions on available operating modes are presented. High-level performance advantages are investigated using a 6-pole machine wound with 2-pole coils. Estimates of this 2-pole/6-pole electronic pole-changing case study include the development of a nearly 9:1 constant power speed ratio; ~3x better than conventional fixed pole and phase count designs. Analytical models are developed to predict the steady state and dynamic performance of high inverter count machines and electronic pole changing. The generalized models are capable of describing induction machines with an arbitrary number of electrical inputs and available pole count operations. Both models are validated using two-dimensional finite element analysis, and allow the effects of numerous electrical and mechanical design decisions on overall system performance to be easily examined. The additional degrees of freedom in multiphase reference frame transformations are utilized to formulate decoupled electromechanical energy conversion subspaces, and enable conventional control technique to be applied to high phase count induction machines with electronic pole changing. Scalar and vector control techniques are used to study controlled transition between two different pole counts, and illustrate the improved performance offered by the more advanced field-oriented control methods. A 36-coil toroidally-wound induction machine testbed is designed, built, and tested. Experimental tests are carried out to examine 2-pole/6-pole electronic pole changing operation with nine electrical inputs. Preliminary results exhibit performance relationships corresponding to previous steady state analytical model estimates, and verify pole-phase modulation operation. Discrepancies in equivalent circuit parameters are attributed to analytical model assumptions and nonidealities of the constructed machine