Control Strategies and Functional Safety for the Intelligent Stator Cage Drive (ISCAD)

Abstract

The novel Stator Cage Drive marks a paradigm shift in electrical machine design by substituting layers of windings with stator bars that are short-circuited on one end of the machine. Those bars are individually fed from the opposite end of the machine, utilizing dedicated power electronic switches. Instead of being limited to one fixed MMF-distribution in the air gap, it is now possible to incorporate new degrees of freedom into the control strategy for such a machine, e.g. pole-switching during operation with an asynchronous rotor and the creation of selected harmonics. Compared to conventional designs of traction drives for HEVs or BEVs, this drive architecture achieves a better efficiency, both in peak operation and using common drive cycles, it is cheaper in manufacturing and it also provides better fail-safety. In order to obtain a high-quality MMF-distribution, a number of individually fed stator bars as high as 60 is preferable, which also implies a higher complexity of the control of this machine than for three-phase counterparts. If for example an induction type rotor is chosen, it is possible to vary the number of poles during operation, thus allowing the machine to always operate in the region of highest efficiency, which usually lies in the field weakening region for induction machines. An overview of the capabilities of the ISCAD-Drive is given, the applicability of well-known control methods is investigated and matters of functional safety in current measurement for a high number of phases are discussed.