Resonant slip ring-less doubly-fed hyper synchronous machine with variable capacitors

A resonant slip ring-less doubly-fed hyper synchronous machine (DFHSM) with variable switched-capacitors is newly proposed in this paper. A rotary transformer with a constant operation frequency is used instead of conventional slip rings to supply three-phase rotor currents without abrasion issues. Moreover, a chronic low power factor problem of high-frequency-DFHSMs, which is mainly due to a high reactance of stator and rotor windings, can be resolved by the compensating variable capacitors. A variable stator frequency control using variable capacitors to deal with not only the start-up operation but also the speed control is proposed to eliminate the damper windings or soft-starters in conventional machines. Operation principles of the proposed DFHSMs were verified with a finite element analysis (FEA) simulation tool, Ansoft Maxwell, by comparing torque results of the simulation and equivalent circuit analyses.