Six-Phase BLDC Reluctance Machines: FEM-Based Characterization and Four-Quadrant Control

In a yet another effort to produce better permanent magnet (PM)-less rotor-winding-less brushless electric motor drives, this paper reports work related to multiphase (m =6) high saliency rotor dual-flat-top alternative current control brushless dc (BLDC) reluctance machine drives. The aim is to produce high torque density, low loss/torque in a PM-less rotor-winding-less machine by full usage of machine windings and core and of inverter kVA. A new derivation of the principle of operation, essential rotary and linear machine topologies, and a 2-D finite-element method (FEM) analysis for torque density and torque pulsations on an already built (6 phase, 6 poles, 35 N·m) lab prototype are made available and show promising results. Experimental flux decay test results are presented, which, together with standstill torque measurements, validate the finite-element model. Advanced iron loss computation by finite-element analysis indicates moderate core loss, although high air-gap magnetic flux density and current harmonics occur as a natural behavior of a BLDC machine. Electrical and mechanical parameter identification is followed by the development of a circuit model based on FEM imported data for parameters and by a four-quadrant control strategy proposal. Running experiments (motoring and generating) with speed-reversal and field-weakening modes using a DSpace platform, which drives three three-phase inverters that power a star-connected six-phase BLDC multiphase reluctance machine are presented, thus showing operation with a reduced number of switches in the inverter.