Efficiency improvement of a high dynamic BLDC linear motor by multiphase control

This paper proposes a multiphase control strategy for a high dynamic brushless DC linear motor as an alternative for conventional three-phase field-oriented control. Analysis of the magnetic field waveforms shows that three-phase control is not optimal for the 6-slot 7-pole motor topology. Therefore, a multiphase control strategy is elaborated which injects currents proportional to the electromotive force into each of the nine stator coil groups. This results in a maximal alignment force per ampere between the stator and slider fields. Furthermore, only the stator coils with a useful contribution to the slider force are excitated. According to the simulation model, this yields a significant reduction of joule and iron losses for equal dynamic performance. The new strategy is implemented on a dSPACE rapid prototyping platform, controlling a custom-built multiphase converter. Measurements confirm the simulation results and show a significant reduction of power consumption compared to conventional three-phase control.