Feedforward Compensation of Torque Ripples in Dual Three-Phase PMSM Fed From Separate DC Links With Different Voltage Levels

Multiphase permanent magnet synchronous machines (PMSMs) with concentrated windings are gaining popularity in the development of fault-tolerant drives. The 12-slot/8-pole PMSM offers the possibility of forming two spatially separated three-phase winding sets, where each spans half of the extent. Additionally, it is attractive in terms of the acoustic noise that the radial magnetic stress is balanced for each quarter of the circumference. Unfortunately, there is no phase shift between the winding sets, which leads to additional torque ripple. A compensation using further construction measures is only partially possible. This article discusses causes for the torque ripples in this type of PMSM. Besides magnetic saturation, additional torque ripples appear when the winding sets are fed by different dc links, which is necessary in some applications in order to increase the availability of the drive in case of a failure. For complete cancellation of the dominant torque harmonics a method for identification of harmonic voltages, and currents is proposed. Using the measured angular acceleration as error signal, an adaptive narrowband filter is adjusted continuously to drive the harmonics to zero. The proposed method does neither suffer from nonlinearities due to magnetic saturation nor from model complexity due to the increased phase number.