An Improved Direct Torque Control for a Single-Winding Bearingless Switched Reluctance Motor

Abstract

The direct torque control (DTC) and direct force control (DFC) method were introduced to reduce the torque and levitation force ripple in single-winding bearingless switched reluctance motors (SWBSRMs). However, it still has some disadvantages. Firstly, the flux-linkage control is not suitable for the DTC method in SWBSRMs. On the one hand, it can increase the torque ripple. On the other hand, the RMS current can be increased and then the torque-ampere ratio is decreased. Secondly, the vectors selection is also unreasonable, which can increase the torque ripple further. In order to solve these problems, an improved control method based on DTC and DFC method for SWBSRMs is proposed in this paper, which can obtain high torque-ampere ratio and low torque ripple simultaneously. In the proposed method, the flux-linkage loop control is not needed and the space voltage vector table is improved. The experimental results show that the torque ripple is reduced by 66.7%, the torque-ampere ratio is increased by 200% and the switching times in one electrical period are reduced by 47.3%. Index Terms-single-winding bearingless switched reluctance motor, direct torque control, direct force control, torque ripple, torque-ampere ratio. NOMENCLATURE θ Rotor angular position. θsr Angle between stator and rotor flux linkage. ia1-ia4 Winding currents of phase A in BSRMs. Ta Instantaneous torque of phase A. Fα , Fβ Radial forces on the direction of α-axis and β-axis, respectively. p0 Number of rotor poles. Lm Mutual inductance. Ls , Lr Stator and rotor inductances amplitude, respectively. Ψs ,Ψr Stator and rotor flux-linkage amplitude, respectively. σ Leakage inductance coefficient. is Current of stator winding in SRMs. c Constant 1.01. h Lamination length of the iron core. l0 Air-gap length between the stator and rotor poles. Ns Number of winding turns. r Radius of rotor. μ0 Permeability of vacuum.

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