Single-Tooth Winding for Synchronous Motor Torque Ripple
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Solution Overview
Problem
Electric power steering systems with permanent-magnet excited, electrically commutated synchronous motors face challenges such as harmonic torques, cogging torque, and increased sensitivity to manufacturing tolerances, leading to torque fluctuations and safety concerns like high braking torque during faults.
Innovation Solution
An electric machine with 18 stator teeth and 14 rotor poles utilizing a crossing-free single-tooth winding design, where each stator coil surrounds only one tooth, reduces torque ripple and cogging torque, and enhances safety by preventing short circuits between stator coils of different phases, while maintaining high power density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a 3/2 topology with non-overlapping stator coils is used, then the winding structure is simplified, but torque fluctuations increase and power density is reduced
Solution Approach 1:
The stator winding is segmented into individual single-tooth coils, each surrounding only one stator tooth. This segmentation allows for a crossing-free arrangement that simplifies the winding structure while the specific configuration of these segmented coils reduces torque fluctuations and maintains power density.
2Device complexity
If stator coils of different phases intersect in end windings, then winding compactness is improved, but short circuits between phases can occur leading to high braking torque
Solution Approach 1:
The harmful intersection of stator coils from different phases is eliminated by extracting the coils from a compact but risky arrangement. Each stator coil is assigned to surround only one stator tooth, which removes the possibility of short circuits between phases while maintaining acceptable winding compactness through the single-tooth configuration.
3Power
If permanent magnets are used for excitation, then power density and efficiency are improved, but harmonic torques and cogging torque increase causing torque fluctuations
Solution Approach 1:
The stator winding is designed with local quality variations through the single-tooth coil configuration, where each coil is specifically arranged around one stator tooth. This local optimization reduces harmonic interactions in the air gap, thereby reducing cogging torque and torque fluctuations while maintaining the high power density provided by permanent magnet excitation.
4Reliability
If a finely distributed winding is inserted, then an ideal sinusoidal air-gap field is generated, but space availability in small machines is insufficient
Solution Approach 1:
Instead of a symmetrically distributed winding that would require more space, an asymmetric single-tooth winding configuration is used where each coil surrounds only one stator tooth. This asymmetric arrangement achieves acceptable air-gap field quality with reduced harmonics while fitting within the limited space of small machines.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design achieves low cogging torque, reduced torque ripple, and increased reliability by minimizing harmonic interactions and preventing short circuits, thus improving the overall performance and safety of the electric machine in electric power steering systems.
Implementation Method 1
permanent-magnet excited, electrically commutated synchronous motors
Implementation Method 2
stator coils surrounding only one of the stator teeth
Implementation Method 3
rotor with 14 rotor poles
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
The invention relates to an electric machine (1) comprising: a rotor (4) having 14 rotor poles (8), which is rotatably arranged about a center axis, a stator (2) having 18 stator teeth (3) extending in a radial direction with respect to the center axis from the stator (2) in the direction of the rotor (4), characterized in that each of the stator teeth (3) is surrounded by a stator coil (9) only surrounding one of the stator teeth.