Asymmetric Electric Motor Design for Sensorless Control
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Solution Overview
Problem
Symmetric construction in permanent magnet (PM) motors leads to uniform but periodic operation, limiting sensorless performance and increasing torque ripple, while also potentially causing greater torque ripple amplitude than desired.
Innovation Solution
Introducing asymmetries in the design of the rotor and stator, such as varying the configuration of magnets, windings, and slot shapes across different segments, to improve operating characteristics like sensorless performance and torque ripple, and potentially reduce costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If symmetric construction is used in PM motors, then uniform operation and periodic performance are achieved, but sensorless performance is limited and torque ripple increases
Solution Approach 1:
The patent applies asymmetry by making one pole pair different from the other pole pairs in the rotor. Specifically, the first pole pair has a different magnetic field configuration compared to the second and third pole pairs. This asymmetric design creates a unique magnetic signature that enables sensorless control systems to determine the absolute mechanical position of the rotor, resolving the limitation of periodic ambiguity in symmetric motors while maintaining uniform operation through controlled asymmetry.
2Reliability
If symmetric construction is used in PM motors, then uniform wear and periodic operation are achieved, but torque ripple amplitude increases beyond desired levels
Solution Approach 1:
The patent applies local quality by creating a specific asymmetric configuration in one pole pair while maintaining symmetry in other aspects. The first pole pair has a different magnetic field strength or distribution compared to the other pole pairs, allowing localized modification of the magnetic field to reduce torque ripple amplitude. This targeted local change addresses the torque ripple issue without compromising the overall uniform wear characteristics achieved by symmetric construction.
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 asymmetrical design enhances sensorless performance, reduces torque ripple, and allows for more precise determination of the rotor's absolute mechanical position, while also potentially lowering the overall cost of the motor.
Implementation Method 1
The magnetic field produced by the permanent magnets interacts with the field generated by a stator current to control rotation of the motor
Data Source
AI summary
An electric motor in which at least one of the rotor and the stator has an asymmetric design is disclosed. The electric motor is divided into a number of segments, where each segment has an equal number of windings and an equal number of poles. The physical construction of each pole within a segment is identical and the number of turns of each winding within a segment is identical. The asymmetry is formed by varying the physical construction of the either the rotor or the stator within one segment from the corresponding construction of the rotor or stator in the other segments. The asymmetries are designed to improve one or more operating characteristics such as sensorless performance, torque ripple, or cogging torque in the motor.