Permanent Magnet Motor Field Offsetting for Torque Pulsation
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Solution Overview
Problem
Electrified vehicle traction motors, particularly permanent magnet motors, experience pulsing and vibrating torque at certain speed ranges and torque levels, leading to passenger discomfort and accelerated wear of structural and powertrain components.
Innovation Solution
The electric motor system incorporates a permanent magnet motor with a hollow cylindrical stator and a cylindrical rotor featuring N pairs of permanent magnets, where N is an even integer. A controller is used to stagger or offset the stator magnetic field relative to the rotor magnetic poles, utilizing N/2 times as many switching transistors to control each electromagnetic coil for different current magnitudes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional solutions such as skew configurations, harmonic current injection, or current modification are used to reduce torque pulsation, then vibration and noise are reduced, but motor efficiency is drastically reduced
Solution Approach 1:
The patent applies asymmetry by deliberately misaligning the magnetic axes of different phase windings relative to the rotor poles. Instead of symmetric alignment that causes periodic cogging torque, the windings are positioned at asymmetric angles to distribute magnetic attraction forces more uniformly, thereby reducing torque pulsation without significant efficiency loss
Solution Approach 2:
The patent changes the angular position parameters of the stator windings relative to the rotor magnets. By adjusting the magnetic axis angles of different phases to asymmetric values, the periodic cogging torque is transformed into a more uniform torque output, reducing vibration and noise while maintaining efficiency
2Object-affected harmful factors
If skew configurations are used to reduce magnetic cogging, then torque pulsation is reduced, but manufacturing complexity increases
Solution Approach 1:
Rather than implementing complex physical skewing of the entire stator or rotor structure, the patent achieves cogging reduction through asymmetric angular positioning of the magnetic axes of individual phase windings. This simplifies manufacturing by using standard laminated stator construction with adjusted winding angles, avoiding the complexity of skewed laminations
3Object-affected harmful factors
If harmonic current injection is used to mitigate torque pulsation, then vibration is reduced, but control complexity increases
Solution Approach 1:
The patent implements the solution at the design stage by pre-positioning the magnetic axes of the windings at asymmetric angles relative to the rotor poles. This preliminary geometric configuration inherently reduces cogging torque across all operating conditions, eliminating the need for complex real-time harmonic current injection control algorithms
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
This solution effectively mitigates or eliminates magnetic cogging, reducing torque pulsation and vibration, thereby enhancing passenger comfort and extending the reliability and durability of the motor system.
Implementation Method 1
a plurality of electromagnetic coils arranged in the plurality of slots, respectively, and a cylindrical rotor disposed within the stator and defining a circular outer portion having N pairs of permanent magnets arranged thereabout to define N rotor poles
Implementation Method 2
controlling each pair of electromagnetic coils to stagger or offset a stator magnetic field generated by the pair of electromagnetic coils relative to the rotor magnetic poles
Implementation Method 3
the controller utilizes N/2 times as many switching transistors to individually control each electromagnetic coil of each pair of electromagnetic coils to receive a different current magnitude
Data Source
AI summary
An electric motor system, such as for an electrified vehicle, includes a permanent magnet motor (PMM) including a hollow cylindrical stator defining a circular inner portion with a plurality of slots, defined between a respective plurality of ferromagnetic teeth, and having a plurality of electromagnetic coils arranged in the plurality of slots, respectively, and a cylindrical rotor disposed within the stator and defining a circular outer portion having N pairs of permanent magnets arranged thereabout to define N rotor poles, respectively, wherein N is an even integer greater than or equal to four, and a controller configured to control the PMM to mitigate or eliminate magnetic cogging by controlling each pair of electromagnetic coils to stagger or offset a stator magnetic field generated by the pair of electromagnetic coils relative to the rotor magnetic poles.