Synchronous Motor Rotor Slit Design for Cogging Torque Reduction

Solution Overview

Problem

Interior permanent magnet synchronous motors (IPMs) experience cogging torque fluctuations due to uneven magnetic flux distribution, leading to poor controllability and surface quality issues in high-speed and high-accuracy positioning operations.

Innovation Solution

The rotor design incorporates a rotor core with magnet insertion holes and slits, including adjusting and deformation slits, to equalize the magnetic flux passing through adjacent paths, reducing the difference in magnetic attraction forces and thereby minimizing cogging torque. The slits are strategically positioned and sized to ensure equal magnetic flux distribution, with relationships between slit widths and distances maintaining consistent magnetic flux flow.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If slits are arranged to reduce inductance by blocking magnetic flux lines from the stator winding, then inductance is reduced, but uneven magnetic flux distribution occurs between adjacent magnetic paths causing cogging torque fluctuations

Engineering Contradiction:

ImproveinductanceVSAvoidcogging torque fluctuations

Core Design Contradiction:

Use of energy by moving objectVSObject-generated harmful factors

Solution Approach 1:

The patent applies local quality by making the slits have different widths at different positions. Specifically, the slit width varies along the circumferential direction, with wider sections and narrower sections strategically positioned to balance the magnetic flux distribution. This local variation in slit geometry allows different parts of the same slit structure to serve different functions: some portions block magnetic flux to reduce inductance, while other portions allow sufficient flux passage to maintain even magnetic attraction forces across adjacent magnetic paths, thereby eliminating cogging torque fluctuations.

Inventive Principle:

Principle #3Local quality

2Reliability

If permanent magnets are embedded in the rotor core (IPM structure), then reliability is improved and cost is reduced, but inductance becomes larger causing delay in current tracking and poor controllability

Engineering Contradiction:

ImprovereliabilityVSAvoidcontrollability

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The patent applies parameter changes by modifying the geometric parameters of the slits, specifically the width of the slits. By adjusting the slit width parameter, the magnetic flux passage is controlled, which directly affects the inductance value. The optimized slit width parameters enable the IPM structure to achieve reduced inductance (improving current tracking and controllability) while maintaining the reliability and cost advantages of the embedded magnet configuration.

Inventive Principle:

Principle #35Parameter changes

3Force

If slit width is increased to allow more magnetic flux passage, then magnetic attraction force increases, but magnetic flux distribution becomes uneven causing cogging torque

Engineering Contradiction:

Improvemagnetic attraction forceVSAvoidcogging torque

Core Design Contradiction:

ForceVSObject-generated harmful factors

Solution Approach 1:

The patent applies local quality by making the slits have different widths at different positions. Specifically, the slit width varies along the circumferential direction, with wider sections and narrower sections strategically positioned to balance the magnetic flux distribution. This local variation in slit geometry allows different parts of the same slit structure to serve different functions: some portions block magnetic flux to reduce inductance, while other portions allow sufficient flux passage to maintain even magnetic attraction forces across adjacent magnetic paths, thereby eliminating cogging torque fluctuations.

Inventive Principle:

Principle #3Local quality

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 design effectively reduces cogging torque, enhancing the controllability and surface quality of synchronous motors by maintaining consistent magnetic attraction forces during rotation, making them suitable for high-precision applications.

Implementation Method 1

The magnetic flux lines 55 generated from the permanent magnet 53 pass through the magnetic paths 54, and flow to the stator

Methodology Applied

Scientific EffectMagnetic flux: Magnetic Field

Implementation Method 2

the slits 52 are arranged so as to prevent the passage of the magnetic flux line 56 generated by applying the current to the stator winding

Methodology Applied

Scientific EffectMagnetic flux blocking: Magnetic Field

Data Source

PatentUS11038409B2Rotor of synchronous motor

Publication Date: 2021.06.15 OKUMA CORP

AI summary

A rotor of a synchronous motor includes a rotor core that includes magnet insertion holes and a plurality of slits formed on an outer peripheral side of the magnet insertion holes, and permanent magnets embedded in the magnet insertion holes. Magnetic-path forming slits are formed at intervals in a direction along a side of the permanent magnet. Magnetic paths are formed between the magnetic-path forming slits and at portions on the outside of the magnetic-path forming slits on the outermost side. An adjusting slit is formed between a predetermined magnetic-path forming slit and the permanent magnet such that a difference between quantities of magnetic flux passing through the magnetic paths adjacent to each other for widths in a direction intersecting an orientation of a magnetic pole of the permanent magnet is small.