Segmented Rotor Structure for PWM Eddy Current Suppression

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Solution Overview

Problem

Existing electronically commutated electric motors with slotless stators suffer from high additional losses due to pulse width modulation (PWM) induced eddy currents, which are not effectively addressed by existing solutions that either require complex control systems or large, heavy, and expensive additional inductors, or result in complex and costly manufacturing processes.

Innovation Solution

The rotor is segmented with permanent magnet segments spaced along sectional planes with normals perpendicular to the axial direction, featuring electrical insulation and optionally soft magnetic laminations, reducing the number of segments required and enhancing inductance to minimize eddy currents.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If axial segmentation of the rotor into permanent magnet segments is used with sectional planes perpendicular to the axial direction, then eddy currents are suppressed, but the number of segments required becomes very large making manufacturing complex and expensive

Engineering Contradiction:

Improveeddy current lossesVSAvoidnumber of permanent magnet segments

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The rotor is segmented into permanent magnet segments along sectional planes perpendicular to the axial direction. This segmentation creates electrical insulation between segments, breaking the path for eddy currents and suppressing them effectively.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Electrical insulation is introduced between adjacent permanent magnet segments along the sectional planes. This intermediary material prevents eddy currents from flowing between segments while maintaining the segmented structure for eddy current suppression.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Loss of energy

If additional inductors are used in the electronics to reduce current ripple, then PWM-induced losses are reduced, but the inductors become large, heavy and expensive with additional ohmic losses

Engineering Contradiction:

ImprovePWM-induced lossesVSAvoidweight of additional inductors

Core Design Contradiction:

Loss of energyVSWeight of moving object

Solution Approach 1:

The rotor structure itself is modified to reduce PWM-induced losses, eliminating the need for additional external inductors. The segmented permanent magnet segments with electrical insulation create inherent resistance to eddy currents, making the system self-regulating without heavy external components.

Inventive Principle:

Principle #25Self-service

3Loss of energy

If winding voltage and intermediate circuit voltage are selected to achieve 100% duty cycle, then PWM-induced losses are avoided, but complex and expensive control systems are required for speed adjustment

Engineering Contradiction:

ImprovePWM-induced lossesVSAvoidcontrol system complexity

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

Instead of modifying the control system to avoid PWM-induced losses by maintaining 100% duty cycle, the approach is inverted by modifying the rotor structure itself to be resistant to eddy currents. This allows normal PWM operation with standard control systems while still suppressing losses.

Inventive Principle:

Principle #13The other way round (Inversion)

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 prevents PWM-induced eddy currents with fewer segments, simplifying manufacturing and reducing costs while maintaining motor performance.

Implementation Method 1

the rotor has a respective electric insulation between the permanent magnet segments along the at least one sectional plane

Methodology Applied

Scientific EffectElectrical insulation: Electrical Resistance

Implementation Method 2

additional losses being induced in the electric motor by the pulse width modulation (PWM) of the power electronics. These losses are particularly high in low-inductance motors such as electrically commutated electric motors with slotless stators. The main effect here is eddy currents in the rotor

Methodology Applied

Scientific EffectEddy currents: Eddy Currents

Data Source

PatentUS20250364855A1Segmented rotor for a slotless, electronically commutated electric motor, and electric motor comprising such a rotor

Publication Date: 2025.11.27 MAXON MOTOR AG

AI summary

The rotor has a slotless stator, an electronic commutator, and permanent magnet segments. The permanent magnet segments are mutually spaced at least over an axial region of the rotor along at least one sectional plane, and the rotor has a respective electric insulation between the permanent magnet segments along the at least one sectional plane. A normal of the respective sectional plane runs perpendicularly to the axial direction of the rotor and perpendicularly to the q-axis of the rotor if the rotor has one pole pair and perpendicularly to one of a plurality of q-axes of the rotor if the rotor has more than one pole pair. A soft magnetic material is introduced between the permanent magnet segments along the sectional plane(s). The material is electrically insulated by means of the electric insulation of the permanent magnet segments.