Common-Mode Inductor with Dual-Torus Magnetic Core for EMC Filtering

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Solution Overview

Problem

High-power speed variators face challenges in preventing common-mode inductor saturation in the resonant frequency range, which can lead to amplification of electromagnetic interference and degradation of filtering performance, especially when driving loads with longer power cables.

Innovation Solution

A common-mode inductor with a magnetic core composed of two tori made from materials with different magnetic permeabilities, where one torus is made from a nanocrystalline material and the other from ferrite, ensuring the inductor does not saturate in the resonant frequency range while maintaining effective filtering above 150 kHz.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a large-sized common-mode inductor is used to prevent saturation, then the filtering performance is improved, but the device size and cost increase

Engineering Contradiction:

Improvefiltering performanceVSAvoidinductor size

Core Design Contradiction:

ReliabilityVSVolume of stationary object

Solution Approach 1:

The magnetic core is divided into two separate toroidal segments made of different magnetic materials. Each torus provides a portion of the total inductance, allowing the system to benefit from the high permeability of nanocrystalline material while using ferrite material to prevent saturation at lower frequencies. This segmentation enables prevention of inductor saturation without requiring a single large-sized inductor.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent employs a composite magnetic core structure combining two different magnetic materials (nanocrystalline and ferrite) with different magnetic permeabilities. The nanocrystalline material provides high permeability for effective filtering at higher frequencies, while the ferrite material prevents saturation at lower resonant frequencies. This composite approach achieves both filtering performance and saturation prevention without increasing overall device size.

Inventive Principle:

Principle #40Composite materials

2Device complexity

If a single-stage (2nd order) filtering device is used, then the device complexity is reduced, but the ability to prevent inductor saturation in resonant frequency range is compromised

Engineering Contradiction:

Improvefiltering device complexityVSAvoidsaturation prevention capability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

Different portions of the magnetic core are assigned different local qualities through the use of two distinct magnetic materials. The nanocrystalline torus is optimized for high-frequency filtering operations, while the ferrite torus is optimized for preventing saturation at lower resonant frequencies. This local differentiation of material properties within a single-stage filter enables both simplicity and effective saturation prevention.

Inventive Principle:

Principle #3Local quality

3Productivity

If the common-mode inductor operates near resonant frequency, then the filtering efficiency is improved, but the inductor may saturate and amplify electromagnetic interference

Engineering Contradiction:

Improvefiltering efficiencyVSAvoidelectromagnetic interference amplification

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The ferrite torus is incorporated into the magnetic core structure to preemptively counteract the saturation effect that would occur at resonant frequencies. By providing a magnetic path with appropriate permeability characteristics, the ferrite material prevents the build-up of magnetic flux that leads to saturation, thereby preventing the amplification of electromagnetic interference before it can occur.

Inventive Principle:

Principle #9Preliminary anti-action

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 prevents inductor saturation, reduces the size and cost of the EMC filter, allows continuous variation of sampling frequency, and minimizes heating and leakage self-inductance, enabling longer power cables without impairing filtering performance.

Implementation Method 1

a magnetic core made up of a first torus and a second torus. The first torus is made from a first material having a first magnetic permeability and the second torus is made from a second material having a second magnetic permeability

Methodology Applied

Scientific EffectMagnetic permeability: Magnetic Field

Implementation Method 2

prevent the common-mode inductor from saturating in a frequency range lying close to the resonant frequency of the EMC filter

Methodology Applied

Scientific EffectMagnetic saturation: Magnetic Saturation

Implementation Method 3

a common-mode inductor comprising a winding on each line of the power supply

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Data Source

PatentUS7868730B2Common-mode filtering device and speed variator comprising such a device

Publication Date: 2011.01.11 SCHNEIDER TOSHIBA INVERTER EUROPE SAS

AI summary

The invention relates to a filtering device which includes a common-mode inductor (LF) comprising a winding (L1, L2) on each line of an AC power supply and a magnetic core made up of a first torus (T1) and a second torus (T2). The first torus (T1) has a first magnetic permeability (μ1) and the second torus (T2) has a second magnetic permeability (μ2, μ′2), the first permeability being equal to or greater than three times the second permeability, in order to prevent the common-mode inductor from saturating in the resonant frequency range of the filtering device. Application to the EMC filter of a speed variator.