Active EMI Filtering via Magnetic Coupling Cancellation

Solution Overview

Problem

Conventional passive EMI filters for power devices using switching converters are large, heavy, and inefficient, occupying significant weight and volume, and struggle to effectively filter high-frequency interference due to limitations in inductor and capacitor design.

Innovation Solution

An active EMI filtering system utilizing a pair of coupled inductors with a secondary winding for sensing and canceling interference currents, employing a wideband amplifier to apply a phase-shifted cancellation signal, reducing the need for large differential mode inductors and capacitors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If traditional passive EMI filters use large inductors and capacitors to filter differential mode interference, then filtering effectiveness is improved, but the volume and weight of the filter increase significantly

Engineering Contradiction:

Improvedifferential mode interferenceVSAvoidfilter weight

Core Design Contradiction:

Object-affected harmful factorsVSWeight of stationary object

Solution Approach 1:

The patent replaces the traditional passive mechanical filtering system (large inductors and capacitors) with an active electronic system using coupled inductors, operational amplifiers, and feedback circuits to achieve the same EMI filtering function with significantly reduced weight and volume

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the filtering approach from passive component-based frequency-dependent impedance to an active system using feedback control and signal cancellation, fundamentally altering the parameter space in which filtering is achieved

Inventive Principle:

Principle #35Parameter changes

2Object-affected harmful factors

If traditional passive EMI filters use large inductors and capacitors to filter differential mode interference, then filtering effectiveness is improved, but the volume of the filter increases significantly

Engineering Contradiction:

Improvedifferential mode interferenceVSAvoidfilter volume

Core Design Contradiction:

Object-affected harmful factorsVSVolume of stationary object

Solution Approach 1:

The patent replaces the traditional passive mechanical filtering system (large inductors and capacitors) with an active electronic system using coupled inductors, operational amplifiers, and feedback circuits to achieve the same EMI filtering function with significantly reduced weight and volume

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the filtering approach from passive component-based frequency-dependent impedance to an active system using feedback control and signal cancellation, fundamentally altering the parameter space in which filtering is achieved

Inventive Principle:

Principle #35Parameter changes

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 active filtering system significantly reduces the volume and weight of EMI filtering components, effectively attenuating differential mode interference across a wide frequency range, from 10 kHz to 5 MHz, while maintaining performance comparable to passive filters.

Implementation Method 1

An active EMI filtering system utilizing a pair of coupled inductors with a secondary winding for sensing and canceling interference currents

Methodology Applied

Scientific EffectMagnetic coupling: Electromagnetic Induction

Implementation Method 2

An active EMI filtering system utilizing a pair of coupled inductors with a secondary winding for sensing and canceling interference currents

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Data Source

PatentUS7898827B2Active EMI filtering using magnetic coupling cancellation

Publication Date: 2011.03.01 HONEYWELL INTERNATIONAL INC

AI summary

An active electromagnetic interference (EMI) filtering may reduce the requirements for high current differential mode inductors. The active EMI filtering of the present invention may be useful in power devices that use switching power converters. Conventional EMI differential mode filtering devices may occupy up to 30% of the total weight and volume of the power electronics. Conventional differential mode filtering inductors tend to be large and heavy, especially so for high current input power lines. The present invention may replace the large conventional differential mode filtering inductors with a smaller set of coupled inductors.