Common-Mode Voltage Cancellation Circuit Using Coupled Inductors

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Solution Overview

Problem

High-speed switching in electrical circuits generates high-frequency common-mode voltages and currents due to parasitic stray capacitance, leading to various issues in electrical systems, particularly in power converters and inverters.

Innovation Solution

A common-mode voltage cancellation (CMVC) circuit utilizing coupled inductors and capacitors, where primary windings are connected to input lines and secondary windings are in series between input and output lines, with capacitors connected in series with primary windings to induce a second voltage that cancels out the common-mode voltage component.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If high-speed switching techniques are used in power converters and inverters, then switching frequency increases and operating characteristics improve, but high-frequency common-mode voltage and current are generated due to parasitic stray capacitance

Engineering Contradiction:

Improveswitching frequencyVSAvoidcommon-mode voltage and current

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The coupled inductor circuit proactively generates a counter-voltage that opposes and cancels the common-mode voltage before it can cause harmful effects. The secondary windings are configured to induce a voltage that is equal in magnitude but opposite in polarity to the common-mode voltage, thereby preventing the harmful common-mode current from flowing through the parasitic capacitance.

Inventive Principle:

Principle #9Preliminary anti-action

Solution Approach 2:

The patent converts the harmful common-mode voltage into a useful signal by using the coupled inductor to sense the common-mode voltage on the primary side and transform it into a compensating voltage on the secondary side. The common-mode voltage, which would normally be harmful, is instead used to generate the cancellation signal through electromagnetic induction.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Object-affected harmful factors

If traditional LC filters are used to reduce common-mode voltage, then common-mode interference is suppressed, but the filters become larger, heavier, and more expensive

Engineering Contradiction:

Improvecommon-mode interferenceVSAvoidfilter weight and size

Core Design Contradiction:

Object-affected harmful factorsVSWeight of stationary object

Solution Approach 1:

The patent changes the fundamental operating principle from passive filtering to active cancellation. Instead of using large inductors and capacitors to physically block common-mode signals, the system uses electromagnetic induction to dynamically generate a counter-voltage that actively cancels the common-mode signal, allowing for much smaller component sizes.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the mechanical/passive LC filter system with an electromagnetic field-based active cancellation system. The coupled inductor uses electromagnetic induction to generate the cancellation voltage, substituting the need for large physical filtering components with a more compact field-based solution.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Weight of stationary object

If coupled inductors with capacitors are used to cancel common-mode voltage, then common-mode voltage is reduced and filter size decreases, but circuit complexity increases

Engineering Contradiction:

Improvefilter weight and sizeVSAvoidcircuit complexity

Core Design Contradiction:

Weight of stationary objectVSDevice complexity

Solution Approach 1:

The coupled inductor serves multiple functions simultaneously: it transforms the differential-mode power frequency voltage, provides galvanic isolation, and generates the common-mode cancellation voltage through its secondary windings. This multi-functionality reduces the need for separate components and simplifies the overall circuit architecture despite the active cancellation mechanism.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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

Effectively reduces common-mode voltage, allowing for the use of smaller, lighter, and less expensive LC filters, thereby improving the stability and efficiency of electrical power systems.

Implementation Method 1

inducing a second voltage on each respective secondary winding via a respective primary winding of the set of coupled inductors

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Data Source

PatentUS11437970B2Method and apparatus for common-mode voltage cancellation

Publication Date: 2022.09.06 GE AVIATION SYSTEMS LLC

AI summary

A common-mode voltage cancellation (CMVC) circuit, is disclosed. The circuit includes a set of input lines arranged to receive a respective phase voltage, and a set of output lines arranged to provide a respective output phase voltage. The circuit further includes a set of coupled inductors, each having a respective primary winding and secondary winding coupled in signal communication at a respective upstream end to a respective input line to receive a respective phase voltage therefrom, each respective phase voltage having a common-mode voltage component. Each primary winding being coupled at a respective downstream end to ground, and each secondary winding being coupled in series between the respective input line and a respective output line. The circuit includes a set of capacitors, each capacitor being electrically coupled to a respective input line and in series with a respective primary winding of the set of coupled inductors.