Hybrid DC Bus Cable Shielding for Common Mode Noise Control

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Solution Overview

Problem

Distributed motor drive systems face challenges with common mode voltages and currents between devices, leading to electromagnetic noise interference and premature failure of Metal Oxide Varistors (MOVs) due to repeated voltage discharges, which can damage circuit components.

Innovation Solution

A hybrid DC bus cable with integrated power and communication conductors, where a shield around the communication conductors is connected to a ground conductor at each end, dividing common mode currents between the ground conductor and the shield, reducing the overall amplitude of common mode current and minimizing interference.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If MOVs are used to discharge common mode voltages, then common mode voltages are protected, but MOVs suffer premature failure due to repeated voltage discharges

Engineering Contradiction:

Improveprotection of common mode voltagesVSAvoidservice life of MOVs

Core Design Contradiction:

ReliabilityVSDuration of action of stationary object

Solution Approach 1:

The invention extracts the harmful common mode currents from the signal conductors by providing a dedicated return path through the shield and ground conductor, preventing these currents from flowing through MOVs and causing their premature failure

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The shield and ground conductor act as an intermediary pathway that mediates the flow of common mode currents, providing a safe discharge route that protects both the signal conductors and MOVs from damage

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If distributed motor drive systems are implemented, then system flexibility is improved, but common mode voltage differences between devices cause electromagnetic noise interference

Engineering Contradiction:

Improvesystem flexibilityVSAvoidelectromagnetic noise interference

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The invention converts the harmful common mode voltage differences into a beneficial feature by using them to drive common mode currents through the shield and ground conductor, thereby protecting signal conductors from interference while maintaining system flexibility

Inventive Principle:

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

Solution Approach 2:

The shield and ground conductor serve as an intermediary that equalizes voltage potentials between distributed devices, allowing common mode currents to flow through this dedicated path rather than through signal conductors, thus eliminating electromagnetic noise interference

Inventive Principle:

Principle #24Intermediary (Mediator)

3Adaptability or versatility

If separate motor drives with rectifiers are used for each motor, then motor control independence is improved, but system cost and housing size increase

Engineering Contradiction:

Improvemotor control independenceVSAvoidsystem cost and housing size

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The invention implements multi-functionality by using a single rectifier unit to supply power to multiple distributed motor drives, eliminating the need for separate rectifiers in each drive while maintaining independent motor control through dedicated communication conductors

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

The solution effectively manages common mode voltages and currents, reducing electromagnetic noise and preventing damage to circuit components by evenly distributing common mode currents, thus enhancing system reliability and reducing cable size and cost.

Implementation Method 1

The braided shield is positioned around the communication conductors and extends along the inner surface of the second jacket. The braided shield is electrically connected to the ground conductor at the first end and the second end of the cable.

Methodology Applied

Scientific EffectElectromagnetic shielding: Faraday Cage

Implementation Method 2

The hybrid cable includes both power and communications conductors within the cable

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Data Source

PatentUS12548953B2Hybrid cable for reducing common mode noise in a distributed dc bus system

Publication Date: 2026.02.10 ROCKWELL AUTOMATION TECH INC

AI summary

A cable for reducing electrical noise within a distributed motor drive system includes an insulating jacket defining an outer periphery of the cable. The insulating jacket extends between a first end and a second end of the cable. At least one power conductor and a ground conductor extend between the first and second ends of the cable. A communication cable also extends between the first and second ends of the cable. The communication cable includes a second jacket having an outer surface and an inner surface, where the outer surface of the second jacket defines an outer periphery of the communication cable. At least one pair of communication conductors and a braided shield extend within the communication cable. The braided shield is positioned around the communication conductors and is electrically connected to the ground conductor at the first and second ends of the cable.