Dual-Filter Motor Controller for Bearing Current Reduction

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Solution Overview

Problem

Electric motors using pulse width modulation (PWM) type inverters experience bearing currents due to common mode voltage induced by semiconductor switching, leading to reduced bearing lifetime and increased electromagnetic interference (EMI) when traditional grounding brushes are used to mitigate this.

Innovation Solution

A motor controller with a three-phase high-frequency inverter and a dual-filter system, comprising a differential mode (DM) filter and a common mode (CM) filter, is implemented to reduce harmonic components and common mode voltage, thereby minimizing bearing currents and EMI. The DM filter has a resonant frequency less than 10% of the switching frequency, and the CM filter is configured to further reduce common mode voltage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If grounding brushes are used to reduce bearing current, then bearing current is reduced, but total common mode current to ground increases leading to increased EMI

Engineering Contradiction:

Improvebearing currentVSAvoidelectromagnetic interference

Core Design Contradiction:

Object-affected harmful factorsVSObject-generated harmful factors

Solution Approach 1:

The patent extracts the harmful common mode voltage component from the motor control system by implementing a common mode filter that specifically targets and removes this voltage component before it reaches the motor bearings, thereby reducing bearing current without requiring grounding brushes that would increase EMI

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent introduces a common mode filter as an intermediary component between the inverter and motor bearings. This filter acts as a mediator that blocks the path of common mode voltage to the bearings while maintaining proper grounding, thus reducing bearing current without creating additional EMI through grounding brushes

Inventive Principle:

Principle #24Intermediary (Mediator)

2Productivity

If high-frequency inverter is used to improve motor control, then motor control performance is improved, but bearing current increases due to common mode voltage from switching behavior

Engineering Contradiction:

Improvemotor control performanceVSAvoidbearing current

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent applies preliminary anti-action by placing a common mode filter in the signal path before the motor bearings to preemptively block common mode voltage generated by the high-frequency inverter switching, thereby preventing bearing current before it can cause damage while maintaining the benefits of high-frequency motor control

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

The solution effectively reduces bearing currents and minimizes EMI in electric motors, enhancing their operational efficiency and extending bearing lifespan while maintaining compact inverter design.

Implementation Method 1

a differential mode (DM) filter coupled in series with the AC output stage of the HF inverter and having a resonant frequency less than 10% of the switching frequency, the DM filter configured to reduce harmonic components of the three-phase output

Methodology Applied

Scientific EffectElectromagnetic filtering: Filter (electronic)

Implementation Method 2

a common mode (CM) filter coupled in series with the DM filter, the CM filter configured to filter the first filtered output to generate a second filtered output having a reduced CM voltage to operate the electric motor with a reduced bearing current

Methodology Applied

Scientific EffectCommon mode voltage filtering: Filter (electronic)

Data Source

PatentUS10530239B2Filter systems for reducing bearing current in high-frequency motor control systems

Publication Date: 2020.01.07 REGAL BELOIT AMERICA INC

AI summary

A motor controller and methods for operating a motor are described herein. The motor controller includes a high-frequency (HF) inverter having a direct current (DC) input stage and an alternating current (AC) output stage, the HF inverter operable at a switching frequency to generate a three-phase output having a fundamental frequency. The motor controller also includes a differential mode (DM) filter coupled in series with the output stage of the HF inverter and having a resonant frequency less than 10% of the switching frequency, the DM filter configured to reduce harmonic components of the three-phase output and generate a first filtered output. The motor controller further includes a common mode (CM) filter coupled in series with the DM filter, the CM filter configured to filter the first filtered output to generate a second filtered output having a reduced CM voltage to operate the electric motor with a reduced bearing current.