Multi-Phase Motor Overload Detection via Stator Resistance Monitoring

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Solution Overview

Problem

Existing multi-phase electric motor control systems struggle to effectively detect overload conditions during normal operation without additional hardware, as they rely on fixed voltage and current monitoring, which is not feasible in all scenarios, and do not account for motor aging which affects efficiency and lifespan.

Innovation Solution

A method and device for detecting overload in multi-phase electric motors by monitoring the thermal increase of stator resistance through a self-commissioning algorithm, modulation index, and duty cycle of the applied voltage, allowing for continuous current monitoring at constant load and speed, enabling detection of maximum current without additional thermal sensing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If additional thermal sensing hardware is used to detect overload conditions, then measurement precision is improved, but device complexity increases

Engineering Contradiction:

Improveoverload detection accuracyVSAvoidhardware requirements

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The motor control system uses its existing current sensors and control MCU to monitor stator resistance changes and detect thermal overload conditions, eliminating the need for separate thermal sensing hardware. The system serves itself by utilizing already-present components for dual purposes (current control and temperature monitoring).

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent replaces physical thermal sensing hardware with an electrical measurement approach by monitoring stator resistance changes through voltage and current measurements. The thermal state is inferred through electrical parameter analysis rather than direct thermal contact sensing.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Device complexity

If fixed voltage and current monitoring is used for overload detection, then device complexity is reduced, but measurement precision deteriorates

Engineering Contradiction:

Improvemonitoring system simplicityVSAvoidoverload detection accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent transitions from monitoring fixed voltage and current levels to dynamically monitoring the relationship between voltage, current, and derived stator resistance. The system calculates resistance changes over time to detect thermal effects, using parameter relationships rather than absolute threshold monitoring.

Inventive Principle:

Principle #35Parameter changes

3Ease of operation

If motor aging effects are not accounted for, then ease of operation is maintained, but reliability decreases

Engineering Contradiction:

Improvecontrol system simplicityVSAvoidmotor lifespan prediction

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The system continuously monitors stator resistance changes and compares them against expected values to detect motor aging effects. This feedback mechanism allows the control system to adapt to motor degradation over time, maintaining reliable operation without complex manual intervention.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent performs preliminary characterization of motor resistance at known temperatures and uses this baseline data to predict aging effects. By establishing reference values in advance, the system can later detect deviations indicating motor degradation without real-time complexity.

Inventive Principle:

Principle #10Preliminary 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

Enables real-time overload detection and maximum current characterization, optimizing motor control to prevent damage, extending motor life, and reducing costs by utilizing existing motor control MCU for computations, without the need for additional sensors.

Implementation Method 1

monitoring a thermal increase of a value of a stator resistance of the multi-phase electric motor during a steady state condition

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Data Source

PatentUS11146205B2Method for controlling electric motors, corresponding circuit and computer program product

Publication Date: 2021.10.12 STMICROELECTRONICS SRL

AI summary

A multi-phase electric motor includes a stator winding. The multi-phase electric motor is controlled by regulating a current flowing in the multi-phase electric motor in response to an applied voltage. An overload condition of the multi-phase electric motor is detected by monitoring a thermal increase of the value of a stator resistance of the stator winding of the multi-phase electric motor during a steady state condition of said multi-phase electric motor in which the current flowing in the motor has constant phase, and the motor is operating at constant load with constant speed.