Motor Drive Failure Detection via Dynamic Brake Current Monitoring

Solution Overview

Problem

Existing motor drive devices cannot detect failures unless the motor is operated, and they lack the ability to detect failures when the motor is not connected, as no feedback current is generated.

Innovation Solution

A motor drive device with an inverter, current detector, current controller, dynamic brake circuit, storage, and failure determiner that compares the change rate of detected currents over time to determine if a failure has occurred, allowing for failure detection even when the motor is not connected or operating.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If the motor is not operated, then power consumption is reduced, but failure detection capability is lost

Engineering Contradiction:

Improvepower consumptionVSAvoidfailure detection capability

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The system performs preliminary failure detection by monitoring current values during the dynamic brake operation phase, before the motor is connected or operated. The storage unit stores current values detected during dynamic brake operation, and the failure determination unit compares these stored values with predetermined thresholds to detect failures in the dynamic brake circuit, power device, or current detection circuit without requiring motor operation.

Inventive Principle:

Principle #10Preliminary action

2Adaptability or versatility

If the motor is not connected to the motor drive device, then the device can operate standalone, but failure detection in the motor drive device alone is impossible

Engineering Contradiction:

Improvestandalone operation capabilityVSAvoidfailure detection capability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The system performs preliminary failure detection by monitoring current values during the dynamic brake operation phase, before the motor is connected or operated. The storage unit stores current values detected during dynamic brake operation, and the failure determination unit compares these stored values with predetermined thresholds to detect failures in the dynamic brake circuit, power device, or current detection circuit without requiring motor operation.

Inventive Principle:

Principle #10Preliminary action

3Measurement precision

If current feedback is used for failure detection, then failure detection accuracy is improved, but the system cannot detect failures without motor operation

Engineering Contradiction:

Improvefailure detection accuracyVSAvoidoperational requirement

Core Design Contradiction:

Measurement precisionVSEase of operation

Solution Approach 1:

The system performs preliminary failure detection by monitoring current values during the dynamic brake operation phase, before the motor is connected or operated. The storage unit stores current values detected during dynamic brake operation, and the failure determination unit compares these stored values with predetermined thresholds to detect failures in the dynamic brake circuit, power device, or current detection circuit without requiring motor operation.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The current detection circuit serves multiple functions: it detects motor current during normal motor operation and also detects current during dynamic brake operation for failure detection purposes. This multi-functionality allows the same hardware to support both motor control and standalone failure detection capabilities.

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

Enables the detection of failures without operating the motor and allows for standalone failure detection in the motor drive device, preventing potential issues by issuing warnings and determining the presence of failures based on current changes.

Implementation Method 1

an inverter provided with a plurality of power devices and configured to convert a direct current (DC) voltage to an alternative current (AC) voltage by switching the plurality of power devices

Methodology Applied

Scientific EffectElectrical switching:

Implementation Method 2

a dynamic brake circuit provided with a plurality of relays and configured to short-circuit an output side terminal of the inverter via a plurality of resistances

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Data Source

PatentUS10823783B2Motor drive device having failure detection function

Publication Date: 2020.11.03 FANUC LTD

AI summary

A motor drive device includes an inverter configured to convert a DC voltage to an AC voltage by switching power devices, a current detector configured to detect a current output from the inverter, a current controller configured to generate a voltage command, a control signal generator configured to control switching of the power devices, a dynamic brake circuit provided with relays and configured to short-circuit an output side terminal of the inverter via resistances, a storage configured to store an initial current value and a first threshold value, and a failure determiner configured to compare a current value and an initial current value after a predetermined time has elapsed since detection of the initial current value, and determine presence or absence of a failure based on a result of comparing a change rate of the current value from the initial current value with the first threshold value.