AC Motor Controller Detecting Step-Out via Motor Constant Variation
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Solution Overview
Problem
Existing methods for detecting abnormal operations in three-phase AC electric motors, such as step-out and demagnetization, are prone to misdetection, especially in weak magnetic fields and during starting with sensorless control, leading to potential damage due to inaccurate power factor and current value assessments.
Innovation Solution
A controller calculates motor constants using current, voltage, and rotational speed, analyzing variations to detect abnormal operations by presetting abnormal values or extracting changes from past data, improving detection precision in low power factor regions and during open driving conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sensorless control is used to avoid sensor failure, then reliability is improved, but the ability to detect abnormal operation is lost
Solution Approach 1:
The patent uses motor constants (back-EMF constant and inductance) as intermediary parameters to detect abnormal operations. These constants are calculated from easily measurable quantities (voltages, currents, rotational speed) and serve as mediators that translate sensorless control data into meaningful abnormality indicators, enabling detection without direct sensors.
Solution Approach 2:
The system continuously calculates motor constants during operation and compares them against reference values or historical data. This feedback mechanism allows the system to detect deviations indicating abnormal operations (step-out, demagnetization, excessive load) and trigger appropriate responses, maintaining reliability while enabling abnormality detection.
2Difficulty of detecting and measuring
If conventional detection methods using current value and power factor are used, then step-out detection is enabled, but misdetection occurs in weak magnetic field region
Solution Approach 1:
The patent changes the detection parameter from direct current value and power factor to motor constants (back-EMF constant and inductance). These constants remain relatively stable across different operating conditions including weak magnetic field regions, unlike current and power factor which vary significantly. This parameter transformation eliminates misdetection in weak magnetic fields while maintaining step-out detection capability.
3Temperature
If motor constant calculation is performed using conventional methods, then temperature estimation is enabled, but abnormal operation detection is not achieved
Solution Approach 1:
The patent segments the motor constant calculation into two distinct components: back-EMF constant (related to temperature) and inductance (related to magnetic properties). By separating these functions, the system can simultaneously monitor temperature through the back-EMF constant while detecting abnormal operations through changes in inductance and the relationship between the two constants, achieving both temperature estimation and abnormality detection.
4Reliability
If detection threshold is set to detect step-out, then abnormal operation detection is improved, but false detection increases in normal low power factor conditions
Solution Approach 1:
The patent transforms the detection parameter from power factor (which varies widely in normal operation) to motor constants (which remain stable). This parameter change allows setting detection thresholds that reliably distinguish abnormal operations from normal low power factor conditions, eliminating false detections while maintaining sensitivity to actual abnormalities.
Data Source
AI summary
Provided is an AC electric motor control device capable of detecting, in an AC electric motor drive device, abnormal operation of an AC electric motor or abnormal operation due to, for example, a sudden change of a load without an erroneous operation regardless of the operational state of the AC electric motor. When driving a three-phase AC electric motor by an inverter, inside a controller, an electric motor constant is calculated using at least one of the current, voltage, and rotational speed of the electric motor and the variation of the constant value is analyzed, thereby detecting abnormal operation of the electric motor or abnormal operation of a load device connected to the electric motor. In order to analyze the constant, a variation to be determined to be abnormal is preset or an abnormal value is calculated in comparison with the accumulated values of past constant changes. Alternatively, only the variation of the constant calculated in the controller is extracted to detect abnormality.