Magnet Temperature Anomaly Detection in Permanent Magnet Synchronous Motors
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Solution Overview
Problem
Existing methods for detecting magnet temperature anomalies in permanent magnet synchronous electric motors used in electric vehicles face challenges due to the difficulty in directly measuring the temperature of the permanent magnet, especially when rotor rotation speed and torque command values change, leading to inaccurate estimation of magnet temperature.
Innovation Solution
An anomaly detector system that calculates q-axis voltage command values for multiple motors and determines magnet temperature anomalies by comparing the differences in these values, allowing for accurate detection without the need for direct temperature measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Difficulty of detecting and measuring
If magnet temperature is estimated by referring to winding wire temperature sensor detection values, then magnet temperature can be estimated without direct measurement, but estimation accuracy deteriorates when rotor rotation speed and torque command value change
Solution Approach 1:
The patent uses q-axis voltage command value as an intermediary parameter to indirectly detect magnet temperature. Instead of directly measuring temperature or relying on winding wire temperature as an imperfect proxy, the system calculates q-axis voltage command values from motor control parameters and uses the difference between these values to detect temperature anomalies, providing a more accurate indirect measurement method.
Solution Approach 2:
The patent changes the detection parameter from temperature-based (winding wire temperature) to voltage-based (q-axis voltage command value). By calculating q-axis voltage command values using motor control equations and comparing their differences, the system detects magnet temperature anomalies without being affected by changes in rotor rotation speed and torque command value, thus maintaining high accuracy under varying operating conditions.
2Measurement precision
If q-axis voltage command value difference is used for anomaly detection, then magnet temperature anomaly detection accuracy is improved, but calculation complexity increases
Solution Approach 1:
The patent uses existing motor control parameters (current command values, rotor rotation speed, torque command value) that are already calculated during normal motor operation to compute q-axis voltage command values. This self-service approach allows the anomaly detection function to utilize readily available data without requiring additional sensors or complex external measurement systems, thereby improving detection accuracy while minimizing added complexity.
Data Source
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AI summary
Under a condition that rotor rotation speeds (ωes are equal, winding wire currents Id, Iq are equal, and winding wire inductances Ld, Lq are equal in first and second electric motors 1, 2, a magnet temperature anomaly detector 30 provided in a microcomputer 5 calculates a change ratio d(|Φml-Φmr - Φmr|)/dt of a magnetic flux difference between the first and second electric motors 1, 2 based on the difference Vql* - Vqr* between a q-axis voltage command value Vqr* corresponding to the first electric motor 1 and a q-axis voltage command value Vqr corresponding to the second electric motor 2, and then when the change ratio d(|Φml - Φmr|)/dt of the magnetic flux difference is more than a predetermined threshold Sh1, it is determined that a permanent magnet of at least any one of the electric motors 1, 2 has a temperature anomaly.