Stator Winding Temperature Monitoring via D-Axis AC Injection
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Solution Overview
Problem
Existing electric motor thermal monitoring methods, such as using thermocouples or thermistors, add complexity and may have estimation errors, while direct temperature measurement systems are cumbersome and costly, failing to accurately and efficiently monitor winding temperatures, especially during prolonged peak output operations.
Innovation Solution
A method involving injecting an AC current synchronized with the control frequency into the D-axis of the stator winding to determine the resistance and subsequently the temperature of the stator windings without additional hardware, using the relationship between resistance and temperature coefficients of the winding material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If thermocouples or thermistors are installed within stator windings for direct temperature measurement, then temperature measurement accuracy is improved, but device complexity and wiring harness complexity increase
Solution Approach 1:
The stator windings themselves serve as the sensing element by utilizing their inherent electrical resistance properties. The resistance of the windings changes with temperature, allowing the windings to self-report their thermal state without requiring separate sensor installations. This eliminates the need for additional thermocouples or thermistors and their associated wiring complexity.
Solution Approach 2:
The patent replaces mechanical/physical temperature sensing systems (thermocouples, thermistors) with an electrical measurement approach. By measuring the electrical resistance of the stator windings and correlating it to temperature through known resistance-temperature relationships, the system substitutes complex physical sensor installations with simpler electrical measurements that can be performed using existing motor control circuitry.
2Device complexity
If known thermal models are used to estimate winding temperature based on motor operating parameters, then device complexity is reduced, but measurement precision deteriorates due to estimation errors
Solution Approach 1:
The system continuously monitors the electrical resistance of the stator windings during motor operation and uses this real-time feedback to determine actual winding temperature. This feedback mechanism allows the system to directly measure temperature conditions rather than relying on predictive models, significantly improving accuracy while maintaining system simplicity by using existing measurement capabilities.
3Reliability
If additional temperature sensors and signal monitoring hardware are installed, then temperature measurement capability is improved, but manufacturing cost increases
Solution Approach 1:
The patent makes the existing stator windings serve multiple functions: they continue to provide the primary electromagnetic function for motor operation while simultaneously serving as temperature sensors. This multi-functionality eliminates the need for separate temperature sensing components, reducing part counts, assembly steps, and manufacturing costs while maintaining reliable temperature monitoring capability throughout the motor's operational life.
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
This approach allows for accurate and efficient temperature monitoring of electric motor windings, reducing the need for additional sensors and wiring, and effectively estimating stator winding temperatures with minimal impact on motor performance, thereby enhancing thermal management and extending motor life.
Implementation Method 1
determining a resistance of the stator winding corresponding to the DC-phase current and an applied voltage, and determining a temperature of the electric motor as a function of the resistance of the stator winding
Data Source
AI summary
A method for determining a temperature of an electric motor including stator windings includes injecting an AC current into a D-axis current of a stator winding at a frequency that is synchronized with a control frequency of the electric motor, determining a DC-phase current, determining a resistance of the stator winding corresponding to the DC-phase current and an applied voltage, and determining a temperature of the electric motor as a function of the resistance of the stator winding.