Inductance-Based Rotor Magnet Temperature Estimation
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Solution Overview
Problem
Existing methodologies for estimating the temperature of rotor magnets in rotary electric machines are complex and susceptible to errors, relying on thermal models that require accurate information about cooling systems and are affected by core and eddy current losses, making them difficult to implement effectively.
Innovation Solution
A method that uses motor control signals to estimate rotor magnet temperature by injecting a high-frequency voltage component into the control voltage, extracting the high-frequency current component, calculating the inductance value, and employing a characterized inductance-temperature-position relationship to generate an estimated temperature, without relying on thermal models.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If thermal models are used to estimate magnet temperature, then temperature estimation can be performed, but the method becomes complex and susceptible to signal errors from cooling system inputs
Solution Approach 1:
The patent extracts the temperature estimation function from complex thermal models and implements it through a simplified inductance-based method. By measuring inductance at different temperatures and creating a lookup table, the complex thermal modeling is removed while retaining temperature estimation capability
Solution Approach 2:
The patent replaces the thermal model-based estimation system with an electrical inductance-based system. Instead of using thermal models that require cooling system parameters, the invention uses inductance measurements which are inherently available in the motor control system
2Measurement precision
If resistance-based temperature estimation is used, then temperature can be estimated, but the estimation is subverted by core losses and eddy current effects
Solution Approach 1:
The patent extracts the temperature-dependent parameter (inductance) that is independent of loss effects. By focusing on inductance rather than resistance, the method separates the temperature measurement function from the harmful core and eddy current losses
Solution Approach 2:
The patent introduces inductance as an intermediary parameter for temperature estimation. Inductance serves as a mediator that correlates with temperature but is not affected by core losses or eddy currents, unlike resistance-based methods
3Measurement precision
If complex thermal models with multiple input signals are used, then temperature estimation is possible, but the method is susceptible to signal errors in cooling system inputs
Solution Approach 1:
The patent removes the dependency on cooling system input signals by extracting temperature information from inductance measurements. This eliminates the harmful effect of signal errors from coolant temperature and flow rate sensors
Solution Approach 2:
The patent enables the motor control system to estimate magnet temperature using its own existing measurements (inductance and position) without requiring external cooling system sensors. The system serves its own temperature monitoring needs using internally available data
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 estimation of rotor magnet temperature, independent of thermal models, allowing for accurate control and regulation of the electric machine's operation and temperature, even when the rotor is stationary.
Implementation Method 1
injecting a high-frequency voltage component onto a control voltage of the electric machine to generate an adjusted voltage command
Implementation Method 2
calculating an inductance value of the electric machine using the extracted high-frequency component
Implementation Method 3
uses a characterized inductance-temperature-position relationship to generate an estimated temperature
Data Source
AI summary
A method for estimating a magnet temperature of a rotor magnet within a rotary electric machine includes, while a rotor of the electric machine is stationary, injecting a high-frequency voltage component onto a control voltage of the electric machine, via a controller, to generate an adjusted voltage command, and extracting a high-frequency component of a resulting current as an extracted high-frequency component. The method also includes calculating an inductance value of the electric machine using the extracted high-frequency component of the resulting current. The magnet temperature is estimated using the calculated inductance value and an angular position of the rotor. The method includes controlling an operation of the electric machine using the estimated magnet temperature. An electric powertrain uses the electric machine and controller noted above.