Rotor Permanent Magnet Temperature Estimation Using Flux and Energy Maps
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Solution Overview
Problem
Existing methods for estimating the temperature of a permanent magnet in a motor rotor are either inaccurate, require excessive resources, or increase production costs, and do not account for changes in magnetic flux due to battery voltage variations or cooling system performance.
Innovation Solution
A system that estimates the temperature of a permanent magnet using both magnetic flux and energy maps, selecting the appropriate method based on rotational speed and current conditions to enhance accuracy, and compensates for nonlinearity in the inverter's voltage and magnetic flux using closed-loop integral controllers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a separate sensor and communication module are used to measure the temperature of the permanent magnet, then the temperature measurement accuracy is improved, but the manufacturing cost increases
Solution Approach 1:
The patent creates a virtual temperature sensor by copying the measurement function from physical sensors. It uses electrical parameters (voltage, current, frequency) that are already measured by the motor control system to calculate and estimate the permanent magnet temperature, eliminating the need for separate temperature sensors while maintaining measurement capability through mathematical modeling and observation of electrical characteristic changes with temperature
Solution Approach 2:
The motor control system performs self-diagnosis and self-monitoring by using its own existing measurement infrastructure (voltage and current sensors) to derive temperature information. The system serves its own temperature measurement needs without requiring external dedicated temperature sensing equipment, thereby reducing overall system cost while maintaining measurement accuracy
2Ease of manufacture
If the first method (assuming stator coil temperature equals permanent magnet temperature) is used, then the manufacturing cost is reduced, but the torque control precision deteriorates
Solution Approach 1:
The patent replaces the simple thermal assumption model with an electrical-based estimation model. Instead of mechanically/thermally assuming temperatures are equal, it uses electrical parameter measurements (voltage, current, frequency) and mathematical relationships to estimate the permanent magnet temperature, providing more accurate results without significant additional cost
Solution Approach 2:
The patent changes the estimation approach from using thermal parameters (assuming thermal equilibrium) to using electrical parameters (voltage, current, frequency relationships). By measuring changes in electrical characteristics that correlate with temperature, the system achieves more precise temperature estimation and consequently better torque control precision
3Measurement precision
If the second method (generating three-dimensional magnetic flux map) is used, then the temperature estimation accuracy is improved, but the device complexity increases due to voltage changes requiring four-dimensional maps
Solution Approach 1:
The patent introduces dynamic adaptation to handle voltage variations. Instead of creating static four-dimensional magnetic flux maps, the system dynamically adjusts the three-dimensional map based on real-time voltage conditions. The estimation algorithm adapts to changing voltage levels, maintaining accuracy without requiring complex pre-computed multi-dimensional maps for every possible voltage scenario
Solution Approach 2:
The patent performs preliminary preparation by pre-computing only three-dimensional magnetic flux maps at representative voltage levels. The system then uses these pre-computed maps as a basis and applies real-time voltage compensation through the estimation algorithm, avoiding the need to pre-compute and store extensive four-dimensional maps for all possible voltage conditions
4Measurement precision
If the third method (using thermal resistance and cooling system characteristics) is used, then the temperature estimation is performed, but the development time increases due to the need to model copper and iron losses
Solution Approach 1:
The patent extracts the essential temperature-dependent electrical characteristics from the complex thermal model. Instead of implementing the full third method with detailed thermal resistance networks, copper loss modeling, and iron loss characterization, it extracts only the key electrical parameters (voltage, current, frequency relationships) that correlate with temperature, creating a simplified estimation approach that achieves comparable accuracy with much less development effort
Data Source
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AI summary
A system for estimating a temperature of a permanent magnet of a rotor of a motor including a first determination unit configured to determine whether a rotational speed of the rotor is greater than or equal to a reference speed, a second determination unit configured to determine whether a current flowing in a coil included in the motor is less than a reference current, and whether a magnitude of q-axis energy of the motor is less than a reference energy magnitude, when the rotational speed is greater than or equal to the reference speed, a magnetic flux map temperature estimation unit configured to estimate the temperature of the permanent magnet using a d-axis magnetic flux map of the motor responsive to conditions being satisfied, and an energy map temperature estimation unit configured to estimate the temperature responsive to conditions not being satisfied in the second determination unit.