Rotor Permanent Magnet Temperature Estimation Under Variable Motor Load
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Solution Overview
Problem
Current methods for estimating the temperature of a permanent magnet in a motor are either inaccurate due to low torque control precision, require excessive CPU memory and time, or are influenced by changes in battery voltage and cooling system performance, leading to increased development time and costs.
Innovation Solution
A system that determines the temperature of a permanent magnet in a motor using a magnetic flux map or energy map, based on rotational speed, current, and energy conditions, employing first-order and second-order equations to estimate temperature, with compensation for nonlinearity and error correction.
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 system uses the motor's own existing sensors and control unit to estimate the permanent magnet temperature through mathematical models and calculations, rather than requiring separate dedicated temperature sensors. The control unit leverages readily available data from current sensors and voltage detectors to compute temperature estimates using magnetic flux maps and thermal resistance models, making the system self-sufficient and avoiding additional hardware costs
Solution Approach 2:
The patent replaces physical temperature sensors with a computational estimation system that uses electrical measurements (current, voltage, frequency) and mathematical models to infer temperature. This substitution of mechanical/physical measurement devices with computational methods eliminates the need for separate temperature sensing hardware while maintaining acceptable 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 introduces thermal resistance values as intermediary parameters that model the heat transfer relationship between the stator coil and permanent magnet. By using thermal resistance models and heat flow calculations, the system bridges the gap between easily measurable stator temperature and the harder-to-measure permanent magnet temperature, enabling accurate temperature estimation without direct sensing of the magnet itself
Solution Approach 2:
The system dynamically adjusts temperature estimation by changing the parameters used in different operating conditions. It switches between using stator temperature directly, thermal resistance-based calculations, and magnetic flux map-based estimates depending on motor speed, load, and temperature conditions, thereby maintaining torque control precision across various operating scenarios without increasing hardware complexity
3Measurement precision
If the second method (generating three-dimensional magnetic flux map) is used, then the temperature estimation accuracy is improved, but the CPU memory occupation and development time increase
Solution Approach 1:
The patent segments the temperature estimation process into multiple discrete methods that can be selected based on operating conditions. Instead of using a single comprehensive three-dimensional magnetic flux map for all conditions, the system divides the estimation approach into: direct temperature assumption for low-speed conditions, thermal resistance-based estimation for medium-speed conditions, and magnetic flux map-based estimation for high-speed conditions. This segmentation reduces the need for large memory structures while maintaining accuracy where needed
Solution Approach 2:
The system dynamically selects which temperature estimation method to use based on real-time operating parameters such as motor speed, load torque, and temperature differences. The control unit switches between different estimation algorithms (stator temperature assumption, thermal resistance calculation, magnetic flux map interpolation) depending on which method is most appropriate for the current operating state, thereby optimizing both accuracy and computational resource usage
4Measurement precision
If the third method (using thermal resistance and cooling system characteristics) is used, then the temperature estimation accuracy is improved, but the development time increases
Solution Approach 1:
The patent performs preliminary characterization of the motor's thermal properties during the design phase, establishing thermal resistance values and heat flow paths between the stator, rotor, and permanent magnet. These pre-determined thermal parameters are stored in the control unit and used during operation without requiring real-time complex modeling. The cooling system characteristics are also pre-modeled, allowing the system to quickly estimate temperatures using stored thermal maps rather than performing extensive development-time modeling during actual temperature estimation
Data Source
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.