Electric Motor Thermal Circuit Model for Temperature Estimation
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Solution Overview
Problem
Current methods for temperature and heat loss estimation in electric motors are inaccurate, as they often focus on single components and rely on empirical rules or neglect certain loss factors, leading to incorrect thermal management and potential motor failure.
Innovation Solution
A thermal circuit model is developed, calibrated offline using empirical studies, and augmented with heat losses as a state variable, allowing for real-time estimation of temperature and heat loss distribution using temperature sensors, enabling accurate thermal management and protection of electric motors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If empirical rules or experiments are used to calculate heat losses, then the calculation process is simplified, but the accuracy of temperature estimation deteriorates due to neglected loss factors
Solution Approach 1:
The patent transforms the thermal management approach by changing from empirical parameter estimation to physics-based parameter calculation. It introduces a comprehensive loss model that calculates heat losses (copper losses, iron losses, permanent magnet losses, windage losses) using fundamental physics equations rather than empirical rules, thereby improving temperature estimation accuracy while maintaining computational feasibility through structured parameter organization
Solution Approach 2:
The patent introduces a thermal circuit model as an intermediary between the motor's heat sources and the temperature estimation process. This thermal circuit model serves as a mediator that systematically accounts for all heat loss pathways and thermal resistance networks, enabling accurate temperature prediction without requiring direct measurement of all thermal parameters
2Device complexity
If heat losses are not identified, then the calculation process is simpler, but temperature cannot be calculated accurately
Solution Approach 1:
The patent segments the total heat loss into distinct components (copper losses in stator and rotor windings, iron losses in stator and rotor cores, permanent magnet losses, windage losses). Each segment is calculated using dedicated physics-based formulas, allowing systematic identification of all heat sources without overwhelming complexity. This segmentation enables reliable temperature calculation by accounting for each loss mechanism separately
Solution Approach 2:
The patent performs preliminary calculation of all heat loss components before conducting temperature estimation. By pre-calculating copper losses, iron losses, permanent magnet losses, and windage losses using motor operating parameters (current, voltage, speed), the system prepares complete heat source information in advance, ensuring reliable temperature calculation without requiring complex iterative procedures
3Measurement precision
If temperature sensors are positioned at all critical locations, then temperature measurement accuracy is improved, but the system complexity and cost increase
Solution Approach 1:
The patent creates a virtual thermal model (thermal circuit model) that copies and represents the physical thermal behavior of the motor. Instead of placing sensors at all critical locations, the system uses a limited number of temperature sensors combined with a physics-based thermal model to estimate temperatures throughout the motor. This virtual copying approach achieves comprehensive temperature monitoring with reduced sensor requirements
Solution Approach 2:
The thermal circuit model acts as an intermediary that bridges the gap between limited temperature sensor measurements and the thermal state of all motor components. The model uses measured temperatures along with calculated heat losses and thermal resistance networks to infer temperatures at locations where no sensors are installed, thereby achieving comprehensive temperature awareness without dense sensor deployment
4Measurement precision
If a comprehensive thermal model accounting for all heat sources is used, then temperature estimation accuracy is improved, but the computational complexity increases
Solution Approach 1:
The patent organizes the comprehensive thermal model using structured parameter representations. Heat losses are calculated using standardized physics formulas with clearly defined parameters (current, voltage, speed, frequency). The thermal circuit model uses systematic thermal resistance and capacitance parameters. This structured parameter organization enables the complex model to be implemented efficiently with manageable computational complexity
Solution Approach 2:
The patent segments the comprehensive thermal model into independent modular components: copper loss calculation module, iron loss calculation module, permanent magnet loss module, windage loss module, and thermal circuit analysis module. Each module handles a specific aspect of heat generation or heat transfer. This modular segmentation allows the complex overall model to be computed through a sequence of simpler, independent calculations, reducing overall computational complexity
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
The solution provides reliable and accurate real-time estimation of temperatures and heat losses, enhancing thermal management, preventing motor failures, and improving operational efficiency by accounting for all heat sources and losses.
Implementation Method 1
a thermal circuit model relating temperatures of a set of nodes of the thermal circuit model with temperature measurements at the first subset of the set of nodes and values of heat losses of heat sources at a second subset of the set of nodes
Implementation Method 2
each node in the thermal circuit model represents a spatial location of the electric motor... values of the temperatures at the set of nodes and values of the heat losses are interdependent on each other
Implementation Method 3
temperature sensors positioned at different locations of the electric motor to collect the measurements during an operation of the motor
Implementation Method 4
Different kinds of the heat sources result in heat losses, such as copper losses, iron losses, permanent magnet losses, windage losses
Implementation Method 5
the iron losses may be due to both eddy current loss and hysteresis loss
Implementation Method 6
the iron losses may be due to both eddy current loss and hysteresis loss
Data Source
AI summary
A system for thermal management of an electric motor, uses an augmented thermal circuit model of the electric motor, which relates temperatures of a set of nodes of the thermal circuit model with the temperature measurements at a first subset of nodes and heat losses of heat sources at a second subset of nodes, for joint estimation of the temperatures at the entire set of nodes and values of the heat losses in the second subset of nodes. The system solves the joint estimation using an estimator/observer. The system outputs one or combination of the values of the temperatures of the set of nodes and the values of the heat losses.