Stator Winding Temperature Estimation for Permanent Magnet Motors
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Solution Overview
Problem
Existing electric motor systems face challenges in accurately estimating stator winding temperatures, particularly at zero speed or with unbalanced currents, leading to potential overheating damage due to reliance on a single temperature measurement sensor.
Innovation Solution
A temperature estimation controller is introduced, comprising a low speed temperature estimation module, a transition module, and a temperature dependent torque command derater block, which determines stator temperatures for each phase using thermal impedances and derates torque commands to prevent overheating, ensuring accurate temperature sensing across all speeds, including near zero speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single temperature measurement sensor is installed on one phase of the stator winding, then the device complexity is reduced and manufacturing cost is lowered, but the measurement precision deteriorates at zero speed or with unbalanced currents
Solution Approach 1:
The patent introduces an intermediary estimation system that uses measurable electrical parameters (currents, voltages, frequencies) as mediators to infer temperature. Instead of directly measuring temperature in all phases with sensors, the system uses thermal impedance models and electrical measurements to estimate temperatures, particularly at zero speed where direct sensing fails.
Solution Approach 2:
The patent replaces the mechanical/physical temperature sensing system with an electrical estimation system. Rather than using physical thermal contact sensors in all phases, the system substitutes thermal-physical measurement with electrical measurement and mathematical modeling, using thermal impedance networks and electrical parameter analysis to determine temperature.
2Ease of manufacture
If a single temperature measurement sensor is used, then the manufacturing cost is reduced, but the reliability deteriorates because the motor cannot be protected from overheating at zero speed
Solution Approach 1:
The patent implements preliminary protective action by continuously estimating temperature and proactively derating torque commands before overheating damage occurs. The system monitors thermal conditions in advance and reduces torque commands when temperature thresholds are approached, preventing overheating damage before it happens rather than reacting after damage occurs.
Solution Approach 2:
The patent establishes a feedback loop where temperature estimation results continuously influence torque command adjustments. The estimated temperature from the thermal impedance model feeds back to the control system, which automatically derates torque commands when temperature thresholds are approached, creating a closed-loop protection mechanism that enhances reliability.
3Measurement precision
If multiple temperature sensors are installed on each phase, then the measurement precision improves, but the device complexity and manufacturing cost increase
Solution Approach 1:
The patent segments the temperature measurement function into two parts: direct measurement in one phase using a single sensor, and indirect estimation for other phases using thermal impedance modeling. This segmentation allows the system to achieve comprehensive temperature monitoring without installing sensors in all phases, reducing complexity while maintaining precision through mathematical estimation for the segmented portions.
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 effectively prevents overheating damage by accurately estimating stator winding temperatures and derating torque commands, ensuring motor protection at all speeds without the need for multiple temperature sensors, thereby enhancing motor reliability and safety.
Implementation Method 1
determining a stator temperature of each of the plurality of phases in response to first thermal impedances measured for each of the plurality of phases with respect to a thermal neutral
Implementation Method 2
determining copper losses in each of the plurality of phases, wherein the copper losses are determined in response to the AC RMS current values and the stator phase resistances
Data Source
AI summary
A temperature estimation controller and methods are provided for controlling a torque command to prevent overheating of one or more of a plurality of phases of a permanent magnet motor. The temperature estimation controller includes a low speed temperature estimation module, a transition module and a temperature dependent torque command derater block. The low speed temperature estimation module determines a stator temperature of each of a plurality of phases of the permanent magnet motor in response to first thermal impedances measured for each of the plurality of phases with respect to a thermal neutral. The transition module is coupled to the low speed temperature estimation module and outputs the stator temperature of each of a plurality of phases of the permanent magnet motor as determined by the low speed temperature estimation module when a detected speed of the permanent magnet motor is less than a first predetermined speed. The temperature dependent torque command derater block is coupled to the transition module and derates the torque command in response to the stator temperature of one or more of the plurality of phases.