BLDC Motor Torque Ripple Reduction via Magnet Temperature Estimation
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Solution Overview
Problem
Brushless DC motors (BLDC) experience torque ripples due to temperature variations between the stator and rotor, affecting torque uniformity and driving comfort, especially in power steering systems, where existing control methods do not accurately account for the temperature-dependent properties of permanent magnets.
Innovation Solution
A control method that estimates the temperature of the permanent magnet using a PT1 element and load variables like speed and current, allowing for precise torque control without additional sensors, and includes a filter to determine the starting temperature of the permanent magnet for quick and accurate torque setting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the temperature of the permanent magnet is not taken into account in control, then the control system remains simple, but torque uniformity deteriorates due to temperature-dependent property changes
Solution Approach 1:
The patent uses the stator temperature as an intermediary variable to estimate the permanent magnet temperature. Instead of directly measuring or controlling the difficult-to-access magnet temperature, the system measures the easily accessible stator temperature and uses it as a mediator to infer and compensate for magnet temperature effects on torque characteristics.
Solution Approach 2:
The patent changes the control parameter by introducing temperature compensation factors based on the estimated permanent magnet temperature. The control signals are adjusted as a function of temperature, allowing the system to maintain optimal torque characteristics across varying thermal conditions without adding complex hardware.
2Measurement precision
If additional sensors are added to measure permanent magnet temperature, then torque control precision improves, but device complexity and cost increase
Solution Approach 1:
The system uses existing sensors (stator temperature sensors) to serve multiple purposes. The stator temperature measurement, originally intended for basic thermal management, is also used to estimate the permanent magnet temperature and compensate for its effects on torque, eliminating the need for separate magnet temperature sensors.
Solution Approach 2:
The patent replaces direct physical measurement (mechanical/thermal contact sensors on the magnet) with a computational estimation approach. By using thermal models and existing stator temperature data, the system substitutes complex sensor installation with software-based temperature inference.
3Ease of operation
If block commutation with fixed voltage is used, then control simplicity is maintained, but torque ripples increase affecting driving comfort
Solution Approach 1:
The patent introduces dynamic adjustment to the block commutation method by varying the voltage applied to the windings based on temperature conditions. Instead of fixed voltage commutation, the system dynamically modifies voltage levels to compensate for temperature-induced changes in permanent magnet properties, reducing torque ripples while maintaining the simplicity of block commutation timing.
Data Source
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AI summary
The invention relates to a brushless direct-current motor (1) comprising a permanent magnet (12a) arranged on a rotor (12) and a stator with windings. The temperature (T_W) of the windings is determined. An observer (28) is used to estimate the temperature (T_M) of the permanent magnet (12a) according to the temperature (T_W) of the windings. A regulating signal for controlling the direct-current motor (1) is determined according to the estimated temperature (T_M) of the permanent magnet (12a).