Rotor Temperature Measurement via Permanent Magnet Field
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Solution Overview
Problem
Existing methods for measuring the temperature of a rotor in electrical machines are challenging due to the rotor's difficult access and high cost, reliability issues with traditional signal transfer methods, and the inability to accurately measure winding currents, leading to potential damage from excessive temperatures.
Innovation Solution
The method involves using a magnetic field sensor to determine the temperature-dependent magnetic field strength or flux density of a permanent magnet on the rotor, eliminating the need for temperature sensors on the rotor and leveraging existing sensors for angular position detection, with calibration to ensure accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If temperature sensors are installed directly in the rotor, then temperature measurement accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent uses a permanent magnet as an intermediary object on the rotor that indirectly indicates temperature through its temperature-dependent magnetic field strength. Instead of placing sensors directly on the rotor, the system measures the magnetic field of the permanent magnet from the stator side, using the magnet's property changes as a mediator to convey temperature information across the air gap.
Solution Approach 2:
The patent replaces the mechanical/physical approach of installing temperature sensors on the rotor with a field-based measurement approach. By measuring the magnetic field strength of the permanent magnet from the stator side, the system eliminates the need for mechanical sensor installation on the rotating rotor, substituting a non-contact field measurement method.
2Loss of information
If inductive transfer units or slip ring-assisted systems are used, then signal transfer is achieved, but cost and operating reliability worsen
Solution Approach 1:
The patent extracts the temperature measurement function from the rotor itself and places it on the stator side by measuring the magnetic field of the permanent magnet. This removes the need for signal transfer mechanisms between rotor and stator, as the measurement is performed on the stationary stator side while the permanent magnet on the rotor naturally modulates the field according to temperature.
Solution Approach 2:
The permanent magnet on the rotor serves its dual purpose: it provides the magnetic field necessary for motor operation and simultaneously serves as the temperature indicator. The magnet's inherent temperature-dependent magnetic properties allow it to self-report temperature information without requiring additional sensors or signal transfer systems.
3Measurement precision
If winding temperature is ascertained from resistance measurement, then temperature can be calculated, but measurement complexity increases due to current measurement requirements
Solution Approach 1:
The patent makes the permanent magnet serve multiple functions: it provides the magnetic field for motor operation and simultaneously acts as the temperature sensor. This multi-functional use eliminates the need for separate temperature sensing arrangements and avoids the complexity of current measurement and resistance-based temperature calculation.
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
This approach allows for accurate rotor temperature measurement without additional hardware, improving power output and reliability while reducing costs and susceptibility to environmental failures, and can be integrated into existing control units for thermal modeling.
Implementation Method 1
The temperature dependence of a magnetic property of the permanent magnet is used and, in particular, the temperature-dependent value (field strength value or flux density value) of the magnetic field generated by the permanent magnet is determined. This is because it is known that the remanence of a permanent magnet, and thus the field strength or flux density of the magnetic field generated by it, decrease with increasing temperature.
Data Source
AI summary
A method for measuring the temperature of a permanent magnet disposed on a rotor of an electrical machine, a magnetic property of the permanent magnet dependent on the temperature of the permanent magnet being sensed and the temperature of the permanent magnet being ascertained therefrom, and to an electrical machine, a processing unit, and a computer program for carrying it out.