Heating Ferrite Permanent Magnets in Electrical Machines
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Solution Overview
Problem
Ferrite permanent magnets in electrical machines are prone to demagnetization at low temperatures, which can lead to performance issues and reduced reliability, especially in applications where temperature fluctuations are common.
Innovation Solution
The implementation of a system that heats ferrite permanent magnets using a secondary current to induce eddy currents or by applying a magnetic field to magnetocaloric elements, preventing demagnetization and enhancing stability and corrosion resistance across a wide range of temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If ferrite permanent magnets are used in PM electrical machines, then cost savings are achieved compared to rare earth magnets, but the ferrite magnets become more susceptible to demagnetization at low temperatures
Solution Approach 1:
The system applies a secondary current to generate a magnetic field that heats the ferrite permanent magnets before they are exposed to low temperature operating conditions. This preliminary heating action raises the magnets' temperature above their Curie point threshold, establishing a thermal state that prevents demagnetization during subsequent low temperature operation, thereby resolving the reliability issue while maintaining cost benefits
Solution Approach 2:
The invention changes the thermal parameter (temperature) of the ferrite permanent magnets by inducing eddy currents through a secondary magnetic field. By dynamically adjusting the temperature parameter above the critical threshold, the system transforms the magnets from a vulnerable state (prone to demagnetization at low temperatures) to a protected state (resistant to demagnetization), thus resolving the contradiction between cost-effectiveness and reliability
2Reliability
If a secondary current is applied to generate a magnetic field for heating ferrite permanent magnets, then demagnetization at low temperatures is prevented, but energy consumption increases
Solution Approach 1:
The system applies the secondary current in a periodic or pulsed manner rather than continuously, activating the heating function only when low temperature conditions are detected and deactivating it when temperatures are sufficient. This periodic application of energy achieves the necessary thermal protection while minimizing overall energy consumption, resolving the contradiction between reliability and energy efficiency
Solution Approach 2:
The invention incorporates a temperature sensing and control system that monitors the thermal state of the ferrite permanent magnets and adjusts the secondary current application accordingly. When the temperature drops below a threshold, the system activates the heating function; when the temperature is sufficient, it deactivates the function. This feedback-controlled approach ensures demagnetization prevention while optimizing energy consumption by applying power only when necessary
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 solution effectively prevents demagnetization of ferrite permanent magnets at low temperatures, ensuring the reliability and performance of electrical machines by maintaining magnetic field integrity and improving resistance to corrosion, thus making ferrite magnet PM machines a viable alternative to rare earth magnet PM machines.
Implementation Method 1
selectively cause a secondary current to be applied to the stator windings to selectively generate a secondary magnetic field, the secondary magnetic field inducing eddy currents in at least one of the stator assembly and the rotor assembly to heat the plurality of ferrite permanent magnets
Implementation Method 2
the secondary magnetic field inducing eddy currents in at least one of the stator assembly and the rotor assembly to heat the plurality of ferrite permanent magnets
Implementation Method 3
heating the plurality of ferrite permanent magnets by applying a magnetic field to a plurality of magnetocaloric elements positioned adjacent the plurality of ferrite permanent magnets, wherein the plurality of magnetocaloric elements heat up when subjected to the magnetic field
Data Source
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AI summary
A system and method for heating ferrite permanent magnets in an electrical machine is disclosed. The permanent magnet machine (10) includes a stator assembly (12) and a rotor assembly (14), with a plurality of ferrite permanent magnets (32) disposed within the stator assembly or the rotor assembly to generate a magnetic field that interacts with a stator magnetic field to produce a torque. A controller (22) of the electrical machine is programmed to cause a primary field current to be applied to the stator windings to generate the stator magnetic field, so as to cause the rotor assembly to rotate relative to the stator assembly. The controller (22) is further programmed to cause a secondary current to be applied to the stator windings to selectively generate a secondary magnetic field, the secondary magnetic field inducing eddy currents in at least one of the stator assembly and the rotor assembly to heat the ferrite permanent magnets.