Aircraft Permanent Magnet Machine Demagnetization for Short-Circuit Protection
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Solution Overview
Problem
Aircraft electric machines with permanent magnet synchronous motors face risks of overheating and damage during short-circuit events due to rapid current intensity increases, which is a concern for reliability and mass efficiency in aeronautical applications.
Innovation Solution
Incorporating a demagnetization device that temporarily increases the temperature of permanent magnets to reduce their magnetic flux, using a duct system to circulate hot fluid in proximity to the magnets, and integrating a winding fault sensor to activate the demagnetization during fault events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If permanent magnet synchronous machines are used to reduce mass, then power density per unit mass is improved, but reliability deteriorates due to winding damage risks during short-circuit events
Solution Approach 1:
The patent applies preliminary anti-action by preemptively neutralizing the magnetic flux of permanent magnets when a short-circuit fault is detected. The control system activates demagnetization coils that generate a magnetic field opposing the permanent magnet's flux, preventing the harmful high current condition before it can damage the winding. This anticipatory protective measure resolves the contradiction by maintaining reliability without requiring additional mass in protective components.
Solution Approach 2:
The patent introduces demagnetization coils as an intermediary element between the permanent magnets and the winding fault. These coils act as a mediator that can rapidly cancel the magnetic flux when needed, providing a controlled way to protect the winding without permanently altering the machine's mass characteristics. The intermediary coils enable reliability protection while maintaining the high power density of the permanent magnet design.
2Reliability
If circuit is dimensioned to tolerate high current, then reliability is improved, but mass increases due to additional copper and insulation
Solution Approach 1:
The patent applies parameter changes by dynamically altering the magnetic flux parameter rather than changing the physical dimensions of the circuit. Instead of increasing copper mass or insulation thickness to tolerate high current, the system changes the magnetic field parameter by activating demagnetization coils. This parameter-based approach maintains reliability while avoiding the mass penalty of oversized components.
3Reliability
If mechanical decoupling device is added to stop rotor rotation, then reliability is improved, but mass increases significantly
Solution Approach 1:
The patent replaces the mechanical decoupling system with an electromagnetic field-based solution. Instead of using clutches or claw couplings that mechanically disconnect the rotor to stop rotation during faults, the system uses demagnetization coils to cancel the magnetic flux. This substitution eliminates the need for heavy mechanical protective devices while maintaining reliability through field control.
4Reliability
If thermal machine is stopped to protect winding, then reliability is improved, but operational versatility deteriorates as the thermal machine cannot continue driving the propeller
Solution Approach 1:
The patent applies local quality by targeting the specific problem area (magnetic flux from permanent magnets) rather than stopping the entire thermal machine. The demagnetization coils locally cancel the magnetic flux in the generator portion while the thermal machine continues operating to drive the propeller. This localized solution maintains both reliability and operational versatility simultaneously.
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 rapidly decreases the counter-electromotive force at the winding terminals, reducing the risk of overheating and damage while maintaining minimal mass impact on the aircraft, thus enhancing reliability and power density.
Implementation Method 1
a device for demagnetizing a permanent magnet suitable for implementing a temporary temperature increase of the permanent magnet, in order to limit, during the temporary temperature increase, an exciter magnetic flux generated by the permanent magnet
Implementation Method 2
using a duct system to circulate hot fluid in proximity to the magnets
Data Source
AI summary
The present invention relates to an electric machine for an aircraft, comprising a stator and a rotor that is rotationally mobile with respect to the stator, the rotor or the stator comprising a plurality of permanent magnets, the machine comprising a device for demagnetising a permanent magnet, suitable for achieving a temporary increase in the temperature of the permanent magnet, in order to limit, during the temporary increase in temperature, an exciting magnetic flux generated by the permanent magnet. The present invention furthermore relates to an assembly comprising an assembly comprising such an electric machine and a hot-fluid source suitable for delivering hot fluid to the demagnetising device of the electric machine. The hot-fluid source may be a gas stream of a turbine engine.