Permanent Magnet Machine Neutral Return Switching for Fault Isolation
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Solution Overview
Problem
Permanent magnet (PM) machines face challenges in fault protection due to continuous electrical energization during rotation, making it difficult to safely isolate electrical faults, especially with the increasing use in high voltage direct current systems where high energy short circuits and arcing faults are more prevalent, and existing solutions are not resettable or efficient.
Innovation Solution
A system incorporating a return switch unit with a feedback system that disconnects the return legs of phase windings from a neutral node upon fault detection, allowing the permanent magnet to continue rotating while isolating faults, and can be externally located or integrated into the PM machine, using a triple pole single throw switch for multi-phase configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an electrically actuated mechanical disconnect is used to remove the PM machine from its input shaft when a fault is present, then the machine is isolated from the fault, but the disconnect is not resettable during aircraft operation and takes time for the machine to stop rotating while still energized
Solution Approach 1:
The invention segments the fault isolation function into two independent parts: (1) a return switch that disconnects only the return legs of phase windings from the neutral node, and (2) the main phase legs that remain connected to the controller. This segmentation allows the machine to remain operational while isolating the fault, and enables rapid reset by simply closing the return switch without mechanical disconnection of the entire machine.
Solution Approach 2:
The invention extracts the fault isolation function from the main power connection by creating a separate return path switch. Instead of disconnecting the entire machine, only the return leg connections are switched off, separating the fault isolation function from the main operational connection and enabling independent control of fault protection.
2Object-affected harmful factors
If the machine is disconnected from the input shaft to protect against faults, then high energy short circuits and arcing faults are prevented, but the machine cannot continue rotating and operation is interrupted
Solution Approach 1:
The invention segments the electrical connections into main phase legs (connected to controller) and return legs (controllable via return switch). This segmentation allows the return legs to be disconnected for fault protection while the main phase legs remain connected, enabling the machine to continue rotating and operating without full disconnection.
Solution Approach 2:
The return switch provides dynamic control over the return leg connections, allowing the system to transition between normal operation (switch closed) and fault protection mode (switch open) without mechanical disconnection. This dynamic switching enables continuous rotation and operation while providing fault protection when needed.
3Reliability
If conventional fault protection methods are used in PM machines, then some level of protection is achieved, but the methods are not resettable during aircraft operation and require the machine to stop rotating
Solution Approach 1:
The invention segments the fault protection function into a separate return switch mechanism that operates independently from the main machine operation. This segmentation enables rapid reset by simply closing the return switch without requiring the machine to stop rotating or complex reset procedures, significantly reducing loss of time.
Solution Approach 2:
The invention replaces the mechanical disconnect system (which requires physical disconnection and time to stop rotation) with an electrical switching system (return switch) that can be operated rapidly without mechanical intervention. This substitution eliminates the need for the machine to stop rotating during reset, reducing operational interruption time.
Data Source
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AI summary
A system includes a permanent magnet (PM) machine (102) including a first phase winding (104) and a second phase winding (106) and a permanent magnet configured to rotate relative to the first and second phase windings. The first phase winding (104) has a main leg (106a) and a return leg (104b) extending from the first phase winding (104). The second phase winding (106) has a main leg (106a) and a return leg (104b) extending from the second phase winding (106). A return switch unit is operatively connected to the return legs (104b) of the first phase winding (104) and the second phase winding (106). The return switch unit includes a switch configured to connect the return legs (104b) of the first phase and second phase to a neutral node in the return switch unit in a normal state, and to disconnect the return legs (104b) of the first and second phase windings from the neutral node in a fault protection state.