PM Machine Return Switch Fault Isolation During Rotation
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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 a concern.
Innovation Solution
A system with a return switch unit connected to the phase windings of PM machines that can disconnect the return legs from a neutral node upon fault detection, allowing the permanent magnet to continue rotating while isolating faults, using a feedback system with sensors and logic to trigger the switch into a fault protection state.
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 fault isolation is achieved, but the machine cannot be reset during aircraft operation and it takes time for the machine to stop rotating while still energized
Solution Approach 1:
The patent divides the fault protection 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 power source. This segmentation allows the machine to remain operational while isolating the fault, enabling resettable protection without requiring the machine to stop rotating.
Solution Approach 2:
The invention extracts the fault isolation function from the main power connection by creating a separate disconnect path through the return switch. Instead of disconnecting the entire machine from the input shaft, only the return path is disconnected, allowing the machine to continue operating while protecting against faults. This enables fast resettable protection during aircraft operation.
2Reliability
If conventional fault protection methods are used in PM machines, then fault isolation is achieved, but the machine must be completely disconnected and cannot be reset during operation
Solution Approach 1:
The patent segments the electrical connection into main phase legs and return legs, with the return switch controlling only the return legs. This allows independent control of the return path, enabling the machine to remain connected to the power source while isolating faults through the return switch, thus providing resettable protection during operation.
Solution Approach 2:
The return switch provides dynamic fault protection by allowing the system to transition between normal operation and fault isolation states without requiring complete disconnection. The switch can be rapidly activated and reset, providing adaptive protection that maintains operational flexibility during aircraft missions.
3Object-affected harmful factors
If the machine is completely disconnected to protect against faults, then high energy short circuits and arcing faults are prevented, but the machine cannot continue operating and must be replaced or repaired
Solution Approach 1:
The patent segments the fault protection function to affect only the return legs through the return switch, while leaving the main phase legs connected to the power source. This selective segmentation prevents high energy short circuits and arcing faults in the return path while maintaining continuous operation capability through the main phase connections.
Solution Approach 2:
The return switch acts as an intermediary component that mediates between fault protection requirements and continuous operation needs. By inserting this switch in the return path, the system can isolate faults without completely disconnecting the machine, allowing protected operation to continue during aircraft missions.
Data Source
AI summary
A system includes a permanent magnet (PM) machine including a first phase winding and a second phase winding and a permanent magnet configured to rotate relative to the first and second phase windings. The first phase winding has a main leg and a return leg extending from the first phase winding. The second phase winding has a main leg and a return leg extending from the second phase winding. A return switch unit is operatively connected to the return legs of the first phase winding and the second phase winding. The return switch unit includes a switch configured to connect the return legs 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 of the first and second phase windings from the neutral node in a fault protection state.