Sliding Rotor Coupling in Permanent Magnet Generators for Over-Voltage
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Solution Overview
Problem
Conventional permanent magnet generators (PMGs) face challenges in maintaining stable voltage output across varying rotational speeds and loads, often requiring a narrow operating point near current saturation to prevent over-voltage, which compromises efficiency and robustness.
Innovation Solution
A PMG system with a rotor assembly that passively attenuates voltage output by sliding between a maximum coupling and misaligned position in response to acceleration above an impulse threshold, using a biasing member like a coil spring and linear guides to maintain optimal coupling until high acceleration occurs, thereby preventing over-voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the generator is designed to operate at a narrow operating point near current saturation to guarantee over-voltage compliance, then over-voltage protection is improved, but efficiency deteriorates
Solution Approach 1:
The rotor assembly is designed to dynamically adjust its position along the shaft based on rotational speed. At normal operating speeds, the rotor maintains maximum magnetic coupling with the stator for optimal efficiency. When rotational speed exceeds a threshold, centrifugal force moves the rotor axially to reduce coupling, thereby passively limiting voltage output and preventing over-voltage conditions without sacrificing efficiency at the design operating point
Solution Approach 2:
The system changes the magnetic coupling parameter between rotor and stator based on operating conditions. By varying the air gap distance through axial rotor movement, the system adapts the magnetic flux linkage to match operating speed, allowing efficient operation at the design point while automatically preventing over-voltage at higher speeds
2Power
If the rotor is fixed in a maximum coupling position to maximize voltage output, then voltage capability is improved, but over-voltage risk increases
Solution Approach 1:
The rotor assembly automatically regulates its own coupling with the stator based on rotational speed without external control. Centrifugal force generated during rotation directly moves the rotor axially along the shaft, reducing magnetic coupling when voltage capability exceeds safe operating limits, thereby self-regulating to prevent over-voltage conditions
3Reliability
If a biasing member is added to enable passive voltage attenuation through rotor displacement, then over-voltage protection is improved, but device complexity increases
Solution Approach 1:
The system replaces complex electronic over-voltage protection systems with a simple mechanical solution. A biasing member (spring or elastomeric element) provides the necessary force to move the rotor axially in response to centrifugal force, creating a passive mechanical governor that limits voltage output without requiring sensors, controllers, or power electronics
Solution Approach 2:
The biasing member enables the rotor position parameter to change dynamically with rotational speed. The spring force balances centrifugal force at different speeds, automatically adjusting the air gap and magnetic coupling to maintain safe voltage levels while minimizing the structural modifications needed
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 allows for improved efficiency and robustness by enabling operation over a wider range, reducing the risk of over-voltage events, and potentially lowering system costs and complexity.
Implementation Method 1
a rotor assembly configured to be magnetically coupled to the stator and to rotate relative to the stator to induce the voltage
Implementation Method 2
The biasing member can be a coil spring disposed coaxially around the shaft
Data Source
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AI summary
A permanent magnet generator, PMG, system can include a stator (101) configured to output a voltage, and a rotor assembly (103) configured to be magnetically coupled to the stator (101) and to rotate relative to the stator to induce the voltage. The rotor assembly (103) can be configured to passively attenuate the voltage output from the stator (101) in response to acceleration of the rotor assembly at or above an impulse acceleration threshold.