Dual-Purpose Permanent Magnet Machine for Aircraft Starter-Generator
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Solution Overview
Problem
In starter/generator systems, especially in aircraft, there is a need for a solution that allows safe shutdown of the generator function without shutting down the prime mover engine, while also enabling initiation of generation with no external power source and providing both speed sensing and control power for induction machines.
Innovation Solution
A dual-purpose permanent magnet machine (PMM) is used, which acts as a shaft speed sensor and power converter, generating a rotating magnetic field and producing AC output voltage proportional to shaft speed, allowing for direct measurement of rotation speed and direction, and providing control power through a power converter system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a DC brushed machine is used to remove field excitation for safe shutdown, then the generator function can be safely shut off without shutting down the prime mover engine, but the system requires brushes and commutators which increase device complexity and maintenance requirements
Solution Approach 1:
The patent replaces the mechanical brush and commutator system with an electronic field control mechanism. Field excitation is removed by controlling the field winding current through electronic switches (transistors or thyristors) that can rapidly disconnect the DC field current, eliminating the need for physical brushes and commutators while maintaining the safe shutdown capability.
Solution Approach 2:
The patent changes the control parameter from mechanical contact (brushes) to electrical parameter control (field current magnitude and polarity). By varying the field current through electronic control, the system can achieve safe shutdown by reducing field current to zero or reversing polarity, replacing the need for mechanical brush-based commutation.
2Device complexity
If an induction machine is used for low cost and brushless operation, then device complexity is reduced, but external power source is required for speed sensing and control which reduces independence and increases system complexity
Solution Approach 1:
The patent combines the speed sensor and control power source functions into a single integrated system. The sensor generates both the speed reference signal and the control power needed by the induction machine, merging two previously separate functions into one self-contained unit that eliminates the need for external power sources.
Solution Approach 2:
The sensor system is designed to be self-powered, generating its own control power from the mechanical input shaft through electromagnetic induction. This self-service capability allows the induction machine to operate independently without external power sources, while maintaining brushless operation and low complexity.
3Ease of manufacture
If separate speed sensor and control power source are used, then each function can be optimized independently, but device complexity increases and space requirements increase
Solution Approach 1:
The patent merges the speed sensor and control power source into a single integrated electromagnetic device. Both functions share common components such as the magnetic circuit, windings, and mechanical shaft, reducing the total number of components while maintaining the ability to independently optimize each function through separate winding designs and control strategies.
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 enables safe shutdown of the generator function, independent operation of each generator, and efficient power utilization by providing both speed sensing and control power to induction machines, enhancing reliability and efficiency in aircraft starter/generator systems.
Implementation Method 1
a permanent magnet rotor that generates a rotating magnetic field and a stator assembly that produces an alternating current (AC) output voltage proportional in amplitude and frequency to the rate of change of the magnetic field generated by the rotor
Data Source
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AI summary
An apparatus is disclosed for simultaneously measuring the rotational speed and/or direction of a shaft, and providing control power in accordance with the shaft rotation. The apparatus includes a permanent magnet machine (PMM) having a multipole rotor and a stator. The rotor has a plurality of permanent magnet poles and connection to the rotating shaft; the stator includes a winding and electrical connections, so that motion of the rotor with respect to the stator causes a voltage signal at the electrical connections. The apparatus also includes a circuit including a power conversion portion and a speed/direction sensing portion. The circuit receives the voltage signal from the PMM, and simultaneously outputs control power from the power conversion portion and a signal indicating the rotational speed and/or direction of the shaft from the sensing portion. (Drawing Figure 2)