Flux Switching Generator Rotor Position Sensing
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Solution Overview
Problem
Conventional wound field synchronous machines (WFSM) face challenges in accurately determining rotor position, especially at high speeds, due to the lack of saliency in surface-mounted permanent magnet rotors, leading to inefficient power conversion and increased component stress, and the high cost and fragility of three-phase PMGs.
Innovation Solution
A three-phase flux switching generator (FSG) is used, which isolates direct axis (D axis) inductance from quadrature axis (Q axis) inductance by directing magnetic fields primarily through the D axis, enabling precise rotor position sensing and reducing the need for costly containment bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If surface-mounted permanent magnet rotors are used in conventional WFSM, then the machine structure is simplified, but rotor position sensing accuracy deteriorates at high speeds due to lack of saliency
Solution Approach 1:
The patent segments the rotor structure by introducing discrete magnetic poles with different flux densities along the circumferential direction. This creates distinct D-axis and Q-axis inductances through the segmented magnetic pole design, enabling saliency-based position sensing while maintaining the surface-mounted permanent magnet structure.
Solution Approach 2:
The patent applies local quality by creating non-uniform magnetic properties in different regions of the rotor. The magnetic poles are designed with varying flux densities and distributions in different angular positions, which generates the required saliency effect for accurate rotor position detection without changing the overall rotor topology.
2Reliability
If three-phase PMG is used for rotor position sensing, then continuous three-phase power is provided, but cost and fragility increase due to containment band requirements
Solution Approach 1:
The patent extracts the position sensing function from the three-phase PMG structure and implements it directly in the main machine's rotor through saliency-based sensing. This eliminates the need for a separate three-phase PMG with containment bands, reducing manufacturing complexity and cost while maintaining continuous power provision capabilities.
Solution Approach 2:
The patent makes the main machine rotor serve multiple functions: it generates torque for motor operation and simultaneously provides position sensing information through its saliency characteristics. This multi-functionality eliminates the need for a dedicated sensing machine, reducing overall system complexity and manufacturing costs.
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
The three-phase FSG improves rotor position sensing accuracy, reduces component stress, and lowers costs by eliminating the need for expensive containment bands, while providing continuous three-phase power and better load regulation.
Implementation Method 1
the PMG generates AC power because the rotating magnets induce AC power in the stator
Implementation Method 2
the stator windings form magnetic north-south pole pairs
Implementation Method 3
A rotating rectifier is often included to convert the exciter AC output to DC
Implementation Method 4
as the rotor rotates, it generates an electromotive force (EMF) and produces power
Data Source
AI summary
A brushless, three phase wound field synchronous machine (WFSM) provides an electromechanical power transfer system wherein it may serve as both a starter and a generator. Power for the excitation system of the WFSM is provided by a three phase flux switching generator (FSG). The three phase FSG also provides position sensor functionality for the WFSM when the WFSM operates in the starter/motor mode.