Pole Shifting Generator for Variable Speed Aircraft Power
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Solution Overview
Problem
Gas turbine engine-based aircraft generators face challenges in producing electric current within the 360-800 Hz frequency range due to varying rotational speeds of the low-pressure spool, which can damage aircraft circuitry or require heavier, bulkier circuitry to accommodate wider frequency ranges.
Innovation Solution
An electric generator with a plurality of windings is designed to operate across a wide range of speeds, using a first exciter field at lower speeds and a second exciter field at higher speeds to reverse current flow and polarity, effectively reducing the number of poles and maintaining frequency within the desired range by forming pseudo poles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the LP spool operates at higher rotational speeds to meet increasing electric power demand, then power output is improved, but the frequency of the electric current produced exceeds the acceptable 360-800 Hz range
Solution Approach 1:
The generator dynamically changes its pole configuration based on operating speed. At lower speeds, it operates with a first number of poles to produce current in the 360-800 Hz range. At higher speeds, it switches to a second number of poles (different from the first) to maintain the acceptable frequency range despite the increased rotational speed, thus adapting to different operating conditions
Solution Approach 2:
The generator changes the parameter of pole number to control output frequency. By having the rotor operate with different numbers of poles at different speed ranges, the system maintains the relationship between rotational speed and electrical frequency within acceptable limits, allowing the LP spool to operate at higher speeds without producing excessive frequency
2Adaptability or versatility
If aircraft circuitry is designed to accommodate a wider frequency range to handle variable LP spool speeds, then adaptability is improved, but weight and volume of the circuitry increase unacceptably
Solution Approach 1:
The generator proactively adjusts its pole configuration before the frequency problem occurs. By switching to an appropriate number of poles based on the LP spool speed range, the system prevents the generation of out-of-range frequencies in the first place, eliminating the need for heavy protective or adaptive circuitry
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 solution allows the generator to produce electricity within the desired frequency range across a broader range of rotational speeds, preventing circuitry damage and reducing the need for heavier, bulkier aircraft circuitry.
Implementation Method 1
The generator, comprising a plurality of windings, is excited by a first exciter field. During a first, lower speed range each pole of the generator has two adjacent poles with opposing polarity. During a second, higher speed range, a second exciter field is activated to alter the generator circuit
Data Source
AI summary
An apparatus and method generate electric current within a specified frequency range from a rotor operating within a broad range of rotational speeds by reducing the number of poles of the generator at higher rotational speeds. At higher rotational speeds, the generator circuit is altered so that a flow of current through half of a plurality of windings is reversed and the polarity in the said half of the windings is reversed. Two adjacent windings with the same polarity create a single pseudo pole, which effectively reduces the number of poles in the generator by half, and reduces the frequency of the electric current produced by the generator. Thus, the generator is operable to produce current within a specified frequency range from a rotor operating within a broad range of rotational speeds.