Variable Speed Generator Pole Configuration Switching
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Solution Overview
Problem
Conventional variable frequency starter generators in aircraft are restricted by the direct mechanical coupling between the engine shaft and generator, limiting the frequency range of electrical output and imposing minimum thrust conditions during idling, which is undesirable for fuel efficiency.
Innovation Solution
A variable speed generator that independently varies the frequency of its output AC current by switching between pole configurations, eliminating the need for brushes and slip rings, and allowing a wider rotational speed range without mechanical speed restrictions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If direct mechanical coupling between engine shaft and generator is used, then generator frequency is directly proportional to engine speed, but frequency range is limited and minimum thrust conditions are imposed during idling
Solution Approach 1:
The patent applies dynamics by making the number of magnetic poles variable rather than fixed. The generator can dynamically change its pole configuration to match different engine speeds, allowing the frequency output to be controlled independently of the mechanical coupling. This enables the generator to adapt to a wider range of operating conditions without being constrained by direct mechanical coupling limitations.
Solution Approach 2:
The patent changes the parameter of magnetic pole number from a fixed value to a variable parameter. By allowing the number of poles to be adjusted, the generator can maintain the relationship frequency = (poles × speed) / 120 even when speed varies, thereby extending the usable frequency range and eliminating minimum thrust requirements during idling operations.
2Loss of energy
If generator frequency range is extended, then fuel efficiency during idling improves, but mechanical coupling and speed range restrictions must be overcome
Solution Approach 1:
The dynamic adjustment of pole number allows the generator to operate efficiently across a broader speed range. During idling, the generator can use a higher pole configuration to maintain appropriate frequency output at lower engine speeds, enabling the engine to operate at minimal thrust for improved fuel efficiency without compromising electrical power quality.
Solution Approach 2:
By changing the magnetic pole parameter, the generator decouples the strict proportionality between engine speed and electrical frequency. This allows the engine speed to be optimized for fuel efficiency during idling while the generator maintains the required frequency output through pole configuration adjustment.
3Ease of operation
If pole number is varied to change frequency, then frequency can be controlled independently of speed, but generator structure must accommodate multiple pole configurations
Solution Approach 1:
The generator structure is segmented into modular components that can be independently configured. The magnetic poles are divided into separate groups that can be selectively activated or deactivated, allowing flexible pole number adjustment without requiring a complete redesign of the generator structure. This segmentation enables ease of frequency control while managing structural complexity.
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
Enables independent control of electrical frequency from engine speed, reducing thrust during idling and improving fuel efficiency by allowing the engine to produce minimal thrust while maintaining the generator within the required frequency range.
Implementation Method 1
The PMA 30 has permanent magnets mounted on its rotor 34. As the rotor spins, an AC main exciter voltage is induced across the stationary armature winding 35 of the PMA.
Implementation Method 2
This winding is connected to a voltage regulator circuit 36 which rectifies a controlled amount of AC current from the PMA stator winding and injects DC current
Implementation Method 3
The DC current injected into the field winding of the main generator comes from a rotating diode rectifier which is powered from the main exciter, which in turn is powered from the PMA.
Implementation Method 4
A rotating diode rectifier circuit 39, producing a DC current, is connected to the armature winding of the exciter.
Implementation Method 5
The output of this rotating rectifier is then connected to the rotating field winding 40 of the main generator 32, inducing a controlled, AC voltage across the generator's stationary armature winding 41.
Data Source
Figure 1~2
Figure 3~4A
Figure 4B~4C
AI summary
A variable speed generator for producing AC electrical power includes an alternator powerable by rotational action to generate a first AC current, and a first rectifier which rectifies the first AC current from the alternator. The generator further includes a main exciter having a first field winding which receives the rectified first AC current, and having a first armature which produces in response a second AC current. The generator further includes a second rectifier which rectifies the second AC current from the first armature. The generator further includes a main generator having a second field winding which receives the rectified second AC current, and having a second armature which produces in response an output AC current. The second field winding is configured to provide a plurality of selectively activatable pole configurations which differ in the number of their poles, such that the frequency of the output AC current can be varied by switching between the pole configurations. The variable speed generator further includes a control arrangement for activating the selected pole configuration.