DFIG APU Generator Control for Constant Frequency at Variable Speed
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Solution Overview
Problem
Conventional auxiliary power unit (APU) generator systems for aircraft are limited to constant speed operation, which does not account for environmental conditions, leading to inefficiencies and inability to adjust speed without varying output frequency, making them less efficient and less adaptable to changing conditions.
Innovation Solution
A doubly-fed induction generator (DFIG) system with a generator control module that adjusts excitation frequency to maintain a substantially constant frequency output, and an APU control module that optimizes fuel efficiency by controlling APU speed based on environmental conditions, such as temperature and density altitude, through fuel flow management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional synchronous generator operates at constant speed, then output frequency remains constant, but fuel efficiency cannot be optimized for varying environmental conditions
Solution Approach 1:
The system transitions from constant speed operation to variable speed operation by using a doubly-fed induction generator (DFIG) that can operate at varying speeds while maintaining constant output frequency through dynamic excitation control. The APU speed is varied based on environmental conditions, and the excitation frequency is dynamically adjusted to compensate, resolving the contradiction between speed variability for efficiency and frequency constancy for reliability.
Solution Approach 2:
The system changes the excitation frequency parameter dynamically to maintain constant output frequency while the APU speed varies. By adjusting the excitation frequency in response to speed changes, the system achieves both fuel efficiency optimization through variable speed and reliable constant frequency output.
2Adaptability or versatility
If APU speed is varied to optimize fuel efficiency, then environmental adaptability improves, but output frequency varies
Solution Approach 1:
The system uses feedback control where the excitation frequency is continuously adjusted based on the APU speed and environmental conditions. The control system monitors the operating state and modifies the excitation frequency to maintain constant output frequency, enabling both environmental adaptability through speed variation and frequency stability through active feedback control.
Solution Approach 2:
The excitation frequency parameter is dynamically changed in response to APU speed variations and environmental conditions. This parameter adjustment allows the system to adapt to different environmental conditions while maintaining stable output frequency, resolving the contradiction between adaptability and reliability.
3Use of energy by moving object
If doubly-fed induction generator is used with variable speed operation, then fuel efficiency is optimized, but system complexity increases
Solution Approach 1:
The doubly-fed induction generator serves multiple functions: it enables variable speed operation for fuel efficiency optimization while simultaneously providing constant frequency output through its unique construction with windings on both stator and rotor. This multi-functionality reduces the need for separate speed control and frequency regulation systems, managing the complexity burden.
Solution Approach 2:
The system combines speed control and frequency regulation functions into a single integrated control approach. By merging the excitation control with the speed control, the system achieves both fuel efficiency and frequency stability without requiring entirely separate control systems, thereby managing overall system 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
The system achieves efficient and adaptable operation by maintaining a constant frequency output while optimizing fuel efficiency across varying environmental conditions, providing a more reliable and efficient alternative to traditional synchronous generators.
Implementation Method 1
a doubly-fed induction generator (DFIG) configured to be operatively connected to an APU to be turned by an APU and to have an output frequency that is a function of an excitation frequency and an APU speed
Data Source
Figure 1
AI summary
An auxiliary power unit (APU) generator system (100) for an APU can include a doubly-fed induction generator (DFIG) (103) configured to be operatively connected to an APU to be turned by an APU and to have an output frequency that is a function of an excitation frequency and an APU speed. The system can include a generator control module (105) configured to control the excitation frequency to the DFIG to output a substantially constant frequency with changing APU speed to supply the substantially constant frequency to a load.