Aircraft Starter Generator Exciter Control
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Solution Overview
Problem
Existing aircraft starter/generator systems are heavy, expensive, and inefficient due to poor exciter stator utilization, requiring large conversion circuitry and high exciter currents, which leads to increased size and complexity, and are prone to corona effects due to high AC voltage requirements.
Innovation Solution
A bidirectional energy conversion system using a three-machine set comprising a main salient synchronous machine, an exciter, and a permanent magnet generator, with an inverter/converter/controller that optimizes excitation by minimizing power transfer from the exciter stator and using a rotating rectifier to generate AC power at reduced frequencies, reducing the physical size of the exciter bridge and minimizing exciter current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If AC excitation is used for both start mode and generate mode with high exciter current, then excitation power is sufficient, but converter size and weight increase
Solution Approach 1:
The patent applies dynamics by making the excitation system adaptive to different operating modes. The exciter operates at high frequency during start mode and low frequency during generate mode, with the controller dynamically adjusting operating parameters. This dynamic operation allows sufficient excitation power during starting while reducing converter size during generation, resolving the contradiction between power sufficiency and weight reduction.
2Power
If high AC voltage is supplied to exciter winding, then excitation power is sufficient at zero or low speeds, but corona effects increase
Solution Approach 1:
The patent changes the frequency parameter of the exciter operation. By operating the exciter at high frequency during start mode, the system achieves sufficient excitation power without requiring excessively high voltages that would cause corona effects. The frequency adjustment allows the system to maintain adequate power transfer while keeping voltage levels within safe operating limits that avoid harmful corona discharge.
3Adaptability or versatility
If winding-selective circuitry is used to switch between AC and DC windings, then mode operation is enabled, but system weight and cost increase
Solution Approach 1:
The patent applies universality by designing the exciter stator to serve multiple functions across different operating modes. The same exciter stator winding provides excitation during both start mode (at high frequency) and generate mode (at low frequency), eliminating the need for separate AC and DC windings and their associated switching circuitry. This multi-functional approach maintains adaptability while significantly reducing weight and complexity.
4Power
If exciter stator is designed for high current operation, then generate mode power is sufficient, but starting mode efficiency decreases
Solution Approach 1:
The patent uses dynamic frequency adjustment to optimize performance across modes. During start mode, the exciter operates at high frequency with reduced current requirements, improving starting efficiency. During generate mode, the exciter operates at low frequency with higher current capability, ensuring sufficient power output. This dynamic adaptation resolves the contradiction between generate mode power sufficiency and starting mode efficiency.
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 weight reduction, fuel savings, and electrical power system optimization by minimizing exciter current and size, eliminating the need for additional circuitry and reducing complexity, while maintaining efficient power generation and starting capabilities.
Implementation Method 1
a permanent magnet generator (PMG) 110... The PMG 110 is a brushless, self-excited machine that converts a portion of the mechanical power... to an electrical output that is supplied to the exciter stator winding 210
Implementation Method 2
an exciter 108... The exciter 108 uses the AC power to provide excitation to the main rotor 114
Implementation Method 3
The output of the armature is connected to a rotating rectifier that is located on the same shaft, and that outputs a desired DC voltage to power the excitation winding of a main machine
Data Source
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AI summary
A starting and generating system for use with an aircraft engine includes a starter / generator and an inverter / converter / controller (ICC) coupled to the starter / generator. The starter / generator is configured to start the aircraft engine in a start mode and Io generate AC power in a generate mode. The starter / generator includes an exciter and a rotational shaft. The ICC is configured to provide AC power at a first frequency the starter / generator in the start mode and to control the exciter during the generate mode such that the generate mode AC power has a second frequency, wherein the first frequency is based on a shaft speed of the shaft.