Variable Frequency Bus for Aircraft Generator Parallel Operation
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Solution Overview
Problem
Aircraft electrical distribution systems require multiple generators due to frequency mismatches, leading to redundant power paths and increased weight from conductors, as generators produce AC output at different frequencies, making it impractical to run them in parallel.
Innovation Solution
Implementing a Doubly-Fed Induction Generator (DFIG) configuration with variable bus frequency that 'drifts' with engine speed, allowing small frequency adjustments and reducing the need for large converters, enabling generators to run in parallel while minimizing converter size and weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple generators are used to provide security of supply, then system reliability is improved, but the weight of conductors increases due to redundant power paths
Solution Approach 1:
The patent merges multiple generator outputs onto a single common bus by enabling parallel operation through frequency synchronization. This eliminates the need for multiple separate power paths and redundant conductors, while maintaining system reliability through coordinated generator operation.
Solution Approach 2:
The patent changes the frequency parameter of generators to enable synchronization. By adjusting generator frequencies to match and maintaining them in sync, the system allows multiple generators to share a common bus, reducing conductor weight while preserving reliability.
2Adaptability or versatility
If generators run at different frequencies to handle speed mismatches, then adaptability to engine speed variations is improved, but the complexity of the distribution system increases due to multiple buses and switches
Solution Approach 1:
The patent dynamically changes the frequency parameter of generators based on engine speed variations. By allowing frequency to vary with engine speed while maintaining synchronization between generators, the system adapts to speed mismatches without requiring complex switching arrangements.
Solution Approach 2:
The patent creates a universal common bus that can accommodate multiple generators operating at varying speeds. This single multi-functional bus replaces the need for multiple dedicated buses and complex switching networks, simplifying the overall distribution system.
3Adaptability or versatility
If converters are used to match frequency to bus frequency, then the ability to parallel generators is improved, but the size and weight of converters increases
Solution Approach 1:
The patent minimizes converter size by using them only for small frequency adjustments rather than large conversions. Generators operate near the bus frequency with minimal deviation, requiring only small-frequency-range converters that are significantly lighter and smaller.
Solution Approach 2:
The patent applies partial frequency conversion by allowing generators to operate within a narrow frequency range close to the bus frequency. This partial adjustment approach requires much smaller converters compared to full frequency conversion, reducing weight while still enabling parallel operation.
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
This approach reduces the total mass of conductors, enhances system robustness, improves reliability, and decreases losses by allowing power sharing between generators, while also enabling efficient operation even if one generator's performance is impaired.
Implementation Method 1
Implementing a Doubly-Fed Induction Generator (DFIG) configuration with variable bus frequency that 'drifts' with engine speed
Data Source
AI summary
An electrical generating system for aircraft with one or more engines includes a plurality of generators associated with the engines so as to produce respective AC outputs. The frequencies of these outputs can differ from each other, as a result of differing engine speeds and/or deliberate design, but they are to be connected to a common bus to avoid redundancy of wiring. One or more converters are present between the generators and the bus for adjusting the output frequency of the generators to provide an AC output voltage at a common bus frequency. The system includes a control system for setting the AC bus frequency in such a way that it can vary with time. The bus frequency may follow the natural frequency of the engine, and only small converters are needed to make the already approximately equal generator frequencies identical, so that they can all feed the common bus.