Variable Ratio Transmission for Aircraft Generator Frequency Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing electrical power generation systems in gas turbine engines face challenges in maintaining required frequency ranges while minimizing torque requirements, leading to increased fuel consumption and weight due to the need for constant ratio gearboxes and heavy power electronics for frequency correction.
Innovation Solution
An electrical power generation system with a main generator, an electrical output frequency controller, and a torque sensor arrangement that adjusts the rotational speed of the gas turbine engine to maintain torque within predetermined limits, allowing for frequency control at reduced engine speeds and preventing overloading, thereby reducing fuel consumption and weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a constant ratio gearbox is used to drive the generator, then the generator can provide electrical power at a required frequency range, but the engine must operate at a minimum rotational speed that increases specific fuel consumption
Solution Approach 1:
The patent applies a variable ratio transmission system that dynamically adjusts the gear ratio between the engine shaft and generator based on operating conditions. This allows the engine to operate at lower rotational speeds while maintaining the generator output frequency within the required 360-800 Hz range, thereby reducing specific fuel consumption during phases like takeoff and climb where minimum engine speed would otherwise be mandated by constant ratio gearbox constraints
Solution Approach 2:
The system changes the transmission ratio parameter dynamically to decouple engine rotational speed from generator output frequency. By varying the gear ratio, the patent enables the generator to produce compliant electrical power across the required frequency range while allowing the engine to operate at optimized speeds for different flight phases, eliminating the need to maintain unnecessarily high minimum engine speeds
2Reliability
If power electronics are used to correct the generator output frequency, then the required frequency range can be achieved, but the system weight increases significantly
Solution Approach 1:
The patent replaces the electrical power electronics frequency correction approach with a mechanical variable ratio transmission system. Instead of using heavy power electronic converters to adjust generator output frequency, the system uses a mechanically variable gear ratio to directly control the relationship between engine shaft speed and generator rotor speed, thereby achieving frequency compliance through mechanical means that are lighter than equivalent power electronics
3Reliability
If the minimum engine rotational speed is increased to maintain generator frequency compliance, then the electrical power frequency requirement is met, but the engine thrust increases leading to higher fuel consumption
Solution Approach 1:
The variable ratio transmission system dynamically adjusts the gear ratio to allow the engine to operate at lower rotational speeds while maintaining generator output within the 360-800 Hz frequency range. This eliminates the need to increase minimum engine rotational speed and associated engine thrust, thereby reducing fuel consumption during flight phases where electrical power frequency compliance would otherwise require higher engine power
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 enables reduced fuel burn and minimized transmission system weight by controlling engine speed based on torque limits, ensuring power quality and frequency compliance across all conditions, including failure scenarios.
Implementation Method 1
The rotor windings are powered by an electrical source, to induce a magnetic field in the rotor. The rotor is surrounded by a stator comprising a plurality of electrical stator windings. As the rotor rotates in use, a rotating magnetic field is produced by the rotor windings, which energises the stator electrical windings to produce an alternating current in the electrical windings of the stator.
Implementation Method 2
control the frequency and phase of the electrical current provided to the individual electromagnetic windings of the rotor, such that a rotating magnetic field is provided from the frame of reference of the rotor
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
An electrical power generation system (100) for an aircraft gas turbine engine (10). The system comprises an alternating current electrical generator (110) having a rotor (114) comprising a plurality of electromagnetic rotor windings (118) and a stator (124) comprising a plurality of electrical stator windings (126). The rotor (114) is mechanically coupled to a shaft (36) of the gas turbine engine (10) by a transmission system (129). The electrical generator (110) further includes an electrical output frequency controller (130), a torque sensor arrangement configured to determine a torque imposed on the transmission system (129) by the generator (110) and a controller (112) configured to operate the electrical power generation system in first mode and second modes. In the first mode, the frequency of the electrical power output of the electrical generator (110) is controlled by the electrical output frequency controller (130) to lie within predetermined limits, and a reduced idle signal is provided to a gas turbine engine controller (132). In the second mode, the frequency of the electrical power output of the electrical generator (132) is not controlled by the electrical output frequency controller (130) and an increased idle signal is provided to the gas turbine engine controller (132). The electrical generator controller (112) is configured to operate the electrical power generation system (100) in the first mode when the torque is below a predetermined limit, and in the second mode when the torque is above a predetermined limit.