Trajectory Tracking Flight Controller Using Nonlinear Compensation
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Solution Overview
Problem
Conventional flight controllers for maneuvering trajectory tracking in fixed-wing aircraft face challenges due to the highly nonlinear and time-varying nature of flight dynamics, leading to imperfect nonlinearity cancellation and instability issues, especially with sensor dynamics and modeling errors.
Innovation Solution
A 6DOF trajectory tracking TLC architecture is developed, comprising a processor-based system with four nested control loops that generate control signals by determining nominal and feedback vectors for body velocity, Euler angles, body rates, and moments, using sensed parameters from avionic sensors to adjust engine throttle and control surface deflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional LTI controllers are used for trajectory tracking, then the control structure is simple and easy to implement, but the nonlinearity cancellation is imperfect due to sensor dynamics and modeling errors, resulting in instability
Solution Approach 1:
The patent introduces a nonlinear compensator as an intermediary component between the LTI controller and the plant. This compensator specifically addresses the imperfect nonlinearity cancellation by incorporating sensor dynamics and modeling error compensation, allowing the simple LTI controller structure to achieve reliable stability performance.
Solution Approach 2:
The patent modifies the control parameters by introducing time-varying gain schedules and adaptive parameters that adjust based on operating conditions. This allows the LTI controller to adapt to nonlinear effects without changing the fundamental control structure, resolving the contradiction between simplicity and stability.
2Reliability
If gain-scheduling approaches are used for trajectory tracking, then the controller can handle nonlinearities, but the controller design and tuning are highly trajectory dependent and require frequent redesigns
Solution Approach 1:
The patent creates a universal control architecture that combines LTI control with nonlinear compensation mechanisms capable of handling multiple trajectory types. The nonlinear compensator is designed to adapt to different operating conditions without requiring complete redesign, providing multi-functional capability across various flight regimes.
Solution Approach 2:
The patent introduces dynamic adaptation mechanisms where controller parameters and compensation terms are adjusted in real-time based on measured states and trajectory requirements. This dynamic behavior allows the controller to maintain performance across different trajectories without static redesign.
3Reliability
If nonlinear control techniques such as feedback linearization are used, then the nonlinearity can be cancelled, but the nonlinearity cancellation is imperfect due to sensor dynamics and modeling errors
Solution Approach 1:
The patent introduces a dedicated nonlinear compensator as an intermediary that specifically addresses the imperfect cancellation issues. This compensator handles sensor dynamics and modeling errors separately, allowing the main LTI controller to focus on stable control while the compensator handles nonlinear imperfections.
Solution Approach 2:
The patent implements feedback mechanisms where the nonlinear compensator continuously monitors tracking performance and adjusts compensation parameters accordingly. This feedback loop corrects for imperfect nonlinearity cancellation in real-time, improving reliability without requiring complete redesign of the control structure.
Data Source
AI summary
A six degree-of-freedom trajectory linearization controller (TLC) architecture (30) for a fixed-wing aircraft (46) is set forth. The TLC architecture (30) calculates nominal force and moment commands by dynamic inversion of the nonlinear equations of motion. A linear time-varying (LTV) tracking error regulator provides exponential stability of the tracking error dynamics and robustness to model uncertainty and error. The basic control loop includes a closed-loop, LTV stabilizing controller (12), a pseudo-inverse plant model (14), and a nonlinear plant model(16). Four of the basic control loops (34, 36, 40, 42) are nested to form the TLC architecture (30).