Integrated Upsampler and Filter for Actuator Control
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Solution Overview
Problem
In flight control systems, the integration of components with different sampling frequencies leads to undesirable start-and-stop behavior, causing high current spikes and potential instability due to mismatched design specifications, resulting in inefficient power usage and reduced component lifespan.
Innovation Solution
A system and method that uses a nonlinear upsampler and linear filtering to smooth low-frequency commands for high-frequency controls, incorporating an incremental command limiter, lead-lag filter, and feed-forward path to attenuate high frequencies and reduce phase loss, thereby stabilizing the system and improving power efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the closed-loop flight control system operates at a higher frequency than the master computer, then the control surfaces can be adjusted more quickly during high speed flight, but the system exhibits start-and-stop behavior that triggers structural modes and causes undesirable behavior
Solution Approach 1:
The patent applies preliminary action by pre-smoothing the command signal before it reaches the high-frequency closed-loop control system. A command smoother filter is applied to the master computer commands to attenuate high-frequency content before the commands are processed by the fast actuator control system, preventing the start-and-stop behavior that would otherwise occur when the fast system responds to unsmoothed commands
Solution Approach 2:
The patent introduces an intermediary component - a command smoother filter - that sits between the master computer and the closed-loop flight control system. This intermediary processes the commands to remove high-frequency content that would cause instability, allowing the fast control system to operate smoothly without directly responding to raw master computer commands
2Speed
If the closed-loop flight control system immediately adjusts control surfaces upon receiving commands, then the system responds quickly to commands, but high current spikes are generated that strain flight control surfaces and reduce component lifespan
Solution Approach 1:
The command smoother filter performs preliminary action by pre-processing commands to limit rate of change and attenuate high-frequency content before they reach the actuator control system. This prevents sudden large commands that would cause high current spikes, thereby reducing strain on flight control surfaces and extending their operational lifespan while maintaining quick response to legitimate control needs
3Stability of the object's composition
If bi-quad filters are applied on the command path to smooth commands, then the start-and-stop behavior is attenuated, but unacceptable phase loss occurs that creates further instability
Solution Approach 1:
The patent changes the parameters of the filtering approach by using a lead-lag filter with specifically tuned time constants rather than a bi-quad filter. The lead-lag filter provides the necessary low-pass filtering to attenuate start-and-stop behavior while its phase characteristics are optimized to minimize phase loss in the critical frequency range, maintaining stability margins that would otherwise be degraded by bi-quad filtering
Data Source
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AI summary
Presented is a system and method for controlling an actuator in a multirate control system using an integrated upsampler and filter, comprising an incremental command limiter for changing a command from a first control system into a limited incremental command in a second control system, a lead-lag filter for filtering the limited incremental command to attenuate high frequencies, and a feed forward path for reducing phase loss in rate output signal at low frequencies. In embodiments, a command position signal received at the sampling rate of the first control system is interpolated into incremental command position signals at the sampling rate of the second control system. Position error signals and rate error signals from the devices being controlled are used as feedback to further stability the control loops.