🛡️ True Robust Control

Operating H∞ Robustness with FSM and LLM

🔗 Links

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Overview

True Robust Control is a design philosophy that redefines classical $H_\infty$ robust control
as an operational capability, rather than a static offline guarantee.

Instead of assuming a fixed worst-case uncertainty,
this framework treats uncertainty as a state that is:

• 🔍 monitored,
• 🧭 interpreted,
• 🛑 and acted upon before theoretical guarantees break.

Core Idea

Robustness is not a number.
It is the ability to detect, decide, and adapt.

In this framework:

• $H_\infty$ control defines the guarantee boundary
• FSM manages operational state transitions
• LLM performs design-level reasoning
• Weight functions $W$ are used as tactical levers

Architecture at a Glance

The framework is built on the AITL (Adaptive Intelligent Three-Layer) structure:

• Inner Loop
  PID / $H_\infty$ control for real-time stability

• Middle Layer
  FSM for degradation-aware mode switching

• Outer Layer
  LLM for weight redesign decisions (offline only)

• Robust Monitor
  Frequency-domain uncertainty evaluation

Key Concepts

• Uncertainty $\Delta$ is decomposed into:
  • low-frequency components
  • high-frequency components
  • input-side components
• When effective $|\Delta|_\infty$ reaches 0.8,
  the system proactively shifts its control strategy
• Only the relevant weight is redesigned:
  • $W_s$ : performance demand
  • $W_t$ : robustness margin
  • $W_u$ : actuator protection
• Never all weights at once

Relationship to AITL Types

• A-Type
  Base architecture and operational mechanism

• True Robust Control (this theme)
  Operational robustness as a first-class design concept

• B-Type
  Reliability-first extension with permissioned adaptation

Documents

• Concept
  Definition and motivation of True Robust Control

• Architecture
  Layered structure and responsibility separation

• Uncertainty as State
  Why $\Delta$ must be monitored, not assumed

• Weight Redesign Strategy
  How and why only specific weights are modified

• Roadmap
  Planned implementation and validation steps

Scope and Intent

This work is:

• ❌ not a replacement for $H_\infty$ theory
• ❌ not an AI-optimized control scheme

It is an attempt to formalize
how experienced control engineers actually operate robustness in the field.

Start Here

If you are new to this theme, begin with:

1. Concept
2. Architecture
3. Uncertainty as State

Robust control is not about never failing.
It is about knowing when and how to step back safely.

This documentation evolves alongside the AITL Controller A-Type project.