Three-Tank System: Hybrid MLD-MPC Control

1. Installation

Open a terminal in the project root and instantiate the environment to download dependencies:

julia --project=. -e 'using Pkg; Pkg.instantiate()'

2. Run the Simulation

The primary entry point is the closed-loop MPC simulation script. This script initializes the plant, sets up the controller, runs the optimization loop, and visualizes the results.

julia --project=. scripts/02_closed_loop_mpc.jl

Output: A plot window will appear showing:

• Water Levels: $h_1, h_2, h_3$ tracking the reference trajectories.
• Inputs: The control actions taken (Pump Flows and Valve States).

How to Configure Inputs

1. Initialize Settings: Create the settings object.
2. Set Active Inputs: Use set_active!(settings, :Symbol...) to tell the MPC which variables it is allowed to toggle/change.
3. Set Nominal Values: Use set_nominal!(settings, :Symbol, value) to fix the state of inputs not under MPC control.

Scenario A: Pumps Only (Classic Control)

In this scenario, the MPC optimizes pump flows, but all valves are fixed manually.

settings = InputSettings()

# 1. Let MPC control Pump 1 and Pump 2
set_active!(settings, :Q1, :Q2)

# 2. Fix physical constraints (e.g., Output Drain VL3 is always open)
set_nominal!(settings, :VL3, 1.0) 

# Note: All other valves (V1, V2, V13, V23, VL1, VL2) default to 0.0 (Closed) 
# unless specified in set_nominal!

Scenario B: Hybrid Control (Pumps + Valves)

Here, the MPC can control Pump 1 and the upper connection valve $V_1$ to satisfy the objective.

settings = InputSettings()

# The MPC will decide when to open V1 and how much to pump Q1
set_active!(settings, :Q1, :V1)

# Ensure the output drain is open
set_nominal!(settings, :VL3, 1.0)

System Description & Inputs

The system models the "COSY Three Tank Benchmark". Below is the mapping between the visual labels, the code symbols used in ThreeTankSystem.jl, and their physical descriptions.

Actuator Mapping Table

Diagram Label	Code Symbol	Description	Control Type
$Q_1$	:Q1	Pump 1 Flow: Inflow to Tank 1.	Continuous ($0 \dots Q_{max}$)
$Q_2$	:Q2	Pump 2 Flow: Inflow to Tank 2.	Continuous ($0 \dots Q_{max}$)
$V_1$	:V1	Upper Valve 1: Connects Tank 1 $\to$ Tank 3 at height $h_v$.	Binary (Open/Closed)
$V_2$	:V2	Upper Valve 2: Connects Tank 2 $\to$ Tank 3 at height $h_v$.	Binary (Open/Closed)
$V_{13}$	:V13	Lower Valve 1-3: Connects bottom of Tank 1 $\to$ Tank 3.	Binary (Open/Closed)
$V_{23}$	:V23	Lower Valve 2-3: Connects bottom of Tank 2 $\to$ Tank 3.	Binary (Open/Closed)
$V_{L1}$	:VL1	Drain Valve 1: Leak/Drain at bottom of Tank 1.	Binary (Open/Closed)
$V_{L2}$	:VL2	Drain Valve 2: Leak/Drain at bottom of Tank 2.	Binary (Open/Closed)
$V_{L3}$	:VL3	Drain Valve 3: Output drain at bottom of Tank 3.	Binary (Open/Closed)

Physical Parameters

• $h_1, h_2, h_3$: Water levels in the respective tanks (State Variables).
• $h_v$: The height of the upper connection pipes. Water only flows through $V_1$ or $V_2$ if the level in the source tank exceeds this height.

📂 Project Structure

ThreeTankSystem/
├── scripts/
│   ├── 01_open_loop_physical.jl  # Test plant physics (no controller)
│   ├── 02_closed_loop_mpc.jl     # MAIN: Run the MPC simulation
│   └── 03_controller_test.jl     # Unit tests for controller logic
├── src/
│   ├── ThreeTankSystem.jl # Module entry point
│   ├── plant.jl           # Nonlinear ODE model (ModelingToolkit)
│   ├── MLDModel.jl        # JuMP Optimization Model (Logic -> MIP)
│   ├── controllers.jl     # MPC loop implementation
│   ├── simulation.jl      # Simulation orchestrator
│   └── types.jl           # Parameter structs & InputSettings
└── Project.toml           # Dependencies