Observability: full observability check meshed network without voltage phasor

[Jerry-Jinfeng-Guo]

Implement Meshed Network Observability Check

Summary

This PR implements #1085 a comprehensive observability checking algorithm for meshed power grid networks without voltage phasor sensors. The implementation adds a spanning tree algorithm based on nodal measurements and connectivity analysis to determine network observability for non-radial (meshed) topologies.

Key Changes

Algorithm Implementation

New Spanning Tree Algorithm for Meshed Networks

• sufficient_condition_meshed_without_voltage_phasor(): Main entry point for meshed network observability checking
• starting_from_node(): Core spanning tree construction algorithm that attempts to build a spanning tree using available measurements
• prepare_starting_nodes(): Smart starting point selection algorithm that prioritizes nodes without measurements and no edge measurements

Data Structures

New Connectivity Status Enum

• ConnectivityStatus enum with 7 states to track measurement usage:
  • is_not_connected (-1): Not connected, redundant
  • has_no_measurement (0): Connected but no measurement available
  • node_measured (0b010): Node has unused measurement
  • node_downstream_measured (0b001): Branch discovered with downstream measurement
  • node_upstream_measured (0b100): Branch discovered with upstream measurement
  • branch_native_measured (0b111): Branch has its own measurement, unused
  • branch_measured_used (0b101): Branch measurement already used

New Neighbor Network Structure

• ObservabilityNNResult: Represents network topology with direct neighbor connections
• Bidirectional neighbor list expansion via expand_neighbour_list()
• Integration with Y-bus structure for efficient connectivity analysis

Algorithm Features

Multi-Priority Spanning Tree Construction

1. Native Edge Measurements (Priority 1): Utilizes branch flow/power sensors directly
2. Downwind Measurements (Priority 2): Uses nodal measurements in downwind mode
3. General Connection Rules (Priority 3): Handles complex measurement assignment scenarios
4. Backtracking with Reassignment (Priority 4): Implements measurement reassignment during backtracking

Smart Measurement Reassignment

• reassign_nodal_measurement(): Dynamically reassigns nodal measurements during backtracking
• Optimizes measurement usage when algorithm gets stuck
• Maintains edge direction consistency through connectivity status updates

Refactored Codfe

Enhanced Network Scanning

• Renamed count_observability_sensors() → scan_network_sensors()
• Added bus injection counting with early-out optimization
• Integrated neighbor list construction during network scanning
• Added comprehensive sensor classification (flow, voltage phasor, bus injection)

Improved Function Organization

• Renamed necessary_observability_condition() → necessary_condition()
• Renamed sufficient_observability_condition() → sufficient_condition_radial_with_voltage_phasor()
• Added namespace observability for better code organization
• Eliminated code duplication through parameterized helper functions

Some Performance Optimizations

Early Exit Conditions

• Sufficient nodal measurements: If bus_injections.back() > n_bus - 2, network is immediately observable
• Multiple starting points: Algorithm tries different starting nodes to find valid spanning trees
• Iteration limiting: Prevents infinite loops with max_iterations = n_bus²

Improvements

Variable Naming Consistency

• Fixed loop variable names: row → bus for clarity
• Consistent use of n_bus sizing
• Improved variable scoping and const correctness

[Copilot]

Pull Request Overview

This PR implements a comprehensive observability checking algorithm for meshed power grid networks without voltage phasor sensors. The implementation adds a spanning tree algorithm based on nodal measurements and connectivity analysis to determine network observability for non-radial (meshed) topologies.

• Adds new meshed network observability algorithm with spanning tree construction
• Introduces bidirectional neighbor network structure and connectivity status tracking
• Refactors existing functions for better organization and adds observability namespace

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
test_observability.cpp	Updates test calls to use new observability namespace
observability.hpp	Core implementation with new meshed network algorithm, data structures, and refactored functions
newton_raphson_se_solver.hpp	Updates observability check call to use new namespace
iterative_linear_se_solver.hpp	Updates observability check call to use new namespace

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[Jerry-Jinfeng-Guo]

Validation test case with meshed topology in ill-conditioned-system is wrongly configured. The network is observable.

[figueroa1395]

Nitpick: The n+1 trick with the number of sensors at the n+1 spot might be useful for voltage_phasor_sensors and flow_sensors as well, since we count them anyway later on.

[figueroa1395]

This is probably a good follow up, as it depends on what will happen with the radial check. Resolving for now.

[nitbharambe]

Unresolving: I dont really like the n+1 trick. The extra .back() makes the intent really confusing. Why not have a counter within the struct itself?

[figueroa1395]

This pattern happens a lot, maybe a good idea to make it a helper function.

[nitbharambe]

We can fill the "expand_neighbour_list" info in this loop too using the col_indices

[Jerry-Jinfeng-Guo]

See #1136 (comment)

This also contradicts the 'single responsibility' paradigm you are promoting.

[nitbharambe]

As discussed yesterday, we can store the neighbour list in YBusStructure order. Adding a note here, but lets think about it later.

[nitbharambe]

Out of scope here. And into future improvement ideas discussion.

[Jerry-Jinfeng-Guo]

Correction: the list is the product/output of a wrapper function/object in between the YBus and the Observability check module. Not in the YBus.

[Jerry-Jinfeng-Guo]

This file was already reviewed. See #1139.

[Jerry-Jinfeng-Guo]

This file was already reviewed. See #1139.

[Jerry-Jinfeng-Guo]

This file was already reviewed. See #1139.

[sonarqubecloud]

Quality Gate passed

Issues
8 New issues
0 Accepted issues

Measures
0 Security Hotspots
94.7% Coverage on New Code
0.5% Duplication on New Code

See analysis details on SonarQube Cloud