Added Support for DCOPF Constrained Expansion by dlcole3 · Pull Request #915 · GenXProject/GenX.jl

dlcole3 · 2026-07-15T14:49:42Z

Description

This PR adds code to support expansion decisions of DCOPF constrained GenX models that can be solved both monolithically or using Benders Decomposition. This work was originally started by @sambuddhac. It includes updates to settings, inputs loading, model construction, and solution methods. Part of the motivation for this work is supporting nodal spatial resolution of CEMs. In these cases, you might solve with DCOPF constraints, and you might also want to have integer decisions on new transmisison or generation builds (e.g., CC might be built in 500 MW increments to avoid unrealistic modular CC construction in lots of different zones). This PR is intended as a second step after the Benders PR (#914) is merged.

There is now a DiscreteInvestments flag in the settings of GenX. This controls whether there can be integer variables in the model (not that I chose to call this DiscreteInvestments over IntegerInvestments because MacroEnergySolvers.jl already has an IntegerInvestments setting). This can be applied to both resources and transmission lines. If DiscreteInvestments is set to 1, then GenX will look for a column header Discrete_Build in the Network.csv, Thermal.csv, and Vre.CSV and throw a warning statement if none of these files have the column header. This header controls which resources or lines can have discrete builds. This also gives the user flexiblity in controlling which components should be treated as integer/binary build decisions.
DC-OPF constraints now support expansion and discrete new builds. Previously, DC-OPF was only applied to fixed, existing networks. Now, there are model constraints permitting line expansion as well as new lines on existing or new corridors.
Network.csv supports additional column names. If the Discrete_Build column has a 1, then there can be at least one new line constructed on that corridor. GenX internally builds a new DataFrame with each line separated out with individual flow variables on them. This is important for handling DC-OPF constraints. In addition, it supports the case where there may be multiple discrete parallel lines on a corridor, and the user can pass these directly with only one line of the CSV. There is an additional constraint added which adds a solve order to identical lines to avoid degeneracy.
Line expansion supports both expansion and discrete new builds in the same model (though new lines cannot be expanded). If a user sets Discrete_Build to zero, but there is a nonzero Line_Max_Reinforcement_MW, then that line will be treated as the traditional line expansion available in GenX (note that this can essentially be thought of as reconductoring). If the discrete build flag is set to 1, then Line_Max_Reinforcement_MW is used to determine the size of the new lines (note: we can restructure this if you think new lines should have more columns to support this instead of using the existing), with the New_Line_Cap_Size_MW column name used to determine how may lines fit into Line_Max_Reinforcement_MW.
When DC_OPF is on with discrete builds, lines are placed into different sets inside the inputs dictionary internally. These are FIXED_LINES which are lines that can't be expanded, EXPANSION_LINES, which are lines that have continuous reinforcement on them, DISCRETE_BUILD_LINES which are lines that have a binary build decision associated with them, and PHANTOM_LINES, which are the DISCRETE_BUILD_LINES which are on new corridors (this is important for the line angle limit constraints, which you only want to have applied if the line is built).
There is a new example case 12 that is a copy of example case 10 but with line data adjusted to support new builds.
There are new tests that example case 12 (but with a smaller time horizon) for testing purposes, both with and without Benders
Benders decomposition has been extended to work with discrete build decisions following the methods outlined in this paper. This includes a transport model and LP hotstarting. MacroEnergySolvers.jl supports the LP relaxation of binary decisions, but I had two concerns with using its methods and defined my own in GenX: 1) I want the flexibility to turn off the stabilization method after hot starting is finished, and 2) binary varaibles do not get an explicit upper bound set on them inside MacroEnergySolvers which I think can cause issues for the big M constraints here.
The documentation has been updated to describe how these new features can be used

A couple of additional notes:

Line losses have not been tested in this PR. I believe that they should still work because all the lines use the vFLOW variable, and this will be zero for any line not constructed. @sambuddhac may have a better idea on whether this is the case.
Multistage runs are not explicitly handled in this PR.
The Changelog has been updated, but it is a continuation of the former Benders PR, so the updates are at the end of the Benders work. Not sure if the Benders PR gets merged if we will need to update that Changelog
For problems with lots of nodes/zones, GenX can be quite slow. There is a need for future model construction improvements to handle problems with large zones. This is planned and will follow up this PR.

@gschivley and I had discussions on the above structuring, so tagging him in case he wants to give input on how it came together.

What type of PR is this? (check all applicable)

Related Tickets & Documents

This PR also address the feature request of #900

Checklist

Code changes are sufficiently documented; i.e. new functions contain docstrings and .md files under /docs/src have been updated if necessary.
The latest changes on the target branch have been incorporated, so that any conflicts are taken care of before merging. This can be accomplished either by merging in the target branch (e.g. 'git merge develop') or by rebasing on top of the target branch (e.g. 'git rebase develop'). Please do not hesitate to reach out to the GenX development team if you need help with this.
Code has been tested to ensure all functionality works as intended.
CHANGELOG.md has been updated (if this is a 'notable' change).
I consent to the release of this PR's code under the GNU General Public license.

How this can be tested

There is a new example case (12) and a new set of unit tests. The unit tests run a smaller time horizon version of example 12 with both monolithic and Benders. In addition, the unit test running the three zone case also runs it with DiscreteInvestments=1 to test integer build decisions on resources.

Post-approval checklist for GenX core developers

After the PR is approved

Check that the latest changes on the target branch are incorporated, either via merge or rebase
Remember to squash and merge if incorporating into develop

…ance for multistage

…d Integer_Build column

…on options

…ansion

…urn conflicts

lbonaldo

Hey @dlcole3, again, thank you so much for this additional PR! I added a few comments, most of them are probably related to the merge with the previous PR. Thank you for preparing them one next to the other. Let me know if you have any questions!

lbonaldo · 2026-08-10T20:11:16Z

+using Gurobi

-run_genx_case!(dirname(@__FILE__))
+run_genx_case!(dirname(@__FILE__), Gurobi.Optimizer)


I guess we can cleanup this file here, am I right?

lbonaldo · 2026-08-10T20:42:57Z

            mysetup = merge(mysetup, mysetup_benders)

+            if mysetup["DC_OPF"] != 1 && mysetup[:RunTransportModel]
+                @warn "`RunTransportModel` only works with DC_OPF = 1 but DC_OPF is set to $(mysetup["DC_OPF"]). Turning off `RunTransportModel`"


do we need to turn off RunTransportModel?

lbonaldo · 2026-08-10T20:46:40Z

+            if get(mysetup, :Distributed, false)
+                target = get(mysetup, :NWorkers, 0)
+                if target > 1
+                    current = nworkers()
+                    if current < target
+                        n_to_add = target - current
+                        @info "Benders: adding $n_to_add worker process(es) to reach $target total workers."
+                        addprocs(n_to_add; exeflags=["--project=$(Base.active_project())"])
+                        Distributed.remotecall_eval(Main, workers(), :(using GenX))
+                    elseif current > target
+                        @warn "Benders: $current workers are already running but NWorkers=$target was requested. Proceeding with $current workers."
+                    else
+                        @info "Benders: $current workers already running — no additional workers needed."
+                    end
+                else
+                    @warn "Benders: Distributed=true but NWorkers=$target (must be > 1 to enable parallel solving). Running sequentially."
+                end
+            end


isn't this part also in setup_benders_workers!?

lbonaldo · 2026-08-10T20:55:13Z

+        :ExpectFeasibleSubproblems    => false,
+        :IntegerInvestment            => false,
+        :Distributed                  => false,
+        :NWorkers                     => 0,


This default value changes from -1 to 0. Is that okay?

lbonaldo · 2026-08-10T21:20:16Z

+        @expression(EP, eChargeDischargeMaxAC[y in VS_SYM_AC, t = 1:T],
+            EP[:vP_AC_DISCHARGE][y, t]+EP[:vP_AC_CHARGE][y, t])
+    end
+


Is this part related to this PR?

lbonaldo · 2026-08-11T15:47:37Z

+    vre_stor!(EP::Model, inputs::Dict, setup::Dict)
+
+Operational-stage coordinator for the VRE-STOR module.
+
+Builds and links component operational blocks (`inverter_vre_stor!`, `solar_vre_stor!`,
+`wind_vre_stor!`, `stor_vre_stor!`, `elec_vre_stor!`) and enforces module-level
+constraints using planning capacities from investment functions.
+
+Core constraints include AC-balance dispatch and grid-interface limits:


are we removing the docstring for vre_stor here?

lbonaldo · 2026-08-11T15:49:03Z

        @variable(EP, vNEW_TRANS_CAP[l in EXPANSION_LINES]>=0)
+        if DiscreteInvestments == 1
+            @variable(EP, vNEW_TRANS_LINES[l in DISCRETE_BUILD_LINES], Bin)
+        end


Same as above. I think this part is also in capacity_decision.jl

lbonaldo · 2026-08-11T15:49:31Z

+    # Guard against unsupported Benders + VRE-STOR combination
+    if setup["Benders"] == 1 
+        if setup["LDSAdditionalConstraints"] == 1
+            @warn "LDSAdditionalConstraints=1 applies to problems with non-representative periods and is not supported in the current Benders implementation. Benders will proceed as if LDSAdditionalConstraints=0"
+        end
+    end


are these lines from the Benders PR?

lbonaldo · 2026-08-11T15:50:29Z

-        else
-            hourly_matching!(EP, inputs)
-        end
+        hourly_matching!(EP, inputs)


We also need to double check the hourly matching for Benders.

lbonaldo · 2026-08-11T15:51:40Z

+    # (Benders case with VRE_STOR already errored at generate_model entry point)
    if !isempty(inputs["VRE_STOR"])
-        if setup["LDES_Feasible"] == 0 && ((setup["Benders"] == 1 && haskey(inputs, "SubPeriod_Index") && !isempty(inputs["VS_LDS"])) || ((inputs["REP_PERIOD"] > 1) && !isempty(inputs["VS_LDS"])))
+        if (setup["Benders"] == 1 && haskey(inputs, "SubPeriod_Index") && !isempty(inputs["VS_LDS"])) || (inputs["REP_PERIOD"] > 1 && !isempty(inputs["VS_LDS"]))


Sorry, can you please remind me why we are removing this part here setup["LDES_Feasible"] == 0?

dlcole3 mentioned this pull request Jul 15, 2026

[Question]: DC-OPF–Based Transmission Expansion in GenX? #900

Open

dlcole3 marked this pull request as ready for review July 21, 2026 00:20

dlcole3 added 28 commits August 6, 2026 17:58

Initial commit of Benders implementation mid debugging

95fee33

Fixed bug in allam cycle

54fde4b

Added support for VRE STOR pre-debugging

fba3c37

Debugged VRE Stor with LDES and non LDES

3d8eaa3

Debugging LDS CAPRES with VRE STOR

9d73440

updated changelog, updated examples

2e818f3

Fixed bug in docs, updated Benders tests

ded9de9

Made benders tests faster via TDR, added doc strings

a211609

removed extra yaml file, added line for debugging tests

0e38082

built benders test cases to use prerun TDR files

060be79

Updated API for accessing more workers

b961555

Fixed @Everywhere call in case runner for Benders

5282a28

Updated tests to avoid numerical issues with HiGHS

e6e384c

Switched to simplex to avoid hanging in Julia 1.9 and increased toler…

807631d

…ance for multistage

attempt to fix error in writing outputs tests workflow

0f419be

Tightened multistage convergence tolerance

51ba878

added fallback on multistage testing for degenerate solutions in DDP

2a4dd7e

Reverted to IPM for writing outputs

411d5cc

Trying parameter scale = 1

ff14589

added fallback

2a6b63d

Initial integer flag addition

6c8ddaa

Removed outdated comments

f0d8bed

Removed println debug statements

ec567fe

Updated loading functions to handle new DCOPF case for networks; adde…

babcd9b

…d Integer_Build column

Added initial DCOPF src code for vFLOW

a281dca

Added bilinear, example, tests, model construction

d371230

Changed names to discrete_builds, added test cases, added LP relaxati…

00425e7

…on options

Docs pages from Claude before readthrough

c7374d5

dlcole3 added 15 commits August 6, 2026 19:00

Read through and edited Claude's documentation

d421c7b

Updated Changelong and added another note to docs

abdb5fe

Cleaned up run files

a4256a3

Added notes on parallel lines on same corridor to docs

52229df

Added note on reconductoring

72945e5

Updated tests to use a different solver method in HiGHS for DCOPF exp…

f35a601

…ansion

Skipping Benders test for Julia v1.6 due to MES issue

11f2475

Updated HiGHS settings to pass test

d84ed49

Turned off HiGSH presolve on multifuels

6c0ffc9

Adding print line to debug Github tests

f09df51

Updated debug call

a80a2c3

Reverted highs settings

ac76f78

Fixed compute_conflicts test so it handles cases where HiGHS does ret…

98b46c1

…urn conflicts

fixed big M constraint on phantom lines

5739d54

Removed legacy model code

0e5e77b

dlcole3 force-pushed the dc/support_dcopf_expansion branch from 692a737 to 0e5e77b Compare August 7, 2026 15:59

dlcole3 added 3 commits August 7, 2026 13:23

Added solve time recoery and key recovery

2fc88f1

Fixed phantom line construction

a8a8eb9

Added changelog, updated settings to speed up test

2a73908

lbonaldo reviewed Aug 11, 2026

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Added Support for DCOPF Constrained Expansion - #915

Added Support for DCOPF Constrained Expansion#915
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dlcole3 commented Jul 15, 2026

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