ADD: voltage limits to slack/ref buses/nodes for improving subproblem…

…s convergence.

CHANGELOG.md

@@ -65,6 +65,7 @@
 
 ## staged Decomposition
 
+- Added voltage limits (0.7-1.5) to slack/ref bus/nodes for the subproblems in the decomposition approach. This addition seems to make a ton of difference for improvong the convergence of the subproblems.
 - Added option `export_models=true` that allows integrated models to be exported as `.nl` file. Indices for all variables (including boundary vars) are exported into a `integrated_vars_indices.txt` file.
 - Added option `export_models=true` that allows decomposition models to be exported as `.nl` files and shared variable indices as `shared_vars.txt`.
 - In the `ref.jl` function `_ref_filter_transmission_integration_loads!`, the initialization of the variables causes a problem that does not allow for multiple distribution systems to connect to the same transmission system bus. So, we commented out this for now (WIP).

src/core/ref_decomposition.jl

@@ -99,13 +99,14 @@ function _ref_filter_distribution_slack_generators_decomposition!(ref::Dict{Symb
 
     # Loops over all nws
     for (nw, nw_ref) in ref[:it][:pmd][:nw]
-        # Unrestrict buspairs connected to reference bus
-        for (j, bus_pair) in nw_ref[:buspairs]
-            if (bus_pair["vm_fr_min"] == 1.0) # only need to check one
-                bus_pair["vm_fr_min"] = 0.0
-                bus_pair["vm_fr_max"] = Inf
-            end
-        end
+
+        # # Unrestrict buspairs connected to reference bus - (Seems to not be needed!)
+        # for (j, bus_pair) in nw_ref[:buspairs]
+        #     if (bus_pair["vm_fr_min"] == 1.0) # only need to check one
+        #         bus_pair["vm_fr_min"] = 0.0
+        #         bus_pair["vm_fr_max"] = Inf
+        #     end
+        # end
 
         # Modify v_min and v_max, remove va and vm, and change bus type for reference bus
         boundary = nw_ref[:pmitd]   # boundary info.
@@ -115,19 +116,18 @@ function _ref_filter_distribution_slack_generators_decomposition!(ref::Dict{Symb
         boundary_number = boundary_keys[1]
         boundary_data = boundary[boundary_number]
 
-        nw_ref[:bus][boundary_data["distribution_boundary"]]["vmin"] = [0.0, 0.0, 0.0]
-        nw_ref[:bus][boundary_data["distribution_boundary"]]["vmax"] = [Inf, Inf, Inf]
-        # nw_ref[:bus][boundary_data["distribution_boundary"]]["bus_type"] = 1 # 3: slack, 1: load, 2: gen. bus
+        # These limits are extremely important. If not present, subproblems has a lot of problems converging
+        nw_ref[:bus][boundary_data["distribution_boundary"]]["vmin"] = [0.7, 0.7, 0.7]
+        nw_ref[:bus][boundary_data["distribution_boundary"]]["vmax"] = [1.5, 1.5, 1.5]
 
-        # Modify slack gen cost & other parameters.
+        # Modify slack gen cost.
         for (gen_indx, gen_data) in  nw_ref[:gen]
             if (gen_data["gen_bus"] == boundary_data["distribution_boundary"])
                 cost_length = length(gen_data["cost"])
                 gen_data["cost"] = zeros(cost_length)
-                # modify the control mode of the slack gen (not penalty related)
-                # gen_data["control_mode"] = 1 # TODO: this may be needed.
             end
         end
+
     end
 end