add constrain_line_amps for multiphase models (with simple test)

src/LinDistFlow.jl

@@ -16,6 +16,7 @@ export
     constrain_substation_voltage,
     constrain_KVL,
     constrain_loads,
+    constrain_line_amps,
     get_bus_values, 
     get_edge_values, 
     # recover_voltage_current,  # TODO validate this method

src/model_multi_phase.jl

@@ -213,3 +213,33 @@ function constrain_loads(m, p::Inputs{MultiPhase})
         end  # reactive loads
     end
 end
+
+
+"""
+    constrain_line_amps(m, p::Inputs{MultiPhase})
+
+Estimating the line amps as ``|\\Delta V / Z|``
+"""
+function constrain_line_amps(m, p::Inputs{MultiPhase})
+    w = m[:vsqrd]
+    m[:amps_pu] = Dict(ek => Dict() for ek in p.edge_keys)
+    for j in p.busses
+        for i in i_to_j(j, p)  # for radial network there is only one i in i_to_j
+            ij_linecode = get_ijlinecode(i,j,p)
+            amps_pu = sqrt(p.Isquared_up_bounds[ij_linecode]) / p.Ibase
+            z = sqrt(rij(i,j,p)^2 + xij(i,j,p)^2)  # in per-unit
+
+            for phs in p.phases_into_bus[j]
+                @constraint(m, [t in 1:p.Ntimesteps],
+                    -amps_pu <= (w[i,phs,t] - w[j,phs,t]) / z[phs,phs] <= amps_pu
+                )
+                m[:amps_pu][i*"-"*j][phs] = Dict()
+                for t in 1:p.Ntimesteps
+                    m[:amps_pu][i*"-"*j][phs][t] = (w[i,phs,t] - w[j,phs,t]) / z[phs,phs]
+                end
+                # TODO better storage of line amps (make an expression?)
+                # TODO line amps in Results?
+            end
+        end
+    end
+end

test/runtests.jl

@@ -255,4 +255,60 @@ end
         @test vs[("633", phs, 1)] ≈ 1.03^2
     end
 
-end
+end
+
+
+@testset "constrain line amps" begin
+
+    p = Inputs(
+        joinpath("data", "13bus", "IEEE13Nodeckt.dss"), 
+        "rg60";
+        Pload=Dict(),
+        Qload=Dict(),
+        Sbase=5_000_000, # msankur has 5,000 kvar * 1e3
+        Vbase=4160, 
+        v0 = 1.00,
+        v_uplim = 1.05,
+        v_lolim = 0.95,
+        Ntimesteps = 1,
+        P_up_bound=1e5,
+        Q_up_bound=1e5,
+        P_lo_bound=-1e5,
+        Q_lo_bound=-1e5,
+    );
+
+    m = Model(HiGHS.Optimizer)
+    build_ldf!(m, p)
+    @objective(m, Min, sum(
+        m[:Pj][p.substation_bus, phs, 1] + m[:Qj][p.substation_bus, phs, 1]
+        for phs in 1:3)
+    )
+    constrain_line_amps(m,p)
+    optimize!(m)
+
+    # find the max amps then constrain it, should get infeasible problem
+    optimal_amps = []
+    for (edge_key, phs_dict) in m[:amps_pu]
+        for (phs, time_dict) in phs_dict
+            for (t, var) in time_dict
+                push!(optimal_amps, value(var) * p.Ibase)
+            end
+        end
+    end
+    max_amps = maximum(optimal_amps)
+    p.Isquared_up_bounds = Dict(
+        k => (max_amps - 10)^2
+        for k in keys(p.Isquared_up_bounds)
+    )
+
+    m = Model(HiGHS.Optimizer)
+    build_ldf!(m, p)
+    @objective(m, Min, sum(
+        m[:Pj][p.substation_bus, phs, 1] + m[:Qj][p.substation_bus, phs, 1]
+        for phs in 1:3)
+    )
+
+    constrain_line_amps(m,p)
+    optimize!(m)
+    @test termination_status(m) == MOI.INFEASIBLE
+end