Change considered non impedance branches values in ACOPF (#91)

* Wip
* Clean
* Add comments/doc
* Update doc

---------

Signed-off-by: p-arvy <pierre.arvy@artelys.com>

docs/optimizer/preprocessing.md

@@ -14,10 +14,11 @@ Let $V_{s}^{min}$ (resp. $V_{s}^{max}$) be the low (resp. high) voltage limit of
 
 Branches with an impedance magnitude, **calculated in per unit**, lower than the configurable threshold `Znull` (see section [Configuration of the run](inputs.md#configuration-of-the-run)) are considered as non-impedant. 
 These branches will have their reactance replaced by the threshold `Znull` (in p.u.), **even if the reactance specified in `ampl_network_branches.txt` is negative**.
+Note that for lines considered as non-impedant and connecting two different nominal voltage levels, the conductances and susceptances are cancelled in order to avoid numerical instabilities.
 
 ## Impedance of transformers
 
-In the calculations of the ACOPF (see [AC optimal powerflow](acOptimalPowerflow.md)), the transformers with an impedance (specified in `ampl_network_branches.txt`) considered as null (see [Zero-impedance threshold](#zero-impedance-threshold))  **are treated as lines**. Then, the transformation ratios/phase shifts are ignored, as well as the impedance specified in the tap changer table `ampl_network_tct.txt`.
+In the calculations of the ACOPF (see [AC optimal powerflow](acOptimalPowerflow.md)), the impedance specified in tap changer table `ampl_network_tct.txt` is ignored for transformers with an impedance (specified in `ampl_network_branches.txt`) considered as null (see [Zero-impedance threshold](#zero-impedance-threshold)). Note that the transformer ratios and phase shiftings are considered anyway.
 
 For phase shifters transformers considered as impedant, the reactance values from the tap changer table (in `ampl_network_tct.txt`) replace the reactance specified in `ampl_network_branches.txt`. The resistance is then calculated proportionally. 
 For the ratio tap changers, the impedance stays as specified in `ampl_network_branches.txt`. **Please notice there is no specified handling for cases where resistance and/or reactance is negative or if there is both a ratio tap changer and a  phase shift transformer on the same branch.**

open-reac/src/main/resources/openreac/commons.mod

@@ -109,21 +109,21 @@ param branch_X_mod{(qq,m,n) in ALL_BRANCHCC} :=
   else branch_X[1,qq,m,n];
 check {(qq,m,n) in ALL_BRANCHCC}: abs(branch_X_mod[qq,m,n]) > 0;
 
-# If in BRANCHZNULL, then set Gor/Gex/Bor/Bex to 0
+# If in BRANCHZNULL and Vnom1 != Vnom2, then set Gor/Gex/Bor/Bex to 0
 param branch_Gor_mod{(qq,m,n) in ALL_BRANCHCC} :=
-    if (qq,m,n) in BRANCHCC and (qq,m,n) in BRANCHZNULL then 0
+    if (qq,m,n) in BRANCHCC and (qq,m,n) in BRANCHZNULL and substation_Vnomi[1,bus_substation[1,m]] != substation_Vnomi[1,bus_substation[1,n]] then 0
     else branch_Gor[1,qq,m,n];
 
 param branch_Gex_mod{(qq,m,n) in ALL_BRANCHCC} :=
-    if (qq,m,n) in BRANCHCC and (qq,m,n) in BRANCHZNULL then 0
+    if (qq,m,n) in BRANCHCC and (qq,m,n) in BRANCHZNULL and substation_Vnomi[1,bus_substation[1,m]] != substation_Vnomi[1,bus_substation[1,n]] then 0
     else branch_Gex[1,qq,m,n];
 
 param branch_Bor_mod{(qq,m,n) in ALL_BRANCHCC} :=
-    if (qq,m,n) in BRANCHCC and (qq,m,n) in BRANCHZNULL then 0
+    if (qq,m,n) in BRANCHCC and (qq,m,n) in BRANCHZNULL and substation_Vnomi[1,bus_substation[1,m]] != substation_Vnomi[1,bus_substation[1,n]] then 0
     else branch_Bor[1,qq,m,n];
 
 param branch_Bex_mod{(qq,m,n) in ALL_BRANCHCC} :=
-    if (qq,m,n) in BRANCHCC and (qq,m,n) in BRANCHZNULL then 0
+    if (qq,m,n) in BRANCHCC and (qq,m,n) in BRANCHZNULL and substation_Vnomi[1,bus_substation[1,m]] != substation_Vnomi[1,bus_substation[1,n]] then 0
     else branch_Bex[1,qq,m,n];
 
 # Busses with valid voltage value
@@ -203,19 +203,20 @@ param branch_admi {(qq,m,n) in ALL_BRANCHCC} =
 
 # Later in this file, a variable branch_Ror_var will be created, to replace branch_Ror when it is not variable
 param branch_Ror {(qq,m,n) in ALL_BRANCHCC} =
-    ( if ((qq,m,n) in BRANCHCC_REGL)
+    ( if (branch_ptrRegl[1,qq,m,n] != -1)
+
       then tap_ratio[1,regl_table[1,branch_ptrRegl[1,qq,m,n]],regl_tap0[1,branch_ptrRegl[1,qq,m,n]]]
       else 1.0
     )
-  * ( if ((qq,m,n) in BRANCHCC_DEPH)
+  * ( if (branch_ptrDeph[1,qq,m,n] != -1)
       then tap_ratio[1,deph_table[1,branch_ptrDeph[1,qq,m,n]],deph_tap0[1,branch_ptrDeph[1,qq,m,n]]]
       else 1.0
     )
   * (branch_cstratio[1,qq,m,n]);
 param branch_Rex {(q,m,n) in ALL_BRANCHCC} = 1; # In IIDM, everything is in bus1 so ratio at bus2 is always 1
 
 param branch_dephor {(qq,m,n) in ALL_BRANCHCC} =
-  if ((qq,m,n) in BRANCHCC_DEPH)
+  if (branch_ptrDeph[1,qq,m,n] != -1)
   then tap_angle [1,deph_table[1,branch_ptrDeph[1,qq,m,n]],deph_tap0[1,branch_ptrDeph[1,qq,m,n]]]
   else 0;
 param branch_dephex {(qq,m,n) in ALL_BRANCHCC} = 0; # In IIDM, everything is in bus1 so dephase at bus2 is always 0