Update DC-OPF with correct PU and additional flow limit constraints

This PR attempts to correct enhance flexibility of per-unit system of units in the DC-OPF and also impose line-flow MW limit constraint to represent thermally constrained lines.

src/model/core/transmission/dcopf_transmission.jl

@@ -43,6 +43,13 @@ function dcopf_transmission!(EP::Model, inputs::Dict, setup::Dict)
             t]==inputs["pDC_OPF_coeff"][l] *
                 sum(inputs["pNet_Map"][l, z] * vANGLE[z, t] for z in 1:Z))
 
+    # Maximum power flows, power flow on each transmission line cannot exceed maximum capacity of the line at any hour "t"
+    @constraints(EP,
+        begin
+            cMaxFlow_out[l = 1:L, t = 1:T], vFLOW[l, t] <= EP[:eAvail_Trans_Cap][l]
+            cMaxFlow_in[l = 1:L, t = 1:T], vFLOW[l, t] >= -EP[:eAvail_Trans_Cap][l]
+        end)
+
     # Bus angle limits (except slack bus)
     @constraints(EP,
         begin