Add ECM variables

pybamm/models/full_battery_models/base_battery_model.py

@@ -786,14 +786,17 @@ def set_voltage_variables(self):
 
         # Battery-wide variables
         V_dim = self.variables["Terminal voltage [V]"]
+        eta_e_av = self.variables.get("X-averaged electrolyte ohmic losses", 0)
+        eta_c_av = self.variables.get(
+            "X-averaged concentration overpotential", 0
+        )
         eta_e_av_dim = self.variables.get("X-averaged electrolyte ohmic losses [V]", 0)
         eta_c_av_dim = self.variables.get(
             "X-averaged concentration overpotential [V]", 0
         )
         num_cells = pybamm.Parameter(
             "Number of cells connected in series to make a battery"
         )
-
         self.variables.update(
             {
                 "X-averaged battery open circuit voltage [V]": ocv_av_dim * num_cells,
@@ -809,6 +812,36 @@ def set_voltage_variables(self):
                 "Battery voltage [V]": V_dim * num_cells,
             }
         )
+        # Variables for calculating the equivalent circuit model (ECM) resistance
+        # Need to compare OCV to initial value to capture this as an overpotential
+        ocv_init = self.param.U_p(
+            self.param.c_p_init(1), self.param.T_init
+        ) - self.param.U_n(self.param.c_n_init(0), self.param.T_init)
+        ocv_init_dim = (
+            self.param.U_p_ref
+            - self.param.U_n_ref
+            + self.param.potential_scale * ocv_init
+        )
+        eta_ocv = ocv - ocv_init
+        eta_ocv_dim = ocv_dim - ocv_init_dim
+        # Current collector current density for working out euiqvalent resistance
+        # based on Ohm's Law
+        i_cc = self.variables["Current collector current density"]
+        i_cc_dim = self.variables["Current collector current density [A.m-2]"]
+        # Gather all overpotentials
+        v_ecm = -(eta_ocv + eta_r_av + eta_c_av + eta_e_av + delta_phi_s_av)
+        v_ecm_dim = -(eta_ocv_dim + eta_r_av_dim + eta_c_av_dim + eta_e_av_dim +
+                      delta_phi_s_av_dim)
+        # Current collector area for turning resistivity into resistance
+        A_cc = self.param.A_cc
+        self.variables.update(
+            {
+                "Change in measured open circuit voltage": eta_ocv,
+                "Change in measured open circuit voltage [V]": eta_ocv_dim,
+                "Local ECM resistance": v_ecm / (i_cc * A_cc),
+                "Local ECM resistance [Ohm]": v_ecm_dim / (i_cc_dim * A_cc),
+            }
+        )
 
         # Cut-off voltage
         voltage = self.variables["Terminal voltage"]