Add a doc page about converters and constants (#132)

Resolves #101

doc/Changelog.md

@@ -4,6 +4,7 @@
 
 **In development**
 
+- {gh-pr}`132` {gh-issue}`101` Document extra utilities including converters and constants.
 - {gh-pr}`130` Mark some internal attributes as private, they were previously marked as public.
 - {gh-pr}`128` Add the properties `z_line`, `y_shunt` and `with_shunt` to the `Line` class.
 - {gh-pr}`125` Speed-up build of conda workflow using mamba.

doc/usage/Extras.md

@@ -0,0 +1,103 @@
+# Extras
+
+`roseau-load-flow` comes with some extra features that can be useful for some users.
+
+## Conversion to symmetrical components
+
+{mod}`roseau.load_flow.converters` contains helpers to convert between phasor and symmetrical
+components. For example, to convert a phasor voltage to symmetrical components:
+
+```pycon
+>>> import numpy as np
+>>> from roseau.load_flow.converters import phasor_to_sym, sym_to_phasor
+>>> v = 230 * np.exp([0, -2j * np.pi / 3, 2j * np.pi / 3])
+>>> v
+array([ 230.  +0.j        , -115.-199.18584287j, -115.+199.18584287j])
+>>> v_sym = phasor_to_sym(v)
+>>> v_sym
+array([[ 8.52651283e-14-1.42108547e-14j],
+       [ 2.30000000e+02+4.19109192e-14j],
+       [-7.10542736e-14-2.84217094e-14j]])
+```
+
+As you can see, for this positive-sequence balanced voltage, only the positive-sequence component
+is non-zero. Converting back to phasor, you get the original voltage values back:
+
+```pycon
+>>> sym_to_phasor(v_sym)
+array([[ 230.-7.21644966e-16j],
+       [-115.-1.99185843e+02j],
+       [-115.+1.99185843e+02j]])
+```
+
+You can also convert pandas Series to symmetrical components. If we take the example network of the
+[Getting Started](Getting_Started.md) page:
+
+```pycon
+>>> from roseau.load_flow.converters import series_phasor_to_sym
+>>> series_phasor_to_sym(en.res_buses_voltages["voltage"])
+bus_id  sequence
+lb      zero        8.526513e-14-1.421085e-14j
+        pos         2.219282e+02+4.167975e-14j
+        neg        -5.684342e-14-2.842171e-14j
+sb      zero        9.947598e-14-1.421085e-14j
+        pos         2.309401e+02+3.483159e-14j
+        neg        -4.263256e-14-2.842171e-14j
+Name: voltage, dtype: complex128
+```
+
+## Potentials to voltages conversion
+
+{mod}`roseau.load_flow.converters` also contains helpers to convert a vector of potentials to a
+vector of voltages. Example:
+
+```pycon
+>>> import numpy as np
+>>> from roseau.load_flow.converters import calculate_voltages, calculate_voltage_phases
+>>> potentials = 230 * np.array([1, np.exp(-2j * np.pi / 3), np.exp(2j * np.pi / 3), 0])
+>>> potentials
+array([ 230.  +0.j        , -115.-199.18584287j, -115.+199.18584287j,
+          0.  +0.j        ])
+>>> phases = "abcn"
+>>> calculate_voltages(potentials, phases)
+array([ 230.  +0.j        , -115.-199.18584287j, -115.+199.18584287j])
+```
+
+Because the phases include the neutral, the voltages calculated are phase-to-neutral voltages.
+You can also calculate phase-to-phase voltages by omitting the neutral:
+
+```pycon
+>>> calculate_voltages(potentials[:-1], phases[:-1])
+array([ 345.+199.18584287j,    0.-398.37168574j, -345.+199.18584287j])
+```
+
+To get the phases of the voltage, you can use `calculate_voltage_phases`:
+
+```pycon
+>>> calculate_voltage_phases(phases)
+['an', 'bn', 'cn']
+```
+
+Of course these functions work with arbitrary phases:
+
+```pycon
+>>> calculate_voltages(potentials[:2], phases[:2])
+array([345.+199.18584287j])
+>>> calculate_voltage_phases(phases[:2])
+['ab']
+>>> calculate_voltage_phases("abc")
+['ab', 'bc', 'ca']
+>>> calculate_voltage_phases("bc")
+['bc']
+>>> calculate_voltage_phases("bcn")
+['bn', 'cn']
+```
+
+## Constants
+
+{mod}`roseau.load_flow.utils.constants` contains some common constants like the resistivity
+and permeability of common conductor types in addition to other useful constants. Please refer to
+the module documentation for more details.
+
+An enumeration of available conductor types can be found in the {mod}`roseau.load_flow.utils.types`
+module.

doc/usage/index.md

@@ -13,4 +13,5 @@ Flexible_Loads
 Short_Circuit
 Catalogues
 Plotting
+Extras
 ```

roseau/load_flow/utils/constants.py

@@ -38,17 +38,17 @@
     ConductorType.CU: Q_(1.2566e-8, "H/m"),
     ConductorType.AL: Q_(1.2566e-8, "H/m"),
     ConductorType.AM: Q_(1.2566e-8, "H/m"),
-    ConductorType.AA: np.nan,  # TODO
-    ConductorType.LA: np.nan,  # TODO
+    ConductorType.AA: Q_(np.nan, "H/m"),  # TODO
+    ConductorType.LA: Q_(np.nan, "H/m"),  # TODO
 }
 """Magnetic permeability of common conductor materials (H/m)."""
 
 DELTA_P = {
     ConductorType.CU: Q_(9.3, "mm"),
     ConductorType.AL: Q_(112, "mm"),
     ConductorType.AM: Q_(12.9, "mm"),
-    ConductorType.AA: np.nan,  # TODO
-    ConductorType.LA: np.nan,  # TODO
+    ConductorType.AA: Q_(np.nan, "mm"),  # TODO
+    ConductorType.LA: Q_(np.nan, "mm"),  # TODO
 }
 """Skin effect of common conductor materials (mm)."""