control side being further side in doc requirement

Signed-off-by: Jerry Guo <Jerry.Jinfeng.Guo@alliander.com>

Author: Jerry-Jinfeng-Guo

docs/user_manual/components.md

@@ -804,18 +804,19 @@ The actual grid state is not changed after calculations are done.
 
 #### Input
 
-| name                       | data type                                                                                                                                                                                                                                                                                                          | unit     | description                                                                                             |           required           |  update  |   valid values    |
-| -------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | -------- | ------------------------------------------------------------------------------------------------------- | :--------------------------: | :------: | :---------------: |
-| `control_side`             | {py:class}`BranchSide <power_grid_model.enum.BranchSide>` if the regulated object is a {hoverxreftooltip}`user_manual/components:transformer` and {py:class}`Branch3Side <power_grid_model.enum.Branch3Side>` if it the regulated object is a {hoverxreftooltip}`user_manual/components:Three-Winding Transformer` | -        | the controlled side of the transformer                                                                  | &#10024; only for power flow | &#10060; |                   |
-| `u_set`                    | `double`                                                                                                                                                                                                                                                                                                           | volt (V) | the voltage setpoint (at the center of the band)                                                        | &#10024; only for power flow | &#10004; |      `>= 0`       |
-| `u_band`                   | `double`                                                                                                                                                                                                                                                                                                           | volt (V) | the width of the voltage band ($=2*\left(\Delta U\right)_{\text{acceptable}}$)                          | &#10024; only for power flow | &#10004; | `> 0` (see below) |
-| `line_drop_compensation_r` | `double`                                                                                                                                                                                                                                                                                                           | ohm (Ω)  | compensation for voltage drop due to resistance during transport (see [below](#line-drop-compensation)) |    &#10060; default `0.0`    | &#10004; |      `>= 0`       |
-| `line_drop_compensation_x` | `double`                                                                                                                                                                                                                                                                                                           | ohm (Ω)  | compensation for voltage drop due to reactance during transport (see [below](#line-drop-compensation))  |    &#10060; default `0.0`    | &#10004; |      `>= 0`       |
+| name                       | data type                                                                                                                                                                                                                                                                                                          | unit     | description                                                                                             |           required           |  update  |                            valid values                          |
+| -------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | -------- | ------------------------------------------------------------------------------------------------------- | :--------------------------: | :------: | :--------------------------------------------------------------: |
+| `control_side`             | {py:class}`BranchSide <power_grid_model.enum.BranchSide>` if the regulated object is a {hoverxreftooltip}`user_manual/components:transformer` and {py:class}`Branch3Side <power_grid_model.enum.Branch3Side>` if it the regulated object is a {hoverxreftooltip}`user_manual/components:Three-Winding Transformer` | -        | the controlled side of the transformer                                                                  | &#10024; only for power flow | &#10060; | `control_side` should be the relatively further side to a source |
+| `u_set`                    | `double`                                                                                                                                                                                                                                                                                                           | volt (V) | the voltage setpoint (at the center of the band)                                                        | &#10024; only for power flow | &#10004; |                               `>= 0`                             |
+| `u_band`                   | `double`                                                                                                                                                                                                                                                                                                           | volt (V) | the width of the voltage band ($=2*\left(\Delta U\right)_{\text{acceptable}}$)                          | &#10024; only for power flow | &#10004; |                          `> 0` (see below)                       |
+| `line_drop_compensation_r` | `double`                                                                                                                                                                                                                                                                                                           | ohm (Ω)  | compensation for voltage drop due to resistance during transport (see [below](#line-drop-compensation)) |    &#10060; default `0.0`    | &#10004; |                               `>= 0`                             |
+| `line_drop_compensation_x` | `double`                                                                                                                                                                                                                                                                                                           | ohm (Ω)  | compensation for voltage drop due to reactance during transport (see [below](#line-drop-compensation))  |    &#10060; default `0.0`    | &#10004; |                               `>= 0`                             |
 
 The following additional requirements exist on the input parameters.
 
 - Depending on the resultant voltage being transformed, the voltage band must be sufficiently large: At zero line drop compensation if the expected resultant voltages are in the proximity of the rated transformer voltages, it is recommended to have the $u_{band} >= \frac{u_2}{1+ u_1 / \text{tap}_{\text{size}}}$
 - The line drop compensation is small, in the sense that its product with the typical current through the transformer is much smaller (in absolute value) than the smallest change in voltage due to a change in tap position.
+- The `control_side` of a transformer regulator should be on the relatively further side to a source in the connected grid.
 
 These requirements make sure no edge cases with undefined behavior are encountered. Typical real-world power grids already satisfy these requirements and they should therefore not cause any problems.