In order to optimally use photovoltaic energy, it is necessary to use the energy surplus variably in times of high PV yield. Flexible energy storage systems, such as a car battery, help to absorb the energy surplus. In the case of car batteries, it must be taken into account that, on the one hand, a maximum of surplus energy should be used, but there are also specifications when the battery must be available for use.
To realise this task, a logic group is used for control in the EIBPORT. For communication with a charging station (wallbox), the APPMODULE is used with the corresponding Smart Home App.
The direct communication of the controller with the wallbox enables dynamic charging in accordance with the PV energy yield.
2 outputs are available for presetting the charging power:
- The available charging power in W, provided that the wallbox can be controlled with it.
- A percentage value: possible charging power in relation to the maximum charging power.
Not included are functions such as monitoring the battery level or stopping charging when the battery is full.
- The charging of the car battery is carried out with variable power. Depending on the available values of the wallbox, the complete status of the vehicle battery can be monitored in addition to the power monitoring for charge control and, if necessary, other functions (charging time, battery level, etc.) can be used for control.
About the function of the logic group
The measured values of the service recording reach a statistics element via the intermediate storage (buffer) every minute. In the statistics element, 10 values are recorded, the mean value is calculated and then sent every 10 minutes. The averaging and the 10-minute interval serve to smooth the measured value for the switching threshold and the power specification for charging. An upper and lower switching threshold is set by the user, whereby the lower switching threshold can be provided with an offset for switching back, otherwise enter an O. This is to prevent charging from not taking place. This is to prevent charging from being too short, even if this means leaving the PV surplus range. When charging, the measured power value must be corrected by the power value of the charging (Wallbox) so that the switching thresholds are not shifted.
Based on the feedback from the wallbox, the correction is realistic, even if the power specification for charging is higher.
Enabling "ON" activates the logic group and "OFF" stops the logic group, as well as the switching command to the wallbox is suspended to "OFF".
The integrated start value is required so that the logic group has a defined output value.
Input values (settings of the user)
Charging station counter
Is the charging power that is read out by the wallbox as a value via the APPMODULE. as this is specified by the wallbox, for example, or must be preset. The measured value is positive.
(EIS9, DPT 14.xxx 4 byte float)
Counter current power
The power values of the house connection meter (bidirectional meter). Where positive values are consumption (power drawn) and negative values are yield (power fed into the public grid).
(EIS9, DPT 14.xxx 4 byte float)
Release
Activation of the pulse generator to start the logic group. With "OFF", the pulse generator stops and the switching command to the wallbox is set OFF.
(EIS1, DPT 1.xxx)
FB Switching
Is the feedback, e.g. of the wallbox, when it is in charging mode. Without active feedback, it is the same group address that is used to switch the wallbox. The feedback from the wallbox starts the correction loop for power equalisation with the power drawn from the wallbox.
(EIS1, DPT 1.xxx).
Switching threshold
Is the limit value for switching to "charging" mode. Only negative values are possible (feed-in level), which would otherwise be fed into the public grid. The user can decide here from which value charging begins, so that the battery is also charged with less yield.
(EIS9, DPT 14.xxx 4 byte float)
Power OFF Offset
Only positive values apply here; from when charging is stopped. The limit value is the sum of the switching threshold plus the power OFF offset.
(EIS9, DPT 14.xxx 4 byte float)
Max. Charging power
For a percentage specification of the charging power, the maximum charging power is entered here.
(EIS9, DPT 14.xxx 4 byte float)
Output values
Value Energy Charging
Is the group address for the available charging power in the PV surplus range. If there is no surplus, the default value here is 0 (no charging).
(EIS9, DPT 14.xxx 4 byte float)
Switching (loading)
Is the group address to switch charging on or off (EIS1, DPT 1.xxx)
Power control
Is the group address for the available charging power in %, in relation to the maximum power of a wallbox. If there is no surplus, the default value here is 0% (no charging).
(EIS5, DPT 6.xxx 1 byte)
Uwe Müller
Haus-Bus-Systeme.de
(230; 2022.09)
