Operation
7.21 Technological functions
SINAMICS DCP
Operating Instructions, 09/2019, A5E34382853K
399
Figure 7-96 Characteristic of a PV array
The characteristic of a PV array, and therefore also the position of the MPP, changes
depending on the intensity of the solar radiation and the temperature.
Two characteristics for different radiation intensities with the applicable MPP are shown in
the diagram above.
The diagram indicates that the MPP position can change significantly during operation.
Therefore, this point must be searched for and corrected continuously. An MPP tracker is
used for this purpose.
The MPP tracker is based on the following principle of operation:
When required, after switching on, the DCP can execute function "PV array flying restart"
(see Chapter "PV array flying restart (Page 347)"). To do this, current is drawn from the PV
array, and starting from the high no-load voltage, the terminal voltage is reduced so that its
lies within the permissible voltage range of the DCP.
The actual PV array characteristic is then determined. To do this, starting at zero, the current
setpoint is increased in small steps by the current step selected (p54006) and the power
measured.
As soon as the complete PV array characteristic has been measured, the global MPP of the
PV array is determined from the captured data.
The current setpoint is then set to the MPP, and the algorithm starts to operate as follows:
Dependent on the change in the power in the previous step, the current setpoint is increased
or decreased by the current step (p54006).
● The direction of this change is kept if the power had increased with the previous current
setpoint change.
– Current setpoint was reduced → current setpoint is reduced further
– Current setpoint was increased → current setpoint is increased further
● The direction of this change is reversed if the power had decreased with the previous
current setpoint change.
– Current setpoint was reduced → current setpoint is now increased.
– Current setpoint was increased → current setpoint is now decreased.
In the steady-state (settled) condition, the current setpoint then continually oscillates around
the global point of maximum power (MPP).
This search algorithm is restricted to an adjustable range (p54037) around the global
maximum.
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