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Part 2: Control value determination

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Note

The content on this page refers only to the blue'Log XC combined with the Hybrid EMS licence.


The control value is a value dynamically calculated by the controller. This value corresponds to the reactive power required from the entire plant to reach the setpoint.

image-20260206-143655.png
Reactive power controller: control value determination

The core of the controller consists of a fast feed-forward PI controller that can operate in open or closed-loop:

  • Closed-loop: The controller continuously compares the setpoint with the measured value. It dynamically adapts the control value sent to the inverters to compensate for any differences between the setpoint and the measured value.

  • Open-loop: The controller processes the setpoint without taking the feedback from the measured reactive power into account. It does not compensate for differences between the setpoint and the measured value.

Select the desired control loop under Power Control > Reactive Power > Controller settings.


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Example

The setpoint is 1000 kVAr. Due to network effects (e.g. connected loads, cables), 300 kVar of reactive power is consumed on-site and do not reach the grid connection point (measuring point).

Closed-loop

  • The controller calculates the error between the setpoint and measured value.

  • The result is a control value of 1000 kVAr + 300 kVAr = 1300 kVAr.

  • This value is sent to the inverters to reach the setpoint at the grid connection point.

  • Qsetpoint = 1000 kVAr, Qmeasured = 1000 kVAr, Qcontrol value = 1300 kVAr

Open-loop

  • The setpoint is processed without measured feedback.

  • The inverters receive a control value of 1000 kVAr.

  • The setpoint of 1000 kVar is not achieved at the grid connection point.

  • Qsetpoint = 1000 kVAr, Qmeasured = 700 kVAr, Qcontrol value = 1000 kVAr

Note: In the examples, the control values are given in absolute terms (kVAr) for illustration purposes only. The blue’log XC usually sends relative values (%) as control values to the inverters.

Configure specific controller parameters under Control Power Control > Reactive power > Extended Settings > Controller Tuning. For details about the specific controller parameters for PV and battery, hover over the image-20260114-145025.png Info icons next to each parameter.

For configuration assistance, we recommend our project-specific controller tuning services. For more information, see Project-specific controller tuning blue'Log XC and contact Sales.