Closed-Loop Ac Voltage Control; External Grid Synchronization - Danfoss iC7 Series Operating Manual

Voltage measurement option

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Operating Guide | Voltage Measurement Option OC7V0

Figure 12: Line Filter Energization and Transformer Magnetization

Closed-loop AC Voltage Control

6.3

The grid converter control can be connected to different network nodes by using the Voltage Measurement Option OC7V0. For example,

the voltage can be measured upstream of the line filter or the main transformer. The measurement location is configured in the

application using the user parameter. An auxiliary voltage measurement transformer is used to step down the voltage to the input

range of the Voltage Measurement Option OC7V0. Thus the measurement can be taken from medium voltage. The voltage loss across

the transformer impedance is compensated using the closed-loop control when the measurement is from the load side. Open-loop

transformer voltage drop compensation is available when the feedback is from the converter side.

Figure 13: Closed-loop AC Voltage Control

6.4

The grid converter can supply an island microgrid and the Voltage Measurement Option OC7V0 can measure the external grid voltage

on the other side of the tie breaker. With the help of the measurement, the grid converter can synchronize the islanded system voltage

with the external grid before the tie breaker is closed. Thus the current transients involved in the breaker closure are minimized. In

addition, there is no need for auxiliary synchronizer equipment. If there are transformers between the 2 circuit nodes, configure the

phase difference of the converter voltage at the external grid measurement point.

Figure 14: External Grid Synchronization

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Oc7v0