Detailed Descriptions Of The Function Modules; Additional Closed-Loop Controls For Current-Controlled Operation; Background Information - Siemens SINAMICS S120 System Manual

Detailed descriptions of the function modules

6.1

Additional closed-loop controls for current-controlled operation

6.1.1

Background information

The following diagram shows the control structure of a grid inverter for feeding power into a
power grid, together with a typical system configuration. The function blocks added to
comply with the different global grid codes are marked in gray. However, it should be noted
that the complete standards can only be complied with by considering the complete
generating system as a whole, e.g. with a drive component, so that for a grid overfrequency
condition, the active power can be reduced.
The control always operates in rotating active-reactive coordinates with the grid frequency;
VDC controller and active current controller form a cascade structure. Using the Park
transformation technique, the output voltages of the active and reactive current controllers
are converted into space phasors with stationary αβ coordinates or into phase voltages. A
PWM modulator determines the switching operations of the grid inverter for the next pulse
clock. The grid phase angle required for the Park transformation is calculated from the grid
voltages using a PLL.
Grid infeed
System Manual, 04/2015, A5E03347436A
6
49