Dynamic operation of the controller

The functional diagram of the controller is shown in Figure 11 - 9. This pole control function is the same for the rectifier and the inverter.

Functional Diagram of the Regulation Unit

The regulation unit essentially consists of two PI (proportional-integral) regulators with limiters: one for the current and the other for the voltage. The delay angle is established by the lowest value among the outputs of the two regulators.

On the rectifier side, the reference current Idref takes on a normal value (e.g. < 1.2 p.u.) while the voltage reference Vdref takes on a very high value (e.g. 2 p.u.). In this way, the regulation unit cannot regulate the voltage and will be forced to operate in current regulation mode. A signal allows users to apply a current reference step for a specified time interval.
On the inverter side, a current margin ΔI is subtracted from the inverter reference, usually equal to that of the rectifier, so that in normal state, there is a ΔI error at the PI input. The inverter regulates the voltage at the DC line input.