Power compensation approach and double frame control for grid connected converters

The handling of weak networks with asymmetric disturbances implies the accurate handling of the second harmonic component appearing under unbalanced networks. This paper proposes a two-step approach using classic vector control for operating the current controller from the network disturbance. First, both voltage and current must be described in the positive and negative sequence with a proper decoupling. The use of a double frame controller for forcing current balance proves to drastically reduce the second harmonic component in the DC-link voltage. As a second step, a current reference computing method is proposed for fully compensating power oscillations on the DC side that is applicable for phase voltage dips up to 50%.