Flexible direct control of power oscillations in converters to meet various grid requirements under unbalanced conditions

Grid-connected power converters must comply with the grid code requirements under unbalanced grid conditions. To address the issue, five control targets are considered in this paper. In order to achieve the targets, this paper proposes a model-free direct power control (DPC), which enables flexible control of active and reactive power oscillations with a power-limiting strategy. The proposed method utilizes only the information of the grid voltage vector and its perpendicular one that lags 90 electrical degrees to avoid any positive and negative sequence extraction of grid voltages and currents. Compared to power-decoupling DPC, the method is model-free, avoids signal extraction, and enjoys flexibility and power-limiting control. Compared to combined control methods, the proposed DPC is not sensitive to system parameters, does not need any filters and converter voltage signals, and exhibits flexible power control with power limiting. The method is examined through both simulation and experimental studies, and its operation is compared with three existing combined control methods. The results demonstrate the effectiveness of the proposed method and its superiority over the combined control methods.