Compound Control System of Hybrid Distribution Transformer

Hybrid distribution transformer (HDT) is a promising device for constructing the future active distribution network. To overcome the limitations of the existing HDT control schemes, a compound control scheme is proposed for an HDT with improved circuit design. In this design, the voltage source converter (VSC) for low-voltage side voltage regulation is moved to the medium-voltage side. The compound control scheme is developed based on the dynamic model of this new HDT, which explicitly considers the external disturbances. In this control scheme, two compound controllers are established to regulate the grid current and load voltage, respectively. For each compound controller, feedforward loops are integrated with the PI regulator, thus suppressing the disturbances. The key feature of this control scheme is that, by using the feedforward loops, the effect of external step disturbance can be equivalently weaken to an impulse disturbance and, hence, the system robustness can be improved. Simulation and experimental results validate the effectiveness of the proposed control scheme.