Quasi-Proportional-Resonant Control for the Hybrid Distribution Transformer With LCL-Type Converters

Hybrid distribution transformer (HDT) is realized by augmenting the traditional low-frequency transformer with a fractionally rated converter. This article improves the HDT topology by assembling the LCL-type converters and presents the grid currents and load voltages quasi-proportional-resonant (PR) control strategies for this improved HDT. The PR control schemes are developed based on the established stationary frame dynamic models of HDT, and the effects of the controller parameters and LCL-filter parameters variation on the HDT's control performance and harmonic suppression ability are analyzed by the Bode diagrams and step responses. The key feature of this article is that, by using the resonant controller and LCL-type filters, the complex coordinate transformation can be avoided and the high-frequency harmonics can be well suppressed in the HDT application. The simulation and experiment results verify the effectiveness of the improved HDT and the proposed control strategies.