Power Flow Analysis and DC-link Voltage Control of Hybrid Distribution Transformer

DC-link voltage control is a key issue for the reliable operation of hybrid distribution transformers (HDTs). This article uncovers the basic power flow principle of HDT based on the established dynamic power balance equations and the proposed power flow diagrams. Based on the derived differential equations and the transfer function models, the dc-link voltage control system with PI controller is developed. With the pure PI controller, the grid currents distortion and asymmetry cannot be well eliminated. To address this, an improved controller that includes a low-pass filter and three notch filters is designed. A disturbance feedforward loop is integrated into the improved controller, thus formulating a novel controller. This novel controller not only controls the dc-link voltage and grid currents with better dynamic performance but also eliminates distortion and asymmetry. Simulation and experiment results verify the correctness of the analyses and proposed methods.