DC-Link Split Capacitors Voltage Balancing Control of Hybrid Distribution Transformer

The dc-link split capacitors' voltage unbalance will damage the normal operation of a hybrid distribution transformer (HDT). Based on the derived dynamic models related to the dc-link of HDT, this article reveals that the dc component of the load currents, modulating dc bias, sampling dc bias, and the capacitors parameters derivation are the main factors leading to the voltages unbalancing, and the active control of the grid currents' zero-sequence component is a simple and key method to eliminating this unbalance. To address these, the split capacitors' voltage balancing control strategy with proportional-integral (PI) controller is developed. To eliminate the static error and improve the system's dynamic performance, the quasi-resonant regulators and load-neutral current feed-forward are added to the PI controller, thus formulating a novel controller. Simulation and experimental results validate the effectiveness of the proposed novel control strategy.