Novel individual phase current control with self-adaption unbalanced-voltage handling capability for power electronics transformer

This paper proposes a novel individual phase current control scheme for star-connected cascaded power electronics transformer (PET) under unbalanced grid voltage conditions, and PET mainly combines the cascaded H-bridge converter with resonant DC-DC converters (CLLC) between medium-voltage distribution and low-voltage customer DC side. Compared with traditional DQ decoupling current control, each cluster of cascaded PET has its own phase current control loop mainly adopting proportional resonant (PR) controller with feed-forward admittance compensation. The proposed control system can offer the operational flexibility for active and reactive power control for medium-voltage AC side based on the simplified single-stage control system structure concept thanks to the characteristics of CLLC resonant converters working under the quasi-resonant frequency mode. Additionally, compared to the existing PET control systems, it offers better features such as simpler control system, self-adaption regulation current, etc. To illustrate the feasibility of the proposed control system, this paper assesses its dynamic performance during normal and unbalanced grid voltages states.