Feedback Linearization-Based Load-Current Feedforward Control Strategy for Fast Dynamic Response of Hybrid Modular DC Transformers

The hybrid modular dc transformer (HMDCT), combining the series resonant dual active bridge (SR-DAB) and phase-shift dual active bridge (PS-DAB), is very suitable for dc bus interlinking applications with bidirectional controllability and high efficiency requirements. However, the coupling between SR-DAB and PS-DAB sub-modules results in a strongly nonlinear dynamic behavior, which in turn poses challenges in instantaneously and coordinately regulating each sub-module to achieve a fast dynamic response of the HMDCT total output. To solve this problem, this article proposes the HMDCT nonlinear input–output large-signal model and a state feedback linearization-based load-current feedforward control (LCFC) strategy. The proposed strategy constructs a linear, load-independent, and easily controllable input–output relationship, while achieving accurate observation of physically nonexistent feedback states in the nonlinear system without relying on complex sampling algorithms and circuits. The system stability including controlled states and uncontrolled internal dynamics is proved, providing a theoretical basis for practical applications. Furthermore, to reduce implementation complexity, the proposed strategy is simplified into improved LCFC form with easily understood physical meaning and less computational effort. Experimental results on a HMDCT prototype show that the proposed strategy significantly improves the dynamic performance in bidirectional operating directions, compared to the conventional feedforward-based strategy.