Trajectory-Switching-Modulation-Based Fast Power Transient Control Strategy for a Bidirectional Hybrid Modular DC Transformer

The hybrid modular dc transformer (HMDCT) combining the series resonant dual active bridge (SR-DAB) and phase shift dual active bridge (PS-DAB) has the advantages of high efficiency and bidirectional power regulation. However, due to the unregulated SR-DAB resonant tank inertia and limited PS-DAB output power, the dynamic response of HMDCT is slower than the pure PS-DAB-based DCT, which could lead to a larger output overshoot. To address the problems, first, a novel trajectory-switching-modulation (TSM) method is proposed to control the SR-DAB resonant tank to track the desired state trajectory rapidly using SR-DAB switch states. Compared with the conventional $LLC$ trajectory control, TSM is more suitable for the SR-DAB in the bidirectional HMDCT because TSM is available under bidirectional power flow without changing the topology or increasing the magnetizing losses. Then, a TSM-based fast power transient control strategy (TSM-FPTC) is proposed to improve the bidirectional HMDCT dynamic performance by controlling the PS-DAB and SR-DAB simultaneously. Besides, PS-DAB current stress can also be reduced during the load transients. Experimental results show that the proposed strategy has better dynamic performance than the classic proportional–integral (PI) feedforward-based strategy.