High-Efficiency Control Strategy for 10-kV/1-MW Solid-State Transformer in PV Application

This article proposes a systematic control strategy for solid-state transformer (SST) composed of dual active bridge (DAB) and cascaded H-bridge, which increases SST efficiency over a wide operating range in PV application. In real practice, the PV panel presents a wide voltage range, which could significantly affect SST efficiency, mainly for DAB. To improve the efficiency, a universal loss model for DAB under frequency domain analysis is established. Based on this, the optimum efficiency modulation scheme is derived. Besides the efficiency improvement of DAB from the modulation scheme, this article fully explores extra control freedom, which is an intermediate voltage between DAB and H-bridge. Then, the variable intermediate voltage control scheme is proposed, which reduces the conduction loss and switching loss of DAB. Furthermore, zero-sequence modulation signal injection and the proportional-resonant controller is implemented in the proposed control strategy, which expands the range for further efficiency improvement. Finally, to verify the effectiveness of the proposed method, the experiment is carried out on the submodule and 10-kV/1-MW SST real scale prototype. Under the proposed method, the SST system achieves 0.9% efficiency improvement compared with the conventional method.