Active Damping of DC Transformer with ISOP Structure Based on Impedance Reshaping

The DC transformers (DCTs) constructed by input-series-output-parallel (ISOP) structure with dual active bridge (DAB) submodules (SMs) would face the risk of instability due to the equivalent inductance of input power line, which are neglected in most existing research. This work evaluates the stability characteristics of DCTs and proposes an active damping method for DCTs to ensure the stability. First, the input impedance of DCT is derived. Then, the stability characteristics of DCT are analyzed based on Nyquist Criterion. Next, an impedance reshaping control scheme (IRCS) for DCT is proposed to reshape the input impedance of DCT to achieve stabilization, which is easy to be implemented and no additional sensors are needed. Finally, the relevant experiments validate the performance of IRCS.