Active Load Stabilization of Cascaded Systems in DC Microgrids Using Adaptive Parallel-Virtual-Resistance Control Scheme

Cascaded configuration of source- and load-side subsystems is a prominent connection form in multi-converter based low voltage power distribution networks (e.g., DC microgrids). Despite instability arising from interactions between the individually designed feedback-controlled converters, supplying active loads that act in a tightly regulated fashion, such as constant power loads (CPLs), can yield system instability. In this work, a new source-side active stabilizing scheme is presented based on positive proportional-derivative feedback of the equivalent load current with an intrinsic self-tuning control parameter. It introduces an adaptive-parallel-virtual-resistance (APVR) strategy without affecting the dynamic performance of the load converter. Using this precise control approach that benefits simple structure in design with straightforward control parameter adjustment, the system stability is ensured by actively suppressing CPL destabilizing effect. Moreover, the high robustness and desirable dynamic performance of the APVR strategy are authenticated by considering the plug-and-play of CPLs and unforeseen variations in input voltage amplitude without knowledge of their value. The operational principles and control concepts of the suggested active stabilizer for the three basic DC/DC converters feeding CPLs in cascaded structures are discussed analytically. The effectiveness and flexibility of the APVR method for these systems have been validated using the simulation and experimental results.