Synchronverter-Enabled DC Power Sharing Approach for LVDC Microgrids

In a classical ac microgrid (MG), a common frequency exists for coordinating active power sharing among droop-controlled sources. Like the frequency-droop method, a voltage-based droop approach has been employed to control the converters in low voltage direct current (LVDC) MGs. However, voltage variation due to the droop gains and line resistances causes poor power sharing and voltage regulation in dc MG, which in most cases are solved by a secondary controller by using a communication network. To avoid such an infrastructure and its accompanied complications, this paper proposes a new droop scheme to control dc sources by introducing a small ac voltage superimposed onto the output dc voltage of converters. Therefore, dc sources can be coordinated together with the frequency of the ac voltage, without any communication network like synchronous generators (SGs) in conventional power systems. Small signal stability analysis, as well as mathematical calculations, is presented to demonstrate the analogy between the proposed strategy and frequency-based droop approach of the SGs. The effectiveness of the proposed control system is evaluated by simulations and verified by experiments.