Precise current sharing and decentralized power management schemes based on virtual frequency droop method for LVDC microgrids

One of the challenging issues in DC microgrids attracted by many researchers is the current sharing enhancement among distributed generations (DGs) with different rated currents and/or lines impedances. In this paper, DG topology is considered comprising photovoltaic (PV) system as power resource and battery energy storage system (BESS). By inspecting the frequency droop control of synchronous generators, a unique corrective sinusoidal term is added to the output voltage in DC-DC converters of each DG with purpose of current sharing control between DC DGs based on their nominal capacities. This virtual decentralized current sharing scheme named as the frequency droop method (FDM) can accurately regulate the point of common coupling (PCC) voltage without any communication link. Moreover, a decentralized power management scheme with different operating modes for PV system and BESS is proposed in this paper based on the state of charge of BESS and the frequency obtained from FDM scheme. The performance of FDM and power management schemes is investigated by time domain off-line and real-time simulations in MATLAB/SIMULINK environment. Seven case studies are implemented considering the effects of load and solar irradiance variations under equality and inequality of lines impedances as well as rated currents, mode transition, and plug-and-play ability. By applying the proposed control schemes, the purposes of precise current sharing and DC-link voltage regulation are achieved smoothly with an acceptable transient compared to an existing power sharing method. Also, FDM scheme is more reliable than available methods due to its independence on line impedance.