Distributed DC-Bus Signaling Control of Photovoltaic Systems in Islanded DC Microgrid

The stability of an islanded DC microgrid (DCMG) is highly dependent on the presence and performance of the backup energy storage system (BESS), due to the lack of main grid support. This condition makes the DCMG vulnerable to the critical situation of absence of the BESS, which could be caused by a fault or being fully charged or flat. This paper presents an enhanced distributed DC-bus signaling control strategy for converters of photovoltaic systems (PVs) to make the islanded DCMG less dependent on the BESS. Unlike a conventional control approach that utilizes PVs to operate in maximum power point tracking (MPPT) mode and the BESS solely regulating DC-bus voltage, the proposed control method maintains DC-bus voltage via intelligently managing output powers of the PVs. The proposed control method continuously monitors DC-bus voltage and regulates the output powers of all the PVs via switching between MPPT mode and voltage regulating mode. Accordingly, if the DC-bus voltage level is less than a predefined maximum level, the PVs work in MPPT mode; otherwise, the PVs work in voltage regulating mode to maintain DC-bus voltage at an acceptable range. Such switching between MPPT and voltage regulating control operations results in protecting the DCMG from unavoidable shutdowns conventionally necessary during the absence of the BESS unit. Moreover, the proposed control method reduces oscillations on the DC-bus voltage during existence of the BESS. The performance and effectiveness of the proposed control strategy are validated through different case studies in MATLAB/Simulink.