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• The present study aimed to develop a new model of a smart PV inverter with novel control schemes. • The proposed LVRT control strategy improved the voltage drop caused by the line-to-line-to-ground fault. • The central control system changed the switching mode of the inverter in the islanded mode. This article proposes a central control system that communicates with both grid-tied and off-grid control systems to offer various control strategies for operating a smart photovoltaic (PV) inverter. The target is to connect two sets of PV panels and one set of battery storage unit to either a 440 V/60 Hz utility grid or to feed local loads at 380 V/50 Hz using a smart inverter. When the smart PV inverter is connected to the grid, on the one hand, it injects fixed and programmed active power into the grid under all operating conditions, both normal and critical conditions, and on the other hand, by reciprocal exchanging reactive power with the grid, it addresses balanced and unbalanced fluctuations of the grid voltage. Also, when the smart PV inverter is disconnected from the grid, it can operate as an islanded mode to feed time-varying three-phase loads. Nonlinear simulations of the time domain in MATLAB-Simulink software show that the set of control strategies offered for the smart PV inverter not only by controlling the active power leads to the sale of electricity to the grid, but also by controlling the reactive power problems on the grid side such as voltage drop as a result of single-line-to-ground (SLG) or line-to-line-to-ground (2LG) faults, balanced grid voltage fluctuations such as voltage sag-swell and unbalanced voltage conditions will be resolved. Also, variable three-phase loads are fed well in off-grid mode. [ABSTRACT FROM AUTHOR]

This paper presents a control scheme including resources and load management in the residential DC microgrid. The DC microgrid is supported by fuel-cell, solar-cell and battery. The DC, AC single-phase and AC three-phase loads with 50 Hz frequency are integrated. The DC microgrid is connected to the external 60 Hz AC three-phase network. An efficient multi-bus topology is proposed for the microgrid and it is formed by various AC/DC buses to supply the loads and managing the resources. The main bus of system is a 470 V DC bus and it is connected to the external 440 V/60 Hz AC grid. The main DC bus supplies three LV, MV and HV DC buses with 100, 220, and 110–380 V, respectively. The HV DC bus produces a variable output DC voltage between 110 and 380 V in order to regulate the load power (i.e., motor speed). The MV DC bus is connected to 220 V/50 Hz AC single-phase loads. The connections between DC microgrid with AC loads and AC external gird are made by single-phase or three-phase inverters. The interface inverters between DC bus and AC loads are operated to control power, torque, speed, frequency and voltage of loads. The unbalanced AC loads are appropriately balanced by proper control of interface inverters. The resources and inverters are efficiently controlled to enable operation of residential building under both off-grid or grid-tied conditions. The coordination of fuel-cell, solar-cell and battery can supply a fixed 8 kW power to external grid and supply the internal loads under all outages and off-grid conditions. The simulations demonstrate that the proposed control realizes all the objectives including AC/DC load management, unbalanced load amendment, frequency adaptation, and off-grid operation. • Designing residential DC microgrid with several voltage levels and frequencies. • Implementing multiple generation/load managements under off-grid and grid-tied. • Multi-bus topology for building including low, medium and high-voltage buses. • Balancing the unbalanced loads from the external network standpoint. • Implementing load shedding strategy in off-grid under critical situations. [ABSTRACT FROM AUTHOR]