Abstract
DC microgrid systems that integrate energy distribution, energy storage, and load units can be viewed as examples of reliable and efficient power systems. However, the isolated operation of DC microgrids, in the case of a power-grid failure, is a key factor limiting their development. In this paper, we analyze the six typical operation modes of an off-grid DC microgrid based on a photovoltaic energy storage system (PV-ESS), as well as the operational characteristics of the different units that comprise the microgrid, from the perspective of power balance. We also analyze the key distributed control techniques for mode transformation, based on the demands of the different modes of operation. Possible reasons for the failure of PV systems under the control of a voltage stabilizer are also explored, according to the characteristics of the PV output. Based on this information, we propose a novel control scheme for the seamless transition of the PV generation units between the maximum PV power tracking and steady voltage control processes, to avoid power and voltage oscillations. Adaptive drooping and stabilization control of the state of charge of the energy storage units are also considered, for the protection of the ESS and for reducing the possibilities of overcharging and/or over-discharging. Finally, various operation conditions are simulated using MATLAB/Simulink, to validate the performance of the proposed control strategy.
Highlights
Microgrid structures consisting of multiple intelligently coordinated heterogeneous networks have greatly improved the operation of power grids [1]
DC microgrids typically consist of distributed generators (DGs), energy storage systems (ESSs), and loads, connected by DC buses
ESSs was below modules supplied the load and were operated in the max max, the PV modules supplied the load and were operated in the state of charge (SOC) of the ESSs was below SOC
Summary
Microgrid structures consisting of multiple intelligently coordinated heterogeneous networks have greatly improved the operation of power grids [1]. These structures have been widely studied as basic units that can be integrated into a larger overall network [2,3,4,5]. DC microgrids, as an alternative option, have been attracting increasing interest in the recent years, owing to their advantages of high system power quality and easy control with neither reactive power nor AC harmonic concerns. The power quality of microgrids is influenced by the fluctuation and intermittence of renewable distributed micro-power. Research on control and management technologies relevant to DC microgrids has become increasingly prevalent
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