Abstract
Currently, the Direct-Current (DC) microgrid has been gaining popularity because most electronics devices require a DC power input. A DC microgrid can significantly reduce the AC to DC energy conversion loss. However, a power grid may experience a line fault situation that may damage important household devices and cause a blackout in the power system. This work proposes a new line fault protection scheme for a DC microgrid system by using a battery energy storage system (BESS). Nowadays, the BESS is one of the most cost effective energy storage technologies for power system applications. The proposed system is designed from a distributed wind farm smart grid. A total of three off-shore wind farms provide power to the grid through a high voltage DC (HVDC) transmission line. The DC microgrid was modeled by a BESS with a bi-directional DC–DC converter, various DC-loads with step down DC–DC converters, a voltage source converter, and a voltage source inverter. Details of the control strategies of the DC microgrid are described. During the line fault situation, a transient voltage was controlled by a BESS. From the simulation analyses, it is confirmed that the proposed method can supply stable power to the DC grid, which can also ensure protection of several loads of the DC microgrid. The effectiveness of the proposed system is verified by in a MATLAB/SIMULINK® environment.
Highlights
This paper proposes a line fault control strategy for a DC microgrid, which is developed from a distributed wind farm based smart grid system
During the line fault situation, the battery energy storage system (BESS) of the DC microgrid controls the DC bus overvoltage by absorbing or delivering power to the DC bus, which protects the equipment of the DC grid
As can be seen in this figure, the stator of the DFIG is directly connected to the power grid, while a back-to-back three-phase voltage source inverter is connected to the grid on the other side
Summary
Due to a large number of DC loads (e.g., computers, televisions, fluorescent lights, medical instruments, and other household equipment), DC microgrid systems have attracted widespread attention globally. Most of the distributed renewable energy sources (DRES) generate a DC power output; it requires conversion into AC power for the AC electric power system, and once again re-conversion into a DC power for feeding the DC loads. This AC–DC conversion (or DC–AC–DC) causes a significant energy loss. In a DC microgrid system, the AC power converts to the DC power using a high efficient rectifier, and converting DC power distributes directly to DC equipment This DC power grid can decrease the energy conversion loss (AC to DC) from 10% to 32% [4]. A fault protection method is needed for a DC grid or a DC microgrid system
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