The ever increasing penetration depth of Distribution Energy Resources (DER) and the development of power electronics devices have a significant impact on the development of DC power transmission and distribution systems. This paper provides an overview of the recent advancement and also envisioned research and development on DC grids, with the objective of identification and discussion of the corresponding issues. Brief descriptions of DC grids at various voltage levels and their benefits are presented and discussed. Different layouts for the DC grids are presented and the associated technical issues are highlighted.
This paper presents an analysis of a new application of different direct matrix converter topologies used as power interfaces in AC, DC, and hybrid microgrids, with model predictive current control. Such a combination of a converter and control strategy leads to a high power quality microgrid voltage, even with a low power quality main grid voltage and even during the connection and disconnection of a variety of loads and generation sources to the microgrids. These robust systems are suitable for applications in which sensitive loads are to be supplied and these loads are connected close to distributed-generation sources with inherent intermittent behavior. The authors also propose the use of new direct matrix converter configurations with a reduced number of switches in order to achieve reduced cost, reduced failure rate, and higher reliability, which are very desirable in microgrids. Finally, the authors also introduce new hybrid direct matrix converter topologies that provide interesting options for the islanded operation of the microgrids with the use of a battery system. In other words, the proposed hybrid direct matrix converters result in flexible hybrid microgrid configurations integrating DC and AC devices with high power quality and high power supply reliability.
This study presents a new microgrid topology that uses a bidirectional interleaved converter performing a power interface between DC buses in a hybrid microgrid allowing for both grid-connected and islanded modes. The authors propose a new control strategy and controllers' design method aiming at achieving a high-performance dynamic response regarding the converter load and generation disturbance rejection capability. In the grid-connected mode, the interleaved converter operates in the buck mode providing a high-power-quality DC microgrid voltage. In the islanded mode, the interleaved converter operates in the boost mode and it is responsible for regulating the DC link of the back-to-back converter that connects the main grid to the AC microgrid. A detailed mathematical model is presented to obtain a MIMO system that takes into account the system's disturbances to analyze both stability margins and disturbance-rejection response. Simulations of the proposed topology are carried out in PSCAD/EMTDC in a microgrid operating in grid-connected and islanded operation modes. Experimental results are provided in order to validate the proposed control tuning method.
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