Droop Control has been a well-established control technique both in AC and DC power distribution grids for many years, because it provides a simple way to equally distribute the load current between remote power sources. With the increasing demand for low voltage DC microgrids supplying high-reliability equipment, like servers in data centers, to work both grid-tied and autonomously without a connection to the AC mains and fueled only by local renewable and conventional power sources, voltage droop control is facing new challenges. With power equipment being delivered from several manufacturers the demand for a communication less control scheme that only uses the voltage at the terminal point or the converter output current as an indicator how the control set point should be changed in order to satisfy the energy demand of the loads arises. In consequence, the commissioning time of the DC microgrid is greatly reduced since all components can be simply plugged together without the need for adaptions. An outline for such an inherently autonomous voltage droop control scheme to keep the system voltage within a narrow band of ± 10 % of its 380 VDC nominal value is given in the following paper by describing voltage droop control modelling basics and the selection of characteristic droop curves for different kinds of power sources as well as by giving simulative results from a small-scale DC microgrid

Overview, comparison and evaluation of common DC micro grid design considerations. The focus of this paper is to explore the main differences and advantages/disadvantages of various topologies and control strategies for DC micro grids. The requirements of various application areas can strongly influence the individual system design. Control strategies, single- or two-phase designs, earthing concepts, system voltages and power levels are discussed as well

This paper describes the application of a distributed DC microgrid in a commercial environment as well as the current state of the art and standardization efforts. The introduced grid features various sources and loads being interconnected with a 380 VDC bus. Here, focus lies on the implementation of a DC fast charge station for electro mobility into a DC grid as well as to elaborate the advantages compared to charging from the AC grid. Additionally, the application of DC nanogrids in workplace environments and their combination with a superordinate DC microgrid is presented. The benefits offered by nanogrids compared to conventional AC power supply in an office are discussed as well. Finally, the hardware to realize a DC microgrid within one electrical cabinet is introduced. Its versatility to fulfill a wide range of functions in the grid is shown as well

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Interconnecting power converters within a low voltage DC grid can be a challenging task since these devices are rarely tested under final operating conditions during their development process in conjunction with converters from different manufacturers, different kinds of loads and appropriate grid impedances. In the worst case, stationary oscillations might occur in the grid setup for which the actual reason is hard to determine and solving the problem will require time-consuming trial and error means. Therefore, theoretical knowledge about how power converters react on grid-side disturbances is crucial for a preliminary analysis of the static and dynamic performance of low-voltage DC grids before plugging the devices together. Based on these considerations general guidelines for the dimensioning of control loops and grid-side capacitors of power converters can be derived. The following outlines describe the fundamentals of power converter behavior when exposed to disturbances occurring on the output current, e. g. from load steps. Another focus lies on shaping grid-side impedances of converters to avoid stability issues. Furthermore, a method to measure the impedances of interest is thoroughly described. All obtained results are verified in a brief case study

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