An advanced voltage droop control concept for grid-tied and autonomous DC microgrids

Abstract

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.