Abstract
ABSTRACT Droop control is an essential component of primary control in hierarchical control paradigm of DC microgrid, which allows for current sharing among power converters without communication, and thus high reliability, plug-and-play (PnP) operation, system expandability and low cost can be achieved. However, the problem with basic droop control with constant coefficient is that higher current sharing accuracy will produce higher bus voltage deviation, and thus degrade power quality and efficiency of DC microgrid. Although secondary control can be applied to restore the bus voltage, the problem with droop control in primary level still exists. In this paper, the general idea of piecewise design of droop curves (GPD) is introduced and three piecewise droop strategies are derived for DC microgrids. Stability and sensitivity analyses of the control system are also carried out based on derived small-signal model of the DC microgrid. Finally, the comparison of the proposed GPD methods, the basic droop control and the nonlinear droop control for both step and ramping load conditions, the impact of multiple piecewise zones, and the influence of the sensing errors are all demonstrated by experimental results.
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