Adjustable Inertial Response From the Converter With Adaptive Droop Control in DC Grids

In a dc grid, the inherent inertial support from the dc capacitors is too small to resist step changes or random fluctuations from the intermittent power resources, which results in lower dc voltage quality. In this paper, an adaptive droop control (ADC) strategy is proposed to achieve an increased inertia from the droop controlled converter. The adaptable droop coefficient according to the dc voltage variation enables fast swing of the droop curve, so that the converter can provide inertial power for the dc grid like synchronous generators in ac grids. The design of the ADC including the calculation and limitation of the adaptable droop coefficient is analyzed in detail. The small signal analysis of the dc grid with ADC is provided to identify its stability issue. Experimental tests on a controller hardware-in-the-loop platform of a low-voltage (LV) dc grid are carried out to validate the proposed method. In this LV dc grid, the proposed ADC is implemented on the energy storage system which provides inertial support to improve the dc voltage quality under different power fluctuations, and smooths the power transmitted to ac grid.