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In this paper a new methodology is presented to calculate the average power quickly and accurately for the single-phase paralleled inverters intended to be applied in a droop-control microgrid system. Most existing droop control systems utilize a simple first-order filter to calculate the active and reactive power. The added filter can smooth the calculated results but it tends to hurt the system dynamic response due to a low cut-off frequency that is intended to get enough ripple attenuation. This low frequency pole in the low-pass filter could also introduce system instability under certain load conditions. A new filter calculation methodology is thus proposed to achieve better ripple attenuation with faster response by combining a low-pass filter, a delay, and summation blocks. Both simulation and experiment are used to verify the effectiveness of the proposed power calculation methodology.