An inverter controlling method is provided for a power system that includes a DC power source and a plurality of inverters connected in parallel to the power source. The method includes the steps of: measuring output power of the power source at a plurality of periodic points; calculating a moving average at each periodic point based on the measured output power; calculating a regression curve by utilizing moving averages at a current periodic point and past periodic points; estimating output power at a next periodic point based on the regression curve; and determining, based on the estimated output power, how many inverters to be actuated.