In this article, a nonlinear control method based on a virtual synchronous inverter is presented in order to maintain the stability of the microgrid in the island and connected mode with the presence of solar renewable energy sources. Uncertainty about solar renewable energy sources is modeled using the distribution function. Also, in order to optimize the parameters of the nonlinear control method, a sailfish optimization algorithm has been used. The proposed method is implemented on a microgrid with three distributed generation sources. The obtained results show the effectiveness of the proposed method in damping power and voltage fluctuations in both islanded and grid-connected modes, as well as when changing the working mode of the microgrid.