Islanded Microgrids (MGs) have low inertia, which leads to faster frequency dynamics, and as a result, effective Load Frequency Control (LFC) is required to maintain the frequency within its permitted ranges under different operating scenarios. Typically, conventional linear fixed-gain PI controllers are employed for MG control. In this article, a nonlinear variable-gain PI controller is proposed to boost the dynamic performance of a stand-alone MG. The structure of this proposed controller consists of a non-linear function of relative error (e) and the change of error (Δe) values connected with a conventional PI controller. Furthermore, the paper utilizes the TS optimization technique to finely adjust the parameters of the presented controllers. To measure the effectiveness of the suggested controller, the system is exposed to various disturbances such as change in load and weather conditions using MATLAB / Simulink software. The obtained simulation results demonstrate that the proposed controller outperforms the conventional PI controller in terms of maximum overshoot and settling time