In this talk we first discuss the conventional proportional and integral (PI) controller which is de facto standard for industrial automation and also for astronomical telescopes. Later, we propose a simple modification to the PI controllers capable of rejecting time varying disturbances encountered in systems like telescopes. We introduce the mathematical model of the proposed controller and present the stability analysis. The model is simulated on Matlab based on which a suitable hardware is developed for validating the model in real-time. We compare the performance of conventional PI controller with the proposed controller and discuss the result.