Lyapunov Stability Theory based Non Linear Controller Design for a Standalone PV System

This paper presents the comparative analysis between different nonlinear controllers based on Lyapunov Stability Theory. Due to the nonlinear characteristics of photovoltaic systems, conventional Hill-Climbing methods like Perturbate and Observe and Incremental Conductance do not show reliable tracking of Maximum Power under various climatic uncertainties. Therefore, these methods requires nonlinear tools to meet the control objectives and design specifications. Out of various nonlinear controlling techniques, the one presented in this paper is the Sliding Mode Approach for Maximum Power Point Tracking (MPPT). In perspective of Lyapunov Stability Theory, sliding mode approach uses a switching manifold. In this approach, the system trajectories are made to follow the sliding surface and to remain there forever to ensure the stability of equilibrium points. Two types of Sliding Mode controllers have been simulated namely Conventional - Sliding Mode Controller (CSMC) and Terminal - Sliding Mode Controller (TSMC). Their results are analyzed and compared scientifically under varying climatic conditions. All the control algorithms are developed in MATLAB/Simulink. They are compared based on various performance parameters, including duty cycle ratio, ideal and PV output power and time taken for error convergence.