Development of an Adaptive MPPT Algorithm and Power Management Strategy for Standalone PV System

Abstract

Because viability and crisis of conventional energy sources, renewable energy sources have become most alternative electrical sources of energy around the global. Among them Photovoltaic (PV) power generation having rapid development and investment because of its advantages such as abundance, pollution free, renewability and maintenance free. However, PV panels shows a nonlinear characteristics which depends on solar irradiation and temperature. Because of this nonlinear behaviour, Extraction of maximum power from PV panel is the most priority on this paper. Until now, numerous Maximum Power Point Tracking (MPPT) algorithm have been developed to track the maximum power point of PV panel. However, some of them still have disadvantages like complex algorithm, slow processing, etc. The most popularly used MPPT is perturb and observe (P&O) algorithm. This algorithm is widely used in PV system because of its advantages like simplicity and robustness. P&O algorithm can be executed either by using direct duty ratio control or by using voltage reference control. However, direct duty ratio control suffers some serious drawbacks, which are the speed tracking time and continuous oscillation around the MPP depends on perturbation step size (?D) . In case of voltage reference P&O algorithm, a controller (PI/PID) compute the duty ratio of the DC-DC converter connected with PV system, which will deduct the drawback of direct duty control. In this P&O algorithm, the gains of the PID calculated for standard test condition (1000W/m2, 25°C) of PV panel. Due to changes in solar irradiation and temperature, PV panel characteristics changes leading to change in system transfer function for different operating conditions. A fixed gain PID controller would not perform preferably for different operating conditions. Therefore, an adaptive method is proposed to decide gains of the controller for different operating conditions. In the proposed method, a linear relation has been developed between PID controller gains calculated under STC with other operating conditions. This linear relation adaptively changes the PID gains for different operating conditions. It is observed from thesimulations and experimental results that the proposed adaptive method precisely tracking the maximum power and optimize the tracking time and oscillations around each perturbation. The stand-alone PV power generation have an intermittent nature. Therefore, energy storage systems such as a battery or a super capacitor are necessary to improve the system dynamics and steady-state characteristics. A three-port converter (TPC), which contains an input port connected to an input source, an output port connected to a load, and a bidirectional port connected to a battery, is a better prospective for such a renewable power system. Therefore, a power management strategy has proposed for the power management between PV panel, battery, and load, along with better switching of TPC should have operated. It is observed from the simulations and experimental results that the proposed adaptive method precisely tracking the maximum power and the power control strategy transfer the power, depending on battery and load power requirement.