MPPT Controller for Partially Shaded Solar PV System

Abstract

Solar energy continues to be a viable renewable energy source owing to its eco-friendly nature and long-term economic prospect. The photovoltaic (PV) systems enjoy the trend of being commercialized in many countries due to their potential long-term benefits. Solar irradiance and temperature appear to be responsible for the nonlinear nature of I–V and P–V characteristics of the PV array. The nonlinear characteristics create an optimal point in the sense when the PV system is operated at the maximum power point; it plays a vital role in optimizing the PV power. One of the simplest methods that allow improving the efficiency of the PV systems relates to maximum power point tracking (MPPT). The MPPT aims to track the maximum power point when the weather conditions change, the variation of the solar irradiation, and the temperature leads to a change of the maximum power point. The extraction of the maximum power follows the matching of the power–voltage operating point of the PV modules with that of the corresponding power converter. However, owing to the nonlinear variation of the power output of the solar panel, the MPPT control method becomes an important part of any solar system. The maximum power point tracker (MPPT) ensures the optimal utilization of a large PV array when employed in conjunction with the power converter. The control becomes more complicated when the entire PV array does not receive uniform irradiance – a condition known as partial shading. Partial shading invites considerable interest due to its significance in influencing the energy yield of a PV system. It can be ascertained by the statistical measure of power loss due to partial shading that varies from 10 to 70% of the system yield. Though many conventional MPPT schemes remain in vogue, most of them remain suited when the irradiance varies very slowly and becomes ineffective when subjected to a sudden change in environmental conditions. The maximum power point tracking (MPPT) algorithm becomes crucial in attaining the maximal PV power, facilitating optimal PV cell performance. The MPPT algorithms demonstrate excellent tracking efficiency in uniform insolation conditions. However, under partially shaded conditions, when the entire array does not receive uniform insolation, the PV characteristics become more complex, displaying multiple peaks, of which one of them constitutes to be the global peak (GP) and the rest being local peaks. The occurrence of partially shaded conditions being quite common (e.g., due to clouds, trees, etc.) echoes a need to develop special MPPT schemes that can track the GP under these conditions. It becomes significant to propose advanced MPPT techniques for a large PV system with an array of PV panels. However, in the scenario of distributed PV system planning, decentralized MPP tracking schemes gather significance, and MPP tracking in a single PV panel under uniform and partial shading conditions needs attention. The main emphasis involves a two-stage approach to track the global peak, wherein it orients to explore the use of the maximum power from the solar PV system under the partially shaded environment. It augurs the role of the closed-loop controller to vary the duty cycle of the converter interface and arrive at the delivery of the maximum power to the load. The exercise relates to modeling the solar PV system under a partially shaded environment and analyzing the performance for different shading patterns in the solar panel. The focus incites improving the global peak tracking in all conditions through an algorithm that can operate in the vicinity of the global peak. It includes the identification of different possible combinations of partially shaded patterns and requires being tested for the effectiveness of the scheme. It further necessitates the implementation of the technique through a prototype model and therefrom demonstrates the effectiveness of the use of a simple controller in place of sophisticated MPPT methods.