Robust Techniques for the Optimal Operation of Photovoltaic Systems

Abstract

Photovoltaic (PV) energy has witnessed tremendous growth in the recent past to meet the growing energy demands. PV system exhibits the (current-voltage) I-V curve, which varies non-linearly according to immediate weather conditions. Considering the high initial capital cost of PV system and its low conversion efficiency, it is imperative to operate the PV array under optimal condition on consistent basis. For this purpose, maximum power point tracking (MPPT) technique plays a pivotal role in the PV system. The main role of the MPPT is to track the unique maximum power point (MPP) on the I-V curve, when PV array is under uniform condition. On the other hand, during partial shading, the matter is further complicated as the I-V curve of PV array is transformed in to the shape containing multiple local maxima, one of them is global maximum. In that scenario, a specialized MPPT is required to search the global maximum. The main aim of this thesis is to design the robust MPPT techniques for PV systems in order to harvest the maximum energy from PV plants. In this work, two novel techniques are designed: one is specialized for uniform conditions and other one for non-uniform conditions, i.e. partial shading. The design procedures, working principles and formulations of the MPPTs are discussed in detail with the help of various simulation models, figures, graphs and tables etc. Numerous simulation studies and experimental tests have been conducted to confirm the efficient operation of proposed MPPTs. Also, based on these tests, comparative analysis has been carried out, which reveals that the proposed MPPTs exhibit superior performance compared to past-proposed MPPTs. In addition, a new modulation control scheme to vary duty cycle of the DC-DC converter is presented, which will assist the MPPTs in their operations. A load criteria for resistive and battery loads is also defined for the stable operation of PV systems