Capacitor charging method for I-V curve tracer and MPPT in photovoltaic systems

摘要

The capacitor charging method can be used in Photovoltaic (PV) systems for two typical applications: a very simple and cheap way (1) to trace the I-V curve of a PV generator of whatever size and (2) to track the Maximum Power Point (MPP), especially when the partial shading occurs. The problem is the correct sizing of the capacitor in order to achieve accurate, uniform and smooth results. In the first application a simplified calculation to design quickly the capacitor is carried out. This is done only as a function of the main characteristics of the PV array and the most important datasheet parameters of the PV modules. Then, the setup of I-V curve tracers at module, string and array levels is presented: these tracers are useful in the detection of underperformance of PV systems. In the second application a MPPT (MPP Tracker) circuit based on capacitor charging is designed and simulated in partial shading conditions. In these conditions the Power-Voltage (P-V) curve of a PV array is characterized by the presence of multiple maxima for the bypass diode action. The PV array is isolated from the load for a negligibly short period and is connected to an external capacitor. During the charging time, the proposed circuit tracks the global MPP. This circuit is easy to implement and shortens the duration needed for scanning the P-V curve of the array