A Modified INC Method for PV String Under Uniform Irradiance and Partially Shaded Conditions

Abstract

Due to the bypass diodes, the partially shaded photovoltaic (PV) string exhibits multiple peaks in the P-V curve. And the conventional Maximum Power Point Tracking (MPPT) methods are not capable of tracking the global peak (GP) under partially shaded condition (PSC). In order to track the GP fast and efficiently under uniform irradiance condition (UIC) and PSC, a modified incremental conductance (INC) method is proposed in this paper. This method can not only detect the occurrence of PSC, but also determine if the other peaks need to be tracked under PSC by using the relationship between the minimum current at other peaks and the short circuit current to enhance the tracking speed. In order to improve efficiency, the converter duty cycle will be regulated slightly to ensure that the operating point reaches in the vicinity of GP, after the approximate GP is located. The Matlab simulation results show that the proposed method is faster and more efficient than other methods. It only requires 3 and 11 sampling cycles to locate the GP under UIC and PSC, respectively. Its overall tracking efficiency is increased by 13.61%, 4.28% and 0.42% under UIC, PSC and one-day irradiance profile respectively, compared to the conventional INC method.

Keywords

• PV string
• maximum power point tracking (MPPT)
• global peak (GP)
• uniform irradiance condition (UIC)
• partially shaded condition (PSC)