A direct current-voltage measurement method for smart photovoltaic modules with submodule level power optimizers

Mismatch between photovoltaic (PV) devices connected in series, caused by degradation or partial shading, may result in the significant power loss of a PV system. Therefore, smart PV (SPV) modules, integrated with power-optimization converters at the submodule level, have been used to overcome this problem. Due to the complex circuit topology of the integrated converters, the current-voltage (I-V) characteristics of most SPV modules cannot be tested directly using the routine method. This study aims to develop an I-V measurement procedure for SPV modules in the laboratory. The characteristic of the SPV module was investigated through theoretical and experimental analysis. The noise generated from the optimizer circuit was considered as the major hindrance in the I-V measurement for SPV modules, which was tested and then analyzed using Fourier analysis. Then, a filter corresponding to the noise characteristics was applied in the measurements to eliminate the noise. The measured result corresponded with the theoretical analysis; furthermore, the power linearity with irradiance and the field test verified the reasonableness of our method. The proposed method is applicable in the laboratory measurement of SPV modules within a few hundred milliseconds, which may be applied in relevant power sorting and measurements in production line.