Technique for the comprehensive characterization of supraharmonic disturbances (9–150 kHz) in the joint time-frequency domain

Abstract

The inverter-based devices connected to the low-voltage (LV) grid, such as photovoltaic panels (PVs) and electric vehicle charging stations (EVCSs), are known to generate supraharmonic distortions in CISPR Band A (9–150 kHz) that may interfere power line communications (PLC). Current measurement methods were designed to provide results of the disturbances only in the frequency domain. Thus, impulsive signals and fast amplitude variations of the disturbances are lost in the calculation process. This work addresses this issue by developing a statistical study of the distribution of supraharmonic disturbances in the joint time-frequency domain, which allows the clear differentiation of impulsive signals. The results show that the amplitudes of the normalized measurements can be modeled by the t Location-Scale probability density function (PDF), which can be used to set a threshold for the differentiation of the impulsive disturbances. The study proposes a measurement method and a set of metrics for the complete characterization of the disturbances present in the LV grid, by characterizing the noise and distortions as a whole and also impulsive emissions separately. The main contribution of this work is that the measurement technique characterizes the disturbances in the joint time-frequency domain, and it is coherent with methods below 9 kHz. The proposed method is applied to some typical grid recordings containing different types of noise and emissions. The results demonstrate that the method allows the complete characterization of the supraharmonic distortions present in the LV grid and a proper differentiation of the impulsive emissions in the joint time-frequency domain.