The total harmonic current emission in a public low-voltage (LV) network is mainly determined by the large number of electronic devices, which use different circuit topologies with different harmonic emission characteristics. Consequently, the total harmonic current measured at the LV busbar can provide valuable qualitative information, for example, about dominating circuit topologies. This paper describes and applies a methodology to characterize the harmonic current emission of an LV network by a prevailing phasor. Using measurements from 130 German public LV networks, the “prevailing” location of 3rd and 5th harmonic current is analyzed with respect to different types of consumers. The results are compared with initial measurements received from other countries. Based on the prevailing phasor, a simplified method for an approximate estimation of the impact (cancellation potential) of a particular LV network or a new equipment technology (e.g., electric-vehicle charging) on the harmonic levels in a public distribution network is proposed.

Widely existing circuit topologies and inverter control strategies for photovoltaic (PV) systems allow customer flexibility but also introduce different kinds of interharmonics into the grid. A complete understanding of interharmonics from PV systems, with reasons behind their origin, remains needed. In addition, the time-varying nature of interharmonics and the potential impacts on other equipment are yet to be understood. In this paper, laboratory and field measurements of seven different inverter types at multiple locations are presented. A comprehensive analysis is performed to understand the existence, persistence, and propagation of interharmonics in PV systems on the dc side as well as grid side for different power levels. The origins of the interharmonics are established with experimental evidence and through a comparative analysis. A rural low voltage six customer network, with two different impedance profiles caused by the installation of PV, is considered to show the potential impact on customer voltage. To address the time-varying nature of interharmonics, a sliding window ESPRIT method is preferred over fast fourier transform (FFT)-based methods.

This paper presents a comparison of measurement methods for current and voltage distortion in low voltage networks in the frequency range from 2 kHz to 150 kHz (supraharmonics). The comparison encompasses the methods informatively described in IEC and CISPR international standards, as well as other innovative techniques presented in the literature. The presented work is carried out within a novel framework that includes advanced and complex synthetic test signals, as well as real grid recordings, that allow an accurate comparison of the performance of the tested methods. Specifically designed indices are employed to characterize the accuracy of the tested methods in the frequency and amplitude assessment. In light of that, strengths and weaknesses of the methods are identified. The results of this paper contribute to the ongoing standardization work carried out by the IEC SC77A/WG9 with the purpose of defining a normative measurement method suitable for assessing grid disturbance levels in the range from 2 kHz to 150 kHz.

This paper introduces a new method for the simultaneous measurement of harmonic and supraharmonic distortion with improved robustness against amplitude and power frequency deviations. The proposed algorithm is based on wavelet analysis and it is designed to analyze a detect-all=true10 cycles measurement interval, something crucial when implementing methods to measure harmonic and supraharmonic content according to the IEC 61000-4-7 standard. Discrete Fourier Transform (DFT)-based methods, instead, must analyze a fixed detect-all=true200 interval in order to avoid apparent shifts of the supraharmonic frequency components. The results of the experimental measurements presented in the paper show that the DFT-based methodology suggested in the IEC 61000-4-7 standard produces results affected by the value of the power frequency and amplitude while the proposed method, instead, is insensitive to them. This feature also removes the need of a previous high pass filtering stage, required for the IEC method. Moreover, the proposed method has the additional advantage of working on the same measurement interval to calculate both harmonics and supraharmonics, which reduces the complexity of data handling by avoiding multithreaded Data Acquisition (DAQ) operations.

This study proposes a novel measurement method to assess the disturbances in the electrical grid for the CISPR Band A (9–150 kHz), as no normative grid measurement method for these frequencies exists yet. Compatibility levels (CL) in IEC 61000-2-2 in this frequency range are defined based on the CISPR 16-1-1 method using the quasi-peak (QP) detector. However, this method is not directly applicable for grid measurements as it was originally designed for laboratory conditions and for measuring radio disturbances and immunity. The method proposed in this article (Light-QP method) overcomes these limitations, along with lower complexity, computational burden, and memory requirements than CISPR 16-1-1. The Light-QP method uses a digital QP detector that processes root mean square (rms) values of spectral components, calculated by adapting the IEC 61000-4-7 standard to the CISPR Band A. The proposed Light-QP method is applied to real measurements from a low-voltage (LV) distribution grid and compared to the QP outputs from a digital implementation of the CISPR 16-1-1 method. The results are comparable and can be used for assessment against CL. The Light-QP method has been presented to IEC SC77A/WG9 for its potential inclusion as a normative measurement method in a new version of the IEC 61000-4-30 standard.

This paper introduces a new black-box approach for time domain modeling of commercially available single-phase photovoltaic (PV) inverters in low voltage networks. An artificial neural network is used as a nonlinear autoregressive exogenous model to represent the steady state behavior as well as dynamic changes of the PV inverter in the frequency range up to 2 kHz. The data for the training and the validation are generated by laboratory measurements of a commercially available inverter for low power applications, i.e., 4.6 kW. The state of the art modeling approaches are explained and the constraints are addressed. The appropriate set of data for training is proposed and the results show the suitability of the trained network as a black-box model in time domain. Such models are required, i.e., for dynamic simulations since they are able to represent the transition between two steady states, which is not possible with classical frequency-domain models (i.e., Norton models). The demonstrated results show that the trained model is able to represent the transition between two steady states and furthermore reflect the frequency coupling characteristic of the grid-side current.