The recent increase in large converter-based devices like electric vehicles and photovoltaics increases supraharmonic emissions in low-voltage grids, potentially affecting customer equipment and the grid. This paper aims to give an overview of the different factors influencing supraharmonic emissions from electric vehicles and studies the propagation of supraharmonic currents through a small, low-voltage grid. Measurements in an unique lab representing a possible future household gave valuable insight on the possible developments in primary and secondary supraharmonic emissions in a conventional or power-electronic-dominated system. Emission is, for some vehicles, influenced by the type of grid connection, whereas others show no difference in emission. The supraharmonic currents mainly stay within the local installation due to absorption of nearby devices. The level of voltage distortion is dependent on the connection impedance. During the measurements, another type of interaction between devices is observed in the form of “frequency beating” and intermodulation, in some cases resulting in the tripping of residual current devices. This interaction is further analyzed in order to better understand the possible impact it can have on the grid.

The aim of this paper is to present a novel phasor measurement unit (PMU) data-based cable temperature monitoring method with an intended application towards facilitating dynamic line rating. First part of the paper presents the method to estimate and track the temperature of a 3-phase cable segment.The benefit of this temperature monitoring method is that no additional temperature measurement sensors are required to be placed along the cable. The method is based on a novel algorithm which gives accurate resistance estimates for 3-phase cable segments even in the presence of random and bias errors in the grid measurements. The performance of the method is demonstrated by utilizing data from PMUs in a distribution grid. The results from the grid data show that the method is capable of monitoring the cable temperature up to an accuracy of ±5°C. The later part of the paper presents a system to utilize the temperature estimates given by the monitoring method to predict the dynamic thermal state of the cable for forecasted power-flow scenarios. This is demonstrated by using the available temperature estimates to initialize and solve the system of equations given by the thermoelectric equivalent (TEE) model the cable

To prepare for the future high penetration level of renewable energy sources, the power grid’s technical boundaries/constraints for the correct operation of powerelectronics interfaced devices need to be further examined and defined. This paper investigates the challenge of integrating Voltage Source Converters (VSC) into low inertia power grids, where the system frequency can vary rapidly due to the low kinetic energy buffer available, which used to be provided by the rotational inertia of synchronous generators. The impact of rate of change of frequency (ROCOF) on the PLL dynamics and its subsequent influence on the VSC power stage output is explained. The Bonaire island network is presented as case study. The performance of the VSC is analyzed under a fast ROCOF event, which is triggered by a short circuit fault. A down-scaled experiment is used to validate the Bonaire island network simulation results. It shows that the phase angle error measured by the synchronous-reference frame phase-locked loop (SRF-PLL) is proportional to the slope of the ROCOF and inversely proportional to its controller integral gain constant.

This work deals with the design of a digital current control applied to a variable-speed low inductance BLDC motor drive. A robust static full-state feedback control law is determined by means of a convex optimization problem, subject to linear-matrix-inequality constraints. The optimization is used to achieve a fast time response with reduced overshoot under the parametric variations. Results from a 5kW/48V BLDC motor prototype is used to validate the proposed approach with a superior performance when compared to two other control strategies.

Estimation of total harmonic current generated by a group of sources is a difficult task, because of time variations of loads and background harmonic voltages caused by the rest of the network. Several simulation techniques have been proposed in the past, which try to address the problem and estimate the maximal levels of current and voltage distortion, but with limited field measurements to verify the results. In this study, the subject of the summation of harmonic currents in industrial installations is reviewed and analysed based on field measurements. Harmonic magnitudes and phase angles of individual load currents and the total current were measured simultaneously, on four locations. The duration of each measurement was approximately 1 week, with a time resolution of 1 s. The assumptions made in probabilistic studies are discussed based on the results, and coefficients for simplified estimation are calculated together with their limit values. Lastly, some considerations about the measurement approach are made.

With the introduction of more non-linear loads, e.g., compact fluorescent lamps, electric vehicles, photovoltaics, etc., the need to determine the harmonic impact of the residential load is rising, illustrated by the many studies performed on their harmonic impact. Traditionally, these studies are performed for a single new device and single penetration level, neglecting the harmonic interaction between new types of devices, as well as giving little information at which moment in time possible problems may arise. A composite approach to access the impact of harmonic sources on the distribution network is therefore proposed. This method combines a bottom-up stochastic modeling of the residential load with harmonic measurement data and harmonic load-flows all based on a scenario analysis. The method is validated with measurement data and shows a good prediction of the current level of harmonics in a residential neighborhood for the current situation. To demonstrate the applicability of the proposed method, case studies are performed on the IEEE European Low Voltage Test Feeder. These case studies show a marked difference between applying individual device-based models and a composite modeling approach, demonstrating why the proposed approach is an adequate method for the determination of the impact of new devices on the harmonics.