Conference Agenda

The growth and integration of renewable energy and control systems in the utility grid represents a challenge for the electric power industry. Power quality monitoring plays a critical role in modern electrical systems for both standards compliance and system security reasons. This paper presents a novel technique for calculating subharmonics, harmonics, interharmonics, supraharmonics, and DC offset in electrical systems. This extended spectral fitting (ESF) approach is a combination of the numerical Laplace transform (NLT) and a modified vector fitting (VF) which we have denominated extended vector fitting (EVF). In this novel approach, it is assumed that frequencies of the harmonics and supraharmonics are known poles and that frequencies of the subharmonics and interharmonics are unknown poles in the frequency domain (FD), resulting in a rational approximation that considers known poles and unknown poles. The advantages of the proposed methodology are demonstrated (1) for synthetic test signals and (2) in an AC-DC-AC converter simulation. Results show that the ESF approach can fully decompose a signal into the aforementioned components with a high degree of accuracy.

This paper presents a solution to the observed ferroresonance (FRR) phenomenon for both energization switching and load shedding conditions in an unconventional rural electrification system. The energy is extracted from the electric field surrounding an extrahigh voltage transmission
line. Ferroresonance occurs in the power transformers of the distribution substation, and the existing solution cannot be directly applied. The mitigation method consists of the insertion of a shunt resistor when the FRR starts. The robustness of the method is shown in a time-domain simulation implemented in PSCAD/EMTDC.

In the design phase of connecting wind power plants (WPPs) to the transmission network, harmonics amplification due to different system parameters (e.g. the long HVAC cable connection) need tobe determined. Not all parameters tocalculate the harmonic voltage distortion gain are known indetail. The aim of this paper is to analyze the impact of some uncertainties on the harmonic voltage distortion gain by the use of a real case study. Impacts of several aspects, such asnetwork condition (e.g. transmission network contingencies and WPP contingencies), modeling approach (cable modeling) and parameter uncertainties (e.g. cable capacitance), are investigated via simulations. It can be concluded that the transmission network contingencies as well as the Windfarm contingencies have the most significant effect on harmonic amplification. The effect of the export cable modeling is also noticeable while the cable capacitance uncertainties have a less critical effect onharmonic amplification.

Ferroresonance in single-phase,line-to-line con-nectedtransformers in an ungrounded distribution system with delta-connected capacitors is possible but has not been reported in recent literature. In this paper, a high voltage event that actually occurred in an ungrounded distribution network with multiple distribution transformers has been simulated for lessons learned. The hypothesis was that ferroresonance was the cause of the overvoltage event in the network after a single-phase event led to sustained voltages of 1.45 p.u. Simulations were performed and ferroresonance was found to be the possible cause for the overvoltages. One of the prevention solutions found to avoid the overvoltages was to balance the loads on the three phases. The increased deployment of CVR/VVO strategies leads to circuit configurations similar to that studied in this paper and could lead to an increased likelihood of ferroresonance, if it is not fully understood and addressed. The impact of additional single-phasesolar inverters on the low voltage side of the transformers was also studied. The results obtained show that the effective loading of the transformers, which is the difference in the actual load connected and the output from the DER, proved to be the deciding factor for initiation of ferroresonance in such networks.

The use of solar photovoltaic (PV) in distribution networks has increased considerably in recent years. Although they have many advantages, PV systems can also result in complex power quality issues in distribution networks, like harmonic distortion, that can interfere with loads and controllers. Harmonic emission from different inverters and their aggregation is thus of interest. In this work, harmonic emission of two PV string inverters and two substations operating in a large PV power plant is presented. The distribution of the full range of current harmonics is analyzed, as well as the correlation between the values of each harmonic and the power level produced, by the inverter or substation, and the correlation between voltage and current harmonics. Significant differences are observed in the harmonic emission of the inverters, despite being under the same operating loading and grid conditions. The results obtained for the substations are in line to those for the inverters. This study was performed in a grid connected 12 MW PV power plant operating in Europe.

To achieve carbon neutrality by 2050, electric vehicles (EVs) are promoted and EV fast chargers are expected to become part of the public infrastructure. To feed power to EV fast chargers installed in highway rest areas, the authors have proposed a 33-kV dedicated cable supply system installed along the highway. Due to the large capacitance of a cable system, harmonics may be of concerns for the operation of the proposed system. Therefore, this paper presents a study of harmonics occurring in the 33-kV dedicated cable supply system to feed EV fast chargers. First, the cause of the harmonics is identified by deriving resonance frequencies of the equivalent circuit of the cable supply system. Then, the harmonic resonance phenomenon is verified by electromagnetic transient (EMT) simulations. The results indicate conditions with which harmonic resonance may occur in the cable supply system. To perform the simulations, the EMT simulation models of distribution substations and EV fast chargers are picked up from the generic EMT simulation models prepared in XTAP (eXpandable Transient Analysis Program) for distribution and microgrid simulations. It should be noted that the harmonics simulations mentioned above can readily be performed by picking up necessary models from the model library.