Abstract
Abstract Lightning hit a transmission power line outside London, England on 9 August 2019. There followed a loss of power from a cascade of generator outages that exceeded contingency reserves, leading to an exceptional fall in grid frequency causing widespread transport disruptions and the disconnection of over 1 m households. Simulating such events typically involves a system of differential equations representing the overall generation and load present at the time. A standard model based on the swing equation assumes unlimited capacity in aggregated resources, and the availability of these services throughout the duration of the frequency deviation. In simulating the effect of outages on the GB Grid frequency on 2019/8/9, the effect of limiting these services to the capacity of resources engaged during the event is examined. It is shown that by taking these refinements into account the timing and extent of the frequency nadir can be successfully estimated. Insight is gained into the responses of various grid characteristics and how they interact with unplanned generation imbalances. Using this adapted model, further events on the GB grid are examined to validate the influence of these features. With the model’s effectiveness validated, novel mitigating measures to preserve the stability of a low-inertia grid can be evaluated.

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Abstract
Smart inverter functionalities can enable higher penetration levels of inverter-based distributed energy resources. The smart inverter voltage-reactive power (Volt-VAr) control function adjusts the injection and/or absorption of reactive power as a function of the voltage at the connection point through the control curve set-points. In this work, an optimization problem is formulated to increase the photovoltaic capacity in distribution systems by determining the best Volt-VAr control curve set-points of the photovoltaic inverter.A simulation-based optimization framework is proposed, which uses the Particle Swarm Optimization algorithm in the optimization stage, while power flows are executed in the simulation stage through OpenDSS. The performance assessment is performed under a real-world distribution feeder of an Ecuadorian electric utility. The proposed method found both the maximum installed capacity of a photovoltaic power plant and the best Volt-VAr control settings for a set of candidate locations. Results showed the most suitable feeder location for the installation of a single photovoltaic power plant. Besides, the Volt-VAr control curve settings determined by the optimization method increased the maximum installed capacity by 45.21% compared to the case when the photovoltaic inverter operates with a unity power factor.

Abstract
The massive interconnection of rooftop solar photovoltaic (PV) generation to the distribution network constitutes a challenge for the operation and planning of distribution network. In this environment, the performance of the distribution network may be affected and a comprehensive analysis of the hosting capacity in the medium and low voltage network is necessary. A quasi-static time-series and short-circuit analysis considering scenarios of PV systems penetration is proposed to accurately capture the effects of resource intermittency and load dynamics. Six metrics are used: overvoltage, voltage unbalance, thermal loading, fault currents, reverse power flow, and network losses. To evaluate the performance of the method, a real distribution feeder is used, as well as characteristic data of the classes of consumers. Since the relevance of a metric in the impact of the operation depends on the particular characteristics of each case, it is convenient to quantify these different metrics.

Abstract
This paper presents an analysis of the distribution system harmonic behavior when a photovoltaic (PV) system is connected at the low-voltage network. Through harmonic power flow simulations in the Open Distribution System Simulator (OpenDSS), harmonic impact at the point common coupling is studied. To reduce the harmonic analysis, simulations are carried out using a simplified equivalent for utility and customer. In order to model a more realistic distribution system, it is necessary to calibrate the harmonic sources before connecting the PV system. The harmonic state estimation method implemented in combination with the simulator is used to calibrate the utility harmonic voltage sources. After calibration, the harmonic levels at medium-voltage are verified. Results for a case study using quality measurements performed by Ecuadorian CENTROSUR electric utility show that the simulated harmonic levels are similar to those measured. It also shows that a PV system does not produce power quality problems.