In general, a major challenge for the exploitation of renewable energies is to improve their efficiency. In electricity generation from the energy of ocean waves, not unlike other technologies, the converter must be optimized to make the energy harvesting economically feasible. This paper proposes a passive tuning control strategy of a point absorber in which the power captured is maximized by controlling the electromagnetic force of the generator with a resistance emulation approach. The proposed strategy consists of mapping the optimal values for regular waves and applying them to irregular waves. This strategy is tested in a wave energy converter in which the generator is connected to a boost rectifier converter whose controller is designed to emulate a resistance. The power electronics system implemented is validated by comparing its performance with the case in which the generator is directly connected to a resistive load. The simulation results show the effectiveness of the proposed strategy as the maximum captured power is concentrated around the optimal values previously calculated and with the same behavior for both excitations.

The increasing penetration of Electric Vehicles (EVs) in LV distribution networks can potentially cause voltage quality issues such as voltage unbalance and under-voltage conditions. According to the EV charger characteristics, some strategies can be adopted to mitigate the aforementioned effects. Smart decentralized charging controls seem to be a more practical solution than centralized controls, since there is no need for communication because they rely only on local measurements. The four most relevant decentralized charging strategies, two for single-phase and two for three-phase EV chargers, have been implemented in a typical three-phase four-wire European LV distribution network. Simulations have been carried out for scenarios with single-phase EV chargers, three-phase EV chargers, and a combination of both. Single-phase controls are aimed at under-voltage regulation, while three-phase controls are focused on mitigating voltage unbalance. Results show that the implementation of a decentralized EV charging control is an adequate solution for Distribution System Operators (DSOs) since it improves the reliability and security of the network. Moreover, even though decentralized charging control does not use any communication, the combination of three-phase and single-phase controls is able to mitigate voltage unbalance while preventing the under-voltage condition.

In recent years, harmonic current levels have increased in residential distribution networks due to the growing penetration of nonlinear loads at customer premises. To properly model the harmonic current injection of residences, probabilistic models that account for the stochastic behavior of domestic loads are needed. As a part of the study reported in this paper, a field measurement campaign was performed in 24 dwellings during a one-week period with a one-minute resolution. Harmonic current magnitudes and phase angles of odd harmonic orders up to the 25th as well as the active and reactive power demanded were recorded. By applying two different unsupervised learning techniques (i.e., nonparametric density estimation and Gaussian mixture models) to these measurements, two probabilistic models of harmonic injection of individual residential sites have been derived. Statistical probability distributions have been determined for the magnitude and phase of each harmonic order segmented in different power demand intervals. The developed models are validated on a test feeder by comparing harmonic voltages caused by the injection of the synthetically generated currents with those obtained from measurements. Both field measurement results and the detailed data defining the probabilistic harmonic current models are made public in an Open Science database repository.

Renewable energy is steadily increasing its penetration level in electric power systems. Wind and solar energy have reached a high degree of maturity, and their impacts on the grid are well known. However, this is not the case for emerging sources like wave energy. This work explores the impact of the fluctuating power injected by a wave energy converter on the distribution grid voltage and proposes a strategy for mitigating the induced voltage fluctuations. The paper describes the mechanics of how a fluctuating active power injection leads to grid voltage fluctuations and presents an unbalanced three-phase power flow tool that allows one to quantitatively analyze the voltage evolution at every phase and bus of a distribution grid driven by this power injection. The paper also proposes a corrective action for mitigating the voltage fluctuations that makes use of the hardware resources already available in the wave energy converter, by means of a control strategy on the reactive capability of the grid-side inverter. The use of a STATCOM as additional reactive compensation equipment is also explored. The effectiveness of the proposal is assessed in the IEEE 13-bus test feeder showing that, in some cases, the wave energy converter by itself is able to mitigate the voltage fluctuations that it causes. If not, a STATCOM can provide the extra reactive capability needed.

Renewable energies, in general, have considerably increased their penetration in electrical power systems. However, they are intermittent energy sources, and large amounts of this power could create problems for the proper operation of the electrical network. In this sense, this paper studies the effects of wave energy generation on the voltages in a distribution network, using the IEEE 34-bus test feeder. In addition, corrective actions based on reactive power compensation, such as reactive compensation from\ud the grid-side converter of the wave energy converter and the use of a STATCOM, are presented. The results show that the use of the grid-side converter as a reactive power compensator improves the voltage quality in the network, although its capability to mitigate voltage fluctuations is limited. The use of a complementary external STATCOM can provide for extra compensation if needed