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The increasing penetration of renewable generation in power systems is causing growing concern about system stability. Grid-forming (GFM) control has been appointed as the technology required for achieving a high penetration of renewables in the grid, as it successfully contributes to the power system stability. This paper proposes a novel grid-forming control scheme for voltage source converters (VSC) achieving the operational characteristics of a virtual synchronous machine (VSM). The proposed scheme is based on the orientation of a defined virtual flux to a reference axis obtained from the emulation of the synchronous generator swing equation. The virtual flux is obtained by the integration of the VSC internal voltage and it is oriented to the reference axis by means of a flux controller that also controls the flux magnitude. In this way, the VSC synchronism is maintained, operating as a voltage source connected to the grid. Moreover, the flux orientation in turn allows to control the VSC active power, while the flux magnitude control allows to regulate the VSC reactive power or terminal voltage in isolated mode. The paper also demonstrates that the stability of GFM converters is negatively affected when emulating high inertia values. So, a stabilizer is also proposed for damping these modes. Finally, due to fact that GFM converters behave as voltage sources, their low voltage ride through capability becomes an issue, because they naturally respond to faults with high short-circuit currents, that cannot be withstand by power electronics converters. Therefore, a method for limiting fault currents is proposed as well in the paper. The proposed grid-forming control scheme has been implemented in a real-time control platform and validated using comprehensive simulation models in a real-time simulator for assessing its grid-forming capability.

Recommender Systems have become one of the most important tools for streaming and marketplace systems in recent years. Their increased use has revealed clear bias and unfairness against minorities and underrepresented groups. This paper seeks the origin of these biases and unfairness. To this end, it analyzes the demographic characteristics of a gold standard dataset and its prediction performance when used in a multitude of Recommender Systems. In addition, this paper proposes Soft Matrix Factorization (SoftMF), which tries to balance the predictions of different types of users to reduce the present inequality. The experimental results show that those biases and unfairness are not introduced by the different recommendation models and that they come from the socio-psychological and demographic characteristics of the used dataset.

The massive penetration of renewable energy sources in electrical systems has been displacing synchronous generators (SGs) from conventional power plants in the last few years. Renewable generation plants are usually connected to power grids through electronic power converters, which cannot provide the same power generation services as SGs due to their mode of operation. Recently, different concepts have been proposed for electronic converter control in an attempt to emulate the performance of SGs, resulting in the so-called grid-forming converters (GFCs). This paper proposes a new GFC control strategy based on the reactive power synchronization (RPS) method, which decouples the synchronizing power and the active power control of renewable generation source to which a converter is connected. For this purpose, this study assesses three power sources: batteries, photovoltaic (PV) plants, and full-converter wind turbines. Moreover, the study proposes models and controls for each of these sources, whose dynamics exert a decisive influence on the grid services provided by renewable energy plants. Thereafter, the study proposes a GFC–RPS control scheme and verifies its effectiveness in different applications; for example, inertial response, which provides power immediately through a fast frequency response after a grid has experienced a load variation. Unlike storage systems and wind turbines, PV plants can only render these services if they are not operating at maximum power. Further, the study validates the GFC–RPS control strategy for regulating AC voltage at the output terminals of a converter. Finally, the paper assesses GFC hot swapping during the transition from a grid-connected to an isolated-operation mode while feeding a dynamic load. Results revealed that both the voltage and frequency remain stable, thereby demonstrating that the proposed GFC–RPS control indeed acts as a true voltage source and emulates the behavior of a conventional SG.

We report on an electronic coincidence detection circuit for quantum photonic applications implemented on a field-programmable gate array (FPGA), which records each the time separation between detection events coming from single-photon detectors. We achieve a coincidence window as narrow as 500 ps with a series of optimizations on a readily-available and affordable FPGA development board. Our implementation allows real-time visualization of coincidence measurements for multiple coincidence window widths simultaneously. To demonstrate the advantage of our high-resolution visualization, we certified the generation of polarized entangled photons by collecting data from multiple coincidence windows with minimal accidental counts, obtaining a violation of the Clauser-Horne-Shimony-Holt (CHSH) Bell inequality by more than 338 standard deviations. Our results have shown the applicability of our electronic design in the field of quantum information.

The increasing penetration of renewable energies in the power system is demanding new services from wind farms. In particular, system operators are concerned about system restoration after a black-out and new grid codes are under consideration that demand the participation of wind farms in the restoration process. Black start requires the wind farms to be capable of controlling voltage and frequency in an isolated grid. This paper proposes the use of a novel grid forming control for doubly fed induction generators (DFIG) for restoring the system after a black-out. The proposed grid forming control uses the rotor flux orientation principle, that allows to generate an internal electromotive force for controlling in this way the terminal voltage and frequency. Then, it is demonstrated that the rotor flux magnitude and frequency can be controlled by means of the rotor voltage applied the rotor side converter of the DFIG. The paper also proposes a wind turbine control system for balancing the power demanded by the load at the wind turbine mechanical system. Black start capability of the proposed control system has been validated through a comprehensive simulation. The simulated system consists of a wind farm with two DFIG-based wind turbines connected in parallel to a point of common coupling that supplies an induction motor through a feeder. Also, the synchronization of the isolated system to a main grid has been simulated, demonstrating the ability of the proposed control system for successfully completing the restoration process.

The increasing incorporation of renewable energy in power systems is causing growing concern about system stability. Renewable energy sources are connected to the grid through power electronic converters, reducing system inertia as they displace synchronous generators. New grid-forming converters can emulate the behavior of synchronous generators in terms of inertia provision and other grid services, like power-frequency and voltage-reactive regulation. Nevertheless, as a consequence of synchronous generator emulation, grid-forming converters also present angle oscillations following a grid disturbance. This paper proposes two novel power stabilizers for damping low-frequency oscillations (LFOs) in the power system. The first power stabilizer provides power oscillation damping through active power (POD-P), and it is implemented in a grid-forming converter, using the active power synchronization loop to damp system oscillations by acting on the converter angle. The second one provides power oscillation damping through reactive power (POD-Q), and it is implemented in a STATCOM, using the voltage control loop to damp system oscillations. Both proposals are first assessed in a small-signal stability study and then in a comprehensive simulation. Moreover, two cases are considered: damping the oscillations of a single machine connected to an infinite bus through a tie-line, and damping the inter-area oscillations in a two-area system. Simulation results, as well as the stability study, demonstrate the ability of both stabilizers to damp power system oscillations, being the POD-P more effective than the POD-Q, but at the cost of requiring some kind of energy provision at the DC bus.

As the use of recommender systems becomes generalized in society, the interest in varying the orientation of their recommendations is increasing. There are shilling attacks' strategies that introduce malicious profiles in collaborative filtering recommender systems in order to promote the own products or services or to discredit those of the competition. Academic research against shilling attacks has been focused in statistical approaches to detect the unusual patterns in user ratings. Nowadays, there is a growing research area focused on the design of robust machine learning methods to neutralize the malicious profiles inserted into the system. This paper proposes an innovative robust method, based on matrix factorization, to neutralize the shilling attacks. Our method obtains the reliability value associated with each prediction of a user to an item. By monitoring the unusual reliability variations in the items prediction, we can avoid promoting the shilling predictions to the erroneous recommendations. This paper openly provides more than 13 000 individual experiments involving a wide range of attack strategies, both push, and nuke, in order to test the proposed approach. The results show that the proposed method is able to neutralize most of the existing attacks; its performance only decreases in the not relevant situations: when the attack size is not large enough to effectively affect the recommendations provided by the system.

Piezoelectric actuators are candidates for use in radioactive environments but specific radiation tests are necessary to understand the radiation effects on the whole actuator assembly. The results of three irradiation tests on a piezoelectric actuator used for Crystal Collimation are presented. The total ionising dose effects are studied with two Gamma (60Co) Tests up to 10 MGy and 1 MGy, whereas the displacement damage effects are studied in a Proton Test up to 2 MGy and 1.14 × 1016 p/cm2 fluence. The main results are summarised for each test, presenting a maximum impedance increase of less than 25% (Proton Test), a maximum free stroke reduction of less than 25% (Proton Test) and a variation in the shape of the hysteresis response of the actuator.

Emergency alert systems (EASs) have been deployed in some countries in order to broadcast emergency alerts and warning messages to the public. In this letter, we describe an innovative electronic embedded solution, named Firetec switch, intended to be placed in the FM radio stations. This switch will be supported by a server placed at the authorized officials, with the capability to generate the audio alerting messages. One interesting challenge is to deliver the messages only to the local public, in the catastrophe neighborhood, by using FM radio stations. This letter focuses on the description of the Firetec switch hardware and software. [ABSTRACT FROM AUTHOR]