Grid synchronization algorithms are of great importance in the control of grid-connected power converters, as fast and accurate detection of the grid voltage parameters is crucial in order to implement stable control strategies under generic grid conditions. This paper presents a new grid synchronization method for three-phase three-wire networks, namely dual second-order generalized integrator (SOGI) frequency-locked loop. The method is based on two adaptive filters, implemented by using a SOGI on the stationary αβ reference frame, and it is able to perform an excellent estimation of the instantaneous symmetrical components of the grid voltage under unbalanced and distorted grid conditions. This paper analyzes the performance of the proposed synchronization method including different design issues. Moreover, the behavior of the method for synchronizing with highly unbalanced grid is proven by means of simulation and experimental results, demonstrating its excellent performance.

This paper presents a sliding mode control for a wound rotor synchronous machine acting as an isolated generator. The standard dq model of the machine is connected to a resistive load. A switching function is defined in order to fulfill control objectives, and the ideal sliding dynamics is proved to be stable. From the desired surface, the standard sliding methodology is applied to obtain a robust and very simple controller. Numerical simulations and experimental results validate the control law and show good performance and a fast response to load and reference changes.

The operation of distributed power generation systems under grid fault conditions is a key issue for the massive integration of renewable energy systems. Several studies have been conducted to improve the response of such distributed generation systems under voltage dips. In spite of being less severe, unbalanced fault cause a great number of disconnections, as it may produce the injection of unbalanced currents that can easily conduct to the tripping of the converter. In this paper a current control strategy for power converters able to deal with these grid conditions, without exceeding the current ratings of the converter is introduced. Moreover, a novel flexible algorithm has been proposed in order to regulate easily the injection of positive and negative currents for general purpose applications.

In this brief two sliding mode control alternatives to regulate the stator voltage amplitude for a stand alone wound rotor synchronous generator are presented. Both controllers use the stator voltage -component error in the sliding surface. In a first case an outer proportional-integral (PI) loop controller is added to provide the proper d-voltage component reference. The second approach consists in extending the dynamic system to include the integral term as state variable and to modify the former sliding surface by adding this new state. Finally, both simulations and experimental results validates the proposed algorithms.

This paper deals with the design, operation, modeling, and grid integration of bioelectrochemical systems (BES) for power-to-gas application, through an electromethanogenesis process. The paper objective is to show that BES-based power-to-gas energy storage is feasible on a large scale, showing a first approximation that goes from the BES design and operation to the electrical grid integration. It is the first study attempting to cover all aspects of a BES-based power-to-gas technology, on authors’ knowledge. Designed BES reactors were based on a modular architecture, suitable for a future scaling-up. They were operated in steady state for eight months, and continuously monitored in terms of power consumption, water treatment, and biomethane production, in order to obtain data for the following modeling activity. A black box linear model of the BES was computed by using least-square methods, and validated through comparison with collected experimental data. Afterwards, a BES stack was simulated through several series and parallel connections of reactors, in order to obtain higher power consumption and test the grid integration of a real application system. The renewable energy surplus and energy price variability were evaluated for the grid integration of the BES stack. The BES stack was then simulated as energy storage system during low energy price periods, and tested experimentally with a real time system.

The level of penetration of grid-connected photovoltaic (PV) systems has grown very quickly in recent years. Nonetheless, network stresses related to the recurrent voltage and frequency oscillations caused by their irregular power production could be a limiting factor on the future expansion of these applications. With the capability of storing and releasing electrical energy on demand, Energy Storage Devices (ESDs) may play a key role in finding an effective solution to overcome these kinds of problems. The aim of this paper is to provide a description of the state-of-the-art power conversion systems used to combine ESDs and grid-connected PV plants. The work has been edited after an accurate analysis of the current scientific literature, focusing particular attention on medium-high-power PV applications utilizing batteries and/or supercapacitors. A detailed analysis on advantages, disadvantages and range of application is provided for each of the reported conversion systems.