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The implementation of ancillary services in renewable energy based generation systems requires controlling bidirectional power flow. For such applications, integrated energy storage systems (ESSs) in such generation platforms have emerged as a promising solution. However, a large variety of ESS solutions are available in the market, and even hybrid systems are proposed to optimize the overall performance. In this regard, the integration of supercapacitors (SCs) and electrochemical batteries is an attractive and feasible solution, as it takes the most of the combination of the large storage capacity of batteries with the high dynamic performance of SCs. This combination enables the implementation of energy and power services, such as inertia emulation, black start, or power oscillation damping among others. This solution avoids oversizing ESS and enlarges the battery lifetime, since the SCs absorve the high dynamic response meanwhile the battery feeds an attenuated power profile. This paper presents a strategy to manage mixed energy storage technologies, composed by a direct connection of a battery and an SC bank interfaced through a dc-dc converter. A power control loop distributes the power flow through each element in order to achieve an optimized performance, meanwhile, it permits to provide grid-frequency support and minimizes the number of cycles applied to the battery. The analysis made and the initial sections are endorsed by simulation and experimental results collected in a 50-kW test-bench. This work was supported in part by Spanish Ministry of Science under Projects ENE2016-79493-R and ENE2017-88889-C2-1-R and in part by the European Commission under Project FLEXITRANSTORE —H2020-LCE-2016-2017-SGS-774407. Peer Reviewed Objectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant

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&rsquo, 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.

This letter introduces a new series of multilevel (ML) converters based on the ML clamping concept. By applying this technique, a ML clamping unit (MCU) conveys additional levels for synthesizing the output waveforms of a diode-clamped ML dc-ac power converter. The basic building block of the ML clamping scheme is the ML clamping cell, which is composed of a pair of dc sources associated with one single-pole/triple-throw type of switch arrangement. The number of series-connected ML-clamping cells will set the number of levels of the synthesized waveform. By depending on the MCU arrangements, different converter configurations can be derived, namely, the common clamping and the modular types. Both approaches can be accomplished by employing classical three-level neutral-point-clamped (NPC) technology. Thus, the overall structure of the resultant converter is kept simple, wherein the number of parts count can be reduced, when compared with conventional NPC counterparts. In this letter, emphasis is given on the common clamping converter configuration. The attractiveness of the proposed ML concept is evidenced by conducting a comparative cost analysis. Experimental results are presented as a practicality proof of the proposed ML power converter.

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.

This paper presents a proposal for a series hybrid electric vehicle propulsion system. This new configuration is based on a wound-rotor synchronous generator (WRSM) and a doubly-fed induction machine (DFIM). The energy-based model of the whole system is obtained taking advantage of the capabilities of the port-based modeling techniques. From the dq port-controlled Hamiltonian description of the WRSM and DFIM, the Hamiltonian model of the proposed Direct Synchronous-Asynchronous Conversion System (DiSAC) is developed. Subsequently, the bond graph models of the DiSAC and associate systems are also provided. Numerical simulations are also presented in order to validate the proposed system. © 2012 Elsevier Ltd. All rights reserved., R. S. Muñoz-Aguilar, A. Dòria-Cerezo and P.F. Puleston were partially supported by the Spanish government research projects ENE2011-29041-C02-01, DPI2010-15110 and Marie Curie FP7-PIIF-911767 (EU), CONICET and UNLP (Argentina), respectively.

In this paper the losses of the DCM-232 topology for a particular modulation strategy has been analyzed. This modulation has as particular that no common mode currents are presented. Some simulation and experimental results are given in order to prove the good behavior of the topology regarding common mode voltage (CMV), the converter efficiency and the THD.

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.

Nowadays transformerless PV converters are widely used in the energy conversion stage of a PV plant, because their good characteristics regarding efficiency, size, cost and weight. The main problem in transformerless PV systems is the common mode voltage variations that can generate leakage ground currents (LGC) through the parasitic capacitance formed between the PV panels and ground. These LGC are a risk for the users in a PV system therefore they should be avoided. The LGC has a clear origin on the pulse width modulation (PWM) strategy and the converter structure. In this paper a three-phase inverter with constant common mode voltage (CMV) is proposed. Simulation results are also provided.

In this paper a modulation strategy for the DCM-232 power converter is proposed. This modulation has as particular a symmetrical ripple and that no common mode currents are presented. Some simulation and experimental results are given in order to prove the good behavior of the topology regarding common mode voltage (CMV).

The continuous and accurate information of generator speed in wind energy application is an essential requirement in order to get the maximum power at given tip speed ratio, since the maximum power is almost an cubic function of generator speed. This paper studies a Frequency Locked Loop (FLL) - based controller for estimating the rotor speed of the Permanent Magnet Synchronous Generator (PMSG) in a Wind Energy Conversion Systems (WECS). The proposed system consist on get the direct sequence component of generator voltage by means a Dual Second Order Generalized Integrator (DSOGI) and applying a FLL for estimating the generator frequency and, hence, its rotor speed. Using a Proportional Resonant (PR) control, the rotor position is not required and thus a lot of mathematical operations are avoided. Simulation using MATLAB/Simulink and PowerSim shows that using a FLL leads to a simpler and reliable sensorless technique.

This paper presents a Sliding Mode Control for a wound rotor synchronous machine acting as an isolated generator connected to an unbalanced load. In order to simplify the control methodology, the standard dq-model of the machine is connected to a balanced resistive load. A switching function is defined in order to fulfill the control objective. From the desired surface, the standard sliding methodology is applied to obtain a robust and very simple controller. Then, the actual measured voltage of the machines is acquired and treated trough a frequency locked loop algorithm in order to extract the positive sequence and control it to guarantee a good definition of the park transformation. A phase locked loop algorithm is also used to avoid speed sensors. Numerical simulations a validate the control law and show good performance and a fast response to load and reference changes.

This work presents the development of the space vector pulse width modulation (SVPWM) of a new multi-level converter topology. First, the proposed converter and its natural space vector diagram are presented. Secondly, a modified space vector diagram based on the virtual-vectors technique is shown. Simulation results by using a space vector approach are presented. Special emphasis is given on the total harmonic distortion (THD) by making a comparison with those of the classical NPC topologies.

This paper presented an overview of harmonic analysis and resonance in large wind power plant. The harmonic related problem becomes a concern as the growing numbers of nonlinear load and the increased possibility of harmonic resonances occurrence. In WPP, several conditions may contribute to the resonance phenomenon that will amplify the effect of the harmonic frequency. General overview of international standards and grid codes and basic modeling of WPP for harmonic analysis is also presented. Furthermore, an overview of the harmonic analysis methods are reviewed with emphasize given on the harmonic resonance analysis. A simple three-bus system example is evaluated applying three resonance analysis methods.

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 paper 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 d-component error in the sliding surface. In a first case an outer 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, simulations results are done in order to validate the proposed algorithms.

This paper presents a sliding mode controller for a wound rotor synchronous machine, acting as a generator for an isolated load. The standard dq-model of the machine is connected to a resistive load. A sliding surface 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, and a robust controller is obtained. Numerical simulations are also presented to validate the control law.

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.

In this paper a modulation strategy based on the classical space vector modulation is applied to the FB10 converter, a new converter topology for PV applications. Firstly, the FB10 converter is presented and the natural modulation is computed. Secondly, the simulation and experimental results are shown. Finally, the conclusions are stated.

In this paper the grid harmonic resonance on long lines is studied, in particular the resonance phenomena between the grid series inductance and the line parallel capacitor. Later, the resonance is attenuated by using a renewable energy generator. Experimental results are depicted and the conclusions are stated.

Ancillary services offered by renewable energy sources frequently requires the capability of bidirectional power flow and power reserve, so an energy storage system (ESS) is a solution for this requirement. A large variety of ESS solutions are in the market, and frequently are mixed to optimize the global performance. This paper presents the integration of supercapacitors (SC) and electrochemical batteries for grid-supporting applications. The large operating voltage range of a SC requires a power conversion stage to adapt the energy stored into a common dc-bus composed by a battery bank. This is achieved through bidirectional dc-dc interleaved buck / boost converters feeding a common higher-voltage dc-bus, composed by the battery. In order to integrate the energy storage mix to the grid, through a grid-supporting inverter, a power control loop has been implemented with the goal of take advantage of the high dynamic performance of the SC bank and high reserve capacity of the battery system.