Abstract-This paper presents a new multiresonant frequencyadaptive synchronization method for grid-connected power converters that allows estimating not only the positive-and negative-sequence components of the power signal at the fundamental frequency but also other sequence components at other harmonic frequencies. The proposed system is called MSOGI-FLL since it is based on both a harmonic decoupling network consisting of multiple second-order generalized integrators (MSOGIs) and a frequency-locked loop (FLL), which makes the system frequency adaptive. In this paper, the MSOGI-FLL is analyzed for singleand three-phase applications, deducing some key expressions regarding its stability and tuning. Moreover, the performance of the MSOGI-FLL is evaluated by both simulations and experiments to show its capability for detecting different harmonic components in a highly polluted grid scenario.

This paper deals with a fundamental aspect in the control of grid-connected power converters, i.e., the detection of the positive-sequence component at fundamental frequency of the utility voltage under unbalanced and distorted conditions. Accurate and fast detection of this voltage component under grid faults is essential to keep the control over the power exchange with the grid avoiding to trip the converter protections and allowing the ride-through of the transient fault.In this paper, the systematic use of well known techniques conducts to a new positive-sequence voltage detection system which exhibits a fast, precise, and frequency-adaptive response under faulty grid conditions. Three fundamental functional blocks make up the proposed detector, these are: i) the quadrature-signals generator (QSG), ii) the positive-sequence calculator (PSC), and iii) the phase-locked loop (PLL). A key innovation of the proposed system is the use of a dual second order generalized integrator (DSOGI) to implement the QSG.For this reason, the proposed positive-sequence detector is called DSOGI-PLL. A detailed study of the DSOGI-PLL and verification by simulation are performed in this paper. From the obtained results, it can be concluded that the DSOGI-PLL is a very suitable technique for characterizing the positivesequence voltage under grid faults.

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The high penetration of distributed generation, as\ud PV or wind power, has forced the Transmission System\ud Operators (TSOs) to set restrictive requirements for the\ud operation of such systems. As it can be extracted from the\ud forthcoming grid codes drafts, the future distributed\ud generation systems will be requested to have the equivalent\ud performance of a synchronous generator, which is seen from\ud the TSOs as the only solution if a massive integration of\ud renewable in the electrical network should be achieved. In this\ud paper a method for controlling PV grid connected power\ud converters as a synchronous generator, namely Synchronous\ud Power Controller (SPC), is presented. As a difference with\ud previous works this method permits to take advantage of\ud emulating the synchronous behavior meanwhile it is able to get\ud rid of its drawbacks. The main concept of the SPC, as well as\ud some simulation and experimental results will be shown in this\ud paper considering a PV power plant as a study case.Peer ReviewedPostprint (published version

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The connection of electronic power converters to the electrical network is increasing mainly due to\ud massive integration of renewable energy systems. However, the electrical dynamic performance of\ud these converters does not match the behavior of the network, which is mainly formed by generation\ud facilities based on big synchronous generation systems. Depending on the desired electrical operation\ud mode different control structures can be implemented in the converters in order to get adapted with the\ud grid conditions. However, changing between different control structures and operation is not an\ud optimal solution, as the resulting system results complex and is not highly robust. As an alternative,\ud this paper presents a new control technique for grid connected power converters based on the concept\ud of virtual admittance. The proposed control permits to emulate the electrical performance of\ud generation facilities based on classical synchronous generators with a power converter, with no need\ud of implementing different control structures, giving rise to a system that provides a friendly and robust\ud operation with the network.Peer ReviewedPostprint (published version

This paper proposes a hierarchical control architecture designed for an arbitrary high voltage multiterminal dc (MTDC) network. In the proposed architecture, the primary control of the MTDC system is decentralized and implemented using a generalized droop strategy. Design criteria for dimensioning the primary control parameters, including voltage limits, are offered by analyzing the transients appearing in the system. The proposed secondary control is centralized and regulates the operating point (OP) of the network so that optimal power flow (OPF) is achieved. Compared to previous works, this paper further elaborates, both analytically and through simulations, on the coordination between the primary and secondary control layers. This includes how local primary controllers have to be driven by the centralized controller in order to ensure a smooth transition to the optimal OP. IndexTerms-Droop control, hierarchical control, multiterminal dc (MTDC) systems, optimal power flow (OPF).

Multi-terminal dc networks based on voltage source converters (VSC) are the latest trend in dc-systems; the interest in the area is being fueled by the increased feasibility of these systems for the large scale integration of remote offshore wind resources. Despite the active research effort in the field, at the moment, issues related to the operation and control of these networks, as well as sizing, are still uncertain. This paper intends to make a contribution in this field by analyzing the sizing of droop control for VSC together with the output capacitors. Analytical formulas are developed for estimating the voltage peaks during transients, and then it is shown how these values can be used to dimension the dc-bus capacitor of each VSC. Further on, an improved droop control strategy that attenuates the voltage oscillations during transients is proposed. The proposed methods are validated on the dc-grid benchmark proposed by the CIGRE B4 working group. Starting from the structure of the network and the power rating of the converters at each terminal, the output capacitors and the primary control layer are designed together in order to ensure acceptable voltage transients.(C) 2014 Elsevier B.V. All rights reserved.Peer ReviewedPostprint (author’s final draft