J.M. Maza-Ortega

Reference Current Computation for Active Power Filters by Running DFT Techniques

This paper analyzes the feasibility and convenience of applying the efficient discrete Fourier transform (DFT) techniques for the computation of reference currents in active power filters. Existing methods designed for this purpose rely on a high-pass filter in order to obtain the harmonic components of the load current to be filtered. Among these methods, the stationary reference frame (SRF) method reveals itself as the most accurate one because of its inherent immunity to distorted voltage conditions. In this paper, two different implementations of the running DFT, including their recursive and nonrecursive versions, are compared to the SRF approach in terms of steady-state performance, adequacy of transient response, and computational effort. In addition to simulation results, an experimental setup is designed to prove the advantages of resorting to the DFT. Conceptual similarities between both schemes are also stressed in this paper.

A software-based tool for optimal design of passive tuned filters

This paper presents a software-based tool for designing passive filters by using an optimization technique. The proposed procedure takes into account the non-convex behavior of any objective function in case of considering harmonics below the tuned frequencies of the filters. In this sense, it is always assured that the optimal filter is obtained with respect to an optimization criterion. The implemented optimization problem also considers usual real constraints such as reactive power limitation provided by the filters. The proposed software includes different optimization criteria depending on the designer concerns. Finally, a case study is proposed including a comparison between the results of different objective functions.

Operational benefits of multiterminal DC-links in active distribution networks

The objective of this paper is to demonstrate the benefits of using multiterminal DC links in distribution systems. A three level control strategy is considered to obtain an optimal power flow and to improve the voltages transient behavior. Analysis and simulations are carried out over a medium voltage benchmark distribution network from IEEE/CIGRE. Power losses reduction and improved voltage profiles can be obtained by an adequate control of the power flows. Two transient analysis showing the fault ride through capability and voltage sag mitigation are performed. In addition a scaled experimental setup is used to validate simulation results.

Enhancing the integration of renewable sources in distribution systems using DC-links

This work proposes the use of DC-links between existing radial distribution feeders so that full advantage is taken of their maximum capacity, which is particularly important when new distributed generators are to be connected at the distribution level. An optimization tool is developed to determine the optimum settings for the DC-link control variables, in order to maximize the penetration of dispersed sources subject to customary electrical constraints. Simulation results regarding two real networks are presented to illustrate the former advantages. Also, improvements in system operation resulting from the presence of DC-links are studied and discussed. A real loss model for the DC link is considered in all test cases.

DC Link Operation in Smart Distribution Systems With Communication Interruptions

DC Links are proposed in the literature as a mean to enhance the system performance and facilitate the integration of dispersed generators in distribution grids. Their operation relies on a centralized controller which gathers the measurements acquired along the network to compute their adequate set points. This system architecture provides several technical benefits but strongly depends on communication infrastructures (meters, data concentrators, etc.) which may fail. When this happens the DC links may not work properly, even forcing the system operator to disconnect them until the communications are restored. This paper proposes operational strategies to avoid the malfunction or disconnection of DC links when communication interruptions occur. Several simulations are done to assess how these strategies affect the performance of the DC links. An actual Spanish 100-bus distribution system with a DC link is used as a test bench in different situations.

Discussion of “An optimization based method for selection of resonant harmonic filter branch parameters”

For original paper by H.L. Ginn and L. S Czarnecki see ibid. vol. 21, no.3, p.1445-1451, July. 2006.

DC link operation in smart distribution systems with communication interruptions

DC Links are proposed in the literature as a mean to enhance the system performance and facilitate the integration of dispersed generators in distribution grids. Their operation relies on a centralized controller which gathers the measurements acquired along the network to compute their adequate set points. This system architecture provides several technical benefits but strongly depends on communication infrastructures (meters, data concentrators, etc.) which may fail. When this happens the DC links may not work properly, even forcing the system operator to disconnect them until the communications are restored. This paper proposes operational strategies to avoid the malfunction or disconnection of DC links when communication interruptions occur. Several simulations are done to assess how these strategies affect the performance of the DC links. An actual Spanish 100-bus distribution system with a DC link is used as a test bench in different situations.

A Multi-Platform Lab for Teaching and Research in Active Distribution Networks

Todays electricity paradigm requires that the notion of active distribution systems be introduced at both undergraduate and graduate curricula. This involves not only the customary theoretical foundations but also a suitable power engineering laboratory, where flexible enough and affordable resources allow students and researchers to carry out hands-on experiments reinforcing the concepts explained in the classroom. This paper describes the smart grid laboratory of the Power Engineering Group at the University of Seville, composed of a scaled-down distribution system, along with the required control and monitoring equipment, designed to help its users easily grasp the major influence that distributed generation and storage devices exert in the operation of medium-voltage distribution systems.

Multiterminal electrical charging station for LV networks

The massive penetration of electric vehicles may create local problems on the LV distribution systems where the charging stations are located. Most of the solutions proposed in the specialized literature are based on centrilized algorithms which are applied to traditional LV distribution systems. This paper proposes a new charging station based on a multiterminal DC-link. This new infrastructure, based on a flexible link between the radial feeders, allows maximizing the use of the current assets and optimizing the network operation by an equalization of the involved MV/LV transformers.

Control strategy for a mid-size wind energy convertion system

A control strategy for a mid-size Permanent Magnet Synchronous Machine (PMSM) based Wind Energy Conversion System (WECS) operating under unbalanced voltages and currents is presented in this paper. The analyzed WECS is based on a PMSM connected through a non-controlled rectifier to the DC-bus. This paper proposes a new control strategy for improving the wind energy conversion efficiency based on the DC voltage regulation. In addition, in order to eliminate over-currents risk during unbalanced conditions, a control scheme has been designed to independently control positive and negative sequence currents. The proposed controller is based on the feedback linearization technique and shows an improvement in the system performance regarding 2ω ripple elimination in the DC voltage arising during AC-side imbalances and an accurate and decoupled active and reactive power tracking.