http://hdl.handle.net/2117/3671 2013-05-25T19:42:00Z http://hdl.handle.net/2117/19336 Title: Secondary control for reactive power sharing in droop-controlled islanded microgrids Authors: Micallef, A.; Apap, Maurice; Spiteri Staines, C.; Guerrero Zapata, Josep Maria Abstract: This paper focuses on the islanded operation of microgrids. In this mode of operation, the microsources are required to cooperate autonomously to regulate the local grid voltage and frequency. Droop control is typically used to achieve this autonomous voltage and frequency regulation. However, droop control has real and reactive power sharing limitations when there are mismatches between the microsources. This paper analyses the effect due to mismatches in the power line impedances connecting the source inverters to the microgrid. From the simulations results obtained, it was shown that the reactive power demand is unequally shared between the microsource inverters when there are mismatches between the power line impedances. To achieve equal reactive power sharing between the inverters, an external loop requiring low bandwidth communications was implemented in a central controller. Simulation results are presented showing the feasibility of the proposed solution in achieving reactive power sharing between the inverters connected to the microgrid. 2013-05-17T12:52:13Z http://hdl.handle.net/2117/16762 Title: Fast grid synchronization technique based on a multiple cascaded general integrator scheme for distributed generation inverters Authors: Matas Alcalá, José; Castilla Fernández, Miguel; García de Vicuña Muñoz de la Nava, José Luis; Miret Tomàs, Jaume; Alarcón Gallo, Eduardo; Camacho Santiago, Antonio Abstract: This paper proposes a new structure for grid synchronization based on generalized integrators (GI) that lead to fast detection of positive and negative components of the grid voltage. The GI are used as a band pass filter (GI-BPF) mainly to provide in-phase and quadrature components of grid voltage. The proposed structure consists in the cascaded connection of multiple GI-BPF to achieve a faster time response than a single GI-BPF but with the same bandwidth characteristics. This structure is used with a frequency locked loop and a positive sequence detector to operate under unbalanced voltage sags. Simulations and experimental results of a photovoltaic power system injecting power to the grid in the stationary reference frame are shown to validate this proposal. Comparisons between this proposal and one that uses a single GI-BPF in the sequence detector are provided. The results show that the proposed cascaded GI-BPF achieves a considerably time response reduction in the sequence grid detection under a fault with the same quality-filter characteristics. 2012-10-19T11:34:41Z http://hdl.handle.net/2117/16760 Title: Coordinated reactive power control for static synchronous compensators under unbalanced voltage sags Authors: Castilla Fernández, Miguel; Miret Tomàs, Jaume; Camacho Santiago, Antonio; Matas Alcalá, José; Alarcón Gallo, Eduardo; García de Vicuña Muñoz de la Nava, José Luis Abstract: Unbalanced voltage sags strongly deteriorate the performance of power converters and electrical machines connected to the distribution network. In particular, a reduction of the power quality is noticed in these equipments, which is caused by a ripple in the output power and an increase of the current harmonic distortion. Several solutions based on reactive power compensation have been introduced to cope with this problem. Among them, static synchronous compensators have confirmed the superior performance due to the possibility of using all rated power exclusively to voltage support. This paper presents a simple reactive power control algorithm for static synchronous compensators operating under unbalanced voltage sags. The main feature of the proposed algorithm is that it allows a fine adjustment of the amount of reactive power injected by the positive- and negative-sequence components. Thus the control algorithm provides voltage support at the output of the static synchronous compensator. Specifically the proposed control conveniently corrects both the positive- and negative-sequence voltage. Selected simulation results are provided to validate the proposal. 2012-10-19T11:04:36Z http://hdl.handle.net/2117/15608 Title: Voltage harmonic compensation of a microgrid operating in islanded and grid-connected modes Authors: Savaghevi, Mehdi; Jalilian, A.; Vásquez Quintero, Juan Carlos; Guerrero Zapata, Josep Maria; Lee, Tzung-Lin Abstract: In this paper, a method for voltage harmonic compensation in a microgrid operating in islanded and grid-connected modes is presented. Harmonic compensation is done through proper control of distributed generators (DGs) interface converters. In order to achieve proper sharing of the compensation effort among the DGs, a power named “Harmonic Distortion Power (HDP)” is defined. In the proposed method, the active and reactive power control loops are considered to control the powers injected by the DGs. Also, a virtual impedance loop and voltage and current proportional-resonant controllers are included. Simulation results show the effectiveness of the proposed method for compensation of voltage harmonics to an acceptable level. 2012-03-18T10:45:17Z http://hdl.handle.net/2117/15607 Title: Modeling, analysis, and design of stationary reference frame droop controlled parallel three-phase voltage source inverters Authors: Vásquez Quintero, Juan Carlos; Guerrero Zapata, Josep Maria; Savaghevi, Mehdi; Teodorescu, Remus Abstract: Power electronics based microgrids consist of a number of voltage source inverters (VSIs) operating in parallel. In this paper, the modeling, control design, and stability analysis of three-phase VSIs are derived. The proposed voltage and current inner control loops and the mathematical models of the VSIs were based on the stationary reference frame. A hierarchical control for the paralleled VSI system was developed based on three levels. The primary control includes the droop method and the virtual impedance loops, in order to share active and reactive power. The secondary control restores the frequency and amplitude deviations produced by the primary control. And the tertiary control regulates the power flow between the grid and the microgrid. Also, a synchronization algorithm is presented in order to connect the microgrid to the grid. The evaluation of the hierarchical control is presented and discussed. Experimental results are provided to validate the performance and robustness of the VSIs functionality during Islanded and grid-connected operations, allowing a seamless transition between these modes through control hierarchies by regulating frequency and voltage, main-grid interactivity, and to manage power flows between the main grid and the VSIs. 2012-03-18T10:33:52Z http://hdl.handle.net/2117/14473 Title: Networked sliding mode control of the double integrator system using the event-driven self-triggered approach Authors: Martí Colom, Pau; Velasco García, Manel; Camacho Santiago, Antonio; Martín Rull, Enric Xavier; Fuertes Armengol, José Mª Abstract: Sliding mode control (SMC) methods rely on applying a high-frequency switching control. In networked control systems (NCS), high-frequency operations/transactions are not desirable because communication bandwidth consumption increases dramatically. This paper studies the application of event-driven self-triggered techniques to sliding mode control over networks as a means for reducing the bandwidth utilization. To this end, sliding mode control with hysteresis is adopted and control updates are forced to only occur at the hysteresis band boundary. This paper elaborates on the conditions that must be fulfilled in order to ensure such operation for the case of the double integrator system. Simulation results illustrate the presented concepts. 2012-01-11T13:27:51Z http://hdl.handle.net/2117/14371 Title: Nonlinear control of single-phase shunt active power filter. Theoretical analysis of closed-loop performances. Authors: Lachkar, I.; Giri, F.; Abouloifa, A; Guerrero Zapata, Josep Maria; Griñó Cubero, Robert; Chaoui, F.Z; Elfadil, H. Abstract: The problem of controlling single-phase shunt active power filter is addressed in presence of nonlinear loads. The control objective is twofold: (i) compensation of harmonic and reactive currents absorbed by the nonlinear load; (ii) regulation of the inverter output capacitor voltage. A two-loop cascade control strategy is developed that includes an inner-loop designed, using the backstepping technique, to cope with the compensation issue and an outer-loop designed to regulate the capacitor voltage. The controller performances are formally analysed, using the averaging theory. The analysis results are illustrated by simulation. 2011-12-30T09:47:42Z http://hdl.handle.net/2117/14058 Title: Power sizing factor design of central inverter PV grid-connected systems: a simulation approach. Authors: Velasco Quesada, Guillermo; Piqué López, Robert; Guinjoan Gispert, Francisco; Casellas Beneyto, Francisco; Hoz Casas, Jordi de la Abstract: This paper presents a simulation approach which can help in the preliminary power sizing design of a gridconnected PV system based on a single inverter configuration. Given a nominal peak power of the PV array, this simulation procedure leads to the PV inverter maximum rated power which maximizes the yearly injected energy to the grid. 2011-11-24T12:39:26Z http://hdl.handle.net/2117/13089 Title: Selective compensation of voltage harmonics in an islanded microgrid Authors: Savaghebi, M.; Jalilian, A.; Vásquez Quintero, Juan Carlos; Guerrero Zapata, Josep Maria Abstract: Recently, distributed generators are applied not only to inject power into the grid/local load, but also to compensate power quality problems. In this paper, a method for selective voltage harmonics compensation in microgrid based on the proper control of distributed generator (DG) interface converter is proposed. In this method, active and reactive power control loops are considered to control the power sharing among the DGs. Also, a virtual impedance loop and voltage and current proportional-resonant controllers are included. Simulation results show the effectiveness of the proposed method for compensating voltage harmonics to an acceptable level. 2011-08-23T08:29:45Z http://hdl.handle.net/2117/11125 Title: Intelligent control agent for transient to an island grid Authors: Rocabert Delgado, Joan; Azevedo, Gustavo; Vázquez Guzmán, Gerardo; Candela García, José Ignacio; Rodríguez Cortés, Pedro; Guerrero Zapata, Josep Maria Abstract: The increasing penetration of generation power plants based on renewable energies in the electrical networks has boosted the number of systems connected to the grid. In this scenario the microgrid, providing advanced functionalities to improve the stability and operation of the network, have become very popular. In this paper a control strategy for the microgrid management is presented. The proposed system improves the performance of microgrids and its interaction with the main network, or another microgrid, under grid voltage transients. This technique gives rise to a simple and robust control scheme to ensure the appropriate microgrid disconnection from the main grid. In the following the control algorithm for the intelligent connection agent will be shown, and the grid synchronization system, as well as the voltage and current control loops will be detailed. Finally simulation results obtained using the MATLAB/Simulink & Psim platform will be presented and discussed. 2011-01-20T12:59:42Z http://hdl.handle.net/2117/10792 Title: A novel robust sliding mode controller for Half-bridge converter Authors: Hang, Lijun; Liu, Sensen; Lu, Zhengyu; Castilla Fernández, Miguel Abstract: This paper proposes one novel sliding mode controller for the Half-bridge converter to reduce the line and load disturbance. Based on the bilinear model of the Half-bridge DC/DC converter, the small signal model and the design consideration of the sliding mode controller for this converter are deduced and presented. The controller is simply implemented in the analog controller board. The validation of the controller is verified both by theory analysis and experimental results. By applying the novel sliding mode controller, the Half-bridge converter can achieve good transient response. 2010-12-28T15:45:09Z http://hdl.handle.net/2117/7391 Title: Impact of NBTI on EMC behaviours of CMOS inverter Authors: Fernández García, Raúl; Berbel Artal, Néstor; Gil Galí, Ignacio; Morata Cariñena, Marta Abstract: In this paper the Electromagnetic Robustness (EMR) of a CMOS inverter has been analyzed when the pFETs are submitted to negative bias temperature instability (NBTI). The impact of pFET and CMOS inverter has been experimentally quantified and the switching noise and electromagnetic susceptibility has been analyzed by means of simulation. The results show that NBTI reduces the switching noise whereas the EMI susceptibility is not modified. 2010-05-27T11:05:36Z http://hdl.handle.net/2117/6826 Title: Modelling and experimental verification of the impact of negative bias temperature instability on CMOS inverter Authors: Berbel Artal, Néstor; Fernández García, Raúl; Gil Galí, Ignacio Abstract: The effects of negative bias temperature instability (NBTI) on the performance of a CMOS inverter have been investigated by means of both simulation and experimental methods. The simulation of NBTI effects on CMOS inverter has been done by shifting the pFET Vtho BSIM parameter. The results show that NBTI shifts the inverter transfer curve, reduces the low noise margin and current consumption but increases the high noise margin. A good agreement between simulation and experimental results has been obtained. Therefore, it can be assumed that the effect of NBTI on CMOS circuits can be mainly predicted by shifting the Vtho pFET parameter. Description: Published in Microelectronics Reliability, Volume 49, Issues 9-11, September-November 2009, Pages 1048-1051 2010-03-29T10:30:43Z