Showing papers by "Marco Liserre published in 2008"

Overview of PI-Based Solutions for the Control of DC Buses of a Single-Phase H-Bridge Multilevel Active Rectifier

Abstract: The H-bridge-based multilevel active rectifier is an attractive topology that allows feeding of multiple dc loads. The main control problem is to manage state variables (one current plus dc voltages) with only switching functions. In this paper, three PI-based solutions are discussed, and the tuning of the best solution is addressed in case resonant controllers are used instead of classical integrators. Moreover, practical problems such as the implementation and the influence of phase-locked-loop systems and of analog filters (first order and Butterworth) on the measurements are discussed.

Common mode voltage in case of transformerless PV inverters connected to the grid

Abstract: For safety reasons grid connected PV systems include galvanic isolation. In case of transformerless inverters, the leakage ground current through the parasitic capacitance of the PV panels, can reach very high values. A common-mode model based on analytical approach is introduced, used to predict the common-mode behavior, at frequencies lower than 50 kHz, of the selected topologies and to explain the influence of system imbalance on the leakage current. It will be demonstrated that the neutral inductance has a crucial influence on the leakage current. Finally experimental results will be shown for the NPC topology, emphasizing the low leakage current for the case of a grid connection without galvanic isolation.

Study of the Effects of Inductor Nonlinear Behavior on the Performance of Current Controllers for Single-Phase PV Grid Converters

Abstract: Resonant and repetitive controllers are well suited for single-phase grid-connected inverters due to their optimum tracking and harmonic rejection capability. In particular, in this paper, their application for single-phase photovoltaic systems is considered. The effects of nonlinear inductance on the performance of current controllers designed to track periodic signals and/or to compensate periodic disturbances are investigated. When the inductance has a nonlinear behavior, a distorted current waveform is produced. Two different nonlinearities have been considered: saturation for high currents and a light nonlinearity, which occurs in the first portion of the magnetization curve, for low currents. A current-dependent model of the nonlinear inductance has been developed. It is mathematically based on the Volterra-series expansion, and it allows us to prove how the harmonic compensation provided by resonant and repetitive controllers can also mitigate the effects of the inductance saturation. This result is the main contribution of this paper, and it is also substantiated with experimental evidence. Moreover, the repetitive controller is able to comply with the harmonic limits reported in IEEE 1547 and IEC 61727, even in very hard saturation conditions.

Comparison of power converter topologies for permanent magnet small wind turbine system

Abstract: Permanent magnet based wind generators are one of the more promising technology. This paper presents a comparison of power converter topologies for permanent magnet small wind turbine systems to improve the power quality and to extract the maximum power from wind. Two detailed models are presented and explained: the first configuration is made by a diode-bridge rectifier, a boost converter and an inverter connected to the grid, the second configuration is a back-to-back converter. The generator control is designed to maximize the power output and achieve a smooth torque and power profile. The operational characteristics of the two configurations are investigated through simulations.

MPPT algorithm for voltage controlled PV inverters

Abstract: This paper presents a novel concept for an MPPT that can be used in case of a voltage controlled grid connected PV inverters. In case of single-phase systems, the 100 Hz ripple in the AC power is also present on the DC side. Depending on the DC link capacitor, this power fluctuation can be used to track the MPP of the PV array, using the information that at MPP the power oscillations are very small. In this way the algorithm can detect the fact that the current working point is at the MPP, for the current atmospheric conditions.

Advances on Remote Laboratories and e-Learning Experiences (Gomes, L. and Garcia-Zubia, J., Eds.) [Book News]

Abstract: This book presents an overview of experiences related to remote laboratory usage for teaching and learning processes. The book covers many topics related to remote laboratories which have the potential to drastically change the economics of the lab experience in science and engineering education. There are five section: "Remote Labs: Past and Future"; "Remote Labs Impact Within the Learning Process"; "Remote Labs Development Issues"; "Remote Labs in Use"; and "New Challenges." This book is strongly recommended for its comprehensive view of the potential for e-learning and usage of remote laboratories backed by an international group of specialists in the field.

Droop control of a multifunctional PV inverter

Abstract: Implementation of ancillary services in photovoltaic systems could facilitate their penetration in power systems. PV converters can be designed to improve grid power quality using power conditioning functionalities. This paper presents a single-phase photovoltaic system which provides grid voltage support at fundamental frequency. The proposed topology is controlled with the droop control technique. Experimental results validate the proposed control.

Grid voltage support by means of a small Wind Turbine System

Abstract: The paper presents a small Wind Turbine System (WTS) improved with voltage compensation functionality. In the WTS the Permanent Magnet Generator (PMG) control is designed to maximize the power output and achieve a smooth torque and power profile. The grid-side converter is controlled in order to maintain constant the voltage for local loads also in presence of grid voltage variations. The proposed control allows to obtain sinusoidal grid currents and high power factor during normal operation conditions while the control of the reactive power injected by the wind turbine system provides voltage support.

Unified power quality conditioner (UPQC) with voltage dips and over-voltages compensation capability

Abstract: Unified power quality conditioners (UPQCs) allow the mitigation of voltage and current disturbances that could affect sensitive electrical loads while compensating the load reactive power. Diverse control techniques have been proposed to evaluate the instantaneous output voltage of the series active power filter of the UPQC but, in most cases, these controllers only can compensate a kind of voltage disturbance. This paper proposes a new digital controller for UPQCs which allows the load current harmonics and reactive power to be compensated at the grid side while avoiding the effect of voltage dips, over-voltages and voltage harmonics on the local loads. The controller characteristics can be established on-line without changing its basic structure. The performance of the proposed controller has been evaluated through simulation tests.

Control of a three-phase four-wire shunt-active power filter based on DC-bus energy regulation

Abstract: This paper presents a nonconventional three-phase four-wire shunt active power filter (APF) topology controlled by using an energy approach. A general study of power terms involved in the operation of the four-wire APF is conducted in order to evidence the relationship between instantaneous energy stored in the DC bus and active power requirements on the APF. Harmonics and imbalances both on the utility voltage and load current have been considered and the power developed by the active power filter has been evaluated. This study allows designing a controller for the APF based on the regulation of the energy-state of its DC-bus. The method has been experimentally tested on a four leg APF based on a neutral-point-clamped DC bus. Such topology allowed the test of the most general case, including harmonics and imbalance in utility voltage and in load currents.

PV system power quality enhancement by means of a voltage controlled shunt-converter

Abstract: PV converters can be designed to improve grid power quality implementing power conditioning functionalities. This paper presents a single-phase photovoltaic system with power quality enhancement capability. It provides grid voltage support at fundamental frequency and compensation of harmonic distortion at the point of common coupling (PCC). The shunt-converter is voltage controlled by means of a repetitive controller which is able to compensate the selected harmonics. Experimental results confirms the validity of the proposed topology also in case of nonlinear loads.

FBD-method based controller for shunt active power filters in marine vessels

Abstract: Shunt active power filters (SAPFs) based on the Fryze-Buchholz-Depenbrock (FBD) method allow electrical power quality (PQ) disturbances related to the load current consumption to be compensated. However, SAPF controllers based on this method require a stable grid fundamental frequency in order to operate properly. In case of isolated electrical grids suffering severe PQ disturbances, which is the case of ships electrical systems, the fundamental grid frequency can be very unstable, which reduces the SAPF performance due to an erroneous evaluation of the equivalent averaged load conductance (Ge). This paper presents a new approach for the evaluation of Ge which attenuates the impact of frequency variations. As a consequence, the performance of the SAPF is improved. Simulation results are given in order to evaluate the proposed controller.

Industrial electronics for renewable energy

Abstract: Energy production based on the use of renewable sources has a huge potential The needed technology is available and it benefits of continuous improvement due to academic and industrial research activity Another mayor issue is the knowledge transfer to industry on the basis of international conferences/workshops and educational programs Selected issues related to renewable energy systems technology and knowledge transfer are discussed in the panel session This summary introduces them: energy conversion, storage and transportation, control, monitoring and communication, technical committees activity and educational programs