Showing papers by "Marco Liserre published in 2007"

Flexible Active Power Control of Distributed Power Generation Systems During Grid Faults

Abstract: The increasing penetration of distributed power generation into the power system leads to a continuous evolution of grid interconnection requirements. In particular, active power control will play an important role both during grid faults (low-voltage ride-through capability and controlled current injection) and in normal conditions (reserve function and frequency regulation). The aim of this paper is to propose a flexible active power control based on a fast current controller and a reconfigurable reference current selector. Several strategies to select the current reference are studied and compared using experimental results that are obtained during an unsymmetrical voltage fault. The results of the analysis allow selection of the best reference current in every condition. The proposed methods facilitate multiple choices for fault ride through by simply changing the reference selection criteria.

A Comparative Analysis of Real-Time Algorithms for Power Signal Decomposition in Multiple Synchronous Reference Frames

Abstract: The monitoring and rejection of voltage and current harmonics in power electronics applications such as power quality conditioners or distributed generation systems require correct estimation algorithms especially if the harmonic amplitudes are time varying. Power signal decomposition in multiple synchronous rotating reference frames (MSRFs) is considered one of the best solutions. The most commonly employed implementations of this signal transformation are based on phase-locked loops (PLLs), recursive discrete Fourier transforms (RDFT), or discrete Kalman filtering (DKF). In this paper, a rigorous analysis of the performance of these implementations has been carried out. Complete tests have been performed to evaluate the computational burden, the frequency domain response, and the tolerance to low frequency amplitude variations. The results make it possible to select the proper method depending on the requirements of each application.

Wavelet-Based Islanding Detection Algorithm for Single-Phase Photovoltaic (PV) Distributed Generation Systems

Abstract: Distributed Generation (DG) systems based on inverters connected to low-voltage electrical grids, such as low power PV systems in buildings, require reliable islanding detection algorithms in order to determine the electrical grid status and operate the inverter properly. Passive and active islanding detection methods are local detection techniques which have been presented and analyzed in literature. The first approach is based on current and voltage measurements at the inverter side of the point of common coupling (PCC) between the electrical grid, the local load and the DG system. Active methods introduce a disturbance at the PCC in order to reveal the islanding condition. This paper proposes a new hybrid detection algorithm based on monitoring of high-frequency components of the DG system output power due to PWM, the output LCL filter and the employed current controller. Wavelet analysis is applied to obtain time localization of the islanding operation mode. Simulation results show the performance of the proposed detection algorithm.

Single-phase grid-connected photovoltaic systems with power quality conditioner functionality

Abstract: Future ancillary services provided by photovoltaic systems could facilitate their penetration in power systems. In fact 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 conditioner capability. It provides grid voltage support at fundamental frequency and compensation of current and voltage distortion at the point of common coupling (PCC). Two topologies have been considered: in the first one the voltage and the harmonic compensation are provided by two different converters, in the second one only one converter is used. Both the proposed topologies are controlled with a repetitive controller that is able to compensate the selected harmonics. Simulation results allows comparing the presented solutions.

Frequency Domain Analysis of Inductor Saturation in Current Controlled Grid Converters

Abstract: In this paper the effects of non-linear inductance on the performance of current controllers designed to track periodic signals and/or to compensate periodic disturbances are investigated with a frequency-domain model. When the inductance has a non-linear behavior a distorted current waveform is produced; if the saturation is symmetric, the current spectrum contains only odd harmonics. A current-dependent model of the non-linear inductance has been developed using the Volterra series expansion. The model allows proving formally how harmonic compensation provided by resonant and repetitive controllers can also mitigate the effects of the inductance saturation. This result is the main contribution of the paper and it is also substantiated with experimental evidence. It has been proven that the resonant and repetitive controllers are able to reduce harmonic distortion introduced by non-linearities. 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.

Passivity-Based Harmonic Control through Series/Parallel Damping of an H-Bridge Rectifier

Abstract: Nowadays the H-bridge is one of the preferred solutions to connect DC loads or distributed sources to the single-phase grid. The control aims are: sinusoidal grid current with unity power factor and optimal DC voltage regulation capability. These objectives should be satisfied, regardless the conditions of the grid, the DC load/source and the converter nonlinearities. In this paper a passivity-based approach is thoroughly investigated proposing a damping-based solution for the error dynamics. Practical experiments with a real converter validate the analysis.

Adjoint network theory to analyse the power converters with respect to their line-side behaviour

Abstract: This chapter presents a straightforward approach for the sensitivity analysis of the line-side connected converters with respect to the variation of their parameters. The sensitivity analysis is carried out based on the adjoint network theory. This allows studying the variation of an electrical quantity with respect to the perturbation of any circuit parameter, considering only one circuit besides the one assigned. As the control of a converter plays an important role in the propagation of the harmonics in the circuit, it is necessary to implement a detailed model of the controller too. Starting from the requirements of the digital controller, an analogue circuit that is able to represent the behavior of the controller is synthesized. Substituting the controller with the virtual circuit, an analogue network, representing the power converter and its control, is obtained. This homogenous model allows a rigorous and straightforward sensitivity analysis. This straightforward approach does not neglect anything of both the physical system and the digital controller. Also, with this approach it is easy to evaluate the problems of the use of the line-connected converter related to the propagation of harmonics in an industrial plant.

Shunt active filters to mitigate harmonic propagation in distribution lines

Abstract: This chapter discusses the use of shunt active filters (SAF) to mitigate the harmonic propagation in distribution lines. It describes a comprehensive approach to the control of SAFs, also demonstrating the procedure to design an advanced control using a predictive framework instead of a trial-and-error procedure. The possibility to use an optimization algorithm to choose the controller parameters correctly is then considered. Following this, some implementation issues in case a general-purpose microcontroller adopted are addressed. The chapter treats the single-phase, three-phase, and four-wire SAFs with respect to control issues and implementation issues. In the first case, traditional control methods and innovative ones are discussed. In the second case, the procedure to develop microcontroller algorithm is addressed. The chapter includes basic topologies and standard operation of shunt active filters. The use of an SAF can lead to the compensation of harmonic current components since it can generate compensating currents that sum up with damaging waveforms. As a result, it reduces harmonic presence in the grid. The traditional control techniques including hysteresis and predictive are described. The innovative control techniques are outlined including fuzzy-logic based and Nelder-and-Mead based.

Design of line front-end converter systems under real line conditions

Abstract: This chapter discusses the design of line front-end converter systems. It also explores their control in view of their steady-state and transient behavior. The main advantages of the active front-end are sinusoidal input current, unity power factor, and regenerative operation. Front-end converters are also beneficial because of active and reactive power control, controllability of the direct current (DC) link, and a limited voltage sag ride-through capability. Areview of the applications of voltage source front-end converters is presented in the chapter. The basic functions, the operating limits and the mathematical models of these converters are also discussed. Some basic and advanced control techniques are then described. The advanced techniques guarantee optimum active front-end performances. The chapter also explores the influence of the non-ideal conditions (grid unbalance, converter dead-time, and presence of unmodeled delays in control and measurement). Finally, the chapter outlines a few drawbacks in the use of the active front-ends.

Frequency DomainAnalysis ofInductor Saturation in Current Controlled GridConverters

Abstract: Inthis papertheeffects ofnon-linear inductance ontheperformance ofcurrent controllers designed totrack periodic signals and/or tocompensate periodic disturbances areinvestigated withafrequency-domain model. Whenthe inductance hasa non-linear behavior a distorted current waveformisproduced; ifthesaturation issymmetric, the current spectrum contains onlyoddharmonics. A current- dependent modelofthenon-linear inductance hasbeen developed usingtheVolterra series expansion. Themodel allowsprovingformally how harmoniccompensation provided by resonant andrepetitive controllers canalso mitigate theeffects oftheinductance saturation. Thisresult is themaincontribution ofthepaperanditisalso substantiated withexperimental evidence. Ithasbeenproventhatthe resonant and repetitive controllers areableto reduce harmonic distortion introduced bynon-linearities. Moreover therepetitive controller isabletocomplywiththeharmonic limits reported inIEEE1547andIEC61727eveninvery hardsaturation conditions. IndexTerms- single-phase gridinverter, current