Rosa Anna Mastromauro

Voltage Support Provided by a Droop-Controlled Multifunctional Inverter

This paper presents a single-phase multifunctional inverter for photovoltaic (PV) systems application. The converter provides active power to local loads and injects reactive power into the grid providing voltage support at fundamental frequency. The proposed topology is controlled by means of the droop-control technique. Hence, it allows the obtaining of voltage-sag-compensation capability, endowing voltage ride-through to the system. A model and analysis of the whole system is given to properly choose the control parameters. Simulation and experimental results validate the proposed control using a 5-kVA PV converter.

Control Issues in Single-Stage Photovoltaic Systems: MPPT, Current and Voltage Control

Photovoltaic Systems (PVS) can be easily integrated in residential buildings hence they will be the main responsible of making low-voltage grid power flow bidirectional. Control issues on both the PV side and on the grid side have received much attention from manufacturers, competing for efficiency and low distortion and academia proposing new ideas soon become state-of-the-art. This paper aims at reviewing part of these topics (MPPT, current and voltage control) leaving to a future paper to complete the scenario. Implementation issues on Digital Signal Processor (DSP), the mandatory choice in this market segment, are discussed.

A Single-Phase Voltage-Controlled Grid-Connected Photovoltaic System With Power Quality Conditioner Functionality

Future ancillary services provided by photovoltaic (PV) systems could facilitate their penetration in power systems. In addition, low-power PV systems can be designed to improve the power quality. This paper presents a single-phase PV system that provides grid voltage support and compensation of harmonic distortion at the point of common coupling thanks to a repetitive controller. The power provided by the PV panels is controlled by a Maximum Power Point Tracking algorithm based on the incremental conductance method specifically modified to control the phase of the PV inverter voltage. Simulation and experimental results validate the presented solution.

Wavelet-Based Islanding Detection in Grid-Connected PV Systems

Distributed power generation systems (DPGSs) based on inverters require reliable islanding detection algorithms (passive or active) in order to determine the electrical grid status and operate the grid-connected inverter properly. These methods are based on the analysis of the DPGS voltage, current, and power in time or frequency domain. This paper proposes a time-frequency detection algorithm based on monitoring the DPGS output power considering the influence of the pulsewidth modulation, the output LCL filter, and the employed current controller. Wavelet analysis is applied to obtain time localization of the islanding condition. Simulation and experimental results show the performance of the proposed detection algorithm in comparison with existing methods.

A Survey of Control Issues in PMSG-Based Small Wind-Turbine Systems

In the field of wind energy generation particular interest has been focused in recent years on distributed generation through small wind-turbines (power unit 200 kW) because of their limited size and lower environmental impact. The field of small generation was dominated by the use of asynchronous generators directly connected to the grid, while recently permanent magnet synchronous generators (PMSG) with power converter, either partially or fully controlled, became popular. This paper reviews the control issues related to these small wind-turbine systems: generator torque control, speed/position estimation, pitch control, braking chopper control, dc/dc converter control, and grid converter control. Specific issues for small wind-turbines arise in the wind energy extraction optimization and limitation and in the innovative concept of “universal” wind-turbine operation, that leads these system to operate grid-connected, standalone or in load supporting mode.

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

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

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.

Monitoring and synchronization techniques for single-phase PV systems

In order to meet standard specifications in terms of power quality and safety for grid-connected systems the phase angle, the amplitude and the frequency of the grid voltage are a critical piece of information. Phase locked loop (PLL) algorithms are very important for grid synchronization and monitoring in most of the grid-connected power converters system. This paper presents a performance comparison of single-phase synchronization techniques: Synchronous Reference Frame-Phase Locked Loop (SRF-PLL), Enhanced Phase-Locked-Loop (EPLL), Quadrature-Phase Locked Loop (QPLL) and Second-Order Generalized Integrator - Phase Locked Loop (SOGI-PLL).

MPPT algorithm for voltage controlled PV inverters

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.

Transformer-less photovoltaic (PV) inverters: A critical comparison

Transformer-less photovoltaic (PV) inverters specifically designed to achieve high efficiency shall also comply with leakage current limits, low current harmonic distortion and reactive power handling capability. This paper aims at benchmarking some recently published or patented topologies with the most successful industrial products and it offers a complete trends scenario and a critical comparison. The performances are evaluated in terms of efficiency, common-mode voltage, leakage current, power quality, reactive power handling capability, size of the grid filter and power converter rating.