1,721,193 research outputs found
A novel five-level single phase grid connected converter for renewable distributed systems
No full textIn low-power grid connected systems (renewable or traditional energy sources) a single phase converter is usually adopted. In order to reduce losses, costs and size the keyword is removing any kind of transformer. This paper deals with a novel five level converter topology that follows this trend. The proposed converter architecture is based on a full bridge topology with two more power switches and two diodes connected to the midpoint of the DC link. Since the two added levels are obtained by the discharge of two capacitors, the balancing of the midpoint voltage is taken into account.
Simulation and experimental results show the effectiveness of the proposed solution
Detection Method of the DC bias in Distribution Power Transformers
No full textNon-linear loads such as AC drives switch-mode
power supplies and grid-connected converters can cause, besides
the generation of unwanted current harmonics, a DC current
component injection into the grid. This DC current component
can lead to magnetic saturation of the distribution power transformers, leading to higher current distortion and overheating.
This paper presents a method to detect the DC current
component flowing into the distribution power transformer with
a precise measurement of the DC voltage component at the
transformer winding. A magnetic sensor has been developed and
implemented in a closed-loop control system to achieve a high
sensitivity and guarantees a good linearity with a high rejection
ratio to grid voltage variations. Simulation and experimental
results confirm the effectiveness of the proposed approach
A Novel Current Sensing DC Offset Compensation Strategy in Transformerless Grid Connected Power Converters
No full textIn grid connected power converters both from renewable or traditional energy sources a line frequency transformer is usually employed in order to suppress the DC component. Recently, solutions based on a high frequency transformer or without transformer, usually referred as transformerless, are being investigated in order to reduce size, weight and costs. As a consequence, unless a suitable remedy is adopted, a DC component, that might overcome limits forced by international standards, may appear.
This paper proposes a simple and cheap solution to reduce the DC current component injected into the grid in case of a full-bridge, single phase, transformerless converter. The proposed strategy is intrinsically insensitive to offset measurement errors and can be utilized as a robust and dynamic offset compensator for the Hall effect sensor mostly used as current transducer. Experimental results, performed for different current values and for different current control architectures, show the effectiveness of the proposed solution
Single-phase series active power filter with transformer-coupled matrix converter
Full text linkThis study presents a series active power filter based on a single-phase matrix converter. Back-to-back voltagesource converters with nested control loops and passive filters are normally used for this application. A matrix converter, as proposed in this study, allows a simpler implementation both in terms of hardware (no grid filter and no DC link) and of control. Moreover, a novel zero-voltage compensation technique is introduced in order to reduce the distortion around the input voltage zero crossing. Simulations and experiments are used to validate the considered control methods, confirming the feasibility of the proposed architecture
Review of oscillating water column converters
Full text linkOcean waves are a huge, largely unexploited energy resource and the potential for extracting energy from waves is great. Research in this area is driven by the need to meet renewable energy targets, but it is relatively immature compared to other renewable energy technologies. This review introduces some device types that represent the state of the art of Oscillating Water Column (OWC) technology, a kind of Wave Energy Converter (WEC). Unlike other works in literature, typically limited to specific aspects of WECs, in this paper will be pursued a system wide perspective, from the sea waves to the grid connection
H8 inverter for common-mode voltage reduction in electric drives
Full text linkThis paper presents a modified two-level three-phase inverter for the reduction of the leakage current. With respect to a traditional two-level inverter, the proposed solution reduces the common-mode voltage (CMV), both in amplitude and frequency. Between the dc source and the traditional three-phase bridge, two active dc-decoupling devices and a voltage-clamping network have been added. A dedicated control strategy was developed adopting a modified space vector pulse-width modulation, oriented to the reduction of the CMV. Simulations showing the good performance of the solution are presented. A preliminary prototype was developed and experimental results are presented
Recent advances in single-phase transformerless photovoltaic inverters
Full text linkPhotovoltaic (PV) power systems have been in the spotlight of scientific research for years. However, this technology is still undergoing developments, and several new architectures are proposed each year. This study describes the main challenges facing grid-connected PV systems without galvanic isolation, then carries out a review of the state-of-the-art of single-phase systems. The converter topology review is focused on the match between the different types of converters and the different PV panel technologies, determined by the common-mode voltage between the PV string terminals and the ground. The ground leakage current, due to time variations of this voltage, is a source of electric safety and electromagnetic interference (EMI)-related problems, and its amplitude is constrained by international standards. The basic principles of operation of the different solutions are described, along with their strengths and drawbacks. Conversion efficiency is evaluated qualitatively comparing the semiconductor power losses. Finally, the future trends regarding semiconductor devices, PV panels and international regulations for single-phase grid-connected equipment are discussed, and indications on how these might steer future research efforts in PV converters are inferred
Compensation strategy of actual commutations for PV transformerless grid-connected converters
No full textPhotovoltaic grid-connected converters usually embed a high-frequency or a line transformer, which guarantees galvanic isolation between the photovoltaic field and the mains. In order to increase efficiency and reduce the total cost of the system, the transformer has been removed, and special topologies of converter have been studied in order to limit the ground leakage current that arises with the galvanic connection. In fact, the parasitic capacitance between the photovoltaic cells and the metallic frame of the panel allows high ground leakage current (i.e. common mode current) to be injected into the grid. Actual solutions rely heavily on the symmetry of the system to address the problem. This paper presents a novel strategy to compensate for non-ideal switching behavior of power devices, which is immune to layout asymmetries and tolerance of parameters. Simulation results show the feasibility of the proposed solution. ©2010 IEEE
A modular speed-drooped system for high reliability integrated modular motor drives
Full text linkFuture transportation challenges include a considerable reduction in pollutant emissions at a time when significant increase in demand is predicted. One of the enabling solutions is the electrification of transport systems as this should lead to improved operability, fuel savings, emission reduction, and maintenance. While state-of-the-art technology has demonstrable benefits there needs to be considerable advancement to meet future transportation affordability and emission targets. Primarily, electrical drives need an improved power density, an increased reliability, and a reduced specific cost. For this reason, integrated modular motor drives (IMMDs) present an attractive solution. Modularity leads to redundancy and easier integration. This paper presents a novel speed-drooped control system applied to motors fed by modular paralleled converters. This control technique allows precise speed regulation and power sharing among different segments showing improved fault tolerance and reliability. The design procedure and the power sharing dynamic have been presented and analyzed by means of MATLAB/Simulink and validated in a 3-kW experimental rig, showing good agreement with the expected performance
Active Rectifier With Integrated System Control for Microwind Power Systems
No full textThis paper presents simple and effective control strategies for the active rectifier stage (AC/DC stage) of a grid-connected low power system for micro wind applications employing Permanent Magnet Synchronous Generator (PMSG). In particular a novel algorithm for the estimation of the rotor angle of the PMSG, based on flux estimators, was implemented using an adaptive low-pass filter coupled with a feed-forward compensator. This enabled a very smooth start-up operation of the PMSG, obtained by pre-loading the values of the flux
estimator and using a single voltage transformer (VT) transducer. The solution for the power flow control between the active rectifier and the other(s) power converters connected to the common DC link was implemented without any digital communication between them, in order to obtain a solution suitable for modular architectures (e.g. to be used in conjunction with a grid-connected converter and/or an energy storage system). Simulation and experimental results confirmed the effectiveness of the proposed solutions. The experimental validation was conducted using a grid-connected converter as load for the proposed active rectifier
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