Alex Reis

A controlled switching methodology for transformer inrush current elimination: Theory and experimental validation

Transformers are generally energized by closing the circuit breakers at random times. Consequently, this operation generates high transient inrush currents as a result of the asymmetrical magnetic flux produced in the windings. In light of these facts, this paper presents a strategy to control the switching phenomena which occurs during power transformer inrush. The general idea consists of calculating the pre-existing magnetic fluxes left on the core limbs as a function of operating voltage previously applied to the transformer, just prior to the moment in which de-energization has happened. By using these data and the equations to predict the most suitable closing moments, it is shown the proposal effectiveness at accomplishing the main target here pointed out. Experimental investigations are carried out in order to demonstrate the application method and its validation. The results show the feasibility of building hardware and software structures to drastically reduce the transformer inrush currents.

Applying the Superposition Procedure for the Harmonic Sharing Responsibility between Renewable Energy Power Plants and the Network

Abstract The increasing penetration of renewable energy sources with nonlinear characteristics, such as wind and photovoltaic power plants, demands a clear procedure for harmonic sharing responsibility between this new kind of generation and the network at the point of common coupling. In fact, there are in literature many procedures regarding the determination of responsibility for violating harmonic distortion limits. Among these proposals, the methodology based on the superposition principle has been one of the most promising procedures. In this context, the present paper is focused on a procedure that applies the superposition methodology to find the harmonic sharing responsibility between a wind power plant and the utility network. To exemplify this application, a case study is performed and analyzed.

A Comparative Performance Analysis of a Controlled D.C. and A.C. Motor Which Emulates Wind Turbines for Teaching and Research Purposes

The growth of wind farms has motivated the development of computational and experimental approaches which supplement needs related to teaching and research in the field of engineering. Even though there have already been recognized advances made in the field of computational modeling, the development of viable means through experiment to clarify the operation of wind farm complexes has become relevant to this area. In light of these facts, this study focuses on a comparative evaluation of two strategies which emulate wind turbines: one based on d.c. motors, the other on three-phase induction motors. In both cases, the apparatus is modeled on time-domain representation techniques and motor driving structures are proposed, allowing for the reproduction of features typically found in wind turbines. Lastly, experiments are realized and the results discussed for the confirmation of potentialities, along with the efficiency of the strategies used.

A critical analysis of the harmonic distortion procedure applied to wind farm connection

By considering the current growth of wind power all over the world, the development of power quality studies towards the evaluation of power quality impacts of wind farm upon the electric grid has become a matter of major importance. Within this context emerges the subject of harmonic interaction between the wind farm plant and the AC commercial system to be supplied by the focused generation. In this particular field one must considerer that the harmonic distortion studies often take into account just the harmonic current injection due to the wind farm and the connection busbar presenting no previous distortions. In case of necessity, the mitigation techniques are based on passive filters design and insertion at the PCC. Due to the adopted operational condition defined by the regulation agencies only the harmonic contribution related to the wind plant are considered and this may find real site difficulties due to the possibility of other source of harmonics originated by the AC grid. Under these circumstances, the filter units may be higher loaded than expected and thermal effects may result in their components failure. With this purpose, this paper is focused on this theme. A case study is described aimed at highlighting that harmonic studies can not neglect previous harmonic distortion already existing on the system.

A laboratory structure for dynamic and power quality studies of wind farms

The growing importance of wind farm resources has motivated the development of computational and experimental approaches to cope with the needs for professional formation and research. Although the recognition that a great computational effort has already being made, it has been found important to idealize and set up a physical structure that topologically and functionally is enable to represent wind conversion complexes as far as its power structure and control strategy are concerned. In light of these facts, this paper presents an experimental arrangement consisting of reduced scale equipment to simulate the operation of wind power conversion system. By utilizing the overall laboratory organization is has been found feasible to represent typical electrical dynamic and power quality operating performance. To highlight the potentiality of the assembled complex at representing field occurrences an experiment has been carried out and the corresponding results are given and discussed.

Mitigation of harmonic current produced by wind turbine throughout converter switching control

When considering grid integration, it is recognized that wind farms are able to bring about power quality impacts at the connection point. Focusing the attention towards this framework, a large amount of effort has been given to achieve the required level of compatibility between the wind turbine and the AC grid. Amongst the various existing power quality phenomena, harmonic distortion emerges as a relevant challenge. In fact, the full or partial power electronics converters existing on wind energy conversion systems has a direct effect upon the THD and the search for solutions to reduce the harmonic current injection emerges as an important issue. Thus, this paper focuses on the use of a control strategy applied to full converter wind systems aiming at reducing the level of harmonic currents similar to an active filter based inverter technique. In addition to the physical and mathematical principles, computational studies are carried out to highlight the methodologys effectiveness.

A voltage regulation strategy through the control of reactive power on wind farms

The growing demand for energy sources with low environmental impact have intensified the importance of wind farms in many countries. However, due to the operational characteristics of these complexes, which are reflected in a variability of the produced energy and the use of electronic converters, the interaction between wind power plants and connecting electrical networks is shown to be an area of strong investigative interest. In fact, among the various phenomena that exist, steady state voltage variations constitute a topic that comes under the constant attention of agencies responsible for the power systems operation. In this context, the present paper is directed towards the analysis of a strategy based on wind generation systems with synchronous machines and full converters. Using such arrangement with specific control strategy, the paper is focused at providing wind farm additional features related to voltage regulation process at the grid connection busbar. By means of computational simulations on the ATP/EMTP platform, results are presented that attest the efficiency of the proposed strategy.

Performance Evaluation of Harmonic Current Summation Law Applying to the Wind and Photovoltaic Generation

The increasing penetration of renewable energy sources with nonlinear characteristics, such as wind and photovoltaic power plants, demands a clear procedure for harmonic current estimation on point of coupling of these sources. The summation law is widely used to estimate the total harmonic current in a coupling point between the network and a distributed generation. This is done for each harmonic order and the analysis is performed by mean harmonic currents provide by an individual wind turbines. In this work, the summation law will be analyzed by a wind park case study.

Physical Concepts Related to Harmonics Produced by Wind Turbines Operation

The increasing demand for low environmental impact energy resources has intensified the importance of wind farms in many countries. However, several technical discussions about the integration of these generators to electrical networks are motivated by the harmonic distortion impacts on the coupling bus. In fact, power electronics devices play an important role in different wind generation schemes, although its harmonic emission affect directly the voltage quality standards. In this context, this work aims at reviewing the operational characteristics of wind turbines with synchronous machines and full-scale power converters, regarding the main factors responsible for harmonic generation. The theoretical concepts presented throughout the paper are supported by computer modelling and simulation, as well as field measurements on a real wind power plant.