Power Electronics course: Analysis and evaluation of the educational software and the environment learning

This paper presents the analysis and evaluation of the Power Electronics course at So Paulo State University-UNESP-Campus of Ilha Solteira(SP)-Brazil, which includes the usage of interactive Java simulations tools and an educational software to aid the teaching of power electronic converters. This platform serves as an oriented course for the lectures and supplementary support for laboratory experiments in the power electronics courses. The simulation tools provide an interactive and dynamic way to visualize the power electronics converters behavior together with the educational software, which contemplates the theory and a list of subjects for circuit simulations. In order to verify the performance and the effectiveness of the proposed interactive educational platform, it is presented a statistical analysis considering the last three years. © 2011 IEEE.

Optimization of the power electronics system associated with ocean wave electric generators

The present thesis is focused on wave energy, which is a particular kind of ocean energy, and is based on the activity carried out during the EU project SEA TITAN. The main scope of this work is the design of a power electronic section for an innovative wave energy extraction system based on a switched-reluctance machine. In the first chapter, the general features of marine wave energy harvesting are treated. The concept of Wave Energy Converter (WEC) is introduced as well as the mathematical description of the waves, their characterization and measurement, the WEC classification, the operating principles and the standardization framework. Also, detailed considerations on the environmental impact are presented. The SEA TITAN project is briefly described. The second chapter is dedicated to the technical issues of the SEA TITAN project, such as the operating principle, the performance optimization carried out in the project, the main innovations as well as interesting demonstrations on the behavior of the generator and its control. In the third chapter, the power electronics converters of SEA TITAN are described, and the design choices, procedures and calculations are shown, with a further insight into the application given by analyzing the MATLAB Simulink model of the system and its control scheme. Experimental tests are reported in the fourth chapter, with graphs and illustrations of the power electronic apparatus interfaced with the real machine. Finally, the conclusion in the fifth chapter offers a global overview of the project and opens further development pathways.

Distributed ControlArchitecture of Power Electronics Building-Block-Based Frequency Converters

The increasing power demand and emerging applications drive the design of electrical power converters into modularization. Despite the wide use of modularized power stage structures, the control schemes that are used are often traditional, in other words, centralized. The flexibility and re-usability of these controllers are typically poor. With a dedicated distributed control scheme, the flexibility and re-usability of the system parts, building blocks, can be increased. Only a few distributed control schemes have been introduced for this purpose, but their breakthrough has not yet taken place. A demand for the further development offlexible control schemes for building-block-based applications clearly exists. The control topology, communication, synchronization, and functionality allocationaspects of building-block-based converters are studied in this doctoral thesis. A distributed control scheme that can be easily adapted to building-block-based power converter designs is developed. The example applications are a parallel and series connection of building blocks. The building block that is used in the implementations of both the applications is a commercial off-the-shelf two-level three-phase frequency converter with a custom-designed controller card. The major challenge with the parallel connection of power stages is the synchronization of the building blocks. The effect of synchronization accuracy on the system performance is studied. The functionality allocation and control scheme design are challenging in the seriesconnected multilevel converters, mainly because of the large number of modules. Various multilevel modulation schemes are analyzed with respect to the implementation, and this information is used to develop a flexible control scheme for modular multilevel inverters.

Simulation Tools of DC-DC Converters for Power Electronics Education

This paper presents interactive simulation tools to support the enhancement of power electronics education considering DC to DC converters. These interactive tools make use of the benefits of Java language to provide a dynamic and interactive visualization of simulations in steady-state for idealized non-isolated DC to DC converters. Additionally, this paper discusses the features and the usage of the interactive educational tools to serve as a first design tool for the laboratory experiments in the power electronics courses. In this way, some results were confronted with a well-known simulator package and with experimental results in order to validate the developed interactive simulation tools.

Power Electronic Converters in Low-Voltage Direct Current Distribution – Analysis and Implementation

Over the recent years, smart grids have received great public attention. Many proposed functionalities rely on power electronics, which play a key role in the smart grid, together with the communication network. However, “smartness” is not the driver that alone motivates the research towards distribution networks based on power electronics; the network vulnerability to natural hazards has resulted in tightening requirements for the supply security, set both by electricity end-users and authorities. Because of the favorable price development and advancements in the field, direct current (DC) distribution has become an attractive alternative for distribution networks. In this doctoral dissertation, power electronic converters for a low-voltage DC (LVDC) distribution system are investigated. These include the rectifier located at the beginning of the LVDC network and the customer-end inverter (CEI) on the customer premises. Rectifier topologies are introduced, and according to the LVDC system requirements, topologies are chosen for the analysis. Similarly, suitable CEI topologies are addressed and selected for study. Application of power electronics into electricity distribution poses some new challenges. Because the electricity end-user is supplied with the CEI, it is responsible for the end-user voltage quality, but it also has to be able to supply adequate current in all operating conditions, including a short-circuit, to ensure the electrical safety. Supplying short-circuit current with power electronics requires additional measures, and therefore, the short-circuit behavior is described and methods to overcome the high-current supply to the fault are proposed. Power electronic converters also produce common-mode (CM) and radio-frequency (RF) electromagnetic interferences (EMI), which are not present in AC distribution. Hence, their magnitudes are investigated. To enable comprehensive research on the LVDC distribution field, a research site was built into a public low-voltage distribution network. The implementation was a joint task by the LVDC research team of Lappeenranta University of Technology and a power company Suur-Savon S¨ahk¨o Oy. Now, the measurements could be conducted in an actual environment. This is important especially for the EMI studies. The main results of the work concern the short-circuit operation of the CEI and the EMI issues. The applicability of the power electronic converters to electricity distribution is demonstrated, and suggestions for future research are proposed.

Performance evaluation of a novel hybrid multipulse rectifier for utility interface of power electronic converters

This paper presents an improved analysis of a novel Programmable Power-factor-corrected-Based Hybrid Multipulse Power Rectifier (PFC-HMPR) for utility interface of power electronic converters. The proposed hybrid multipulse rectifier is composed of an ordinary three-phase six-pulse diode-bridge rectifier (Graetz bridge) with a parallel connection of single-phase switched converters in each three-phase rectifier leg. In this paper, the authors present a complete discussion about the controlled rectifiers' power contribution and also a complete analysis concerning the total harmonic distortion of current that can be achieved when the proposed converter operates as a conventional 12-pulse rectifier. The mathematical analysis presented in this paper corroborate, with detailed equations, the experimental results of two 6-kW prototypes implemented in a laboratory.

Programmable PFC based hybrid multipulse power rectifier for utility interface of power electronic converters

In this paper it is proposed a novel hybrid three-phase rectifier capable to achieve high input power factor (PF), and low total harmonic distortion in the input currents (THDI). The proposed hybrid high power rectifier is composed by a standard three-phase 6-pulses diode rectifier (Graetz bridge) with a parallel connection of single-phase Boost rectifiers in each three-phase rectifier leg. Such topology results in a structure capable of programming the input current waveform and providing conditions for obtaining high input power factor and low harmonic current distortion. In order to validate the proposed hybrid rectifier, this paper describes its principles of operation, with detailed experimental results and discussions on power rating of the required Boost converters as related to the desired total harmonic current distortion. It is demonstrated that only a fraction of the output power is processed through the Boost converters, making the proposed solution economically viable for very high power installations, with fast pay back of the investment. Moreover, retrofitting to existing installations is also feasible since the parallel path can be easily controlled by integration with the existing de-link. A prototype rated at 6 kW has been implemented in laboratory and fully demonstrated its operation, performance and feasibility to high power applications. © 2005 IEEE.

Nonlinear constrained and saturated control of power electronics and electromechanical systems

Power electronic converters are extensively adopted for the solution of timely issues, such as power quality improvement in industrial plants, energy management in hybrid electrical systems, and control of electrical generators for renewables. Beside nonlinearity, this systems are typically characterized by hard constraints on the control inputs, and sometimes the state variables. In this respect, control laws able to handle input saturation are crucial to formally characterize the systems stability and performance properties. From a practical viewpoint, a proper saturation management allows to extend the systems transient and steady-state operating ranges, improving their reliability and availability. The main topic of this thesis concern saturated control methodologies, based on modern approaches, applied to power electronics and electromechanical systems. The pursued objective is to provide formal results under any saturation scenario, overcoming the drawbacks of the classic solution commonly applied to cope with saturation of power converters, and enhancing performance. For this purpose two main approaches are exploited and extended to deal with power electronic applications: modern anti-windup strategies, providing formal results and systematic design rules for the anti-windup compensator, devoted to handle control saturation, and “one step” saturated feedback design techniques, relying on a suitable characterization of the saturation nonlinearity and less conservative extensions of standard absolute stability theory results. The first part of the thesis is devoted to present and develop a novel general anti-windup scheme, which is then specifically applied to a class of power converters adopted for power quality enhancement in industrial plants. In the second part a polytopic differential inclusion representation of saturation nonlinearity is presented and extended to deal with a class of multiple input power converters, used to manage hybrid electrical energy sources. The third part regards adaptive observers design for robust estimation of the parameters required for high performance control of power systems.

LOCAL DIGITAL CONTROL OF POWER ELECTRONIC CONVERTERS IN A DC MICROGRID BASED ON A-PRIORI DERIVATION OF SWITCHING SURFACES

In power electronic basedmicrogrids, the computational requirements needed to implement an optimized online control strategy can be prohibitive. The work presented in this dissertation proposes a generalized method of derivation of geometric manifolds in a dc microgrid that is based on the a-priori computation of the optimal reactions and trajectories for classes of events in a dc microgrid. The proposed states are the stored energies in all the energy storage elements of the dc microgrid and power flowing into them. It is anticipated that calculating a large enough set of dissimilar transient scenarios will also span many scenarios not specifically used to develop the surface. These geometric manifolds will then be used as reference surfaces in any type of controller, such as a sliding mode hysteretic controller. The presence of switched power converters in microgrids involve different control actions for different system events. The control of the switch states of the converters is essential for steady state and transient operations. A digital memory look-up based controller that uses a hysteretic sliding mode control strategy is an effective technique to generate the proper switch states for the converters. An example dcmicrogrid with three dc-dc boost converters and resistive loads is considered for this work. The geometric manifolds are successfully generated for transient events, such as step changes in the loads and the sources. The surfaces corresponding to a specific case of step change in the loads are then used as reference surfaces in an EEPROM for experimentally validating the control strategy. The required switch states corresponding to this specific transient scenario are programmed in the EEPROM as a memory table. This controls the switching of the dc-dc boost converters and drives the system states to the reference manifold. In this work, it is shown that this strategy effectively controls the system for a transient condition such as step changes in the loads for the example case.

Design and Characterization of an Active Three-Phase EMI Noise Separator for Three-Phase Power Electronics Systems

One of the major issues for power converters that are connected to the electric grid are the measurement of three phase Conduced Emissions (CE), which are regulated by international and regional standards. CE are composed of two components which are Common Mode (CM) noise and Differential Mode (DM) noise. To achieve compliance with these regulations the Equipment Under Test (EUT) includes filtering and other electromagnetic emission control strategies. The separation of differential mode and common mode noise in Electromagnetic Interference (EMI) analysis is a well-known procedure which is useful especially for the optimization of the EMI filter, to improve the CM or DM attenuation depending on which component of the conducted emissions is predominant, and for the analysis and the understanding of interference phenomena of switched mode power converters. However, separating both components is rarely done during measurements. Therefore, in this thesis an active device for the separation of the CM and DM EMI noise in three phase power electronic systems has been designed and experimentally analysed.

A Family of Autoconnected Transformers for 12-and 18-Pulse Converters-Generalization for Delta and Wye Topologies

Multipulse rectifier topologies based on autoconnections are increasingly applied as interface stages between mains and power electronics converters. These topologies are attractive and cost-effective solutions for meeting the requirements of low total harmonic distortion of line current and high power factor. Furthermore, as only a small fraction of the total power required by the load is processed in the magnetic core, the overall resulting volume and weight are reduced. This paper proposes a mathematical analysis based on phasor diagrams that results in a single and general expression capable of unifying all delta and wye step-up or step-down autotransformer connections for 12-and 18-pulse ac-dc converters. The expression obtained allows the choice of a wide range of input/output voltage ratio for step-up or step-down autotransformer, and this general expression is also presented in a graphical form for each converter. Moreover, it simplifies the procedure for determining turn ratios and polarities for all windings of the autotransformer. A routine for easy and fast calculations is developed and validated by a design example. Finally, experimental results are presented along with comments on a 6-kW 220-V line voltage, 400-V rectified voltage, and 18-pulse delta-autoconnected prototype.

Power Electronics Didactic Modules for Direct Current Machine Control

Several didactic modules for an electric machinery laboratory are presented. The modules are dedicated for DC machinery control and get their characteristic curves. The didactic modules have a front panel with power and signal connectors and can be configurable for any DC motor type. The three-phase bridge inverter proposed is one of the most popular topologies and is commercially available in power package modules. The control techniques and power drives were designed to satisfy static and dynamic performance of DC machines. Each power section is internally self-protected against misconnections and short-circuits. Isolated output signals of current and voltage measurements are also provided, adding versatility for use either in didactic or research applications. The implementation of such modules allowed experimental confirmation of the expected performance.

The improvement of enclosure protection class of power electronics device

Tässä diplomityössä tutkittiin vaihtoehtoja tehoelektroniikkalaitteiden kotelointiluokan kehittämiseksi. Haasteena paremman suojauksen suunnittelussa on laitteiden tuottama suuri määrä lämpöä, joka vaatii tehokkaan jäähdytyksen. Työn tuloksena saatu prototyyppi IP33 luokkaa varten täyttää standardissa SFS-EN 60529+A1 asetetut vaatimukset kyseiselle kotelointiluokalle. Rakenteessa ja valmistettavuudessa havaittiin muutama ongelma, jotka ovat korjattavissa pienillä muutoksilla. Korkeampia suojausluokkia varten testattiin IP54-luokiteltujen filtterituulettimien vaikutusta laitteen jäähdytykseen. Testien perusteella jäähdytysteho on riittävä ja filtterituulettimet todettiin toimivaksi ratkaisuksi korkeammille suojausluokille. Työn perusteella voidaan todeta, että nykyiset laitteet voidaan muokata vastaamaan IP33 luokan vaatimuksia kohtuullisen pienillä muutoksilla. Tätä korkeammat suojausluokat vaatisivat niin suuria muutoksia designiin, että todennäköisesti täysin uuden laitteen suunnittelu olis kannattavin vaihtoehto.

Simulation Tools for Power Electronics Courses Based on Java Technologies

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

A Family of Autoconnected Transformers for 12-and 18-Pulse Converters-Generalization for Delta and Wye Topologies

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)