Advanced Power Electronics Research Articles

Active Torque Control for Gearbox Load Reduction in a Variable-Speed Wind Turbine

With the advent of power electronics, the size, weight, and cost of power converters have been drastically reduced while efficiency is improved. The use of variable-speed wind power generators has seen considerable growth. The use of gearboxes in the wind turbines allows for smaller size, lower weight, and higher speed generators. However, gearboxes have shown to be one of the least reliable components of the wind turbines. In this paper, we propose a method that can extend the life and reliability of wind turbine gearboxes by reducing the mechanical stress on gearbox components. Reduction of mechanical stress is achieved by the generator torque control that minimizes resonant torsional vibrations within a drivetrain caused by variations in wind velocity. A detailed model for the drivetrain of a 750-kW wind turbine, including a gearbox is presented. Experimental results are used to calculate the parameters of the gearbox. A controller is designed to adjust the generator torque at the end of the drivetrain to remove the unwanted and damaging torque variations from the drivetrain. Simulation results verify the effectiveness of the proposed method.

A Carrier-Based PWM Modulation Technique for Balanced and Unbalanced Reference Voltages in Multiphase Voltage-Source Inverters

The advancement in power electronics has made the use of any number of phases in ac machines possible since with the inverter, any number of phase voltages can be realized as long as the corresponding inverter exists. To supply multiphase drives requires multiphase voltage source inverters (VSIs) whose output voltages depend very much on the methods of generating the pulses to turn on and turn off the inverter devices appropriately. This paper presents an analytical technique for the determination of the expressions for the modulation signals used in the carrier-based sinusoidal and generalized discontinuous pulse width modulation schemes for two-level, five-phase voltage source converters. These expressions can be used for both balanced and unbalanced phase voltages generated by any two-level multiphase inverter, in generating the required reference signals appropriately. An example of a five-phase VSI is presented to illustrate the strategy. Simulation and experimental results are presented in which a close examination shows that both results are similar for the balanced and unbalanced load voltage cases.

Special Section on Sustainable Transportation Systems

The 11 papers in this special section focus on state-of-the-art research and development, as well as future trends in the modeling, design, control, and optimization of advanced power electronics, energy storage, motor drives, and power train systems for future sustainable transportation systems.

Integrated Control Technique for Compliance of Solar Photovoltaic Installation Grid Codes

Energy policies along with technological advancements in power electronics have allowed a high penetration of photovoltaic installations. To normalize grid connections, in particular for solar photovoltaic (PV) installations, an arrangement of requirements have been set as a grid code to prove that this penetration can provide support and fully control during both steady-state and transient conditions of the grid. In this paper, a control system for a PV installation connected to the grid is developed to accomplish the requirements raised in the 2010 draft version of the Spanish grid code P.O. 12.2. Control loops for steady-state conditions as well as transient conditions (voltage dips, swells, and frequency control) have been implemented. Simulations have been performed using PSCAD/EMTDC™ program and supported by field tests of an existing PV installation in Spain using the voltage dip generator.

Novel Method for Selective Nonlinear Flux Guide Switching for Contactless Inductive Power Transfer

Efficient inductive power transfer has become an area of increasing scientific interest as it can solve some problems associated with traditional wired or contact power transmission. These include but are not limited to corrosion, mechanical friction, clutter and impracticality in places like underwater and subterranean applications. This wireless energy transfer is made possible by the optimization of electromagnetic induction, circuit frequency resonance all achieved with advanced power electronics. One of the components of this technology is the precise delivery of the incident electromagnetic fields to the precise location to which they are converted to power via induction, without indiscriminate emission of these electromagnetic fields inefficiently into the surrounding areas. This paper presents a method in achieving bounded spatial freedom using flux-guide saturation for flux delivery to one or more secondary coils for contactless inductive power transfer. The experiments demonstrate the principle of using the nonlinearity of a ferrite flux shield in order to “open up” a flux path from the primary to the secondary coil to achieve inductive power transfer.

Hybrid and Electric Systems R&D at DOE: Fiscal Year 2011-2012 Status

This paper presents an overview of the recent highlights and accomplishments, for fiscal years (FYs) 2011- 2012, by the hybrid and electric systems (HES) R&D Team at the Vehicle Technologies Program (VTP) Office of the United States Department of Energy (DOE) Energy Efficiency and Renewable Energy (EERE) Office. There is significant U.S. commitment to HES R&D and additional responsibilities were assigned under the American Recovery and Reinvestment Act (ARRA) of 2009, an economic stimulus package from the 111th United States Congress. DOE has supported the development of HES technologies, including advanced automotive energy storage technologies, power electronics and electric machines, and simulation and testing tools, over the long term. This support has involved leveraging resources and expertise from automobile manufacturers, battery, motor, and electronics developers, small businesses, national laboratories, and universities to address the technical barriers which prevent the market introduction of vehicles which would use those advanced technologies. The HES R&D Team has had many significant accomplishments and continues to advance the state of the art for many technologies. This paper provides a discussion of the most recent highlights and a description of R&D coordination efforts with other government agencies in associated areas.

Dynamic contribution of variable-speed wind energy conversion system in system frequency regulation

Frequency regulation in a generation mix having large wind power penetration is a critical issue, as wind units isolate from the grid during disturbances with advanced power electronics controllers and reduce equivalent system inertia. Thus, it is important that wind turbines also contribute to system frequency control. This paper examines the dynamic contribution of doubly fed induction generator (DFIG)-based wind turbine in system frequency regulation. The modified inertial support scheme is proposed which helps the DFIG to provide the short term transient active power support to the grid during transients and arrests the fall in frequency. The frequency deviation is considered by the controller to provide the inertial control. An additional reference power output is used which helps the DFIG to release kinetic energy stored in rotating masses of the turbine. The optimal speed control parameters have been used for the DFIG to increases its participation in frequency control. The simulations carried out in a two-area interconnected power system demonstrate the contribution of the DFIG in load frequency control.

Research on cascade multilevel inverter with single DC source by using three-phase transformers

One of the most significant recent advances in power electronics is the multilevel inverter. Using this concept the power conversion is performed with enhanced power quality. In this scenario cascade H-bridge multilevel inverter (CHBMLI) is an exceptional one and it has many inherent benefits like: (1) its modular structure, (2) it can be easily implemented through the series connection of identical H-bridges, (3) generate near sinusoidal voltages with only fundamental frequency switching and finally and (4) no electromagnetic interference or common-mode voltages. This flexibility has resulted CHBMLI topology in various applications like medium-voltage industrial drives, electric vehicles and the grid connection of photovoltaic-cell generation systems. But one of the major limitations of the cascade multilevel converters is requirement of isolated dc voltage sources for each H-bridge, this increases the converter cost and reduces the reliability of the system. This drawback is the key motivation for the present work. The present paper investigates different cascade multilevel inverter (CMI) based topologies with reduced dc sources and finally the proposed CMI with single dc source by employing low frequency transformers is presented. Proposed topology significantly reduces size when compared with conventional topologies and increases the reliability. To verify the performance of proposed architecture, prototype experiments are carried out and adequate results are presented.

Electrical energy quality: Modeling and H∞ control of a three-phase shunt active filter

The main contribution of the paper is the modeling approach used to describe a pure threephase shunt active filter, and the application of the H∞ control design tool in order to improve the quality of electrical energy. Advanced power electronics devices have widely contributed to the degradation of power quality due to the injection of non-sinusoidal currents into the utility system. Therefore, it is essential to use an active compensator which can attenuate current harmonics to an acceptable level on the line side of the power source. In this work, a three-phase active filter connected in parallel to a supply system feeding a non-linear load is described, in a complex framework, by a linear multivariable state space representation in order to guarantee that the system is mathematically decoupled and therefore to simplify the controller design. This representation includes a sensor to measure perturbations, and allows one to calculate a linear robust control law. The originality of this paper is that a Linear Matrix Inequality based H∞ synthesis is performed to design a static state feedback controller with complex-valued parameters. The robustness of this controller with respect to network impedance uncertainties is investigated. Moreover, simulation and experimental results are given to reveal the effectiveness of the synthesized control law.

Harmonic Control Based on Fuzzy Logic

Proliferation of nonlinear loads in power systems has increased harmonic pollution and deteriorated power quality. Passive filtering has typically been the standard technology for harmonic and reactive power compensation .With the advancements in power electronics, active filtering is being more widely considered given its flexibility and precise control. However, cost, complexity, and reliability are considered the major drawbacks of active filters. In this paper a new fuzzy logic is introduced to control the harmonic in the power system, which has more advantages such as simplicity, ease of application, flexibility, speed and ability to deal with imprecision and uncertainties .The introduction of fuzzy logic can not only reduce harmonic,but also correct the power factor.

Development of High-Dielectric-Strength Ceramic Film Capacitors for Advanced Power Electronics

Ceramic film capacitors with high dielectric constant and high breakdown strength are promising for use in advanced power electronics, which would offer higher performance, improved reliability, and enhanced volumetric and gravimetric efficiencies. We have grown lead lanthanum zirconate titanate (PLZT) on nickel foils and platinized silicon (PtSi) substrates by chemical solution deposition. A buffer layer of LaNiO3 (LNO) was deposited on the nickel foils prior to the deposition of PLZT. We measured the following electrical properties for PLZT films grown on LNO buffered Ni and PtSi substrates, respectively: remanent polarization, ≈25.4 μC/cm2 and ≈10.1 μC/cm2; coercive electric field, ≈23.8 kV/cm and ≈27.9 kV/cm; dielectric constant at room temperature, ≈1300 and ≈1350; and dielectric loss at room temperature, ≈0.06 and ≈0.05. Weibull analysis determined the mean breakdown strength to be 2.6 MV/cm and 1.5 MV/cm for PLZT films grown on LNO buffered Ni and PtSi substrates, respectively. Residual stress analysis by x-ray diffraction revealed compressive stress of ≈-520 MPa in the ≈2-μm-thick PLZT grown on LNO buffered Ni foil, but a tensile stress of ≈210 MPa in the ≈2-μm-thick PLZT grown on PtSi substrates.

Development of a Modular Mobile Robot Platform: Applications in Motion-Control Education

Electric drives and motion-control systems represent an engineering discipline that has rapidly developed over the last few decades. Today, high-performance motor drive systems have become the preferred choice in many industrial applications, and there is a strong interest to develop new control tools to further enhance their performance and intelligence. Motor drives are encountered in various industrial applications, such as rolling mill drives, traction systems, and robotics, covering the general field of motion control and mechatronics. With the recent advances in power electronics and microprocessors, digital control of motor drives has become increasingly popular. Nowadays, a microcomputer-based control system with digital-control strategies is an essential component for a high-performance adjustable speed drive system. This rapid technology change calls for the need to upgrade the standard educational methodologies in electric drives and motion-control systems to offer students a more flexible, effective, and up-to-date curriculum.

(Invited) High Power Semiconductor Devices for FACTS: Current State of the Art and Opportunities for Advanced Materials

Flexible AC Transmission Systems (FACTS) use advanced power electronics to minimize reactive power loss on the grid. Power devices used in FACTS systems must be capable of switching several thousand amps at voltages of 1-10 kV. Traditionally, these systems have relied on silicon thyristors, but recently have also began to incorporate insulated gate bipolar transistors. FACTS systems present an opportunity for emerging SiC and GaN power transistors, which offer major efficiency gains. However, for these advanced materials to be considered for use in high consequence grid level systems like FACTS controllers, excellent reliability must be demonstrated.

Ground Fault Location Testing of a Noise-Pattern-Based Approach on an Ungrounded DC System

Finding the phase-to-ground faults in ungrounded distribution systems is very difficult and time consuming. In recent years, the advances in power electronics favor dc distribution, particularly for transportation systems such as ships. Therefore, this paper presents a fault location approach which is based on the pattern recognition of inherent high-frequency noise associated with the switching events of converters. This paper demonstrates the feasibility of the approach through a hardware laboratory test. Specifically, a low-voltage dc system, representative of the salient high-frequency behavior of a real zonal electrical distribution system for ships, was used. Closely matching the results obtained from a computer simulation model of the circuitry, the experimental test results show the ability of the approach to appropriately differentiate various fault locations in the laboratory environment. It is concluded that the approach is feasible and can be applied toward the development of an effective ground fault location system for converter-dominated dc systems.

Renewable Energy Use Advantages of Maglev-Based Personal Rapid Transit

Maglev personal rapid transit (MPRT) is a personal rapid transit (PRT) system that uses renewable energy in usage, distribution, and generation. A PRT system provides on-demand service in a manner similar to the automobile. Different types of PRT have different impacts on the electrical grid load. Recent advances in power electronics and maglev technology allow for the design of a novel MPRT system characterized not only by exceptionally low power requirements but also by a unique capacity to incorporate energy distribution and storage infrastructure into the greater transportation architecture. A hypothetical hybrid MPRT design incorporating energy storage and transmission capabilities is described. In addition, thorough carbon dioxide and cost analyses are undertaken to more fully understand the spectrum of benefits of an MPRT solution, in comparison to conventional vehicle and plug-in hybrid electric vehicle approaches. An MPRT system not only offers significant advantages over other technologies in efficiently using renewable energy but also represents the unique potential to address urgent energy challenges by incorporating power transmission, storage, and generation infrastructure.

Modeling Magnetic Hysteresis Under DC-Biased Magnetization Using the Neural Network

The excitation conditions of electrical steel are generally sinusoidal but, with the advent of power electronics in recent years, dc-biased excitation is sometimes experienced. The use of an iron core under dc-biased magnetization gives rise to asymmetrical hysteresis loops and the hysteresis loss in the iron core also increases with the value of dc excitation. For iron cores working with dc-biased excitation, accurate modeling of the nonlinear characteristics for the iron core that includes the dc-bias is very important for the computation of the exciting current and the iron loss. In this paper, an efficient approach for simulating the hysteresis loop of iron core under dc-biased excitation using neural-network theory is presented. The proposed method has the merits that a specific hysteresis loop can be identified conveniently and effectively to ensure that accurate electromagnetic-field analysis can be realized.

A Cooperative Imbalance Compensation Method for Distributed-Generation Interface Converters

Distributed generation has attracted great attention in recent years, thanks to the progress in new-generation technologies and advanced power electronics. The Microgrid has been a successful example by integrating various generation sources with the existing power distribution network through power electronic converters. Microgrid converters are required to operate in a decentralized fashion, and power-frequency and reactive-power-voltage droop controls have been adopted for this purpose. In this paper, a droop control technique for imbalance compensation within the three-phase AC distributed generation system is proposed for Microgrid converters. The proposed technique allows even sharing of imbalance current among various converters and can thus be seamlessly integrated with the existing active-power-frequency and reactive-power-voltage droop controls to improve the power quality within the distributed power system. Its control functionalities are discussed, and simulation and laboratory test results are also presented to validate the proposed method.

Review of Soft—Switching Technologies for High—Frequency Switched—Mode Power Conversion

Given the rising demand for increases in the switching frequency and efficiency of switched–mode power conversion, the introduction of an undergraduate/postgraduate course on Advanced Power Electronics is both timely and important, and new teaching materials must be designed. This paper presents the evolution of soft–switching technologies, as well as a discussion of operating principles, performance characteristics, experimental results, merits and limitations. The purpose of the new course is to provide the students with up–to–date and comprehensive knowledge of advanced power electronic circuits. Additionally, this paper can help the academic community in developing an intimate understanding of various soft–switching topologies.

An integrated approach to hydrogen economy in Sicilian islands

Abstract CNR–ITAE is developing several hydrogen and fuel cell demonstration and research projects, each intended to be part of a larger strategy for hydrogen communities settling in small Sicilian islands. These projects involve vehicle design, hydrogen production from renewable energy sources and methane, as well as implementation strategies to develop a hydrogen and renewable energy economy. These zero emission lightweight vehicles feature regenerative braking and advanced power electronics to increase efficiency. Moreover, to achieve a very easy-to-use technology, a very simple interface between driver and the system is under development, including fault-recovery strategies and GPS positioning for car-rental fleets. Also marine applications have been included, with tests on PEFC applied on passenger ships and luxury yacht as power system for on-board loads. In marine application, it is under study also an electrolysis hydrogen generator system using seawater as hydrogen carrier. For stationary and automotive applications, the project includes a hydrogen refuelling station powered by renewable energy (wind or/and solar) and test on fuel processors fed with methane, in order to make the power generation self-sufficient, as well as to test the technology and increase public awareness toward clean energy sources.

Fabrication of antiferroelectric PLZT films on metal foils

Fabrication of high-dielectric-strength antiferroelectric (AFE) films on metallic foils is technically important for advanced power electronics. To that end, we have deposited crack-free Pb 0.92La 0.08Zr 0.95Ti 0.05O 3 (PLZT 8/95/5) films on nickel foils by chemical solution deposition. To eliminate the parasitic effect caused by the formation of a low-permittivity interfacial oxide, a conductive buffer layer of lanthanum nickel oxide (LNO) was coated by chemical solution deposition on the nickel foil before the deposition of PLZT. Use of the LNO buffer allowed high-quality film-on-foil capacitors to be processed in air. With the PLZT 8/95/5 deposited on LNO-buffered Ni foils, we observed field- and thermal-induced phase transformations of AFE to ferroelectric (FE). The AFE-to-FE phase transition field, E AF = 225 kV/cm, and the reverse phase transition field, E FA = 190 kV/cm, were measured at room temperature on a ≈1.15 μm-thick PLZT 8/95/5 film grown on LNO-buffered Ni foils. The relative permittivities of the AFE and FE states were ≈600 and ≈730, respectively, with dielectric loss ≈0.04 at room temperature. The Curie temperature was ≈210 °C. The thermal-induced transition of AFE-to-FE phase occurred at ≈175 °C. Breakdown field strength of 1.2 MV/cm was measured at room temperature.