Showing papers on "Power electronics published in 2006"

Stability of photovoltaic and wind turbine grid-connected inverters for a large set of grid impedance values

Abstract: The aim of this paper is to analyze the stability problems of grid connected inverters used in distributed generation. Complex controllers (e.g., multiple rotating dq-frames or resonant-based) are often required to compensate low frequency grid voltage background distortion and an LCL-filter is usually adopted for the high frequency one. The possible wide range of grid impedance values (distributed generation is suited for remote areas with radial distribution plants) challenge the stability and the effectiveness of the LCL-filter-based current controlled system. It has been found out and it will be demonstrated in this paper that the use of active damping helps to stabilise the system in respect to many different kinds of resonances. The use of active damping results in an easy plug-in feature of the generation system in a vast range of grid conditions and in a more flexible operation of the overall system able to manage sudden grid changes. In the paper, a vast measurement campaign made on a single-phase system and on a three-phase system used as scale prototypes for photovoltaic and wind turbines, respectively, validate the analysis.

Constant power loads and negative impedance instability in automotive systems: definition, modeling, stability, and control of power electronic converters and motor drives

Abstract: Power electronic converters and electric motor drives are being put into use at an increasingly rapid rate in advanced automobiles. However, the new advanced automotive electrical systems employ multivoltage level hybrid ac and dc as well as electromechanical systems that have unique characteristics, dynamics, and stability problems that are not well understood due to the nonlinearity and time dependency of converters and because of their constant power characteristics. The purpose of this paper is to present an assessment of the negative impedance instability concept of the constant power loads (CPLs) in automotive power systems. The main focus of this paper is to analyze and propose design criteria of controllers for automotive converters/systems operating with CPLs. The proposed method is to devise a new comprehensive approach to the applications of power electronic converters and motor drives in advanced automotive systems. Sliding-mode and feedback linearization techniques along with large-signal phase plane analysis are presented as methods to analyze, control, and stabilize automotive converters/systems with CPLs

Power electronics intensive solutions for advanced electric, hybrid electric, and fuel cell vehicular power systems

Abstract: There is a clear trend in the automotive industry to use more electrical systems in order to satisfy the ever-growing vehicular load demands. Thus, it is imperative that automotive electrical power systems will obviously undergo a drastic change in the next 10-20 years. Currently, the situation in the automotive industry is such that the demands for higher fuel economy and more electric power are driving advanced vehicular power system voltages to higher levels. For example, the projected increase in total power demand is estimated to be about three to four times that of the current value. This means that the total future power demand of a typical advanced vehicle could roughly reach a value as high as 10 kW. In order to satisfy this huge vehicular load, the approach is to integrate power electronics intensive solutions within advanced vehicular power systems. In view of this fact, this paper aims at reviewing the present situation as well as projected future research and development work of advanced vehicular electrical power systems including those of electric, hybrid electric, and fuel cell vehicles (EVs, HEVs, and FCVs). The paper will first introduce the proposed power system architectures for HEVs and FCVs and will then go on to exhaustively discuss the specific applications of dc/dc and dc/ac power electronic converters in advanced automotive power systems

Digital control in power electronics

Abstract: This book presents the reader, whether an electrical engineering student in power electronics or a design engineer, a selection of power converter control problems and their basic digital solutions, based on the most widespread digital control techniques. The presentation is primarily focused on different applications of the same power converter topology, the half-bridge voltage source inverter, considered both in its single- and three-phase implementation. This is chosen as the test case because, besides being simple and well known, it allows the discussion of a significant spectrum of the most frequently encountered digital control applications in power electronics, from digital pulse width modulation (DPWM) and space vector modulation (SVM), to inverter output current and voltage control, ending with the relatively more complex VSI applications related to the so called smart-grid scenario. This book aims to serve two purposes: (1) to give a basic, introductory knowledge of the digital control techniques applied to power converters; and (2) to raise the interest for discrete time control theory, stimulating new developments in its application to switching power converters.

Power Electronics Handbook: Devices, Circuits and Applications

Abstract: Power electronics, which is a rapidly growing area in terms of research and applications, uses modern electronics technology to convert electric power from one form to another, such as ac-dc, dc-dc, dc-ac, and ac-ac with a variable output magnitude and frequency. It has many applications in our every day life such as air-conditioners, electric cars, sub-way trains, motor drives, renewable energy sources and power supplies for computers. This book covers all aspects of switching devices, converter circuit topologies, control techniques, analytical methods and some examples of their applications. Designed to appeal to a new generation of engineering professionals, "Power Electronics Handbook, 3rd Edition" features four new chapters covering renewable energy, energy transmission, energy storage, as well as an introduction to Distributed and Cogeneration (DCG) technology, including gas turbines, gensets, microturbines, wind turbines, variable speed generators, photovoltaics and fuel cells, has been gaining momentum for quite some time now. With this book readers should be able to provide technical design leadership on assigned power electronics design projects and lead the design from the concept to production involving significant scope and complexity. It contains 45 chapters covering all aspects of power electronics and its applications. It features three new chapters now including coverage Energy Sources, Energy Storage and Electric Power Transmission. It includes contributions from more than fifty leading experts spanning twelve different countries.

Analytical loss model of power MOSFET

Abstract: An accurate analytical model is proposed in this paper to calculate the power loss of a metal-oxide semiconductor field-effect transistor. The nonlinearity of the capacitors of the devices and the parasitic inductance in the circuit, such as the source inductor shared by the power stage and driver loop, the drain inductor, etc., are considered in the model. In addition, the ringing is always observed in the switching power supply, which is ignored in the traditional loss model. In this paper, the ringing loss is analyzed in a simple way with a clear physical meaning. Based on this model, the circuit power loss could be accurately predicted. Experimental results are provided to verify the model. The simulation results match the experimental results very well, even at 2-MHz switching frequency.

Flyback-Type Single-Phase Utility Interactive Inverter With Power Pulsation Decoupling on the DC Input for an AC Photovoltaic Module System

Abstract: In recent years, interest in natural energy has grown in response to increased concern for the environment. Many kinds of inverter circuits and their control schemes for photovoltaic (PV) power generation systems have been studied. A conventional system employs a PV array in which many PV modules are connected in series to obtain sufficient dc input voltage for generating ac utility line voltage from an inverter circuit. However, the total power generated from the PV array is sometimes decreased remarkably when only a few modules are partially covered by shadows, thereby decreasing inherent current generation, and preventing the generation current from attaining its maximum value on the array. To overcome this drawback, an ac module strategy has been proposed. In this system, a low-power dc-ac utility interactive inverter is individually mounted on each PV module and operates so as to generate the maximum power from its corresponding PV module. Especially in the case of a single-phase utility interactive inverter, an electrolytic capacitor of large capacitance has been connected on the dc input bus in order to decouple the power pulsation caused by single-phase power generation to the utility line. However, especially during the summer season, the ac module inverters have to operate under a very high atmospheric temperature, and hence the lifetime of the inverter is shortened, because the electrolytic capacitor has a drastically shortened life when used in a high-temperature environment. Of course, we may be able to use film capacitors instead of the electrolytic capacitors if we can pay for the extreme large volume of the inverter. However, this is not a realistic solution for ac module systems. This paper proposes a novel flyback-type utility interactive inverter circuit topology suitable for ac module systems when its lifetime under high atmospheric temperature is taken into account. A most distinctive feature of the proposed system is that the decoupling of power pulsation is executed by an additional circuit that enables employment of film capacitors with small capacitance not only for the dc input line but also for the decoupling circuit, and hence the additional circuit is expected to extend the lifetime of the inverter. The proposed inverter circuit also enables realization of small volume, lightweight, and stable ac current injection into the utility line. A control method suitable for the proposed inverter is also proposed. The effectiveness of the proposed inverter is verified thorough P-SIM simulation and experiments on a 100-W prototype

Control of variable-speed wind turbines: standard and adaptive techniques for maximizing energy capture

Abstract: This article considers an adaptive control scheme previously developed for region 2 control of a variable speed wind turbine. In this paper, the question of theoretical stability of the torque controller is addressed, showing that the rotor speed is asymptotically stable under the torque control law in the constant wind speed input case and L/sub 2/ stable with respect to time-varying wind input. Further, a method is derived for selecting /spl gamma//sub /spl Delta/M/ in the gain adaptation law to guarantee convergence of the adaptive gain M to its optimal value M*.

Dynamic Maximum Power Point Tracking of Photovoltaic Arrays Using Ripple Correlation Control

Abstract: A dynamically rapid method used for tracking the maximum power point of photovoltaic arrays, known as ripple correlation control, is presented and verified against experiment The technique takes advantage of the signal ripple, which is automatically present in power converters The ripple is interpreted as a perturbation from which a gradient ascent optimization can be realized The technique converges asymptotically at maximum speed to the maximum power point without the benefit of any array parameters or measurements The technique has simple circuit implementations

Control Design Techniques in Power Electronics Devices

Abstract: Modelling.- Modelling of DC-to-DC Power Converters.- Controller Design Methods.- Sliding Mode Control.- Approximate Linearization in the Control of Power Electronics Devices.- Nonlinear Methods in the Control of Power Electronics Devices.- Applications.- DC-to-AC Power Conversion.- AC Rectifiers.

Usefulness of DC power flow for active power flow analysis with flow controlling devices

Abstract: DC power flow is a commonly used tool for contingency analysis. Recently, due to its simplicity and robustness, it also becomes increasingly used for the real-time dispatch and techno-economic analysis of power systems. It is a simplification of a full power flow looking only at active power. Aspects such as voltage support and reactive power management are possible to analyse. However, such simplifications cannot always be justified and sometimes lead to unrealistic results. Especially the implementation of power flow controlling devices is not trivial since standard DC power flow fundamentally neglects their effects. Until recently, this was not an issue as the application of power flow controlling devices in the European grid was limited. However, with the liberalisation of European electricity market and the introduction of large wind energy systems, the need for real power flow control has emerged and therefore, the use of these devices has been reconsidered. Several phase shifting transformers (PST) are being installed or planned in order to control flows. Therefore, it is important to fundamentally re-validate the fast, but less accurate, DC power flow method. In this paper the assumptions of DC power flow are analysed, and its validity is assessed by comparing the results of power flow simulations using both the DC and AC approaches on a modified IEEE 300 bus system with PSTs.

Automotive DC-DC bidirectional converter made with many interleaved buck stages

Abstract: Interleaving technique is used in some applications due to its advantages regarding filter reduction, dynamic response, and power management. In dual battery system vehicles, the bidirectional dc-dc converter takes advantage of this technique using three-to-five paralleled buck stages. In this paper, we propose the use of a much higher number of phases in parallel together with digital control. It will be shown that this approach opens new possibilities since changes in the technology are possible. Thus, two 1000-W prototypes have been designed using surface mount technology devices (SO-8 transistors). An additional important feature is that due to the accuracy of the digital device [field-programmable gate array (FPGA)], current loops have been eliminated, greatly simplifying the implementation of the control stage

Quasi-Resonant Zero-Current-Switching Bidirectional Converter for Battery Equalization Applications

Abstract: A systematic approach to reform and analyze a soft-switching bidirectional dc-to-dc converter is proposed for cell voltage balancing control in a series connected battery string. quasi-resonant converter circuits have been designed to achieve the zero-current-switching (ZCS) to reduce the switching loss in bidirectional battery equalizers. The results indicate that the switching loss and energy transfer efficiency can be substantially improved using the quasi-resonant ZCS (QRZCS) technology in a battery charging system with an individual cell equalizer (ICE). The validity of the battery equalization is further verified using an experimental installation involving a battery string of three lithium-ion cells. The simulation and experimental results show that the proposed QRZCS battery equalization schemes can achieve bidirectional battery equalization performance and reduce the MOSFET transistor switch power losses by more than 96% and increase the efficiency by around 20%~30% compared with the conventional battery equalizer during an identical equalization process

Power Electronics and Motor Drives: Advances and Trends

Abstract: Introduction Power Semiconductor Devices Phase-Controlled Converters and Cycloconverters Voltage-Fed Converters and PWM Techniques Current-Fed Converters AC Machined for Drives Induction Motor Drives-Control and Estimation Synchronus Motor Drives-Control and Estimation Microprocessor/DSP Priciples and Applications Fuzzy Logic Pronciples and Applications Neural Network Principles and Applications

Analytical calculation of the RMS current stress on the DC-link capacitor of voltage-PWM converter systems

Abstract: A simple analytical expression for the current stress on the DC-link capacitor caused by the load-side inverter of a voltage DC-link-converter system is derived. The DC-link capacitor-current RMS value is determined from the modulation depth and by the amplitude and the phase angle of the inverter output current assuming a sinusoidal inverter output current and a constant DC-link voltage. Despite neglecting the output-current ripple, the results of the analytical calculation are within 8% of measurements made from digital simulation and an experimental system, even if the output-current ripple is relatively high as in the case of low-frequency IGBT inverter systems. The simple analytical expression provides significant advantages over simulation methods for designing the DC-link capacitor of PWM converter systems.

A Comparison of Diode-Clamped and Cascaded Multilevel Converters for a STATCOM With Energy Storage

Abstract: The progression of distributed generation within a bulk power system will lead to the need for greater control of transmission-line power flows. Static synchronous compensators (STATCOMs) provide a power-electronics-based means of embedded control of transmission-line voltage and power flows. The integration of energy storage with a STATCOM can extend traditional STATCOM capabilities to four-quadrant power flow control and transient stability improvement. This paper discusses energy storage systems (ESSs) integrated with conventional and multilevel bidirectional power converters for a hybrid STATCOM/ESS. Conventional, diode-clamped, and cascaded multilevel converter-based STATCOM/ESSs are developed, and their performances for a variety of power system applications are compared using battery energy storage. The advantages and disadvantages of each topology are presented. Both simulation and experimental results are provided to validate the conclusions

A Digital Current-Mode Control Technique for DC–DC Converters

Abstract: The objective of this paper is to propose a simple digital current mode control technique for dc-dc converters. In the proposed current-mode control method, the inductor current is sampled only once in a switching period. A compensating ramp is used in the modulator to determine the switching instant. The slope of the compensating ramp is determined analytically from the steady-state stability condition. The proposed digital current-mode control is not predictive, therefore the trajectory of the inductor current during the switching period is not estimated in this method, and as a result the computational burden on the digital controller is significantly reduced. It therefore effectively increases the maximum switching frequency of the converter when a particular digital signal processor is used to implement the control algorithm. It is shown that the proposed digital method is versatile enough to implement any one of the average, peak, and valley current mode controls by adjustment of the sampling instant of the inductor current with respect to the turn-on instant of the switch. The proposed digital current-mode control algorithm is tested on a 12-V input and 1.5-V, 7-A output buck converter switched at 100kHz and experimental results are presented

A bidirectional DC–DC converter for fuel cell electric vehicle driving system

Abstract: This paper presents a power converter for a fuel cell electric vehicle driving system. A new bidirectional, isolated topology is proposed in consideration of the differing fuel cell characteristics from traditional chemical-power battery and safety requirements. The studied converter has the advantages of high efficiency, simple circuit, and low cost. The detailed design and operating principles are analyzed and described. The simulation and experimental waveforms for the proposed converter are shown to verify its feasibility.

A New Simplified Multilevel Inverter Topology for DC–AC Conversion

Abstract: Multilevel converters offer high power capability, associated with lower output harmonics and lower commutation losses. Their main disadvantage is their complexity, requiring a great number of power devices and passive components, and a rather complex control circuitry. This work reports a new multilevel inverter topology using an H-bridge output stage with a bidirectional auxiliary switch. The new topology produces a significant reduction in the number of power devices and capacitors required to implement a multilevel output. The new topology is used in the design of a five-level inverter; only five controlled switches, eight diodes, and two capacitors are required to implement the five-level inverter using the proposed topology. The new topology achieves a 37.5% reduction in the number of main power switches required (five in the new against eight in any of the other three configurations) and uses no more diodes or capacitors that the second best topology in the literature, the Asymmetric Cascade configuration. Additionally, the dedicated modulator circuit required for multilevel inverter operation is implemented using a FPGA circuit, reducing overall system cost and complexity. Theoretical predictions are validated using simulation in SPICE, and satisfactory circuit operation is proved with experimental tests performed on a laboratory prototype

A Passive EMI Filter for Eliminating Both Bearing Current and Ground Leakage Current From an Inverter-Driven Motor

Abstract: This paper presents a practical approach to eliminating both bearing current and ground leakage current from an inverter-driven motor rated at 400 V and 3.7 kW. When the shaft voltage with respect to the motor frame exceeds the dielectric breakdown voltage of thin lubricating grease films in two metal bearings at the drive and non-drive ends, an electrical discharge machining (EDM) current flows through the bearings. A passive electromagnetic interference (EMI) filter can keep the shaft voltage in check, as a result of having eliminated high-frequency common-mode voltage from the motor terminals. Hence, no dielectric breakdown occurs in the grease films, so that no EDM current flows in the bearings. Experimental results verify the viability and effectiveness of the passive EMI filter designed in this paper

Natural Balance of Multicell Converters: The General Case

Abstract: This paper focuses on the development of the natural balancing theory for the p-cell case. It describes the relationship between the models for different numbers of cells in a generic model for a p-cell multicell converter. The model discussed is based on the same principles that were used to develop the two-cell model in , except that the mathematics is much more involved. The same conclusions that were found to be true for the two-cell case was also found to be true for the general case of p cells. These conclusions include that the natural balancing mechanism of multicell converters depends on the overlap of the groups of harmonics of the switching function as well as on the load impedance. It will also be shown that the self-balancing mechanism ensures safe operation under most operating conditions where a high enough switching frequency is chosen and the load is not purely reactive. Two new aspects of the balancing theory were identified in the p-cell case: 1) for fixed duty-cycle modulation there exists certain values of the duty-cycle that causes the natural balancing mechanism to fail and 2) for p-cell converters the balance booster concept can be extended to a number of balance boosters tuned to multiples of the switching frequency. A "DesignTool" based on the balancing theory was developed to aid practicing engineers in designing multicell converters

Extended operation of flying capacitor multilevel inverters

Abstract: Recent research in flying capacitor multilevel inverters (FCMIs) has shown that the number of voltage levels can be extended by changing the ratio of the capacitor voltages. For the three-cell FCMI, four levels of operation are expected if the traditional ratio of the capacitor voltages is 1:2:3. However, by altering the ratio, the inverter can operate as a five-, six-, seven-, or eight-level inverter. According to previous research, the eight-level case is referred to as maximally distended (or full binary combination schema) since it utilizes all possible transistor switching states. However, this case does not have enough per-phase redundancy to ensure capacitor voltage balancing under all modes of operation. In this paper, redundancy involving all phases is used along with per-phase redundancy to improve capacitor voltage balancing. It is shown that the four- and five-level cases are suitable for motor drive operation and can maintain capacitor voltage balance under a wide range of power factors and modulation indices. The six-, seven-, and eight-level cases are suitable for reactive power transfer in applications such as static var compensation. Simulation and laboratory measurements verify the proposed joint-phase redundancy control.

Power quality and stability improvement of a wind farm using STATCOM supported with hybrid battery energy storage

Abstract: A large penetration of wind generation info the power system will mean that poor power quality and poor stability margins cannot be tolerated from wind farms This requires that methods to improve power qualify and stability for such systems be found The static compensator (STATCOM) with hybrid battery energy storage (BES) has great potential to fulfil this role, though considerable advances in the control of this system are still to be made From an economic point of view, rating the STATCOM for steady-state power-quality improvement duty is appropriate Rating the STATCOM to absorb large amounts of additional power in excess of its transient overload capability during network faults is inappropriate A hybrid of BES and braking resistor is therefore proposed A new hybrid STATCOM–BES control technique is developed and discussed in the context of improving the stability and power quality to fixed speed, induction generator, wind turbines The variation of the network voltage, active and reactive power with the fluctuation of the wind generation is studied A wind generation system with a STATCOM battery energy storage unit and the new control was simulated and the results demonstrate that both power quality and the stability margin can be improved significantly for wind farms

Sensorless optimization of dead times in dc–dc converters with synchronous rectifiers

Abstract: This paper introduces an approach to achieve optimum dead times in dc–dc converters with synchronous rectifiers without sensing any of the power-stage signals other than the output voltage. The dead times are adjusted adaptively to minimize the duty-cycle command, which results in maximization of the converter efficiency. The method is particularly well suited for digital controller implementation, requiring no additional analog components or modifications of standard gate-drive circuitry. Experimental results for a digitally controlled 5 V-to-1 V, 5-A synchronous buck converter demonstrate practical implementation of the sensorless dead-time optimization algorithm.

Adaptive feedforward and feedback control schemes for sliding mode controlled power converters

Abstract: A major disadvantage of applying sliding mode control to dc/dc converters is that the steady-state switching frequency is affected by line and load variations This is undesirable as it complicates the design of the input and output filters To reduce switching frequency deviation in the events of line and load variations, an adaptive feedforward control scheme that varies the hysteresis band according to the change of line input voltage and an adaptive feedback control scheme that varies the control parameter (ie, sliding coefficient) according to the change of the output load are proposed This paper presents a thorough investigation into the problem and the effectiveness of the proposed solutions In addition, methods of implementing the proposed adaptive control strategies are discussed Experimental results confirm that the adaptive control schemes are capable of reducing the switching frequency variations caused by both line and load variations

Analysis and design of a low-stress buck-boost converter in universal-input PFC applications

Abstract: In converters for power-factor-correction (PFC), the universal-input capability, i.e., the ability to operate from any ac line voltage world-wide, comes with a heavy penalty in terms of component stresses and losses, and with restrictions on the dc output voltage. In this paper, we propose a new two-switch topology, boost-interleaved buck-boost (BoIBB) converter, which can offer significant performance improvements over single-switch buck-boost converters (including flyback, SEPIC, or Cuk topologies) or other two-switch buck-boost converters in universal-input PFC applications. The paper presents an analysis of the converter operation and component stresses, as well as design guidelines. High efficiency (over 93%) throughout the universal-input ac line voltage range is demonstrated on an experimental 100-W, 200-V dc output, universal-input BOIBB PFC rectifier.

Design and performance evaluation of subsynchronous damping controller with STATCOM

Abstract: A long transmission line needs controllable series as well as shunt compensation for power flow control and voltage regulation. This can be achieved by suitable combination of passive elements and active FACTS controllers. In this paper, series passive compensation and shunt active compensation provided by a static synchronous compensator (STATCOM) connected at the electrical center of the transmission line are considered. It is possible to damp subsynchronous resonance (SSR) caused by series capacitors with the help of an auxiliary subsynchronous damping controller (SSDC) on STATCOM. The objective of this paper is to investigate the SSR characteristics of the system and propose a new design procedure for SSDC based on nonlinear optimization to meet the specifications on the damping torque in the range of critical torsional frequencies. The SSDC uses the Thevenin voltage signal to modulate the reactive current reference of STATCOM. The Thevenin voltage signal is derived from the locally available STATCOM bus voltage and reactive current signals. The STATCOM configurations considered in this paper are 12 pulse, two- and three-level voltage source converter with Type-2 and Type-1 control, respectively. The controller regulates either reactive current (supplied by the STATCOM) or the bus voltage. The 3-phase model of the STATCOM is based on switching functions. By neglecting harmonics in the switching function, D-Q model is derived which is combined with similar models of the other system components for linear analysis. The results of the linear analysis are validated by carrying out transient simulation based on the detailed nonlinear models. The study is performed on the system adapted from the IEEE First Benchmark Model.

Radio frequency rectifiers based on organic thin-film transistors

Abstract: One important technical hurdle that has to be overcome for using organic transistors in radio-frequency identification tags is for these devices to operate at rf frequencies (typically 13.56MHz) in the front end. It was long thought that organic transistors are too slow for this. In this letter we show that organic transistor based full-wave rectifier circuits utilizing pentacene, a p-channel organic semiconductor, can operate at this frequency with a useful efficiency. In order to achieve such high-frequency operation, we make use of the nonquasistatic state of the transistors.

Application of voltage- and current-controlled voltage source inverters for distributed generation systems

Abstract: Voltage source inverters (VSI) have been widely used in uninterruptible power supplies, unified power flow controllers or unified power quality conditioners, and distributed generation systems (DGS) VSIs are inherently efficient, compact, and economical devices used to control power flow and provide quality supply VSIs can be classified as voltage-controlled VSIs (VCVSIs) and current-controlled VSIs (CCVSIs), depending on their control mechanism In this paper, a detailed comparison of VCVSIs and CCVSIs for DGS applications is presented This paper examines the advantages and limitations of each control technique in a single-phase DGS, without incorporating additional hardware and/or extra complex control techniques Discussions on the concepts, hypotheses, and computer simulations of different VSIs in the presence of different loads and conditions are presented The experimental results confirm the validity of the analysis and simulations outlined The paper provides design recommendations for the use of VCVSIs and CCVSIs in various applications