Showing papers in "IEEE Transactions on Industry Applications in 2005"

A review of single-phase grid-connected inverters for photovoltaic modules

Abstract: This review focuses on inverter technologies for connecting photovoltaic (PV) modules to a single-phase grid. The inverters are categorized into four classifications: 1) the number of power processing stages in cascade; 2) the type of power decoupling between the PV module(s) and the single-phase grid; 3) whether they utilizes a transformer (either line or high frequency) or not; and 4) the type of grid-connected power stage. Various inverter topologies are presented, compared, and evaluated against demands, lifetime, component ratings, and cost. Finally, some of the topologies are pointed out as the best candidates for either single PV module or multiple PV module applications.

A comparison of three-level converters versus two-level converters for low-voltage drives, traction, and utility applications

Abstract: This paper evaluates three-level topologies as alternatives to two-level topologies in converters for low-voltage applications. Topologies, semiconductor losses, filter aspects, part count, initial cost, and life-cycle cost are compared for a grid interface, a conventional drive application, and a high-speed drive application.

A detailed comparison of system topologies for dynamic voltage restorers

Abstract: In this paper, four different system topologies for dynamic voltage restorers (DVRs) are analyzed and tested, with particular focus on the methods used to acquire the necessary energy during a voltage sag. Comparisons are made between two topologies that can be realized with a minimum amount of energy storage, with energy taken from the grid during the voltage sag, and two topologies that take energy from stored energy devices during the voltage sag. Experimental tests using a 10-kVA DVR show that the no-energy storage concept is feasible, but an improved performance can be achieved for certain voltage sags using stored energy topologies. The results of this comparison rank the no-storage topology with a passive shunt converter on the load side first, followed by the stored energy topology with a constant dc-link voltage.

Fuel consumption minimization of a microgrid

Abstract: A cost optimization scheme for a microgrid is presented. Prior to the optimization of the microgrid itself, several schemes for sharing power between two generators are compared. The minimization of fuel use in a microgrid with a variety of power sources is then discussed. The optimization of a small power system has important differences from the case of a large system and its traditional economic dispatch problem. Among the most important differences is the presence of a local heat demand which adds another dimension to the optimization problem. The microgrid considered in this paper consists of two reciprocating gas engines, a combined heat and power plant, a photovoltaic array and a wind generator. The optimization is aimed at reducing the fuel consumption rate of the system while constraining it to fulfil the local energy demand (both electrical and thermal) and provide a certain minimum reserve power. A penalty is applied for any heat produced in excess of demand. The solution of the optimization problem strongly supports the idea of having a communication infrastructure operating between the power sources.

Analysis of multiloop control strategies for LC/CL/LCL-filtered voltage-source and current-source inverters

Abstract: Multiloop control strategies have commonly been used to control power inverters of both the voltage-source and current-source topologies for power conversion applications including uninterruptible power supplies and utility interfaces for distributed power generation. However, these control strategies tend to be developed and comparatively evaluated for a particular application, with strategies for other applications presented as independent new developments. This paper presents a generalized analysis of different multiloop control approaches using alternative feedback control variables for several popularly adopted system configurations, highlighting similarities and identifying a generalized optimal control-variable selection criterion that is applicable across most multiloop-controlled inverter systems. The generality of the presented optimal variable selection criterion has been verified through the close similarities between the time-domain waveforms of the different inverter systems simulated in MATLAB Simulink and implemented experimentally in the laboratory.

Five-phase permanent-magnet motor drives

Abstract: A five-phase brushless permanent-magnet (PM) motor is introduced. The proposed motor has concentrated windings such that the produced back electromotive force is almost trapezoidal. The motor is supplied with the combined sinusoidal plus third harmonic of currents. This motor, while generating the same average torque as an equivalent PM brushless dc motor (BLDC), overcomes its disadvantages. The motor equations are obtained in the d/sub 1/q/sub 1/d/sub 3/q/sub 3/0 rotating reference frame. Therefore, the so-called vector control is easily applicable to this kind of motors and the motor has the same controllability as a PM synchronous motor (PMSM). For presenting the superior performance of the proposed five-phase motor, its three and five-phase PMSM and BLDC counterparts are also analyzed. Finite element method is used for studying the flux density and calculating the developed static torque. Also, the developed torque is obtained using the mathematical model in the d-q reference frame. The average torque and the torque ripple for all cases are calculated and compared. Experimental results are in good agreement with the simulation results.

Optimal flux weakening in surface PM machines using fractional-slot concentrated windings

Abstract: A design approach is presented for achieving optimal flux-weakening operation in surface permanent-magnet (SPM) synchronous machines by properly designing the machine's stator windings using concentrated, fractional-slot stator windings. This technique makes it possible to significantly increase the machine inductance in order to achieve the critical condition for providing wide speed ranges of constant-power operation. The conditions for optimal flux weakening can be achieved while simultaneously delivering sinusoidal line-to-line back-electromotive-force waveforms and low cogging torque. A closed-form analytical model is described that can be used to design SPM machines to achieve optimal flux-weakening conditions. This technique is applied to design a 6-kW SPM machine that achieves constant-power operation over a wide speed range. Performance characteristics of this machine are compared using both closed-form and finite-element analysis.

PM wind generator topologies

Abstract: The objective of this paper is to provide a comparison among permanent magnet (PM) wind generators of different topologies. Seven configurations are chosen for the comparison, consisting of both radial-flux and axial-flux machines. The comparison is done at seven power levels ranging from 1 to 200 kW. The basis for the comparison is discussed and implemented in detail in the design procedure. The criteria used for comparison are considered to be critical for the efficient deployment of PM wind generators. The design data are optimized and verified by finite-element analysis and commercial generator test results. For a given application, the results provide an indication of the best-suited machine.

Initial rotor position estimation of an interior permanent-magnet synchronous machine using carrier-frequency injection methods

Abstract: This work presents a method using carrier-frequency injection to estimate the initial rotor position and magnetic polarity for an interior permanent-magnet synchronous machine. A nonsaturating inductance model of the machine provides no information about the polarity of the rotor magnet because the position observer based on this model is locally stable at both poles. To distinguish the polarity of the rotor magnet, the magnetic saturation effect can be used. The Taylor series can be used to describe the nonlinear magnetic saturation relationship between the current and the flux linkage in the d-axis rotor reference frame. The second-order term produces the second harmonic component of the carrier frequency, and the sign of its coefficient identifies the polarity of the rotor magnet being tracked. Both simulation and experimental results show good response of the position observer at several rotor electrical positions using either a rotating vector in the stationary reference frame or a oscillating vector in the estimated rotor reference frame.

A novel three-phase high-power soft-switched DC/DC converter for low-voltage fuel cell applications

Abstract: An efficient dc/dc converter is needed as the interface between a low-voltage fuel cell source and a high-voltage bus for inverter operation. In this paper, a three-phase transformer-isolated dc/dc converter utilizing phase-shift (PS) modulation is proposed. The converter must be able to boost the voltage significantly and operate at current levels above 240 A on the source side. Key features of the proposed converter include reduced transformer turns ratio by a factor of two while maintaining the same output voltage, reduced size of passive components including output filter and input dc bus capacitor using three-phase interleaving, eliminated inductor current ripple at PS angles above 120/spl deg/, and achieved soft switching over a wide load range without auxiliary circuitry. The proposed converter has been analyzed, simulated, and implemented in hardware. An efficiency of above 96% was achieved using the prototype unit. Experimental results were used to verify all designs and analyses.

An improved robust predictive current regulation algorithm

Abstract: Current regulation techniques for pulsewidth-modulated (PWM) voltage source inverters (VSIs) can be classified as either linear or nonlinear. Linear techniques consist principally of either a proportional-integral (PI) or a predictive current control strategy, while nonlinear schemes are usually based on a hysteresis strategy. Of the two linear strategies, predictive current control offers the advantages of precise current tracking with minimal distortion and can also be fully implemented on a digital platform. However, the conventional implementation of the predictive current regulation (PCR) algorithm is sensitive to noise and errors in the load inductance estimate, particularly when the back EMF is also estimated. This paper presents an improved PCR algorithm that retains all the benefits associated with PCR while achieving significantly increased robustness to load parameter mismatch and reduced zero current clamped oscillation effects. It is also relatively insensitive to noise in the sampled current measurements. The algorithm is equally applicable to variable fundamental frequency applications such as variable speed drives and to fixed fundamental frequency applications such as PWM rectifier systems or active filters. Simulation and experimental results are presented to confirm the improved robustness of the new algorithm.

Elimination of harmonics in a multilevel converter with nonequal DC sources

Abstract: Eliminating harmonics in a multilevel converter in which the separate dc sources vary is considered. That is, given a desired fundamental output voltage, the problem is to find the switching times (angles) that produce the fundamental while not generating specifically chosen harmonics. Assuming that the separate dc sources can be measured, a procedure is given to find all sets of switching angles for which the fundamental is produced while lower order harmonics are eliminated. This is done by first converting the transcendental equations that specify the elimination of the harmonics into an equivalent set of polynomial equations. Then, using the mathematical theory of resultants, all solutions to this equivalent problem can be found. Experimental results are presented to validate the theory.

A single-phase inverter system for PV power injection and active power filtering with nonlinear inductor consideration

Abstract: This paper proposes a single-phase two-wire inverter system for photovoltaic (PV) power injection and active power filtering (APF) with nonlinear inductor consideration. The proposed system can fully or partially perform APF, process PV power, eliminate harmonic currents, improve power factor, and take into account the nonlinear effect of its output filter inductor. In the system, even though only the utility current is sensed, both APF and maximum power point tracking features can be still achieved, reducing the number of current sensors and cost significantly. To prevent output current from exceeding switch ratings, inverter current is properly controlled through a current estimator and a defined limit circle. A self-learning algorithm is also proposed to determine nonlinear inductance, which can increase the accuracy of the estimated current. Simulations and experimental results have verified the feasibility of the proposed PV inverter system and the algorithm.

A carrier-based PWM scheme for neutral-point voltage balancing in three-level inverters

Abstract: A significant problem with neutral-point-clamped three-level inverters is the fluctuation in the neutral-point voltage. In this paper, a capacitor voltage balancing technique for carrier-based three-level pulsewidth modulation (PWM) is developed, with improved voltage control capability at high modulation index. The method incorporates a novel scheme that requires measurements of only the motor currents and capacitor voltages to implement voltage balancing control, and does not need to determine the direction of power flow between the inverter and the motor.

Analytical approach of the stator current frequency harmonics computation for detection of induction machine rotor faults

Abstract: The aim of this paper is to analyze theoretically and experimentally the stator current of a three-phase squirrel-cage induction machine in order to show how it is influenced by electrical rotor faults. The approach used for this study analyzes the modification introduced by n broken rotor bars in the rotor cage magnetomotive force and then estimates the resulting frequency spectrum in the stator current. This approach is validated in a 3-kW 230-V/400-V 50-Hz 2850-r/min two-pole three-phase induction machine, showing the sensitive frequency components to rotor fault condition.

The future of electronic power processing and conversion

Abstract: At a workshop held on the Aeolian Islands in Sicily during May 2004 a group of academic and industry engineers from all over the world discussed the medium- and long-term future of power electronics and its applications in specific areas. The following main issues were identified and discussed: The demand is not for power electronic solutions but for system integration of electronic power processing. A more multidisciplinary approach is needed. We will witness a proliferation of energy storage in systems. The technology is in place and the improvement in system performance makes it worth while. A large penetration of power electronics into power systems will happen within the next 25-30 years. The main transmission grid will not be affected. The power electronics development will be in distributed generation and in the loads. The success of the integrated starter/generator (ISG), hybrid, or electric cars depends on political decisions more than on technological advances. However, the success of a recent Japanese hybrid car and the cost of oil could trigger the critical momentum for large-scale use of power electronics in automotive applications. We are moving toward standardized power supply building blocks for computers and other applications. The main push is for lower cost, and production technology becomes the important issue. Demands for improved performance in a diversity of applications will stimulate R&D in power electronics in the future. Intelligent control and energy management will come easily. Thermal and passive component integration is equally important and will require attention.

Reactive compensation techniques to improve the ride-through capability of wind turbine during disturbance

Abstract: World wind energy capacity expanded at an annual rate of 25% during the 1990s. The total world wind turbine installation capacity was approximately 40 000 MW at the end of 2003. Germany has the highest installed capacity of over 10 000 MW, while Denmark, where the wind energy accounts for more than 13% of electricity consumed, has the highest wind energy level per capita. The United States is catching up in the development of wind farms, with several large-scale wind generation projects currently being materialized. Even though there is significant progress in the wind generation technology, most of the currently installed wind turbines utilize induction generators to produce the electricity. Since the induction generators do not perform voltage regulation and absorb reactive power from the utility grid, they are often the source of voltage fluctuations. It is necessary to examine their responses during the faults and possible impacts on the system stability when the percentage of the wind generation increases. This paper compares the steady-state voltage profile and the voltage ride-through capabilities of the induction-generator-based wind farms with different reactive compensation techniques.

High-dynamic four-quadrant switched reluctance drive based on DITC

Abstract: This paper presents the development of a four-quadrant switched reluctance machine (SRM) drive for high dynamic applications. Comprehensive fundamentals and analysis for operating switched reluctance machines in four quadrants are presented. The drive is designed based on a high dynamic control strategy called Direct Instantaneous Torque Control (DITC). The functionality of DITC is discussed in detail for both motoring and generating operation. A methodology to generate switching functions directly by the hysteresis torque controllers for SRMs is proposed. The proposed controller was prototyped and tested on a digital signal processor/field-programmable gate array development platform. High dynamic operation in both motoring and generating mode and the transition between these modes are validated by experimental results presented at the end of this paper.

Transient analysis of self-excited induction Generator with electronic load controller (ELC) supplying static and dynamic loads

Abstract: This paper presents a transient analysis of a self-excited induction generator (SEIG) with electronic load controller (ELC) used in stand-alone micro-hydro power generation employing uncontrolled turbines. In view of the need to feed both dynamic [three-phase induction motor (IM)] and static loads from such systems, the transient behavior due to switching in of such loads is of interest and is carried out here. A composite mathematical model of the total system has been developed by combining the modeling of prime mover, SEIG, ELC, and load. Simulated results are compared with the experimental ones, obtained on a developed prototype of an SEIG-ELC system for the starting of an IM and switching in a resistive load. For the starting of an IM, a star/delta starter is used to avoid inrush current. Harmonic analysis is carried out to find total harmonic distortion of the terminal voltage and current to assess its power quality.

Control of a high-speed flywheel system for energy storage in space applications

Abstract: A novel control algorithm for the charge and discharge modes of operation of a flywheel energy storage system for space applications is presented. The motor control portion of the algorithm uses sensorless field oriented control with position and speed estimates determined from a signal injection technique at low speeds and a back electromotive force technique at higher speeds. The charge and discharge portion of the algorithm use command feedforward and disturbance decoupling, respectively, to achieve fast response with low gains. Simulation and experimental results are presented demonstrating the successful operation of the flywheel control up to the rated speed of 60 000 r/min.

Very-low-speed variable-structure control of sensorless induction machine drives without signal injection

Abstract: A sensorless induction machine drive is presented, in which the principles of variable-structure control and direct torque control (DTC) are combined to ensure high-performance operation in the steady state and under transient conditions. The drive employs a new torque and flux controller, the "linear and variable-structure control", which realizes accurate and robust control in a wide speed range. Conventional DTC transient merits are preserved, while the steady-state behavior is significantly improved. The full-order state observer is a sliding-mode one, which does not require the rotor speed adaptation and provides accurate state estimation in the entire speed range. The proposed scheme is a complete variable-structure solution that allows persistent sensorless operation of the drive at very low speeds, including zero and 3 r/min, with full load. Simulations and extensive experimental results confirm the robustness, accuracy, quickness, and low-chattering operation of the drive.

Diagnosis tool for motor condition monitoring

Abstract: In the modern industrial environment there is increasing demand for automatic condition monitoring. With reliable condition monitoring, faults such as mechanical motor failures could be identified in their early stages and further damage to the system could be prevented. Successful monitoring is a complex and application-specific problem, but a generic tool would be useful in preliminary analysis of new signals and in verification of known theories. A generic condition diagnosis tool is introduced in this paper. The tool is based on discriminative energy functions which reveal discriminative frequency-domain regions where failures can be identified. The tool was applied to induction motor bearing fault detection and succeeded in finding characteristic frequencies which allow accurate detection of bearing faults.

A wavelet-based multiresolution PID controller

Abstract: A novel controller based on multiresolution decomposition using wavelets is presented. The controller is similar to a proportional-integral-derivative (PID) controller in principle and application. The output from a motion control system represents the cumulative effect of uncertainties such as measurement noise, frictional variation, and external torque disturbances, which manifest at different scales. The wavelet is used to decompose the error signal into signals at different scales. These signals are then used to compensate for the uncertainties in the plant. This approach provides greater expanse over the degree of control applied to the system. Through hardware and simulation results on motion control systems, this controller is shown to perform better than a PID in terms of its ability to provide smooth control signal, better disturbance, and noise rejection.

Comparative assessment of different nonthermal plasma reactors on energy efficiency and aerosol formation from the decomposition of gas-phase benzene

Abstract: This work presents a comparative assessment of five different types of plasma reactors (pulsed corona, dielectric-barrier discharge (DBD), surface discharge (SD), BaTiO/sub 3/ packed-bed reactor, and plasma-driven catalyst (PDC) reactor) using the decomposition of gas-phase benzene. The parameters used in the assessment include energy constant, carbon balance, product selectivity, and nanometer-sized aerosol formation. The DBD reactor, the pulsed corona reactor, and the SD reactor, where the gas-phase chemical reactions prevail, showed similar performance both in the decomposition efficiency and in the aerosol formation. Size distribution and number concentration of the aerosol formed in the SD and the pulsed corona were 10-80 nm and /spl sim/10/sup 5/ particles/cm/sup 3/, respectively. The PDC reactor showed the highest removal efficiency as well as the highest CO/sub 2/ yield. Carbon balances were strongly related to the nanometer-sized aerosol formation. Negligible amounts of aerosol were formed in the BaTiO/sub 3/ packed-bed reactor and the PDC reactor packed with Ag/TiO/sub 2/ catalyst.

A practical comparison among high-power-factor electronic ballasts with similar ideas

Abstract: This paper provides a comparative analysis among four electronic ballast topologies with high power factor, employing the same switch for inverter and power factor correction stage. The analyses done are based on experimental results. A commercial electromagnetic ballast (EMB) is tested to provide a comparison with implemented electronic ballasts. The features of each topology are shown through the discussion of their advantages and disadvantages. The electronic ballasts are made for two 40-W fluorescent lamps at 50-kHz switching frequency and for a 110-V/sub rms/ 60-Hz utility line.

Challenges of connecting shipboard marine systems to medium voltage shoreside electrical power

Abstract: Ship service electrical power consumption at the pier side is rapidly growing and now exceeds 10-MW power range on many of the latest commercial ships. Short circuit current interruption capability of the switchgear and cables servicing the ship load at the port dictate the use of medium voltage power distribution systems at voltages from 5- to 21-kV range. Many of the high power medium voltage electrical loads must operate during unloading and loading of the docked ships. At the same time, environment protection regulations in many sea ports (California's largest ports are examples of the most restrictive requirements) do not allow ships to operate their prime movers while at berth. Many ship operators and port authorities are struggling with the absence of appropriate standards and specifications for interconnecting the ship service loads to onshore power distribution systems. The intent of this paper is first to review the theory, practice, and existing interconnection standards and then to outline what can be done to achieve a secure, reliable, safe, and cost-effective operation of the ship service loads inside international ports. This paper will review the current state of cold ironing, existing applicable standards for ship interconnections to shore power, proven techniques for shore power interconnections, as well as approaches to mitigate challenges of high power and high voltage shore power

Highly accurate fiber-optic DC current sensor for the electro-winning industry

Abstract: A fiber-optic current sensor for direct currents up to 500 kA is presented. Applications include current measurement for process control and protection in the electro-winning industry, for example at aluminum smelters. The sensor offers significant advantages with regard to performance and ease of installation compared to state-of-the-art Hall effect based current transducers. The sensor exploits the Faraday effect in an optical fiber and measures the path integral of the magnetic field along a closed loop around the current-carrying bus bars. The differential magneto-optic phase shift of left and right circular light waves propagating in the fiber is detected by means of a novel polarization-rotated reflection interferometer. Fiber gyroscope technology is employed for signal detection and processing. The fiber is packaged in a flexible strip of fiber re-enforced epoxy, which can be installed without opening the current-carrying bus bars. Subsequent re-calibration is not necessary. The sensor achieves accuracy within /spl plusmn/ 0.1% over a wide range of currents and temperatures.

NO/sub x/ reduction after treatment system using nitrogen nonthermal plasma desorption

Abstract: In the flue emission from an internal combustion system using diffusing combustion such as coal or oil fuel boiler, incinerator, or diesel engine, around 10% oxygen is usually included. It is difficult to reduce the NO/sub x/ in the emission completely using catalysts or plasma alone because part of the NO/sub x/ is oxidized under an O/sub 2/-rich environment. In order to overcome these difficulties, we proposed a new after treatment system of NO/sub x/ included in the exhaust gas of the combustion system using nonthermal plasma (NTP) desorption and reduction. In this system, exchangeable adsorbent columns are equipped. First, the exhaust gas including NO/sub x/ is adsorbed to an NO/sub x/ adsorbent for a period of /spl Delta/t/sub a/. After the period of /spl Delta/t/sub a/, the path of the exhaust gas is changed with a pair of rotary valves and NO/sub x/ adsorbent is changed. The adsorbed NO/sub x/ is desorbed from the adsorbent and reduced by applying NTP for a period of /spl Delta/t/sub d/ using N/sub 2/ or low-oxygen-concentration gas. The exhaust gas is always kept clean by the exchange of adsorbent. Further, total electric energy can be reduced because NTP is not applied for /spl Delta/t/sub a/. This system can be operated at atmospheric temperature because no catalyst is used. As an initial step to realize such kind of after treatment system, the basic characteristics of the N/sub 2/ NTP desorption and NO/sub x/ reduction were examined experimentally using a pulse corona NTP reactor. After several adsorption/desorption processes, the amount of NO/sub x/ adsorbed becomes equal to that of the NO/sub x/ desorbed, that is, all the NO/sub x/ was desorbed in a single desorption process. It is confirmed that the NO/sub x/ complete reduction using N/sub 2/ NTP desorption is possible not only for a simulated exhaust gas but for a real diesel engine gas. The effective specific energy density can be decreased down to 22 Wh/m/sup 3/.

Winding short circuits in the switched reluctance drive

Abstract: The switched reluctance drive is known to be fault tolerant, but it is not fault free. This paper takes an in-depth look at winding short circuits in this particular machine. Modeling and testing complement a theoretical analysis. Two cases need to be distinguished, one where a complete pole is shorted, and one where a few turns are shorted. Pole short circuits lead to torque reduction that can be easily compensated for with increased current. With few turns shorted, the impact on overall torque may actually be negligible, however, significant currents may circulate through the shorted turns, the worst case being with a single turn shorted with a zero resistance. These results are discussed with a view toward possible remediation schemes aside from simply turning off the faulted phase.

Design and simulation of a permanent-magnet electromagnetic aircraft launcher

Abstract: This paper describes the basic design, refinement, and verification using finite-element analysis, and operational simulation using the Virtual Test Bed, of a linear machine for an electromagnetic aircraft launcher, for the aircraft carrier of the future. Choices of basic machine format and procedures for determining basic dimensions are presented. A detailed design for a permanent-magnet version is presented, and wound-field coil and induction machine versions are briefly discussed. The long armature-short field geometry is justified, and in particular the impact of this geometry on the scale of the power electronic drive system is examined.