A New Variable-Speed Wind Energy Conversion System Using Permanent-Magnet Synchronous Generator and $Z$-Source Inverter

With the growth of wind energy conversion systems (WECSs), various technologies are developed for them. Permanent-magnet synchronous generators (PMSGs) are used by these technologies due to special characteristics of PMSGs such as low weight and volume, high performance, and the elimination of the gearbox. In this paper, a new variable-speed WECS with a PMSG and $Z$-source inverter is proposed. Characteristics of $Z$-source inverter are used for maximum power tracking control and delivering power to the grid, simultaneously. Two control methods are proposed for delivering power to the grid: Capacitor voltage control and dc-link voltage control. Operation of system with these methods is compared from the viewpoint of power quality and total switching device power (TSDP). In addition, TSDP, current ripple of inductor, performance, and total harmonic distortion of grid current of proposed system is compared with traditional wind energy system with a boost converter.      

Rotor Position Phase-Locked Loop for Decoupled $Phbox{-}Q$ Control of DFIG for Wind Power Generation

Implementation of decoupled $Phbox{-}Q$ control of doubly fed induction generators requires the positions of the rotors to be known. The rotor position phase-lock loop (PLL) is an invention that extracts rotor position and speed simultaneously by “sensorless” means. The rotor position PLL is parameter-insensitive because, apart from an approximate value of the magnetization reactance, knowledge of the other parameters is not required for it to function. Experimental results obtained under noisy conditions demonstrate that it is also insensitive to noise.      

An Experimental Study and Nonlinear Modeling of Discharge I–V Behavior of Valve-Regulated Lead–Acid Batteries

Valve-regulated lead–acid battery continues to be studied in some cost-sensitive applications, such as microhybrid electric vehicle and scooters. A dynamic battery $I$ –$V$ model is needed for system design, simulation, and real-time control purposes. Battery discharging behavior is one of the most important parts of the model. By reviewing previous studies, the authors find that there is a contradiction between the linear and nonlinear I–V behaviors, and this serves as a motivation for the current experimental study. Through regression analysis of experimental data, the nonlinear behavior is verified and a nonlinear dynamic Thevenin model is developed. The model is validated by voltage response tests with multistep current profiles as model input. The calculated voltage response results from the model fit the test results well.      

Online Synchronous Machine Parameter Extraction From Small-Signal Injection Techniques

This paper proposes using a novel line-to-line voltage perturbation as a technique for online measurement of synchronous machine parameters. The perturbation is created by a chopper circuit connected between two phases of the machine. Using this method, it is possible to obtain the full set of four complex small-signal impedances of the synchronous machine $d$– $q$ model over a wide frequency range. Typically, two chopper switching frequencies are needed to obtain one data point. However, it is shown herein that, due to the symmetry of the machine equations, only one chopper switching frequency is needed to obtain the information. A 3.7-kW machine system is simulated, and then constructed for validation of the impedance measurement technique. A genetic algorithm is then used to obtain IEEE standard model parameters from the $d$ –$q$ impedances. The resulting parameters are shown to be similar to those obtained by a series of tests involving synchronous reactance measurements and a standstill frequency response.      

Linear Models for Optimization of Infrastructure for $hbox{CO}_{2}$ Capture and Storage

This paper presents linear models of the most common components in the value chain for $hbox{CO}_{2}$ capture and storage. The optimal investment planning of new gas power plants traditionally includes the cost of fuel versus sales of electricity and heat from the plant. If a new power plant also causes additional investments in gas infrastructure, these should be included in the optimization. With the increasing focus on global $hbox{CO}_{2}$ emissions, yet another aspect is introduced in the form of technology and infrastructure for capture, transport, and storage of $hbox{CO}_{2}$. To be able to include all these aspects in the planning of new power plants, linear models for $hbox{CO}_{2}$ capture and storage are formulated consistent with current models for gas, electricity, and heat infrastructures. This paper presents models for the following $hbox{CO}_{2}$ infrastructure: source, combined cycle gas turbine producing electricity, heat and exhaust, capture plant, pipeline, liquefaction plant, storage, ship transport, injection pump, and demand/market.      

Analysis of Flux Leakage in a Segmented Core Brushless Permanent Magnet Motor

This paper presents an analytical model to analyze the leakage flux associated with a brushless permanent magnet motor that utilizes segmented stator core. Due to the presence of a segmented stator structure, the leakage of flux through the tooth tips becomes worthy of analysis and consideration in such a motor. A leakage parameter $alpha$ is developed to show the effects of various design parameters on tooth-tip flux leakage that is essential in accurately predicting the air gap flux density and other output parameters in the motor. Finite-element analysis and experimental verifications are also done to validate the analytical model.      

Enhanced Control and Operation of DFIG-Based Wind Farms During Network Unbalance

This paper investigates the control and operation of doubly fed induction generator (DFIG)-based wind generation systems under unbalanced voltage conditions. DFIG system behaviors under unbalanced voltage are analyzed and different control targets are discussed. A new rotor current control strategy containing a main controller and an auxiliary controller is proposed. The main controller is implemented in the positive $(dq)^{+}$ frame without involving positive/negative sequence decomposition, whereas the auxiliary controller is implemented in the negative $(dq)^{-}$ frame with negative sequence current extracted. The impact of providing unbalanced control on converter voltage rating is investigated. Simulation results using EMTDC/PSCAD are presented for a 2-MW DFIG wind generation system to validate the proposed control scheme and to demonstrate the enhanced system operation during “small” steady state and “large” transient unbalances.      

Modulation and Control of Three-Phase Paralleled Z-Source Inverters for Distributed Generation Applications

This paper presents a modulation and controller design method for paralleled $Z$-source inverter systems applicable for alternative energy sources like solar cells, fuel cells, or variable-speed wind turbines with front-end diode rectifiers. A modulation scheme is designed based on simple shoot-through principle with interleaved carriers to give enhanced ripple reduction in the system. Subsequently, a control method is proposed to equalize the amount of power injected by the inverters in the grid-connected mode and also to provide reliable supply to sensitive loads on-site in the islanding mode. The modulation and controlling methods are proposed to have modular independence so that redundancy, maintainability, and improved reliability of supply can be achieved. The performance of the proposed paralleled $Z$-source inverter configuration is validated with simulations carried out using Matlab/Simulink/Powersim. Moreover, a prototype is built in the laboratory to obtain the experimental verifications.      

Analysis of Critical-Speed Increase of Induction Machines via Winding Reconfiguration With Solid-State Switches

Commonly used speed-control concepts permit speed ranges up to two–three times the base speed via voltage to frequency ($V$/$f$ ), that is, field-weakening control. This paper teaches the extension of the speed-control range up to nine times the base speed through online reconfiguration of the motor windings via electronic switches. The switchover of the windings, either from a winding with $p_{1}$ poles to $p_{2}$ poles, or from series to parallel connection of the number of turns per phase—so-called ($V$/ $N$·$f$) control—lasts less than a 60-Hz cycle. Such fast switchover causes small transients only, and therefore, this concept is applicable to most variable-speed drives.      

“Active Flux” DTFC-SVM Sensorless Control of IPMSM

This paper proposes an implementation of a motion-sensorless control system in wide speed range based on “active flux” observer, and direct torque and flux control with space vector modulation (DTFC-SVM) for the interior permanent magnet synchronous motor (IPMSM), without signal injection. The concept of “active flux” (or “torque producing flux”) turns all the rotor salient-pole ac machines into fully nonsalient-pole ones. A new function for $L_{q}$ inductance depending on torque is introduced to model the magnetic saturation. Notable simplification in the rotor position and speed estimation is obtained, because the active flux position is identical with the rotor position. Extensive experimental results are presented to verify the principles and to demonstrate the effectiveness of the proposed sensorless control system. With the active flux observer, the IPMSM drive system operates from very low speed of 2 r/min at half full-load up to 1400 r/min. Higher speed is possible, in principle, with flux weakening.      

Estimation of Energy Yield From Wind Farms Using Artificial Neural Networks

This paper uses the data from seven wind farms at Muppandal, Tamil Nadu, India, collected for three years from April 2002 to March 2005 for the estimation of energy yield from wind farms. The model is developed with the help of neural network methodology, and it involves three input variables—wind speed, relative humidity, and generation hours—and one output variable, which give the energy output from wind farms. The modeling is done using MATLAB software. The most appropriate neural network configuration after trial and error is found to be 3-5-1 (3 input layer neurons, 5 hidden layer neurons, 1 output layer neuron). The mean square error for the estimated values with respect to the measured data is $7.6 times 10^{-3}$. The results demonstrate that this work is an efficient energy yield estimation tool for wind farms.      

Modeling and Control of Grid-Connected Voltage-Sourced Converters Under Generalized Unbalanced Operation Conditions

This paper proposes a unified mathematical model of a voltage-sourced converter (VSC) based on positive and negative synchronously rotating frames under both unbalanced grid supply and imbalanced input impedances. Based on the developed model, a new definition of instantaneous reactive power is introduced, and an accurate mathematical model of the instantaneous active and reactive powers at different locations of the VSC is derived. To avoid the use of band-trap filter for decomposing the positive- and negative-sequence dq components of current and voltage, a new control scheme with multifrequency proportional-resonant controller in the stationary $alphabeta$ frame is employed to improve the steady state and dynamic response under generalized unbalanced operation conditions. Simulation and experimental studies with various factors were conducted and compared under different types of unbalanced conditions. The simulated and experimental results demonstrate that the proposed control scheme in the stationary $alphabeta$ frame provides sufficiently steady-state tracking capability for ac input current, and a better transient response in compensation for wide-range generalized unbalanced operation conditions.      

Saturation Modeling and Stability Analysis of Synchronous Reluctance Generator

A new method of representing magnetic saturation in synchronous reluctance generator has been proposed in this paper. A linearized model of synchronous reluctance generator has been developed applying the proposed saturation model to perform the steady-state stability analysis. The effect of $d$ - and $q$-axis saturation on the steady-state stability of a synchronous reluctance generator has been investigated using the proposed linearized machine model. Effects of different loading conditions such as active power, reactive power, and power factor on the steady-state stability have also been looked into. Moreover, the effect of $d$- and $q$-axis saturation on the transient stability analysis has been investigated in the case of a three-phase symmetrical ground fault at the machine terminals.      

A Compact Electrical Model for Microscale Fuel Cells Capable of Predicting Runtime and $I$–$V$ Polarization Performance

The growing popularity and success of fuel cells (FCs) in aerospace, stationary power, and transportation applications is driving and challenging researchers to complement and in some cases altogether replace the batteries of portable systems in the hopes of increasing functional density, extending runtime, and decreasing size. Direct-methanol fuel cell (DMFC) batteries have now been built and conformed to low-cost technologies and chip-scale dimensions. Conventional FC models, however, fail to accurately capture the electrical nuances and runtime expectancies of these microscale devices, yet predicting that these electrical characteristics are even more critical when designing portable low-power electronics. A Cadence-compatible model of a DMFC battery is therefore developed to capture all pertinent dynamic and steady-state electrical performance parameters, including capacity and its dependence to current and temperature, open-circuit voltage, methanol-crossover current, polarization curve and its dependence to concentration, internal resistance, and time-dependent response under various loading conditions—the model can also be extended to other micro- and macroscale FC technologies. The simulation results of the proposed electrical model are validated and compared against the experimental performance of several DMFC prototypes, resulting in a runtime error of less than 10.8% and a voltage error under various current loads of less than 80 mV for up to 95% of its operational life. The root cause of the remaining errors and relevant temperature effects in the proposed model are also discussed.      

Fatigue limit of carbon and CrMo steels as a small fatigue crack threshold in high-pressure hydrogen gas

The fatigue limit properties of a carbon steel and a low-alloy CrMo steel were investigated via fully-reversed tension-compression tests, using smooth specimens in air and in 115-MPa hydrogen gas. With respect to the CrMo steel, specimens with sharp notches were also tested in order to investigate the threshold behavior of small cracks. The obtained SN data inferred that the fatigue limit was not negatively affected by hydrogen in either of the steels. Observation of fatigue cracks in the unbroken specimens revealed that non-propagating cracks can exist even in 115-MPa hydrogen gas, and that the crack growth threshold is not degraded by hydrogen. The experimental results provide justification for the fatigue limit design of components that are to be exposed to high-pressure hydrogen gas.     

Numerical analysis of H2 formation during partial oxidation of H2SH2O upon activation of oxidizer by an electric discharge

The numerical analysis of H₂ production during partial oxidation of H₂SH₂O in a plug-flow reactor at atmospheric pressure and a rather low temperature (T₀ = 500 K) was conducted, when the oxidizer (oxygen or air) was preliminarily activated by an electrical discharge with different values of reduced electric field and input energy. It was shown that a significant hydrogen yield in flow reactor can be obtained only after ignition of the mixture. The ignition delay length depends on the reduced electric field E/N and input energy E_s in the discharge and is minimal at E/N～8–10 Td for the discharge in oxygen and at E/N～4–10 and 120–150 Td in air discharge, when O₂(a¹Δ_g) mole fraction in the discharge products is maximal. If the H₂SH₂OO₂(air) mixture ignites inside the flow reactor, the mole fraction of hydrogen and its relative yield do not depend on E/N. The relative hydrogen yield increases monotonically with an addition of water to H₂S. It was found, that the approach based on the partial oxidation of the H₂SH₂O mixture upon activation of oxygen by an electric discharge can ensure very low energy cost for H₂ production. The minimum specific energy requirement, obtained for the H₂SO₂ mixture, was found to be 0.83 eV/(molecule H₂) and 0.18 eV/(molecule H₂S) at atmospheric pressure and can be further decreased if the energy released during partial oxidation of H₂S is spent on heating the reagents. The use of air as an oxidizer requires higher energy costs and seems to be less promising.     

Extraordinary room-temperature hydrogen sensing capabilities with high humidity tolerance of PtSnO2 composite nanoceramics prepared using SnO2 agglomerate powder

Two kinds of PtSnO₂ composite nanoceramics have been prepared using SnO₂ nanoparticles and SnO₂ agglomerate powder separately. One is of a relatively uniform and porous microstructure with a specific surface area of 8.1 m²/g, and the other is of a rather non-uniform microstructure with large SnO₂ agglomerates and crack-like pores and a specific surface area of 6.4 m²/g. While the samples of uniform microstructure typically show a sensitivity of 150 to 1% H₂ – 20% O₂ – N₂ in air of 50% relative humidity (RH) at room temperature, those of non-uniform microstructure surprisingly show much higher sensitivities of 850 and 450 in air of 50% and 70% RH, respectively, to the same concentration of hydrogen. The influence of humidity on the samples has been further studied and a much higher humidity tolerance has been revealed for those samples of non-uniform microstructure. All these results demonstrate a clear and unexpected advantage of a non-uniform microstructure over a uniform one in humidity tolerance for room-temperature hydrogen-sensitive PtSnO₂ composite nanoceramics.     

Interface stability between bare,MnCo spinel coated AISI 441 stainless steel and a diopside-based glass-ceramic sealant

This study is focused on a diopside-based glass-ceramic sealant for solid oxide fuel cells and its compatibility with AISI 441 stainless steel interconnect. The morphological and chemical stability with both bare and MnCo spinel coated AISI 441 steel, after 3500 h exposure at 800 °C in air, is reviewed and discussed. Post-mortem samples are morphologically and chemically analysed by SEM-EDS. Reaction products at the glass-ceramic/bare AISI 441 interface, resulting from the reaction of Mg from the sealant and Cr and Mn from the steel, are detected, without affecting negatively the integrity of the joints. In the case of MnCo spinel coated AISI 441, interactions between the glass-ceramic and the outer part of the MnCo spinel coating, along with crystallization of oxides rich in Si and Mg, are detected, but still no corrosion phenomena are present. The glass-ceramic is found to be compatible with both bare and coated AISI 441.     

Effective excitons separation on graphene supported ZrO2TiO2 heterojunction for enhanced H2 production under solar light

A novel photocatalyst comprises of ZrO₂TiO₂ immobilized on reduced graphene oxide (rGO) – a ternary heterojunction (ZrO₂TiO₂/rGO) was synthesized by using facile chemical method. The nanocomposite was prepared with a strategy to achieve better utilization of excitons for catalytic reactions by channelizing from metal oxide surfaces to rGO support. TEM and XRD analysis results revealed the heterojunction formed between ZrO₂ and single crystalline anatase TiO₂. The mesoporous structure of ZrO₂TiO₂ was confirmed using BET analysis. The red shift in absorption edge position of ZrO₂TiO₂/rGO photocatalyst was characterized by using diffuse reflectance UV–Visible spectra. ZrO₂TiO₂/rGO showed greater interfacial charge transfer efficiency than ZrO₂TiO₂, which was evidenced by well suppressed PL intensity and high photocurrent of ZrO₂TiO₂/rGO. The suitable band gap of 1.0 wt% ZrO₂TiO₂/rGO facilitated the utilization of solar light in a wide range by responding to the light of energy equal to as well as greater than 2.95 eV by the additional formation of excited high-energy electrons (HEEs). ZrO₂TiO₂/rGO showed the enhanced H₂ production than TiO₂/rGO, which revealed the role of ZrO₂ for the effective charge separation at the heterojunction and the solar light response. The optimum loading of 1.0 wt% of ZrO₂ and rGO on TiO₂ showed the highest photocatalytic performance (7773 μmolh^?1$g_{cat}^{?1}$) for hydrogen (H₂) production under direct solar light irradiation.