Design and analysis of dynamic voltage restorer for deep voltage sag and harmonic compensation

A dynamic voltage restorer (DVR) to compensate deep voltage sags and harmonics is proposed. The DVR consists of shunt and series converters connected back-to-back through a DC-to-DC step up converter. The presence of the DC-to-DC step converter permits the DVR to compensate deep voltage sags for long duration. The series converter is connected to the supply side whereas the shunt converter is connected to the load side. With this configuration, there is no need for large DC capacitors. A design procedure for the components of the DVR is presented under a voltage sag condition. The control system of the proposed DVR is based on hysteresis voltage control. Besides voltage sag compensation, the capability of compensating load voltage harmonics has been added to the DVR to increase the power quality benefits to the load with almost negligible effect on the sag compensation capability. The proposed DVR is modelled and simulated using SIMULINK/MATLAB environment. Time domain simulations are used to verify the operation of the DVR with linear and non-linear loads.     

Control strategy for dynamic voltage restorers to achieve minimum power injection without introducing sudden phase shift

A power injection control strategy is proposed for dynamic voltage restorers (DVR) under voltage sag or swell conditions. Under such a strategy, the error between the voltage of the energy storage capacitor in the DVR and a given reference voltage is extracted to control the injected power such that during an upstream voltage disturbance, zero or minimum power injection can be achieved automatically, while sudden phase jump of the load-side voltage can also be avoided. The proposed control strategy is analysed in detail and numerical examples are provided to demonstrate the effectiveness of the scheme.     

Design and control of single-phase dynamic voltage restorer

Dynamic voltage restorer (DVR) is a custom power device used in electrical distribution system for power quality improvement. It ensures regulated voltage supply to the sensitive loads, even in case of voltage sag and swell disturbances in the distribution network. It is a series connected device and compensates voltage sag and swell by injecting a voltage with the help of a series transformer. The injection of an appropriate voltage component in the event of a voltage disturbance requires a certain amount of real and reactive power. Conventionally, DVR consists of an energy storage device, which supplies the required power over the limited duration of the sags. Large magnitude and long duration of sags lead to heavy financial investment in energy storage unit. To overcome this limitation, a single-phase back-to-back converter-based DVR is implemented in this work, which eliminates energy storage requirement. The integration of series and shunt converter makes the DVR capable of bidirectional flow of energy. Therefore, the key advantage of this topology is its capability to compensate for long-term voltage sag and swell. Modelling of the DVR and its controller design is included in this paper. The effectiveness of control schemes, protection schemes and starting sequence of operation of DVR is verified through detailed simulation studies. A scaled down laboratory prototype of DVR is developed. The viability of these schemes is confirmed by the experimental results generated from the laboratory prototype. Various challenges faced during the prototype development and corresponding solutions are also discussed in this paper.     

敏感用户高品质交-直流级联供电方案研究

工业过程中大量使用的变频器(variable frequency drive,VFD)在采用传统交流供电时易受到电压暂降影响,传统治理方式存在检测延时、控制复杂等问题。为此,该文从敏感负荷变频器在电网扰动工况下的供电需求量化出发,围绕供电拓扑设计、DC/DC变换器的控制策略及储能单元容量配置等方面,构建一种实用化工业用交-直流级联供电方案。该文利用电压暂降过程中直流供电回路与敏感负荷间的压差自感应控制,实现交-直流供电回路无扰动切换,提高电压暂降治理响应的快速性;采用两相交错并联DC/DC变换器接入集中式储能,减少储能系统纹波系数,并给出两相均流控制方法。最后,通过Matlab/Simulink中的建模仿真与样机的实验测试,验证所提方案能够在交流系统发生不同严重程度电压暂降过程中为各类敏感负荷提供稳定的连续供电,为解决工业敏感用户高品质供电问题提供可实用的新思路。     

Considerations in the Validation and Application of Models for Eddy Current Inspection of Cracks Around Fastener Holes

To improve the detection and characterization of cracks around fastener holes in multilayer structures without removing the fastener, model-based approaches are proposed to support the design of advanced eddy current (EC) NDE systems. This work demonstrates the validation and application of models to simulate EC inspection as part of the design process. The volume integral method (VIM) and finite element method (FEM) are both used to simulate eddy current inspection of fastener sites for fatigue cracks. Convergence studies, validation with existing models, experimental validation studies and validation through inverse method demonstrations are presented, providing a continuum of methods to ensure the quality of measurement models. Consideration concerning convergence and validation is also given with features sensitive to the sample geometry and flaw characteristics. A novel calibration technique is also presented to practically evaluate the transformation between model-based impedance calculations and experimental voltage data. A series of studies are presented concerning the detection of cracks around fastener holes demonstrating the quality of the simulated data to represent experimental measurements.     

A simplified time-domain design and implementation of cascaded PI-sliding mode controller for dc–dc converters used in off-grid photovoltaic applications with field test results

A time-domain design methodology for voltage regulation control of dc–dc boost and buck-boost converters based on a multi-loop controller with PI regulator for the outer loop and an inner loop with sliding mode current controller has been developed for renewable energy applications such as photovoltaic (PV)-fed dc–dc converters. This paper proposes a new method for the design of PI regulators in such multi-loop control scheme. The proposed design presents a simple analytical method for selecting controller gains and has been validated by simulation as well as hardware implementation. Also, this paper presents an illustrative example based on the proposed design for the voltage regulation control of PV-fed boost converters for off-grid applications. The simulation results for varying irradiation, temperature and load along with stability analysis have been presented in this paper. The proposed controller is implemented in hardware for a 1.1 kW PV-array-fed boost converter. Performance analysis based on field test results using real-time weather data validates the proposed design. Therefore the proposed controller could be considered as an attractive solution for off-grid renewable energy applications like PV- or fuel-cell-fed dc–dc converter, where the variations are stochastic in nature.     

动态电压恢复器检测分析

动态电压恢复器DVR(Dynarnic Voltage Restorer)串联于电网络，用来保护敏感负荷免受电压波动尤其是电压凹陷的影响。该文讨论了动态电压恢复器实时补偿的检测原理及其特点，并结合负荷特性进行了综合比较。     

Smart demand for improving short-term voltage control on distribution networks

Smart grids must involve active roles from end users in order to be truly smart. The energy consumption has to be done in a flexible and intelligent manner, in accordance with the current conditions of the power system. Moreover, with the advent of dispersed and renewable generation, increasing customer integration to aid power system performance is almost inevitable. This study introduces a new type of smart demand side technology, denoted demand as voltage controlled reserve (DVR), to improve short-term voltage control, where customers are expected to play a more dynamic role to improve voltage control. The technology can be provided by thermostatically controlled loads as well as other types of load. This technology is proven to be effective in case of distribution systems with a large composition of induction motors, where the voltage presents a slow recovery characteristic due to deceleration of the motors during faults. This study presents detailed models, discussion and simulation tests to demonstrate the technical viability and effectiveness of the DVR technology for short-term voltage control.     

Study on the new control scheme of class-E inverter for IH-jar application with clamped voltage characteristics using pulse frequency modulation

A new control scheme of Class-E inverter for induction heating jar applications with clamped voltage characteristics using pulse frequency modulation (PFM) is introduced. To reduce the voltage stress of a switch, the proposed PFM control scheme does not need any auxiliary circuit. It can decrease the voltage stress of a switch through the modulation of switching frequency. The Class-E inverter using the proposed control scheme has the advantages of not only the same output power when it is compared with an active clamped class-E (ACCE) inverter, but also zero-voltage-switching, which are characteristics of conventional Class-E and ACCE inverter. The control principles of the proposed method are explained in detail and its validity is verified through experimental results     

DC reactor type transformer inrush current limiter

A new inrush current limiter (ICL) is presented to limit the inrush current of transformers. The proposed ICL consists of three similar sets. Each set includes a diode-bridge and a single DC reactor and is connected in series with the individual phases of transformer. The ICL has almost no effect on normal operation of transformer. It needs no control, measurement and gate driving system and has a simple power circuit topology. The equivalent instantaneous inductance of transformer is used for analysis of circuit operation. The theoretical analysis, design features, power losses and voltage distortion because of using ICL are presented. The proposed method has been tested by simulation and laboratory experiments. Both results show that the proposed ICL successfully limits the inrush current.     

Radial basis functions and level set method for structural topology optimization

Level set methods have become an attractive design tool in shape and topology optimization for obtaining lighter and more efficient structures. In this paper, the popular radial basis functions (RBFs) in scattered data fitting and function approximation are incorporated into the conventional level set methods to construct a more efficient approach for structural topology optimization. RBF implicit modelling with multiquadric (MQ) splines is developed to define the implicit level set function with a high level of accuracy and smoothness. A RBF–level set optimization method is proposed to transform the Hamilton–Jacobi partial differential equation (PDE) into a system of ordinary differential equations (ODEs) over the entire design domain by using a collocation formulation of the method of lines. With the mathematical convenience, the original time dependent initial value problem is changed to an interpolation problem for the initial values of the generalized expansion coefficients. A physically meaningful and efficient extension velocity method is presented to avoid possible problems without reinitialization in the level set methods. The proposed method is implemented in the framework of minimum compliance design that has been extensively studied in topology optimization and its efficiency and accuracy over the conventional level set methods are highlighted. Numerical examples show the success of the present RBF–level set method in the accuracy, convergence speed and insensitivity to initial designs in topology optimization of two‐dimensional (2D) structures. It is suggested that the introduction of the radial basis functions to the level set methods can be promising in structural topology optimization. Copyright © 2005 John Wiley & Sons, Ltd.     

Peptide electroextraction for direct coupling of in-gel digests with capillary LC-MS/MS for protein identification and sequencing

An electrophoretic method has been developed for the extraction of peptides following in-gel digests of SDS-PAGE separated proteins. During electroextraction, the peptides are trapped on a strong cation-exchange microcartridge, before analysis by capillary LC--ESI-tandem mass spectrometry. The spectra obtained by tandem mass spectrometry are searched directly against a protein database for identification of the protein from which the peptide originated. By minimizing surface exposure of the peptides during electroextraction, a reduction of the detection limits for protein identification is realized. The performance of the peptide electroextraction was compared directly with the standard extraction method for in-gel protein digests, using a standard dilution series of phosphorylase B and carbonic anhydrase, separated by SDS-PAGE. The lowest gel loading in which phosphorylase B was identified using the standard extraction method was 2.5 ng or 25 fmol, and the lowest gel loading in which phosphorylase B was identified using electroextraction was 1.25 ng or 12.5 fmol. The design of the microextraction cartridge allows for direct interfacing with capillary LC, which is crucial for maintaining low detection limits. Furthermore, this method can be used for high-throughput proteomics since it can be easily multiplexed and requires only voltage control and low pressures (approximately 15 psi) for operation. We believe that peptide electroextraction is a significant advance for identification of proteins separated by one-dimensional or two-dimensional gel electrophoresis, as it can be easily automated and requires less protein than conventional methods.     

Simple measurement of the AC transport current loss for HTS conductors using an active power detection method

Reducing AC loss in a superconducting apparatus is one of the most important issues, and the precise measurement and estimation of AC losses are essential to reduce them. The four-terminal method is universally used as an electric measurement method of AC losses for superconducting tapes and wires. In this method, noise and inductive voltage superposed on the terminal voltage of the superconductor are eliminated by a lock-in amplifier and cancel coil, respectively, and then measurement of very small resistive voltage is achieved. However, using this conventional method, a plurality of measuring instruments and apparatuses are needed, and therefore the measuring system becomes complicated and much time is consumed in the calibration process. In this paper, we present a simple and precise measurement system based on an active power detection method, which is proposed as a quench detection method. The proposed system consists of a small number of instruments and apparatus and is less susceptible to noise. Its usefulness is verified by comparing the proposed method and the conventional four-terminal method in measuring the AC transport current loss of a Bi2223/Ag tape.     

Null Detector Circuit Design Scheme for Detecting Defective AC-Coupled Capacitors in Differential Signaling

This paper presents a novel method for detecting defective ac-coupling capacitors in high-speed differential signaling connections by designing a circuit with null detectors at the differential receiver. The design parameters of selecting the null ranges in the receiver buffer are proposed to efficiently detect the voltage droop that creates erroneous jitter. The null detectors in the proposed method enable the use of a lower test signal speed than the mission data rate at differential connections to detect defective capacitors. The proposed design method of null detectors combines four design and test factors, namely, regular null, voltage doubling, fail–safe, and defect sensitization, to determine the stretched null used for test purposes. The null-detection scheme has been implemented and verified in the design using a regular current-mode logic (CML) differential buffer in the 0.18- $muhbox{m}$ complementary metal–oxide–semiconductor (CMOS) process. The detection capability of the proposed method to check for traditional defects with the same null detector is also demonstrated through SPICE-based fault simulations. The proposed method is also verified with the board developed for parameter measurements. The parameters proposed in this paper showed excellent agreement among calculated, simulated, and measured values. In particular, measured parameters showed strong closeness up to 99% to its calculated values.      

Single-phase induction motor drive system using z-source inverter

Employing conventional three-phase inverter in variable speed single-phase drive suffers from limited maximum output voltage applied to motor or voltage utility factor (VUF). In this study, a z-source inverter (ZSI) has been used to drive a single-phase induction motor (SPIM). By the proposed topology, VUF and consequently torque speed characteristic of the single-phase motor is improved. The equations for employing ZSI in SPIM drive and modulation method are described. Results of two simulations using conventional inverter and ZSI are presented. The results show that using ZSI leads to an increase in motor electromagnetic torque compared to conventional three-phase inverter due to improved VUF. The experimental results confirm the theory and simulation.     

A simple and effective load-pull system for RF power transistorlarge-signal measurements for wireless communication power amplifierdesign

Conventional load-pull methods for RF power transistor large-signal measurements usually need complicated RF measurement instrumentation. A simple load-pull measurement setup and a test procedure with IEEE-488 GPIB control and data acquisition capability has been developed. This is used to facilitate the design of an RF power amplifier (PA) for wireless communication applications. Compared with the conventional load-pull method, it is simpler and less costly, yet effective. Measured examples of Siemens GaAs FET's CLY-2 and CLY-10, which are used to design a RF PA module for ISM-band (902-928 MHz) wireless communications, are presented     

压电水听器线阵与DFB光纤水听器线阵的分析

分布反馈式(Distributed Feedback,DFB)光纤激光水听器因其多方面优越的性能近些年发展迅速,国内已对由其组成的线阵进行了成功的湖试.为检验更大规模DFB光纤激光水听器线阵的实用性能及与传统压电水听器线阵的性能区别,在某湖进行了实验,获得了传统压电水听器线阵和8元DFB光纤水听器线阵的相关数据.分析了...     

Direct torque and flux control of an IPM synchronous motor drive using a backstepping approach

A novel direct torque and flux controlled interior permanent magnet synchronous motor (IPMSM) drive using an adaptive backstepping technique is presented. Closed-loop regulation of the speed, torque and stator flux linkage is achieved by a non-linear controller. Using Lyapunov analysis, the stability of the controller is guaranteed. The reference voltage vectors are generated by a space vector modulation (SVM) unit, which replaces the switching table in the conventional direct torque control (DTC) scheme. While retaining its main advantages, the proposed backstepping controller features reduced torque and flux ripples as compared to the classical DTC. On the one hand, a comparison with the proportional-integral (PI) direct torque and flux control (DTFC) scheme shows that the proposed approach is superior. Experimental results confirm the effectiveness of the proposed method.     

Critical Flow Method: A New Reliability Allocation Approach for a Thermonuclear System

In the present work, starting from well‐known methodologies, a new reliability allocation method [critical flow method (CFM)] has been proposed. We focused on the most important conventional methods and discussed their limitations in order to motivate the current research. The results show the main common problem of the most conventional reliability allocation methods: they are developed for complex systems with series configurations but not for series–parallel ones. The consequence is an increase of the required units' reliability (series configuration) in order to guarantee the reliability system target. Actually, the design and manufacturing of a subsystem with an extremely low failure rate would consume a considerable amount of economic resources. The proposed method can solve the shortcomings of the conventional methods with a new reliability approach useful to series–parallel configurations in order to obtain an important cost saving. The CFM has been applied to a liquid nitrogen cooling installation in a thermonuclear system, with many series–parallel configurations in order to guarantee the whole safety system. The proposed technique can be applied to working complex systems, and, in general, in the design phase of new installations. By comparing the CFM application results with real parameters, the new technique has been validated. The computational results clearly demonstrate the advantages of the proposed method. In particular, by applying the method to series–parallel configurations, it allocates failure rates higher than conventional methods, with a component cost reduction. Copyright © 2015 John Wiley & Sons, Ltd.     

A TWO-LEVEL DECOMPOSITION METHOD FOR DESIGN OPTIMIZATION

In this paper, a two-level decomposition method for design optimization is proposed which is an extension of the model coordination methods. The method couples the global monotonicity analysis of the first-level subproblem(s) with an optimization method (single-level method) or the second-level problem. Three classes of problems are considered where in the first-level they have: (1) one subproblem with one local variable, (2) several subproblems with one local variable, and (3) several subproblems with several local variables. Some test results have been presented which shows the improved performance of the proposed approach over a conventional single-level optimization method.