Multi-line Transmission Research Articles

Spatial Coherence of Backscattered Signals in Multi-Line Transmit Ultrasound Imaging and Its Effect on Short-Lag Filtered-Delay Multiply and Sum Beamforming

In Multi-Line Transmission (MLT), high frame-rate ultrasound imaging is achieved by the simultaneous transmission of multiple focused beams along different directions, which unfortunately generates unwanted artifacts in the image due to inter-beam crosstalk. The Filtered-Delay Multiply and Sum (F-DMAS) beamformer, a non-linear spatial-coherence (SC)-based algorithm, was demonstrated to successfully reduce such artifacts, improving the spatial resolution at the same time. In this paper, we aim to provide further insights on the working principle and performance of F-DMAS beamforming in MLT imaging. First, we carry out an analytical study to analyze the behavior and trend of backscattered signals SC in MLT images, when the number of simultaneously transmitted beams and/or their angular spacing change. We then reconsider the F-DMAS algorithm proposing the “short-lag F-DMAS” formulation, in order to limit the maximum lag of signals used for the SC computation on which the beamformer is based. Therefore, we investigate in simulations how the performance of short-lag F-DMAS varies along with the maximum lag in the different MLT configurations considered. Finally, we establish a relation between the obtained results and the signals SC trend.

Programmable FPGA-based 32-channel transmitter for high frame rate ultrasound channel excitation applications

This paper describes the design and results of a field programmable gate array (FPGA) designed for ultrasound transient elastography transmitter. The high frame rate is achieved by multi-line transmission. The design is capable of achieving frame rates up to 8,000 frames per second by excitation of all the channels simultaneously. The FPGA also generates the drive signals for the commonly available CMOS transmit pulsers for high voltage excitation of the ultrasound transducer. The FPGA is configured from a microcontroller using a parallel interface. The FPGA also generates the synchronisation pulses for the receiver. The FPGA has a flexible design where parameters like ultrasound frequency, number of pulses per burst, pulse repetition frequency, and so on are programmed from the microcontroller. One FPGA caters for 32 channels and has a maximum frequency of operation of 8 MHz. The novelty of this study is in the design and implementation of an open FPGA architecture for 32 channel high frame rate ultrasound application.

High Frame-Rate, High Resolution Ultrasound Imaging With Multi-Line Transmission and Filtered-Delay Multiply And Sum Beamforming.

Multi-Line Transmission (MLT) was recently demonstrated as a valuable tool to increase the frame rate of ultrasound images. In this approach, the multiple beams that are simultaneously transmitted may determine cross-talk artifacts that are typically reduced, although not eliminated, by the use of Tukey apodization on both transmission and reception apertures, which unfortunately worsens the image lateral resolution. In this paper we investigate the combination, and related performance, of Filtered-Delay Multiply And Sum (F-DMAS) beamforming with MLT for high frame-rate ultrasound imaging. F-DMAS is a non-linear beamformer based on the computation of the receive aperture spatial autocorrelation, which was recently proposed for use in ultrasound B-mode imaging by some of the authors. The main advantages of such beamformer are the improved contrast resolution, obtained by lowering the beam side lobes and narrowing the main lobe, and the increased noise rejection. This study shows that in MLT images, compared to standard Delay And Sum (DAS) beamforming including Tukey apodization, F-DMAS beamforming yields better suppression of cross-talk and improved lateral resolution. The method's effectiveness is demonstrated by simulations and phantom experiments. Preliminary in vivo cardiac images also show that the frame rate can be improved up to 8-fold by combining F-DMAS and MLT without affecting the image quality.

Location Optimization of IPFC for Congestion Management using Cuckoo Search Algorithm

This paper presents a new methodology based on cuckoo search algorithm (CSA) for enhancing the performance of interline power flow controller (IPFC) under multiline transmission. In this approach we perform priority process through the contingency analysis for finding the severity of the line outage. For determining the severity, bus voltage limit violation, overloading of lines and power loss are taken into account. We are applying CSA to determine the optimal location and transmission congestion management of IPFC. An adaptive proportional integral derivative with filter (PIDF) controller is developed to control the deviation and power flow. The simulation is performed using MATLAB for two case studies using an IEEE 118-bus and IEEE 300-bus test system. Simulation results indicate that the location and parameters optimized by using CSA, minimizing the bus voltage abuse, congestion management, and overloaded lines. This method is designed in such a way that it improves the security of the power system. For further improvement of the system, the IPFC is placed in tie-line. The performance of PIDF controller has been studied under different conditions and the simulation result shows that PIDF performs better than PID controller. The performance of CSA is compared with other two optimization techniques such as particle swarm optimization (PSO) and genetic algorithm (GA) under both the IEEE 118-bus and IEEE 300-bus test systems. The result shows that the proposed CSA outperforms the other two models and it best suits the power system security.

Multi-line transmission combined with minimum variance beamforming in medical ultrasound imaging.

Increasing medical ultrasound imaging frame rate is important in several applications such as cardiac diagnostic imaging, where it is desirable to be able to examine the temporal behavior of fast phases in the cardiac cycle. This is particularly true in 3-D imaging, where current frame rate is still much slower than standard 2-D, B-mode imaging. Recently, a method that increases frame rate, labeled multi-line transmission (MLT), was reintroduced and analyzed. In MLT scanning, the transmission is simultaneously focused at several directions. This scan mode introduces artifacts that stem from the overlaps of the receive main lobe with the transmit side lobes of additional transmit directions besides the one of interest. Similar overlaps occur between the transmit main lobe with receive side lobes. These artifacts are known in the signal processing community as cross-talk. Previous studies have concentrated on proper transmit and receive apodization, as well as transmit directions arrangement in the transmit event, to reduce the cross-talk artifacts. This study examines the possibility of using adaptive beamforming, specifically, minimum variance (MV) and linearly constrained minimum variance (LCMV) beamforming, to reduce the cross-talk artifacts, and maintain or even improve image quality characteristics. Simulation results, as well as experimental phantom and in vivo cardiac data, demonstrate the feasibility of reducing cross-talk artifacts with MV beamforming. The MV and LCMV results achieve superior spatial resolution, not only over other MLT methods with data-independent apodization, but even over that of single-line transmission (SLT) without receive apodization. The MV beamformer is shown to be less sensitive to wider transmit profiles required to reduce the transmit crosstalk artifacts. MV beamforming, combined with the wider transmit profiles, can provide a good approach for MLT scanning with reduced cross-talk artifacts, without compromising spatial resolution, and even improving it. We also demonstrate that the MV and LCMV beamformers lead to almost identical results. This is because of their very similar beampatterns, except for the sharp nullifying properties that the LCMV beamformer has around interfering beams.

FUZZY LOGIC AND PSO BASED HYBRID TECHNIQUE FORMULATION FOR OPTIMAL PLACEMENT AND SIZING OF INTERLINE POWER FLOW CONTROLLER

Maximum utilization of the available transmission lines is advisable than introducing a new transmission line to the existing power system because of various reasons such as regulatory, environmental, and public policies, as well as escalating costs. This can be achieved by using FACTS controllers which are one of the power electronics based static equipment to control one or more AC transmission system parameters for enhancing controllability and increase power transfer capability. Placing and Sizing of the FACTS controllers in transmission line is a challenging task. To perform this task, we propose a new hybrid technique based on fuzzy logic (FL) and Particle swarm optimization (PSO). Here, we have considered Interline Power Flow Controller (IPFC) as we are discussing multiline transmission systems. The purpose of fuzzy system is to determine the capacity of IPFC in terms of voltage deviation. The optimal location of IPFC is done by PSO. The proposed technique maintains the voltage stability and minimizes the transmission loss of the power system. For analyzing the nonlinear power flow of the transmission system, Newton-Raphson method is utilized. The proposed multi objective approach is implemented in MATLAB and the performance of the proposed fuzzy-PSO is compared with fuzzy-GA.

Wideband transmission line model for Archimedean spiral slot structures

Spiral slot structures appear in a variety of microwave applications such as circuit elements, transmission lines and broadband antennas. However, design methodologies for these structures that are accurate above the first resonance involve multi-line transmission line models – requiring difficult to compute multi-line characteristics. This study presents the methodology for a transmission line model for an Archimedean spiral slot structure that uses singly-coupled line characteristics, which can be found analytically, to approximate the multi-line transmission line. With this model, the first resonance and many higher-order resonant frequencies of the spiral structure are well predicted, enabling multi-frequency use of the spiral slot. The results of the model compare well with full-wave simulations and are validated with measurements.

Investigation of Modified Generalized Interline Power Flow Controller (GIPFC) and Performance Analysis

Nowadays in the restructured scenario, the main challenging objective of the modern power system is to avoid blackouts and provide uninterrupted quality power supply with dynamic response during emergency to improve power system security and stability. In this sense the convertible static compensator (CSC) that is the Generalized Inter line power flow controller (GIPFC), can control and optimize power flow in multi-line transmission system instead of controlling single line like its forerunner FACTS (Flexible AC Transmission System) controller. By adding a STATCOM (Static synchronous Shunt Converter) at the front end of the test power system and connecting to the common DC link of the IPFC, it is possible to bring the power factor to higher level and harmonics to the lower level and this arrangement is popularly known as Generalized Inter line power flow controller (GIPFC). In this paper a new concept of GIPFC based on incorporating a voltage source converter with zero sequence injection SPWM technique is presented for reinforcement of system stability margin. A detailed circuit model of modified GIPFC is developed and its performance is validated for a standard test system. Simulation is done using MATLAB Simulink.Index Terms—Convertible static controller, Flexible AC Transmission System (FACTS), Generalized Interline Power Flow Controller (GIPFC),STATCOM, SSSC, Reactive power compensation.

Voltage Compensation with Interline Power Flow Controller (IPFC) Using Control Magnitude and Phase Angle Control

The Interline Power Flow Controller (IPFC) is a voltage-source-converter (VSC)-based flexible ac transmission system (FACTS) controller for series compensation in a multiline transmission system of a substation. The capability of injecting series voltages with controllable magnitude and phase angle makes it a powerful tool for better utilization of existing transmission lines in a multiline transmission system. IPFC is used to regulate active and reactive power flow in a multiline system, usually. In this paper, a control method for IPFC is proposed to control magnitude and phase angle of one sending bus of a substation. All degrees of freedom of IPFC and decoupled synchronous frame concept are used in the proposed control structure. Simulation results in Matlab/Simulink are presented to show the capability of IPFC in compensating the bus voltage.

Correspondence - Multi-line transmission in medical imaging using the second-harmonic signal

The emergence of three-dimensional imaging in the field of medical ultrasound imaging has greatly increased the number of transmissions needed to insonify a whole volume. With a large number of transmissions comes a low image frame rate. When using classical transmission techniques, as in two-dimensional imaging, the frame rate becomes unacceptably low, prompting the use of alternative transmission patterns that require less time. One alternative is to use a multi-line transmission (MLT) technique which consists of transmitting several pulses simultaneously in different directions. Perturbations appear when acquiring and beamforming the signal in the direction of one pulse because of the pulses sent in other directions. The edge waves from the pulses transmitted in a different direction add to the signal transmitted in the direction of interest, resulting in artifacts in the final image. Taking advantage of the nonlinear propagation of sound in tissue, the second-harmonic signal can be used with the MLT technique. The image obtained using the second-harmonic signal, compared with an image obtained using the fundamental signal, should have reduced artifacts coming from other pulses transmitted simultaneously. Simulations, backed up by experiments imaging a wire target and an in vivo left ventricle, confirm that the hypothesis is valid. In the studied case, the perturbations appear as an increase in the signal level around the main echo of a point scatterer. When using the fundamental signal, the measured amplitude level of the perturbations was approximately -40 dB compared with the maximum signal amplitude (-27 dB in vivo), whereas it was around -60 dB (-45 dB in vivo) for the second-harmonic signal. The MLT technique encounters limitations in the very near field where the pulses overlap and the perturbation level also increases for images with strong speckle and low contrast.

Modified Approach for Harmonic Reduction in Transmission System Using 48-pulse UPFC Employing Series Zig-Zag Primary and Y-Y Secondary Transformer

In this paper THD (Total Harmonic Distortion) is analysed and compared by using UPFC in a multi-line transmission system of 500 KV having 5- buses in two different arrangements. The UPFC converters are arranged as a Diode Clamped multilevel Converter (DCMLC) that leads to the cost reduction as compared with other multi-level converters. The comparison has been done by both series zig-zag/2Y- 2Δ and series zig-zag/4Y transformer configuration for 48-pulses GTO based diode clamped converter. The THD is reduced to 42.59% and 58.82% of input waveform at bus B2 by using series zig-zag/4Y transformer configuration. This transformer converter configuration also reduces the difficulty of designing the transformer winding ratio. For calculation of THD, FFT analysis is carried out using MATLAB.

Multi-line transmission in 3-D with reduced crosstalk artifacts: a proof of concept study.

Multi-line transmission (MLT) is a technique in which ultrasound pulses for several directions are transmitted simultaneously. The purpose is increased frame rate, which is especially important in 3-D echocardiography. Compared with techniques purely based on parallel beamformation, MLT avoids the need for reducing the transmit aperture and thus maintains a high harmonic signal level. The main disadvantage is that artifacts are caused by cross-talk between the simultaneous beams. In a conventional MLT implementation, simultaneous transmits would be spaced regularly in the azimuth and elevation planes. However, using rectangular geometry arrays, most of the acoustic side-lobe energy is concentrated along these planes. The results in this work show that the crosstalks can be pushed below the typical display range of 50 dB used in cardiac applications if the parallel transmit directions are aligned along the transverse diagonal of the array. Dispositions with 2 to 5 MLT for a typical cardiac 2-D phased-array were investigated using simulation software. Using the proposed alignment, the maximal crosstalk artifact amplitudes decreased 20 to 30 dB compared with conventional MLT dispositions. In water-tank measurements, side-lobe levels of a commercially available rectangular probe were 15 to 25 dB lower along the transverse diagonal, confirming that similar suppressions can be expected using actual transducers.

Application of refined bacterial foraging algorithm technique to control of optimal power dispatch with interline power flow controller

This paper presents a novel refined bacterial foraging algorithm (RBFA) to solve a multi-objective optimal power dispatch (MOOPD) problem incorporating multiline flexible AC transmission system (FACTS) devices in modern power systems and to seek optimal parameters of the same. This paper also deals with the concept of the interline power flow controller (IPFC) for providing better power flow management in a multiline transmission system. The optimal control parameters thus obtained are used to enhance the stability of the system and minimize transmission losses. The stability of modern power systems is improved by installing fast reacting devices such as IPFC together with the optimal parameters of IPFC. The optimal location of IPFC and solving optimal power dispatch (OPD) problems are required to employ the introduction of multi-objective based optimization techniques. This paper proposes a new algorithm based on the bacterial foraging algorithm (BFA) with a proposed multi-objective optimization technique. The proposed approach is tested with standard IEEE 30 bus system and comprehensive simulation results show better in constraint handling, finding optimal control parameters of IPFC, handling of voltage profile, minimize the transmission losses and quality of solution.

Digital Simulation of the Generalized Unified Power Flow Controller System with 60-Pulse GTO-Based Voltage Source Converter

The Generalized Unified Power Flow Controller (GUPFC) is a Voltage Source Converter (VSC) based Flexible AC Transmission System (FACTS) controller for shunt and series compensation among the multiline transmission systems of a substation. The paper proposes a full model comprising of 60-pulse Gate Turn-Off thyristor VSC that is constructed becomes the GUPFC in digital simulation system and investigates the dynamic operation of control scheme for shunt and two series VSC for active and reactive power compensation and voltage stabilization of the electric grid network. The complete digital simulation of the shunt VSC operating as a Static Synchronous Compensator (STATCOM) controlling voltage at bus and two series VSC operating as a Static Synchronous Series Capacitor (SSSC) controlling injected voltage, while keeping injected voltage in quadrature with current within the power system is performed in the MATLAB/Simulink environment using the Power System Block set (PSB). The GUPFC, control system scheme and the electric grid network are modelled by specific electric blocks from the power system block set. The controllers for the shunt VSC and two series VSCs are pre- sented in this paper based on the decoupled current control strategy. The performance of GUPFC scheme connected to the 500-kV grid is evaluated. The proposed GUPFC controller scheme is fully validated by digital simulation.

SIMULATION AND DESIGN OF IPFC SYSTEM FOR VOLTAGE SAG COMPENSATION

Inter line power flow controller is a new concept for the compensation and effective power flow management of multi-line transmission systems. The IPFC employs a number of Voltage Sourced Converters (VSCs) linked at the same DC terminal, each of which can provide series compensation for the selected line of the transmission system. Through common dc link, any inverters within the IPFC is able to transfer real power to any other and thereby facilitate real power transfer among the line. In this work the IPFC system used for compensation of voltage sag in two identical lines like 11kv and 10kv systems. The prototype IPFC system was developed and verified with hardware results. When the voltage sag is compensated, reactive power is controlled and transmission line efficiency is improved.

Analysis of SSR With Three-Level Twelve-Pulse VSC-Based Interline Power-Flow Controller

The interline power-flow controller (IPFC) is a voltage-source-converter (VSC)-based flexible ac transmission system (FACTS) controller for series compensation with the unique capability of power-flow management among the multiline transmission systems of a substation. The reactive voltage injected by individual VSCs can be maintained constant or controlled to regulate active power flow in the respective line. While one VSC regulates the dc voltage, the others control the reactive power flows in the lines by injecting series active voltage. This paper presents the modelling of IPFC with 12-pulse, three-level converters and investigates the subsynchronous-resonance (SSR) characteristics of IPFC for different operating modes. The analysis of SSR is carried out based on eigenvalue analysis and transient simulation of the detailed system. It is illustrated with the help of a case study on a system adapted from the IEEE Second Benchmark Model. The analysis uses both D-Q model (neglecting harmonics in the output voltages of VSCs) and the three-phase model of VSCs using switching functions. While the eigenvalue analysis and controller design is based on the D-Q model, the transient simulation considers both models.

Voltage Sag Mitigation in Multi-line Transmission System Using Generalized Unified Power Flow Controller

Voltage Sag Mitigation in Multi-line Transmission System Using Generalized Unified Power Flow Controller

The interline power flow controller concept: a new approach to power flow management in transmission systems

The interline power flow controller (IPFC) proposed is a new concept for the compensation and effective power flow management of multi-line transmission systems. In its general form, the IPFC employs a number of inverters with a common DC link, each to provide series compensation for a selected line of the transmission system. Because of the common DC link, any inverter within the IPFC is able to transfer real power to any other and thereby facilitate real power transfer among the lines of the transmission system. Since each inverter is also able to provide reactive compensation, the IPFC is able to carry out an overall real and reactive power compensation of the total transmission system. This capability makes it possible to equalize both real and reactive power flow between the lines, transfer power from overloaded to underloaded lines, compensate against reactive voltage drops and the corresponding reactive line power, and to increase the effectiveness of the compensating system against dynamic disturbances. The paper explains the basic theory and operating characteristics of the IPFC with phasor diagrams, P-Q plots and simulated waveforms.

Transmission imaging of large attenuators using a slant hole collimator on a three‐headed SPECT system

By combining conjugate views, truncation-free attenuation profiles of patients can be obtained by using slant hole collimators on three-headed SPECT systems. The alterations in reconstruction algorithms necessary for use with slant hole collimators and potential image artifacts are discussed. Based on an evaluation of the size of objects that can be imaged without truncation and the size of the overlap region in the conjugate views, a 15 degrees slant angle was determined to be optimal. Studies with a 30 degrees slant hole collimator verified the ability of slant hole transmission imaging to provide accurate, truncation-free attenuation maps of a 56 cm lateral width phantom. The center of rotation was determined to be dependent on the slant angle and radius of rotation of the slant collimator. These studies also demonstrated that the spatial resolution in the transaxial plane of the attenuation maps depends on radius of rotation of the slant hole collimator, but does not depend on the radius of rotation of an uncollimated transmission source. A multiline transmission source was investigated for use with estimating the attenuation map in Tc-99m labeled sestamibi perfusion imaging.

Numerical analysis of transmission lines with branches and junctions

AbstractSome of the analyses which are important in practice are: the analysis of induction noise between lines on the printed board; and the analysis of extraordinary phenomena in the multiline transmission system. These problems can be reduced to the transient analysis of the transmission‐line network composed of a number of transmission‐lines with different phases, their branches and junctions, as well as a number of lumped‐constant elements. By the analysis in the s‐domain through Laplace transform, the general solution for the basic equation for the transmission‐line is obtained containing arbitrary constants, and the arbitrary constants can be determined from the system of linear equations derived from the boundary conditions. This paper presents a method of deriving this system of linear equations for the case with only lumped sources and for the case with distributed sources. By determining the arbitrary constants, the solution is obtained in the operator domain, and the time‐solution is obtained by the inverse transform. The solution in the time‐domain is obtained by the numerical inverse Laplace transform, and the computation is performed by substituting a sequence of complex values into s. The effectiveness of the proposed method is verified by applying the method to several examples.