Impedance Of Transmission Line Research Articles

Synthesis of a Transfer Function With Real Poles From Tabulated Frequency Response Data for Transmission-Line Impedance Modeling

Synthesis of a Transfer Function With Real Poles From Tabulated Frequency Response Data for Transmission-Line Impedance Modeling

Broadband Permittivity and Permeability Extraction of 3-D-Printed Magneto-Dielectric Substrates

A broadband microwave magneto-dielectric spectroscopy technique is introduced and dedicated to the characterization of 3-D-printed magneto-dielectric substrates. Complex permittivity and permeability are extracted for the material-under-test fabricated in the same manner and with the same orientation of the electro-magnetic (EM) field as in the intended applications that include, for example, miniaturized and efficient antennas. The information is derived from the measured characteristic impedance and propagation constant of a test microstrip transmission line. To exclude the influence of the coaxial-to-microstrip transitions, printed launchers are proposed with puzzle-like interlock to test substrate which is used together with a printed thru-reflect-line (TRL) de-embedding set. The presented technique was experimentally validated on an example of specialized magnetic polylactic acid (PLA) filament printed substrate in the frequency range 0.1–6 GHz and a reference PLA substrate measured with two different techniques to yield comparable results.

Analytic Model and Optimization of Transmission-Line Impedance Transformers for Tens of MA-Class Pulsed Power Accelerator

The monolithic radial transmission line (MRTL) is a key component in tens of MA-class pulsed power accelerators, which connects the multiparallel modules of the prime pulsed power sources to the central vacuum insulator stack and magnetically insulated transmission line (stack-MITL system). The choice of electrical parameters of MRTL is essential for the entire accelerator design, which would bring great influences on the peak output current and the power couple efficiency. In Phys. Rev. Special Topics-Accel. Beam s, 2015, 18(10): 110401, some semianalytical formulae have been proposed to optimize the MRTL impedance that maximizes the peak current or peak power on the stack-MITL system. However, the formulae are only valid under several assumptions that are thought to be unpractical. In this article, an analytic model of the accelerator is developed to optimize the electrical parameters of MRTL. Analytical expressions of the output voltage and current at the terminal of MRTL are deduced. By simplifying the analytic model, mathematical expressions of the optimal MRTL output impedance that maximizes the peak current or peak power delivered from the prime power sources to the stack-MITL system are obtained. The factors that contribute to the optimal impedance are analyzed comprehensively with short-circuit load and Z-pinch load. Conclusions are beneficial to design the pulsed power accelerator in the future.

Computer‐aideddesign methodology for inductive compensated microwaveclass‐Epower amplifier

This article presents a simulation-based analysis to first evaluate the impact of excessive transistor output capacitance on class-E power amplifiers and to second show how inductive compensation can be used to recover optimum class-E operating conditions. As a starting point, the finite-feed inductor in a parallel-circuit topology is replaced by a frequency-dependent inductor, which in turn can be substituted by a network composed of a series inductor and additional subharmonic resonators. This complex lumped-element network is then replaced by a generalized transmission line equivalent topology, suitable for microwaves. Calculation of the transmission line impedances and electrical lengths of the proposed generalized network is shown in detail and a design procedure for this modified class-E is provided. The analysis presented here is further extended by using a simplified large-signal model for the employed GaN HEMT device, which allows evaluating the effects of non-ideal switching as well as of capacitance voltage-dependency and feedback capacitance. The analysis is validated by simulation and design of a test board. Measurements of the test board showed a drain efficiency of 80.3%, power-added efficiency of 76.3% and output power of 40.1 dBm at 1.96 GHz, demonstrating the validity of the proposed approach.

Partial stability criterion for a heterogeneous power grid with hub structures

One of the priority tasks in studying power grids is to find the conditions of their stable operation. The fundamental requirement is synchronizing all the elements (generators and consumers) of a power grid. However, various disturbances can destroy the synchronization. Moreover, desynchronization occurring in a small part of the grid can lead to severe large-scale power outages (or blackouts) due to numerous cascading failures. Here we consider the model of a heterogeneous power grid with hub structures (subgrids), taking into account arbitrary lengths and impedances of grid’s transmission lines and also their arbitrary amount. Using the auxiliary comparison systems approach, we analyze the dynamics of a hub subgrid. Based on the findings, we develop a novel criterion of partial stability of power grids featuring hub structures. The criterion makes it possible to identify the regions of safe operation of individual hub subgrid elements. First, the criterion allows obtaining parameters’ values that guarantee existence and local stability of either synchronous or quasi-synchronous modes in individual hub subgrid elements, i.e. steady-state stability. Second, the criterion allows obtaining the safe values of abrupt frequency and phase disturbances that eventually vanish, i.e. imply transient stability with respect to state disturbance. Third, the criterion permits determining the safe ranges of parameters’ disturbances that do not lead to catastrophic desynchronizing effects, i.e. imply transient stability with respect to parameters’ disturbance. Also, we discover typical dependences of the safe regions on the parameters of transmission lines. We demonstrate the applicability of the criterion on two test power grids with arbitrary distributions of powers as well as effective lengths and impedances of transmission lines. The results may help optimize stability and contribute to developing new real-time control schemes for smart grids that can automatically recover from failures.

A new protection scheme for transmission line of three-terminal hybrid HVDC system

Since the line-commutated converter-voltage source converter (LCC-VSC) hybrid technology combines the advantages of line-commutated converter-based high voltage direct current (LCC-HVDC) and voltage source converter-based high voltage direct current (VSC-HVDC), it has a very good prospect for engineering applications. But, the LCC-VSC HVDC system has characteristics such as LCC converter and VSC converter control strategies, fault response, and uneven boundary elements, which makes it difficult to directly apply the existing protection schemes. To solve the above problems, this paper proposes a single-ended protection scheme based on wave impedance. First, the amplitude-frequency characteristics of the wave impedance of the LCC-VSC three-terminal hybrid DC transmission line are analyzed. Subsequently, a protection scheme is proposed to identify internal faults and external faults by combining the wave impedance amplitude criterion with the current starting criterion. Finally, the model of the LCC-VSC three-terminal transmission system is used for simulation. The simulation results show that the proposed protection scheme has a strong anti-fault capability (800 Ω) and noise interference (20 dB).

S-Band Bifrequency MILO With Improved Performance

In this article, we present an improved design of a bifrequency magnetically insulated line oscillator (BFMILO). We begin with design expressions for the output section parameters considering transmission line impedance across the extractor. This helps in proper impedance matching so as to maximize the RF power exchange arising out of the intense beam-wave interaction. In order to reproduce more RF energy from the space charge limiting current at the load, a metal plate is inserted inside the collector cavity depth. Two tapered extractor vanes are imposed at the load side along with the stub, to enhance the RF power extraction and proper RF coupling. Simulation results show that the modified collector design generates an RF output power of ~3.8 GW at dual operating frequencies, namely, 3.05 and 3.32 GHz. The peak power conversion efficiency was estimated as 16.17% with an applied voltage of 500 kV and a beam current of 47 kA.

An Improved Algorithm for a High Speed Distance Relay Using Walsh Functions.(Dept.E)

An algorithm for calculating the apparent transmission line impedance to the point of fault is presented. This algorithm is based on a half-cycle Window using walsh function technique. The real and the imaginary components of the fundamental frequency voltage and current of the faulty phases are evaluated and used to calculate the impedance, as seen from the relay location. The sampling rate used to test this algorithm is 16 samples/cycle. The algorithm has been tested using digital computer simulation of the sample model. A comparison between this algorithm and four other algorithms, suitable for fault impedance measurement was carried on here with particular reference to their accuracy and speed of calculations.

Improvement of Power Quality in Distribution System using Photovoltaic based DPFC

In Modern Power System power quality is the main issue of the power companies. Improvement of power quality in distribution system using photovoltaic based DPFC is declared in this paper. Flexible AC Transmission System (FACTS) device which is known as distributed power flow controller (DPFC)is used. DPFC is derived from UPFC by eliminating common dc link between series and shunt converter. Unified power flow controller (UPFC) is widely used and control all parameters of the system. The UPFC handle the current and voltage with high rating; therefore, the cost of system is high. Therefore, distributed power flow controller (DPFC) is used due to high control capability, high Reliability & low cost. DPFC also measures the transmission angle, line impedance and bus voltage. In distribution system problems occur like voltage sag/swell, Harmonics etc. Photovoltaic system is used as source for DPFC.

Interpreting Ionic Conductivity for Polymer Electrolyte Fuel Cell Catalyst Layers with Electrochemical Impedance Spectroscopy and Transmission Line Modeling

A cathode catalyst layer containing optimally distributed ionomer is critical to reduce the platinum loading and increase its utilization in polymer electrolyte fuel cells. Here, electrochemical impedance spectroscopy (EIS) was used to measure effective ionic conductivity of pseudo catalyst layers (PCLs) at a relative humidity (RH) range of 50%–120%. These results are compared to previous work using the hydrogen pump (HP) method. EIS effective ionic conductivity results reported here are higher than those from the HP because in the HP set-up ionic pathways must be effectively connected through the PCL to be counted, whereas in the EIS measurement, ionomer segments that are in contact with the membrane but are not effectively connected all the way through the PCL can be detected. Double layer capacitances and effective ionic conductivities of Pt/C catalyst layers with various supports and ionomer to carbon (I/C) ratios were studied. High surface area carbon support resulted in a lower effective ionic conductivity compared to the graphitized carbon support due to worse ionomer dispersion. Effective ionic conductivities of Pt/C layers were compared to that of PCLs. On average, effective ionic conductivities of Pt/C layers were higher than PCLs because of possible carbon agglomeration within the PCLs.

Frequency Selective Impedance Transformer With High-Impedance Transforming Ratio and Extremely High/Low Termination Impedances

This article presents a novel frequency selective impedance transformer (ITs) with high transforming ratio and extremely low/high termination impedances ( 1 Ω or 2 Ω and several kΩ). The design equations are derived for both low and high termination impedances and effectively demonstrated. For transforming extremely low or high termination impedances, the characteristic impedances of open or short-circuited transmission line (TL) load can be very high or low, which cannot be fabricated with normal substrates because of the very narrow or broad width of TL. To solve the practical realization problem, the parallel-coupled lines can be adopted instated of TL. For the validation, two types of ITs are designed and measured at a center frequency ( f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ) of 3.5 GHz with impedance transforming ratios of r = 25 and r = 71.43 ( 2 Ω: 50 Ω and 35 Ω: 2500 Ω). The measurement results are consistent with simulation and theoretical predicated results. For achieving frequency selectivity, transmission zeros are generated very close to passband with stop-band suppression of higher than 40 dB.

Controller design for output constrained thyristor controlled series capacitor (TCSC) of time-delayed power system

Abstract Thyristor Controlled Series Capacitor (TCSC) is employed as actuator in an interconnected power system using Supplementary Damping Controller (SDC) to enhance the power transfer capabilities between areas as well as damp out the Inter-Area Low-Frequency (IALF) oscillations by varying the impedance of transmission lines. The time-varying delays in the feedback loop and asymmetric saturation limits at the output of TCSC may reduce the performance of the designed controller and lead to closed-loop instability if these are not considered in the process of controller design. Usually, a Minimum Absolute Saturation Bound technique (MASB) is used to convert asymmetric saturation limits into symmetric one. However, such consideration provides an apparent conservative and degrades the performance of the control system. To reduce the conservative in the control design process, a Normalized Saturation Bound (NSB) technique is used in this paper to convert asymmetric saturation limits of TCSC of time-delayed power system. The L-K functional and generalized sector conditions are utilized in the proposed controller design process to compensate the effect of time-varying delay and converted symmetric saturation limits. Sufficient conditions required for controller design are formulated in LMI form. 2-area 4-machine power model is used to verify the performance of the designed controller. From the simulation results, it is observed that the designed controller is giving superior performance in the present of time-varying delays and asymmetric saturation as compared to the designed controller using MASB technique.

Traveling Wave Propagation Characteristic-Based LCC-MMC Hybrid HVDC Transmission Line Fault Location Method

Aiming at the fault traveling wave on the LCC-MMC HVDC transmission line, this paper analyzed its reflection and refraction characteristics at the DC buses and the fault point, plotted its propagation grid diagrams, obtained the relationship between the polarity of fault traveling wave and the boundary elements, and drew the conclusion that when the impedance of DC filter is far less than the wave impedance of transmission line, the existing fault location methods that need to distinguish these two waves according to their polarities are not applicable to the LCC-MMC HVDC system. On these bases, this paper proposed a modal traveling wave arrival time difference-based location principle for pole-to-ground fault, and a fault traveling wave propagation path ratio-based location principle for pole-to-pole fault, these principles neither need to identify the wave polarity, nor need the wave velocity value. In order to better extract the wave heads and their arrival time, this paper pre-treated the sampling data to make sure all the wave heads are extracted from the same frequency band, then the wave heads and their arrival time can be extracted with the empirical mode decomposition. The simulation results verified the effectiveness of the proposed fault location principle.

Unequal Power Dividers Using Uniform Impedance Transmission Lines with Stubs

This study proposes an impedance control method in transmission lines using open- or short-circuit stubs for unequal power dividers. The proposed method is based on the conversion of a two-port to a three-port transmission line, which is equivalent to multiplying the impedance at the internal transmission line by a scaling factor and then connecting open- or short-circuit stubs in parallel to each port on the three-port transmission line. To verify the effectiveness of the proposed method, Wilkinson and Gysel power dividers with splitting ratios of 9:1 and 5:1, respectively, using uniform impedance transmission lines with open- or short-circuit stubs at an operating frequency of 2 GHz were designed. The experimental measurements of the two power dividers agree well with those of the simulation.

Broadband 90° differential phase shifter using improved H‐shaped network

AbstractIn this letter, a single‐layer broadband 90° phase shifter using H‐shaped network is proposed. To achieve broadband performance, we present an H‐shaped network by combining a section of stepped impedance transmission line with two pairs of λg/8 short‐ and open‐circuited stubs. Even‐odd mode analysis is carried out and the resulted equations is derived for the proposed device. The prototype is implemented on single‐layer printed circuit board for verification. The measured results agree well with the simulations, which demonstrates better than 15 dB return loss, less than 5° phase deviation and 0.76 dB insert loss across a fractional bandwidth of 101.7%.

Optimal Siting and Sizing of SSSC Using Modified Salp Swarm Algorithm Considering Optimal Reactive Power Dispatch Problem

The Flexible alternating current transmission systems (FACTS) is considered one of the most developed technologies applied for enhancing the performance of system due to their ability of adjusting different parameters in the transmission systems such as the buses voltage, the transmission line impedance, the active and reactive powers flow in transmission lines. The static synchronous series compensator (SSSC) is an effective member of the FACTS which is connected in series with the transmission lines and it consists of a solid-state voltage source inverter coupled with a transformer which aims to control and secure the operation of the power system. The main function of SSSC is inserting a controllable voltage in series with the transmission line to control the active and reactive powers flow in transmission lines. Solving the optimal reactive power dispatch (ORPD) problem is nonlinear, non-convex and it becomes a complex problem with integration of the SSSC. The contributions of article include, 1) an efficient and reliable optimization algorithm is developed to solve the ORPD problem and identify the optimal location and ratings of the SSSC, 2) The proposed algorithm is based on modifying the salp swarm algorithm (SSSA) using Levy Flight Distribution and spiral movement of particles to enhance the searching capabilities of the SSA, 3) an efficient model of SSSC based on power injection approach is used for representation the SSSC in ORPD. The ORPD is solved with and without the SSSC controller to minimize power losses and voltage deviations as well as improve the voltage stability. The proposed algorithm for ORPD is tested on the standards IEEE 30-bus and 57-bus systems. The simulation results demonstrate that MSSA is more effective and superior for solving the ORPD compared with some other reported meta-heuristic techniques. Moreover, the system performance is enhanced considerably with optimal inclusion the SSSC.

Four-Stage Linear Transformer Driver With Sharing Shell: EM Model, Simulation, and Performance

A four-stage fast linear transformer driver (LTD) with sharing shell was constructed as a fundamental component of China’s next-generation Z-pinch driver CZ34. Separate metal rods replaced conventional independent cavity shells for the ease of installation and maintenance. SF6 was utilized for the first time as insulating medium instead of transformer oil. To investigate the electrical performance of the LTD module, a 3-D full-scale electromagnetic model was developed by field-circuit co-simulation method in Computer Simulation Technology Studio Suite. Fundamental discharging brick was modeled as a conductive current path in 3-D model, excitation was employed through exterior circuits coupled to the field model. The applicability of the simulation model was validated by primary experiments. Compared to circuit simulation, the field-circuit co-simulation modeled the impedances of transmission lines and load impedance accurately since specific structures were included. Annular liquid resistor in experiment configurations brought in extra load inductance, which influenced greatly on output voltage fluctuations in each stage due to the mismatch of load impedance. Simulation results were in good agreement with experiments, except that the switch performances were not entirely up to expectations. It was indicated that several switches showed notable delays according to calculations, leading to voltage and current loss in measurements.

사후 고장분석에 기초한 송전케이블 선로정수 산정기준의 개선

The symmetrical impedances of a transmission line are important parameters for both accurate fault calculation and reliable protective relay setting. While overhead line impedance calculation results generally agree well with measured impedances at reasonable accuracy, underground transmission line impedances do not agree well very often. So there has been an urgent need for better guideline to determine which impedance should be used among measured and calculated cable transmission line impedances. In this paper, various post-fault analysis of 154kV cable transmission lines were conducted to improve the current KEPCO guideline based on sound technical background as possible.

Adaptive Virtual Impedance-Based Reactive Power Sharing in Virtual Synchronous Generator Controlled Microgrids

As a new emerging approach, virtual synchronous generator (VSG) control for interfacing inverters in renewable distributed generation (DG)-based microgrids has attracted significant research interest. However, VSG control cannot ensure proportional reactive power sharing among DG units when unequal transmission line impedances are involved, although active power sharing remains proportional among DGs. In this article, an adaptive virtual impedance-based VSG control approach for grid-connected and islanded microgrids is proposed to alleviate impedance difference at the inverter output and improve proportional reactive power sharing among DGs. The virtual impedance consists of an adaptive virtual resistance and a fixed virtual inductance, where the virtual resistance is designed adaptively based on operation points of the microgrid. In this article, the proposed adaptive virtual impedance control is implemented on a modified VSG control, known as fuzzy secondary controller-based VSG control, offering excellent voltage and frequency regulation at the PCC. Its performance is demonstrated through case and sensitivity studies using MATLAB/Simulink simulation; and further validated by comparing with an existing method.

Interpreting Ionic Conductivity for Polymer Electrolyte Fuel Cell Catalyst Layers with Electrochemical Impedance Spectroscopy and Transmission Line Modeling

An optimal cathode catalyst layer with uniform ionomer distribution is critical to reduce the platinum loading and increase the utilization in polymer electrolyte fuel cells (PEFCs). Having well distributed ionomer with low ionomer to carbon (I/C) ratio is desirable, as it will also minimize local oxygen transport resistance. In this work, we used electrochemical impedance spectroscopy (EIS) method and transmission line model (TLM) to measure and evaluate ionic conductivity of pseudo catalyst layers (PCLs) comprised of Vulcan XC72 carbon black and 3M 825 EW ionomer with I/C ratios of 0.3, 0.6, 1 and 1.4 at a relative humidity (RH) range of 50 to 120 %. These results were compared with our previous hydrogen pump (HP) measurements, where PCL was sandwiched between the two membranes and protons had to transport through the entire PCL to be counted towards current. EIS effective ionic conductivity results reported here are higher than the results of HP because in the HP set-up ionic pathways must percolate all the way through the PCL to be effectively counted, whereas in EIS measurement, ionomer segments that are in contact with the membrane but not percolating all the way through the PCL can be detected. Additionally, three effects were studied: 1) hot press, 2) platinum content and carbon black support, and 3) ionomer content or lack of ionomer. Ionic conductivity increased significantly by hot pressing PCL onto the membrane, however, it was independent with respect to the hot press conditions, such as pressure and temperature. Hot pressing with low I/C ratio had more impact than high I/C ratio because at high I/C ratio even without hot press there is a sufficient amount of contact points between catalyst layer and membrane. At high RHs, catalyst layer containing Pt has higher ionic conductivity compared to PCL because of Pt particles being hydrophilic, which helps to distribute the ionomer more uniformly. To investigate the effect of condensed water, PTFE dispersion was used as a binder for Pt/C layer instead of ionomer, resulting ionic conductivity decreased with increasing applied potential at 100% and 120% RH conditions. At lower RHs, ionic conductivity is independent of the applied potentials.