Series Impedance Research Articles

Online Non-Iterative Estimation of Transmission Line and Transformer Parameters by SCADA Data

Utilization of abundant measurements provided by supervisory control and data acquisition (SCADA) system has attracted increasing attention. Real-time estimation of transmission line parameters, utilizing voltage and power flow measurements provided by remote terminal units (RTUs) located at two substations across the line, has been investigated, recently. This paper improves this approach by introducing a novel exact linear reformulation of the problem, which can be solved in closed form. The distributed-parameter model of long transmission lines is considered and its parameters are estimated in a non-iterative manner using RTU measurements. The method is also extended to estimate transformer series impedance and tap position by SCADA measurements, linearly. As such, the disadvantages associated with the previous iterative approach, e.g. concern over convergence, for transmission line parameters are avoided. Moreover, the novel technique for estimating transformer parameters allows to determine the tap position as well as updated transformer series impedance. Furthermore, a thorough analysis is presented to take the measurement accuracy into account. Simulation results for different transmission lines and transformers in the IEEE 118-bus test system are reported, where the result indicate successful performance of the proposed algorithms.

A Model for SSTDR Signal Propagation Through Photovoltaic Strings

The ability of spread spectrum time domain reflectometry (SSTDR) to detect and locate faults in photovoltaic (PV) systems is considered in this article. This article provides a simulation that could be used for studying how faults and other parameters affect the reflectometry response and evaluating fault detection algorithms, for providing comparison simulations in iterative inversion algorithms used to detect and locate faults, or it could potentially be used to replace the measured baseline for these algorithms. The simulation uses an enhanced systematic solution procedure to find the reflection signature of the PV system, and is capable of modeling elements with complex impedance in both series and parallel separated by transmission lines. This article is an expansion of previous work to be capable of simulating systems containing n number of elements (such as PV panels and transmission lines) in series or parallel. The simulation was tested for 20 systems containing up to four resistors, capacitors, and PV cells, and was compared to the measured data.

Second Harmonic Current Reduction for Two-Stage Inverter With DCX-LLC Resonant Converter in Front-End DC–DC Converter: Modeling and Control

In a two-stage inverter, the instantaneous output power pulsates at twice the output frequency (2fo), generating the second harmonic current (SHC), which will propagate into the front-end dc-dc converter. This article aims for suppressing the SHC in the front-end dc-dc converter with dc transformer (DCX)-LLC resonant converter. The small-signal model of the DCX-LLC resonant converter is proposed, and based on which, the unified small-signal model of the preregulator+LLC converter is built. Then, the basic ideas for reducing the SHC are proposed, including the determination of the filter capacitors in the preregulator+LLC converter and the control approach. After that, from a perspective of output impedance, the control schemes for reducing the SHC in the front-end preregulator+LLC converter are proposed. By inserting a notch filter in the voltage loop and/or introducing a virtual impedance in series with the output rectifier of the LLC resonant converter, the output impedance of the preregulator+LLC converter at 2fo is increased and, thus, the SHC can be reduced. Finally, a 6-kVA two-stage three-phase inverter with boost+LLC converter as the front-end dc-dc converter was fabricated and tested. The experimental results are provided to verify the proposed control schemes.

Transmission expansion planning via power flow controlling technologies

The transition from conventional towards renewable energy systems requires additional transmission capacities and higher operational flexibility to overcome contingency situations. This study presents a novel transmission expansion planning approach for the simultaneous placement of AC systems and power flow controlling technologies including high voltage direct current, phase shifting transformers (PSTs) and thyristor controlled series compensators (TCSCs). The approach is formulated as a mixed-integer linear programming optimisation problem and the operating point of power flow controlling devices is endogenously determined by minimising expansion costs. Both PSTs and TCSCs are integrated into the optimisation problem by means of new mathematical formulations. PSTs are presented in more detail considering the PST impedance, which is modelled as an equivalent phase shift. The controllable series impedance of TCSCs is also represented as an equivalent phase shift. Exemplary results based on a synthetic 120 bus system show a significant potential of PSTs and TCSCs to reduce expansion costs as well as to lower the requirement for new transmission capacities. The simultaneous employment of these technologies reduces the expansion costs within the test system between 18.7 and 32.4% compared to those costs generated by the sole reinforcement by AC systems.

Use of Discrete Wavelet Transform to Assess Impedance Fluctuations Obtained from Cellular Micromotion.

Electric cell–substrate impedance sensing (ECIS) is an attractive method for monitoring cell behaviors in tissue culture in real time. The time series impedance fluctuations of the cell-covered electrodes measured by ECIS are the phenomena accompanying cellular micromotion as cells continually rearrange their cell–cell and cell–substrate adhesion sites. Accurate assessment of these fluctuations to extract useful information from raw data is important for both scientific and practical purposes. In this study, we apply discrete wavelet transform (DWT) to analyze the concentration-dependent effect of cytochalasin B on human umbilical vein endothelial cells (HUVECs). The sampling rate of the impedance time series is 1 Hz and each data set consists of 2048 points. Our results demonstrate that, in the Daubechies (db) wavelet family, db1 is the optimal mother wavelet function for DWT-based analysis to assess the effect of cytochalasin B on HUVEC micromotion. By calculating the energy, standard deviation, variance, and signal magnitude area of DWT detail coefficients at level 1, we are able to significantly distinguish cytotoxic concentrations of cytochalasin B as low as 0.1 μM, and in a concentration-dependent manner. Furthermore, DWT-based analysis indicates the possibility to decrease the sampling rate of the micromotion measurement from 1 Hz to 1/16 Hz without decreasing the discerning power. The statistical measures of DWT detail coefficients are effective methods for determining both the sampling rate and the number of individual samples for ECIS-based micromotion assays.

Analytical Evaluation of the Low-Frequency Magnetic Shielding of Thin Planar Magnetic and Conductive Screens

A recent analytical formulation for the low-frequency magnetic shielding effectiveness of a thin metal screen against a circular loop source is extended to the case of a screen exhibiting both magnetic and conductive properties. The presence of magnetic properties introduces a series impedance in the equivalent network of the structure, in addition to the shunt admittance associated with the screen conductivity. However, the fields scattered by the two elements do not interact and hence can be treated independently; furthermore, the series impedance gives rise to integrals akin to those stemming from the shunt admittance. A generalized analytical formulation for a combined magnetic and conductive screen is thus obtained, that is favorably compared with both classical approximate formulations and exact results.

Impedance of copper electrode in slightly acid Cu(II)-glycine solutions

Electrochemical impedance spectroscopy was used to study the kinetics of reduction of Cu (II) in weakly acidic (pH 4 and 5) solutions of Cu (II) containing glycine (0.04 or 0.1 M) as a complexing agent. A rather slow equilibration was observed at pH 4 and glycine concentration cL = 0.04 M. With increasing pH or cL, the total concentration of intermediate Cu(I) decreases. At the same time, impedance increases over the entire range of frequencies applied. An equivalent circuit with two parallel sub-circuits, each containing the charge transfer resistance and Warburg impedance in series, was used to quantify the impedance spectra. The exchange current densities of two consecutive one-electron transfers were estimated. Their average values are ~1 µA cm–2 and ~0.1 mA cm–2.

Simulation Test of a DC Fault Current Limiter for Fault Ride-Through Problem of Low-Voltage DC Distribution

The low voltage direct current (LVDC) distribution networks are connected with too many kinds of loads and sources, which makes them prone to failure. Due to the small damping value in the DC lines, the fault signal propagates so fast that the impact current with the wave front of millisecond and the transient voltage pose great challenges for fault detection. Even worse, some faults with small currents are difficult to detect and the communication is out of sync, resulting in protection misoperation. These problems have severely affected the new energy utilization. In view of this, a DC fault current limiter (FCL) composed of inductance, resistance, and power electronic switch was designed in this paper. The rising speed of fault current can be decreased by the series inductance and the peak value of the fault current can be limited by series impedance, thus in this way the running time can be gained for fault detection and protection. For distributed energy access, by deducing the short circuit fault characteristic expression of LVDC distribution network, the feasibility of FCL was verified. Based on the structure of the bridge-type alternating current (AC) current limiter, the structure and parameters of the DC FCL were determined according to the fault ride-through target. Then, a low voltage ride-through strategy based on DC FCL was proposed for the bipolar short-circuit fault of LVDC distribution network. Finally, MATLAB/Simulink simulation was used to verify the rationality of the proposed FCL and its ride-through strategy.

Impact of the Ground on the Series Impedance of Overhead Power Lines

An overhead power line is a structure used in the electric power system to transmit electrical energy. The performance of overhead power lines depends on their parameters. There are four basic electrical parameters of power lines: resistance, inductance, capacitance, and shut conductance. The paper focuses on the calculation of the series impedance of overhead lines (resistance and inductance) by three different methods (Carsonʹs method, Rüdenbergʹs method and the theory of complex penetration depth) considering the impact of the ground return path. There is also the comparison of these methods and their application on models of real power lines of different voltage levels provided in this paper.

A second‐generation voltage conveyor (VCII)–based simulated grounded inductor

SummaryIn this paper, an implementation of a simulated grounded inductor (SGI) based on a recently developed active building block called second‐generation voltage conveyor (VCII) is proposed. The proposed SGI employs two VCIIs, two resistors, and one grounded capacitor, which is preferred when integration is involved. More importantly, unlike most of the other previously reported SGIs, this one is free from any restrictive matching conditions. A complete analysis of nonidealities along with sensitivity treatment by considering parasitic impedances and nonideal gains of the VCII are performed. A simple VCII circuit is designed to be used in the implementation of the proposed SGI. To support the presented theory, Pspice simulation results using 0.18‐μm CMOS technology parameters and supply voltage of ±0.9 V are provided. On the basis of the achieved results, the proposed SGI operates in a good agreement with an ideal inductor. The power consumption is only 0.65 mW, and the parasitic series impedance is approximately 191.9 Ω. The applicability of the proposed SGI is tested by using it in a standard second‐order high‐pass RLC filter.

Equivalent Model of Modular Multilevel Converter Considering Capacitor Voltage Ripples

Modular multilevel converter (MMC) is regarded as a topology with high potential for high-voltage direct current transmission system. However, the distributed capacitors lead to significant submodule capacitor voltage ripples, which have great influence on the terminal characteristics of MMC. In this paper, an equivalent model considering submodule capacitor voltage ripples and circulating current suppression control is established to explore the terminal characteristics of MMC. In the model, MMC is equivalent to the cascade of buck/boost converter and two-level voltage source converter (VSC) from a terminal perspective. The influence of capacitor voltage ripples is represented by the equivalent series impedances, whose characteristics are investigated in detail with harmonic linearization method. Then, the simplified equivalent series impedances are obtained. Based on the equivalent model, the study of terminal characteristics is greatly simplified by directly applying conclusions of two-level VSC and buck/boost converter to MMC. Furthermore, the control strategy design and impedance modeling of MMC have been carried out to show how the equivalent model can be used in practical applications. Finally, the effectiveness of the proposed model is verified by detailed simulation results.

MIM capacitors as simple test vehicles for the DC/AC characterization of ALD-Al2O3 with auto-correction of parasitic inductance

Metal-insulator-metal capacitors were used for determining the DC and frequency-dependent characteristics of ultra-thin Al2O3 (Thox = 22 nm). For this purpose, a state-of-the-art insulating layer was formed using atomic deposition, which enables enhanced performance of devices and application within the back-end of line stage of a CMOS process. As part of the analysis, DC and low frequency CV measurements are used to determine the electric field to breakdown, the dominant conduction mechanisms, and the dielectric constant, whereas small-signal modelling allows for characterizing the frequency-dependent behaviour of the Al2O3 layer using LCR measurements from 100 Hz to 1 MHz. This avoids using dedicated RF test structures as for measuring S-parameters. Moreover, since it is demonstrated here that the parasitic effect of the series impedance associated with the metal electrodes is significant within this frequency range, an RLGC equivalent circuit is used to determine the intrinsic properties of the layer. In this way, the effective loss tangent and dielectric constant were straightforwardly extracted from AC data.

Fault Ride-Through Enhancement of Grid Supporting Inverter-Based Microgrid Using Delayed Signal Cancellation Algorithm Secondary Control

The growing level of grid-connected renewable energy sources in the form of microgrids has made it highly imperative for grid-connected microgrids to contribute to the overall system stability. Consequently, secondary services which include the fault ride-through (FRT) capability are expected to be possessed characteristics by inverter-based microgrids. This enhances the stable operation of the main grid and sustained microgrid grid interconnection during grid faults in conformity with the emerging national grid codes. This paper proposes an effective FRT secondary control strategy to coordinate power injection during balanced and unbalanced fault conditions. This complements the primary control to form a two-layer hierarchical control structure in the microgrids. The primary level is comprised of voltage/power and current inner loops fed by a droop control. The droop control coordinates grid power-sharing amongst the voltage source inverters. When a fault occurs, the participating inverters operate to support the grid voltage, by injecting supplementary reactive power based on their droop gains. Similarly, under unbalanced voltage condition due to asymmetrical faults in the grid, the proposed secondary control ensures the positive sequence component compensation and negative and zero sequence components clearance using a delayed signal cancellation (DSC) algorithm and power electronic switched series impedance placed in-between the point of common coupling (PCC) and the main grid. While ensuring that FRT ancillary service is rendered to the main utility, the strategy proposed ensures relatively interrupted quality power is supplied to the microgrid load. Consequently, this strategy ensures the microgrid ride-through the voltage sag and supports the grid utility voltage during the period of the main utility grid fault. Results of the study are presented and discussed.

Design Consideration of a Dual-Functional Bridge-Type Fault Current Limiter

To sufficiently utilize a bridge-type fault current limiter (BTFCL) in the distribution grids, this article proposes a dual-functional BTFCL (DF-BTFCL), which can work either at the BTFCL mode to limit faulty currents or at the dynamic voltage restorer (DVR) mode to compensate grid-voltage fluctuations. The proposed DF-BTFCL can flexibly switch between the two modes by either activating a dc capacitive circuit or a dc inductive circuit. The inductive circuit can adjust the equivalent series impedance to limit the faulty current in an acceptable range, and the dc capacitance circuit can provide dc support to enable the DVR operation. The proposed DF-BTFCL can immediately limit the increasing rate of the faulty current without any fault detection delay, and it is similar to the conventional BTFCL. Transient processes between the switch of the two operation modes are analyzed, and the key parameters of the DF-BTFCL system are designed in detail. Simulations and experimental results both clearly prove the feasibility and effectiveness of the proposed DF-BTFCL.

Feasibility of early activation after cochlear implantation

The purpose of the study is to investigate feasibility of early activation after cochlear implantation by evaluating long-term impedance change and speech perception. Case-control study SETTING: Between July 2015 and December 2016, we prospectively enrolled 20 subjects for early activation (within 24hours after cochlear implantation). On the other hand, from November 2013 to July 2015, 20 age- and sex-matched control subjects from the database of cochlear implantees treated with conventional activation schedule (4weeks after surgery) were retrospectively enrolled. Forty patients who underwent cochlear implantation surgeries. The series impedance and speech perception score of both groups were compared. No statistical difference in long-term follow-up between the two groups was found using GEEs and multivariate analysis. In the early activation group, impedance reached a steady level by the 2nd postoperative week, and the hearing perception ability significantly improved by the 4th postoperative week. This comparative study illustrated sequential impedance data during early activation (24hours) and conventional activation (4weeks) after CI surgery. There were no major complications in either group, and the safety of early activation with respect to impedance changes, postoperative residual hearing preservation and speech perception scores were non-inferior to that of the conventional group. Therefore, in this study, we established the feasibility of early activation 24hours after cochlear implantation.

Voltage Slump Compensation using Facts Controllers on Power System

This article dispense the different FACTS controllers integrated circuits using a simulation program that emphasis with PSPICE. The FACTS controller controls series impedance, shunt impedance, voltage, current and phase angle. In this paper, a simplified circuit model of Series Compensator and Unified Power Quality conditioner has been analyzed and the simulation results coincides with the theoretical results..

Power Quality Services Provided by Virtually Synchronous FACTS

The variable and unpredictable behavior of renewable energies impacts the performance of power systems negatively, threatening their stability and hindering their efficient operation. Flexible ac transmission systems (FACTS) devices are able to emulate the connection of parallel and series impedances in the transmission system, which improves the regulation of power systems with a high share of renewables, avoiding congestions, enhancing their response in front of contingencies and, in summary, increasing their utilization and reliability. Proper control of voltage and current under distorted and unbalanced transient grid conditions is one of the most critical issues in the control of FACTS devices to emulate such apparent impedances. This paper describes how the synchronous power controller (SPC) can be used to implement virtually synchronous FACTS. It presents the SPC functionalities, emphasizing in particular the importance of virtual admittance emulation by FACTS devices in order to control transient unbalanced currents during faults and attenuate harmonics. Finally, the results demonstrate the effectiveness of SPC-based FACTS devices in improving power quality of electrical networks. This is a result of their contribution to voltage balancing at point of connection during asymmetrical faults and the improvement of grid voltage quality by controlling harmonics flow.

Analysis of Steady-State Characteristics for a Newly Designed High Voltage Gain Switched Inductor Z-Source Inverter

This paper aims to develop a new switched inductor assisted strong boost Z-source inverter (SL-SBZSI) topology with high voltage gain and analyze the steady-state characteristics of the proposed topology. In the proposed topology, two switched inductors are used within the series impedance structure of the Z-source inverter (ZSI) in order to achieve the high voltage gain. The steady-state characteristics of the proposed topology are analyzed to disseminate its several advantages as compared to traditional ZSIs. The key advantages include the higher boost factor with lower shoot-through duty ratio and lower voltage stresses on capacitors as well as on switches of the inverter bridge. Furthermore, the proposed topology has the soft-start ability which significantly reduces the inrush start-up current while comparing with the traditional ZSI. In the proposed topology, a common ground is shared between the output AC voltage and the input DC voltage source which categorizes this topology to the doubly grounded inverter. The characteristics of the proposed SL-SBZSI are analyzed by considering two operating condition where the simple boost pulse width modulation (PWM) scheme is used to extract the shoot-through pulses. The characteristics of the proposed topology are also compared with different existing topologies along with the conventional modified capacitor assisted Z-source inverter (MCA-ZSI), whose boost factor is much closer to the proposed topology. Rigorous mathematical analyses are presented to clearly demonstrate the benefits of the proposed topology while simulation studies are carried out to demonstrate its distinct features as compared to the existing topology. Finally, experimental studies are conducted to further validate the theoretical and simulation results.

Modeling series compensation effect on the bus impedance matrix for online applications

This paper derives new expressions for updating Bus Impedance Matrix (Zbus) elements to account for the modification of the series impedance of a line connected between two existing buses. Such kind of modification is not accounted for in Brown's method and requires building Zbus all over again which is time-consuming, and redundant. Afterwards, we show that a modified form of Sherman–Morisson identity is the generalization of our work. We test our modeling approach with seven systems of different sizes. Results show very minor errors between the predictions of our techniques and Brown's method. Further, speed comparison shows that our method substantially improves calculation speed from a few minutes with Brown and Bus Admittance Matrix (Ybus) inversion methods to seconds (1.35s and 2.9s for 2383 and 3120 bus systems, respectively) making it more suitable for online applications.

Simulation of implementing the function of SSSC converted from grid paralleling device based on power transmission

Grid paralleling device based on power transmission can be converted into a static synchronous series compensator after grid connecting successfully. At present, the power grid becomes more and more complicated, and short-circuit faults occur frequently. In order to regulate the system power flow and limit the short-circuit current of the system, it is worthwhile to develop the function taking advantage of the characteristics of the existing equipment. In this paper, the control strategy of adjusting power is obtained by establishing SSSC model. Meanwhile, according to the nature of SSSC which can be equivalent to series impedance, the current limiting function of SSSC in the event of short circuit fault is further analyzed. Finally, building the equivalent model of SSSC in PSCAD / EMTDC, the simulation results show that changing the equivalent impedance of SSSC can regulate the flow of line transmission effectively, and prove that SSSC has a certain current limiting function in case of short-circuit.