Power Line Impedance Research Articles

Stability Enhancement Method of Standalone Modular Multilevel Converters Based on Impedance Reshaping

Modular multilevel converters (MMCs) are susceptible to subsynchronous oscillations (SSOs) caused by impedance interactions in the power line. Current research into the stability of MMCs focuses mainly on voltage feed-forward control, while the effect of current feed-forward control is neglected. This paper proposes a current feed-forward compensation method based on impedance reshaping for standalone MMCs. Initially, an impedance model was developed to identify the stability risks caused by the interaction between the MMC and power line impedance. The proposed method feeds the current compensation signal into the modulation circuit, thereby improving the control signal and suppressing the impedance interaction between the MMC and the power line. The analysis of the harmonic state space (HSS) method verifies that the proposed approach effectively reduces the negative damping region in the frequency band where the SSO is located. Additionally, the impedance frequency scanning method confirms the accuracy of impedance modeling. Using the MATLAB/Simulink platform and StarSim HIL hardware-in-the-loop experimental platform, the SSO phenomenon of the MMC is simulated, and the results show that the proposed method can effectively suppress harmonic currents during SSO, which verifies the accuracy of the stability analysis and the feasibility of the proposed method.

Research on Phase-to-phase Fault Location Method of Active Distribution Network

Due to the weak feed characteristic of active distribution networks, the sensitivity of the original fault phase selection method and the accuracy of fault location are decreased. Most of the existing fault section location methods focus on the phase selection and location of the earth fault, and there is a lack of relevant research on the location of the fault section to the phase-to-phase fault. Moreover, most of the methods need to install the signal measuring device in the system as large as possible, which is not economical. The operation condition of active distribution networks is complicated, the fault characteristics are weak, and the location result is easily affected by non-fault disturbances such as DG access capacity and location. In this paper, the phase-to-phase fault of active distribution networks is taken as the research object. Firstly, phase current and zero-sequence current combined criterion is used for fault phase selection, and then combined with the phase-frequency characteristics of mode impedance of distribution line and photovoltaic power line, a fault section location method based on transient characteristic frequency band is proposed, which is not affected by non-fault disturbance such as photovoltaic control strategy and DG access capacity and location. Simulation results show that the method is effective.

Novel approach for modeling and attenuation of power waves in large – scale power systems

In this paper modeling and attenuation of electromechanical power waves in large – scale power systems are discussed. Mathematical model of power wave is derived using Euler – Lagrange equation. The proposed modeling procedure is based on kinetic and potential energies of the system, as well as system’s dissipation power. A novel method for incorporation of spatially dependent power losses into Euler – Lagrange equation is defined as well. The obtained mathematical model is simple for derivation, straightforward and practical for use, so it can easily be applied to derive wave equation of other technical systems or natural phenomena as well, which is an additional advantage compared to the existing models. Based on the developed model, an appropriate control system is proposed. The main idea for control system synthesis is to reduce transmitted waves inside the system. It is shown that the series power line impedance and voltage amplitude have the greatest impact on the wave transmission coefficient. Since unified power flow controller (UPFC) is capable of simultaneously modulating both these parameters, this device is chosen to perform control tasks in proposed operation mode. The effectiveness of the proposed solution has been verified by thorough computer simulations on artificial generator array and IEEE benchmark simplified Australian system. The results show significant power wave reduction. Some future works such as derivation of the mathematical model of inverter array or incorporation of artificial intelligence algorithms in UPFC control system based on transmission coefficient reduction might rely on this work.

Research on concentrated frequency-dependent parameter model for short overhead transmission lines based on first-order rational function fitting

The impedance of power lines is influenced by geological conditions and skin effect, resulting in frequency-dependent characteristics. In this study, a centralized parameter frequency-dependent line model based on first-order rational function fitting is investigated for short overhead transmission lines. The proposed model incorporates a parallel branch consisting of resistance and inductance obtained through rational function fitting, which mimics the frequency-dependent behavior of the line. The coupling between multiple conductors is represented using controlled sources. Comparative analysis of fitting accuracy and computational efficiency across various orders of rational functions reveals that the first-order rational function fitting offers superior computational efficiency while maintaining high accuracy in the medium and low-frequency range. Simulation results demonstrate that the proposed model, when disregarding wave propagation effects, exhibits comparable accuracy to the distributed parameter line model while achieving higher computational efficiency. Moreover, in transient analysis predominantly influenced by power frequency, the proposed model outperforms the frequency-independent pi(π) line model in terms of accuracy.

Impedance-Based Aggregation of Paralleled Power Factor Correction Converters in Data Centers

Existing aggregation methods for large-scale data center power systems often overlook disparities in power supply units, leading to reduced accuracy in the small signal dynamics of aggregated model. To fill this gap, this article develops an impedance-based aggregation method for paralleled power factor correction (PFC) converters with heterogeneities in power levels, conduction modes, and line impedances. The closed-loop input admittances of PFC converters operating in continuous conduction mode (CCM) and discontinuous conduction mode (DCM) are presented first. The parametric scaling is then derived to aggregate multiple PFC converters at different power levels and operation modes, including the CCM, DCM, and mixed conduction mode, at the rack level. Furthermore, the aggregation rule and criteria for paralleled PFC converters with unequal line impedances is developed to provide a reduced-order dynamic model for adjacent server racks. The proposed parameter scaling and aggregation method allow efficient interaction analysis and stability assessment for data center power systems. The accuracy and robustness of the impedance-based aggregation are finally validated by simulations and experimental tests.

A New Decentralized Robust Secondary Control for Smart Islanded Microgrids.

Dealing with the islanded operation of a microgrid (MG), the micro sources must cooperate autonomously to regulate the voltage and frequency of the local power grid. Droop controller-based primary control is a method typically used to self-regulate voltage and frequency. The first problem of the droop method is that in a steady state, the microgrid's frequency and voltage deviate from their nominal values. The second concerns the power-sharing issue related to mismatched power line impedances between Distribution Generators (DGs) and MGs. A Secondary Control Unit (SCU) must be used as a high-level controller for droop-based primary control to address the first problem. This paper proposed a decentralized SCU scheme to deal with this issue using optimized PI controllers based on a Genetic Algorithm (GA) and Artificial Neural Networks (ANNs). The GA provides the appropriate adjustment parameters for all adopted PI controllers in the primary control-based voltage and current control loops and SCU-based voltage and frequency loops. ANNs are additionally activated in SCUs to provide precise online control parameter modification. In the proposed control structure, a virtual impedance method is adopted in the primary control scheme to address the power-sharing problem of parallel DGs. Further, in this paper, one of the main objectives includes electricity transmission over long distances using Low-Voltage DC Transmission (LVDCT) systems to reduce power losses and eradicate reactive power problems. Voltage Source Inverters (VSIs) are adopted to convert the DC electrical energy into AC near the consumer loads. The simulation results illustrated the feasibility of the proposed solutions in restoring voltage and frequency deviations, reducing line losses, as well as achieving active and reactive power sharing among the DGs connected to the MG.

In-Place Evaluation of Powering and Signaling Within Fan-Out Multiple IC Chip Packaging

This article confirms the advantage of fan-out (FO) packaging in the electrical performance of power delivery among integrated circuit (IC) chips with the best use of land side capacitors (LSCs). On-chip in-place waveform measurements quantitatively evaluate the integrity of powering and signaling within FO wafer level packaging (FOWLP) multiple chip module (MCM) demonstrators, where a pair of IC chips are assembled with LSCs with different sizes and structures. The IC chip incorporates an array of 12 digital cores and on-chip waveform monitor (OCM) circuits. Each digital core consists of a low-voltage differential signaling (LVDS) transceiver channel that is backed by a static random access memory (SRAM)-based built-in self test (BIST) module and supplied by an on-chip voltage regulator module (VRM). The LSCs are placed on the bottom side of an FO interposer and inserted between the output of VRM and the ground plane almost ideally with the shortest length of physical traces. A Si membrane capacitor of 10 nF sustains the lowest power line impedance over the frequency range of 2.0 GHz more constantly than a multilayer ceramic counterpart, and attenuates the high-order harmonic frequency components to the clocking frequency at 750 MHz. The leverage of LSCs in powering also improves signaling and helps achieve the wider eye openings in LVDS channels. The implications are elaborated for the capacitor selections with respect to the physical types of capacitors, the size of capacitances, and the level of shares in power delivery among digital cores, all toward the higher level of integrity in powering and signaling in FOWLP MCMs.

Optimal locating method of edge computing device in cyber physical distribution system

With the development of interconnection of massive terminals, high maintenance of equipment data and complexity of network structure in distribution system, the traditional information processing mode based on single cloud master station has some disadvantages, such as high data transmission delay, high congestion, information far away from equipment and slow queuing processing. Edge computing can make local fast analysis and decision for data in the near terminal device side, which can effectively make up for the deficiency of cloud computing. As the cornerstone of edge computing, edge control processing node is the first premise to realize fast response control of cyber physical distribution system (CPDS). In this paper, a new method of edge computing node deployment is proposed for the distributed edge computing requirements of cyber physical distribution system, considering the cyber stability and power stability. The community theory based on distribution network power flow and line impedance is used to divide the edge computing autonomous region, and the calculation model of cyber stability and power stability of CPDS network is established, then the optimal deployment of CPDS edge computing nodes is solved by the hybrid entropy calculation of cyber and power. Finally, an improved standard example is used for simulation analysis. The simulation results show that the ECN deployment scheme proposed in this paper can effectively reduce network congestion, improve network response speed and realize optimal control of distribution network.

Control of series impedance of power lines using power flow controller

In this paper, the possibility of unified power flow controller (UPFC) to modulate both series resistance R and series reactance X of an overhead power line is discussed. The classical power flow control system of the UFPC is modified in the manner that standard input references signals (active and reactive powers) are replaced by reference signals of series resistance and reactance. Using the procedure described in this work, the reference signals for active and reactive powers are generated indirectly. The operation of UPFC in proposed operation mode is analyzed using computer simulation, based on a model of single machine infinite bus (SMIB) with constant impedance loads and two parallel lines. The goal is to show that UPFC is capable to control both series line parameters (R and X) directly and independently by means of a simple control system without additional decoupling controllers. An additional task is to show that power flows can be indirectly controlled this way. The step response of series line resistance and reactance is used to validate the operation of the proposed control system. The obtained results clearly show that all goals are fulfilled.

Design of Op-Amp Based ECG Signal Acquisition Using MULTISIM

The electrocardiogram has the extensive diagnostic significance, and utilizations of ECG observing are assorted and in wide use. ECG signal after procurement contains noises, for example, power line impedance, instrumentation noise, external electromagnetic field obstruction, commotion because of arbitrary body developments and breath developments. These noises can be classified according to their frequency content. It is fundamental to decrease these unsettling influences in ECG sign to improve exactness and dependability. The bandwidth of the noise overlaps that of wanted signals, so basic filtering can’t adequately improve the signal to noise ratio. Current biomedical enhancers have an exceptionally high common mode rejection ratio. All things considered, accounts are often contaminated by residual power-line interference. Conventional simple and advanced channels are known to suppress ECG segments close to the electrical cable recurrence. This paper deals with design filter for ECG signal utilizing operational amplifier using Multisim.

A dual-mode successive approximation register analog to digital converter to detect malicious off-chip power noise measurement attacks

An on-chip noise monitor using a dual-mode analog to digital converter (ADC) is developed to detect the insertion of off-chip components as malicious attempts of power noise measurement attacks. A two-step sampling scheme selecting either synchronous or asynchronous clocking enables both real-time monitoring and high-resolution diagnosis of power supply noise, respectively. The monitor detects the change in power-line impedance and assumes the happening of physical contacts by an attacker’s device. A wide-band ADC with the bandwidth of 1 GHz facilitates the analysis of on-chip captured waveforms and the recognition of potentially inserted devices. Fabricated in 65 nm CMOS, the on-chip noise monitor is examined for the detectability of series resistors as well as parallel capacitors that are intentionally inserted on power lines. The experiments demonstrated the detection of a power current sensor in series to power lines, and also the attachment of an oscilloscope probe, through the analysis of on-chip captured power noise waveforms.

ПРОДОЛЬНОЕ СОПРОТИВЛЕНИЕ ОДНОЦЕПНОЙ ЛЭП С ДВУМЯ ГРОЗОЗАЩИТНЫМИ ТРОСАМИ В ЗАДАЧЕ ДИСТАНЦИОННОГО ОМП

One of the most important tasks in remote fault location in a 110 kV+ network is modeling the power lines taking into account the electromagnetic and electrostatic interaction of their conductive elements. A common approach is to use the mathematical models recommended by the guidelines for calculating short-circuit currents for relay protection. However, these models of power transmission lines take into account the geometric mean distance between the wires and the lightning protection cables, which means they average the values of the mutual induction impedances. In cases where wires and cables are located asymmetrically relative to each other, this leads to an overestimation of the zero-sequence impedance of power lines and, as a consequence, to an underestimation of the single-phase short-circuit current. This situation can affect the results of remote fault location. To eliminate this drawback, the article proposes a combined equivalent circuit for a single-circuit power transmission line with two lightning protection cables, based on a combination of methods of phase coordinates and symmetric components. The given equivalent circuit of power transmission lines allows calcula¬ting the mode parameters using the method of symmetric components and, at the same time, simulating those of interest for calculating power lines using phase coordinates.

Research of electrodynamics characteristics of antennas in the form of an open end of a rectangular waveguide with partial dielectric filling and excitation pin

The electrodynamics characteristics of the antenna in the form of an open end of a rectangular waveguide with partial dielectric filling and a pin of excitation are studied. In the antennas in the form of an open end of a rectangular waveguide with a pulse drive and a pin excitation there is insufficient coordination of the input resistance of the pin with the wave impedance of the coaxial power line. It is proposed to reduce the influence of this disadvantage by taking into account the effective dielectric permeability, the size of the excitation pin and its displacement relative to the waveguide axis with the help of the obtained improved expression for calculating the conductivity of the coaxial-waveguide transition from the side of the rectangular waveguide. In accordance with the given method, the graphs of the active and reactive resistance of the excitation pin on its geometric dimensions and location are constructed, the normalized far field pattern of the antenna in planes E and H, which show the possibility of reducing the dimensions of the cross section of the waveguide for its constant electric size, as well as the improvement of coordination antennas in a defined frequency band.

Design and Evaluation of Band-Pass Matching Coupler for Narrow-Band DC Power Line Communications

In power line communication (PLC), coupling transformers are usually required for coupling, band-pass filtering and impedance matching. However, coupling transformer design involves so many parameters that it is typically an imprecise and experimental procedure. In addition, the cost and size of transformers prevent them from being an economic and compact solution for PLC couplers. This paper first analyzes a simplified, distributed parameter model of the power line, which can be used to calculate power line impedance easily and accurately. Next, a low-cost, band-pass matching coupler with compact architecture is designed to replace the coupling transformer for direct current PLC (DC-PLC), which ensures impedance matching on the basis of an accurate power line impedance instead of using an average value. Finally, simulations as well as laboratory tests are conducted under 95–125[Formula: see text]kHz (CENELEC B-band), which confirm the new coupler’s excellent band-pass filtering and impedance matching performance.

Characteristic Impedance Analysis of Medium-Voltage Underground Cables with Grounded Shields and Armors for Power Line Communication

The characteristic impedance of a power line is an important parameter in power line communication (PLC) technologies. This parameter is helpful for understanding power line impedance characteristics and achieving impedance matching. In this study, we focused on the characteristic impedance matrices (CIMs) of the medium-voltage (MV) cables. The calculation and characteristics of the CIMs were investigated with special consideration of the grounded shields and armors, which are often neglected in current research. The calculation results were validated through the experimental measurements. The results show that the MV underground cables with multiple grounding points have forward and backward CIMs, which are generally not equal unless the whole cable structure is longitudinally symmetrical. Then, the resonance phenomenon in the CIMs was analyzed. We found that the grounding of the shields and armors not only affected their own characteristic impedances but also those of the cores, and the resonance present in the CIMs should be of concern in the impedance matching of the PLC systems. Finally, the effects of the grounding resistances, cable lengths, grounding point numbers, and cable branch numbers on the CIMs of the MV underground cables were discussed through control experiments.

Distributed Generation Systems: An Approach in Instrumentation and Monitoring

This paper presents an active instrumentation approach for distributed generation systems. The basic inherent tasks of such active instrumentation are (1) measurement, (2) control, (3) operation, (4) monitoring, and (5) correction of undesirable power quality issues in response to power parameters deviations, with the particularity of presenting the control scheme flexible and easy-to-adapt to new grid codes. The technology discussed in this paper is an approach to improve the life-cycle cost applied to distributed generation systems for instrumentation and monitoring in smart grids. It is based on designing an intelligent instrument to achieve the highest performance, to allow for flexibility in generating data suitable for each destination, to involve validation for the credibility of operation, and to adapt itself to new grid codes. Such intelligent power instruments are implemented with knowledge of measurement processes, their variables, and parameters, with a response to the universe of data that must be monitored and controlled. Also, the active instrumentation performs efficient, reliable, and safe operation of distributed power plants enhancing the power quality and economy. Such approach is based on triple loop control, and it can be expanded to any distributed generators ranging from grid-feeding to grid-supporting, whether using current-based or voltage-based control schemes ensuring immunity against power line impedances change without the previous knowledge of their values. This approach in instrumentation, i.e., ACTSENSOR Power Instrument is thoroughly described and analyzed by simulation results developed in the MatLab platform. Hardware-in-the-loop simulation through Typhoon HIL is used to validate its control, and experimental results validate its dynamic during transition between grid-connected and islanded modes.

Decentralized Reactive Power Sharing and Frequency Restoration in Islanded Microgrid

P-f and Q-V droop methods are the most common decentralized control methods in islanded microgrid. Although with the P-f droop method, an accurate active power sharing can be achieved among distributed energy resources (DERs), by Q-V droop, the reactive power sharing among DERs often deteriorates due to its highly dependence on the power line impedances and the local load. Variation of frequency and voltage by load changes is another challenge in droop control method. In this paper, a new autonomous control method is proposed to share reactive power among DERs accurately and restore frequency of a microgrid. The proposed method does not require any communication link and so maintains reliability and simplicity of the network. The synchronizing among DERs is obtained by the load change detection, which is accomplished by wavelet transform. The method operation principle is explained and analyzed. Simulation results are presented to validate the effectiveness of the proposed method.

Measurement and Analysis of Channel Transmission Characteristics for Low-Voltage Power Networks

This paper presents a channel measurement method for low-voltage power networks. Firstly, the measurement parameters and tools for the channel transmission characteristic are introduced. Then the basic principles for measuring Low-voltage power line noise, signal transmission loss, power line impedance characteristics are introduced too. In the end, the measurement and the analysis results are given. Those results show that the environmental noise are large in the middle and low frequency bands large, the lines attenuate seriously when the frequency is 220kHz, as well as that the impedance characteristics is stable when the power frequency nearby zero in the high-frequency regions, from which we can conclude that the optimal transmission frequency is between 350kHz~450Khz. Besides, the noise is low and the impedance is stable when power frequency nearby zero-crossing, and it means that the low-voltage power grid presents high impedance and stable, low noise level, suitable for signal transmission, and to facilitate the system time synchronization.

On the Existence and Linear Approximation of the Power Flow Solution in Power Distribution Networks

We consider the problem of deriving an explicit approximate solution of the nonlinear power equations that describe a balanced power distribution network. We give sufficient conditions for the existence of a practical solution to the power flow equations, and we propose an approximation that is linear in the active and reactive power demands of the PQ buses. For this approximation, which is valid for generic power line impedances and grid topology, we derive a bound on the approximation error as a function of the grid parameters. We illustrate the quality of the approximation via simulations, we show how it can also model the presence of voltage controlled (PV) buses, and we discuss how it generalizes the DC power flow model to lossy networks.

Expansion of Power System Corridors Using Tier-1 Technique for Reactive Power Compensation

This paper develops a novel strategy for the expansion of the power system corridors for the release of the embedded transmission capacity. Both theoretical and practical network models are presented with a focus on power flow studies which concentrates on the steady state or static behavior of electrical power system. The methodology involves the power flow analysis revalidation of the existing standard IEEE 14 bus system and simulation using Newton- Raphson method in both MATLAB and Powerworld simulator (PWS) environment. This paper therefore establishes that an original designed network could be modified to take more loads without building new generators or transmission lines. The expansion of the existing IEEE 14 bus network to accommodate more load involves the use of static compensators incorporated at the transmission lines. This technique is then analyzed extensively when distributed along the lines through the use of a distributed capacitors compensators, (DCC). DCC can affect significant change in power line impedance to improve the power transfer capacity of an interconnected power system. The application of the DCC on the line is the tier-1 technique. The results obtained show that by applyingthe tier-1 techniques to the transmission line, the system’s capacity will remarkably improve and the transmission line will accept extra loading.