Series Impedance Research Articles

An Extra-High Voltage Test System for Transmission Expansion Planning Studies Considering Single Contingency Conditions

This paper presents an extra-high voltage synthetic test system that consists of 500 kV and 765 kV voltage levels, specifically designed for transmission expansion planning (TEP) studies. The test network includes long transmission lines whose series impedance and shunt admittance are calculated using the equivalent π circuit model, accurately reflecting the distributed nature of the line parameters. The proposed test system offers technically feasible steady-state operation under normal and all single contingency conditions. By incorporating accurate modeling for long transmission lines and EHV voltage levels, the test system provides a realistic platform for validating models and theories prior to their application in actual power systems. It supports testing new algorithms, control strategies, and grid management techniques, aids in transmission expansion planning and investment decisions, and facilitates comprehensive grid evaluations. Moreover, a TEP study is conducted on this test system and various scenarios are evaluated and compared economically.

Analytical Calculation of Series Impedance for Deeply Buried Coaxial Cables

Analytical Calculation of Series Impedance for Deeply Buried Coaxial Cables

Dual polarity open circuit voltage in triboelectric nanogenerators originated from two states series impedance

Experimental and simulation studies demonstrated that the initial voltage setting significantly influences the open-circuit voltage (VOC) in triboelectric nanogenerators (TENGs). Utilizing diode configurations, we consistently observed two distinct VOCs independent of the initial settings. A lower VOC corresponded to the surface voltage (VSurface), while a higher VOC was amplified by the product of the VSurface and the TENG's characteristic impedance ratio. Notably, a lower measurement system capacitance provided a more precise representation of the inherent characteristics of the TENG. Conversely, an increase in system impedance led to a convergence of the two VOCs and a reduction in their magnitudes relative to VSurface. These findings suggest that optimizing the initial/repeated charge balancing and minimizing capacitive loads are crucial for maximizing TENG output power in practical applications.

Research on simulation accuracy of equivalent aggregate electromagnetic model optimization for large renewable energy stations

Abstract The traditional power grid is rapidly transforming into a new power system with high penetration of new energy. Simulation modeling plays an important role in supporting the cognition and research of the new power system. A high proportion of renewable energy is connected to the grid through power electronic components, which puts forward a higher demand for research on the accuracy and stability of power grid simulation modeling. Renewable energy plants usually have a large number of single units, and equivalent aggregation modeling is the usual way to simplify the modeling of renewable energy plants. However, the transmission line power multiplier equivalent module inevitably introduces series impedance into the network, resulting in errors between simulation and actual engineering. Therefore, the study of lossless multiplier elements based on Modified Nodal Analysis (MNA) can improve the simulation accuracy, and it is verified with the simulation results of detailed models in actual scenarios, proving that MNA lossless multiplier elements can optimize the accuracy and stability of equivalent aggregation modeling of large-scale multi-unit renewable energy stations.

Miniaturized Multi-Cantilever MEMS Resonators with Low Motional Impedance.

Microelectromechanical system (MEMS) cantilever resonators suffer from high motional impedance (Rm). This paper investigates the use of mechanically coupled multi-cantilever piezoelectric MEMS resonators in the resolution of this issue. A double-sided actuating design, which utilizes a resonator with a 2.5 μm thick AlN film as the passive layer, is employed to reduce Rm. The results of experimental and finite element analysis (FEA) show agreement regarding single- to sextuple-cantilever resonators. Compared with a standalone cantilever resonator, the multi-cantilever resonator significantly reduces Rm; meanwhile, the high quality factor (Q) and effective electromechanical coupling coefficient (Kteff2) are maintained. The 30 μm wide quadruple-cantilever resonator achieves a resonance frequency (fs) of 55.8 kHz, a Q value of 10,300, and a series impedance (Rs) as low as 28.6 kΩ at a pressure of 0.02 Pa; meanwhile, the smaller size of this resonator compared to the existing multi-cantilever resonators is preserved. This represents a significant advancement in MEMS resonators for miniaturized ultra-low-power oscillator applications.

A Series Impedance Reshaping Control Method Considering PLL Dynamics for Grid-Connected Inverters Under Weak Grid Conditions

Grid-connected inverters are the key part in renewable energy power generation systems. Usually, phase-locked loop (PLL) is adopted in grid-connected inverters to achieve synchronization. However, prior-art works have revealed that the negative resistance behavior in the low-frequency band caused by PLLs may lead to system instability under weak grids. In this paper, first, a comprehensive small-signal output impedance modeling of the LCL-filtered single-phase grid-connected inverter is derived for stability analysis, where the digital control delays and PLL dynamics have been taken into account. Then, a simple but effective virtual series based impedance reshaping method is proposed. With that, the inverter system can operate stably even under a very weak grid (e.g., short-circuit ratio (SCR) is as low as 1.2). Compared with the traditional grid impedance compensation by virtually increasing grid resistance or reducing the grid inductance, the proposed method does not require grid impedance estimation and is robust against system parameter variations. Thus, its feasibility is improved. Finally, experimental tests are carried out on a single-phase 5-kW prototype, validating the effectiveness of the proposed scheme.

Geometric optimisation of a multiple coiled-up resonator for broadband and octave band acoustic absorption

This study presents a comprehensive approach to designing sound absorption metamaterials, aiming to achieve broadband absorption capabilities while maintaining a compact thickness, starting from an exceptionally low frequency of 100 Hz. By employing a parallel arrangement of resonators with varying lengths, the proposed approach exploits the envelopes of absorption frequencies to realize broad-spectrum sound absorption.An analytical model is utilized in the geometric optimization phase, accounting for inlet losses and thermo-viscous losses near the walls. The absorption for multiple ducts coupled in parallel is derived using the series and parallel impedance method. A geometric parameterization procedure is implemented to maximize normal incidence acoustic absorption, leading to design optimization for both broadband and octave-band absorbers. Design maps are established to assess acoustic performance and physical space requirements, facilitating informed decision-making in metamaterial design.Prototype fabrication and experimental validation involve 3D printing of optimized geometries using polylactic acid, followed by testing within impedance tubes according to ISO 10534–2 standards. The results demonstrate the effectiveness of the proposed method in achieving broadband sound absorption across specified frequency ranges.

Hybrid Adaptive Impedance and Admittance Control Based on the Sensorless Estimation of Interaction Joint Torque for Exoskeletons: A Case Study of an Upper Limb Rehabilitation Robot

Physiotherapy is the treatment to recover a patient’s mobility and limb function after an injury, illness, or disability. Rehabilitation robots can be used to replace human physiotherapists. To ensure safety during robot physical therapy, the patient’s limb needs to be controlled to track a desired joint trajectory, and the torque due to interaction force/torque needs to be measured and regulated. Therefore, hybrid impedance and admittance with position control (HIPC) is required to track the trajectory and simultaneously regulate the contact torque. The literature describes two structures of HIPC: (1) a switched framework between admittance and impedance control operating in parallel (HIPCSW); and (2) a series connection between admittance and impedance control without switching. In this study, a hybrid adaptive impedance and position-based admittance control (HAIPC) in series is developed, which consists of a proportional derivative-based admittance position controller with gravitational torque compensation and an adaptive impedance controller. An extended state observer is used to estimate the interaction joint torque due to human stiff contact with the exoskeleton without the use of force/torque sensor, which is then used in the adaptive algorithm to update the stiffness and damping gains of the adaptive impedance controller. Simulation results obtained using MATLAB show that the proposed HAIPC significantly reduces the mean absolute values of the actuation torques (control inputs) required for the shoulder and elbow joints in comparison with HIPC and HIPCSW.

Enhancement of Power Transfer Capability of Transmission Line Using Thyristor Controlled Series Capacitor (TCSC)

Electricity demand is increasing with the increase in urbanization and industrialization. And to meet this increasing demand, the power generation system has been rapidly increased. But along with increase in generation capacity, transmission capacity also needs to be increased simultaneously. For this, either new transmission line needs to be added in the network or power transfer capability of the existing transmission line needs to be enlarged. Latter is the more preferred choice as it involves less cost and time than to erect the new transmission lines. Power transfer capability of a transmission line can be improved by the adjustment of various parameters of a power system network such as voltage phase angles of the buses connected by the lines, impedance of the lines, etc. For this several power electronics-based FACTS devices have been developed, which are most effective in manipulating these parameters to control the power flow through the lines. In this paper, the use of thyristor-controlled series capacitor (TCSC) is highlighted. In this paper, TCSC is implemented in series with line, connecting two buses, to reduce line series impedance. From the results, it is seen that TCSC implementation increases power transfer capability and stability limit, while improving voltage regulation.

Steady-state electrical properties and loss reduction measures analysis for 220 kV tunnel cable system

This paper aims to reduce the tunnel cable systems’ power loss using different grounding and loss reduction methods. The submarine tunnel power cable project at Ningbo–Zhoushan in China is considered here as a case study. The cable is divided into micro-element segment, and their nodal admittance matrices are established using the telegraph equation. This approach helps to avert the prerequisite of diagonalizing the propagation matrix. For the analysis of induced voltage and circulating current in the cable sheath, the cascading algorithm is used while considering the presence of grounding node. It is found that the mixed cable laying methods and different lengths between minor sections result in a high circulating sheath current. This study finds that coordinating the amplitude and phase angle of series impedance inserted at the cross-bonded joint can reduce the cable system's power loss.

Analytical computation of driving point impedance in mutually coupled inhomogeneous ladder networks

SummaryElectrical systems are traditionally modeled as homogeneous ladder networks, disregarding the inherent inhomogeneity found in real‐world systems. This can result in inaccuracies in analysis and design. The driving point impedance (DPI) is a crucial parameter for studying electrical systems, as it can be conveniently measured at the terminals. However, existing methods for calculating DPI have limitations, including increased complexity, high computational demands, convergence issues, and challenges in capturing high‐frequency effects. A new approach for computing DPI of inhomogeneous ladder networks, reducible to series and shunt impedance circuit form, is introduced in this research. The method is based on state‐space formulations and projective matrix analysis. It offers improved accuracy as compared with existing methods and can be applied to a wide range of networks. Simulation results from a six‐section mutually coupled inhomogeneous ladder network validate the effectiveness of the proposed approach. This research addresses the disregarded factors of inhomogeneity and mutual coupling within traditional approaches, presenting a significant advancement in the analysis and design of electrical systems.

Design and Analysis of Complementary Metal–Oxide–Semiconductor Single-Pole Double-Throw Switches for 28 GHz 5G New Radio

We propose a single-pole double-throw (SPDT) switch with low insertion loss (IL), high isolation, and high linearity for a 28 GHz 5G new radio. The transmit (TX) path is a π-network consisting of a parallel dynamic-threshold metal–oxide–semiconductor (DTMOS) transistor, M1, with large body-floating resistance, RB (DTMOS-R M1), a series one-eighth-wavelength (λ/8) transmission line (TL), and a parallel capacitance, Cant. The series λ/8-TL in conjunction with the parallel Cant and transistors’ capacitance constitute an equivalent λ/4-TL with a characteristic impedance of 50 Ω. This leads to low IL in the TX mode and decent isolation in the receive (RX) mode. The RX path is an L-network constituting a series impedance (of parallel inductance L1 and DTMOS-R M2) and a parallel DTMOS-R M3. This leads to a decent IL in the RX mode and isolation in the TX mode. The first SPDT switch (SPDT SW1) is designed and implemented in a 90 nm complementary metal–oxide–semiconductor (CMOS) with a top metal thickness (TMT) of 3.4 μm. A comparative SPDT switch (SPDT SW2) in a 0.18 μm CMOS with a thinner TMT of 2.34 μm is also designed and implemented. In the TX mode, SPDT SW1 achieves a measured IL of 0.67 dB at 28 GHz and 0.58–1 dB for 17–34.9 GHz and a measured isolation of 44.3 dB at 28 GHz and 25.6–62.3 dB for 17–34.9 GHz, one of the best IL and isolation results ever reported for millimeter-wave CMOS SPDT switches. The measured input 1 dB compression point (P1dB) is 28.5 dBm at 28 GHz. Moreover, in the RX mode, SPDT SW1 attains a measured IL of 1.9 dB at 28 GHz and 1.83–2.1 dB for 25–38.3 GHz and an isolation of 25 dB at 28 GHz and 24.5–27 dB for 25–38.3 GHz. The measured P1dB is 24 dBm at 28 GHz.

Concept of Condition Monitoring for AC-DC Converter Output Capacitors via Discriminative Features

This paper discusses recent research on the condition mon- itoring (CM) approach for aluminium electrolytic capacitors (AEC) used in power electronics equipment such as switched- mode power supplies (SMPS). Capacitors are identified as the most critical component with the highest percentage of failure in AEC. CM offers a better paradigm for AEC due to its long- lasting ability (endurance). This study proposes accelerated life testing through electrical stress and long-term frequency testing for the AEC component. An experiment test bench was set up to monitor the critical electrical parameters such as dissipation factor (D), equivalent series resistance (ESR), capacitance (Cp), and impedance (Z), which serve as health indicators (HI) for the evaluation of the AECs. Time-domain features were extracted from the measured data, and the best features were selected using the correlation-based technique. This research contributes to developing a cost-effective CM approach for AECs used in power electronics equipment, which can reduce downtime and maintenance costs.

Passivity-Oriented Impedance Shaping for LCL-Filtered Grid-Connected Inverters

The passivity theory provides an effective way to tackle the instability due to the inverter-grid interaction, which tells that the system stability can be guaranteed if the grid impedance and the inverter output impedance are both passive. Since the grid impedance is generally passive, the system stability can be immune to the grid impedance variation if the inverter output impedance is also passive. This paper develops a series and parallel impedance shaping method to ensure that the output impedance of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> -filtered grid-connected inverter is dissipative up to the Nyquist frequency. Since the inverter output impedance can be decomposed into two passive elements and one active element, its non-dissipative property results from the latter, and thus the virtual series impedance shaping is introduced to cancel out the active element. Unfortunately, it poses impact on the low-frequency loop gain and system phase margin in the meantime. To alleviate this impact, a high-pass filter is inserted in the series impedance shaping function. Subsequently, a virtual parallel impedance is introduced to enhance the passivity robustness, such as against filter parameter variations. Moreover, the proposed method does not require any additional sensors. Experiments from a 6-kW prototype confirm the effectiveness of the proposed method.

Current-Fed Phase-Shifted Full-Bridge Converter With Secondary Harmonic Current Reduction for Two-Stage Inverter in Energy Storage System

For the low voltage, high current, isolated DC-DC converter applications, current-fed type converter has the chance to achieve higher efficiency due to the lower transformer root mean square current compared with other well-known converters such as dual active bridge or LLC. A current-fed phase-shifted full-bridge, CFPSFB converter has the advantages of nearly full range zero-voltage-switching and soft-commutating without large size of passive or active snubber circuit because the phase-shift of secondary full-bridge is controlled to be proportional to the input current. However, as a front-end stage of a single phase inverter, the input secondary harmonic current (SHC) propagating from the output AC load may cause large voltage spike to damage the primary MOSFETs due to losing the soft-commutating property. SHC may also reduce the conversion efficiency and the lifespan of battery intensely. This paper proposes a simple control scheme based on virtual series impedance method with a notch filter in control loop to reduce the SHC and maintain good dynamic performance. A small-signal model of CFPSFB for a reliable controller design is derived and verified by simulation. A 48 V/3 kW maximum output power inverter prototype is built to verify the theoretical analysis. The maximum efficiency of the DC-DC stage is 97.4% and the peak to peak SHC is less than 10% of the average input current.

Impact of solenoid effects on series impedance of three-core armoured cables

Impact of solenoid effects on series impedance of three-core armoured cables

Numerical Modeling of Litz Wires Based on Discrete Transpositions of Strands and 2-D Finite Element Analysis

A new numerical method is proposed to model the electric behavior of a single bundle litz wire with a large number of strands. The method is first based on a two-dimensional (2D) finite element analysis (FEA) to evaluate the series impedance matrix of a multistrand cable with parallel strands. Then a mathematical algorithm for a discrete transposition of all strands is applied to simulate the bunching and twisting of the strands. The new procedure is very efficient and accurate, as demonstrated by the excellent agreement of the numerical results with those obtained by experiments or with 3D FEA. The error in terms of AC-to-DC resistance ratio is less than 10% in the tested configurations. Furthermore, the computational cost of the proposed method is very low and comparable with a simple 2D FEA.

Improving fault ride‐through capability for doubly‐fed induction generator based on improved system structure and corresponding control scheme

AbstractAlthough there are many methods to improve the fault ride‐through (FRT) capability of doubly‐fed induction generator (DFIG) systems at present, each method has its shortcomings, especially the applicability under different voltage dips (VDs), so an improved system structure with a dynamic switching topology and a corresponding control scheme is proposed. Based on the mechanism analysis that the series impedance of the stator can effectively reduce the overcurrent on the rotor side, and considering the feasibility of the FRT scheme in engineering, the dynamic switching topology is designed. The selection of theoretical parameters in different cases is also analysed and designed. Simultaneously, to cooperate with the hardware measures, the control scheme of the rotor side converter (RSC) under different conditions is also improved. The RSC can use the control scheme of active flux attenuation to effectively and quickly reduce the overcurrent on the rotor side, and use reactive power support to accelerate the voltage recovery. The novelty of the FRT scheme is that the scheme can dynamically adjust the topology structure and control scheme under different voltage dips. Thus, its ride‐through performance during fault is better under different conditions. A simulation model of the improved system structure and control scheme is built on the MATLAB/Simulink platform. Through the comparison of simulation data, the validity and correctness of the proposed FRT scheme are verified.

Analytical formulas for calculating the electrical characteristics of multiparameter arbitrary configurational homogenous ladder networks

SummaryMost electrical systems are represented as ladder networks made up of resistances, inductances and capacitances. Electrical characteristics of these networks, such as voltages, currents and equivalent impedance, are difficult to compute because they require solving multiple differential‐algebraic equations. Further, circuit simulator‐based modelling is a time‐consuming and tedious process for simulating large networks with multiparameters present in various configuration. This paper presents generalised analytical formulae for computing the electrical properties of any multiparameter arbitrary section homogenous ladder network that can be reduced to series and shunt impedances. Circuit principles, chain matrix decomposition and linear transformation are used to derive the symbolic expressions. Simply plugging the values of the series and shunt impedances, as well as the number of sections, into the derived expression yields the impedance. Thereafter, the calculated impedances can be used to calculate the nodal voltages and mesh currents. Simulation results of a six‐section homogeneous ladder network are presented and compared with those of other existing techniques to validate the derived expressions. The derived expressions eliminate the need for recursive relations, complex integro‐differential equations, large state‐space matrices and simulator‐based circuit modelling, which are all clearly advantageous.

Unbalance compensated distance relay for active distribution networks

Integration of Distributed Energy Resources (DER) into the Active Distribution Networks (ADN) causes issues in conventional overcurrent protection. Additionally, another conventional protection, such as the distance function, has been used, but ADN characteristics require new well-fitted approaches. This paper proposes a strategy to improve conventional distance relays when applied in unbalanced distribution lines. The strategy is based on the relay’s current and voltage measurements and the line series impedance matrix. Different overhead line cases are studied considering several pole geometrical arrangements and fault types. Based on the results, the new set of equations for distance-based protection can achieve a more accurate fault impedance estimation, with a maximum error of 0.1% in the analysed situations and despite the fault conditions. The high proposal performance and the straightforward application make this proposal suitable for the nowadays ADN protection.