Frequency Characteristics Of Impedance Research Articles

Analysis of AC filter detuning characteristics and improvement measures in converter station

Shift of parameters of the double-tuned AC filter component and failure in prompt correction of detuning frequency may affect the filtering effect of the AC filter. Therefore, this paper studies impedance-frequency characteristics of the double-tuned AC filter according to detuned recording data of the A-typed double-tuned AC filter in the Congxi converter station. It analyzes the variation of the impedance-frequency characteristic curves and relative change rate of resonant frequency as there are deviations between actual values and rated values of each filter capacitance and inductance elements in different degrees, and concludes that variation of the parameter of each element in different degrees may cause different deviations of resonant points of the double-tuned AC filter. MATLAB simulation has proved it can reduce the detuning degree and improve the filtering performance of the filter by adjusting the parameters of the variable reactor to change in the opposite direction of the parameters of the resonant capacitor.

Algorithm for identifying RLC parameters

The article discusses an algorithm capable of determining the substitution scheme of the investigated circuit and calculating the parameters of its elements without operator intervention, based on the admittance frequency characteristics. This algorithm enhances the functional capabilities of RLC meters and can be applied to solve practical problems related to identifying the substitution scheme of the investigated circuit. As an RLC meter measures the total resistance only at one or several fixed frequencies, obtaining an understanding of the substitution scheme from these measurements is challenging. To select the substitution scheme, an analysis of the impedance or admittance frequency characteristics is required. Typically, this analysis is performed manually and is time- consuming. The proposed algorithm automates the analysis of the admittance frequency characteristics. The algorithm associates values and the sequence of slopes of the admittance frequency characteristics with an array of known sequences and slope values for known substitution schemes. The calculation of substitution scheme parameters is based on the resonance frequencies and the heights of zero slopes. To minimize the impact of noise on result accuracy, a synchronous signal detection method is employed. The article introduces a criterion for assessing the algorithm's performance and conducts testing on several types of circuits. During testing, the relative error in calculating substitution scheme parameters was evaluated, with a maximum value not exceeding 6 %.

Analytical method of DC input impedance for stability analysis of IPM motor drive system

AbstractThis paper proposes an analytical calculation method of frequency characteristics of DC input impedances of an IPM motor drive system for design and stability analysis by the impedance method. The proposed method is based on an averaged frequency model linearized at an operating point. The developed small‐signal model considers control principles and mechanical perturbations. It is an analog and digital mixed model which is controlled by a digital signal processor system. Analysis examples of frequency characteristics for the impedance method by the proposed method are investigated and validated analytically and experimentally.

Measuring impedance frequency characteristics of magnetic rings with DC-bias current

This paper reports on a comprehensive study on a measurement method for the impedance characteristics in the frequency domain of magnetic rings as a function of DC-bias current up to saturation. The reported measurements in a one-wire coil arrangement with DC-bias current reproduce the operating conditions of rings used in high-power equipment and are useful for the development of circuit models used in power system simulators. The method and its key features are shown on an example of a nanocrystalline ring with large physical dimensions relevant for heavy power equipment. Low magnetic permeability of the ring material and large size of the ring were chosen as the most challenging case with respect to measurement system arrangement, allowing us to highlight the key aspects of the method. The measurement results are reported for frequency ranging from 50 Hz to 30 MHz and for the DC-bias current up to 800 A. The problems and difficulties encountered are highlighted and discussed how they were controlled and overcome.

Radiofrequency Sensing Method and Algorithm of Inhomogeneous Conductive Structures

The paper proposes a method and algorithm for frequency probing of the internal inhomogeneous structure of electrically conductive objects based on the skin effect for diagnostics and control. The essence of the method consists in frequency control of electromagnetic field penetration depth into an electrically conductive object, and according to the measured frequency characteristic of the surface impedance, the profiles of electrophysical parameters characterizing the structural properties of the medium under study. An electrical model of an inhomogeneous medium with distributed RL parameters has been developed on the basis of electrodynamic presentations. The relationship of resistance and inductance linear parameters of the electrical model with the local parameters of the conductive medium results from their relationship with the electrical resistivity and magnetic permeability of the medium. The mathematical model of an inhomogeneous conducting medium is based on the Riccati equation with respect to the impedance characteristics of the medium. The mathematical statement of the probing problem is formulated as an inverse operator problem solution of mathematical physics. A numerical iterative algorithm for inhomogeneous medium frequency sensing based on Tikhonov regularized solution of the inverse problem is proposed. The proposed algorithm can also be extended to probe the internal structure of semiconductor and low-conducting objects containing a capacitive component in the impedance. The results of numerical simulation of the proposed algorithm for various distributions of inhomogeneity in the frequency characteristics of the impedance, measured with a known error, are presented. Solutions to various control and measurement problems in thermophysical applications based on the proposed method are given in the patents of the authors.

Simulation and Analysis of Harmonic High Voltage Filters for Wind Farm

With the rapid development of the wind power industry, the total installed capacity of wind power has increased dramatically worldwide, and a large number of wind power installations need to be connected to the grid. In wind turbines, voltage flicker due to output power fluctuations caused by wind speed changes, and the application of a Voltage Source Converter (VSC) cause harmonic richness and other power quality problems to become more and more prominent. In this regard, the research is focused on the harmonic and reactive current distribution, impedance frequency characteristics, and voltage distortion rate of several offshore wind farm access systems, including the establishment of a harmonic current simulation model of the offshore wind farm delivery system, simulation analysis of network impedance frequency characteristics, simulation analysis of harmonic currents, and proposed a preferred filtering scheme. Taking into full consideration the characteristic harmonics of the wind farm, the system resonance generated by the submarine cable and the background harmonic level of the power grid, combined with the simulation results of the harmonic voltage, harmonic current, and network impedance frequency characteristics of each node, the technical solution of adding a direct-mounted high-voltage filtering device to the 220 kV bus at the metering station is proposed, which can destroy the system resonance conditions of the 3rd to 6th times of the submarine cable. Various wind farms and system operating conditions are able to form a stable harmonic absorption point to avoid the problem of harmonic amplification.

A modeling method for the DC side simplified impedance of line commutated converter based on the simplified switching function

With a large amount of new energy access and the wide application of high voltage direct current (HVDC) transmission technology based on line commutated converter (LCC), it is of great significance to study the impedance frequency characteristics of the converter to analyze the stability of the LCC-HVDC system. Due to the complexity and inefficiency of the existing modeling techniques, in this paper, a simplified impedance modeling method for the DC side of LCC based on the simplified switching function is proposed. Firstly, the commutation process of LCC is deduced according to the converter valve opening sequence and circuit principle, and the simplified switching function of LCC is proposed. Next, based on the dynamic phasor method, through the analysis and calculation of harmonic transmission between the AC and DC sides of LCC, the simplified impedance of the DC side of LCC is obtained. Then, a simulation model is established in PSCAD, and the impedance scanning results of the simulation model show that the error is small between the method proposed in this paper and the method without simplification, which verifies the validity of the proposed model. The proposed method can reduce modeling complexity and provide a fast calculation model of the DC side impedance of LCC for analyzing the stability of large complex transmission systems.

Impedance-frequency characteristic analysis of bypass damping filter in suppressing AC–DC system’s subsynchronous resonance

Recently, subsynchronous resonance (SSR) in HVDC transmission is considered to be related to electronic converter equipment and complex control systems. Aiming at the subsynchronous resonance problem caused by frequent topology changes of AC–DC systems, this paper firstly proposes an impedance-frequency characteristic analysis method based on Thevenin Equivalent and Fast Fourier Transform (FFT) algorithm. This method is used to analyze the impedance frequency characteristics of AC–DC systems after the bypass damping filter (BDF) is configured. Firstly, based on the IEEE first benchmark model, the mechanism of BDF in suppressing subsynchronous resonance is explained by quantitative analysis, and the BDF parameter setting method is proposed. Then, the time domain simulation model of a single-machine HVDC system with BDF is established in PSCAD/EMTDC. Finally, according to Thevenin’s theorem, the equivalent structure of each subsystem is simplified, and the FFT algorithm is used to solve the harmonic equivalent impedance of each subsystem. After BDF is configured, the mechanical resonance frequency ”transfers” from 16Hz to 10Hz, and the minimum electrical damping changes from -0.9637 to -0.4581. The results show that the BDF configuration can change the impedance-frequency characteristics of the system, thereby improving the electrical damping in the torsional vibration mode in a targeted manner, and has a certain effect on suppressing the subsynchronous resonance of AC–DC systems.

Direct Interface Circuit for Capacitive Sensors Affected by Parasitic Series Resistances

This article presents a novel circuit to directly interface a capacitive sensor affected by parasitic series resistances to a digital processor (DP). The presence of such resistances distorts the estimation of the capacitance to be measured. Current measurement procedures for these sensors, such as impedance-frequency characteristics, are complex and require significant hardware resources, power consumption, and time. To eliminate these drawbacks, a new circuit based on the so-called direct interface circuits (DICs) is introduced, which performs the digital reading of the sensors taking advantage of the presence of DPs in many applications. The hardware requirements in the new design are minimal: just two resistors and an operational amplifier in addition to the DP. The circuit requires only two time measurements to estimate sensor capacitance. These are obtained during a single capacitor charging-discharging process, simultaneously reducing power consumption and measurement time. The circuit has been implemented using a field-programmable gate array (FPGA), as the DP, in a general-purpose board to evaluate its performance. Although it is not an application-specific design, the circuit shows a maximum systematic error of 0.37% for capacitances in the 100 pF–96 nF range with parasitic series resistances up to 1200 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $ </tex-math></inline-formula> . The maximum measurement time for this range is just 4.5 ms.

Equivalent circuit of an inductor on a nanocrystalline core with a high magnetic permeability

Based on the measured impedance of the inductors based on a toroidal core wound from a thin (18 m) nanocrystalline tape, with a different number of winding turns, an equivalent high frequency (0 Hz - 500 MHz) circuit model was built. The equivalent circuit model was built taking into account the physical processes occurring in the inductor: effect of wire resistance, effect of core material, mutual effect of wire and core material. The attempt explaining why the frequency characteristics (modulus and phase) of the inductor complex impedance have such a character in a wide frequency band (up to 500 MHz) was made. It was shown that for constructing an equivalent circuit model (structure and parameters), measuring only the inductors resistance modulus is not enough. It is also necessary to measure the phase of the inductor complex resistance, which is ignored in many works on the synthesis of an e inductor equivalent circuit. The fundamental difference between the operation of a nanocrystalline core and a ferrite core as applied to high-frequency filters is shown.

Comparative Analysis of a New Class of Symmetric and Asymmetric Supercapacitors Constructed on the Basis of ITO Collectors

The paper presents the results of research on new electroconductive polymer materials, based on polypyrrole, for the different supercapacitor constructions, i.e., the symmetric and asymmetric constructions. All the supercapacitors considered contain ITO collectors. Measurements of the complex impedance frequency characteristics were performed for these elements using the electrochemical impedance spectroscopy (EIS) method. Selected fractional-order models, known from the literature, have been used to model the impedance of these elements. The Particle Swarm Optimization (PSO) algorithm was used to estimate the model parameters. Selected estimation results, their comparison, and conclusions are also presented in the paper. The type of active electrolyte component has the greatest impact on the shape of the impedance frequency characteristics. In most cases, the highest capacitance values and the smallest resistance values were obtained for asymmetric supercapacitors.

Equivalent circuit of a dielectric in a wide frequency range (0 Hz – 500 MHz)

Based on the measured impedance of the dielectrics an equivalent high frequency (0 Hz - 500 MHz) circuit model was built. The equivalent circuit model was built taking into account the physical processes occurring in the dielectric. The attempt explaining why the frequency characteristics (modulus and phase) of the dielectric complex impedance have such a character in a wide frequency band (up to 500 MHz) was made. It was shown that for constructing an equivalent circuit model (structure and parameters), measuring only the dielectrics resistance modulus is not enough. It is also necessary to measure the phase of the dielectric complex resistance, which is ignored in many works on the synthesis of an e dielectric equivalent circuit.

Elucidation of impedance frequency characteristics of cast resin transformer and application to partial discharge diagnostic method

AbstractIt is desired to establish an insulation diagnosis method for cast resin transformers (CRTrs), which is often used in distribution systems. Partial discharge (PD) detection is considered to be an effective method, but its phenomenon has not yet been clarified. This paper presents investigation on the frequency characteristics of PD generated inside CRTrs to improve PD detection technology. It is clarified that dominant frequency of PD signal detected by a high frequency current transformer (CT) depends on the frequency characteristics of the impedance between the primary and secondary windings. It is suggested that the dominant frequency could be predicted in advance by analysis using a high‐frequency equivalent circuit model of CRTrs. PD diagnostic technology that utilizes the frequency characteristics of the CRTrs impedance has also been proposed. It is found that a PD generated external to CRTrs does not have resonance at the dominant frequency of the CRTrs itself, even though it passes through the CRTrs. In conclusion, it is suggested that the frequency analysis of CRTrs impedance could identify degraded CRTrs and external noise.

Equivalent circuit of a ferrite-wound inductor in a wide frequency range (0 Hz – 500 MHz)

Based on the measured impedance of the inductors wound on various ferrite cores and with a different number of turns, an equivalent high frequency (0 Hz 500 MHz) circuit model was built. The equivalent circuit model was built taking into account the physical processes occurring in the inductor: effect of wire resistance, effect of core material, mutual effect of wire and core material. The attempt explaining why the frequency characteristics (modulus and phase) of the inductor complex impedance have such a character in a wide frequency band (up to 500 MHz) was made. It was shown that for constructing an equivalent circuit model (structure and parameters), measuring only the inductors resistance modulus is not enough. It is also necessary to measure the phase of the inductor complex resistance, which is ignored in many works on the synthesis of an e inductor equivalent circuit.

ИССЛЕДОВАНИЯ ЗВУКОИЗОЛИРУЮЩИХ МАТЕРИАЛОВ В СЕЛЬХОЗМАШИНОСТРОЕНИИ НА РОБОТИЗИРОВАННОМ СТЕНДЕ

The article provides information about a stationary robotic stand designed for experimental research, a description of the operation of this stand is given. A feature of the stand is the implementation of a research facility with the possibility of programmatic research without the obligatory presence of a researcher. A remotely controlled power amplifier, a remotely controlled sound generator and a personal computer with special software are used. The sound source is located close to one of the end walls of the soundproof chamber. The sound receiver in the form of a high-precision microphone is located on the opposite end wall of the soundproof chamber and is connected to the sound processing module, which is connected to a personal computer. The developed stand is an example of the concept of robotic research, a direction for improving the methodology of research work. A description of the design of the stand is given; information about known similar research equipment is given. A scheme of the stand and a description of its design are given. Some results of studies of soundproof materials are given. The effect of the structure of soundproofing materials on the frequency characteristics of acoustic impedance is shown. The essence of test bench automation lies in programmatic change of research modes for each experiment. The robotic stand ensures the reliability of the results of experimental studies, allows you to speed up the results.

Passivity‐based stabilization of converter in DC power supply system using feedforward control

AbstractThis paper proposes a passivity‐based stabilization control of a converter in a DC power supply system using feedforward (FF) control to improve output frequency impedance characteristics that satisfy the Nyquist stability criterion. The principle is that the output impedance is designed to be passive, and the system is sufficiently stable for any filter impedances. The new design principle for the proposed stabilization method consists of four steps. First, the state feedback (FB) control gains with a mitigated integral compensator are designed to possess a good response characteristic according to the optimal control. The designed characteristic of the output impedance may not be passive at a lower frequency band due to an essential characteristic of an integral compensator. Second, the integral characteristic is modified and a resistive characteristic is added to the band by a new FF control design based on a fitting method to make the total characteristic passive and to ensure stability. Third, the correction coefficients are tuned to eliminate a deviation between the measured and reference output voltage values at transient operations. Finally, the system passivity is re‐checked, and a resistive characteristic is re‐added using the FF control design if a nonpassive band exists. The effectiveness of the proposed method to render the system passive and stable is investigated and validated using simulated and experimental results.

Elucidation of Impedance Frequency Characteristics of Cast Resin Transformer and Application to Partial Discharge Diagnostic Method

Elucidation of Impedance Frequency Characteristics of Cast Resin Transformer and Application to Partial Discharge Diagnostic Method

A novel method for effecting flexible guided wave propagation in elliptical vibration cutting

As a key part of elliptical vibration cutting (EVC) technology, a two-dimensional ultrasonic elliptical vibration cutting (UEVC) device has become a prevalent area of importance and research interest. This paper dissects through the conventional structural design and creatively proposes the UEVC device with flexible guided wave propagation. The device resolves the problems of poor coupling efficiency of two-way excitation signal, complex structure design, non-orthogonal, and the difficulty in controlling the ellipse trajectories of the tool tip. It has been confirmed that a flexible guided wave exhibits an effective unidirectional propagation and lateral load decoupling ability via establishing its system dynamic response and frequency impedance characteristics. Here, we explain the coupling mechanism of the two-way flexible guided wave in the UEVC device. Results suggested that the experimental measurement of the impedance for the cutting device and the individual transducer shows that the cutting device with the transducer and the tool bar connected by the flexible guided wave has a lower impedance increase ratio compared to the individual transducer, and hardly influence the tool bar mode of the cutting device. At the same time, the tool tip trajectory of the cutting device having a phase difference of 90° showed a satisfactory “elliptical” shape, while the microstructure processed by the tool tip ellipse trajectory with a phase difference of 60° reached a burr-free state. Theoretical and experimental findings reveal that the flexible guided waves exhibit excellent weak coupling characteristics in the non-transmitting direction. This is convenient to the independent, orthogonal and stable propagation of signals in the two directions. Based on flexible guided wave propagation technology, our findings provide theoretical foundation and application value for the design of a two-dimensional UEVC device.

Impedance Modeling and Analysis of Medium-Frequency Oscillation Caused by VSC-HVDC Connected to Local Weak Grid and DFIG-Based Wind Farms

In the northwest of China, a strategy to transmit the wind-thermal–bundled power from the local grid and doubly fed induction generator (DFIG)–based wind farms through a voltage source converter–based HVDC (VSC-HVDC) can be widely applied. However, since the local grid is usually weak, a new type of electrical oscillation in the medium-frequency region may occur in the sending-end converter (SEC) of VSC-HVDC with PQ-control. The mechanism of this oscillation caused by the interaction between the DFIG, local grid, and SEC is not entirely understood. In this study, the sequence impedance model of the sending-end converter (SEC) of VSC-HVDC with the PQ-control outer loop and PLL is derived with the explicit analytic expression, and then, the oscillation mechanism is explored based on the intuitive analysis of the system impedance frequency characteristics. Compared with the subsynchronous oscillation (SSO) caused by the DFIG or power inverter, the theoretical analysis shows that this medium-frequency oscillation (MFO) mainly originates from the SEC due to its negative damping effect between about 100 and 200 Hz. In addition, the impact of the system controller parameters and operating conditions of the DFIG, local grid, and SEC on the oscillation characteristics is analyzed in detail. Finally, the correctness of the theoretical analysis is validated by time-domain simulation.

High frequency impedance characteristics of a tunable microplasma device

Computational studies on high frequency impedance characteristics of a microplasma device are reported. While microplasma is ignited using a primary excitation signal, frequency response of plasma impedance is determined by a secondary high frequency probe signal with significantly lower voltage amplitude such that it does not influence the plasma parameters. The computational model utilizing the drift–diffusion approximation is first validated by comparing with experimental data for microplasmas ignited at pressures ranging from 1 to 5 Torr. In spite of quantitative discrepancies, good overall agreement is obtained between the measured frequency response of impedance of the discharge. Comparisons are also presented for various plasma parameters including mean electron number density, sheath thickness, mean electron temperature, and collision frequency that were inferred from the impedance measurements. The computational model is then used to perform simulations of near-atmospheric pressure microplasmas with the probe signal frequency ranging from 3 to 20 GHz. The simulations demonstrate the presence of a resonance frequency at which the impedance vanishes. More importantly, it is shown that this resonant frequency can be tuned effectively by suitably modifying the operating parameters (gap size, pressure, and excitation voltage). The simulated impedance characteristics are used to determine the effective plasma inductance and capacitance using a non-linear fitting approach, thereby showing the dependence of these electrical parameters on the plasma operating conditions.