Equivalent Impedance Method Research Articles

Novel Double-Damped Tuned AC Filters in HVDC Systems

This paper presents a performance analysis of novel double-damped tuned alternating current (AC) filters in high voltage direct current (HVDC) systems. The proposed double-damped tuned AC filters offer the advantages of improved performance of HVDC systems in terms of better power quality, high power factor, and lower total harmonic distortion (THD). The system under analysis consists of an 878 km long HVDC transmission line connecting converter stations at Matiari and Lahore, two major cities in Pakistan. The main focus of this research is to design a novel AC filter using the equivalent impedance method of two single-tuned and double-damped tuned AC filters. Additionally, the impact of the damping resistor on the AC channel is examined. The THD of the HVDC system with and without current AC filters was also compared in this research and a double-damped tuned AC filter was proposed. The results of the simulation represent that the proposed double-damped tuned AC filter is far smaller in size, offers better power quality, and has a much lower THD compared to the AC filters currently in place in the converter station. The simulation analysis was carried out utilizing power systems computer-aided design (PSCAD) software.

Analytical Model and Experimental Verification of Permanent Magnet Eddy Current Loss in Permanent Magnet Machines With Nonconcentric Magnetic Poles

Permanent magnet synchronous motors (PMSMs) with nonconcentric magnetic poles (NCMP) structure are widely used as high-precision servo motors. The current subdomain method mainly equates the NCMP to a rectangular magnet to make each subdomain boundaries of magnet parallel when calculating the magnet eddy current loss (ECL), which results in a lower accuracy of the calculation. This article divides the NCMP into nonconcentric region and concentric region along the radial direction. The nonconcentric region is further divided along the circumferential direction, and each divided region has a single thickness. Based on the subdomain method, a novel analytical method of magnet ECL in PMSMs with NCMPs is proposed. Moreover, the three-dimensional distribution coefficient of ECL in the NCMP is derived by the equivalent impedance method. The effects of eddy current reaction and stator slotting are taken into account to improve the calculation accuracy. Then, through theoretical derivation, the relationship between the minimum magnet loss and the pole parameters is obtained, which provides a reference for the design of NCMPs. Finally, the loss separation experiment is performed on four prototypes with NCMPs. The experimental results, finite element method results and analytical results are compared to verify the correctness of the model.

A method of DC short-circuit analysis and thyristor determination for high power nuclear fusion converter

In the design of fusion power supply, the DC side fault analysis and the thyristor determination of converter is a very important step. In this paper, to improve the accuracy of fault current prediction and reduce the waste of device selection, the equivalent impedance method of the converter system is proposed to calculate the converter fault current, and then the formula of steady and transient parameters of thyristor is proposed. The equivalent impedance model is established for typical faults of converter, and the calculated fault current is compared with the simulation result. Finally, the style and number of thyristors in parallel is determined by the consideration of junction temperature and fault current thermal accumulation in short time (I2t).

System-level modeling and design method of an array of piezoelectric energy harvesters under typical ambient vibration

Vibration-based piezoelectric energy harvesting has received significant attention recently due to its ability to convert vibration energy from the surrounding environment into electric energy to power wireless sensors. In this work, two typical types of vibration sources, that is, engine-induced floor vibration and train-induced bridge vibration, are considered. The array of piezoelectric energy harvesters (PEHs) is adopted to harvest the energy of vibration with different frequencies. The aim of this work is to give a stable system-level modeling method and present a method to select operating point for designing energy harvesters connected with nonlinear energy harvesting circuits under complex excitations. The system-level modeling method is based on Krylov’s subspace model order reduction algorithm. With the help of this method, the harvester can be modeled using conventional finite element software and co-simulated with nonlinear circuits at a system-level. The proposed method is validated using equivalent circuit method, equivalent impedance method and experiment results, and then employed to investigate the performances of harvesters under typical real vibrations. Finally, design suggestions for PEHs under different types of vibration sources are presented.

Analytical Modeling for Rotor Eddy Current Loss of a Surface-Mounted PMSM With Both Non-Ferromagnetic Conductive Retaining Sleeve and Shielding Cylinder

It is recognized that the rotor with shielding cylinder (SC) is one of the effective measures to restrain the rotor eddy current loss (RECL) for high-speed surface-mounted permanent magnet synchronous motors (PMSMs). At present, the RECL of PMSMs with multilayer composite rotor structure is mainly analyzed by the finite element method (FEM), which has obvious shortcomings in time-consumption and the mesh generation of thin SC. In this paper, a multi-layer subdomain analytical model for calculating the RECL of high-speed PMSMs with both non-ferromagnetic retaining sleeve and SC is proposed by taking the effects of eddy current reaction, stator slotting and current harmonics into account. Moreover, the 3-D distribution coefficient of eddy current in the SC is derived by the equivalent impedance method and the effects of temperature on the conductivity of the SC and RECL are obtained through equivalent thermal network (ETN) model. Based on the analytical model, the SC parameters are calculated to obtain the variation ranges when the RECL is minimum. Finally, the C-shape core experiment was built up to verify the correctness of the multilayer analytical model under different shielding layer conductivities and thicknesses.

Design of soft and hard composite patterns for electromagnetic scattering controlling at both normal and grazing incidence

AbstractIn this paper, the soft and hard composite patterns for electromagnetic scattering control at both normal and grazing incident angle is proposed. The soft and hard parts are composed of dielectric substrate sandwiched by transverse or longitude metal strips with metal via and the perfect electrical conductor ground, and these two parts are combined at a certain inclination angled to form the soft and hard composite patterns. The simulation results demonstrate that the proposed composite patterns have the monostatic radar cross‐section (RCS) reduction of 20.79 and 18.36 dB at 11.24 GHz under normal incidence for transverse electric polarization and transverse magnetic polarization, respectively. Also, this structure achieves 2.78 and 5.43 dB monostatic RCS reduction under grazing incidence from 60° to 90°. The simulation results are in good agreement with the experimental ones. The physical mechanisms of the proposed composite patterns can be elucidated by the equivalent impedance method based on its near‐field distribution. The proposed composite patterns can be functionalized by changing the electromagnetic parameters of the soft and hard surfaces, which has a great potential to be used as the traveling wave antenna enclosure for scattering control.

Broadband energy harvester for low-frequency rotations utilizing centrifugal softening piezoelectric beam array

Harvesting the rotational energy has drawn great attention in the past decade with its abundance in our living environment and its great potential to power the wireless transmitter. However, issues exist that small-scale and resonant-frequency-based linear harvesters typically have high natural frequencies and narrow operating frequency bandwidth. Therefore, to design a broadband energy harvester for low-frequency rotations, this paper proposes the centrifugal softening beam array harvester. The broad bandwidth is achieved by arranging groups of inverted piezoelectric beams at different rotational radii in a straight array, which results in different centrifugal softening coefficients. This eliminates the tedious work of pre-designing and manufacturing beams with different geometries in a conventional beam array harvester. Furthermore, the centrifugal softening effect can decrease the resonant frequency of the harvester, leading to the higher energy output under low-frequency rotations. In addition, the analytical model of such centrifugal softening beam array with different interface circuits is firstly proposed based on the equivalent impedance method. Results show that for both parallel and series connections of piezoelectric beams, the output power is highest and the bandwidth is broadest with the parallel-SSHI circuit compared with those with the standard AC/DC and series-SSHI circuits. Despite that both the parallel-SSHI and series-SSHI circuits can significantly improve the output power compared with the standard circuit, the series-SSHI circuit has a degradation on the frequency bandwidth compared with the other two circuits. Specifically, when attached to the parallel-SSHI circuit, for ten identical parallel-connected beams with decreasing centrifugal softening coefficients, the 3 dB bandwidth can be broadened by up to 1240.7% within the frequencies lower than 20 Hz compared with that of a single beam.

Polarization Properties of Obliquely Incident EM Waves in Nonuniform Weakly Ionized Dusty Plasma

Effects of nonuniform weakly ionized dusty plasma on the polarization properties of obliquely incident electromagnetic (EM) waves were theoretically investigated in this paper. The dielectric coefficient of magnetized dusty plasma is obtained based on the Bhatnagar–Gross–Krook collision model. Then, the effects of external magnetic field, dust radii, and density on the polarization mismatch loss of obliquely incident EM waves in the L-band were analyzed using the equivalent impedance method. Results indicate that the larger the external magnetic field, the greater the polarization mismatch loss. In addition, we also found that dusty particles alleviate the deterioration of the polarization state significantly; regulating and controlling dust radius and density can avoid polarization reversal and reduce the polarization mismatch loss. We further analyzed the variation of the polarization state under different reentry heights. Our analysis reveals interesting features concerning polarization properties of obliquely incident EM waves, which provide an important theoretical basis for information reception in the plasma sheath containing ablative particles.

Transient response of a nonlinear energy sink based piezoelectric vibration energy harvester coupled to a synchronized charge extraction interface

Integration of a piezoelectric transducer with a nonlinear energy sink (NES) has been realized for both vibration mitigation and broadband energy harvesting. However, to ensure that a harvester can generate power in a truly broadband manner, the impedance matching issue of the interface circuit should be addressed. The synchronized charge extraction (SCE) is one technology that has been proved to be able to address this issue for linear energy harvesters. This work intends to investigate the transient response of an NES-based piezoelectric vibration energy harvesting system interfaced with an SCE interface (NESVEH-SCE). The nonlinear normal mode of such an electromechanically coupled system is analyzed on the basis of the equivalent impedance method and complexification-averaging method. The frequency-energy plots are depicted and verified by wavelet analysis. The effects of electromechanical coupling strength, electrical load in the SCE interface and initial input energy level on the performance of the proposed system are discussed by using the circuit simulation tool. Finally, experiments are performed to verify the consequences obtained from the theoretical and numerical methods, and demonstrate that the energy harvested during the transient response of the NESVEH-SCE system is independent of the electrical load in the SCE interface.

Modeling and harmonic analysis of energy extracting performance of a piezoelectric nonlinear energy sink system with AC and DC interface circuits

Nonlinear energy sink (NES) has been successfully integrated with vibration energy harvesters to enhance energy extracting performance in a broadband manner. This article intends to evaluate a piezoelectric energy harvester based on the NES technique and coupled to a pure resistive load (EHNES-AC) and a standard rectifying energy extracting circuit (EHNES-DC) under harmonic excitation. A new approach for the analysis of the EHNES-DC system is proposed by simplifying the DC circuit on the basis of the equivalent impedance method (EIM). The theoretical solutions and analyses of the EHNES-AC system, the EHNES-DC system with an original DC circuit based on Shockley diode model and the EHNES-DC system with a simplified DC circuit based on EIM are then derived by the harmonic balance method (HBM). On the other hand, the holistic circuit simulation is performed by employing the equivalent circuit model (ECM) to validate those approximate theoretical analyses. With the assistance of the proposed models and simulation tool, the effect of the load resistance on the efficiencies of the EHNES-AC and EHNES-DC systems is parametrically studied. Experiments are also conducted and verify the main conclusions given by theoretical and numerical studies.

Vibration energy harvesting based on a piezoelectric nonlinear energy sink with synchronized charge extraction interface circuit

Nonlinear energy sink (NES) conventionally designed for vibration control has been recently explored for energy harvesting purpose. To simplify the analysis, a pure resistive load is usually used in the evaluation of the performance of NES-based energy harvesting systems. This paper investigates the performance of an NES-based energy harvesting system interfaced to a synchronized charge extraction (SCE) circuit (EHNES-SCE). For the ease of analysis, the SCE interface circuit is simplified by the equivalent impedance method. An equivalent circuit model for system-level simulation of the EHNES-SCE system is also established to confirm the feasibility of using the simplified SCE circuit. Subsequently, with the simplified SCE circuit, approximate analytical solutions of the EHNES-SCE system are derived using the harmonic balance method and the performance of the EHNES-SCE system under harmonic excitation is investigated. With the established modelling and simulation tools, the influences of electrical load and electromechanical coupling on the performance of the EHNES-SCE system are revealed. Finally, experimental results are presented to confirm the main findings from the theory and simulation and reveal that the EHNES-SCE system is able to harvest energy in a wide frequency range, regardless of the load resistance in the SCE circuit.

Overvoltage analysis and protection of lightning arresters in distribution systems with distributed generation

The objective of this paper is to address an issue that arises from the increasing penetration of distributed energy resources in power systems: the design and analysis of protective devices with more complex topology and power flow patterns. In particular, this paper investigates lightning arrester overloading and failure from fault-induced overvoltages. Currently, the length of time from the fault inception until the lightning arrester’s failure is unknown, forcing utility companies to assume the worst-case scenario and install more costly and complex protection schemes than might otherwise be needed.In this paper, the Thevenin Equivalent Impedance method is proposed to analyze a distributed generation (DG) source’s effect on the transformer high side voltage. After examining the voltage transients and determining the magnitude of the overvoltage, an optimal and cost-effective protective relaying strategy is developed and implemented. To complete this study, various types of DG sources were modeled and simulated using two test systems. Finally, the implementation of the suggested solution of intentional islanding operation of the distribution system is discussed. This solution allows the DG source to continue to supply a portion of the distribution system’s load, thereby increasing the reliability of the system.

Elastic-electro-mechanical modeling and analysis of piezoelectric metamaterial plate with a self-powered synchronized charge extraction circuit for vibration energy harvesting

Structural vibrations usually exist in the form of low-frequency and broadband elastic waves, so cantilever-like harvesters are not appropriate due to space limitations and high quality factor. Piezoelectric metamaterial plate with local resonators (PMP-LR) has been explored to overcome it. However, how to model and analyze the whole energy harvesting system is still a challenge. In this paper, a self-powered synchronized charge extraction circuit is presented and connected to the PMP-LP as the interface circuit. An elastic-electro-mechanical model is built based on the Kirchhoff plate theory and equivalent impedance method, where equivalent impedance of the self-powered synchronized charge extraction circuit is first derived. Then the elastic-electro-mechanical model is numerically solved by using the Bloch theorem and wave finite element method. By numerical simulations, it is found that the synchronized charge extraction circuit has few effects on vibration bandgaps of the PMP-LR. While by inserting an inductor (Lr) parallel with the clamped capacitor (Cp) of the piezoelectric patch, we can see that a new dispersion curve is induced by the Lr-Cp electrical resonance and the inductor is beneficial for low-frequency and broadband vibration energy harvesting. In particular, the inductor can greatly improve the harvesting performance when the resonant frequency is equal to the excitation frequency. In the end, experiments are done and the results are consistent with the numerical ones. Excitingly, the output voltage amplitude of the piezoelectric patch is enlarged about 200% after using the resonant inductor.

Equivalent impedance method for determining the junction temperature of LED array

LED junction temperature is an important parameter for LED performance and life. Experiment investigation of the equivalent impedance method for determining the junction temperature of single LED chip has been reported in the past. In this work, this method was expanded to any LED array. The outcome showed that the average junction temperature of any LED array had a linear relationship with the equivalent impedance, which was in agreement with experiments. Therefore, the equivalent impedance can be used to determine the LED junction temperature.

Equivalent Impedance Method for Attentuation in Ducts

It is suggested in this paper that, within certain limitations, a variety of effects responsible for attenuation in ducts could be lumped together in the form of an “equivalent impedance” attributed to the duct walls. First- and second-order approximations for attenuation for plane and higher-order modes, when such admittance is either very small or very large, are determined if modal coupling is neglected. An integral-equation approach is suggested for the “intermediate” impedance range. An analysis has been conducted in terms of a nonorthogonal but complete set of modes; expressions for relevant modal distribution functions have been determined. Expressions for sound pressure show the usual decay as well as a modulation in attenuation along the length of the duct. A brief discussion indicating the analytical approach to estimate the modifications due to mean flow and shear is also presented.