Sinusoidal Voltage Research Articles

Influence of Voltage Harmonics on Partial Discharge Diagnostics in Electric Motors Fed by Variable-Frequency Drives

Typically, in partial discharges (PD) diagnostics tests carried out in a laboratory, harmonic content in a voltage waveform is ignored. However, during the operation of variable-frequency drives (VFD)-fed electric motors, the distorted voltage waveform is produced due to the addition of harmonics components in the sinusoidal voltage waveform. The distortion level increases when the VFD is operated at a lower speed ratio. The additional spectral components in the applied voltage waveform can have a significant impact on the PD behavior in the insulation of the electric motor. Therefore, during online PD monitoring, overlooking the harmonic regime in the applied voltage may lead to a false interpretation of PD data. This article investigates the influence of voltage harmonics distortion produced during the variable-speed operation of VFD on PD characteristics. For this purpose, online PD measurements have been carried out by performing a series of experiments on eight VFD-fed motors under variable operating conditions. The PD severity at different harmonic compositions is experimentally investigated by determining various PD characteristic parameters including PD inception voltage, accumulated apparent charge, average discharge current, discharge power, and quadratic rate. Also, two terms Gaussian models have been mathematically developed using 288 data samples to quantify the variations in PD characteristic parameters against distortion parameters. The article proposes a framework for properly evaluating harmonics impact in PD for electric motors and correctly estimating stator insulation degradation.

Analysis of frequency dependence of complex impedance and electrical characterization of Fe2O3/kaolin ceramics for civil engineering applications

The complex impedance spectroscopy (CIS) method is usually used in order to analyze the electrical response of different semiconducting disordered materials as a function of frequency at different temperatures. The real and imaginary parts of the complex impedance can show different semicircles in the complex plane that give evidence for the presence of both bulk and grain boundary contributions. Many parameters can be deduced from the analysis of CIS data, such as relaxation times and activation energies. There are some literature data concerning electrical properties of clays and (semiconductor, sand, cement,…)/clay mixtures. Most of the published works are related to the AC conductivity of rocks with the effect of water or oil content but there are no similar studies on the characterization of the microstructure of individual clays as ceramic materials by analyzing their temperature and frequency dependence of their electrical conductivities. Hence, this paper presents an analysis of electric complex impedance of the Fe2O3/Kaolin composite in the high temperature range up to 740 °C. Sinusoidal voltage with frequency in the range [100 Hz, 1 MHz] is applied to the material in order to measure the electrical conductivity for various concentrations of Fe2O3 from zero to 100 %. The activation energies for the conduction and for the relaxation processes are determined and their dependence on the density of Fe2O3 analyzed. Furthermore, let’s found that Fe2O3 have the effect to increase the electrical conductivity in our samples. From the Nyquist diagrams, only one semi-circle related to the contribution of the grains to the total electrical conduction is identified for all investigated samples.

고조파 보상을 위한 하이브리드 능동전력필터(HAPF)에서 APF의 정현파 전압 주입에 따른 무효전력 상관 관계 분석 및 보상방안

Active power filter (APF) is the preeminent solution against nonlinear loads, current harmonics, and power quality problems. Hybrid APF topologies combining low-power rating APF with LC-based passive power filters(PPF) are used to reduce the power rating of voltage source inverter. If the parameter of the PPF part of the HAPF for decreasing the THD is not properly designed to match the system, efficiency degradation due to control error and overcompensation of reactive power may occur, leading power factor. In order to properly design the capacity of the passive filter of the HAPF, this paper proposes a capacity selection method that considers harmonics and reactive power at the same time.BRAlso, in this paper, reactive power analysis and compensation method in HAPF is presented, operating with the injected sinusoidal waveform voltage of APF. The compensated reactive power performance when considering the variable injection voltage as the proposed method was compared through simulation. As a result, THD was minimized and the controlled reactive power could be reached.

Co-Simulation of Three Phase Induction Motor Controlled by Three Level Inverter

The main objective of this research is to build and control a three-phase induction motor using the ANSYS Simplorer and Maxwell2D program to obtain a high-quality sinusoidal voltage profile with little distortion and therefore low harmonics. A control circuit has been proposed using diodes to control the motor speed by v/f method. This method depends on the principle of changing the source voltage in addition to the frequency in a fixed ratio to obtain the best working conditions and the best characteristics of the motor with the least possible losses. The modeling results show the effectiveness of the proposed circuit in controlling the motor speed effectively and enhancing the motor performance by reducing losses when using traditional methods of controlling the motor speed. The effectiveness of the control system is verified by analyzing the results using the ANSYS program.

An application of four‐wire grid‐forming power inverter in unbalanced distribution network

The modelling of a three-phase four-leg four-wire grid-forming inverter in a low voltage distribution system 18-bus European Cigré under unbalanced conditions in an autonomous distribution network is presented. The case study has two types of inverters control strategy: (i) grid-forming to supply all the system demand in the interval of the intentional supply interruption and (ii) grid-following to integrate photovoltaic renewable energy resources into power systems. The model suggests a control scheme with two loops: An inner current loop with a proportional-integral controller and an outer voltage loop with a proportional controller, both in the synchronous reference frame (dq0), in which dq-axis are decomposed in positive and negative sequences. Simulation results, carried out using the PSCAD software, showed the effectiveness of the suggested control strategy with smooth synchronization where the grid-forming inverter was able to form a network with an unbalanced degree lower than 2%, sinusoidal voltage and frequency within standard limits 49.5–50.5 Hz.

Parameter Determination of Coupled and Decoupled Admittance Matrix Methods of the Norton Equivalent Model for an Air Extractor

Context: Studies carried out in low voltage networks have explored the modeling of linear single-phase loads (such as motors) and non-linear ones (such as those based on power electronics). However, induction motors exhibit non-linear characteristics between voltage and current due to the saturation of their magnetic parts. Therefore, it is necessary to study induction motors in the frequency domain with a model that allows reviewing the characteristic nonlinearity of their voltage-current interaction. Methodology: This article presents the frequency domain modeling of a single-phase induction motor used as a silent air extractor (127 V, 60 Hz, 66 W), which presents a capacitive behavior (fp = 0,93 in leading) and harmonic distortion due to a third-order component (7,0%) when fed with a pure sinusoidal voltage of 127 V. Results: This work establishes the parameters of two approaches to the Norton equivalent model (coupled and decoupled admittance matrix) which are used to estimate the distorted current signal and the values ​​of consumed active and non-active power. The results show comparisons errors of P, Q, THDi, and NRMSE indices of less than 7, 4, 14, and 3%, respectively. Conclusions: The parameters of the Norton equivalent model estimated for the single-phase induction motor allow calculating the current signal with a high degree of precision. This signal exhibits nonlinear characteristics and a capacitive behavior due to the permanent presence of a capacitor aiding the start and operation of the engine.

Application Status and Prospect of Impedance Spectroscopy in Agricultural Product Quality Detection

The nondestructive testing of agricultural products has always been a key technology for the modernization of agriculture and food. By applying a sinusoidal voltage (current) excitation signal of variable frequency, the relationship between the amplitude, frequency and phase of the response signal is obtained, and the measured response function in a certain frequency range is obtained, constructing the correlation between impedance spectroscopy and matter properties. Electrical impedance spectroscopy (EIS) is a widely used method for the nondestructive characterization of agricultural products, and its applications in the agricultural field has attracted increasing attention. This paper summarizes the research of electrical impedance spectroscopy (EIS) in the detection of grain quality, fruit and vegetable quality, meat quality and food quality from 2005 to 2022. The potential and development direction of electrical impedance spectroscopy in the nondestructive testing of agricultural product quality are prospected, which provides a reference for scientific researchers who applied electrical impedance spectroscopy in agricultural product quality detection.

Family of single‐phase high‐frequency isolated AC–AC converters

AbstractThis work presents a family of single‐phase ac–ac converters with high‐frequency isolation based on the association of interleaved transformers and the dual active bridge (DAB) converter. From distinct configurations of the dc link in terms of half‐bridge (HB), full‐bridge (FB), and interleaved full‐bridge (IFB) arrangements, one can obtain three symmetrical and six asymmetrical structures, with distinct trade‐offs among the number of active switches, total dc‐link voltage, and effective operating frequency of the filter elements. Prominent advantages of the derived circuits include input power factor correction (PFC), a nearly sinusoidal load voltage, the operation of active switches under soft‐switching condition during part of the line period, reduced current stresses, good current sharing due to the interleaved transformers, as well as multilevel voltage waveforms on both sides of the high‐frequency transformer (HFT). Experimental results obtained from an experimental prototype of an ac–ac FB‐IFB converter are presented to validate the theoretical assumptions.

A High-Gain and High-Efficiency Photovoltaic Grid-Connected Inverter with Magnetic Coupling.

Conventional photovoltaic (PV) grid-connected systems consist of a boost converter cascaded with an inverter, resulting in poor efficiency due to performing energy processing twice. Many pseudo DC-link inverters with single energy processing have been proposed to improve system efficiency and simplify circuits. However, their output voltage gain is limited by the non-ideal characteristics of the power diode, making them difficult to apply in high-output voltage applications. This paper proposes combining a boost converter with magnetic coupling and a full-bridge unfolding circuit to develop an inverter featuring high voltage-gain and high efficiency. According to the desired instantaneous output voltage, the high-gain boost converter and the full-bridge unfolding circuit are sequentially and respectively controlled by SPWM. A sinusoidal output voltage can be generated by performing energy processing only once, effectively improving the conversion efficiency. Magnetic coupling is adopted to increase the voltage gain of step-up, and the step-down function is realized by the full-bridge unfolding circuit to reduce conduction loss. Finally, a 500 W prototype was fabricated for the proposed high-gain inverter. The experimental results were used to verify the correctness of the theoretical analysis and the feasibility of the circuit structure.

Preview repetitive learning control for islanded microgrids based on equivalent input disturbance approach

Due to the rapid drop in peak dc-link voltage (PDV) caused by environmental changes, as well as the majority of loads being naturally nonlinear, the output voltage of the microgrid inverters is always distorted. To boost the PDV at a low cost and reduce the total harmonic distortion (THD) of output voltage, a strategy is proposed in this paper to synchronously control ac- and dc-sides voltage. A double closed-loop PI controller is used to indirectly control the PDV of Z-source inverter (ZSI). Sinusoidal reference voltage generated by the primary power layer is merged to construct an augmented dynamic system, and an integrated optimal controller on the ac-side is obtained. Preview repetitive control (PRC) and error compensation can improve output voltage tracking accuracy. The state feedback component effectively suppresses the resonance of the filter, lowering the system’s sensitivity to parameter perturbation. Combined with this, the equivalent input disturbance (EID) is used to eliminate the potential interference in microgrids, which can shorten the recovery time of the system. Both simulations and experiments are provided to demonstrate the better performance of the proposed approach in comparison to other different repetitive controllers.

Hybrid Pulse High-Frequency Voltage Injection Control Algorithm of Sensorless IPMSM for Vehicles

A hybrid pulse vibration high-frequency voltage signal injection method is proposed to solve the problems that the conventional sensorless control algorithm of vehicle IPMSM may generate a large estimated rotor position error and opposite directions in identifying the polarity of magnetic poles under zero-speed and high-torque starting and low-speed operation. The magnetic pole polarity is identified by the saturation effect of the flux chain by injecting a high-frequency sinusoidal voltage signal and opposite pulse voltage signal into the axis of the assumed coordinate system simultaneously. Subsequently, the position relationship between the assumed axis and the actual d axis is studied in accordance with the amplitude of response current to acquire the rotor position and speed information. The simulation and experimental results suggest that the algorithm is capable of accurately identifying the magnetic pole polarity and estimating the rotor position at zero speed and low speeds, starting the motor smoothly at zero speed, and then operating the motor stably at low speeds.

Experimental study of optical emission in the DBD excimer lamp containing a mixture of neon xenon

We report in this study detailed measurements of optical characteristics of the barrier discharge filled with Ne (50 %) and Xe (50 %) gas compositions. The discharge is driven by a sinusoidal voltage regime and was achieved and studied in the pressure of 250 mbar, at frequency of 40 kHz and for applied voltage going from 800 V up to 2 kV. The input electric power is measured with an oscilloscope, combined with a voltage probe and a current probe. The light intensity for the spectral region from 200 nm to 1100 nm was measured with a optical spectrometer. The lamp spectrum contained 826,877 nm, 822,021 nm, 879,995 nm, 881,999 nm, 902,998 nm and 915,011 nm radiations is studied in order to analysis the chemical kinetics in Ne/Xe mixture flat lamp in DBD emitting in the infrared (IR) and visible band. This study is done to explain the role of excited higher states in production of metastable states of xenon responsible for UV emission. The results discuss the effect of applied voltage and for different gas pressure on the luminance and efficacy of the lamp. The results predict that under the typical operating conditions of the DBD the total efficiency is very high with an optimum pressure at 400 mbar and an optimum voltage of 1200 V.

Control Strategy of AC-DC Converter Based on Dual Active Bridge With Minimum Current Stress and Soft Switching

This article presents a control strategy for the single-stage dual active bridge (DAB) ac-dc converters. To reduce the conduction loss and achieve zero voltage switching (ZVS), the global optimal working modes are reviewed. Based on the global optimal working modes, the input current of the DAB ac-dc converter is analyzed for the sinusoidal input voltage. The control algorithm of the DAB ac-dc converter is proposed to achieve the unit power factor with the minimum current stress and ZVS. The range of the working modes is analyzed to meet the wide load power. The working mode is varied with the line-frequency angle and load power, which guarantees that the DAB ac-dc converter works in the optimal working modes. The conduction loss in the converter with the variation of the series inductance and the turns ratio of the transformer is analyzed. The series inductance and the turns ratio of the transformer are designed to further improve the conduction loss. The proposed control strategy is applied to a 1 kW DAB ac-dc converter with 220 V/50 Hz input voltage and 200 V output voltage. The experimental results demonstrate the working mode, the soft switching performance, fast dynamic response, high efficiency, and high power quality.

Reduction of harmonics emission of a WECS in the electrical grid using multilevel inverters

<span lang="EN-US">Wind energy conversion system (WECS) is composed of many non-linear power electronic sub systems, which contribute significantly in harmonic emissions that is a threat for the quality of electrical power. Hence, for a better integration of WECS in the electrical grid and in order to satisfy IEEE 519 standards, WECS must inject a quality power with a rate of total harmonics distortion (THD) that is less than 5%. Multilevel Inverters are an emerging solution for having a perfect sinusoidal output voltage with minimum harmonic content and lower switching losses than the two-level inverter so that only a smaller filter size is required. Thus, in this paper we are presenting a significantly improved results of the reduction of the grid injected current THD using three types of inverters (two-levels, three-levels NPC, and five-levels H-bridge cascade) for a WECS and comparing the THD performances of using each of the studied inverter. All results of THD are verified by a Fast Fourier transform simulation using MATLAB/Simulink. </span>

Decomposition of the structural response of the Francis-99 runner during resonance.

In this work, the complex structural response of the Francis-99 turbine runner is further investigated by decomposition of the output signal from previous Laser Doppler Vibrometry (LDV) measurements into the motion of each nodal diameter. During the structural measurements, the non-rotating runner was installed in the turbine pit, submerged in a non-flowing water, and excited with piezoelectric patches mounted on the hub. The patches were excited with phase shifted sinusoidal voltage to create overall excitation of the runner with a desired number of nodal diameters. The deflection of selected locations on the trailing edges were scanned with LDV, one point at a time, and the global movement was reconstructed by combining the data for all points.The Francis-99 runner has its blades bolted to an over-dimensioned hub and shroud, where the hub is not fully axi-symmetrical and has several hollows in it. This, together with the fact that one patch was found to be non-functional, is believed to have excited other ND patterns in addition to the one that was intentionally excited, therefore contaminating the movement of the trailing edges with movements that does not belongs to the excited ND. To mitigate this and create a better representation of the movement of the trailing edge, which is not affected by the bleed from other ND, the LDV signal for each excited frequency of a particular ND is post-processed using discreet Fourier transformation to decompose the motion of each nodal diameter in the range ND0 to ND7. This unveils the contribution of each nodal diameter within the output signal where a spike is seen for the excited ND in all measurements. Influence from other nodal diameters were found, where the failed patched is believed to cause a ND1 like movement. In addition the clustering of multiple eigenmodes with differing nodal diameters previously found in narrow frequency bands were also found as interfering contribution when exciting at the relevant frequencies.

Characterization of Partial Discharges in High-Frequency Transformer Under PWM Pulses

Partial discharge (PD) is a phenomenon often occurring in insulation system defects (cavities), which can significantly affect life and reliability. While broad knowledge on PD phenomenology of high-frequency transformers (HFT) has been achieved under ac sinusoidal voltage, much less work has been done to infer PD behavior under emerging high frequency pulsewidth modulation (PWM) operation conditions. An impediment has been the limited appropriate test equipment. A recently developed novel ±5 kV GaN-based high-frequency PWM supply with controllable <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dV/dt</i> , voltage level and frequency has been developed. This article explores the application of these measurements to the testing of materials in this electrical environment. Two commonly used windings for HFT were tested under different applied voltage magnitudes, frequencies, and slew rates. According to the test results, at high frequency (up to 50 kHz) the electric field generated by space charge deposited by PD occurring during previous PWM pulses plays an important role in PD behavior. The frequency dependent permittivity of the insulation material can also affect PD measurement results.

Characterisation of surface charge density and net electric field during parallel-plate dielectric barrier discharge generated in atmospheric-pressure air

We measured the surface charge density in a parallel-plate dielectric barrier discharge (DBD) using the Pockels effect, and the axial and lateral components of the net electric field were evaluated for different gap lengths and applied voltages. The DBD was driven by a 5 kHz sinusoidal voltage in gap lengths of 0.5, 0.3, and 0.1 mm at atmospheric pressure with Bi4Ge3O12 crystal as a dielectric. Typical microdischarges (MDs) were observed for every gap length, and the number of MDs increased with the increasing applied voltage. As the gap length decreased, the spot radius of a single MD decreased, whereas the peaks of charge density were almost the same, indicating that the amount of charge transported per unit MD is limited for short gaps. The spatial memory effect, in which MDs occur at the same position in successive cycles, was not always observed under the experimental conditions, and it was evaluated considering the surface charge density distributions. Whether the memory effect works is determined by the surface charge density, and it is likely to occur under a balance between positive and negative charges across successive half-cycles. The net electric field was estimated from surface charge measurements. The axial component of the net electric field strength increased up to 150–170 Td before the MD occurred, and it decreased below 100 Td by the surface charge deposited by MD, being approximately 50%–60% of the external field amplitude. The maximum value of the lateral component of the electric field was approximately 150 Td at the edge of the MD spot with a gap length of 0.5 mm, and it decreased as the gap length decreased. As a negative surface charge generated a weaker lateral field than a positive one, the electric field distribution differed between anodic and cathodic dielectrics.

Comparing Study on Formation of Large Discharge Currents in Atmospheric Pulse-Modulated Radio Frequency Discharges

In recent years, pulse-modulation is introduced in atmospheric radio frequency (RF) discharges to further control the discharge operation. In this article, a comparing study is performed by a 1-D fluid model to investigate the formation of large discharge currents (LDCs) in the first RF cycle during the power-on phase in an atmospheric pulse-modulated RF discharge controlled by dielectric barriers. The current–voltage characteristics and helium metastable (He*) distributions show the enhancement of a pulsed voltage on the ignition of RF discharge, which agrees well with the experimental observation. On the other hand, in a dielectric barrier discharge driven by a sinusoidal voltage of 500 MHz, double LDCs are observed in the positive and negative half-cycles, respectively, and the large pulse rise rate of applied voltage essentially influences the distribution of charged particles in the first cycle during the power-on phase. In this study, according to computational data the reverse electric field near the anode contributes greatly to the generation of LDCs in both types of discharge, and the appropriate discharge conditions are suggested to optimize the pulse-modulated RF discharges in applications.

Three Phase Grid Connected Inverter for Solar Photovoltaic Systems

Abstract: The main aim is to convert the Solar PV DC voltage into AC voltage by using 3 phase inverter and getting sinusoidal AC output voltage. To convert solar PV which is in DC needs to be converted into AC by using the devices like 3 phase inverter and boost converter. The solar PV is a variable DC that is to be converted into pure DC for which will convert variable DC to pure DC. The MPPT is designed and is applied to boost converter which increases the solar PV’s efficiency. Then the output of boost converter which is DC voltage is given to 3 phase inverter. The 3 phase inverter which is connected to output of boost converter will convert the DC voltage into AC and we get sinusoidal AC. A three-phase grid-connected inverter designed for a photovoltaic power plant that features a maximum power point tracking (MPPT) scheme based on fuzzy logic. The whole system simulate in MATLAB. This fuzzy MPPT will shows accurate and fast response, and is integrated in the inverter.

Current Oscillator Based on Pyragas Model for Electrical Bioimpedance Applications

Current sources play an essential role in tissue excitation used in bioelectrical impedance spectroscopy. Most investigations use Howland current sources that, despite their practicality and simplified implementation, have operating frequency limitations and dependence on the load impedance due to their narrow output impedance, especially at higher frequencies. The objective of this work is to propose a model for a robust current-controlled sinusoidal oscillator. The oscillator is based on fully analog electronics, which enables controlling the oscillation phase and amplitude by using a voltage reference. The mathematical model is based on Pyragas control application to the classical harmonic oscillator. From the modeling process, an oscillator topology was built based on second-generation current carriers and on transconductance amplifiers. A sinusoidal voltage source having a frequency of 1 MHz and an amplitude of 1Vpp was used as a reference signal to drive the oscillator. The oscillator output current synchronized the oscillations’ phase and amplitude using the reference, regardless of their magnitude before the control signal acted in the circuit at t≈13.5μs. SPICE simulations using ideal components have confirmed the successful operation of the proposed oscillator. This type of oscillator can be implemented in SOIC, then allowing oscillation control interface with logic circuits.