Non-sinusoidal Currents Research Articles

AC losses in HTS coils for high-frequency and non-sinusoidal currents

AC losses in racetrack coils that are wound of YBCO tapes are measured for sinusoidal and non-sinusoidal transport currents with fundamental frequencies up to 1 kHz. An electrical method to measure losses for non-sinusoidal currents is developed for this purpose. The measured losses are compared to the losses calculated by 2D finite element models with power-law material models. The frequency and waveform-dependency of the measured losses are shown and compared to the results of the models over a wide range of frequencies and waveforms. Finally, it is shown that the finite element models can accurately predict AC losses resulting from non-sinusoidal transport currents as are present in highly dynamic motors with AC armature coils.

Application of PI Current Controller in Single Phase Inverter System Connected to Non Linear Load

This study is concerned with the problem of network power quality when inverter systems are connected to a nonlinear load. Nonlinear loads are well known as one of the biggest source of harmonics in the power system. Besides that, inverter systems also have their nonlinearity characteristic because of the electronic components. As the inverter system is connected to nonlinear load, it resulting in harmonic distortion-related problem and draw non-sinusoidal currents in the system, thus reducing the power quality in the system. The application of Proportional Integral controller in this system is the main interest of this study. This current controller capable of reducing total harmonic distortion and improve the state of current waveform. This paper focuses on application of simple manual trial and error tuning technique to produce the optimum value for the gains. The result of study verifies the trial and error manual tuning of PI current controller in compensating harmonic distortions. Simulation and modelling of the system are successfully developed using Matlab/Simulink.

Implementation of Echo-State Network-Based Control for Power Quality Improvement

This paper proposes a new control algorithm for mitigation of power quality problems at the distribution level. The control algorithm is designed on the basis of echo-state network, which is a type of recurrent neural network. This technique is used to extract fundamental weight components from nonsinusoidal load currents. These weight components are used to evaluate reference grid currents and consequently generate switching logic for the voltage source converter used in the active filter. The shunt-connected active filter with the proposed control algorithm is used to overcome several current-related power quality problems and provides the load compensation. Problems such as the presence of lower order harmonics, insufficient reactive power, and load unbalancing are corrected using a shunt filter in both the power factor correction and voltage regulation modes. The proposed control algorithm is validated on a real time system which is a prototype of a shunt filter. The algorithm is tested in MATLAB using Sim Power Systems and SIMULINK and implemented on a digital signal processor.

Modelling and control of an interface power converter for the operation of small diesel gen-sets in grid-connected and stand-alone modes

This paper presents the modelling and control design steps of a two-stage static conversion structure used as interface to integrate a diesel generator set into a secondary distribution network. In order to guarantee that the inverter works within the PWM linear range, a boost converter is used to increase the DC voltage level. The proposed structure allows two operation modes, connected to the AC mains or isolated. In the isolated mode the interface converter may be controlled as grid-forming or grid-conditioning (active power filter). The inverter current controllers are designed in the synchronous reference frame together with multiple integrators in order to effectively track non-sinusoidal currents. The stability analysis is performed through the Nyquist plot. Experimental results obtained with a 5.5kW diesel generator set are presented to validate the proposed system operation and control strategies.

Modified Ac/Dc Bi-Directional Converter with Power Factor Correction And Harmonics Reduction

Most existing power semi converters and industrial motor drive systems draw non- sinusoidal currents from the supply. Non-sinusoidal currents contain harm harmonics that disturb the power supply, which is important serious concern for reliability. Other equipment that use the same power supply are adversely affected. This paper suggests the operation and performance of a new modified AC-DC converter that allows bi-directional power flow, provides improved power factor, and reduces harmonic magnitude and disturbance to the supply by system. The bi- directional feature allows recovery of regenerative energy of loads, back to the power supply and the converters. The proposed converter has high potential for industrial drives applications, such as electronically controlled traction system, lifts and general industrial motor drive systems can increase overall efficiency and reliability.

Method of Calculating the Correction Factors for Cable Dimensioning in Smart Grids

One of the main causes of overloading electrical equipment by currents of higher harmonics is the great increasing of a number of non-linear electricity power consumers. Non-sinusoidal voltages and currents affect the operation of electrical equipment, reducing its lifetime, increases the voltage and power losses in the network, reducing its capacity. There are standards that respects emissions amount of higher harmonics current that cannot provide interference limit for a safe level in power grid. The article presents a method for determining a correction factor to the long-term allowable current of the cable, which allows for this influence. Using mathematical models in the software Elcut, it was described thermal processes in the cable in case the flow of non-sinusoidal current. Developed in the article theoretical principles, methods, mathematical models allow us to calculate the correction factor to account for the effect of higher harmonics in the current spectrum for network equipment in any type of non-linear load.

Anomalous transport effects on switching currents of graphene-based Josephson junctions

We explore the effect of noise on the ballistic graphene-based small Josephson junctions in the framework of the resistively and capacitively shunted model. We use the non-sinusoidal current–phase relation specific for graphene layers partially covered by superconducting electrodes. The noise induced escapes from the metastable states, when the external bias current is ramped, given the switching current distribution, i.e. the probability distribution of the passages to finite voltage from the superconducting state as a function of the bias current, that is the information more promptly available in the experiments. We consider a noise source that is a mixture of two different types of processes: a Gaussian contribution to simulate an uncorrelated ordinary thermal bath, and non-Gaussian, α-stable (or Lévy) term, generally associated to non-equilibrium transport phenomena. We find that the analysis of the switching current distribution makes it possible to efficiently detect a non-Gaussian noise component in a Gaussian background.

MODEL CALCULATING THE INSTANTANEOUS MODE PARAMETER A TRACTION POWER SYSTEM MOVING ELECTRIC LOCOMOTIVES

Based on the methods of analysis for calculating the electrical parameters of the mode of the traction power supply systems identified deficiencies related to the readability of the calculation and use of non-sinusoidal currents difficulties in that peculiar modern traction complexes with semiconductor converters. Using the methods of electrical engineering theory developed a model for calculating a continuous instantaneous mode parameters of the traction power supply systems, is different from the calculation methods that have been used previously by the fact that the original data is not averages, and pre-defined instantaneous values of electric current and speed. The model, in contrast to these methods is not large discreteness calculations, which greatly improves the quality of the calculation of the sudden change between the different modes of operation of electric and informative value in the calculation of power quality. The possibility of continuous operation for the entire simulation interval based on the location of the place of electric locomotives that move count distribution of voltage drop, loss of power and non-sinusoidal voltage coefficient for each of the electric contacts in place.

A Novel Power Factor Correction System Based on Sliding Mode Fuzzy Control

In this study, a novel Power Factor Correction System based on Sliding Mode Fuzzy Control is presented. This structure is used as an AC/DC/AC drive system for asynchronous machine. Non-sinusoidal source current of the system is improved to a sinusoidal waveform by the novel Power Factor Correction System controlled by Sliding Mode Fuzzy Controller. Sliding mode control technique (variable structure control) is preferred because of its robustness. Additionally, fuzzy control algorithm is adapted to Sliding Mode Control for eliminating or reducing chattering problem. A DC–DC boost converter is used to provide DC-link voltage to the inverter Three-phase voltages for Space Vector Pulse Width Modulation technique are represented by a voltage space vector in α-β space using the Clarke transformation for two-level voltage source inverter. The harmonic performance of the AC/DC/AC drive system, source side and load side current waveforms, and total harmonic distortion (THD) values are given in figures. Experimental results show the significant improvement in source current with eliminated harmonics and increased power factor from 0.63 to 0.998 value.

Online learning control for harmonics reduction based on current controlled voltage source power inverters

Nonlinear loads in the power distribution system cause non-sinusoidal currents and voltages with harmonic components. Shunt active filters U+0028 SAF U+0029 with current controlled voltage source inverters U+0028 CCVSI U+0029 are usually used to obtain balanced and sinusoidal source currents by injecting compensation currents. However, CCVSI with traditional controllers have a limited transient and steady state performance. In this paper, we propose an adaptive dynamic programming U+0028 ADP U+0029 controller with online learning capability to improve transient response and harmonics. The proposed controller works alongside existing proportional integral U+0028 PI U+0029 controllers to efficiently track the reference currents in the d-q domain. It can generate adaptive control actions to compensate the PI controller. The proposed system was simulated under different nonlinear U+0028 three-phase full wave rectifier U+0029 load conditions. The performance of the proposed approach was compared with the traditional approach. We have also included the simulation results without connecting the traditional PI control based power inverter for reference comparison. The online learning based ADP controller not only reduced average total harmonic distortion by 18.41 U+0025, but also outperformed traditional PI controllers during transients.

Comparative analysis of reactive power definitions in the presence of harmonics

In this paper, the most significant definitions of reactive power in single-phase and three-phase three-wire systems with non-sinusoidal voltages and currents are presented. Comparative analysis of these definitions has been performed. Fundamental principles on which these definitions rely are stated, and the application of these definitions to solving the problems of compensation is explained. Contrary to single-phase or three-phase symmetrical systems operating under sinusoidal conditions, reactive power compensation in systems operating under non-sinusoidal conditions does not result in maximal efficiency of electric energy delivery. Less efficiency in comparison to the theoretical maximum is being explained by the presence of harmonics and asymmetries in the system. Therefore, in the context of the reduction of losses during electric energy delivery to the load, the possibilities of nonactive power reduction should be contemplated instead of the possibilities of reactive power reduction.

A Simplified Synchronous Reference Frame for Indirect Current Controlled Three-level Inverter-based Shunt Active Power Filters

This paper presents a new simplified harmonics extraction algorithm based on the synchronous reference frame (SRF) for an indirect current controlled (ICC) three-level neutral point diode clamped (NPC) inverter-based shunt active power filter (SAPF). The shunt APF is widely accepted as one of the most effective current harmonics mitigation tools due to its superior adaptability in dynamic state conditions. In its controller, the SRF algorithm which is derived based on the direct-quadrature (DQ) theory has played a significant role as a harmonics extraction algorithm due to its simple implementation features. However, it suffers from significant delays due to its dependency on a numerical filter and unnecessary computation workloads. Moreover, the algorithm is mostly implemented for the direct current controlled (DCC) based SAPF which operates based on a non-sinusoidal reference current. This degrades the mitigation performances since the DCC based operation does not possess exact information on the actual source current which suffers from switching ripples problems. Therefore, three major improvements are introduced which include the development of a mathematical based fundamental component identifier to replace the numerical filter, the removal of redundant features, and the generation of a sinusoidal reference current. The proposed algorithm is developed and evaluated in MATLAB / Simulink. A laboratory prototype utilizing a TMS320F28335 digital signal processor (DSP) is also implemented to validate effectiveness of the proposed algorithm. Both simulation and experimental results are presented. They show significant improvements in terms of total harmonic distortion (THD) and dynamic response when compared to a conventional SRF algorithm.

A Review of Harmonics Detection and Measurement in Power System

A load is said to be “linear” when it draws a current from the supply which is proportional to the applied voltage (linear). And in the case of “non-linear” load, impedance changes with applied voltage. The current drawn from such non-linear load is also non-linear i.e. non-sinusoidal even when it is connected to a sinusoidal voltage source. Harmonic currents contents which are present in non-sinusoidal currents intermingle with the impedance of the power distribution system to create voltage distortion which affects the distribution system and the loads connected to it. The serious power-line pollution is a result of increasing use of power electronic systems and time-variant nonlinear loads in industry. Hence, power supply quality is degraded. It results in the reduction of system efficiency, apparatus overheating, and increase power. As the utilization of the number of harmonics-producing loads has increased over the years, it has become highly mandatory their influence and analysis when making any additions or changes to an installation. In this paper various harmonics detection and measurement techniques have been outlined.

Instrument current transducer for measurements in asymmetrical conditions in three-phase circuits with upper harmonics

The theme of the article is protection of electrical circuits against negative sequence currents both with sinusoidal and trapezoidal waveforms. The suggested solution is enhancement of instrument current transducers used in industrial relaying and control applications. The instrument negative sequence current transducer connected to Rogowski coils designed by the authors is presented in the article. To protect circuits with extremely non-sinusoidal currents (such as trapezoidal waveforms), instrument transducers with 2nd order low pass filter are suggested. In the presence of higher-order harmonics in the protected three-phase circuit the low pass filter will reduce the THD in the output voltage of instrument negative sequence current transducer (as compared to harmonics in currents of the protected circuit) and compensate for the differentiation effect typical of such transducer schemes.The paper may be of interest for investigators and engineers engaged in research, design and commissioning of protection and control equipment, current instrument and measurement devices used in industrial applications, and also for undergraduate and postgraduate students in electrical engineering.

CPC Power Theory for Analysis of Arc Furnaces

Electric Arc Furnaces (EAFs) are facilities with an intensive use of energy where small improvements in their control imply significant electrical energy savings. The electric arcs are highly nonlinear and chaotic; a power theory for non-sinusoidal voltages and currents is needed for the analysis of the EAF electrical parameters. The current and power decomposition proposed by Czarnecki in the Current's Physicals Components (CPC) power theory allows an advanced engineering analysis of the energy transfer at the arc furnaces. Each one of the current components can be used to dynamically diagnose either the energy transfer or the heat process conditions. This solid and complete power theory can help to design power control algorithms to optimize the energy efficiency at arc furnaces.

Kinetic interpretation of resonance phenomena in low pressure capacitively coupled radio frequency plasmas

Low pressure capacitive radio frequency (RF) plasmas are often described by equivalent circuit models based on fluid approaches that predict the self-excitation of resonances, e.g., high frequency oscillations of the total current in asymmetric discharges, but do not provide a kinetic interpretation of these effects. In fact, they leave important questions open: How is current continuity ensured in the presence of energetic electron beams generated by the expanding sheaths that lead to a local enhancement of the conduction current propagating through the bulk? How do the beam electrons interact with cold bulk electrons? What is the kinetic origin of resonance phenomena? Based on kinetic simulations, we find that the energetic beam electrons interact with cold bulk electrons (modulated on a timescale of the inverse local electron plasma frequency) via a time dependent electric field outside the sheaths. This electric field is caused by the electron beam itself, which leaves behind a positive space charge, that attracts cold bulk electrons towards the expanding sheath. The resulting displacement current ensures current continuity by locally compensating the enhancement of the conduction current. The backflow of cold electrons and their interaction with the nonlinear plasma sheath cause the generation of multiple electron beams during one phase of sheath expansion and contribute to a strongly non-sinusoidal RF current. These kinetic mechanisms are the basis for a fundamental understanding of the electron power absorption dynamics and resonance phenomena in such plasmas, which are found to occur in discharges of different symmetries including perfectly symmetric plasmas.

Enhancement of Time-Domain Electromagnetic Inverse Method for Modeling Circuits Radiations

To ensure the reliability and safety of the modern electronic systems face of these electromagnetic interference which are becoming more and more important, modeling methods based on the emissions in the near field of these systems are needed. However, the developed methods and in particular the electromagnetic inverse method in the frequency domain have several limitations to model and characterize the systems which emit a nonsinusoidal electromagnetic radiation. To cope with these limitations, in this paper, the electromagnetic inverse method in the time domain has been developed. Using measured near-field cartography above the studied system, the method, based on genetic algorithms, consists in identifying equivalent emitting dipoles. The identification traverses the entire mapping by identifying all sources from the most intense to the lowest source. The proposed method has been validated, first, using calculated cartographies above known dipoles and, second, using measured cartographies above actual dc–dc converters. A very good agreement has been observed between the near magnetic field cartography calculated using the obtained model and that's emitted by the studied system. The proposed method can be used for the identification of equivalent emitting sources of systems excited by nonsinusoidal currents in a widely lowest time as that of the frequency method.

Adaptive Neurofuzzy Inference System Least-Mean-Square-Based Control Algorithm for DSTATCOM

This paper proposes the real-time implementation of a three-phase distribution static compensator (DSTATCOM) using adaptive neurofuzzy inference system least-mean-square (ANFIS-LMS)-based control algorithm for compensation of current-related power quality problems. This algorithm is verified for various functions of DSTATCOM, such as harmonics compensation, power factor correction, load balancing, and voltage regulation. The ANFIS-LMS-based control algorithm is used for the extraction of fundamental active and reactive power components from nonsinusoidal load currents to estimate reference supply currents. Real-time validation of the proposed control algorithm is performed on a developed laboratory prototype of a shunt compensator. The real-time performance of shunt compensator with ANFIS-LMS-based control algorithm is found satisfactory under steady-state and dynamic load conditions. The performance of the proposed control algorithm is also compared with fixed-step LMS and variable-step LMS (VSLMS) to demonstrate its improved performance.

Influence of back-EMF and current harmonics on sensorless control performance of single and dual three-phase permanent magnet synchronous machines

Purpose – The purpose of this paper is to investigate the influence of back-EMF and current harmonics on position and speed estimation accuracy for single and dual three-phase (DTP) permanent magnet synchronous machines (PMSMs) with two fundamental-model-based sensorless control strategies which are widely utilized for AC machines, i.e. flux-linkage observer (FO) and simplified extended Kalman filter (EKF). Design/methodology/approach – The effect of distorted back-EMF is studied for sensorless vector control of single three-phase PMSM. For the influence of current harmonics, unlike the existing literature where the current harmonics are deliberately injected, in this paper, sensorless switching-table-based direct torque control (ST-DTC) strategies for DTP-PMSM which inherently suffer from non-sinusoidal stator currents in addition to the distorted back-EMF, are investigated experimentally. Findings – By employing the FO and simplified EKF-based sensorless vector control of single three-phase PMSM, it can be concluded that the rotor position estimation accuracy is less affected by the back-EMF harmonics when the simplified EKF method is utilized since it is less sensitive to such noises. When the influence of non-sinusoidal stator currents together with back-EMF harmonics is investigated for the conventional and modified ST-DTC of DTP-PMSM, it is indicated that the simplified EKF exhibits better position and speed estimation accuracy in both the conventional and modified ST-DTC strategies. In addition, its steady-state performance shows a slight superiority over that based on FO, in terms of flux and torque ripples, and THD of phase currents. For the dynamic performance, the estimated speed of simplified EKF shows less phase lag and fluctuations compared to that of FO. Originality/value – This paper introduces the influence of back-EMF and current harmonics on sensorless control performance for single and DTP PMSMs. Detailed experimental results show that the simplified EKF exhibits better rotor position and speed estimation accuracy compared to that of FO due to its higher noise-rejection ability.

Thermal Analysis of the Laminated Busbar System of a Multilevel Converter

Laminated busbar systems are commonly used in power electronic converters because of their low stray inductance. While the electromagnetic analysis of a busbar system is widely presented in the literature, there is a lack of accurate thermal modeling. In this paper, the thermal analysis of the busbar system is presented. An analytical lumped parameter thermal model (LPTM) of the busbar system is developed. The LPTM is applied to the fast estimation of the mean temperature and temperature-dependent power losses of the busbars by the proposed algorithm. Joule losses produced by nonsinusoidal currents flowing through the busbars in the converter are estimated. The skin and proximity effects, which have a strong influence on the ac resistance of the busbars, are considered in the loss estimation. Thus, a comprehensive electrothermal model of the busbar system is developed, which is of practical use in the converter design. It allows optimizing the stray inductance, material consumption, and cost of the busbar system as long as the specified temperature limits are not exceeded. The finite-element method thermal modeling validates the developed LPTM. Laboratory measurements in two operating points of the converter have been performed, and they show good correlation with the simulation results.