Types Of Nonlinear Loads Research Articles

Single-Phase Grid Connected Axial Flux Permanent Magnet Generator System with Harmonic Mitigation Functionality for Various Types of Nonlinear Loads

This paper proposes the implementation of a single-phase low cost grid connected axial flux permanent magnet (AFPM) generator system with harmonic mitigation functionality for various types of nonlinear loads. The design, construction and testing of the AFPM generator are given. The method of current reference calculation derived from a combination between power transfer and harmonic compensation for nonlinear loads is described. The synchronization with the grid does not require phase locked loop (PLL). It employs a simple technique based on a sinusoidal look-up table The whole converter system is implemented on a low cost dsPIC30F4011 microcontroller. The simulation and experimental results confirm the validity of the proposed system under various conditions.

Stability Analysis and Parameters Optimization of Islanded Microgrid With Both Ideal and Dynamic Constant Power Loads

In this paper, a framework for stability analyses of a typical inverter-based islanded microgrid with two types of nonlinear loads is presented, namely ideal constant power loads (CPLs), which are the loads supplied by tightly regulated power electronics converters, and dynamic CPLs, which are used to represent motor-drive systems with large time constants. The comprehensive dynamic model of the considered microgrid is first developed, based on which a bunch of small-signal models are deduced using Taylor expansion made at different stable operating points. Afterward, eigenvalue-theorem-based stability analysis and parametric sensitivity analysis are successively performed on the obtained small-signal models to verify the stability of the system, predict the system's unstable regions, and identify the effects of parameters on the stability boundaries. In the meantime, the impacts of different kinds of nonlinear loads on the system stability are studied. Hardware-in-the-loop (HIL) real-time simulation platform of a 30-kVA microgrid, which is mainly formed by a 10-kVA photovoltaic (PV) system, a 10-kVA wind energy conversion system, a 10-kVA lithium-ion battery energy storage system, and two CPLs, is established in Typhoon HIL 602 device. The validity of the theoretical results is verified by real-time simulation results.

A Supervised Event-Based Non-Intrusive Load Monitoring for Non-Linear Appliances

Smart meters generate a massive volume of energy consumption data which can be analyzed to recover some interesting and beneficial information. Non-intrusive load monitoring (NILM) is one important application fostered by the mass deployment of smart meters. This paper presents a supervised event-based NILM approach for non-linear appliance activities identification. Firstly, the additive properties (stating that, when a certain amount of specific appliances’ feature is added to their belonging network, an equal amount of change in the network’s feature can be observed) of three features (harmonic feature, voltage–current trajectory feature, and active–reactive–distortion (PQD) power curve features) were investigated through experiments. The results verify the good additive property for the harmonic features and Voltage–Current (U-I) trajectory features. In contrast, PQD power curve features have a poor additive property. Secondly, based on the verified additive property of harmonic current features and the representation of waveforms, a harmonic current features based approach is proposed for NILM, which includes two main processes: event detection and event classification. For event detection, a novel model is proposed based on the Density-Based Spatial Clustering of Applications with Noise (DBSCAN) algorithm. Compared to other event detectors, the proposed event detector not only can detect both event timestamp and two adjacent steady states but also shows high detection accuracy over public dataset with F1-score up to 98.99%. Multi-layer perceptron (MLP) classifiers are then built for multi-class event classification using the harmonic current features and are trained using the data collected from the laboratory and the public dataset. The results show that the MLP classifiers have a good performance in classifying non-linear loads. Finally, the proposed harmonic current features based approach is tested in the laboratory through experiments, in which multiple on–off events of multiple appliances occur. The research indicates that clustering-based event detection algorithms are promising for future works in event-based NILM. Harmonic current features have perfect additive property, and MLP classifier using harmonic current features can accurately identify typical non-linear and resistive loads, which could be integrated with other approaches in the future.

Real-Time Implementation of a Three-Phase THSeAF Based on a VSC and a P+R Controller to Improve the Power Quality of Weak Distribution Systems

This paper proposes a novel three-phase transformerless hybrid series active filter (THSeAF) based on voltage-fed type of converters (VSCs) to address major power quality issues related to residential and commercial buildings. This power quality compensator presents an affordable solution to overcome current-related issues as well as integrating renewables to ensure a sustainable supply to the loads. The controller is based on a novel combination of the synchronous reference frame and pq theory to extract voltage and current harmonics as well as voltage unbalances. A proportional resonant (P+R) regulator is producing gate switching signals for the three-phase THSeAF. The generated duty-cycle waveforms will produce compensating voltage to rectify harmonic currents initiated from typical nonlinear loads. The device ensures a reliable and dynamically restored power supply on the load's point of common coupling by means of three auxiliary dc supplies. This paper describes mitigation of power-quality-related issues of a microgrid systems and smart distribution grids along with the proposed solution to enhance the power system performances. A combination of simulations and experimental laboratory results are carried out to validate the study.

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.

Cross-Connected Source Multilevel Inverter for Active Power Filtering Using Unified Constant-Frequency Integration Control

This paper proposes an Active Power Filter (APF) system which utilizes a five-level nonconventional Cross-Connected Source Multilevel Inverter (CCSMI) with a modified Unified Constant-Frequency Integration (UCI) control. The CCSMI consists of six power switches which can produce five output voltage levels. With the use of the CCSMI, the parts count is reduced with equivalent or better performance compared to the use of conventional multilevel inverters. The capability of the proposed system is tested using three types of nonlinear loads with different characteristics. The APF system is simulated under steady-state condition using MATLAB/Simulink. The results obtained show improvement in the supply current Total Harmonic Distortion (THD) with room for enhancement, using the proposed APF system.

Performance of Shunt Active Power Filter Based on Instantaneous Reactive Power Control Theory for Single-Phase System

Recently more aware people had more concern on the quality of power supply. One of the reasons is due to the increasing demand of nonlinear loads. One of the major power quality (PQ) problems that causing malfunction of sensitive electronic equipment is harmonics. The Instantaneous Reactive Power (IRP) theory is the method that is used to calculate the harmonic compensation current for three-phase system. This technique is commonly used in the shunt active power filter (APF) for reducing the harmonics and providing a good harmonic compensation for unbalanced and nonlinear load conditions. This control theory will treat the three-phase system as three single-phase system thus it is also can implement in the single-phase system. To implement IRP theory for single-phase system can be done by using two methods, which are Clarke’s transformation method and Phase-shift method. For Clarke’s transformation method, the single-phase system need to transform into three-phase system. However, for Phase-shift method only need to shift the single-phase signal 90o, to perform the active and reactive power calculation. Therefore, the Phase-shift method is much more simplified. The aim of this paper is to discuss the performance shunt APF based on IRP theory for single-phase power system based on Clarke’s transformation method and phase-shift method to compensate current harmonics generated by nonlinear loads. Three types of nonlinear loads with different power ratings and harmonics characteristic are tested in MATLAB/Simulink to show the effectiveness of the tested control methods. As the results, show that Clarke’s transformation method given better harmonics compensate ability compared to Phase-shift method.

Analyzing power quality issues in electric arc furnace by modeling

Rapid growth of non-linear loads in distribution network has attracted power system engineers' attention from power quality point of view. Electric arc furnace (EAF) is one of the typical industrial non-linear loads responsible for deteriorating the power quality in the distribution network by introducing harmonics, propagating voltage flicker and causing unbalance in voltages and currents. Therefore, the EAF model is required to be studied and the power quality required to be analyzed in the distribution network. This paper presents a novel time domain EAF model to study power quality problems. The proposed model is a combination of two previous EAF models called-exponential and hyperbolic model-using transition functions. The functioning of the proposed model has been validated by comparing its various performance characteristics with the existing Cassie-Mayr's EAF model and with real measured data available. Current harmonics, voltage harmonics along with voltage flickers are considered as power quality problems for study and analysis. Simulation is carried out in SIMULINK/MATLAB environment.

수동형 필터 적용시 무효전력의 변화에 관한 연구

Generally, the low-voltage customer has been used with a linear load and nonlinear load in the 3-phase 4-wire distribution system. Linear load has usually configured the resistance and inductance, current phase is slower than the voltage phase, so power factor is low. It is required for the power factor correction device prior to the phase of the current than the voltage. The capacitor is connected in parallel to the load in order to ensure a low power factor. Power converter such as an inverter is a typical non-linear load. Non-linear load generates harmonic currents in the energy conversion process. Many electrical equipment may be adversely affected by the harmonic current. There, passive or active filter have been used to reduce these harmonics current. Passive filter consisting of inductor and capacitor generates a reactive power. According to the combination of filter inductor and capacitor, reactive power can be adjusted. In this paper, we analyzed how the combination of inductor and capacitor affects the overall power factor by simulation and measurement.

Simplified Adaptive Linear Neuron Harmonics Extraction Algorithm for Dynamic Performance of Shunt Active Power Filter

This paper presents a single-phase shunt active power filter with artificial intelligence based algorithms by introducing a new Simplified Adaptive Linear Neuron (ADALINE) algorithm for harmonics extraction. The proposed harmonics extraction is an innovative work over the established algorithm, known as Modified Widrow-Hoff ADALINE algorithm. Three significant major improvements are made by modifying weight updating technique which leads to introduction of fundamental active current updating technique, removing cosine component according to symmetrical theory of periodic signal, and minimizing large average square error by removing sum of elements. The SAPF with the proposed harmonics extraction algorithm was simulated in MATLAB/Simulink. For practical validation, the experimental laboratory prototype was also developed, and the algorithm was implemented using Digital Signal Processor TMS320F28335. Both simulation and experimental tests cover different types of nonlinear loads and dynamic operation of loads. From simulation and experimental results, significant improvements in terms of Total Harmonic Distortion and response time are shown together with comparison analysis with the established algorithm.

Experimental Investigation on a Hybrid Series Active Power Compensator to Improve Power Quality of Typical Households

In this paper, a transformerless hybrid series active filter using a sliding-mode control algorithm and a notch harmonic detection technique are implemented on a single-phase distribution feeder. This method provides compensation for source current harmonics coming from a voltage fed type of nonlinear load (VSC) and reactive power regulation of a residential consumer. The realized active power filter enhances the power quality while cleaning the point of common coupling (PCC) from possible voltage distortions, sags, and swells initiated through the grid. Furthermore, to overcome drawbacks of real-time control delay, a computational delay compensation method, which accurately generates reference voltages, is proposed. Based on an improved compensation strategy, while the grid current remains clean even with a small compensation gain, voltage disturbances initiated by the power system are obstructed by the compensator, and the PCC became free of voltage harmonics and protected from sag and swell. Simulation and experimental results carried on a 1.6-kVA prototype are presented and discussed.

Research on Voltage Balance Control and Simulation of Chain-Type APF in High Magnetic Field

Steady-state magnetic field superconducting magnet power adopted double-inverse-star thyristor rectifier solutions, it is a typical non-linear load which will bring great reactive power impact and harmonic pollution at runtime. In this paper, according to the scheme of scientific facility chain-type high voltage active power filter (APF), a three-grade voltage balance control of capacitor method was proposed. Considering the non-linear characteristics of APF, we using fractional order PI controller instead of ordinary PI controller. The solution of fractional order calculus is realized based on the improved Oustaloup algorithm. Finally, the working effect of fractional order PI controller and ordinary PI controller are comparative analysis through simulation and experimental results, the results show that the DC voltage balance control strategy used in this paper is correct, and has a certain reference value.

Research and Application of Chain Type APF Using PI<sup>λ </sup>Current Inner-Loop Controller in the Outer Superconducting Magnet

Steady-state magnetic field Superconducting magnets power supply with double inverse star thyristor rectifier technology solutions, is a typical non-linear loads, will bring great reactive power impact and harmonic pollution at runtime. This paper according to the scheme of scientific facility chain type high voltage active power filter (APF), combined with the non-linear characteristics of the active filter system and proposed a current inner-loop decoupling method using fractional order PI controller instead of ordinary PI controller. Based on the improved Oustaloup algorithm, the solution of fractional order calculus is realized. Finally, the working effect of fractional order PI controller and ordinary PI controller are comparative analysis through simulation and experimental results, the results show that: fractional order current inner-loop PI controller used in this paper is correct, and has a certain reference value.

A simulation based case study for control of DSTATCOM

This paper presents a distribution static compensator (DSTATCOM) for power quality improvements in terms of harmonics and power factor correction in a three-phase four-wire distribution system. The DSTATCOM is implemented with PWM current controlled six-leg voltage source converter (VSC) and the switching patterns are generated through a novel synchronous reference frame controller (SRFC). The insulated gate bipolar transistor (IGBT) based VSC is supported by a capacitor and is controlled for the required compensation of the load current. The DSTATCOM is connected to the power system feeding nonlinear loads. Nonlinear loads include either current-source type or voltage-source type. Harmonic spectrum of the source current is compared in between without DSTATCOM and with DSTATCOM by considering both types of nonlinear loads. The SRFC based DSTATCOM system is validated through extensive simulation for diode-rectifier and unbalanced R–L loads with a case study.

Characteristic and Model Analysizes of Steady-State Harmonic Source for DC Charger

The objective of this paper is to present the system construction and operational principle for a DC charger of electric vehicle. By means of analyzing AC and DC sides for the chargers, a reason was derived theoretically for producing specified harmonic current while absorbing fundamental wave of electric power system. The modeling and measuring procedures of multi-harmonic source for single and multiple chargers were proposed. The summation effect of harmonics for charge/exchange station which was regard as a public coupling circuit (PCC) of the electric power system. The simulation and measuring results indicate that as a new type of nonlinear load, the charger represented a characteristic of steady-state harmonic source.

Lyapunov Function-Based Current Controller to Control Active and Reactive Power Flow From a Renewable Energy Source to a Generalized Three-Phase Microgrid System

In this paper, a novel current control technique, implemented in the a-b-c frame, for a three-phase inverter is proposed to control the active and reactive power flow from the renewable energy source to a three-phase generalized microgrid system. The proposed control system not only controls the grid power flow but also reduces the grid current total harmonic distortion in the presence of typical nonlinear loads. The control system shapes the grid current taking into account the grid voltage unbalance, harmonics as well as unbalance in line side inductors. The stability of the control system is ensured by the direct method of Lyapunov. A SRC is also proposed to improve the performance of the current controller by estimating the periodic disturbances of the system. The proposed control system (implemented digitally) provides superior performance over the conventional multiple proportional-integral and proportional-resonant control methods due to the absence of the PARK's transformation blocks as well as phase lock loop requirement in the control structure. A new inverter modeling technique is also presented to take care of unbalances both in grid voltages and line side inductors. Experimental results are provided to show the efficacy of the proposed control system.

A Novel Hysteresis Current Control Strategy with Fuzzy Bandwidth for Active Power Filter

This paper presents a novel hysteresis current control strategy with fuzzy bandwidth for Active Power Filter. Based on the structure of traditional hysteresis current unit of APF and with the analysis of the variation of hysteresis bandwidth, an internal fuzzy controller is designed in order to dynamically adjust the loop width of hysteresis comparator device. Compared to traditional hysteresis method, progresses are made not only in limiting the switching frequency of power switches so that protect the APF device, but also in achieving a more excellent dynamic response and precision of compensation. Finally, the harmonic compensating efficiency to the typical non-linear loads of the approach presented is further verified by the simulation and experiment results in this paper. Ill. 10, bibl. 11, tabl. 1 (in English; abstracts in English and Lithuanian). DOI: http://dx.doi.org/10.5755/j01.eee.120.4.1442

A Neural-Network-Based Method of Modeling Electric Arc Furnace Load for Power Engineering Study

It is known that artificial neural network is a powerful scheme for function learning and modeling nonlinear loads. However, a direct application of artificial neural network for modeling time-varying loads may lead to inaccuracies. This paper presents an accurate neural-network-based method for modeling the highly nonlinear voltage-current characteristic of an ac electric arc furnace (EAF). The neural-network-based model can be effectively used to assess waveform distortions, voltage fluctuations, and performances of reactive power compensation devices associated with the EAF in a power system. Simulation results obtained by using the proposed model are compared with the actual measured data and two other traditional neural network models. It is shown that the proposed method yields favorable performance and can be applied for modeling similar types of nonlinear loads for power engineering studies.

Curve-fitting-based method for modeling voltage–current characteristic of an ac electric arc furnace

Field measurements of voltage and current are the most effective way for characterizing the electric response of an ac electric arc furnace that describes its nonlinear behavior. Sufficient measured information can be adopted to determine the background harmonic level in a power system, to characterize specific sources of harmonics, and to develop an appropriate nonlinear voltage–current characteristic. In this paper, a curve-fitting-based method called cubic spline interpolation is proposed to model the voltage–current characteristic of an ac electric arc furnace in the steady state. Meanwhile, the actual measured data are collected for modeling use. Two classic methods, harmonic current injections and equivalent harmonic voltage sources, for modeling the electric arc furnace load are reviewed and used to evaluate the performance of proposed model. Results obtained from the measured data and computer simulations of the three electric arc furnace models are then compared according to the voltage and current waveforms, as well as the voltage–current characteristic. It is shown that the proposed model is more accurate than the two classic approaches for harmonic assessment of electric arc furnaces and can be used for modeling similar types of nonlinear loads in the harmonic penetration study.

Studies on the Unusual Maloperation of Transformer Differential Protection During the Nonlinear Load Switch-In

Several cases of abnormal maloperation of the transformer differential protection with second harmonic blocking scheme are reported, which occurs when a type of nonlinear load, such as furnace, is switched-in to the transformer involved power systems. Different from well-known maloperation due to unloaded transformer energization, this type of maloperation does not occur on the time of load switching-in, but with a considerable time delay. The previous theories, including that interpreting sympathetic inrush, cannot be utilized directly to analyze this phenomenon. In this paper, a model for analyzing the transient course of the nonlinear load switching in, together with the description of the simplified characteristics of the transformer core and the nonlinear load is proposed to explain above-mentioned category of mal-operations. A set of nonlinear differential equations are formed using this model and a 4-order Runge-Kutta algorithm is utilized to solve the flux linkages and currents. The waveform and harmonic characteristic of the differential current are analyzed. It is disclosed that the maloperation of the transformer differential protection during the nonlinear load switching in mainly results from the saturation of transformer core caused by the interaction of the two nonlinear elements. This point of view is verified with the simulation tests.