Types Of Nonlinear Loads Research Articles

Nonlinear Loads Modelling and Harmonics Analysis: A Review

Abstract: In modern life, the applications of nonlinear loads are increasing, especially electronic loads, such as computers, monitors, and battery chargers. Moreover, the usage of semiconductors has increased in modern lighting systems, such as LED lamps and dimmers which are used to control the lighting level. Nonlinear loads may also be in the form of variable speed drive or arc furnace loads. Due to the spread of nonlinear loads, large amounts of harmonics are generated. To study the harmonics of nonlinear loads, it is essential to represent nonlinear loads by their equivalent models in the simulation programs. This paper presents a comprehensive review of modeling methods of nonlinear loads, including time domain methods, frequency domain methods, and state space methods. Equivalent circuits are presented for different types of nonlinear loads, including static loads, dynamic loads and arc furnace loads. The paper also presents the harmonic analysis performed by the Fourier transform of different types of nonlinear loads, including harmonic percentage and its angle. This paper is considered as a comprehensive reference for researchers and engineers to model nonlinear loads and is useful in power system planning for connecting nonlinear loads where mixing nonlinear loads of similar harmonic profiles causes worse situations. Moreover, knowing the nonlinear load profile will help in the suitable mixing of linear loads to achieve lower harmonics levels.

Comparison of Control Techniques for Harmonic Isolation in Series VSC-Based Power Flow Controller in Distribution Grids

The application of power electronics equipment in medium voltage (MV) distribution grids can provide new management solutions for power flow control, load balancing and voltage problems. A series MV VSC-based power flow controller has recently been presented to interconnect two radial distribution feeders performing active and reactive power transfers to improve the flexibility and utilization of these circuits in a controlled and secure way. Although not previously explored, this power flow controller can integrate the functionality of a series power filter, accomplishing independent control of the fundamental power flow while isolating the harmonic content between the two interconnected feeders. This prevents harmonic pollution from one feeder from propagating to the other, improving the voltage quality. To implement the harmonic isolation, several control strategies can be used. Therefore, this paper provides a comparative analysis between two of the main harmonic control techniques found in the literature: the Synchronous Reference Frame (SRF) controller and the Proportional Resonant (PR) controller. Assessments are conducted both through simulations and experimental results in a meshed network at 13.8 kV with different types of non-linear loads. In the simulation cases, both algorithms showed similar results; however, in the experimental cases, the PR-based solution exhibited better performance in isolating the harmonics from one feeder to the other.

An Appropriate Index to Assess the Global Cancellation Level of the Harmonic Currents Consumed by a Set of Single-Phase Uncontrolled Rectifiers and a Set of Fluorescent Lamps

An in-depth study of harmonic current reduction in European commercial buildings due to the harmonic cancellation effect when a set of single-phase uncontrolled rectifiers and a set of fluorescent lamps are connected at the same voltage level is essential, since both types of non-linear loads are very present in commercial and residential sectors. This paper provides an appropriate index to assess the global cancellation level of the harmonic currents for this study. The equivalent circuit per phase of the typical three-phase power system of European commercial installations is presented and simplified for the cancellation analysis of the harmonic currents consumed by a set of multiple identical single-phase uncontrolled rectifiers and a set of multiple identical fluorescent lamps connected at the same voltage level. The suitability and usefulness of the proposed index are shown by applying it to that analysis, which leads to some results of practical interest. This index can be generalized to any number of sets of multiple identical non-linear loads and can be applied in graphical and optimization studies that will allow a greater benefit from the harmonic cancellation effect to be obtained given the global nature of the index.

A wavelet feature-based neural network approach to estimate electrical arc characteristics

Electric Arc Furnaces (EAFs) account for almost half of the North American steel production. Arc furnaces draw high and dynamic electrical power to melt scrap metal loads and as the result, they are highly non-linear and time-varying in nature. Because of the power system problems associated with EAFs, there is an ongoing need to accurately model EAFs to properly assess the impact of these types of nonlinear loads. This paper proposes a wavelet feature-based neural network approach for modeling the dynamic voltage-current (v-i) characteristic of the EAF. This method uses the data from the operational electric arc furnaces to describe the underlying processes, and unlike conventional mathematical techniques does not rely on presumed model structures, or simplified assumptions. The simulation results obtained by using the proposed method are compared with the actual measured data, and it is shown that the proposed method accurately models the EAF dynamic v-i behavior.

A general review of power quality standards and terminologies

In the next few years, more than 80% of AC power is to be processed through power converters owing to their benefits of energy conservation, flexibility, network interconnection, and weight and volume reduction in a number of equipment such as lighting arrestors, HVAC computers, fans, and so on.This paper gives an introduction on power quality (PQ), causes and effects of power quality problems. It also deals with power quality definitions, terminologies, standards, bench-marks, monitoring requirements, financial loss, and analytical quantification. It also discusses various types of nonlinear loads, which cause these power quality problems, they are illustrated, classified, modeled, quantified, and analyzed forassociated power quality issues.

Simulation of passive filter design to reduce Total Harmonic Distortion (THD) in Energy-Saving Lamps (LHE) and Light Emitting Diodes (LED)

This paper discusses the design of a passive filter system for Energy-Saving Lamps (LHE) and Light Emitting Diodes (LED) using the MATLAB Simulink software. This type of lamp is a type of non-linear load that produces harmonics of current and voltage. However, this harmonic problem can be reduced using passive filters. To determine the size of the passive filter components, research was carried out in the form of measurements of power, power factor, voltage, current, THDi and THDv produced by the LHE and LED. The results of these measurements were simulated using MATLAB Simulink to determine the passive filter design that reduces the THD value on the LHE and LED. To reduce the level of current harmonics, a single tuned LC passive filter was designed. The filter, designed to work at a frequency of 50 Hz and is expected to reduce the level of harmonics in the 3rd, 5th, 7th, 9th, 11th harmonic orders so that the THD produced by LHE and LED meets the IEEE 519-2014 standards. The simulation results of single tuned LC passive filter design can reduce THDi by 46.78% from the initial THD of 84.55% so that it becomes 37.77%.

A general review of power quality standards and terminologies

In the next few years, more than 80% of AC power is to be processed through power converters owing to their benefits of energy conservation, flexibility, network interconnection, and weight and volume reduction in a number of equipment such as lighting arrestors, HVAC computers, fans, and so on. This paper gives an introduction on power quality (PQ), causes and effects of power quality problems. It also deals with power quality definitions, terminologies, standards, bench- marks, monitoring requirements, financial loss, and analytical quantification. It also discusses various types of nonlinear loads, which cause these power quality problems, they are illustrated, classified, modeled, quantified, and analyzed for associated power quality issues.

Real Time Harmonic Load Identification Based on Fast Fourier Transform and Artificial Neural Network

Harmonics at nonlinear loads have different values for each load. These characteristics can be used as identification of the type of load from the harmonic value produced from nonlinear load. Therefore, this paper proposes harmonic load identification using Fast Fourier Transform (FFT) and Artificial Neural Network (ANN). In order to obtain harmonic values, a prototype of measuring instruments is used, while the method for obtaining harmonic values is FFT. The harmonic value obtained will be used as training data and testing data in ANN. Then, the type of training used as the classification of load type is the Levenberq Marquardt. The input of this method is a harmonic value of three types of nonlinear loads with seven combinations. The training process is carried out in MATLAB. Then, the weight and the bias values of each neuron are obtained and programmed in microcontroller. In order to validate the proposed algorithm, testing is conducted by three nonlinear load combinations. The results show that the proposed algorithm has good results in load identification with the highest accuracy of 99.94%.

Impact of Harmonic Currents of Nonlinear Loads on Power Quality of a Low Voltage Network–Review and Case Study

The paper presents a power-quality analysis in the utility low-voltage network focusing on harmonic currents’ pollution. Usually, to forecast the modern electrical and electronic devices’ contribution to increasing the current total harmonic distortion factor (THDI) and exceeding the regulation limit, analyses based on tests and models of individual devices are conducted. In this article, a composite approach was applied. The performance of harmonic currents produced by sets of devices commonly used in commercial and residential facilities’ nonlinear loads was investigated. The measurements were conducted with the class A PQ analyzer (FLUKE 435) and dedicated to the specialized PC software. The experimental tests show that the harmonic currents produced by multiple types of nonlinear loads tend to reduce the current total harmonic distortion factor (THDI). The changes of harmonic content caused by summation and/or cancellation effects in total current drawn from the grid by nonlinear loads should be a key factor in harmonic currents’ pollution study. Proper forecasting of the level of harmonic currents injected into the utility grid helps to maintain the quality of electricity at an appropriate level and reduce active power losses, which have a direct impact on the price of electricity generation.

Nonlinear Load Harmonic Prediction Method Based on Power Distribution Internet of Things

A large number of nonlinear loads have an impact on the stable operation of the power system. To solve this problem, this article proposes a nonlinear load harmonic prediction method based on the architecture of Power Distribution Internet of Things. Firstly, this method integrates the characteristics of edge computing technology and Power Distribution Internet of Things technology and proposes a Power Distribution Internet of Things framework applied to nonlinear load harmonic prediction, which provides top-level design for subsequent harmonic prediction methods of Power Distribution Internet of Things; then, considering the electrical characteristics of the typical nonlinear load, the mathematical model of nonlinear load data is constructed based on the harmonic coupling admittance matrix model on the edge side. At the same time, a nonlinear load harmonic prediction model based on dynamic time warping and long-term and short-term memory network (DTW-LSTM) is established in the cloud computing center to realize high accuracy and high real-time prediction and analysis of nonlinear load harmonics. Finally, the simulation results based on the general data set show that the MAE evaluation index of the proposed method is less than 5% in the experimental group, which shows good generalization ability, and has some advantages over the current method in operation efficiency.

A modified harmonic pricing scheme for customers based on quantifying the harmonic comprehensive contribution

The growing application of various types of nonlinear loads aggravates the harmonic distortion in distribution networks. To effectively address the harmonic issues, implementing an incentive pricing mechanism is a feasible solution. In this paper, a modified scheme is proposed to achieve fair and reasonable harmonic pricing for every customer. The scheme uses a new quantitative index for determining the harmonic comprehensive contribution without any prior assumptions about harmonic impedance. By aggregating multiple time scales and harmonic orders, this new index outperforms the traditional index in representing the overall harmonic distortion responsibility. Moreover, the proposed scheme introduces the harmonic metering price and the harmonic penalty price, and it aims to rationally evaluate the costs of energy metering and harmonic mitigation. The efficacy of the proposed scheme is verified by computer simulation and field test. The simulation and experimental results demonstrate that the proposed scheme is better than the conventional scheme to provide a fairer harmonic price and encourage customers to reduce harmonic emissions.

An Intelligent PI Controller-Based Hybrid Series Active Power Filter for Power Quality Improvement

The quality of power that is degrading day by day is an important issue for all the consumers. The important factor for this is harmonics in the voltage and current waveforms which can be resolved by the use of hybrid series active power filter. The combination consists of a series active power filter and a shunt passive filter connected in parallel to the load. The method used in this paper is for the purpose of achieving good harmonic compensation and reduced total harmonic distortion for various types of nonlinear loads as per the standards of IEEE 519. The proposed HSAPF technique uses the synchronous reference frame method for generating the compensating signal with an intelligent PI controller that uses particle swarm optimization (PSO) technique to obtain the required gain values needed to improve the steady state response of the system. The concept of vigorous HSAPF has been authenticated through MATLAB simulation analysis, and the results obtained validate the accuracy of the method for the different load conditions.

Deep learning and signal processing based algorithm for autorecognition of harmonic loads

A convolution neural network (CNN) based deep learning method has been proposed for automatic classification and localization of nonlinear loads present in an interconnected power system. The identification of nonlinear loads has been previously dealt with the use of Nonlinear Auto Regression neural network with eXogenous inputs (NARX), Backpropagation Neural Network (BPNN), Probabilistic Neural Network (PNN), Artificial Neural Networks (ANN) and Fuzzy Logic (FL). However, these techniques had not explored the area of classification of industrial and domestic nonlinear loads in an interconnected power system. Also, a Deep learning-based solution for identification of the type of nonlinear load has not been reported in the literature to date. Hence, to address these shortcomings, an IEEE-9 Bus system with industrial nonlinear loads has been used to obtain various current waveforms with distortions. The recorded current waveforms are transformed into a time-frequency (TF) domain plane, and the obtained images are then fed to the deep learning algorithm. The colored images of the TF plots of each type of nonlinear load in Red-Green-Blue (RGB) index provide the best visual features for extraction. The TF domain signatures of individual events are scaled to a standard size before feeding to the algorithm. Through these TF signatures, unique features were extracted with the deep learning algorithm, and then passed on to different stages of convolution and max-pooling with fully connected layers. The softmax classifier at the end classifies the input data into the type of nonlinear present in the power system. The algorithm, when run at different buses, also identifies the location of the nonlinear load. The proposed methodology avoids the usage of any additional fusion layer for obtaining unique features, reduces the training time and maintains the highest accuracy of 100%.

Analysis of Harmonic Characteristics of Pulse Load Based on Switching Functions

As a kind of special nonlinear load, pulse load (PL) has the characteristics of two typical nonlinear loads. Compared with the traditional rectifier load, the harmonic characteristics of the PL are more complicated. In this paper, the harmonic characteristics of the PL is investigated. By analysing the working mode of the PL, an equivalent circuit model and a switch function model of the PL are introduced. It is analysed that the PL will inject a large number of inter-harmonics and even sub-harmonics in addition to the integer harmonics to the power system, and the harmonics are symmetrically distributed. The experiments were conducted on diesel generator sets (DGS) with PL and public grids with PL. The results show that the established model and analysis method can accurately calculate the harmonic distribution of the system, moreover, the influence of PL mode on harmonic characteristics can be revealed.

Performance Comparison of a Typical Nonlinear Load Supplied by ac and dc Voltages

This paper presents a performance comparison of a typical nonlinear load when supplied by ac or dc voltages with the same rms value. The performance of the nonlinear load towards its connection to ac and dc power grids is accomplished in terms of the waveforms and efficiency. A simulation model was

Uncertainty and Disturbance Estimator Based Controller Equipped With a Multiple-Time-Delayed Filter to Improve the Voltage Quality of Inverters

In this paper, a two-degrees-of-freedom control algorithm based on uncertainty and disturbance estimator (UDE), aimed to minimize the total harmonic distortion of inverter output voltage is proposed, possessing enhanced robustness to fundamental frequency variations. A multiple-time-delay action is combined with a commonly utilized low-pass UDE filter to increase the range of output impedance magnitude minimization around odd multiples of fundamental frequency for enhanced rejection of typical single-phase nonlinear loads harmonics. Marginal robustness improvement achieved by increasing the number of time delays is quantified analytically and revealed to be independent of delay order. The performance of the proposed control approach and its superiority over two recently proposed methods is validated successfully by experimental results.

Procedure to Evaluate the Impact in Distribution Single Phase Transformers Due to Insertion of New Nonlinear Load Which Changes Daily Demand Graphs

Power electronic development determines the introduction of nonlinear devices in electric power systems. Introduction of nonlinear devices increase current harmonics in transmission and distribution power systems. Distribution transformers and feeders increase power losses and their nominal parameters are reduced. The present work introduces a procedure to evaluate maximum permissible load in single phase distribution transformers with the introduction of a new type of nonlinear load which changes daily demand graphs.

Effect of Non-Linear Electricity Loads Against Harmonics in One Phase Inverters

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A Wide-Range Frequency Model for Dielectric Barrier Discharge Type Ozone Generators Powered by Series Resonant Inverters

Dielectric Barrier Discharge (DBD) type ozone generators (OGs) are widely used for industrial ozone generation. As OGs are typical non-linear load, different models are presented to analyze the characteristic of OGs and the models of OGs have proven to be an effective tool to design power supplies for OGs. However, most of the models are only applicable to nominal conditions and not suitable for a wide working range at present. Considering that almost all of the series resonant inverters use resonant tanks operating in resonance or near of it, the current through OGs can be substituted by a sinusoidal current source with variable amplitude and frequency. According to the concept, a wide-range frequency model composed of an equivalent resistance in series of an equivalent capacitance for OGs is proposed. Because the equivalent resistance and the equivalent capacitance are closely related to switching frequency of inverter and the current through OGs, the model can be used in the wide working range. Based on the model, the characteristic of OGs is analyzed and a methodology for power supplies is developed. Through a combination of the proposed model and the four limit parameters of ozone generators and power supplies in the methodology, the main circuit parameters of the power supply for maximizing the ability of OGs are obtained. To validate the wide-range frequency model and the design methodology, an ozone generation system powered by a 14-kW series resonant inverter is built. The differences between the experimental results and the analytical results show that the proposed model has satisfying accuracy in a wide working range. Compare to the conventional methodology for power supplies, the main circuit parameters of the power supply can be obtained conveniently regardless of the heavy-load condition and light-load condition of OGs.

Power Management of Heterogeneous Autonomous DC Microgrid System with EVs Using Modified SoC Reference Based DC Bus Voltage Control

Due to stochastic and intermittent nature of distributed generation (DG) sources, different types of nonlinear loads, different transmission lines and heterogeneous energy storage devices (ESDs) the system becomes complex and diverse in nature. The b