Use Of Nonlinear Devices Research Articles

An artificial neural network based approach for harmonic component prediction in a distribution line

With the increasing use of nonlinear devices in both generation and consumption of power, it is essential that we develop accurate and quick control for active filters to suppress harmonics. Time delays between input and output are catastrophic for such filters which rely on real-time operation. Artificial Neural Networks (ANNs) are capable of modeling complex nonlinear systems through adjustments in their learned parameters. Once properly trained, they can produce highly accurate predictions at an instantaneous time frame. Leveraging these qualities, various complex control systems may be replaced or aided by neural networks to provide quick and precise responses. This paper proposes an ANN-based approach for the prediction of individual harmonic components using minimal inputs. By extracting and analyzing the nature of harmonic component magnitudes obtained from the survey of a particular area through real-time measurements, a sequential pattern in their occurrence is observed. Various neural network architectures are trained using the collected data and their performances are evaluated. The best-performing model, whose losses are minimal, is then used to observe the harmonic cancellation for multiple unseen cases through a simplified simulation in hardware-in-the-loop. These neural network structures, which produce instantaneous and accurate outputs, are effective in harmonic filtering.

Mitigation of Grid Current Harmonics by ABC- ANN based Shunt Active Power Filter

Harmonics are being introduced into power system networks as a result of the increasing use of nonlinear devices. These harmonics cause distortion of current and voltage signals, which in turn causes damage to power distribution systems. As a result, the suppression of harmonics is of extreme significance in power systems. This paper proposes Shunt Active Power Filters (SAPF) based on neural network algorithms like Artificial Neural Network (ANN) as a feasible approach to mitigating harmonic distortion and raising power quality in electrical distribution systems. This research shows that using shunt active power filters (SAPF), which use the Artificial Bee Colony Optimized Artificial Neural Network Controller (ABC-ANN), is an efficient method for enhancing power quality and minimizing harmonic distortion in distribution systems. The ABC-ANN algorithms have been produced for SAPF with the goal of improving system performance by reducing Grid current Harmonics .In the first stage of this work, PSO Technique is used to tune a standard PI controller to its optimum gain values (Ki ,Kp). Then, these target and input data of PSO tuned PI controller will be supplying inputs to the ANN controller. To find the optimal weight and bias values, this ANN controller has been tuned with the help of the ABC algorithm. Using MATLAB/SIMULINK software, we compare the performance of the proposed algorithm to that of other optimization algorithm like Differential Evaluation (DE) algorithm, as well as the PSO tuned PI controller and traditional PI controller. The findings from the simulation suggest that a SAPF utilizing an ABC trained ANN controller could improve THD in the supplying current while maintaining harmonics within IEEE-519 accepting levels.

Comparison of Methods for Determining Harmonic Distortion Contributions Using the IEEE Benchmark Test System

The growing use of nonlinear devices has raised the harmonic levels in power systems. A challenging power quality problem is determining how much each installation contributes to the harmonic voltages measured at a point of common coupling so that the costs of mitigation solutions can be fairly divided. Currently, there is still no practical worldwide established method to solve this problem. The IEEE PES Task Force on Harmonic Modeling and Simulation developed a Benchmark Test System to support this line of research. Therefore, this study uses the IEEE PES Benchmark to evaluate and compare harmonic contribution determination (HCD) methods. To do so, this Benchmark Test System was implemented in MATLAB/Simulink and used to test five HCD methods proposed in the literature under different network operating cases, including cases with background distortions and resonance. The methods are the Voltage Harmonic Vector Method, the IEC Method, the Dominant Impedance Method, the Capacitor Switching Method, and the Harmonic Current Injection Method. It has been found that the HCD methods generally led to similar contribution percentages, proving the convergence of the methodologies. In addition, an analysis of the methods' sensitivity to input measurement errors was done.

A novel negative feedback phase locked loop-based reference current generation technique for shunt active power filter

The use of nonlinear devices introduces current and voltage harmonics into power distribution networks. The presence of harmonics, an undesirable power quality issue, causes transformer overheating, malfunctioning of sensitive loads, power losses, and significantly reduced distribution system efficiency. Therefore, harmonics mitigation in power systems has become absolutely essential and is widely addressed, utilizing shunt active power filters (SAPFs) around the globe. The performance of SAPF in generating adequate compensating current depends on the working of three control loops used for the purpose of reference current generation, dc-link voltage control, and switching pulse generation. The existing approaches for reference current generation suffer from inherent complexity and the inability to extract positive sequence signals required for obtaining synchronizing angle during source disturbance conditions. Therefore, this paper proposes a novel negative feedback phase-locked loop-based modified synchronous reference frame technique to overcome the drawback of the existing approaches. The effectiveness of the proposed approach is investigated under ideal and non-ideal grid voltage conditions with different load perturbations. The proposed control strategy is first tested using a number of simulation-based experiments and, thereafter, validated using OPAL-RT 4510 real-time digital simulator. Compared to other existing approaches, the proposed technique has offered improved results in terms of reduced total harmonics distortion.

IMPACT OF ELECTRIC ENERGY QUALITY ON FIRE SAFETY OF TRANSFORMERS

The use of non-linear devices causes unfavourable changes in the operation of the power system. First of all, they are a source of higher harmonics in network waveforms, which tend to increase the eddy currents. Their effect consists in raising the temperature of transformer cores. This, in turn, translates into their failure rate and fire safety, including reducing the actual value of rated power. The article describes the results of experimental studies carried out on a large scale. An analysis was performed of the quality of electric power depending on the type of network load. The results have shown that the increase in the use of non-linear receivers such as LED lighting, electronic chargers, inverters, etc. may have a tangible impact on the fire hazard of distribution transformers. Examples of calculations have been presented, which prove the necessity of taking into account the influence of higher harmonics on the reduction of the real rated power of power transformers.

Power quality analysis of a mechanical industry – A case study

This study discusses the power quality of heavy industry at MIDC area in Pune city of Maharashtra state (India). Power quality issues are rapidly increasing in electrical distribution networks due to industrial revolution. Use of nonlinear devices and heavy load equipments is increasing with industrial revolution. Also due to industrialization the rate of environmental pollution and electrical pollution is also growing. This study examines and measures the electrical pollution associated with heavy mechanical industry. Power quality analysis is conducted with application of power quality analyzer in mechanical industry. The input side of the loads is considered for various required measurements for the presented study. The objective of this paper is to find out the harmonics contents in mechanical industry, analyze readings and determine the level of harmonics in voltage and current.

Adaptive Fuzzy Logic Controller for Harmonics Mitigation Using Particle Swarm Optimization

An excessive use of non-linear devices in industry results in current harmonics that degrades the power quality with an unfavorable effect on power system performance. In this research, a novel control technique-based Hybrid-Active Power-Filter (HAPF) is implemented for reactive power compensation and harmonic current component for balanced load by improving the Power-Factor (PF) and Total–Hormonic Distortion (THD) and the performance of a system. This work proposed a soft-computing technique based on Particle Swarm-Optimization (PSO) and Adaptive Fuzzy technique to avoid the phase delays caused by conventional control methods. Moreover, the control algorithms are implemented for an instantaneous reactive and active current (I_d-I_q) and power theory (Pq0) in SIMULINK. To prevent the degradation effect of disturbances on the system's performance, PS0-PI is applied in the inner loop which generate a required dc link-voltage. Additionally, a comparative analysis of both techniques has been presented to evaluate and validate the performance under balanced load conditions. The presented result concludes that the Adaptive Fuzzy PI controller performs better due to the non-linearity and robustness of the system. Therefore, the gains taken from a tuning of the PSO based PI controller optimized with Fuzzy Logic Controller (FLC) are optimal that will detect reactive power and harmonics much faster and accurately. The proposed hybrid technique minimizes distortion by selecting appropriate switching pulses for VSI (Voltage Source Inverter), and thus the simulation has been taken in SIMULINK/MATLAB. The proposed technique gives better tracking performance and robustness for reactive power compensation and harmonics mitigation. As a result of the comparison, it can be concluded that the PSO-based Adaptive Fuzzy PI system produces accurate results with the lower THD and a power factor closer to unity than other techniques.

Neural Networks Based Shunt Hybrid Active Power Filter for Harmonic Elimination

The growing use of nonlinear devices is introducing harmonics in power system networks that result in distortion of current and voltage signals causing damage to power distribution systems. Therefore, in power systems, the elimination of harmonics is of great significance. This paper presents an efficient techno-economical approach to suppress harmonics and improve the power factor in power distribution networks using Shunt Hybrid Active Power Filters (SHAPF) based on neural network algorithms like Artificial Neural Network (ANN), Adaptive Neuro-Fuzzy Inference System (ANFIS), and Recurrent Neural Network (RNN). The objective of the proposed algorithms for SHAPF is to enhance system performance by reducing Total Harmonic Distortion (THD). In our filter design approach, we tested and compared conventional pq0 theory and neural networks to detect the harmonics present in the power system. Moreover, for the regulation of DC supply to the inverter of the SHAPF, the conventional PI controller and neural networks-based controllers are used and compared. The applicability of the proposed filter is tested for three different nonlinear load cases. The simulation results show that the neural networks-based filter control techniques satisfy all international standards with minimum current THD, neutral wire current elimination, and small DC voltage fluctuations for voltage regulation current. Furthermore, the three neural network architectures are tested and compared based on accuracy and computational complexity, with RNN outperforming the rest.

Intelligent Hybrid-Fuzzy Controller using VLLMS Based Shunt Active Filter

The power quality problem in the power system is increased with the use of non-linear devices. Due to the use of non-linear devices like power electronic converters, there is an increase in harmonic content in the source current. Due to this there is an increase in the losses, instability and poor voltage waveform. To mitigate the harmonics and provide the reactive power compensation, we use filters. There are different filters used in the power system. Passive filters provide limited compensation, so active filters can be used for variable compensation. In this work, a shunt active filter has been made adaptive using a Variable Leaky Least Mean Square (VLLMS) based controller. Proposed adaptive controller can be able to compensate for harmonic currents, power factor and nonlinear load unbalance. DC capacitor voltage has been regulated at a desired level using a PI controller and a self-charging circuit technique. But, this scheme as two disadvantages such as, tuning issues of current controller pre-requisites the traditional PI controller, which is controlled by intelligent based Hybrid-Fuzzy-Logic controller for achieving good performance features. The design concept of proposed intelligent Hybrid-Fuzzy controller for shunt active filter has been verified through simulation analysis and results are presented with proper comparisons.

Power Quality Improvement using Intelligent Fuzzy-VLLMS Based Shunt Active Filter

The power quality problem in the power system is increased with the use of non-linear devices. Due to the use of non-linear devices like power electronic converters, there is an increase in harmonic content in the source current. Due to this there is an increase in the losses, instability and poor voltage waveform. To mitigate the harmonics and provide the reactive power compensation, we use filters. There are different filters used in the power system. Passive filters provide limited compensation, so active filters can be used for variable compensation. In this paper, a shunt active filter has been made adaptive using a Variable Leaky Least Mean Square (VLLMS) based controller. Proposed adaptive controller can be able to compensate for harmonic currents, power factor and nonlinear load unbalance. DC capacitor voltage has been regulated at a desired level using a PI controller and a self-charging circuit technique. But, this scheme has two disadvantages such as, tuning issues of current controller pre-requisites the traditional PI controller, which is controlled by intelligent based Fuzzy-Logic controller for achieving good performance features. The design concept of proposed intelligent Fuzzy controller for shunt active filter has been verified through simulation analysis and results are presented with proper comparisons.

Power Quality Improvement Using VLLMS Based Adaptive Shunt Active Filter

The power quality problem in the power system is increased with the use of non-linear devices. Due to the use of non-linear devices like power electronic converters, there is an increase in harmonic content in the source current. Due to this there is an increase in the losses, instability and poor voltage waveform. To mitigate the harmonics and provide the reactive power compensation, we use filters. There are different filters used in the power system. Passive filters provide limited compensation, so active filters can be used for variable compensation. In this paper, a shunt active filter has been made adaptive using a Variable Leaky Least Mean Square (VLLMS) based controller. Proposed adaptive controller can be able to compensate for harmonic currents, power factor and nonlinear load unbalance. DC capacitor voltage has been regulated at a desired level using a PI controller and a self-charging circuit technique. The design concept of proposed adaptive controller for shunt active filter has been verified through simulation and experimentation.

On the Time-Varying Non-Linearity Effects Over the Spectrum of MIMO-OFDM Wireless Communications Systems

This article presents analytical expressions that can be used in the evaluation of the effects of a non-linear mobile (multi-path) channel on the spectrum of MIMO-OFDM communications systems, such as 4G systems (LTE, WiMax) and probably the future 5G systems. The channel is modeled by a time-varying Volterra Series and the MIMO-OFDM signal by a complex, proper, wide-sense stationary Gaussian random process with zero mean. The resulting mathematical expressions are applied to a specific situation, allowing a quantitative evaluation of the out-band spectrum regrowth of MIMO-OFDM wireless communications systems produced by the use of non-linear devices in mobile channels.

Study and Analysis of the Effect of Harmonics on the Hot Spot Temperature of a Distribution Transformer Using Finite-Volume Method

Transformers are critical components in power systems and their failure can cause long interruption of power supply. The condition of a transformer can be monitored by performing thermal analysis. The use of non-linear devices, such as rectifiers and converters, draws harmonic currents that increase losses in transformers, thereby increasing their operating temperature. In this article, a new numerical approach is presented for determining the rise in hot spot temperature in a 5-kVA, 400/400-V dry-type three-phase transformer laboratory prototype. The key novelty is that the additional winding eddy current loss due to non-linear loads is considered in the numerical modeling. The winding eddy current loss corresponding to harmonic distortion is estimated by conducting experiments and calculations. Numerical simulations are carried out for a wide range of non-linear loads using a commercial computational fluid dynamics package, FLUENT 6.3. The proposed numerical methodology is validated by performing experiments on the transformer for possible non-linear loads and comparing the measured hot spot temperature with the simulated values. Correlation equations for rise in hot spot temperature as a function of total harmonic distortion are presented, which can be used for estimating the life of transformers when connected to different types of loads.

The Effect of Harmonic Distortion on the Performance of Differential Relay for Distribution Transformer Protection

This paper aims to analyzing and probing the influences of power system harmonics on a differential relay used for distribution transformer protection. The increased use of nonlinear devices in industry, commercial and residential areas can lead to a significant increase the level of harmonic distortion in the power system. This harmonic has the significant effects to the differential protection systems components such as current transformer (CT) and relay. The CT tends to saturate due to the presence of current harmonics in power system, so it will produce magnitude secondary current error and make the differential relay to miss operations. The harmonic distortion effects on the differential protection have been investigated through laboratory test. To determine the CT errors when operates under harmonic condition, the CT has been test with certain level of THDi. The result of this testing was found that with increasing of the THDi, the magnitude of secondary current error increased and differential relay will operate at no fault conditions.

Power quality index based on discrete wavelet transform

Changing power system regulations and increased use of nonlinear devices have made power quality (PQ) a highly important issue. The short duration transient disturbances, along with the stationary harmonics have become very common due to the increased use of power electronic switches. These transients are defined in terms of their spectral content, duration and magnitude by IEEE 1159-2009 standards and are non-stationary in nature. The conventional PQ indices based on Fourier transform fails to indicate them, since Fourier transform gives amplitude frequency distribution and the time information gets void. In this paper, a PQ index, based on discrete wavelet transform (DWT) is proposed in order to determine the amount of deviation from the desired pure signal. The proposed PQ index is defined as the weighted sum of percentage energy deviation of the DWT details. The test system is simulated using ATP/EMTP software. Transients resulted from ten different switching instants covering a full cycle of the signal and having natural frequency ranging from 500Hz to 47kHz, are considered to validate the proposed index. The proposed index is also tested with the signals containing harmonics. Further, the proposed index is verified with the real signals acquired by the laboratory experimentation.

Neural Network Based Method for Predicting Nonlinear Load Harmonics

Generation of harmonics and the existence of waveform pollution in power system networks are important problems facing the power utilities. The increased use of nonlinear devices in industry has resulted in direct increase of harmonic distortion in the industrial power system in recent years. Interaction between loads and sources in a power distribution network is a complex process and often not possible to explain analytically without making assumptions. The determination of true harmonic current distortion of a load is further complicated by the fact that the supply voltage waveform at the point of common coupling (PCC) is rarely a pure sinusoid. This paper proposes a neural network based method to find a way of distinguishing between load contributed harmonics and supply harmonics, without disconnecting any load from the network. A neural network structure with memory is used to model the admittance of the nonlinear load. Once training is achieved, the neural network predicts the true harmonic current of the load if it could be supplied with a clean sine wave. The main advantage of this method is that only waveforms of voltages and currents have to be measured and is applicable for single phase as well as multiphase loads. This could be integrated into a commercially available power quality instrument or be fabricated as a standalone instrument that could be installed in substations of large customer loads, or used as a hand-held clip on instrument

Industrial power quality considerations when installing adjustable speed drive systems

Developments in digital electronics and power semiconductors have led to a rapid increase in the use of nonlinear devices including adjustable speed drives. For this reason harmonics have become a common problem in many industrial electrical systems. The importance of a complete power system analysis prior to the installation of new equipment is discussed in this paper. Methods of harmonic mitigation and the effect of the IEEE 519 Guideline-1992 on industry are also discussed.

Error Rates in Differentially Coherent Phase Systems in Non-Gaussian Noise

A theoretical analysis of the differentially coherent phase-shift keying system acting under a wide range of noise and signal conditions is given. In addition to the elemental error rate, it is desirable to know the error rates for sequences of errors, since there is intersymbol dependency in this system. To determine the probability of a sequence of r errors requires, at most, integrations over volumes up to 2r + 2 dimensions, which are performed by Monte Carlo techniques. The analysis and computational schemes are such that any noise and signal statistics, as well as the use of nonlinear devices (noise suppression equipment), can be taken into account in calculating the error rates (for a k -phase system) as long as the resulting joint distributions of the instantaneous SNR at the phase detector can be determined in some form. A sequence of r errors requires knowledge of the ( r + 1 )st-order distribution. Since nothing is known of the joint densities of atmospheric or other non-Gaussian interference, and since many systems have slow enough bit rates for the noise to be independent from one integration period to the next, examples are given for the independent case for Gaussian noise and characteristic samples of atmospheric noise. Results for both constant and slow, flat, Rayleigh fading signal for the two and four phase systems are given, and comparisons of experimental results with the theoretical error rates are made. Also, for comparison, expressions are derived and results given for the error rates corresponding to the above for the coherent PSK system.