Harmonics In Distribution Networks Research Articles

Comparison and Optimization of the Use of Passive and Active Power Filters to Mitigate Harmonics in Distribution Networks with non-linear loads

Comparison and Optimization of the Use of Passive and Active Power Filters to Mitigate Harmonics in Distribution Networks with non-linear loads

Calculation of probabilistic harmonic power flow based on improved three-point estimation method and maximum entropy as distributed generators access to distribution network

Uncertainty and volatility are the features of distributed generation (DG), which can impact greatly on the operational status of distribution network. Thus, an improved three-point estimation method and maximum entropy theory (ITPEM&ME) for calculating the probabilistic harmonic power flow in distribution network is proposed in this study. Firstly, the probabilistic model is constructed according to the uncertainty of input variables and the improved three-point estimate method is utilized to convert a probabilistic problem into a deterministic problem. Secondly, in order to obtain the distribution of the random harmonics in distribution network, the maximum entropy theory is adopted to reconstruct the statistical characteristics after the deterministic calculation is realized for each harmonic voltages. The case of an IEEE-33 system under various conditions is conducted. The results by the different algorithms indicate that the proposed method ITPEM&ME has a smaller error than the traditional method, as well as the fitting effect of the probability density function (PDF) is much closer to the practical engineering. It is feasible and accurate in dealing with probabilistic harmonic power flow problems.

Transfer of Harmonics in Distribution Networks

This paper presents the role of the medium-voltage network and low-voltage loads in harmonic voltages with low-voltage customers and harmonic propagation. A general model as well as a detailed transfer function-based model are used. By applying them to an existing network, it is shown that remote low-voltage loads have a significant impact on the source and transfer impedance. The main impact occurs for a specific range of frequencies below the resonant frequency of the low-voltage network. The general model is able to estimate this frequency range with an acceptable level of accuracy. Furthermore, by utilizing the concept of overall transfer impedance, it is shown that voltage harmonic levels for harmonic orders around this frequency range are determined mainly by aggregated remote emission rather than local emission.

Modelling and prediction of current harmonics generated by power converters in distribution networks

Predicting current harmonics in distribution networks is essential to find harmonic losses and power quality indices. In order to predict the current harmonics, the effect of grid impedance and voltage distortions on grid-connected power converters need to be considered. The effects of these parameters on current harmonics can be nonlinear, which complicates the system analysis. Consequently, this paper investigates the impacts of background voltage harmonics, grid impedance, and multi-parallel grid-connected converters on current harmonics at a point of common coupling. Moreover, a novel method called combined least squares and kriging (CLSK) is proposed to predict the current harmonics after evaluating the level of system nonlinearity. In the proposed CLSK method, the prediction model is developed by measured voltage and current harmonics at the point of common coupling to identify and predict the current harmonics. This analysis shows that using the proposed CLSK method, the accuracy of the current harmonic prediction is increased compared to the existing methods. The accuracy and the efficiency of the proposed CLSK method are verified by lab experimental results and field measurement data.

Analysis on voltage characteristics of distribution network considering rolling mill load and Research on control measures

In view of the voltage fluctuation and flicker of distribution network caused by rolling mill type typical load in some distribution networks and the reduction of power quality of power grid, it is necessary to analyze the voltage characteristics of distribution network, and adopt an effective governance measure to suppress harmonics in distribution network and improve power quality of power grid. The mathematical models of several typical loads corrected based on the measured data are established, and the influence radiation range of the corrected rolling mill load model on the distribution network voltage is analyzed, and a SVC (static var compensator) governance measure with SOGI phase-locked strategy is adopted for governance. Finally, combined with the actual operation parameters of a substation of State Grid, the power system simulation model is built by using simulation software, and the effectiveness of the governance measures adopted in this paper is verified by simulation analysis.

Impacts of Grid Voltage Harmonics Amplitude and Phase Angle Values on Power Converters in Distribution Networks

Motor drive systems based on diode-rectifier are utilised in many industrial and commercial applications due to their cost-effectiveness and simple topology. However, these diode rectifier-based systems can be affected by power quality and harmonics in distribution networks. Thus, this paper investigates the impact of grid voltage harmonics on the operation of power converters with three-phase diode rectifier using mathematical formulation of the drive voltage and current harmonics based on grid voltage harmonics. Simulation analysis and practical tests have been then carried out to validate the mathematical equations and the impact of grid voltage harmonics on the power converter harmonics. The results illustrate that even a small amount of grid voltage harmonics (around 4%) could significantly impact the input current harmonic contents of the three-phase diode rectifier. It is also shown that the phase-angle of grid voltage harmonics plays a crucial role to improve or deteriorate the input current harmonics of the power converters. In the next step, the optimum condition of grid voltage harmonics to minimise the input current harmonics has been evaluated and verified based on different grid codes. Finally, a harmonic mitigation technique in multi-drive systems using Electronic Inductor is proposed to mitigate the current harmonics at the PCC.

Adaptive fuzzy controlled hybrid shunt active power filter for power quality enhancement

A novel switching pulse generation methodology based on adaptive fuzzy hysteresis current controlled hybrid shunt active power filter (A-F-HCC-HSAPF) is presented in this paper for compensating reactive power and harmonics in distribution network. The harmonic problems are mainly evolved because of extensive use of nonlinear loads in industry and domestic sectors. There are some adverse effects of harmonics such as: malfunctioning of sensitive equipment, resonance issues, conductors heating, power losses and reduced efficiency in distribution system. To mitigate harmonics issues passive, filters are used but when the harmonic component increases the design of passive filters is complex and becomes bulky. With the advancement in power electronic, the active power filter has been designed. Generally, the rating of the active filter is very high for some applications; hence hybrid shunt active power filter (HSAPF) is proposed by low-rated shunt active power filter (SAPF) and low-cost shunt passive filter. Proportional-integral or fuzzy logic controller is used to estimate the reference current and to regulate the dc capacitor voltage. To generate the switching pulse for the voltage source inverter of the SAPF, a novel adaptive fuzzy hysteresis current controller (A-F-HCC) is adopted. The performance of the proposed A-F-HCC-HSAPF is investigated during steady-state and transient conditions using MATLAB/Simulink and real-time environments.

A Modular Power Converter With Active Front-End System to Mitigate Harmonics in Distribution Networks

Power quality improvement of power electronics systems in many applications such as adjustable speed drive (ASD) is vital due to the high penetration of grid-connected converters in distribution networks. Conventional diode bridge rectifiers are widely utilized in three-phase systems due to their cost-effectiveness, simplicity, and reliability. To improve their harmonic behavior, in this article, a three-phase bridge rectifier with harmonic mitigation function using an electronic inductor is proposed. The proposed system can mitigate current harmonics caused by other conventional rectifiers connected at the same point of common coupling (PCC). Based on the proposed harmonic reduction technique, a combination of three-phase rectifiers can comply with low-order harmonic emission limits according to IEC 61000-3-12 standard. Simulation and practical measurements are performed to validate the proposed method.

Detection algorithm of ultra-high harmonics in distribution networks

Power quality of distribution network is an emerging issue due to rapid increase in usage of non-linear loads on the one hand and utilization of sensitive devices on the other hand. Especially, harmonic emission is an important concern in both electric utilities and end users of electric power. Therefore, an accurate and rapid harmonic analysis method is of interest. New technologies have enabled the investigation of electricity consumption mode at an unprecedented scale and in multiple dimensions. However, an effective method that can capture the complexity of all the factors relevant to understanding a phenomenon such as ultrahigh harmonics (2–15 kHz). How to detect the super high order harmonic accurately has become the premise and foundation of the study of super high order harmonic. The key challenge in developing such approaches is the identification of effective models to provide a comprehensive and relevant systems view. An ideal method can identify super high harmonics and predict outcomes, by measured data across several dimensions variation. In this paper, the data integration, current methods and available implementation is discussed. Finally, the current challenges in integrative methods is discussed.

Guest Editorial: Medpower 2018 Selected Papers

Guest Editorial: Medpower 2018 Selected Papers

Impact of photovoltaic and biogas power plant on harmonics in distribution network

Here, the impacts of biogas power plants and photovoltaic (PV) power plants on the power quality in the distribution network are presented and analysed. The biogas power plant's influence on the current harmonics is explored, as a synchronous generator powers the biogas power plant, and the PV plants are connected to the distribution network via the inverter. All the analyses are based on actual measurements that are performed in the last 10 years. Results of the analysis of these numerous measurements were a challenge for investigation how large share of PV systems in distribution network with non-linear loads influence on THD from one side and how biogas power plant with a synchronous generator can improve THD from the other side. In order to investigate interaction of the biomass power plant and PV power plants on the power quality in distribution network, computer model was developed in DIgSILENT Power Factory where PV power plant and household were modelled as a source of current harmonic injections and biomass power plant was modelled as synchronous machine, as a source of voltage harmonics. Analysis of harmonic behaviour in different scenarios is examined through the performed simulations.

Reduction of harmonic monitors and estimation of voltage harmonics in distribution networks using wavelet analysis and NARX

The use of power quality monitors is necessitated for optimizing power systems to improve efficiency and decrease power system-related failures. These monitors are expensive and their installation at all buses is not economic. With regard to optimum allocation approaches, power quality monitors should be installed for the assessment of the power quality of sensitive loads. Monitoring of sensitive loads is eliminated in this paper, and an estimator is used for virtually monitoring voltage harmonics. This paper presents an intelligent system based on the nonlinear autoregressive model with exogenous input (NARX) and wavelet analysis. The wavelet transform is utilized for extracting the feature of waveforms, and NARX is employed to detect the voltage harmonic distortion waveforms (VHDWs) at non-monitored sensitive loads in distribution networks using the information gained through the nearest monitoring data. The proposed estimator can be considered as a virtual monitor, eliminating the monitor of sensitive load such that the optimum number of power quality monitors and monitoring cost of the distribution network would be reduced. The estimator is examined on the IEEE test system and the performance of the intelligent system has been verified in many different ways.

Practical Approaches to Assessment of Harmonics Along Radial Distribution Feeders

A high level of delivered power quality is becoming one of the key performance indicators for both contemporary and future power networks. The increased proliferation of converter connected generation and load in power networks will lead to increased levels of harmonics in distribution networks. A general knowledge of the distribution network performance in terms of harmonics is essential for distribution network operators for both operating and planning networks while considering power quality performance. The main limitation is the reduced monitoring infrastructure compared to transmission networks. This paper presents an efficient method for assessment of harmonic levels along medium voltage radial distribution feeders based on a single measurement at a substation. The methodology is illustrated in a case study involving a real life medium voltage 35 bus radial distribution feeder.

Condition Monitoring of Distribution Transformers

Harmonics in distribution networks cause power quality problems that increase heat on transformer. This heat influence transformer performance. Distribution transformer condition monitoring avoids further consequences by continuously monitoring transformer performances. This paper proposes condition monitoring schema for distribution transformer within PLN network as the transformer capacity is small but its number is a lot. Harmonics, load and temperature are analysed to extract condition monitoring tendencyfor period of three months. Preliminary study shows that the proposed method suits the limited available data.

Harmonic analysis for street lighting lamps

One of the most challenging discussions in distribution companies is power quality. Harmonics is one of power quality issues which generated in any non-linear electrical/electronic systems. The presence of harmonics in distribution networks can lead to various problems in terms of performance and operation. High-pressure sodium (HPNa) lamps are currently the main lamps used in public lighting. However, the possibility of using high-power light emitting diodes (LEDs) for street lighting is growing continuously due to their greater energy efficiency, robustness, long life and light control. In Alexandria Electricity Distribution Company (AEDC), public street lighting sector constitutes around 3.7% of the total consumption. A suitable selection of the lamp type is very important. In Alexandria, most lamps are HPNa, with rare high-pressure mercury and compact fluorescent lamps. Large connecting roads are mostly HPNa, sized 400 or 250 W, and mounted on 12 m poles. City lamps are a mixture of HPNa 400, 250, 150, 100 and 70 W, mounted on short poles (3–7 m high) or long poles (8–12 m high); but nowadays LED lamps are being presented as a more energy-efficient alternative. AEDC started to replace HPNa, sized 400 or 250 W with LED lamps 100 or 60 W which leads to decrease the total street light consumption from 4% in 2014 to 3.7% in 2015 and green house emission. The aim of this study is to study the power quality lighting street networks based on LED and HPNa lamps. Measurements carried out to HPNa lamps with electronic ballast and LED lamps and compared with IEC61000-3-2 limits. It is shown that measured values are less than the limits given in IEC61000-3-2.

Hadoop‐based framework for big data analysis of synchronised harmonics in active distribution network

Synchronised harmonic analysis that utilises GPS signals to synchronise harmonic measurements enables advanced power quality analysis in smart grid. However, it is difficult to put this promising technology into practice due to an extremely high requirement on data storage and processing. To overcome this problem, this study presents a novel Hadoop-based framework for big data analysis of synchronised harmonics in distribution networks. The proposed framework facilitates harmonic data processing associated with data storage and advanced analysis based on big data techniques. Under this framework, a big matrix multiplication algorithm based on MapReduce programming model solving the harmonic state estimation problem is deployed in the stage of data processing. A MapReduce-based harmonics distortion calculation is implemented as an advanced analysis for harmonics. Comprehensive numerical studies are carried out to analyse the characteristics of the proposed algorithm and verify the effectiveness of the proposed framework.

Design a new OUPQC to mitigate harmonics in distribution networks like adjustable speed drive (non-linear) loads.

Design a new OUPQC to mitigate harmonics in distribution networks like adjustable speed drive (non-linear) loads.