Background Voltage Distortion Research Articles

Influence of Background Voltage Distortion on Operation of Passive Harmonic Compensation Devices

This paper discusses the issues of assessing the influence of external distortion sources on the functioning of a shunt passive harmonic filter. In this study, we evaluated the overload of a passive harmonic filter based on determining the contributions of distortion sources. A method was proposed for assessing the contributions of distortion sources, which allowed us, regardless of background distortions, to determine the contributions of consumer loads, as well as the contribution of background distortions. The simulation was carried out using the Simulink MatLab software (version R2023a). Several scenarios were considered in which the following values were varied: supply feeder impedance, level of background distortions, consumer electrical load composition, and passive filter parameters. It was found that the contribution of the background distortion source decreases with increasing impedance of the supply grid. It was determined that the consumer load contribution is independent of background voltage harmonics and can be used to estimate the overload of a passive harmonic filter. It was shown that it is necessary to take into account the overload of the passive filter by currents from background distortion sources, which did not exceed 135% of the rated rms current for the conditions under consideration. A mathematical model was proposed to estimate the overload of a passive filter in the presence of background voltage distortions. This model was obtained during analytical studies and allows one to evaluate the overload of a passive filter, taking into account the short circuit ratio, detuning frequency and power of the passive filter, and the share contribution of background distortion sources.

Framework to assess the stable operation of commercially available single-phase inverters for photovoltaic applications in public low voltage networks

This paper presents a framework to assess the grid compatibility of single-phase inverters connected to public low voltage network, which is characterized by a stable operation at reasonable emission. The assessment is based on considering emission, immunity and stability. The state of the art for commercially available devices relies only on the classical, impedance-based stability analysis based on the Nyquist criterion. However, experiences have shown that this is not sufficient for a statement towards the stable operation of an inverter, since the stable operation can also be affected by other factors than the network impedance, e.g. a background voltage distortion. Exemplary laboratory measurements of two commercially available single-phase PV inverters are presented to validate the statement by showing that despite the impedance-based stability criterion is met, inverters can still trip in presence of a high background voltage distortion. The paper concludes that the immunity of the inverter with regard to the voltage distortion at the point of connection (PoC) is additionally of importance for its stable operation.

Comparison of Models of Single-Phase Diode Bridge Rectifiers for Their Use in Harmonic Studies with Many Devices

Harmonic modeling of low-voltage networks with many devices requires simple but accurate models. This paper investigates the advantages and drawbacks of such models to predict the current harmonics created by single-phase full-bridge rectifiers. An overview is given of the methods, limiting the focus to harmonic analysis. The error of each method, compared to an accurate numerical simulation model, is quantified in frequency and time domain considering realistic input scenarios, including background voltage distortion and different system impedances. The results of the comparison are used to discuss the applicability of the models depending on the harmonic studies scale and the required level of detail. It is concluded that all models have their applicability, but also limitations. From the simplest and fastest model, which does not require a numerical solution, to the more accurate one that allows discontinuous conduction mode to be included, the trade-off involves accuracy and computational complexity.

Performance assessment of hybrid active filtering technique to enhance the hosting capacity of distorted grids for renewable energy systems

Increased green energy presence in distribution power networks can resolve rising energy demands while also reducing fossil fuel consumption, as well as providing economic and technical merits. However, the quantity of power delivered to customers cannot be allowed to take precedence over the quality of that electricity. This is because the high penetration of the renewable-based power generation comes at the cost of power quality (PQ) deterioration, especially at the point of common coupling (PCC), owing to nonlinear characteristics of renewable-based distributed generation (DG) systems and pre-contamination of modern distribution grids. So, the function of PQ improvement technologies unavoidably comes into the picture when the hosting capacity (HC) of renewable energy systems is constrained by any of the grid PQ performance indices. This paper investigates the application of a hybrid active power filter (HAPF) to improve the harmonic-constrained HC (HC-HC) of renewable DG systems in harmonically polluted distribution systems. A shunt type HAPF designing to achieve maximum HC-HC is considered as an optimization problem and solved by the firefly algorithm under several constraints the system particularly related to individual and total harmonic distortion limits in line current and voltage at PCC, harmonic currents overloading of distribution feeder. Aside from harmonics, constraints related to voltage rise and drop limits, as well as power factor, are also taken into account to ensure the optimal use of the HAPF as a compensator. The proposed HAPF-based HC-HC improvement approach's findings and efficacy are compared to those acquired from one of the literature's recently proposed techniques. Besides, the study is extended for HC-HC enhancement by HAPF, under changing the utility-side's background voltage distortion and the load-side's nonlinearity level conditions. The performed extended investigation of the system shows that HC-HC enhancing the effectiveness of the proposed approach is rather less susceptible to utility or customer side contribution to background distortion at the PCC. Highlights Hybrid harmonic filtering is investigated for enhancing the harmonic-constrained hosting capacity of distributed generation in distorted grid conditions. A hybrid filter has been found as a better alternative to achieve an advanced level of renewable energy penetration in distorted distribution grids. Along with increasing the penetration level of distributed generation the harmonic distortion is also substantially reduced instead of being at the verge of the standard limit. With the increase in background voltage distortion, the percentage enhancement in HC-HC degrades. High load-side's nonlinearity also results in a relatively lower enhancement in HC-HC. Background nonlinearity negatively influences the percentage of HC enhancement more than the load-side's nonlinearity. Though the utility, as well as customer-side nonlinearity, affect the performance of the hybrid filter also yet the variation is significantly lesser than the purely passive filtering-based approach.

Harmonic Transfers for Quantifying Propagation of Harmonics in Wind Power Plants

In this paper, primary and secondary emissions in wind power plants are studied by using transfer admittance and current transfer functions between turbines and the public grid. The use of such transfer functions allows harmonic propagation studies without knowledge of the emission from individual turbines or the background voltage distortion. The transfer functions are calculated for one synthetic and one existing wind power plant, and results are discussed. Primary emission, secondary emission from other turbines and secondary emission from the public grid are shown to be of the same order of magnitude. Furthermore, the paper addresses the impact of turbine converter modelling, public grid impedance and the change in the aggregation exponent with frequency on the propagation. All three are shown to have a significant impact and should be considered. The main challenge for future studies is in obtaining relevant models for turbine impedance versus frequency.

A global power quality index for assessment in distributed energy systems connected to a harmonically polluted network

ABSTRACT Renewable-based generation technologies are gradually making their way into modern delivery grids due to their various advantages, but power quality (PQ) remains a deciding factor for their satisfactory operation. The assessment of overall power quality performance of grid-connected renewable-based distributed energy systems (DESs) is undeniably a complicated process due to their susceptibility to load side and background PQ disturbances, as well as quite a few PQ disturbances produced by the distributed generator (DG) itself. The aim of this article to make the PQ evaluation of the identical rather streamlined by integrating the apprehensive PQ indices at separate bus groups along with the total PQ performances of separate bus groups in one composite index by making use of the analytic hierarchy process (AHP). The technique suggested for formulation yields a centralized global power quality index (GPQI) intended for three categories of bus, namely utility, load, and DG, as well as the overall system. The proposed GPQI is supposed to be exclusively ample to benchmark the global PQ performance of grid-connected DGs with respect to the customized threshold level, in addition to the PQ performance levels grading between the diverse DG systems differentiated by either resource forms or sittings in a large distribution power system. This kind of global index would significantly facilitate the PQ evaluation of grid-integrated DESs. In addition, it may also be extremely useful for distribution network operators (DNOs) to track and penalize DG operators for working inadequately on PQ perspective, and to inspire them to follow the best alternative across numerous power quality improvement (PQI) technologies. The proposed methodology’s applicability is developed and authenticated by applying it in MATLAB on a grid-integrated solar energy conversion system (SECS). The obtained values of GPQIs, by applying the proposed approach in the test system, for the utility, DG, load bus and overall system respectively are 1.530, 1.727, 1.719, and 1.659, respectively, indicating the poor PQ performance of the DG unit under study. The effects of background voltage distortion (BVD) on the utility side and nonlinearity level (NLL) on the load side on the proposed index are also thoroughly investigated. The simulation findings obtained at different NLL and BVD levels affirm the proposed approach’s efficacy in correctly indicating the status of overall PQ in the concerned DG system.

Hosting capacity enhancement of renewable-based distributed generation in harmonically polluted distribution systems using passive harmonic filtering

In spite of being economically viable for numerous applications, renewable energy cannot realise its true penetration potential until some of the barriers are not tackled with excellence. Such barriers are harmonic distortion, distribution cable’s ampacity and voltage rise limits, those put bound on the maximum allowable penetration level of renewable energy. This paper formulates the enhancement of power quality-constrained hosting capacity (HC) as a multi-objective optimization (MOO) problem under several constraints of system’s performance indices (PIs). The considered performance indices are individual order and total harmonic distortion in the line current and point of common coupling (PCC)’s voltage, load power factor (PF), distribution line’s ampacity and steady-state voltage profile. In the formulated multi-objective optimization model, an optimal design of a third-order damped filter and size of the distributed generation (DG) unit is simultaneously determined for achieving maximum hosting capacity and power factor at the PCC while keeping system’s other indices such as total voltage harmonic distortion (TVHD) and total filter cost (FC) incurred at a minimum by obtaining a best-compromised solution using the newly proposed Pareto-based multi-objective firefly algorithm (MOFA). The extension of the multi-objective firefly algorithm is considered for producing the Pareto optimal front and various conclusions are drawn by analysing the trade-offs among the objectives by plotting the same on different 2-axis planes. The optimization efficiency and superiority of the proposed multi-objective firefly algorithm based hosting capacity enhancement approach is validated by comparing the results with those obtained by popular multi-objective PSO (MOPSO) and non-dominated sorting genetic algorithm (NSGA-II) under similar objectives. Also, the results of the proposed methodology are compared with those achieved from one of the most recently introduced hosting capacity enhancement approaches in literature. Eventually, the impacts of different background voltage distortion (BVD) levels and load-side’s nonlinearity levels (NLLs) on filter performance, particularly filter cost as well as enhanced hosting capacity, are analysed and various conclusions are drawn.

Optimal Design of Passive Power Filter Using Multi-Objective Pareto-Based Firefly Algorithm and Analysis Under Background and Load-Side’s Nonlinearity

In this paper, the optimal designing of passive power filter (PPF) is formulated as a multi-objective optimization (MOO) problem under several constraints of system's performance indices (PIs) such as individual as well as total harmonic distortion (THD) in the line current and the point of common coupling's (PCC) voltage, distribution line's ampacity under harmonic currents overloading, steady-state voltage profile, load power factor (PF) and a few associated with the filter itself. The optimal design parameters of a third-order damped filter are simultaneously determined for achieving maximum PF at the PCC while keeping system's other indices such as total demand distortion (TDD) in the line current, total voltage harmonic distortion (TVHD) at the PCC and total filter cost (FC) incurred at a minimum by obtaining a best-compromised solution using the newly proposed multi-objective Pareto-based firefly algorithm (pb-MOFA). A novel MOO approach inspired by the modified firefly algorithm and Pareto front is established in order to deal with PPF design problems. The extension of MOFA is considered for producing the Pareto optimal front and various conclusions are drawn by analysing the trade-offs among the objectives. The efficiency and accuracy of the proposed pb-MOFA, in solving the concerned MOO problem, is validated by comparing an obtained solution and three computed PIs viz. convergence metric (CM), generational distance (GD) and diversity metric (DM) with those obtained from popular multi-objective Pareto-based PSO (pb-MOPSO), non-dominated sorting genetic algorithm (NSGA-II) and recently introduced multi-objective slime mould algorithm (MOSMA). The need for true Pareto front (TPF) is served by the one obtained by Monte Carlo method. At last, the impacts of different background voltage distortion (BVD) levels and load-side's nonlinearity levels (NLLs) on filter performance are analysed.

Multi-Point Time-Synchronized Waveform Recording for the Analysis of Wide-Area Harmonic Propagation

This paper focuses on studying the phenomenon of harmonic distortion propagation through distribution networks. This phenomenon is governed by a combination of factors involving the nature of harmonic loads and their dynamic interaction, the influence of background voltage distortion, and harmonic impedance values. The objective of the proposed research includes evaluation of the network response at different nodes to harmonic current injections via utilizing a time-synchronized distributed measurement system. The study is performed in a fully controlled and flexible test network with three medium voltage/low voltage (MV/LV) distribution substations and several managed LV harmonic sources, namely PV inverter, single-phase EV charger and emulated harmonic load with reference current injections. A selection of the results is analyzed and interpretation of the observed phenomena is given with implications that synchronized harmonic measurements can be considered as potential powerful instruments for analyzing power quality disturbances.

Harmonic Overloading Minimization of Frequency-Dependent Components in Harmonics Polluted Distribution Systems Using Harris Hawks Optimization Algorithm

This paper presents a novel approach to optimal planning of a resonance-free C-type harmonic filter to minimize the harmonic overloading level of frequency-dependent components in a non-sinusoidal distribution system. In the studied system, the non-sinusoidal conditions are represented by the utility side's background voltage distortion and the load side's current distortion in addition to the harmonic characteristics of the utility, power cable, distribution transformer, and hybrid linear and nonlinear loads. A constrained optimization problem is formulated to find the optimal filter design that can enhance the power quality performance of the system while complying with the harmonic limits reported in the IEEE Standard 519, filter operation limits reported in the IEEE Standard 18, and other sets of operational ranges to maintain voltage and power factors within their acceptable limits, in addition to diminishing harmonic resonance hazards that may arise due to the filter connection. The problem is solved using a recent swarm intelligence optimization algorithm called the Harris hawks optimization (HHO) algorithm. The results obtained by the conventional methods presented in the literature, namely loss-based and adjusted power factor expressions, are compared with the results obtained by the proposed methodology for validation of the solution. Besides, the problem is solved using other swarm intelligence methods and these methods are compared with the HHO algorithm. The results obtained show the effectiveness of the approach proposed using HHO in finding the minimum power loss and harmonic overloading level of the frequency-dependent components compared to the other optimizers.

Increasing PV hosting capacity in distorted distribution systems using passive harmonic filtering

Adding new capacity expansion alternatives using distributed generation (DG) technologies, particularly penetration of renewable energy, has several economical, and technical advantages such as the reduced system costs, the improved voltage profile, lower line loss and enhanced system’s reliability. However, the DG units may lead to power quality, energy efficiency, and protection problems in the system when their penetration exceeds a particular value, generally called as the system’s hosting capacity (HC) in the literature. In this paper, the HC determination of a distorted distribution system with Photovoltaic (PV)-based DG units is handled as an optimization problem by considering over and under voltage limitations of buses, current carrying capabilities of the lines, and harmonic distortion limitations as constraints. It is seen from simulation results that the HC is dramatically decreased with the increment of the load’s nonlinearity level and the utility side’s background voltage distortion. Accordingly, a C-type passive filter is designed to maximize the harmonic-constrained HC of the studied system while satisfying the constraints. The results indicate that higher HC level can be achieved using the proposed filter design approach compared to three conventional filter design approaches as voltage total harmonic distortion minimization, line loss minimization and power factor maximization.

Factors Affecting the Harmonics Generated by a Group of CFLs: Experimental Measurements

The penetration of nonlinear loads on power systems increases the harmonics that can cause detrimental problems to power systems such as an increase in voltage distortion, equipment failure, system resonance, increase system losses and decrease system efficiency. Many factors affect the harmonics produced by nonlinear loads. Hence, the aim of this paper is to evaluate the impacts of system voltage, impedance, frequency and background voltage distortion on the harmonics generated by a group of Compact Fluorescent Lamps (CFLs). Experimental measurements are performed for this purpose.

Harmonic aspects of wind power integration

This paper discusses a number of ways in which wind power installations can impact the harmonic levels in the power system. Wind turbines are an additional source of harmonic emission, especially when it concerns “non-characteristic harmonics.” Parallel resonances can amplify the emission from individual turbines. A mathematical model is developed to quantify this amplification. Series resonances can result in high currents, driven by the background voltage distortion in the transmission grid, flowing into the wind park. Weakening of the transmission grid will increase lower order harmonics but reduce higher order harmonics.

Influence of Steinmetz circuit capacitor degradation on series resonance of networks

The Steinmetz circuit is used in AC traction systems to balance consumed currents. In these systems, locating resonances between Steinmetz circuit capacitors and system inductors avoids harmonic problems. In particular, the paper locates analytically the series resonance “observed” from the supply system considering the influence of capacitor degradation with respect to its design value. The study of this resonance is important to avoid problems associated with background voltage distortion. The analytical results are validated with experimental measurements. Copyright © 2010 John Wiley & Sons, Ltd.

Analytical Study of the Series Resonance in Power Systems With the Steinmetz Circuit

In traction systems, it is usual to connect reactances in delta configuration with single-phase loads to reduce voltage unbalances. This set is called a Steinmetz circuit. Parallel and series resonances can occur between the Steinmetz capacitor and system inductors, increasing harmonic voltage distortion. It is important to analyze the series resonance ldquoobservedrdquo from the supply system to avoid harmonic problems due to background voltage distortion. The paper studies this resonance analytically and presents simple expressions to locate it. Experimental measurements are also provided to validate the obtained analytical results.

Design and Implementation of a Robust Current Controller for VSI Connected to the Grid Through an LCL Filter

This paper describes the design and implementation of a discrete controller for grid-connected voltage-source inverters with an <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> filter usually found in wind power generation systems. First, a theorem that relates the controllability of the discrete dynamic equation of the inverter with <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> filter and the sampling frequency is derived. Then, a condition to obtain a partial state feedback controller robust to grid impedance uncertainties and based on linear matrix inequalities is proposed. This controller guarantees the stability and damping of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> filter resonance for a large set of grid conditions without requiring self-tuning procedures. Finally, an internal model controller is added to ensure asymptotic reference tracking and disturbance rejection, significantly reducing the impact of grid background voltage distortion on the output currents. Experimental results are presented to support the theoretical analysis and to demonstrate the system performance.

Projeto e implementação de um controlador de corrente robusto para inversores com filtro LCL conectados à rede com incertezas paramétricas

Este artigo trata do projeto e implementação de um controlador discreto de corrente para um inversor trifásico alimentado em tensão e conectado à rede através de um filtro LCL, geralmente encontrado em sistemas de geração eólica. Primeiramente, é desenvolvido um teorema que relaciona a controlabilidade da equação dinâmica discreta, que representa o comportamento do conversor conectado à rede, aos parâmetros do filtro e a freqüência de amostragem do sistema. Então é derivada uma condição para a obtenção dos ganhos de retroação parcial robusta de estados baseada em desigualdades matriciais lineares. Este controlador garante a estabilidade e o amortecimento ativo da ressonância do filtro LCL conectado à rede, mesmo com incertezas paramétricas no ponto de conexão sem a necessidade de procedimentos de auto-sintonia ou algoritmos adaptativos. Finalmente, um controlador com modelo interno é adicionado a fim de prover rastreamento assimptótico da referência e rejeição do distúrbio, diminuindo significativamente o impacto dos distúrbios harmônicos de baixa freqüência da tensão da rede nas correntes de saída. Resultados experimentais e de simulação são apresentados para dar suporte a análise teórica desenvolvida bem como para demonstrar o desempenho do sistema.

Background voltage distortion influence on power electric systems in the presence of the Steinmetz circuit

In traction systems, it is usual to connect reactances in delta configuration with single-phase loads to reduce voltage unbalances and avoid electric system operation problems. This set is known as Steinmetz circuit. Parallel and series resonances can occur due to the capacitive reactance of the Steinmetz circuit and affect power quality. In this paper, the series resonance “observed” from the supply system is numerically located. The study of this resonance is important to avoid problems due to background voltage distortion. Experimental measurements are also presented to validate the obtained numerical results.

Mitigating grid voltage harmonics using a line converter with active filtering feature

A line converter equipped with an LCL-line filter is used as an active filter directly compensating grid voltage harmonics. The control of four individual grid voltage harmonics is implemented using an individual control of corresponding harmonic line currents. The knowledge of the grid impedance is essential to efficient control of the grid voltage harmonics. To overcome the problem of an unknown grid impedance an identification method is used. The method uses the converter control system to measure the grid impedance at selected frequencies. The active voltage harmonic cancellation is tested with a 19 kVA line converter by compensating background voltage distortion and distortion caused by a nonlinear load.