Power Quality Standards Research Articles

Forces and Stresses in the Windings of a Superconducting Fault Current Limiter

This paper presents the design of a Superconducting Fault Current Limiter (SFCL) and calculation results of forces and stresses in the windings of a resistive fault current limiter. The design of the fault current limiter consists of two parallelly connected and magnetically coupled windings, cooled by a single stage cryocooler. Magnetically compensated windings made of HTS tape give a very low voltage on the limiter at a nominal current. Limitation of the short-circuit time and the value of the maximum initial fault current reduces the thermal and dynamic effects of the passage of a fault current. Using devices which limit the value of a fault current can lower the level of required short-circuit capacity of the elements in a system. However, selected means of fault currents limitation must maintain the power quality standards. A perfect fault current limiter is required to have substantial impedance in fault conditions and zero impedance at work currents. Such requirements are met by a SFCL. An increase of current caused by the occurrence of a fault current results in the transition of the superconducting material from the superconducting state into the resistive state. This increases the impedance of short-circuit loop, allowing the fault current value to decrease. During a short-circuit, the forces generated from the short-circuit current also act on the limiter windings. Short-circuit current causes stresses in the superconducting tape. Exceeding the permissible stress value results in an irreversible reduction in the critical current of the superconducting tape. Calculations of the forces and stresses in the HTS tape for the maximum value of the short-circuit current were carried out using the finite element method. The constructed limiter was tested and the winding design ensures that the tape stresses are at a safe level even for short-circuit currents.

A Machine-Learning Pipeline for Large-Scale Power-Quality Forecasting in the Mexican Distribution Grid

Electric power distribution networks face increasing factors for power-quality (PQ) deterioration, such as distributed, renewable-energy generation units and countless high-end electronic devices loaded as controllers or in standalone mode. Consequently, government regulations are issued worldwide to set up strict PQ distribution standards; the distribution grids must comply with those regulations. This situation drives research towards PQ forecasting as a crucial part of early-warning systems. However, most of the approaches in the literature disregard the big-data nature of the problem by working on small datasets. These datasets come from short-scale off-grid configurations or selected portions of a larger power grid. This article addresses a study case from a region-sized state-owned Mexican distribution grid, where the company must preserve essential PQ standards in approximately 700 distribution circuits and 150 quality-control nodes. We implemented a machine-learning pipeline with nearly 4000 univariate forecasting models to address this challenge. The system executes a weekly forecasting pipeline and daily data ingestion and preprocessing pipeline, processing massive amounts of data ingested. The implemented system, MIRD (an acronym for Monitoreo Inteligente de Redes de Distribution—Intelligent Monitoring of Distribution Networks), is an unprecedented effort in the production, deployment, and continuous use of forecasting models for PQ indices monitoring. To the extent of the authors’ best knowledge, there is no similar work of this type in any other Latin-American distribution grid.

The impact of events in the Slovene high – voltage network on the power quality in the distribution networks

This work analyses the impact of different events in Slovene high-voltage network on power quality in the 20 kV and 0.4 kV distribution networks. In order to perform the analysis a simplified dynamic model of the Slovene power system was build in the program package Matlab/Simulink, using toolbox PowerSys. The obtained model is appropriate for simulation of electromagnetic transients in duration up to a few seconds. It contains simplified dynamic models of all main generators and power transformers installed in the Slovene power system, detailed models of 400 kV, 220 kV and 110 kV networks, simplified models of the neighboring power systems and models of important consumers. The 20 kV and 0.4 kV distribution networks are modeled in the details only in the area of interests. Everywhere else, they are represented as constant loads connected to the 110 kV network. The aforementioned dynamic model was applied to analyze the impact of different events in the Slovene power system on power quality in the 0.4 kV distribution network during transients and in steady states. The power quality in distribution network was analyzed on 0.4 kV busbars in five substations (Cerkno, Škofja Loka, Vevče, Šentjur, Rače) for the following set of events: a switch-off of a 300 MVA (400 kV/110 kV) power transformer in the substation Okroglo; a three-phase short circuit on 110 kV busbars in the substation Kleče; a three-phase short circuit on 20 kV busbars in the substation Rogaška Slatina and a switch-on in a pumping regime of pump-turbine plants Avče and Kozjak which are currently at the design stage. The results obtained show that aforementioned events in some points of Slovene distribution network can cause power quality distortion over that allowed by the power quality standards.

Selected Harmonic Mitigation PWM Power Matching Control Strategy for Asymmetric Cascaded H-Bridge Multilevel Inverter

In order to suppress high-order harmonics to meet the requirements of power quality standards and solve the power mismatching problem of asymmetric multilevel inverter, an improved power matching control strategy of asymmetric selected harmonic mitigation pulse width modulation (ASHM-PWM) is proposed in this article. This strategy is based on asymmetric dc-link voltage applied asymmetric cascaded H-bridge (ACHB) multilevel inverter. First, a new harmonic mitigation model based on the power matching control is proposed and the output active power of each H-bridge cell is analyzed theoretically. Second, switching angles are obtained by transforming multiobjective inequality problems of ASHM-PWM into single objective equation groups combined with improved particle swarm optimization (IPSO), which can simplify the solving process. Finally, the simulation model and experimental platform of ACHB multilevel inverter have been implemented to verify the ASHM-PWM power matching control strategy proposed in this article. The result shows that each H-bridge cell of ACHB can have power matching performance by meeting the power match of 1: <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k1$ </tex-math></inline-formula> : <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k2$ </tex-math></inline-formula> in one cycle. Meanwhile, the total harmonic distortion (THD) of the output line–line voltage is reduced and the performance of harmonic mitigation is better.

Power Quality Enhancement using A Unified Power Quality Conditioner (UPQC)

This project proposes effective work to increase the power quality in the power system by using a Unified Power Quality Conditioner (UPQC) The advanced use of power electronic devices introduces harmonics in the power system which creates a problem in the quality of power delivered. Although several methods are there for improving power quality standards, including the use of active and passive filters, and Hybrid filters have been developed, these methods face issues and are ineffective due to the growing number of applications. The UPQC is an advanced technique for mitigating voltage and load current supply fluctuations. In this project the combination of series active filter and shunt active filter is studied. UPQC is used to reduce the power quality issues like harmonics and sag. The shunt active filter and series active filter performs the simultaneous elimination of current and voltage problems. The project work presents the working of the UPQC filter in such a way that the harmonics are reduced.

Power Quality and Electromagnetic Compatibility Aspects at Personal Computers

In this article, issues related to electromagnetic compatibility and energy/power quality for a laptop are addressed. Power quality problems are outlined. Testing frameworks (developed by authors) are presented and discussed for a laptop when two different sampling frequencies are used: 80 kHz and 19.2 kHz. Waveforms corresponding to the voltage across the laptop’s terminals and current absorbed by it were acquired. Recordings and numerical processing, based on original software using Fast Fourier Transform, are discussed, and the analysis of waveforms in both cases is performed. Various power quality indices were calculated. Theoretical and practical aspects related to the determination of power quantities, power flows, and power factor are presented. Some conclusions concerning different ranges of frequencies are presented, along with some considerations for power quality problems. Tests for conducted emissions (single phase and neutral wire respectively) and for the radiated emissions (for horizontal and vertical polarizations) are presented. Comparisons to the emission standards were made. The immunity behavior for a laptop is discussed according to immunity standards. It is shown that new measures (e.g., active filters) are necessary for network protection when connecting a laptop to the network. Some considerations, based on the authors’ observations concerning new standards for power quality and electromagnetic compatibility, are outlined.

Golden Eagle Optimized Control for a Dual Stage Photovoltaic Residential System with Electric Vehicle Charging Capability

ABSTRACT In this article, the control of a grid-connected, single-phase, dual-stage photovoltaic (PV) residential system with electric vehicle (EV)-charging capability is being presented. A residential system faces a lot of dynamic conditions such as changing atmospheric condition or random patterns of load connection or disconnection as well as power failure. In this regard, this article proposes the optimization of proportional and integral gains selection of the bidirectional DC/DC converter (BDC) PI controller through golden eagle optimization (GEO) algorithm to improve the system performance. The system is subjected to various induced dynamic conditions simulated in MATLAB Simulink environment and the performance is compared with particle swarm optimization, genetic algorithm, and gains obtained through hit and trial. In comparison with other techniques, GEO algorithm provides optimum BDC PI gains, as a result, the DC-link voltage achieves 1.5 times shorter settling time. During the non-linear load changes and voltage swell condition, the settling time is 2 times shorter. Settling time of the EV battery power shows 1.7 times reduction. The transient response of the PV power also shows dramatic improvement with 3 times faster settling time during solar insolation changes. During the sudden non-linear load changes, the momentary transients die 1.5 times faster. Moreover, a seamless control is developed to achieve a seamless transition from islanded mode to grid connected mode and vice versa. The proposed system achieves unity power factor and complies with the IEEE -519 power quality standard.

Operation mode selection algorithm development of a wind-diesel power plant supply complex

The power supply system is affected by external disturbances, so it should be stable and operate normally in compliance with power quality standards. The power supply system goes into abnormal modes operation when, after a short-term failure or disturbance, it does not restore normal mode. The electrical complex, which includes a wind power plant, as well as a battery and a diesel generator connected in parallel, is able to provide reliable power supply to consumers which meets the power quality indicators. The article develops an algorithm that is implemented by an automatic control system to select the operating mode depending on climatic factors (wind) and the forecast of energy consumption for the day ahead. Forecast data is selected based on the choice of the methods, which will have the smallest forecast error. It is concluded that if the energy consumption forecast data is added to the automatic control system, then it will be possible to increase the efficiency of the power supply complex. In the developed algorithm the verification of normal and abnormal modes of operation is considered based on the stability theory. The criteria for assessing the normal mode of operation are identified, as well as the indicators of the object’s load schedules for assessing the load of power supply sources and the quality standards for power supply to consumers for ranking the load by priority under critical operating conditions and restoring normal operation are considered.

A Generic Robust Model-Based Estimator for Active Damping of Single-Phase GridTied Inverters

This paper presents the design and analysis of a signal estimator with improved robustness applied in the active damping (AD) of a single-phase grid-tied inverter with LCL low-pass filter. The proposed estimator is based on the mathematical model of the LCL filter, with resistors in series with the converter-side inductor and capacitor for improving robustness. The implementation method is also capable of estimate multiple filter signals. The control strategy presented uses a virtual resistor based AD, that suppresses the resonance ensuring stability and robustness, helping comply with power quality standards, such as IEEE 1547 and IEC 61727. The signal necessary for achieving the AD is obtained through the estimator, dismissing the use of additional sensors. The current control structure uses grid-side current feedback with proportional-resonant controller and harmonic compensation. The system is designed by the root locus approach to achieve stability despite grid parameter variance. The estimator and overall system is analyzed through mathematical modeling, computational simulation and experimental setup. The results show that the estimator presented is capable of providing the necessary AD feedback signal, even with grid inductance variation.

Headroom-based optimization for placement of distributed generation in a distribution substation

This paper presents a headroom-based optimization for the placement of distributed generation (DG) in a distribution substation. The penetration limits of DGs into the existing distribution substations are often expressed as a function of the feeder’s hosting capacity (headroom). Therefore, it is important to estimate the reliability of the network's operation as well as that of the limits imposed by the power quality standards by evaluating of the hosting capacity (headroom) of the existing distribution feeder substation. This study aims at developing a novel algorithm for positioning a bus with permissible headroom capacity for DG positioning without causing voltage violations but maximizing the active power supply. Since DG increases short-circuit faults, the algorithm is useful for utility companies to select feeder substations that have permissible headroom capacity for DG installation and thus, contributing to reducing high DG penetration in the network. The modeling and optimization were carried out the Power System Software for Engineers (PSS/E) environment using the IEEE 14-bus test system. The results obtained from the case study show that only two (2) feeder substations out of fourteen (14) have the permissible headroom capacity for DG connections.

Adjustable Speed Induction Motor Drive Fed by 13-Level Cascaded Inverter and 54-Pulse Converter

In this article, a 13-level asymmetric configured cascaded H-bridge (CHB) inverter is used with a 54-pulse ac&#x2013;dc converter to feed a medium voltage indication motor (IM). A thorough analysis is carried out to design an isolated multiwinding transformer (MWT) based 54-pulse converter. Accordingly, the main aim of this converter is to extract the power from the grid as per the power quality standard. Moreover, a higher number of voltage levels in CHB inverter are used to adhere the power quality due to asymmetric dc supplies, having a 1:2:3 voltage ratio. Hence, a 13-level CHB-MLI is implemented with nine dc voltage sources. The converters of this drive system ensure that the quality of the grid currents and drive currents are excellent and meet the IEEE 519 power quality successfully. A nearest-level control technique is implemented to generate the switching logic for a 13-level CHB- CHB inverter. Simulated results demonstrate the performance of a 298.4&#x00A0;kW induction motor drive in steady-state and dynamic state. A validation study is conducted on an experimental setup with a 7.5&#x00A0;kW IM at steady and dynamic states. Test results show a good agreement in terms of total harmonics distortions, power loss, and efficiency.

Analysis of Power Quality Problems in Large-Scale Application of Air-Source Heat Pump

With the implementation of electric energy alternatives, the large-scale application of electric energy substitution represented by air-source heat pumps has replaced traditional coal-fired heating, which is beneficial for the environment and alleviates air pollution. However, the large-scale application of air-source heat pumps has brought power quality problems such as voltage sags, harmonic pollution, and three-phase imbalance to the distribution network. This paper studies the fixed-frequency and variable-frequency air-source heat pump, introduces its working principle, analyzes the mechanism of its power quality problem. Moreover, the paper establishes a simulation model for the fixed-frequency heat pump and variable-frequency heat pump to connect to the distribution network. This research mainly studies the impact of large-scale fixed-frequency heat pumps on the depth of voltage sags in the distribution network and the impact of large-scale variable-frequency heat pumps on the harmonic content of the distribution network under different penetration rates and uses measured data to verify the reliability of the simulation results. This paper uses experimental data for the first time to verify the real power quality problems of large-scale heat pumps, which can provide a reference for determining the power quality standards for heat pumps connected to the power grid. At the same time, it can also provide a reference for the power quality management of the distribution network that is actually connected to electric heating.

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.

Voltage Profile Analysis on a Grid with Power Injection from a Wind Farm

Wind power penetration into the grid is increasing throughout the world due to centralized power generation constraints such as shortage of fossil fuel, need to reduce gas emissions, long transmission losses and need for more supply of electrical power. Connection of wind power into the grid results in power quality issues such as voltage profile changes and harmonics. This necessitates coming up with correction measures in order to meet power quality standards. This paper deals with the analysis of the effects of injecting wind power to the grid on voltage profile. Branch participation factors are used to analyze the sections of the grid where effects on voltage profile are highest due to wind power penetration. Reactive power-voltage sensitivity analysis is used to determine the buses that are more sensitive to the changes brought by the wind power injection. Two cases were considered for the injection of the wind power: IEEE 14 test bus system and IEEE 39 test bus system.

Analysis and Suppression of Voltage Violation and Fluctuation with Distributed Photovoltaic Integration

In recent years, the violation and fluctuation of system voltage has occurred with greater frequency with the integration of high-penetration distributed photovoltaic generation. In this paper, the voltage violation and fluctuation in a high-penetration distributed photovoltaic integrated system is analyzed, and then a corresponding suppression strategy is proposed. Firstly, based on solar cell and photovoltaic control system models, the influence factors of photovoltaic output are analyzed. Secondly, the voltage violation and fluctuation caused by photovoltaic integration is analyzed, and the quadratic parabola relationship between bus voltage fluctuation and photovoltaic power variation is constructed. Next, according to the virtual synchronous generator characteristic of distributed photovoltaics, a double-hierarchical suppression strategy is proposed to make full use of reactive power regulation capability, which can maintain the symmetry of power supply while meeting standard requirements. The proposed strategy can conveniently realize quick response and support the photovoltaic extensive access. Moreover, with the employment of the proposal, the system voltage violation and fluctuation can be suppressed effectively. Finally, considering the photovoltaic access location, capacity, and partial shading, the effectiveness of the proposed strategy is verified in IEEE 33-bus distribution system with field measured data. After distributed photovoltaic accesses the system, more than 60% of buses appear to have undergone bus voltage violation. With the proposed method, more than 20% of the voltage deviation and more than 6% of the voltage fluctuation are effectively suppressed so that the system voltage can be kept below 1.07 p.u. and the voltage fluctuation can be kept within 4%, meeting the requirements of power quality standards.

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.

Design of Power Quality Virtual Lab Toolbox using LabVIEW/Multisim

This paper presents a Power Quality (PQ) virtual lab that can be used by electrical engineers (EE) to enhance their knowledge and awareness on power quality disturbances in accordance to power quality standards. It will offer the EE the facility to become more aware about the problems tackling power systems and nonlinear devices, and their effects on the power quality indices. This work is built using NI LabVIEW/Multisim and is composed out of many simulations and experiments each with its learning objectives. The established measured power quality indices are mainly the root mean square (RMS), the total harmonic distortion (THD), the distortion index (DIN), the telephone influence factor (TIF), the crest factor (CF), the voltage transformer product (VT), the current transformer product (IT), the displacement power factor (DPF), the true power factor (TPF) and the unbalance factor (UF). Each of these indices is measured and analyzed in order to check how they are affected by the PQ issues.

Power Quality Improvement in Distribution Grids via Real-Time Smart Exploitation of Electric Vehicles

Integration of electric vehicles into electric power system brings both challenges and solutions in the operation of power grids. On the one hand, simultaneously charging a large number of electric vehicles causes branch congestion or large voltage drop. Operating the electric vehicles in the discharging mode, on the other hand, introduces the provision of several ancillary services like peak power shaving and spinning reserves. From the electric vehicles operation point of view, thus, the distribution system operators require a real-time monitoring infrastructure to capture the states of electric vehicle chargers and accordingly operate their grids in the safe mode with respect to the power quality standards (e.g., EN 50160). In this context, the real-time smart charging and storage platform of the EU Horizon 2020 “MEISTER” project, based on the information and communication technology, manages the availability of electric vehicles as a potential source of energy in the need of one or more flexibility services demanded by low voltage distribution system operators. In addition to the implemented information and communication technology platform, this paper presents how the smart use of the electric vehicle resources supports the power quality of the distribution system in terms of system voltage support, bidirectional power flow management, harmonic alleviation and power factor control.

Induction motor drive based on direct torque controlled used multi-pulse AC-DC rectifier

This paper presents the direct torque-controlled induction motor drives (DTCIMDs) based on a retrofit 44-pulse rectifier (44PR). A 22-phase polygon autotransformer (PA) is designed to supply the rectifiers. The above structure improves the power quality standards in the power grid and complies with the requirements of the IEEE-519 standard for different loads. Besides, a power factor close to one is obtained for a wide range of DTCIMD performance. The results show that the total harmonic distortion (THD) of the input current under variable loads for 44PR is less than 3%.

Power quality multi-step predictions with the gradually increasing selected input parameters using machine-learning and regression

Autonomous off-grid systems dependent upon Renewable Energy (RE) sources are characterized by stochastic supplies of the fluctuating low short-circuit power. Power Quality (PQ) standards define load characteristics in electric power systems and their ability to function properly without failures. Monitoring, prediction and optimization of PQ parameters are necessary to maintain their alterations steady within the prescribed range, which allow fault-tolerant operation of various electrical devices. It is not possible to measure complete PQ data for all possible combinations of dozens of grid-connected appliances, whose load specifics and collisions primarily determine the course of PQ parameters and their eventual disturbances. Self-adapting PQ prediction models based on Artificial Intelligence (AI) are required as induced power is influenced particularly by changeable weather conditions in real off-grid operation mode of systems using RE. A novel multi-step PQ prediction algorithm is proposed, which develops AI models with the gradually increasing number of selected input PQ-parameters. In each next step a more complex model is formed, using an additional co-related PQ-input to calculate its target PQ-output with a better accuracy. PQ-models with the progressively growing PQ-inputs, using their data predicted in the previous step, can better approximate and estimate the target quantity. The presented results show this training and feature selection procedure can step by step improve accuracy of PQ-models for unknown combinations of off-grid connected household appliances.