Book

# Understanding Power Quality Probems - Voltage Sags and Interruptions

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## Abstract

“Power quality problems have increasingly become a substantial concern over the last decade, but surprisingly few analytical techniques have been developed to overcome these disturbances in system-equipment interactions. Now in this comprehensive book, power engineers and students can find the theoretical background necessary for understanding how to analyze, predict, and mitigate the two most severe power disturbances: voltage sags and interruptions. This is the first book to offer in-depth analysis of voltage sags and interruptions and to show how to apply mathematical techniques for practical solutions to these disturbances. From UNDERSTANDING AND SOLVING POWER QUALITY PROBLEMS you will gain important insights into Various types of power quality phenomena and power quality standards Current methods for power system reliability evaluation Origins of voltage sags and interruptions Essential analysis of voltage sags for characterization and prediction of equipment behavior and stochastic prediction Mitigation methods against voltage sags and interruptions.
... Voltage sags are reductions in the RMS value of voltage for a short time. The main reasons for sags are short-circuiting faults and the starting of large motors [1][2][3][4], characterized by their magnitude of voltage and duration. The magnitude lies between 10% and 90%, and the sag duration lasts for between 10 ms and 1 min [5]. ...
... The method of fault position for calculating the frequency of sags was suggested by Bollen [2]. It is a simple technique used to compute the probable frequency of voltage sags in a meshed system. ...
... Equations (2)-(4) can be expressed in terms of vector sequence components as shown in Equation (5). (1) [2]. ...
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Article
In this paper, different mathematical expressions are derived to compute the residual magnitude of voltage caused by faults along the line and on the bus. Symmetrical and unsymmetrical faults are taken into consideration, and the consequences of the various fault distributions are considered. A new way of assessing a sag is proposed that incorporates the method of fault position and mathematical expression based on sequence currents and voltages. The fault impedance is introduced to obtain a better result. A fast and efficient load flow analysis technique produces quick computational results. In addition, the sag analysis is performed using the bivariate joint discrete probability distribution method that gives a clear idea about the probability of occurrence of sag in a meshed network. The suggested approach is applied in the IEEE 39-bus system and with an existing real-time electrical power distribution system in India.
... The detection and measurement of these low-frequency disturbances is easy but restitution is monotonous work. On the other hand both detection and reparation of Transients is less complicated than low-frequency events [2]. There are various measures available to deal with low frequency disturbances like Isolation transformers, Voltage regulators, Static Uninterruptible Power Sources (UPSs), Rotary UPS. ...
... However, these methods have limitation for removal of low frequency variations [2]. To eliminate the distortion the source voltage most common device used is Series Voltage Regulator which is often called as Dynamic Voltage Restorer or Series Active Power filter. ...
... The dq transformation and the phase information of load voltages is used to covert three phase source currents (Isa, Isb, Isc) to d-q domain currents Isd and Isq. These currents are further passed through a low pass filter to generate reference control signals Ised and Iseq given by (2) and (3). ...
Article
A compensation method for mitigation of voltage related power quality problems with the use of Series Voltage Regulator well known as Series Active Power Filter or Dynamic Voltage Restorer is presented in this paper. The classical control algorithm used for series voltage regulator based on the Park transformation is modified by introducing a Selective Harmonic Filter at detection stage of source current in order to compensate harmonic frequencies which mainly affect power frequency voltages. The significant outcomes are sag restoration, reduction of total harmonic distortion and removal of transients from the supply voltage. Thus it makes possible to improve performance of series voltage controller as power conditioner to mitigate various voltage related power quality issues. The proposed approach is cost effective because same series voltage controller can be used as power conditioner by modifying control strategy used. Also it is possible to eliminate use of PI controller from control circuitry. The usefulness and robustness of the proposed mitigation strategy is confirmed by simulation studies. The presented series voltage controller has ability to mitigate the power quality issues arising due to charging of electric vehicles.
... Grid faults cause voltage sags (also known as dips), which are one of the most common grid disturbances [4]. They originate a decrease in the value of the rms voltage between 0.1 pu and 0.9 pu with respect to the pre-fault steady-state voltage, and the duration is between 1/2 cycle and 1 minute [5]. ...
... The following sag types have been simulated: A-type sag (caused by three-phase faults), C-type sag (caused by 2phase faults) and F-type sag (caused by 2-phase-to-ground faults after a Dy transformer) [4]. The fault conditions have been simulated assuming a sag depth h = 0.7 (i.e., a voltage decrease of 30% with respect to the pre-fault steady-state conditions) and a duration Δt = 100 ms. ...
... Truly, note that R = 1 mΩ and L = 5 mH, so τ = L/R = 5 s, which is the time constant of the system, so it will take 4τ = 20 s for the spiral to be closed. Note that this term appears in equation (4). The inverter's behavior can be exaggerated in order to show this damping effect on a 3D plot, for example by considering sags with very high durations, e.g. ...
Article
The aim of this work is to describe the behavior of three-phase inverters connected to a faulty grid by means of a parametric approach which gives rise to limaçon of Pascal curves and 3D figures formed by the injected currents during the fault. The analytical study is given in the complex form of the transformed Park variables, and the simulation results are obtained by means of MATLABTM. The results show that the parametric analysis can be an easy and useful tool to predict the behavior of three-phase inverters operating under voltage sags, with the aim of achieving fault ride-through (FRT) capability.
... A continuously growing concern about the power quality (PQ) delivered to consumers is a big challenge for power distribution utilities. Among various power quality disturbances (PQDs), voltage sags are considered one of the most critical influences on the electric power system's security and stability due to their higher frequency of occurrence and substantial economic impact [1]. Usually, voltage sag is recognized as a sudden reduction in the root mean square (RMS) voltage magnitude below a given threshold, lasting a defined short duration [2]. ...
... The causes of voltage sag include a short duration increase in current due to heavy motor starting, short-circuit faults, and transformer energization. The residual voltage and the event duration are two main indices of voltage sag characterization, though they do not fully characterize the voltage sag [1][2][3]. However, an accurate estimation of these two indices is crucial to help the designers to select appropriate equipment specifications for critical systems and processes. ...
... The proposed method is evaluated with two recorded voltage sag waveforms, namely 'SagR1' from IEEE 1159.2 Working Group database [1] and 'SagR2', a real signal containing voltage sag obtained from a 138 kV substation of a milk pasteurization facility [25]. The real characteristics of these recorded voltage sag waveforms have been summarized in Table 3. ...
Article
Wavelet-based techniques are strongly recommended as a good alternative for the fast detection and characterization of voltage sags. However, the accuracy and effectiveness of these techniques greatly depend on selecting an appropriate mother wavelet. Therefore, in this work, a wavelet correlation-based technique has been developed to select the most appropriate mother wavelet for the characterization and detection of voltage sag. The efficacy and accuracy of the proposed method are tested with twenty different mother wavelets on various voltage sag signals, namely, recorded industrial, multi-stage, and synthetic signals under different conditions of unbalanced. It is shown that the mother wavelet having the highest similarity with a voltage sag provides the best results for its characterization and detection. Further, the various performance parameters of voltage sags, namely magnitude, duration, sag initiation, recovery, are evaluated with the proposed method and results are compared with Independent Component Analysis (ICA), hybrid wavelet, dq-transformation, Enhanced Phase Locked Loop (EPLL), Fast Fourier Transform (FFT) methods showing that the performance of the proposed method is better than other existing methods for sag detection. In addition, the proposed method can also be used for estimating the magnitude of voltage sags.
... Voltage sag is defined as a momentary reduction in the "RMS" value of the nominal voltage for a duration ranging from 0.5 cycles to one minute [1], [2]. Voltage dips are mainly caused by power line faults such as short circuits and large induction motors starting [3]. ...
... Electrical voltage sags are mainly characterized by their amplitude and phase, various classifications of three-phase voltage dips were presented by Bollen [1]. Voltage dips can be symmetrical or non-symmetrical in nature [23]- [25]. ...
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Article
Several strategies have been developed for identifying power quality issues, monitoring them, and compensating for relevant disturbances. In this field, online estimate of amplitudes and phase angles of network voltages and currents is commonly used. The adaptive linear neuron (ADALINE)-based voltage sag detection algorithm with least mean square (LMS) adaptation allows for rapid convergence of estimate techniques based on artificial neural networks (ANN). This approach has the advantage of being straightforward to implement on hardware and based on simple calculations (essentially multiply and accumulate "MAC"). This paper gives a comparison of the performance of two ADALINE approaches ("with" and "without" error supervision) for detecting and estimating voltage dips. The described techniques and models of a two-coupled motor system were implemented in MATLAB/Simulink/SimPowerSystems to run simulations under various fault scenarios in order to create the three-phase voltage sag alarm signal. The simulation outcomes are presented and debated.
... Multiple techniques for transient stability enhancement are discussed in the literature [18][19][20][21][22][23][24][25][26]. ...
... One is SITPF, in which the smart node improves the power grid for load flow balancing, and the second is the case of MITPF. In MITPF, a UPFC is incorporated into the transmission network and is used to fully improve the power system for balancing load flow in order to mitigate the transients [24]. Multi-agent systems, incorporation of FACT devices, UPFC, and others are included and discussed in detail here. ...
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Article
Super smart grids (SSGs) are a wide area transmission network that mainly uses renewable energy resources (RERs), contributing to the reduction of greenhouse gas (GHGs) emissions and supporting the power infrastructure of multiple countries. The SSGs comprise two-way communication between the loads and sources of different countries, and these loads can be mostly served with numerous types of RERs tied with the grids. The RERs will play a pivotal role in the development of future grids and the generation of electricity. However, the main challenge to tackle in these RERs is that they are intermittent in nature. Due to intermittency in these RERs, transient stability issues have become one of the critical research challenges in SSGs. These stability issues are escalated and become more difficult to handle if a network is vulnerable to an arising of different kinds of faults. To address these problems, multiple approaches to enhance transient stability already exist in the current literature. After reviewing the literature, flexible alternating current transmission systems (FACTS) devices proved more promising in improving transient stability. Among FACTSdevices, UPFC is a versatile FACTS device, which provides complete stability to power system networks in the form of series and shunt compensations. Considering this scenario, a hypothetical network for SSGs is designed in this research work based on the interconnection between two countries, i.e., Denmark and Norway, to address the transient stability issues in SSGs. The complete probabilistic model of the system is also designed to enhance the stability of the system. The results clearly showed that the insertion of UPFC is an effective technique to enhance the transient stability and resilience of the power system networks as compared to other purposed techniques in the literature. The main contribution of this paper is that extensive simulation studies employing accurate RERs models are used to analyze and investigate various problems arising due to the integration of many clusters of RERs in SSGs.
... During non-linear load condition, the conventional methods are used for compensation of voltage sag and which gives ineffectual performance. Decrease in RMS voltage value with short duration fault longer than 1 min is defined as voltage sag or drop and sudden increase in RMS voltage value with a short period of fault longer than 1 min is called voltage swell [1]. Voltages swell/sag affects in a distributed system and it cause reduction of voltage and mitigation of power quality. ...
...  X e Vcompensat Vsource (1) The required amount of voltage that should be injected /drawn by the DVR, and it depends on how much voltage is to be required for compensating the demanded by the load. There are many algorithms, control techniques and theories are used to establish the real and reactive power in the power system. ...
Article
This paper deals with the implementation of interline dynamic voltage restorer (IDVR) system using three-phase inverter integrated with PLL based MSRF controller for regulating the DC link voltage, and reducing the voltage sag. Voltage variation that frequently occurs either in the form of voltage sag or swells and it can cause major damage to the environment and distribution station. In this paper, interline dynamic voltage restorer has proposed which consist of more than one DVR's are commonly connected with the DC link capacitor of the system. Suitable control methods are developed for reduce the voltage sag in the line. Modified synchronous reference frame control has designed and implemented for both controls, and compensation of voltage sag. Conventional control method has some constraints such as high settling time of dc link voltage, and increase in harmonics that could be overcome by a new approach of MSRF based PLL has presented in this paper, which helps to compensate the voltage sag occurs in the system. Furthermore design and analysis of MSRF based IDVR is proposed to improve the efficiency, reducing the settling time of DC link voltage, reducing the harmonics distortion, and minimize the power quality issues by using MATLAB/SIMULINK.
... UE to its high ruggedness, good efficiency and relatively low cost, the three-phase squirrel-cage induction motor (SCIM) is still the dominant motor technology in the industry [1]. It is well-known that the performance of SCIMs is significantly affected by voltage supply unbalance (SVU), which is a common situation in the industry [2] and may lead to the motor failure due to excessive and asymmetrical temperature rise of the phase windings [3], [4]. Even a low SVU can produce a high phase current unbalance (PCU) due to the relatively low negative-sequence impedance of SCIMs. ...
... The resulting line-to-line voltages given by (2) are the phase voltages applied to D-connected dual windings (Fig. 3, Fig. 6a). For ungrounded Y-connected dual windings (Fig. 4, Fig. 6b), the phase (or line-to-neutral) voltages are: ...
Conference Paper
In this paper, an analytical and experimental study on the tolerance to supply voltage unbalance of three-phase squirrel-cage induction motors with different dual-winding configurations, is presented, with focus on the phase current unbalance rate, the maximum amplitude of phase currents, and the per-slot stator Joule losses. Fifteen different dual-winding configurations were tested in an induction motor with reconfigurable windings, at no-load condition. The dual-winding configurations tested include the star-series, star-parallel, delta-series, delta-parallel, and star-delta connection modes, with different angular displacements between the dual windings, namely, 0, 20, 40, 120, and 300 electrical degrees. The two configurations leading to the lowest phase current unbalance rate and per-slot Joule losses under voltage unbalance, at no-load, were identified, which, in relation to the commonly used delta-connected single windings, may provide more motor tolerance to supply voltage unbalance, ultimately extending the useful lifetime of the stator winding.
... The primary reason behind this is the proliferation of non-linear loads, solid-state switching devices, power electronics converters, power transfer switches, and protective equipment. Moreover, the grid signals have become more distorted due to the disturbed generation and the excessive use of renewable energy sources [2], [3]. Therefore, the nature of the PQ signal is continuously changing due to the aforementioned reasons which demand more accuracy in the identificationofthe complex PQ disturbances. ...
... In this tool, the model information (e.g., harmonic model or autoregressive model) from which a signal is generated may be recognized based on the prior knowledge of a disturbance. MUSIC methods, Kalman filter (KF), and ESPIRIT methods are some of the common methods used for harmonic modeling [2], [3]. Before choosing an appropriate DSP technique for PQ assessment, its characteristics and disadvantages should be known. ...
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Article
The increasing trends toward the accurate identification of power quality disturbances (PQD) via power quality (PQ) monitoring require an appropriate digital signal processing (DSP) technique and a robust classifier. To this end, Stockwell transform (ST), one of the most efficient feature extraction DSP tools, and its several variants play an utmost role in PQ assessment framework. Its time-varying spectral characteristics generally extract the local instantaneous frequency spectrum from the global temporary behavior of PQD signal. However, the Standard ST suffers from thepoor time-frequency resolution because of its frequency-dependent Gaussian window (GW). While the analysis of the statistically time-varying signals requires a suitable balance between time and frequency resolution. To this end, this paper provides a comprehensive literature review on several modified versions of Standard ST for the first time to reduce the computational complexity of the algorithm as well as maximize the energy concentration of the time-frequency plane. A comparative analysis of all the modified STs has been presented in tabular form to provide the key characteristics of each technique. Additionally, a case study has been presented to substantiate the highest accuracy of the proposed algorithm over the other ST variants. Apart from the PQD classification, miscellaneous applications of Standard ST and its modified variants have been indicated. This review paper may provide a valuable resource to the researchers for further improvement of the time-frequency resolution of ST not only in classifying PQD but also for its other wide applications.
... Voltage sags have two main characteristics; magnitude and duration (Bollen, 1999). The sag magnitude is the most common application used when defining the sagging magnitude, the smallest remaining pu value of the effective stress during the sagging event. ...
... Most voltage quality monitors take the smallest value of the voltage obtained during the event. Since normally the deepest part of the sag has a fixed effective value, it is acceptable to use the smallest value (Bollen, 1999). ...
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Conference Paper
Sheet metal parts are widely used in the white goods industry, especially in oven manufacturing. After the baking trays are produced in progressive molds, they are exposed to temperatures of 800-860 °C for enamel coating. Due to the thinness of the trays or the different form structures, distortion problems are observed in the trays during the enameling process. In this study, thermal analysis was applied to unembossed and embossed trays in Ansys program. According to the results of the analysis, the maximum stress value of the embossed trays exposed to 850 °C temperature decreased from 11293 MPa to 9460 MPa compared to the unembossed trays resulting in an improvement of % 16,23. Maximum strain value decreased from 0,061 to 0,051 resulting in an improvement of % 16,39.
... Voltage sags have two main characteristics; magnitude and duration (Bollen, 1999). The sag magnitude is the most common application used when defining the sagging magnitude, the smallest remaining pu value of the effective stress during the sagging event. ...
... Most voltage quality monitors take the smallest value of the voltage obtained during the event. Since normally the deepest part of the sag has a fixed effective value, it is acceptable to use the smallest value (Bollen, 1999). ...
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Conference Paper
Sheet metal materials are used in parts of white appliances that require strength. In order for the products to be durable and light, the most appropriate sheet thickness is important in terms of cost and quality. Sheet metal parts are produced in presses and molds, so they are exposed to different drawing, cutting and drilling forces. In this study, the deformations of the formed and unformed trays used in the ovens as a result of the applied force were investigated. While the maximum total deformation value of the formless tray was 6,6747 mm, this value decreased to 6,3842 mm with the addition of the form, resulting in an improvement of % 4,35. The maximum equivalent stress value of the formed tray decreased from 761,23 MPa to 742,39 MPa compared to the unformed tray, resulting in an improvement of % 2,47. According to these results, the embossed baking tray was found to be more resistant to mechanical forces than the unembossed trays.
... Poor quality of electric supply to the equipment is normally caused by power line disturbances such as transients, momentary interruptions, notches, voltage swell and sag, under-voltages, over-voltage, and harmonic distortions. We are using filters to better the power quality [4]. People demand quality power continuously for their appliance's operation. ...
... The performance of the consumer end equipment is heavily dependent on the quality of power supplied to it. But the quality of power delivered to the consumer is affected by various internal and external factors, like voltage and frequency variations, faults, outages, etc. [4]. These power quality problems reduce the lifetime and efficiency of the equipment. ...
Article
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.
... These symptoms can negatively affect the operation of street lighting controls, household dimmers, semiconductor manufacturing equipment, medical scanners, security systems, and transportation controls. Traditional technologies used on the grid today may not have the capability to properly measure and detect supraharmonic threat to the electric power system reliability [2][3]. ...
Conference Paper
The penetration of renewable energy is increasing worldwide and initiatives such as distributed energy resources (DERs) and microgrids play a vital role in generating electrical power with less environmental impacts. The inherent nature of these inverter based DERs creates significant technical challenges to power industry. As the grid continues to evolve towards renewable power generation, grid stability and power quality monitoring will become more prominent to maintain a reliable grid. This paper presents a data driven based understanding of how DERs impact the power quality of the grid. Several test scenarios were performed at a Utility microgrid test site, consisting of various DER sources and measurement instrumentation. These tests were performed to intentionally introduce disturbances and measure the resulting impact with measurement instruments including low power capacitive voltage dividers (CVDs) sensors and a power quality analyzer. In addition to these tests, the microgrid was monitored for 10 months (Aug 2020-June 2021) and subjected to all 4 seasons. Throughout this monitoring period, an event was observed that exhibited significant power quality disturbances. The voltage magnitude, frequency, conducted emissions (supraharmonic frequencies), total harmonic distortion (THD), and flicker were recorded to observe behavior and its impact to the system. The measurement observations demonstrate that DERs do have an impact on grid power quality and that supraharmonic frequencies are present beyond what traditional technologies can measure at the medium voltage level. Traditional instrument transformer technologies may have frequency cutoff measurement limitations that inhibit their ability to measure supraharmonic frequencies. Traditional intelligent electronic devices (IEDs) may have frequency measurement limitations if they are designed to measure up to typical industry guidelines at the 50th harmonic (3kHz). While the impact of supraharmonic activity to medium voltage grid reliability is not thoroughly understood, this study demonstrates DERs do generate them, and that they can be measured with capable sensors and power quality analyzers. The CVD sensor and power quality analyzer system applied in this microgrid test bed have demonstrated frequency measurement of 4kHz-24kHz that may be limited or undetectable with traditional measurement systems. CIGRÉ is an international non-profit association for promoting collaboration by sharing knowledge and joining forces to improve electric power systems of today and tomorrow. The NGN exists to develop the next generation of power industry professionals.
... The RES respects the FRT capability shown in Figure 3, if it maintains its connection to the electrical grid in case of voltage sags that exceed the LVRT profile limits (red line). It should be noted out that LVRT requirement is related to voltage dips with short durations (hundreds of milliseconds), which are caused generally by short-circuits events [24]. To analyze the LVRT requirement, all the possible scenarios causing voltage sags that could exceed the LVRT profile limits have been identified by the calculation of the voltage dips due to the faults in the critical locations. ...
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Article
p>Most countries of the world have adopted renewable energy sources (RES) because of consistent policy and industry support. The use of these sources is expanding and will cover a larger part of the generation capacity in the future. Thus, power systems (PS) are experiencing the high scale RES integration. For a power system dominated by RES, the electrical grid characteristics, namely, the inertia constant (Hs) and the rate of change of frequency (ROCOF), should be evaluated. Furthermore, the requirements related to these characteristics should be specified in the grid code (GC) to reflect the actual needs of the transmission system operator (TSO) and to prepare the evolution of the RES penetration level. Due to the delay in specifying or updating these GC requirements, RES that are incorporating unsuitable functionalities for the future perspective, regarding fault-ride-through (FRT) and frequency support requirements, will remain operational by 2030; this will create additional constraints on the PS frequency stability after large-scale RES integration. In this paper, the impact assessment of deployed RES technologies on the Moroccan PS frequency stability is assessed by the year 2030, using MATLAB/Simulink environment. The main reason for focusing on the case study of Morocco is the country’s target of installing 52% of the energy supply from RES in the horizon of 2030.</p
... El Ministerio de Energía y Minas (MINEM) y el Organismo Supervisor de la Inversión en Energía y Minería (OSINERGMIN) son las dos entidades claves responsables de la implementación del marco regulatorio y del cumplimiento de las regulaciones del sector energético y minero del Perú. La calidad del servicio eléctrico es uno de los indicadores más importantes para analizar la regulación de calidad de los servicios públicos, según Bollen (2000) es el "conjunto de características que se debe cumplir en la interacción entre los suministradores del servicio eléctrico, los usuarios del mismo y la población en general" [3]. A nivel mundial se observa la tendencia a un cambio en la matriz energética, debido al impacto ambiental de las tecnologías convencionales de generación de energía; por ello, se vienen utilizando ya de manera sostenible la producción de energía eléctrica utilizando fuentes renovables como la energía solar, energía eólica, biomasa, de manera importante. ...
... If the frequency set points are different for the inverters, then the error in power sharing among parallel unit occurs. Real power deviation due to the deviation of frequency set points i   by Equation (8) is (19) When two inverters are connected in parallel with 2 1 2 1 r r P P P P    , the relative power sharing error which may exist due to the measurement of frequency ...
Article
Technical advances in power electronics and generation capabilities have made the possibility of Distributed Generation (DG) systems. A microgrid is an effective division of a distributed generation system which is analysed by its capability of its operation both as a grid connected and isolated condition. All independent sources operate separately when the main grid is capable of supporting voltage. In case of islanded mode, dynamics is greatly influenced by the connected sources and on the power handling ability. Control of power interfaced converters is of major concern in both the modes of operation. In grid connected mode of operation, the current of the voltage developed needs to be controlled whereas, in Isolated condition, building of voltage is required.In the islanded mode of operation, all the resources in a microgrid should be controlled in coordination with each other so that a stable and a balanced three-phase sinusoidal voltage is obtained. Conventional droop controller is modified for accurate sharing among power converters even when the measured voltage and frequency of the inverters are not the same. Droop coefficients are estimated so that power sharing is more accurate for the respective changes in the power values. They also enable the flawless transfer of the operation mode from islanded to grid connected or vice versa.
... In the ABC classification seven different grid sag types are defined based on the fault type, transformer winding connection and load connection [30]. For the application presented in this paper, grid sag types -A, B and E -were selected. ...
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Article
In recent publications statistical model checking (SMC) has been proposed as a method for verifying the performance of finite-set model predictive control (FS-MPC) algorithms applied to power electronics converters. One of the reasons the full potential of the method in the power electronics systems (PES) has not yet been explored is the time consuming modelling process. In this paper we propose a modular method of modelling the power electronics system components by providing simple building blocks, which can be connected to build different PES. The modelling method is here demonstrated on a direct matrix converter, which operates in a stochastic grid with different harmonic distortion levels and voltage sags. By applying the SMC, the performance of the control algorithm in terms of the output current distortion, effects of the weighting factor selection and grid distortions on the device utilization can be evaluated. The obtained results confirm, that high grid distortions and voltage sags will increase the stress of several devices. This information can be of great importance to identify the most stressed components and how the control algorithm can be adapted to extend the lifetime of the components and thereby the system during different grid conditions. The verified FS-MPC algorithm has also been implemented in an experimental set-up.
... Switching big capacitors or removing huge loads are the two primary sources of voltage surges. Industrial equipment such as motor drives, surge arresters, and relays may be overheated, tripped, or even destroyed by voltage surges [8][9][10]. For delicate loads, harmonic contamination is a concern. ...
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Article
This paper proposes a novel integration of solar PV and lithium-ion battery-based dynamic voltage restorer (DVR) which is implemented in distribution grids to meet the necessary power and for power quality improvement. In the proposed model, the DC source of the DVR is the PV array and energy storage system consisting of a lithium-ion battery.Moreover, the renewable energy source can supply the DVR or charge the lithium-ion battery occasionally. Solar photovoltaic with boost converter is implemented by Perturb and Observe (P&O) method to track the Maximum power. In addition, the lithium-ion battery is assigned with the bidirectional buck boost converter to conduct the charge/discharging operation. The DVR is regulated using a fuzzy logic controller FLC method to compensate for load voltage sag, swell, and harmonies. The control strategies aim to regulate the DVR voltage via an injection transformer to compensate for the required voltage while maintaining the load voltage constant. The proposed DVR ability to mitigate voltage sag, swell, and harmonies in a low voltage distribution system was demonstrated by experimental results.
... Power quality is the group of working characteristics of an electrical system, including voltage and current attributes and their effects. The interest relies in the search for the correction of anomalies of what is advocated as ideal [131]. The problems of power quality consist of voltage, current (magnitude and waveform) and frequency deviations that negatively affect power equipment. ...
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Article
Microgrids are relatively smaller but complete power systems. They incorporate the most innovative technologies in the energy sector, including distributed generation sources and power converters with modern control strategies. In the future smart grids, they will be an essential element in their architecture. Their potential to offer many economic, social and environmental services through advanced electrical techniques has led to a growing interest in the theme. Although the islanding condition is a very important feature of microgrids, only with the implementation of grid connection and seamless transition they will demonstrate their full capacity. However, there are still many questions surrounding these operation modes and this paper tries to answer part of them. To do that, several aspects in the field are approached. The history and late development of microgrids are revisited. The main concepts are presented. The islanded mode is revised, since it is intrinsically linked to the other working states of the microgrid. The requirements for the interconnection of microgrids to an external grid are discussed. The operation elements are also analyzed. A crucial part of the grid-connected microgrids and their seamless transfer conditions, the control methods found in the literature are extensively reviewed. The paper is concentrated in the analysis of control methods for AC microgrids and AC power systems, therefore, it does not enter in detail or investigates profoundly the topologies applied in the power electronics structures nor DC microgrids and DC power systems.
... Voltage sag is a dropping of a effective voltage value from 0.9 pu to 0.1pu of nominal value for durations from 0.5 cycle to 1min [1], which can be caused by many reasons such as heavy motors starting. Voltage sag affects the sensitive loads in power system network. ...
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Article
Voltage quality effect is the major power quality problem in power system network which affects the customer load operation in distribution systems. Voltage quality problem exists in terms of sags and swells whose detection is a major issue in power system network. Redundancy identification method (conventional method) has low accuracy due to the co-relativity between voltage sag and sag disturbances and hence, detection of existence of sag, identifying its causes and its mitigation is a major problem in power network. Most of the voltage quality problems in distribution networks occur due to non identification of type of fault or sag in a particular phase and is a major challenge. Several algorithms are existing for identification of sag and swell in literature. This work is mainly focuses on simple sag identification in power system network using Fast Fourier Transformation (FFT). The proposed FFT is modeled to detect the fault, identify the type and depth of the fault. A MATLAB/SIMULINK model is developed for testing the various fault conditions. Simulation results of the proposed method shows that the comprehensive feature indices takes less time with more accuracy for identification of sources of disturbance for voltage sag under different types of symmetrical and un-symmetrical fault conditions than the conventional identification features indices.
... Power quality issues like transients, sags, swells, and alternative distortions to the curving wave shape of the availability voltage have an effect on the performance of those instrumentality items. Voltage sags and swell in an electrical grid aren't forever attainable to avoid as a result of the finite clearing time of the faults that cause the voltage sags, swells and therefore the propagation of sags and swells from the transmission and distribution systems to the lowtension hundreds [1][2][3][4]. Voltage sags and swells are the common reasons for interruption in production plants and for end instrumentality malfunctions generally, specifically, in economical identification will cause disruption and vital prices attributable to loss of production. One solution to the present downside is to create the instrumentality itself additional tolerant to sags, either by intelligent management or by storing energy within the instrumentality. ...
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Typical power quality (PQ) disturbances include sag, swell, harmonics, transients and temporary, momentary and sustained interruptions in a power distribution network. Among all these disturbances, sags and swells get prime importance, as they can cause sufficient damage to industrial consumer's equipment and can ultimately lead to shut down of their system. To be able to detect existence of sag, swell and identify its cause for determining mitigation options, Due to the correlativity and redundancy of the features, the identification method for voltage sag and swell disturbance source is low accuracy, to determine the probable origin of the event leading to the voltage sag. It is usual to have power quality related events, more specifically a sag or swell, surfacing at the distribution level due to a fault at the transmission level. This paper presents a new approaches for the identification and analysis of the two main power quality parameters (sags and swells) using Fast Fourier Transform analysis. The proposed Fast Fourier Transform is modeled in such a way that to identify the type of fault, duration of fault and the depth of fault. The simulation results show that comprehensive feature indices with less time requirement for identification and the identification accuracy which is obtained using FFT analysis indices is higher than the conventional identification features indices in the classification and identification of disturbance sources of voltage sag and swell under different types of symmetrical and un-symmetrical fault conditions.
... To analyse these electrical disturbances, models of the operation of static converters are necessary. A voltage sag is defined as a momentary decrease in the RMS value of the nominal voltage for a duration ranging from 0.5 cycles to 1 minute [3] [4]. Short circuits and the starting of large induction motors are the main causes of voltage sags. ...
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In this study, a functional model for diode bridge rectifiers (DB) is developed based on the concept of switching functions. The developed model is suitable for the estimation of the average voltage at the rectifier terminals from the fundamental three-phase voltage estimation based on the Adaline method and a DC bus estimator based on the switching function method, The performance of the detection estimator was validated in simulation using Matlab software under normal, unbalanced and line fault conditions. The high accuracy and efficiency of the developed estimator were demonstrated by comparison with rectifier models from SPS (SimPowerSystems), PSIM, and a reel rectifier from the pedagogical model (THREE-PHASE EDUCATIONAL INVERTER SEMITEACH 08753450BB)
... The SES can be considered as microgrids with many sources of disturbances in power supply of the consumers onboard [1]. The problems regarding the power quality have been identified and studied by many researchers [2,3,4]. The protection of the consumers against the various emergency modes that may occur in the power systems needs to be fast, reliable and cost effective [4,5,6,7,8]. ...
... Voltage sags caused by faults in power distribution networks are the most common power quality problem [1]. However, it has obvious influences on the security and stability of the electrical equipment with sensitive loads, such as computers, micro-controllers and new power electronic equipment [2]. ...
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... In the ABC classification, seven grid sag types are defined based on the fault type, transformer winding connection and load connection [15]. For the application presented in this paper, grid sag types -A, B and E -were selected. ...
... Voltage sags, as defined by the IEEE-1159 standard, are brief drops in rms voltage to between 0.1 and 0.9 pu for durations ranging from 0.5 to 1 minute [4]. Short-circuiting faults, such as single line-to-ground faults in a power system, and the start-up of large rating motors are the most common causes of voltage dips. ...
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In many continuous manufacturing processes such as paper, textile, winding and plastic extrusion, electric drives are frequently required to work in synchronization, often with high tolerances to ensure uniform product quality and avoid failure of the product. In a multi-motor system (MMS), voltage dips are the most common cause of the motor stoppage, and the transient loss of synchronism between motors can result in a complete system shutdown. This paper proposes a multi-motor system controlled by a Backstepping strategy to ensure servo-control and synchronization of induction motors. This technique includes indirect rotor field-oriented control (IRFOC), linear speed control, and mechanical tension control, of induction motors. Investigations of symmetrical voltage sag effects on speed, torque, and mechanical tension are also carried out. Simulation results obtained using Matlab®/SimulinkTM/SimPowerSystems® are presented to demonstrate the efficiency of the proposed control strategy.
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In a modern power system, a unified power quality conditioner (UPQC) is considered an effective and promising mitigating equipment for all types of power quality (PQ) problems. Use of variable phase angle control (PAC) technique for controlling UPQC results in increased utilization of both PECs most efficiently making the system more attractive economically. In this research work, the Rao-1 algorithm along with variable PAC is implemented to find the optimal loading of UPQC. The outcomes obtained from Rao-1 are compared with the JAYA optimization to show the dominance and competence of the Rao-1 over JAYA. This research work will help in developing instantaneous control techniques based on optimization techniques.KeywordsPower electronic converterRao algorithmUPQC
Chapter
The ITIC curve standard evaluates the impact of voltage sag by counting the voltage sag characteristic distribution on the receiving side of low voltage sensitive devices. However, direct use of medium and high voltage sag data for power quality on-line monitoring may result in large evaluation errors. To solve these problems, this paper presents an on-line monitoring system ITIC curve sag severity assessment method to improve the accuracy of voltage sag severity assessment in the absence of low voltage side voltage data. Firstly, the transient transfer between power grid side and equipment side is analyzed according to the sequence component transfer characteristics of transformer. Secondly, the recording data is processed by DFT to obtain the voltage sag data of the equipment side. Then the ITIC curve is used to evaluate the voltage sag severity of the low-voltage side equipment and the state after the voltage sag of the equipment. Finally, the validity of the method is verified by the measured data.
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In recent years, power quality (PQ) has become an important issue for utilities and users. In order to improve PQ, a method for detecting and classifying power quality disturbances (PQDs) is proposed. Hence in addition to identifying the disturbance signals, the proposed method is able to determine its type when occurring. This approach is based on Multilayer perceptron and Levenberg-Marquardt training rule. It is inspired by the desire to take advantage of the parallelism inherent to neural networks in view of hardware implementation using reconfigurable chips. The inputs of these networks are the samples obtained on the power grid in various conditions. The proposed method is tested for sags and swells. To classify the disturbances, the neural architectures have been generalized and configured according to the number and type of disturbances to be treated. To validate and test the proposal, a grid model was built with a three-phase fault generator under Matlab / Simulink R2017a. After comparing the results with those obtained by certain methods in the literature, the proposal proves to be an efficient and reliable tool for monitoring PQ. In fact it has the smallest mean square error and a highperformance with precision of 96%.
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The power control based on the GPCC (Generalized Predictive Current Control) applied in the power electronic converter connected to the grid is presented in the paper. A design process of the control structure and its parameters, and the results of simulation and experimental validation are presented. The power responses to changes in power references and to grid failures are shown and discussed. The algorithm works well with unbalanced grid voltage. Steady state responses of both powers are oscillation-free for an unbalanced grid, and the network currents remain sinusoidal at the same time. The strategy is also able to ensure that limit values of grid current magnitudes are not exceeded during changes of power references or grid voltage and responses are fast and smooth at the same time. The combination of these favorable properties, which was not observed with other power control methods, can be assessed as the main benefit of the strategy developed.
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In Restructured power systems, Power quality is one of the major concerns in the present era. The problem of voltage sags and swells and its major impact on sensitive loads are well known. To (DVR), which is one of the most efficient and effective modern custom power devices used in power distribution networks. A new FLC control algorithm for the DVR is proposed in this paper to regulate the load terminal voltage during sag, swell in the voltage at the point solve this problem, custom power devices are used. One of those devices is the Dynamic Voltage Restorer of common coupling (PCC).This new control scheme, it is based on fuzzification rules are used for the generation of reference voltages for a dynamic voltage restorer (DVR). These voltages, when injected in series with a distribution feeder by a voltage source inverter (VSI) with PWM control, can regulate the voltage at the load terminals against any power quality problem in the source side. Wavelets based analyzes the power circuit of the system in order to come up with appropriate control limitations and control targets for the compensation voltage control through the DVR. The control of the DVR is implemented through derived reference load terminal voltages.
Chapter
With the increasing consumer electric power demand, centralized power plants have converted into decentralized power plants. But sometimes, due to numerous faults, there are problems of electric power production. This problem has especially been overcome by commissioning of hybrid electric power systems. By employing hybrid systems, it is possible to install a solar photovoltaic (PV) array and synchronize its generation with conventionally installed large‐scale power generation systems. In recent times, it has been observed that hybrid system offers the best solution in energy production and harnessing good quality electric power at output. It is possible by operating two or more renewable energy sources (RESs) through effective and efficient controlling systems. Moreover, renewable energy (RE) sector has been supported by Indian Government in recent times. Additionally, numerous policies for granting financial aids are being framed in promoting research‐based activities. Hybrid systems, thus, have become a reliable option for rural and remote areas in ensuring the availability of uninterrupted electric power. However, the integration of RESs may pose some immediate power quality (PQ) problems. However, due to integration of RES with conventional energy sources, turning into microgrid leads to PQ issues. These problems can be overcome by implementing power conditioning systems. This chapter deals with designing of different modes of hybrid energy systems in order to have an understanding of their operation that is possible under various variable constraints and PQ assessment with different dynamic and static controlling mechanisms.
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