Showing papers on "Voltage sag published in 2017"
TL;DR: A novel control strategy to mitigate the double grid frequency oscillations in the active power and dc-link voltage of the two-stage three-phase grid-connected photovoltaic (PV) inverters during unbalanced faults is introduced.
Abstract: Power quality and voltage control are among the most important aspects of the grid-connected power converter operation under faults. Nonsinusoidal current may be injected during unbalanced voltage sag, and active or/and reactive power may include double frequency content. This paper introduces a novel control strategy to mitigate the double grid frequency oscillations in the active power and dc-link voltage of the two-stage three-phase grid-connected photovoltaic (PV) inverters during unbalanced faults. With the proposed control method, PV inverter injects sinusoidal currents under unbalanced grid faults. In addition, an efficient and easy-to-implement current limitation method is introduced, which can effectively limit the injected currents to the rated value during faults. In this case, the fault-ride-through operation is ensured, and it will not trigger the overcurrent protection. A non-maximum power point tracking (non-MPPT) operation mode is proposed for the dc–dc converter. The mode is enabled under severe faults when the converter cannot handle the maximum PV power. Finally, experimental validation is provided by implementing a method in an experimental setup, including a 2 kW PV inverter.
186 citations
TL;DR: In this article, the authors provide a comprehensive review on the DVR topologies, control strategies and applications, and some comparative conclusions are also provided for the researchers and engineers, who want to do investigations on DVRs.
123 citations
TL;DR: The effectiveness of the DVR using Synchronous reference frame (SRF) control is investigated for FRT capability in DFIG-WT during both balanced and unbalanced fault conditions.
Abstract: Fault ride through (FRT) capability in wind turbines to maintain the grid stability during faults has become mandatory with the increasing grid penetration of wind energy. Doubly fed induction generator based wind turbine (DFIG-WT) is the most popularly utilized type of generator but highly susceptible to the voltage disturbances in grid. Dynamic voltage restorer (DVR) based external FRT capability improvement is considered. Since DVR is capable of providing fast voltage sag mitigation during faults and can maintain the nominal operating conditions for DFIG-WT. The effectiveness of the DVR using Synchronous reference frame (SRF) control is investigated for FRT capability in DFIG-WT during both balanced and unbalanced fault conditions. The operation of DVR is confirmed using time-domain simulation in MATLAB/Simulink using 1.5 MW DFIG-WT.
90 citations
TL;DR: The improvement in performance of the DVR using CFFFB control compared with the conventional feed-forward control is observed in terms of voltage sag mitigation capability, active and reactive power support without tripping, dc-link voltage balancing, and fault current control.
Abstract: This paper investigates the fault ride through (FRT) capability improvement of a doubly fed induction generator (DFIG)-based wind turbine using a dynamic voltage restorer (DVR). Series compensation of terminal voltage during fault conditions using DVR is carried out by injecting voltage at the point of common coupling to the grid voltage to maintain constant DFIG stator voltage. However, the control of the DVR is crucial in order to improve the FRT capability in the DFIG-based wind turbines. The combined feed-forward and feedback (CFFFB)-based voltage control of the DVR verifies good transient and steady-state responses. The improvement in performance of the DVR using CFFFB control compared with the conventional feed-forward control is observed in terms of voltage sag mitigation capability, active and reactive power support without tripping, dc-link voltage balancing, and fault current control. The advantage of utilizing this combined control is verified through MATLAB/Simulink-based simulation results using a 1.5-MW grid connected DFIG-based wind turbine. The results show good transient and steady-state response and good reactive power support during both balanced and unbalanced fault conditions.
84 citations
TL;DR: In this article, the authors proposed an approach based on Hilbert-Huang transform (HHT) and Extreme learning machine (ELM) to detect an islanding condition in a distribution system with distributed generations (DGs).
79 citations
TL;DR: In this article, a control design strategy of modular multilevel converters (MMC) for HVDC applications to operate during normal and AC fault conditions is described, which enables full control of the MMC internal energy.
64 citations
TL;DR: The dynamic behavior of the proposed grid interfaced DG system is experimentally evaluated in maintaining constant loading on grid, transient-free operation, and power factor improvement close to UPF operation of the utility grid, by compensating total reactive power and harmonic current demanded by variable linear as well as nonlinear load.
Abstract: This paper presents real-time implementation of a grid interfaced distributed generation (DG) system with modified current control loop using three phase amplitude adaptive notch filter (AANF) based synchronization tool. A grid current feedback based modified $dq$ -current control technique for interfacing inverter is developed in order to achieve constant loading on the grid, transient-free operation, and power factor improvement close to unity power factor (UPF) of the utility grid during sudden load variations. This technique does not require separate calculation of reference reactive component and harmonics component of currents hence reduces control circuit complexity. In addition, it requires only three voltage and three current sensors. Three phase AANF is developed and is used for online extraction of utility voltage phase angle to generate synchronized reference current signals for interfacing inverter. AANF is used because of its adjustable accuracy and amplitude adaptability even under unbalanced voltage sag and swell, frequency variation, and distorted grid conditions. Fast and accurate behavior of three phase AANF improves the dynamic response of entire DG system control performance for sudden load variations. The dynamic behavior of the proposed grid interfaced DG system is experimentally evaluated in maintaining constant loading on grid, transient-free operation, and power factor improvement close to UPF operation of the utility grid, by compensating total reactive power and harmonic current demanded by variable linear as well as nonlinear load.
53 citations
TL;DR: In this paper, the authors present the results of a power quality study carried out in an industrial distribution system and quantify the negative impact caused by voltage sags in industrial processes and its relationship to generated interruptions.
Abstract: This paper presents the results of a power quality study carried out in an industrial distribution system. The main objective of this study was to quantify the negative impact caused by voltage sags in industrial processes and its relationship to generated interruptions. A series of measurements of power quality variations were taken at the substation that feeds the circuit and at the point-of-common coupling of each industrial user. The new standard IEEE Std 1564-2014 “Guide for Voltage Sag Indices” was used to determine the indicators to assess the severity of voltage sags and also the calculation method. Sag severity was selected as it allows the calculation of the probability of voltage sags to generate interruptions in industrial processes or electrical equipment. Thus, an analysis of the quality of the supply voltage can be done. Severity was initially calculated at the substation that feeds the industrial circuit and later, at the point-of-common coupling of each user. Subsequently, the relationship between user interruptions and severity values was determined. Finally, recommendations of good engineering practices in industrial processes were done.
44 citations
TL;DR: In this article, the Dynamic Voltage Restorer (DVR) is modelled to protect sensitive load from source side voltage disturbances under nonlinear load conditions, and the real coded GA optimized fuzzy logic controller is used to control both d and q components of the voltage.
38 citations
TL;DR: In this paper, a fuzzy sliding mode pulse width modulation (FSMPWM) control strategy for three-phase three-wire unified power quality conditioner (UPQC) is proposed.
37 citations
TL;DR: In this article, a mini-size GdBCO magnet for hybrid energy storage (HES) application in a kW-class dynamic voltage restorer (DVR) is presented.
Abstract: This paper presents the design and evaluation of a mini-size GdBCO magnet for hybrid energy storage (HES) application in a kW-class dynamic voltage restorer (DVR). The HES-based DVR concept integrates with one fast-response high-power superconducting magnetic energy storage (SMES) unit and one low-cost high-capacity battery energy storage (BES) unit. Structural design, fabrication process, and finite-element-modeling simulation of a 3.25 mH/240 A SMES magnet wound by state-of-the-art GdBCO tapes in SuNAM are presented. To avoid the internal soldering junctions and enhance the critical current of the magnet simultaneously, an improved continuous disk winding (CDW) method is proposed by introducing different gaps between adjacent single-pancake coil layers inside the magnet. About 4.41% increment in critical current and about 3.42% increment in energy storage capacity are demonstrated compared to a conventional CDW method. By integrating a 40 V/100 Ah valve-regulated lead-acid battery, the SMES magnet is applied to form a laboratory HES device for designing the kW-class DVR. For protecting a 380 V/5 kW sensitive load from 50% voltage sag, the SMES unit in the HES-based scheme is demonstrated to avoid an initial discharge time delay of about 2.5 ms and a rushing discharging current of about 149.15 A in the sole BES-based scheme, and the BES unit is more economically feasible than the sole SMES-based scheme for extending the compensation time duration.
TL;DR: A series voltage regulator for a distribution transformer which addresses power quality issues in the electrical power distribution system and satisfies needs of smart distribution grids in terms of improved availability, equipment protection, and resilience.
Abstract: This paper presents a series voltage regulator for a distribution transformer which addresses power quality issues in the electrical power distribution system. The proposed system is comprised of a line frequency transformer connected to a power electronic converter which is autoconnected on the secondary side. This autoconnection is facilitated by use of a high-frequency or medium-frequency transformer. A simplified strategy to compensate for voltage sags and swells on the grid side, by providing continuous ac voltage regulation, is discussed. When a voltage sags or swells occur, the power electronic converter generates a compensating voltage, which is vector-added to the grid voltage in order to regulate the output voltage supplied to the load. The proposed system satisfies needs of smart distribution grids in terms of improved availability, equipment protection, and resilience. Detailed analysis is provided with experimental results in order to validate the effectiveness of the proposed system.
TL;DR: In this paper, the fault rate of each line is calculated using type reduction Karnik-Mendel algorithm and selection of the location of fault is done by Monte Carlo simulation to assess voltage sag in each bus of the distribution system.
Abstract: Power quality (PQ) is the key concern in every corner of the world today. Regarding PQ voltage sag is one of the most relevant issues. The causes of faults in distribution system resulting voltage sag are impact of wind speed on conductors and attachments, faults caused by cattle, animal, mice, rat, birds, bat, snakes and vagaries of weather seems to be definite but found unpredictable in quantum. Considering the intensity and the impacts of these uncertainties as an input interval type-2 fuzzy system is applied to ascertain fault rates of individual lines in distribution systems. The fault rate of each line is calculated using type reduction Karnik–Mendel algorithm. Selection of the location of fault is done by Monte Carlo simulation to assess voltage sag in each bus of the distribution system. This approach is applied to IEEE 30-bus system and Barak Valley 37-bus distribution system for validation.
TL;DR: In this article, a comprehensive review on methods for voltage sag source location is presented and also nine generalized methods using positive sequence phasors, instantaneous positive sequence components, Clarke's components and integration are introduced.
TL;DR: In this article, an effective numerical method to determine an accurate AOV in a large scale power system and to overcome limitations of other well-known methods is presented. But the method is not suitable for large-scale power systems.
Abstract: This paper describes a systematic method for determining an area of vulnerability (AOV) to fault induced voltage sags. The concept of an AOV is very useful for evaluating vulnerability and the relationship between sensitive loads and system voltage sag performance. In general, a system performance assessment pertaining to voltage sags requires a determination of AOVs for system buses. Because voltage sags can be caused by remote faults in a transmission system, to completely identify an AOV, a large part of the power system including adjacent circuits and remote supply systems should be considered. Therefore, accurately calculating critical points and identifying AOVs are challenging tasks. In this paper, we present an effective numerical method to determine an accurate AOV in a large scale power system and to overcome limitations of other well-known methods.
TL;DR: In this paper, the impact of different flexible AC transmission system (FACTS) devices on critical power quality (PQ) phenomena including voltage sags, harmonics and unbalance from the perspective of both mitigation effect and potential negative impact is investigated.
Abstract: This study investigates the impact of different flexible AC transmission system (FACTS) devices on critical power quality (PQ) phenomena including voltage sags, harmonics and unbalance from the perspective of both mitigation effect and potential negative impact. The FACTS devices, including static VAR compensator, static compensator (STATCOM) and dynamic voltage restorers, are modelled in commercially available software PowerFactory/DIgSILENT to study their impacts on the critical PQ phenomena. Two control strategies, voltage regulation and reactive power compensation, are considered for STATCOM. For DVR, a PI-controller is developed for the purpose of voltage sag mitigation. The merit of the proposed controller is presented by the dynamic response of during fault voltage and the capability of post-fault voltage recovery. The study is carried out on a large-scale generic distribution network. The impact of various devices on PQ phenomena is assessed using appropriate evaluation methodologies, and the results obtained with and without mitigation are presented and compared using heatmaps.
TL;DR: This study shows that the preclassification can be reformulated as a pure model order selection problem and proposes two preclassifiers based on Information Theoretical Criteria, the former of which yields the highest statistical performances, whereas the latter has a lower computation complexity.
Abstract: In this paper, a new technique for power quality disturbance classification is proposed It focuses on voltage sags and swells that are first preclassified into four classes that depend on the number of nonzero symmetrical components and can contain different types of sag and swell Using the estimated symmetrical component values, we can afterward classify the corresponding sag or swell signature In this study, we show that the preclassification can be reformulated as a pure model order selection problem To solve this problem, we propose two preclassifiers based on Information Theoretical Criteria The former yields the highest statistical performances, whereas the latter has a lower computation complexity The performances of the proposed classification algorithms are evaluated using Monte Carlo simulations on synthetic signals and using real power system data obtained from the DOE/EPRI National Database of Power System Events The achieved simulations and experimental results clearly illustrate the effectiveness of the proposed algorithms for voltage sag and swell classification
TL;DR: A cascaded multilevel inverter type DSTATCOM and DVR to compensate voltage sag in utilities in power distribution network and the proposed neuro-fuzzy controller follow itself to the sag and provides effective means of mitigation.
Abstract: STATCOM is one of the shunt type FACTS controllers which can supply reactive power and improve bus voltage. STATCOM, a controlling device used on alternating current transmission networks, has advantages like transient free switching and smooth variation of reactive power. This paper proposes a cascaded multilevel inverter type DSTATCOM and DVR to compensate voltage sag in utilities in power distribution network. The proposed DSTATCOM is implemented using multilevel topology with isolated dc energy storage and reduced number of switches. A DVR injects a voltage in series with the system voltage and a D-STATCOM implant a current into the system to correct the voltage sag, swell and interruption. The phase shifter PWM technique is described to generate firing pulse to cascaded inverter. The proposed neuro-fuzzy controller follow itself to the sag and provides effective means of mitigation. The voltage sag with the minimum harmonic at the efficacy end. The proposed technique is simulated using MATLAB/Simulink.
TL;DR: In this article, a novel Multi-Level Inverter (MLI) is introduced to provide a staircase sinusoidal voltage with high level numbers against less switch numbers as compared to the other kinds of MLIs.
TL;DR: In this article, a sliding mode control (SMC) technique for doubly fed induction generators (DFIGs) based on the fast exponential reaching law (FERL) is proposed.
Abstract: This paper proposes a novel sliding mode control (SMC) technique for doubly fed induction generators (DFIGs) based on the fast exponential reaching law (FERL). The proposed FERL-based SMC is capable of reducing to a large extent the chattering phenomena existing in the sliding stage. Meanwhile, the reaching stage is accelerated with the introduction of an adaptive gain. The proposed method is employed in a DFIG-based wind energy conversion system (WECS) for direct power control (DPC). The FERL-based DPC approach is tested with simulations conducted in Matlab/Simulink under the scenarios of unbalanced grid voltage, grid fault conditions and highly unstable wind speed accompanied by an experimental study. The simulations and experimental results reveal the better performance of the proposed control method in active/reactive power tracking and dc-link voltage maintenance.
TL;DR: In this article, a probabilistic method aimed at estimating the voltage sag frequency of non-monitored sites given the number of sags recorded by a limited set of voltage sag monitors is proposed.
Abstract: This paper proposes a probabilistic method aimed at estimating the voltage sag frequency of nonmonitored sites given the number of sags recorded by a limited set of voltage sag monitors. The proposed method is based on simulating a representative database of feasible pseudomeasurements by using probabilistic values of fault coefficient, fault impedance, fault type, and fault location. This information is processed through Bayesian filtering based on the Bayes' probabilistic theorem. This enables obtaining the most probable voltage sag index at nonmonitored busbars given the index measured at monitored busbars. This statistical estimation of sag indices at locations where there are no monitors constitutes the main contribution of this paper. This study is developed in three power systems: the IEEE 24-busbar reliability test system, the IEEE 118-busbar test system, and the transmission network of Ecuador with 357 busbars.
01 Oct 2017
TL;DR: The negative influence of utilizing LED lamp as a lighting source on power grid and on public health is addressed and the need for power quality improvement techniques for such an application also the need of new developments that improve LEDs internal power electronic driving circuit is highlighted.
Abstract: Continuous research to achieve high luminous efficiency with low cost LED lamps has widen the field of LED lighting applications, which dictates the need to study different characteristics of commercial LEDs and their impact on power quality parameters. This paper addresses the negative influence of utilizing LED lamp as a lighting source on power grid and on public health. The operation of the LED and its behavior as a nonlinear load has been further discussed. Various experimental tests that include harmonic analysis, voltage flickering voltage sag, swell and voltage harmonics have been conducted to investigate current and voltage quality issues. This paper aims at a better understanding to the characterization of commercial LED lamps in order to highlight the need for power quality improvement techniques for such an application also the need for new developments that improve LEDs internal power electronic driving circuit.
01 Aug 2017-Canadian Journal of Electrical and Computer Engineering-revue Canadienne De Genie Electrique Et Informatique
TL;DR: In this article, an 11-level cascaded multilevel inverter (CMLI)-based distribution static compensator (DSTATCOM) is implemented to mitigate the harmonic content of an induction furnace (IF) in a steel plant.
Abstract: Use of nonlinear loads in power distribution networks is expanding day by day, which results in the deterioration of the power quality of the system. An induction furnace (IF), which is an indispensable component of the steel industry, is one such typical example of a nonlinear load. It injects a considerable amount of harmonics into the supply network and consequently the performance of other loads in its vicinity gets affected. An 11-level cascaded multilevel inverter (CMLI)-based distribution static compensator (DSTATCOM) is implemented to mitigate the harmonic content of an IF in a steel plant. A Simulink model of an IF has been developed using experimental data obtained on-line from an industrial IF using a power quality analyzer. The solution methodology proposed using CMLI-based DSTATCOM reveals the effectiveness of the proposed control strategy for voltage sag mitigation and total harmonic distortion improvement of both load current and voltage as per the IEEE standards. The results obtained are also compared with that reported in the literature recently.
TL;DR: In this paper, a comparative analysis is performed between some of the discussed methods by applying extensive numerical simulations in a Brazilian regional utility by using PSCAD/EMTDC and MATLAB.
Abstract: Locating the source of voltage sags in order to identify the events causing the problem and improving mitigation strategies is a major issue. When two utilities manage interconnected networks or manage a micro grid and an upstream grid, an occurred fault in one area may cause voltage sags that affect sensitive customers/critical loads in another area. From this viewpoint, this paper first reviews and analyses with detail different methods for voltage sag source location. Then eleven generalized method are introduced. A comparative analysis is performed between some of the discussed methods by applying extensive numerical simulations in a Brazilian regional utility by using PSCAD/EMTDC and MATLAB. The location of each monitor represents a difference kind of system topology (radial, interconnected, one source, two sources and interconnected microgrids). In the following, the effectiveness of methods was obtained and comprised for each monitor location and for the whole system.. The results obtained show that the effectiveness of methods based on instantaneous positive sequence components and Clarke's components is equal in many methods except distance relay and resistance sign methods, and that the effectiveness is lower, higher or equal than methods based on positive sequence phasors. The phasor based methods had less effectiveness. The generalized methods based on reactive power using instantaneous positive sequence components and Clarke's components gave the right location in 88% of total simulated cases. The results also provided a comprehensive background to propose future works and to select the best method especially at interconnection point of a micro grid with the presence of renewable distributed energy sources.
TL;DR: In this paper, a direct power control algorithm for a Doubly Fed Induction Generator-based wind system, robust to the machine parameters variations, is projected, which employs two loops designed using the discretized equations of the generator to obtain a high performance.
TL;DR: In this paper, a hybrid fuzzy back-propagation control scheme for a unified power quality conditioner is presented, where the reference voltages for the controllers are estimated using fuzzy logic controllers for the dc voltage regulator with a terminal voltage, and a dc voltage for the input control parameters.
TL;DR: In this article, a single-phase back-to-back converter-based dynamic voltage restorer (DVR) is implemented, which eliminates energy storage requirement, and the integration of series and shunt converter makes DVR capable of bidirectional flow of energy.
Abstract: Dynamic voltage restorer (DVR) is a custom power device used in electrical distribution system for power quality improvement. It ensures regulated voltage supply to the sensitive loads, even in case of voltage sag and swell disturbances in the distribution network. It is a series connected device and compensates voltage sag and swell by injecting a voltage with the help of a series transformer.
The injection of an appropriate voltage component in the event of a voltage disturbance requires a certain amount of real and reactive power. Conventionally, DVR consists of an energy storage device, which supplies the required power over the limited duration of the sags. Large magnitude and long duration of sags lead to heavy financial investment in energy storage unit. To overcome this limitation, a single-phase back-to-back converter-based DVR is implemented in this work, which eliminates energy storage requirement. The integration of series and shunt converter makes the DVR capable of bidirectional flow of energy. Therefore, the key advantage of this topology is its capability to compensate for long-term voltage sag and swell. Modelling of the DVR and its controller design is included in this paper. The effectiveness of control schemes, protection schemes and starting sequence of operation of DVR is verified through detailed simulation studies. A scaled down laboratory prototype of DVR is developed. The viability of these schemes is confirmed by the experimental results generated from the laboratory prototype. Various challenges faced during the prototype development and corresponding solutions are also discussed in this paper.
TL;DR: In this article, a bidirectional dc-dc converter-based dynamic voltage restorer (DVR) is proposed for compensation of severe voltage sag/swell problems in a medium voltage system.
Abstract: In this study, bidirectional dc–dc (BDC) converter-based dynamic voltage restorer (DVR) is proposed for compensation of severe voltage sag/swell problems in a medium voltage system. Among these problems, voltage swells provoke the voltage rise at dc-link capacitor of DVR. This undesirable situation may explode the dc-link capacitors and switches, and cause high-power losses. In DVR topologies, unidirectional dc–dc converter-based DVRs allow only monodirectional power energy transfer from battery to dc-link capacitor. To prevent voltage rise at dc-link capacitor under severe voltage swell conditions, bidirectional power flow must be achieved between dc-link capacitor and battery. The main contribution of this study is that BDC converter is first exploited in DVR to solve voltage rise problem at dc-link capacitor during voltage swell. Owing to this topology, power can flow both from battery to dc-link capacitor of multilevel inverter or vice versa. For this purpose, proportional-integrator (PI) controller-based algorithm is improved for BDC converter to compensate voltage sags/swells. This algorithm keeps the dc-link voltage constant during voltage sag/swell. The validity of proposed topology and control method is verified with PSCAD/EMDTC. The performance results demonstrate that BDC converter-based DVR achieves good performance to control dc-link voltage under voltage sag/swell situations.
01 Mar 2017
TL;DR: In this paper, a cost-effective control scheme for two-stage grid-connected PhotoVoltaic (PV) systems in Low Voltage Ride-Through (LVRT) operation is proposed.
Abstract: In this paper, a cost-effective control scheme for two-stage grid-connected PhotoVoltaic (PV) systems in Low Voltage Ride-Through (LVRT) operation is proposed. In the case of LVRT, the active power injection by PV panels should be limited to prevent from inverter over-current and also energy aggregation at the dc-link, which will challenge the dc-link capacitor lifetime if remains uncontrolled. At the same time, reactive currents should be injected upon any demand imposed by the system operators. In the proposed scheme, the two objectives can be feasibly achieved. The active power is regulated automatically through a proportional controller according to the voltage sag level and PV inherent characteristics (i.e., the voltage and power droop). Compared to prior-art LVRT schemes, the proposed method is cost-effective, as it is achieved by simply plugging the proportional controller into a maximum power point tracking controller without significant hardware or software modifications. In this way, the PV system will not operate at the maximum power point, whereas the inverter will not face any over-current challenge but can provide reactive power support in response to the grid voltage fault. Simulations have been performed on a 3-kW two-stage grid-connected single-phase PV system in the case of LVRT operation, where the results have verified the proposed control scheme in terms of fast dynamics and seamless operation mode transitions.
TL;DR: This paper focuses on the use of model predictive control (MPC) to control a DC/DC boost converter in order to regulate the PV power.