Showing papers on "Voltage sag published in 2018"

Data mining for classification of power quality problems using WEKA and the effect of attributes on classification accuracy

Abstract: There is growing interest in power quality issues due to wider developments in power delivery engineering In order to maintain good power quality, it is necessary to detect and monitor power quality problems The power quality monitoring requires storing large amount of data for analysis This rapid increase in the size of databases has demanded new technique such as data mining to assist in the analysis and understanding of the data This paper presents the classification of power quality problems such as voltage sag, swell, interruption and unbalance using data mining algorithms: J48, Random Tree and Random Forest decision trees These algorithms are implemented on two sets of voltage data using WEKA software The numeric attributes in first data set include 3-phase RMS voltages at the point of common coupling In second data set, three more numeric attributes such as minimum, maximum and average voltages, are added along with 3-phase RMS voltages The performance of the algorithms is evaluated in both the cases to determine the best classification algorithm, and the effect of addition of the three attributes in the second case is studied, which depicts the advantages in terms of classification accuracy and training time of the decision trees

Control Strategy for Distribution Generation Inverters to Maximize the Voltage Support in the Lowest Phase During Voltage Sags

Abstract: Voltage sags are considered one of the worst perturbations in power systems. Distributed generation power facilities are allowed to disconnect from the grid during grid faults whenever the voltage is below a certain threshold. During these severe contingencies, a cascade disconnection could start, yielding to a blackout. To minimize the risk of a power outage, inverter-based distributed-generation systems can help to support the grid by appropriately selecting the control objective. Which control strategy performs better when supporting the grid voltage is a complex decision that depends on many variables. This paper presents a control scheme that implements a smart and simple strategy to support the fault: the maximum voltage support for the lowest phase voltage. Therefore, the faulted phase that is more affected by the sag can be better supported since this phase voltage increases as much as possible, reducing the risk of undervoltage disconnection. The proposed controller has the following features: 1) maximizes the voltage in the lowest phase, 2) injects the maximum rated current of the inverter, and 3) balances the active and reactive power references to deal with resistive and inductive grids. The control proposal is validated by means of experimental results in a laboratory prototype.

A Fault-Tolerant Control Paradigm for Microgrid-Connected Wind Energy Systems

Abstract: Wind power is a promising alternative energy source; however, its integration to the microgrid is challenging and requires the consideration of voltage regulation, power quality, and voltage variations. This paper proposes a novel fault-tolerant control paradigm for a microgrid-connected doubly fed induction generator (DFIG)-based wind energy system to: 1) achieve ride through during any kind of voltage sag conditions including deep sags and 2) enable the strict satisfaction of recent grid code requirements. The proposed paradigm includes a novel integral terminal sliding mode controller (ITSMC) for the rotor- and grid-side converters along with a series grid-side converter (SGSC) to maintain the voltage levels across the stator windings at their prefault values. A fuzzy logic and a Posicast approach are also proposed to control the SGSC and further improve the performance of the wind energy system. The effectiveness of the proposed fault-tolerant configuration in riding through different types of grid faults is evaluated via detailed computer experiments. The merits of the proposed approach are further compared to those of the standard state of the art in voltage sag mitigation, namely, the shunt current injection approach and the dynamic voltage restorer. Results clearly show that the proposed control paradigm is able to protect the converters from damages and ensure continuous connection of the WT to the grid during faults, hence maintaining power quality.

A Grid-Interactive Permanent-Magnet Synchronous Motor-Driven Solar Water-Pumping System

Abstract: This paper deals with an effective power transfer scheme between the solar photovoltaic (PV) array and single-phase grid, feeding a field-oriented-controlled (FOC) permanent-magnet synchronous motor (PMSM) drive applied to a water-pumping system (WPS). Owing to the intermittency associated with solar (PV) system, the requirement of constant water supply is not possible with the standalone system. In order to mitigate this, a grid-intergraded WPS is proposed here. The grid integration enables the consumer an uninterrupted operation of water pump irrespective of solar insolation level. Moreover, the PV power can be fed to the utility grid when water pumping is not required. To make it possible, one voltage-source converter (VSC) and one voltage-source inverter connected to a common dc link are used for utility grid and PMSM control, respectively. The unit vector template theory is utilized to generate switching pulses for VSC to control the bidirectional power flow between the solar PV system and utility grid through the common dc link. A sensorless FOC is used to drive the PMSM coupled to the water pump. An intermediate stage boost converter is used for extracting optimum power from solar PV array under variable insolation. A perturb and observe algorithm is used for generating the duty ratio for the maximum power point (MPP) operation. The applicability of overall system constituting utility grid in conjugation with PV array fed PMSM-coupled water pump ensuring bidirectional power flow control with MPP tracking of PV array and abiding the utility grid, IEEE-519 standard for power factor, and total harmonic distortion is simulated in MATLAB/Simulink environment with SimPowerSystem toolbox and validated on a prototype developed in the laboratory. The system prototype is tested under variable solar insolation and grid abnormalities such as voltage sag and voltage swell.

A review on economics of power quality: Impact, assessment and mitigation

Abstract: The quality of electrical power supply directly influence the function and operation of the electrical devices feed by the electrical power system distribution network. Poor power quality(PQ) can cause peculiar operation of electrical devices which causes heavy economic loss to the customer and network operator. Poor PQ includes many phenomenon in which some are; voltage sag and interruptions, harmonics, surges, flickers, etc., and for each phenomenon the behaviour of electrical devices varies, which makes the quantification of losses due to poor PQ a complex subject. Among various PQ problems, voltage sag is more focussed by researchers from the mid of 90 s, because voltage sag directly affect the operation of electrical devices by causing interruptions (either small or large) in the process which further causes heavy economic losses. But the input (information) needed to quantify economic loss due to poor PQ varies from one method to other, and this makes a need to study the proposed methods and come to a meaningful conclusion. Quantification of cost of poor PQ (except voltage sag) is a research topic which has to be addressed to know the need of expenditure for smooth power supply. This research work includes some case studies to show the effect of PQ problems in various regions of the world. The paper includes a discussion on various indices and methodologies proposed by researchers in past to quantify PQ phenomenon, and some curves which shows the sensitivity of various equipments towards PQ problems. In this work one method is proposed for voltage sag cost calculation. At the end, proposed solutions of poor PQ problems and their implementation costs are also discussed and concluding remarks for the study is presented.

Voltage Sag Estimation in Sparsely Monitored Power Systems Based on Deep Learning and System Area Mapping

Abstract: This paper proposes a voltage sag estimation approach based on a deep convolutional neural network. The proposed approach estimates the sag magnitude at unmonitored buses regardless of the system operating conditions and fault location and characteristics. The concept of system area mapping is also introduced via the use of bus matrix, which maps different patches in input matrix to various areas in the power system network. In this way, relevant features are extracted at various local areas in the power system and used in the analysis for higher level feature extraction, before feeding into a fully-connected multiple layer neural network for sag classification. The approach has been tested on the IEEE 68-bus test network and it has been demonstrated that the various sag categories can be identified accurately regardless of the operating condition under which the sags occur.

A Two Degrees of Freedom Resonant Control Scheme for Voltage-Sag Compensation in Dynamic Voltage Restorers

Abstract: This paper presents a two degrees of freedom (2DOF) control scheme for voltage compensation in a dynamic voltage restorer (DVR). It commences with the model of the DVR power circuit, which is the starting point for the control design procedure. The control scheme is based on a 2DOF structure implemented in a stationary reference frame ( $\alpha \text{--}\beta$ ), with two nested controllers used to obtain a passband behavior of the closed-loop transfer function, and is capable of achieving both a balanced and an unbalanced voltage-sag compensation. The 2DOF control has certain advantages with regard to traditional control methods, such as the possibility of ensuring that all the poles of the closed-loop transfer function are chosen without the need for observers and reducing the number of variables to be measured. The use of the well-known double control-loop schemes that employ feedback current controllers to reduce the resonance of the plant is, therefore, unnecessary. A simple control methodology permits the dynamic behavior of the system to be controlled and completely defines the location of the poles. Furthermore, extensive simulations and experimental results obtained using a 5-kW DVR laboratory prototype show the good performance of the proposed control strategy.

A Comprehensive AC-Side Single-Line-to-Ground Fault Ride Through Strategy of an MMC-Based HVDC System

Abstract: When a single-line-to-ground (SLG) fault occurs on the ac side of the modular multilevel converter (MMC) in an high-voltage direct-current transmission (HVDC) system, it results in the ac-side voltage sag and leads to an instantaneous reduction of the MMC power capacity. Thus, it calls for the fault ride through (FRT) strategy to coordinate two MMC stations in the HVDC system to protect the MMCs against the submodule (SM) capacitor overvoltage in case of the SLG fault. In the meantime, the HVDC system is expected to track the prefault active power as much as possible during the FRT to secure the power system stability. In this paper, a comprehensive FRT strategy is proposed, which is free of interstation communication. The proposed FRT strategy presents fast dynamic response, and it can prevent effectively the MMC SM-capacitor overvoltage and HVDC transmission line overvoltage. Moreover, the second-order voltage and current fluctuations in the HVDC transmission line caused by the grid unbalance are inherently avoided. Validity of the proposed strategy and its superiority over existing methods are demonstrated by simulation of a 200-kV, 400-MW cable-based HVDC system.

A Transformer-Less Unified Power Quality Conditioner with Fast Dynamic Control

Abstract: A single-phase transformer-less unified power quality conditioner (TL-UPQC) is presented. Apart from having no isolation transformer, the proposed structure utilizes four switching devices only, forming two half-bridge voltage-source inverters—one connected in parallel with the load and another one connected in series with the ac mains. The two inverters share the same dc link. The parallel inverter, which is controlled by a hysteresis current controller, is used to shape the current drawn from the ac mains and regulate the dc-link voltage. The series inverter, which is controlled by a boundary controller with second-order switching surface, is used to regulate the steady-state load voltage and provide voltage sag/swell ride-through. A dc-link capacitor voltage balancing control that coordinates the operations of the hysteresis and boundary controllers is designed. Modeling, design, and analysis of the whole system will be given. A 1 kVA, 110 V, 60 Hz prototype has been built and evaluated on a setup with a nonlinear load. The steady-state and transient responses under a voltage sag will be given. Experimental results are favorably compared with the theoretical predictions and the performance of other UPQCs.

Energy Management Scheme for an EV Smart Charger V2G/G2V Application with an EV Power Allocation Technique and Voltage Regulation

Abstract: The increasing penetration of electric vehicles (EVs) in the distribution grid has established them as a prospective resource for ancillary services. These services require adequate control strategies for prompt and efficient operation. In this study, an energy management scheme (EMS) has been proposed to employ an off-board EV smart charger to support the grid during short-term variance of renewables and reactive load onset. The scheme operates by calculating power references for the charger instantaneously. The EMS incorporates a proportional power division methodology, proposed to allocate power references to the individual EVs connected to the charger DC-bus. This methodology considers the state-of-charge and battery sizes of the EVs, and it can aggregate energy from various types of EVs. The proposed scheme is compared with another power allocation method, and the entire EMS is tested under the scenarios of power mismatch and voltage sag/swell events. The results show that the proposed scheme achieves the goal of the aggregation of EVs at the charger level to support the grid. The EMS also fulfills the objectives of voltage regulation and four-quadrant operation of the smart charger.

Performance Evaluation of a MW-Class SMES-BES DVR System for Mitigation of Voltage Quality Disturbances

Abstract: Performance evaluations of a MW-class dynamic voltage restorer (DVR) system are presented for mitigation of voltage quality disturbances. A presag compensation strategy is introduced to lock the instantaneous magnitudes and phase angles of real-time line voltages, and thus to compensate the improper voltage components exactly after symmetrical or asymmetrical voltage disturbances. A 0.3-H/1.76-kA superconducting magnetic energy storage (SMES) magnet is used to cooperate with conventional battery energy storage (BES) device for developing a high-performance hybrid energy storage (HES) system. In the SMES-BES HES-based DVR system, the SMES can compensate the worst voltage sag for five cycles (1 MW, 100 ms, and absorb the highest voltage swell for six cycles (1 MW, 120 ms). The accessorial high-capacity BES device is subsequently discharged or charged for lasting long-time mitigation operations. Various simulation cases with regard to combined voltage sag, swell, and harmonic disturbances are carried out. The simulations and comparisons among the SMES-based, BES-based, and HES-based DVR schemes have demonstrated that the HES-based DVR scheme integrates the merits of fast response speed and high-power density from the SMES-based scheme, and the merits of low capital cost and high-energy density from the BES-based scheme.

A Novel Fourth-Order Generalized Integrator Based Control Scheme for Multifunctional SECS in the Distribution System

Abstract: This paper presents a novel fourth-order generalized integrator using a frequency locked loop (FOGI-FLL) based control algorithm for a single-stage three-phase grid-interfaced solar energy conversion system (SECS) with the distribution static compensation (DSTATCOM) capabilities. The proposed FOGI-FLL control algorithm suffices multifarious power quality objectives in the distribution network such as harmonics mitigation, reactive power compensation, load balancing, etc. The FOGI-FLL has good frequency tracking performance along with high dc offset rejection and high-order harmonic filtering capabilities. Simulated results demonstrate the satisfactory response of the system under load unbalancing, variable insolation, and system frequency variation. The effectiveness and advantages of the proposed algorithm are shown by comparing it with conventional algorithms. To validate the control algorithm, an experimental prototype is developed and test results depict the performance and behavior of the system under various conditions such as load unbalancing, variable insolation, photovoltaic (PV) to DSTATCOM mode, DSTATCOM to PV mode, and voltage sag and swell. The total harmonics distortions in grid currents and grid voltages are found well within limits according to IEEE-519 and −929 standards.

Photovoltaic-STATCOM with Low Voltage Ride through Strategy and Power Quality Enhancement in a Grid Integrated Wind-PV System

Abstract: The traditional configurations of power systems are changing due to the greater penetration of renewable energy sources (solar and wind), resulting in reliability issues. At present, the most severe power quality problems in distribution systems are current harmonics, reactive power demands, and the islanding of renewables caused by severe voltage variations (voltage sag and swell). Current harmonics and voltage sag strongly affect the performance of renewable-based power systems. Various conventional methods (passive filters, capacitor bank, and UPS) are not able to mitigate harmonics and voltage sag completely. Based on several studies, custom power devices can mitigate harmonics completely and slightly mitigate voltage sags with reactive power supplies. To ensure the generating units remain grid-connected during voltage sags and to improve system operation during abnormal conditions, efficient and reliable utilization of PV solar farm inverter as STATCOMs is needed. This paper elaborates the dynamic performance of a VSC-based PV-STATCOM for power quality enhancement in a grid integrated system and low voltage ride through (LVRT) capability. LVRT requirements suggest that the injection of real and reactive power supports grid voltage during abnormal grid conditions. The proposed strategy was demonstrated with MATLAB simulations.

Simultaneous optimisation of photovoltaic hosting capacity and energy loss of radial distribution networks with open unified power quality conditioner allocation

Abstract: This study presents a multi-objective planning approach to optimally place open unified power quality conditioner (UPQC-O) by simultaneously optimising the photovoltaic (PV) hosting capacity (PVHC) and energy loss of distribution networks. The modelling of UPQC-O consisting of a series and a shunt inverter is carried out so as to place in distribution networks. The Pareto-dominance-based approach is used to simultaneously optimise the objective functions to determine the optimal PV generation capacity in each bus and the locations of the inverters of UPQC-O. The limits on bus voltage magnitude, line current flow, maximum PV generation capacity in each bus, and the percentage of voltage sag mitigated load are considered to be the operational constraints in this planning problem. The solution strategy used is the multi-objective particle swarm optimisation. The approach provides the Pareto-approximation set consisting of a number of trade-off solutions in view of PVHC and energy loss. A utility can choose a solution for implementation depending on its desired PVHC and/or energy loss level. The results show that the PV deployment in distribution networks reduces the energy loss. However, the amount of energy loss reduction diminishes with higher and higher values of PV capacity integration.

Control of a Solar Photovoltaic Integrated Universal Active Power Filter Based on a Discrete Adaptive Filter

Abstract: In this work, a novel technique based on adaptive filtering is proposed for the control of a three-phase universal active power filter with a solar photovoltaic array integrated into its dc bus. Two adaptive filters along with a zero crossing detection technique are used to extract the magnitude of a fundamental active component of distorted load currents, which is then used in estimation of a reference signal for the shunt active filter. This technique enables extraction of an active component of all three phases with reduced mathematical computation. The series active filter control is based on synchronous reference frame theory and it regulates load voltage and maintains it in-phase with voltage at point of common coupling under conditions of voltage sag and swell. The performance of the system is evaluated on an experimental prototype in the laboratory under various dynamic conditions such as sag and swell in voltage at point of common coupling, load unbalancing, and change in solar irradiation intensity.

Quasi-Z-Source Indirect Matrix Converter Fed Induction Motor Drive for Flow Control of Dye in Paper Mill

Abstract: This paper describes a flow control of the dye in the paper mill with the quasi-Z-source indirect matrix converter (QZSIMC) fed induction motor drive. More than a decade the voltage-source inverter (VSI) and current-source inverter (CSI) have been used to control the speed of the induction motor, which in turns controls the flow of dye. Recently, the matrix converter (MC) has been an excellent competitor for the VSI or CSI for its compactness. The voltage transfer ratio of the VSI, CSI, and MC has been limited to 0.866. Thus, the efficiency of these converters is less. To improve the voltage transfer ratio the quasi-Z-source network (QZSN) is to be used between voltage source and indirect MC (IMC). The modification in the shoot-through duty ratio of the QZSN varies the voltage transfer ratio greater than 0.866. Different voltage transfer ratios are needed for different voltage sag conditions. For a variation of the duty ratio of the QZSN, the fuzzy logic controller has been presented. To control the IMC vector control with space vector modulation has been presented. This paper proposes the implementation of QZSIMC adjustable speed drive for the flow control of dye in paper mill during different voltage sag conditions. A 4-kW prototype has been built and the effectiveness of the proposed system is verified with simulation results and experimental setup. Simulation is done in MATLAB, Simulink platform. Experimental setup is done with the aid of a TMS320F2812 (Texas Instrument) processor. The experimental results validate the maintenance of the speed of an induction motor at the set condition, thus controlling the perfect flow of dye in paper manufacturing technology.

Dual-Buck AC–AC Converter With Inverting and Non-Inverting Operations

Abstract: In this paper, a novel buck–boost ac–ac converter is proposed. The basic switching unit of the proposed converter is a unidirectional buck circuit; therefore, it has no shoot-through worries. It can achieve safe commutation without using RC snubbers or soft commutation strategies. It can be implemented with power MOSFETs without their body diodes conducting and, for current freewheeling external diodes, can be used to minimize the reverse recovery issues and related loss. It has a bipolar voltage gain with both inverting and non-inverting operations. The non-inverting operation can be used to compensate voltage sag, and inverting operation can be used to compensate voltage swell. Therefore, the proposed converter as a dynamic voltage restorer is capable of compensating for both voltage sag and swell in a wide range. The detailed theoretical analysis followed by detailed experimental results of a 300-W prototype converter is provided.

Fuzzy Logic Based FOGI-FLL Algorithm for Optimal Operation of Single-Stage Three-Phase Grid Interfaced Multifunctional SECS

Abstract: This paper presents a fuzzy-logic-based fourth-order generalized integrator (FOGI) frequency locked loop (FLL) based control for optimal operation of solar energy conversion system (SECS) having distribution static compensator (DSTATCOM) capabilities along with supplying active power to the distribution network. The proposed SECS is multifunctional having capabilities of power factor correction, load balancing, and harmonics mitigation in a three-phase distribution system. The FOGI-FLL has higher order filtering capabilities compared to conventional algorithms. The frequency tracking capabilities of proposed control technique exhibit better performance as compared to a conventional algorithm. The comparative performance of harmonics filtering and frequency tracking capabilities is demonstrated between FOGI-FLL and various conventional algorithms. Simulation results demonstrate the behavior of the system at various conditions. To validate the proposed algorithm, a prototype is developed and test results demonstrate the reliable performance of the system at various conditions, such as load unbalancing, variable insolation, solar photovoltaic to DSTATCOM mode at abnormal grid conditions, such as distorted grid voltages, unbalanced grid voltages, voltage sag, and swell. The total harmonics distortions of grid voltages and currents are found well within limit of the IEEE 519 standard.

A Multifunctional Dynamic Voltage Restorer for Power Quality Improvement

Abstract: Power quality is a major concern in electrical power systems. The power quality disturbances such as sags, swells, harmonic distortion and other interruptions have an impact on the electrical devices and machines and in severe cases can cause serious damages. Therefore it is necessary to recognize and compensate all types of disturbances at an earliest time to ensure normal and efficient operation of the power system. To solve these problems, many types of power devices are used. At the present time, one of those devices, Dynamic Voltage Restorer (DVR) is the most efficient and effective device used in power distribution systems. In this paper, design and modeling of a new structure and a new control method of multifunctional DVRs for voltage quality correction are presented. The new control method was built in the stationary frame by combining Proportional Resonant controllers and Sequence-Decouple Resonant controllers. The performance of the device and this method under different conditions such as voltage swell, voltage sag due to symmetrical and unsymmetrical short circuit, starting of motors, and voltage distortion are described. Simulation result show the superior capability of the proposed DVR to improve power quality under different operating conditions and the effectiveness of the proposed method. The proposed new DVR controller is able to detect the voltage disturbances and control the converter to inject appropriate voltages independently for each phase and compensate to load voltage through three single-phase transformers.

Conceptual Design and Performance Evaluation of a 35-kV/500-A Flux-Coupling-Type SFCL for Protection of a DFIG-Based Wind Farm

Abstract: In this paper, a flux-coupling-type superconducting fault current limiter (SFCL) is suggested to protect a 15-MW class doubly fed induction generator (DFIG)-based wind farm. Detailed conceptual design and performance evaluation of the SFCL are conducted. From the technical requirements and operational parameters of the DFIG wind farm, a 35-kV/500-A flux-coupling-type SFCL is designed, taking into consideration: 1) the winding type, core selection, and inductance values of the coupling transformer (CT); and 2) the structural style, tape length, and quenching resistance of the superconducting coil (SC). By use of different simulation tools, the electrical and electromagnetic characteristics of the SFCL are evaluated. The results show that the maximum magnetic field of the CT is 2.4 T, and the ac loss of the SC is 0.51 W. Not only the electromagnetic properties and loss of the SFCL are acceptable, but also using the SFCL in the wind farm enables to suppress the fault current, compensate the voltage sag, and mitigate the wind power fluctuation. Thus, the robustness of the DFIG-based wind farm against the fault is enhanced, and the effectiveness of the proposed SFCL design is verified.