Showing papers on "Voltage sag published in 2011"
TL;DR: In this paper, a low-voltage ride-through technique of a doubly fed induction generator (DFIG) wind turbine system using a dynamic voltage restorer (DVR) was proposed.
Abstract: This paper proposes a low-voltage ride-through technique of a doubly fed induction generator (DFIG) wind turbine system using a dynamic voltage restorer (DVR). For effective control of the DVR, digital all-pass filters are used for extracting the positive-sequence component from the unbalanced grid voltage since they have the advantages of giving a desired phase shift and no magnitude reduction over conventional low- or high-pass filters. Using the positive-sequence component, the phase angles for the positive- and negative-sequence components of the grid voltage are derived. A control algorithm for the DVR that is dual voltage controllers only is implemented for the two sequence components in the dq synchronous reference frame. In order to achieve the power rating reduction of the DVR, the stator power reference for the DFIG is reduced during faults. In addition, a control scheme of pitch angle system is applied to stabilize the operation of the wind turbine system in the event of grid faults. PSCAD/EMTDC simulations show the effectiveness of the proposed technique and a feasibility of reducing the power rating of DVR for the fault ride-through capability of DFIG. The validity of the proposed control scheme for the DVR has also been verified by experimental results.
262 citations
TL;DR: In this paper, a new concept of optimal utilization of a unified power quality conditioner (UPQC) is introduced, where the series inverter of UPQC is controlled to perform simultaneous voltage sag/swell compensation and load reactive power sharing with the shunt inverter.
Abstract: This paper introduces a new concept of optimal utilization of a unified power quality conditioner (UPQC). The series inverter of UPQC is controlled to perform simultaneous 1) voltage sag/swell compensation and 2) load reactive power sharing with the shunt inverter. The active power control approach is used to compensate voltage sag/swell and is integrated with theory of power angle control (PAC) of UPQC to coordinate the load reactive power between the two inverters. Since the series inverter simultaneously delivers active and reactive powers, this concept is named as UPQC-S (S for complex power). A detailed mathematical analysis, to extend the PAC approach for UPQC-S, is presented in this paper. MATLAB/SIMULINK-based simulation results are discussed to support the developed concept. Finally, the proposed concept is validated with a digital signal processor-based experimental study.
222 citations
TL;DR: In this article, the impacts of various symmetrical and asymmetrical voltage sags on doubly fed induction generator (DFIG)-based wind turbines are investigated in MATLAB/Simulink to investigate the transient overshoots and ripples that appear in the rotor current and dc-link voltage.
Abstract: This paper presents a new analysis into the impacts of various symmetrical and asymmetrical voltage sags on doubly fed induction generator (DFIG)-based wind turbines. Fault ride-through requirements are usually defined by the grid codes at the point of common coupling (PCC) of wind farms to the power network. However, depending on the network characteristics and constraints, the voltage sag conditions experienced at the wind generator terminals can be significantly different from the conditions at the PCC. Therefore, it is very important to identify the voltage sags that can practically affect the operation of wind generators. Extensive simulation studies are carried out in MATLAB/Simulink to investigate the transient overshoots and ripples that appear in the rotor current and dc-link voltage when the DFIG is subjected to various types of (a)symmetrical faults. For the first time, the impacts of phase-angle jump and operational constraints of circuit breakers are examined. Furthermore, the influences of sag parameters including type, initial point-on-wave instant, depth, and impedance angle are investigated. Complementary theoretical analyses are also presented to support the validity of observations made in the simulation studies.
189 citations
TL;DR: In this article, the current reference calculation for the control of grid-connected voltage source converters meant to operate under voltage unbalanced sags produced by grid faults is analyzed and the theoretical results are confirmed using simulation tools and experimental tests.
Abstract: This paper analyzes the current reference calculation for the control of grid-connected voltage source converters meant to operate under voltage unbalanced sags produced by grid faults. The well-known reference calculation method that allows to control the active power ripple produced by the existence of negative-sequence components in the grid voltage is extensively analyzed. A type of voltage sag that produces unfeasible current reference values is identified and a possible workaround is proposed. Also, the need to compensate the power ripple produced by the filter inductance of the converter is demonstrated and an extension of the calculation method to compensate for this is introduced. The theoretical results are confirmed using simulation tools and experimental tests.
139 citations
TL;DR: In this article, a reference signal generation method for the unified power quality conditioner (UPQC) adopted to compensate current and voltage quality problems of sensitive loads is proposed, which consists of a shunt and series converter having a common dc link.
Abstract: This paper proposes a novel reference signal generation method for the unified power quality conditioner (UPQC) adopted to compensate current and voltage-quality problems of sensitive loads. The UPQC consists of a shunt and series converter having a common dc link. The shunt converter eliminates current harmonics originating from the nonlinear load side and the series converter mitigates voltage sag/swell originating from the supply side. The developed controllers for shunt and series converters are based on an enhanced phase-locked loop and nonlinear adaptive filter. The dc link control strategy is based on the fuzzy-logic controller. A fast sag/swell detection method is also presented. The efficacy of the proposed system is tested through simulation studies using the Power System Computer Aided Design/Electromagnetic Transients dc analysis program. The proposed UPQC achieves superior capability of mitigating the effects of voltage sag/swell and suppressing the load current harmonics under distorted supply conditions.
132 citations
TL;DR: In this article, a fault location method based on matching calculated voltage sag data and data gathered at some nodes in the network is proposed to reduce amount of transferred data, which can pinpoint fault location precisely.
Abstract: Fault location in distribution systems is an important function for outage management and service restoration directly impacting feeder reliability. In this paper, a fault location method based on matching calculated voltage sag data and data gathered at some nodes in the network is proposed. A method for characterization of voltage sags is utilized to reduce amount of transferred data. The proposed method can pinpoint fault location precisely, and is applicable to any complex distribution systems with load taps, laterals, and sub-laterals, single-phase loads, as well as networks with heterogeneous lines. The performance of the proposed method is demonstrated on the IEEE 123-node distribution test system via computer simulations in Alternate Transients Program software.
121 citations
TL;DR: In this paper, a novel control scheme for the dynamic voltage restorer (DVR) is proposed to achieve fast response and effective sag compensation capabilities, where fast least error squares estimated filters considerably reduce the effects of noise, harmonics, and disturbances on the estimated phasor parameters.
Abstract: A novel control scheme for the dynamic voltage restorer (DVR) is proposed to achieve fast response and effective sag compensation capabilities. The proposed method controls the magnitude and phase angle of the injected voltage for each phase separately. Fast least error squares digital filters are used to estimate the magnitude and phase of the measured voltages. The utilized least error squares estimated filters considerably reduce the effects of noise, harmonics, and disturbances on the estimated phasor parameters. This enables the DVR to detect and compensate voltage sags accurately, under linear and nonlinear load conditions. The proposed control system does not need any phase-locked loops. It also effectively limits the magnitudes of the modulating signals to prevent overmodulation. Besides, separately controlling the injected voltage in each phase enables the DVR to regulate the negative- and zero-sequence components of the load voltage as well as the positive-sequence component. Results of the simulation studies in the PSCAD/EMTDC software environment indicate that the proposed control scheme 1) compensates balanced and unbalanced voltage sags in a very short time period, without phase jump and 2) performs satisfactorily under linear and nonlinear load conditions.
114 citations
TL;DR: In this article, a novel topology for symmetrical cascade multilevel converter is presented, which consists of series connected sub-multilevel converters units and it can generate DC voltage levels similar to other topologies.
95 citations
TL;DR: In this article, a single-phase unified power quality conditioner (UPQC) is proposed to enhance power quality problem in single phase systems using a simple control approach and validated through simulation as well as experimental studies.
Abstract: This study is based on a single-phase unified power quality conditioner (UPQC) to enhance power quality problem in single-phase systems. A simple control approach is implemented and validated through simulation as well as experimental studies. A laboratory prototype of UPQC is designed and developed using a digital signal processor. The performance of UPQC is validated experimentally under several operating conditions. It is found that the UPQC in single-phase system effectively compensates the important power quality issues, such as the load reactive power, load current harmonics, voltage harmonics, voltage sag, voltage swell and voltage flicker. Under distorted source voltage having total harmonics distortion (THD) of 14.1% with a non-linear load producing a distorted current (THD of 30.98%), the UPQC simultaneously compensates these harmonics resulting sinusoidal source current (THD of 3.77%) and load voltage (THD of 2.54%).
95 citations
TL;DR: The proposed method for automatic detection and classification of voltage disturbances for problems related to power quality using signal processing techniques and intelligent systems is efficient, robust and has high computing performance (low processing time), which allows, a priori, its application in real time.
93 citations
TL;DR: In this article, a new structure of fault current limiter (FCL) is proposed to prevent voltage sag and phase-angle jump of the substation PCC after fault occurrence.
Abstract: In this paper, voltage sag compensation of point of common coupling (PCC) using a new structure of fault current limiter (FCL) is proposed. The proposed structure prevents voltage sag and phase-angle jump of the substation PCC after fault occurrence. This structure has a simple control method. Using the semiconductor switch (insulated-gate bipolar transistor or gate turnoff thyristor at dc current rout leads to fast operation of the proposed FCL and, consequently, dc reactor value is reduced. On the other hand, the proposed structure reduces the total harmonic distortion on load voltage and it has low ac losses in normal operation. As a result, other feeders, which are connected to the substation PCC, will have good power quality. Analytical analysis and simulation results using PSCAD/EMTDC software and experimental results are presented to validate the effectiveness of this structure.
TL;DR: In this article, a dynamic voltage restorer (DVR) is proposed to protect the point of common coupling (PCC) voltage and protect the DVR itself during a three-phase short circuit fault.
Abstract: The dynamic voltage restorer (DVR) is one of the modern devices used in distribution systems to protect consumers against sudden changes in voltage amplitude. In this paper, emergency control in distribution systems is discussed by using the proposed multifunctional DVR control strategy. Also, the multiloop controller using the Posicast and P+Resonant controllers is proposed in order to improve the transient response and eliminate the steady-state error in DVR response, respectively. The proposed algorithm is applied to some disturbances in load voltage caused by induction motors starting, and a three-phase short circuit fault. Also, the capability of the proposed DVR has been tested to limit the downstream fault current. The current limitation will restore the point of common coupling (PCC) (the bus to which all feeders under study are connected) voltage and protect the DVR itself. The innovation here is that the DVR acts as a virtual impedance with the main aim of protecting the PCC voltage during downstream fault without any problem in real power injection into the DVR. Simulation results show the capability of the DVR to control the emergency conditions of the distribution systems.
24 Jul 2011
TL;DR: In this article, a fault location method based on matching calculated voltage sag data and data gathered at some nodes in the network is proposed to reduce amount of transferred data, which can pinpoint fault location precisely.
Abstract: Fault location in distribution systems is an important function for outage management and service restoration directly impacting feeder reliability. In this paper, a fault location method based on matching calculated voltage sag data and data gathered at some nodes in the network is proposed. A method for characterization of voltage sags is utilized to reduce amount of transferred data. The proposed method can pinpoint fault location precisely, and is applicable to any complex distribution systems with load taps, laterals, and sub-laterals, single-phase loads, as well as networks with heterogeneous lines. The performance of the proposed method is demonstrated on the IEEE 123-node distribution test system via computer simulations in ATP software.
TL;DR: This paper assesses and analyses the effects of superconducting fault current limiter installed in power distribution system on voltage sags and modeled resistor-type SFCL using PSCAD/EMTDC to represent the quench and recovery characteristics based on the experimental results.
Abstract: This paper assesses and analyses the effects of superconducting fault current limiter (SFCL) installed in power distribution system on voltage sags. First of all, resistor-type SFCL is modeled using PSCAD/EMTDC to represent the quench and recovery characteristics based on the experimental results. Next, typical power distribution system of Korea is modeled. When the SFCL is installed in various locations from the starting point to end point of feeders, improvement of voltage sag is evaluated using the Information of Technology Industry Council (ITIC) curve of customer's loads when a fault occur. Finally, future studies needing to apply SFCL to power distribution system are presented.
TL;DR: In this paper, the authors present the application of calculated non-linear voltage sag profiles and voltage sag measurement at primary substation to locate a fault in distribution networks, and the proposed method has been tested under different fault scenarios that include various fault resistance, loading variation and data measurement errors.
TL;DR: In this article, a hybrid current control scheme is proposed to enhance low and high voltage ride-through capacities of DIF-based wind turbines, which is composed of two switching strategies integrated with a supervisory control unit: standard PI current controllers and vector-based hysteresis current controllers.
TL;DR: The Dynamic Voltage Restorer (DVR) as mentioned in this paper is a power electronic based device that provides three-phase controllable voltage source, whose voltage vector (magnitude and angle) adds to the source voltage during sag event, to restore the load voltage to pre-sag conditions.
Abstract: The Dynamic Voltage Restorer (DVR) is fast, flexible and efficient solution to voltage sag problem. The DVR is a power electronic based device that provides three-phase controllable voltage source, whose voltage vector (magnitude and angle) adds to the source voltage during sag event, to restore the load voltage to pre-sag conditions. The DVR is designed for protecting the whole plant with loads in the range of some MVA. The DVR can restore the load voltage within few milliseconds. Several configurations and control methods are proposed for the DVR. In this paper, an overview of the DVR, its functions, configurations, components, compensating strategies and control methods are reviewed along with the device capabilities and limitations.
TL;DR: In this paper, the authors presented the modeling of Flexible AC Transmission System (FACTS) devices to minimize the voltage sag induced financial losses in a real Indian distribution system.
TL;DR: In this paper, the authors investigated the effects of voltage sag profile estimation, plant load profile modelling, and process cycle modelling on the financial risk associated with process failure, and introduced the stochastic net present value method as a financial analysis tool.
Abstract: This paper investigates the factors that influence the outcome of financial-loss analysis in voltage sag studies. Focusing on industrial processes, this paper considers the effects of voltage sag profile estimation, plant-load profile modelling, and process cycle modelling on the financial risk associated with process failure. Based on voltage sag monitoring records, sag profile is probabilistically modeled for the estimation of future sag characteristic. Variations in financial risk due to varying process activities in different stages of a process (process cycle) and load profile are also investigated. The effects of the individual factors are analyzed through Monte Carlo simulation. The stochastic net present value method is introduced as a financial analysis tool.
TL;DR: In this article, a new methodology is proposed to mitigate the unbalanced voltage sag with phase jumps by UPQC with minimum real power injection, where an objective function is derived along with practical constraints, such as the injected voltage limit on the series active filter, phase jump mitigation, and angle of voltage injection.
Abstract: The unified power-quality conditioner (UPQC) is used to mitigate the current and voltage-related power-quality (PQ) problems simultaneously in power distribution systems. Among all of the PQ problems, voltage sag is a crucial problem in distribution systems. In this paper, a new methodology is proposed to mitigate the unbalanced voltage sag with phase jumps by UPQC with minimum real power injection. To obtain the minimum real power injection by UPQC, an objective function is derived along with practical constraints, such as the injected voltage limit on the series active filter, phase jump mitigation, and angle of voltage injection. Particle swarm optimization (PSO) has been used to find the solution of the objective function derived for minimizing real power injection of UPQC along with the constraints. Adaptive neuro-fuzzy inference systems have been used to make the proposed methodology online for minimum real power injection with UPQC by using the PSO-based data for different voltage sag conditions. The proposed method has been validated through detailed simulation and experimental studies.
TL;DR: In this article, the authors proposed a hybrid current controller to enhance the fault ride-through capability of doubly-fed induction generators (DFIGs) through keeping the rotor current below the safety limits.
Abstract: Recent fault ride-through (FRT) requirements have proven problematic for variable-speed wind generation systems. A particular problem regarding to doubly-fed induction generators (DFIGs) is that standard proportional integral (PI) current controllers, designed with very limited control bandwidth, cannot eliminate rotor current oscillations that occur during a grid fault. As a consequence, the current in the rotor-side converter can exceed the safety limits of semiconductor switches, which potentially leads to converter failure. This study introduces a hybrid current controller to enhance the FRT capability of DFIGs through keeping the rotor current below the safety limits. The proposed current controller includes two switching strategies: the standard PI current controller for normal operating conditions and a vector-based hysteresis current controller (with very fast transient response) for overcurrent protection during grid faults. Simulation studies are carried out to demonstrate the effectiveness of the proposed hybrid current controller under various symmetrical and asymmetrical voltage sag conditions.
TL;DR: In this paper, a passive resistive network consisting of shunt and series elements that are applied at the stator side of a doubly fed induction generation wind turbine is presented, which is inactive during steady-state operation and enabled for short intervals of time during the initiation of voltage sag and recovery events.
Abstract: With the increasing penetration of wind turbines in the utility grid, new regulation codes have been issued that require them to have low-voltage ride-through capability. In this paper, a passive resistive network consisting of shunt and series elements that are applied at the stator side of a doubly fed induction generation wind turbine is presented. The network is inactive during steady-state operation and enabled for short intervals of time during the initiation of voltage sag and recovery events. Computer simulation and experimental results confirming the validity of this operation during balanced and unbalanced voltage sags are shown in this paper.
06 Jun 2011
TL;DR: In this article, a DVR with pulse width modulation (PWM) based controller using Matlab/Simulink is presented and the performance of the DVR depends on the efficiency of the control technique involved in switching the inverter.
Abstract: Voltage sag is literally one of power quality problem and it become severe to industrial customers. Voltage sag can cause miss operation to several sensitive electronic equipments. That problem can be mitigating with voltage injection method using custom power device, Dynamic Voltage Restorer (DVR). This paper presents modeling and analysis of a DVR with pulse width modulation (PWM) based controller using Matlab/Simulink. The performance of the DVR depends on the efficiency of the control technique involved in switching the inverter. This paper proposed two control techniques which is PI Controller (PI) and Fuzzy Logic Controller (FL). Comprehensive results are presented to assess the performance of each controller as the best power quality solution. Other factors that also can affect the performance and capability of DVR are presented as well.
TL;DR: In this article, the authors proposed a new current mode controller to overcome the problem of single-phase disturbances in electrical networks that cannot be avoided by the conventional voltage mode controllers, which are also not capable of responding fast enough to the changes expected of a network system.
24 Jul 2011
TL;DR: In this paper, different operation modes of multiterminal HVDC-VSC systems for large offshore wind farms are analyzed and different control schemes for each power converter are proposed.
Abstract: The different operation modes of multiterminal HVDC-VSC systems for large offshore wind farms are analyzed. Control schemes for each power converter are proposed. The wind farm VSCs inject the power to the HVDC grid and are controlled as ideal voltage sources that absorb all the incoming power in normal operation, and reduce the injected power whenever a fault occurs and the DC voltage rises. The grid-side VSC inject the power to the main grid and control the DC voltage using a droop control scheme. The proposed controllers are tested in a case study by means of dynamic simulations with a four terminal system. The results show good performance for changing wind speeds, a voltage sag and a loss of a converter.
TL;DR: In this paper, the authors analyzed unsymmetrical voltage sag effects on the torque and speed deviation in induction motor (IM) adjustable speed drives and derived analytical expressions for dc-link voltage variations incorporated into the corresponding drive models as well as formulas for assessment of current/torque deviation.
Abstract: This study analyses unsymmetrical voltage sag effects on the torque and speed deviation in induction motor (IM) adjustable speed drives. The following three general types of IM drives control are analysed: scalar controlled (V/Hz), rotor-field oriented and direct-torque controlled. The analytical expressions for dc-link voltage variations incorporated into the corresponding drive models as well as formulas for assessment of current/torque deviation are derived depending on the applied control algorithm. The analytically predicted theoretical results for the IM drive performance deterioration as a result of voltage sags have been validated experimentally. Measurements of sag-caused current/torque ripple and mechanical vibrations have been used for additional verification of the obtained results.
TL;DR: In this article, an improved sinusoidal pulse width modulation (PWM) voltage controller for the series compensator is proposed which adjusts continuously the amplitude modulation ratio in response to the dc link voltage deviations.
TL;DR: In this paper, a new topology based on a direct ac/ac converter is proposed for a single-phase dynamic voltage restorer (DVR) which uses the minimum switches and does not require dc-link energy storage elements.
TL;DR: A novel dual-connection of fault current limiters for use when connecting new distributed generation plants to the electric grid limits fault currents sufficiently to avoid disturbing the original protection relay schemes of the utilities, and also improves synchronism between the new generator and the grid.
Abstract: A novel dual-connection of fault current limiters is described for use when connecting new distributed generation plants to the electric grid. The operation and control scheme of this connection are described and analysed. The proximate arrangement of the two current limiters has the advantage that they can share one cryogenic system. The dual connection limits fault currents sufficiently to avoid disturbing the original protection relay schemes of the utilities, and also improves synchronism between the new generator and the grid. These benefits are proven by simulations of a 36 MW, 4.16 kV gas turbine generator connected to an infinite grid. This dual-FCL connection reduces fault current contributions of the DG by 97% (from 41 to 1 kA), and maintains the circuit breakers within their duty limits when a three-phase fault occurs at a bus connected to the DG. Otherwise, when a three-phase fault occurs in the infinite system, this connection limits the fault current contribution of the DG from 4.8 to 0.4 kA, and frequency oscillations of the DG from 0.14 to 0.01 Hz. The power continuity in the local network is improved, as the voltage sag at the bus connected to the DG is reduced by 96% (from 851 to 32 V) during and after serious short-circuit faults.
TL;DR: In this article, the electric power system analysis and design of an expanding steel cogeneration plant is presented, where the site and capacity of shunt capacitor banks as well as the tap position of transformers are determined according to the power flow analysis.
Abstract: This paper presents the electric power system analysis and design of an expanding steel cogeneration plant. The site and capacity of shunt capacitor banks as well as the tap position of transformers are determined according to the power flow analysis. Also, to comply with the restriction of circuit breaker capacity, the high-impedance transformers are designed. In addition, the voltage fluctuation resulted from the dramatic reactive power variation of hot strip rolling mill can be greatly reduced if proper static var compensator is installed. The significant voltage sag due to the starting of induction motor can be effectively improved by applying wye-delta transformer starter. Furthermore, the total voltage harmonic distortion and the total current demand distortion are both acceptable if the proper filters are installed. It is also found that the cogeneration system can keep stable operation in autonomous mode by applying the governor control action and the load-shedding scheme after tie line tripping. It is concluded that the power system analyses are important for the steel plant with cogeneration unit to identify hidden problems and remedy strategy to ensure the system power quality and operation performance.