The booming electronics itself carries an impact on power quality. Superconducting Magnetic Energy Storage (SMES) is proposed to enhance power quality in three-phase systems under various loads. This paper aimed to co...The booming electronics itself carries an impact on power quality. Superconducting Magnetic Energy Storage (SMES) is proposed to enhance power quality in three-phase systems under various loads. This paper aimed to compensate the voltage sags under various faults in the grid systems. The SMES is selected as an energy storage unit to improve the capability of voltage sag compensation. Optimized Dual Fuzzy Flow (ODFF) logic controller is designed to prevent the voltage sag time during excessive phase voltage variation. Hence the proposed controller strategy reduces the total harmonic distortion during various fault conditions. To regulate the contribution of active power, the least possible value is improved using ODFF. The depth of voltage sags compensation is achieved by the over modulation and an iterative loop is designed in the control block. While protecting sensitive loads from voltage disturbances, and sags initiated by the power system, the proposed configuration is advantageous for an industrial implementation. It is found that the proposed method can result in more than 50% additional sag support time when compared with the previous methods such as PI and PSO. Utilizing MATLAB Simulink, compensation of sag and minimization of THD is established, and the simulation tests are performed to evaluate the performance of the proposed control method.展开更多
Voltage sag is one of the most common power quality disturbances in industry,which causes huge inrush currents in stator windings of induction motors,and adversely impacts the motor secure operation.This paper firstly...Voltage sag is one of the most common power quality disturbances in industry,which causes huge inrush currents in stator windings of induction motors,and adversely impacts the motor secure operation.This paper firstly introduces a 2D Time-Stepping multi-slice finite element method(2D T-S multi-slice FEM)which is used for calculating the magnetic field distribution in induction motors under different sag events.Then the paper deduces the transient analytical expression of stator inrush current based on the classical theory of AC motors and presents a separation method for the positive,negative and zero sequence values based on instantaneous currents.With this method,the paper studies the influences of voltage sag amplitude,phase-angle jump and initial phase angle on the stator positive-and negative-sequence peak currents of 5.5 kW and 55 kW induction motors.This paper further proposes a motor protection method under voltage sag condition with the stator negative-sequence peak currents as the protection threshold,so that the protection false trip can be avoided effectively.Finally,the calculation and analysis results are validated by the comparison of calculated and measured stator peak value of the 5.5 kW induction motor.展开更多
An alternative method was introduced for voltage sag source location based on S and TT transformed disturbance powers. It is done to avoid the wrong and inconclusive detection of conventional disturbance power method ...An alternative method was introduced for voltage sag source location based on S and TT transformed disturbance powers. It is done to avoid the wrong and inconclusive detection of conventional disturbance power method proposed in the literature. Unlike in the case of the traditional method, the proposed method first transforms the recorded voltage and current during the sag event to some special features before calculating the new version of disturbance powers. The effectiveness of the proposed method has been verified through simulation and actual data from an industrial power system. The results show that the presented method can correctly detect the location of voltage sag source.展开更多
A method for improving the level of reliability of distribution systems is presented by employing an integrated voltage sag mitigation method that comprises a two-staged strategy,namely,distribution network reconfigur...A method for improving the level of reliability of distribution systems is presented by employing an integrated voltage sag mitigation method that comprises a two-staged strategy,namely,distribution network reconfiguration(DNR)followed by DSTATCOM placement.Initially,an optimal DNR is applied to reduce the propagated voltage sags during the test period.The second stage involves optimal placement of the DSTATCOM to assist the already reconfigured network.The gravitational search algorithm is used in the process of optimal DNR and in placing DSTATCOM.Reliability assessment is performed using the well-known indices.The simulation results show that the proposed method is efficient and feasible for improving the level of system reliability.展开更多
Unified power quality conditioner(UPQC)holds the capability of solving power quality problems,especially shows good performance in the voltage sag compensation. In this paper, a compensation strategy based on simultan...Unified power quality conditioner(UPQC)holds the capability of solving power quality problems,especially shows good performance in the voltage sag compensation. In this paper, a compensation strategy based on simultaneous reactive power injection for UPQC(namely UPQC-SRI) is proposed to address the issue of voltage sag. The proposed UPQC-SRI determines the injection angle of compensation voltage with consideration of optimal configuration of UPQC current-carrying.Moreover, the compensation strategy also considers the current-carrying limit of UPQC, and then the zero active power injection region of UPQC-SRI(also called UPQCSRI region) is obtained. Under the conditions which exceed the UPQC-SRI region, the limit value of shunt current is determined by this proposed strategy. Finally, the proposed strategy and the corresponding algorithm are verified under the PSCAD/EMTDC platform. The result indicates the proposed UPQC-SRI strategy in this paper can provide more persistent voltage sag compensation than the previous strategies for the sensitive load.展开更多
Introduction:This paper uses a dynamic voltage restorer(DVR)to improve the voltage quality from voltage sags.It is difficult to satisfy various of compensation quality and time of the voltage sag by using single compe...Introduction:This paper uses a dynamic voltage restorer(DVR)to improve the voltage quality from voltage sags.It is difficult to satisfy various of compensation quality and time of the voltage sag by using single compensation method.Furthermore,high-power consumption of the phase jump compensation increases the size and cost of a dynamic voltage restorer(DVR).Methods&Results:In order to improve the compensating efficiency of DVR,an optimized compensation strategy is proposed for voltage sag of micro-grid caused by interconnection and sensitive loads.The proposed compensation strategy increases the supporting time for long voltage sags.Discussion:Firstly,the power flow and the maximum compensation time of DVR are analyzed using three basic compensation strategies.Then,the phase jump is corrected by pre-sag compensation.And a quadratic transition curve,which involves the injected voltage phases of pre-sag strategy and minimum energy strategy,is used to transform pre-sag compensation to minimum energy compensation of DVR.Conclusions:The transition utilizes the storage system to reduce the rate of discharge.As a result,the proposed strategy increases the supporting time for long voltage sags.The analytical study shows that the presented method significantly increases compensation time of DVR.The simulation results performed by MATLAB/SIMULINK also confirm the effectiveness of the proposed method.展开更多
The impact of voltage sag on sensitive devices is related to the time when the sag occurs.However,the point-on-wave of a sag is uncertain.Therefore,this paper presents a nov-el approach to evaluate the voltage sag sev...The impact of voltage sag on sensitive devices is related to the time when the sag occurs.However,the point-on-wave of a sag is uncertain.Therefore,this paper presents a nov-el approach to evaluate the voltage sag severity considering a random point-on-wave.First,the uncertainty of equipment malfunction is revealed.Second,under a given residual voltage,the relationship between the point-on-wave and the duration that the device can withstand is described with a fitting curve.Third,a voltage sag probabilistic index is proposed to describe the severity.The evaluation procedure is also presented.Finally,three types of releasers are tested and analyzed to determine the effectiveness of the proposed method.The evaluation method can help instruct electrical engineers establish more well-grounded sag mitigation proposals.展开更多
Control strategy affects directly the working performances of dynamic voltage regulator (DVR). One-cycle control is an effective nonlinear signal modulation control method. In this paper, a new one-cycle control sch...Control strategy affects directly the working performances of dynamic voltage regulator (DVR). One-cycle control is an effective nonlinear signal modulation control method. In this paper, a new one-cycle control scheme for DVR was proposed in single phase supply system. On the basis of principle analysis, the corresponding one-cycle control model for DVR was built up, which is characterized by simple control circuits, good control performance, and high control precision. As an example, a control model for single-phase DVR was simulated by using Matlab/Simulink and SimPowerSystem. The results show that the load voltage could be compensated quickly at the points of supply voltage stepping down and up, and the relative error was less than 4% in the whole voltage sag process. Both theory analysis and simulation results show that the new one-cycle control scheme for DVR is effective.展开更多
The modular multilevel converter (MMC) is a highly modular, easy to expand; the output voltage waveform is good, especially suitable for application in high voltage power system. This article first introduces the ci...The modular multilevel converter (MMC) is a highly modular, easy to expand; the output voltage waveform is good, especially suitable for application in high voltage power system. This article first introduces the circuit topology and principle of MMC, and the main technical characteristics of MMC. And according to the relationship between the drop power voltage and the load power factor, proposed three working modes of the minimum energy compensation strategy. It is shown that MMC has good application prospect in future medium or high- voltage high power applications, especially be one of candidates for HVDC system application.展开更多
Power quality is one of the major concerns among consumers and electric utility companies. CUPS (custom power systems) devices are used to improve the quality of power and enhance the reliability of the power supply...Power quality is one of the major concerns among consumers and electric utility companies. CUPS (custom power systems) devices are used to improve the quality of power and enhance the reliability of the power supply in the distribution networks. The DVR (dynamic voltage restorer) is an important CUPS device used to mitigate voltage sag/swell and imbalances. Various control techniques have been implemented to control the DVR, among which the PID (proportional-integral-derivative) controller is dominant because of its model independent property and its error driven technique. In this paper, a new controller based on the ADRC (active disturbance rejection control) concept is developed, and its performance is compared to that of the PID controller. The model of the DVR and its ADRC and PID controllers were developed under the MATLAB (matrix laboratory)/Simulink environment. The simulation results demonstrated the effectiveness of the ADRC over the PID controller.展开更多
The inter-line dynamic voltage restorer (IDVR) consists of several voltage source inverters connected to different independent distribution feeders with common dc bus. When one of the inverters compensates for volta...The inter-line dynamic voltage restorer (IDVR) consists of several voltage source inverters connected to different independent distribution feeders with common dc bus. When one of the inverters compensates for voltage sag that appears in its feeder (voltage control mode), the other inverters pump the required power into the dc bus (power control mode). Each inverter will have both voltage and power controllers; only one controller is in use during the abnormal conditions according to its feeder state. The voltage controller uses one of the dynamic voltage restoration techniques. In this paper, the in-phase technique is applied and two types of loads are considered (constant impedance and three phase induction motor). Since the voltage restoration process may need real power injection into the distribution system, the power controller injects this power via voltage injection. This voltage injection is simulated by voltage drop across series virtual impedance. A new scheme is proposed to select the impedance value. The impedance value is selected such that the power consumed by this impedance represents the required power to be transferred without perturbing the load voltage. The performance of this system is also studied during voltage swell. A scheme for operation of multi-feeder IDVR system is proposed in this paper. Simulation results substantiate the proposed concept.展开更多
This paper proposes about a powerful control mechanism of UPQC (Unified Power Quality Conditioner) work on voltage source inverter which can effectively compensate source current harmonics and also mitigate all voltag...This paper proposes about a powerful control mechanism of UPQC (Unified Power Quality Conditioner) work on voltage source inverter which can effectively compensate source current harmonics and also mitigate all voltage collapse such as dip, swell, voltage unbalances and harmonics. The consolidation of series and parallel active power filters sharing mutual DC bus capacitor forms UPQC. PI (Proportional Integral) controller is mainly used in order to maintain continual DC voltage along with the hysteresis current controller. The parallel and series power filters were designed using 3-phase voltage source inverter. The reference signals for shunt and series active power filters were obtained by Synchronous Reference Frame (SRF) theory and Power Reactive (PQ) theory respectively. By using these theories, reference signals were obtained which was fed to the controllers for generating switching pulses for parallel and series active filters. The UPQC dynamic performance is obtained through testing terms like the compensation of voltage, current harmonics and all voltage distortion associated with 3-phase 3-wire power system which is simulated using MATLAB-Simulink software.展开更多
With the implementation of electric energy alternatives,the large-scale application of electric energy substitution represented by air-source heat pumps has replaced traditional coal-fired heating,which is beneficial ...With the implementation of electric energy alternatives,the large-scale application of electric energy substitution represented by air-source heat pumps has replaced traditional coal-fired heating,which is beneficial for the environment and alleviates air pollution.However,the large-scale application of airsource heat pumps has brought power quality problems such as voltage sags,harmonic pollution,and three-phase imbalance to the distribution network.This paper studies the fixed-frequency and variablefrequency air-source heat pump,introduces its working principle,analyzes the mechanism of its power quality problem.Moreover,the paper establishes a simulation model for the fixed-frequency heat pump and variable-frequency heat pump to connect to the distribution network.This research mainly studies the impact of large-scale fixed-frequency heat pumps on the depth of voltage sags in the distribution network and the impact of large-scale variable-frequency heat pumps on the harmonic content of the distribution network under different penetration rates and uses measured data to verify the reliability of the simulation results.This paper uses experimental data for the first time to verify the real power quality problems of large-scale heat pumps,which can provide a reference for determining the power quality standards for heat pumps connected to the power grid.At the same time,it can also provide a reference for the power quality management of the distribution network that is actually connected to electric heating.展开更多
This paper presents an analysis of the electric power flows in a hot rolling mill plant using a power quality analyzer and developing simulation models with Matlab-Simulink. The model inputs have been taken from proce...This paper presents an analysis of the electric power flows in a hot rolling mill plant using a power quality analyzer and developing simulation models with Matlab-Simulink. The model inputs have been taken from process data by the process computer of the plant. Data from different rolling campaigns have been analysed. A STATCOM (static synchronous compensator) with a control strategy based on voltage oriented control with d-q coordinates is used as solution to improve the reactive compensation as well as to minimize the voltage fluctuations and sags effect. The overall electric model has been simulated with the STATCOM to check the improvement in the voltage stability and the consumption.展开更多
The experimental results by the simulated PV (photovoltaic) system for understanding the cause of disconnection when instantaneous voltage sag occurs are reported in this study. Moreover, it is understood that the P...The experimental results by the simulated PV (photovoltaic) system for understanding the cause of disconnection when instantaneous voltage sag occurs are reported in this study. Moreover, it is understood that the PCS with the voltage phase jump detection method which is one of the main causes of the disconnection. We modeled it in the simulation. When fault occurs, even though the residual voltage is more than 20% and the voltage sag time is within 1.0 s, the PCS disconnected by the voltage phase jump detection was confirmed in the simulation results. Ifa large number of PV systems are interconnected in the power system, this study is verified through the simulation that the interaction caused by the disconnection which generated by the voltage phase jump detection. This study is proposed threshold limit value of islanding detection. The validity of proposed method was verified through the simulation in this study.展开更多
In recent years, a rapid decrease in the cost of various energy storage technologies and their integration into grid becomes a reality with the advent of smart grid. The Dynamic Voltage Restorer (DVR) is a custom powe...In recent years, a rapid decrease in the cost of various energy storage technologies and their integration into grid becomes a reality with the advent of smart grid. The Dynamic Voltage Restorer (DVR) is a custom power device that has an excellent dynamic capability used to provide voltage sag, swell compensation in distribution systems. Among the energy storage devices, Ultra-Capacitors (UCAP) have ideal characteristics such as high power and low energy density essential for the compensation of voltage sag and swell, which require high power for short interval of time. This paper presents an integration of rechargeable UCAP with DVR. This UCAP-DVR presents a modular, flexible system configuration that will have an active power capability and also provide deep, extended mitigation for power quality problems. The DVR is integrated into UCAP via bidirectional DC-DC converter which supports a rigid dc-link voltage for DVR and also helps in compensating temporary voltage sag and swell. FUZZY LOGIC Controller is used to enhance the performance of UCAP-DVR. The simulation model for the proposed system has been developed in MAT-LAB and the performance over conventional DVR is compared with the results obtained.展开更多
Accurate sag source location and precise sag type recognition are both essential to verifying the responsible party for the sag and taking countermeasures to improve power quality.In this paper,an attention-based inde...Accurate sag source location and precise sag type recognition are both essential to verifying the responsible party for the sag and taking countermeasures to improve power quality.In this paper,an attention-based independently recurrent neural network(IndRNN)for sag source location and sag type recognition in sparsely monitored power system is proposed.Specially,the given inputs are voltage waveforms collected by limited meters in sparsely monitored power system,and the desired outputs simultaneously contain the following information:the located lines where sag occurs;the corresponding sag types,including motor starting,transformer energizing and short circuit;and the fault phase for short circuit.In essence,the responsibility of the proposed method is to automatically establish a nonlinear function that relates the given inputs to the desired outputs with categorization labels as few as possible.A favorable feature of the proposed method is that it can be realized without system parameters or models.The proposed method is validated by IEEE 30-bus system and a real 134-bus system.Experimental results demonstrate that the accuracy of sag source location is higher than 99%for all lines,and the accuracy of sag type recognition is also higher than 99%for various sag sources including motor starting,transformer energizing and 7 different types of short circuits.Furthermore,a comparison among different monitor placements for the proposed method is conducted,which illustrates that the observability of power networks should be ensured to achieve satisfactory performance.展开更多
The major aim of power quality(PQ) enhancing techniques is to maintain a specified voltage magnitude at a desired frequency for sensitive loads irrespective of faults on the power distribution network.The dynamic volt...The major aim of power quality(PQ) enhancing techniques is to maintain a specified voltage magnitude at a desired frequency for sensitive loads irrespective of faults on the power distribution network.The dynamic voltage restorer(DVR) is a device used to mitigate voltage sags to regulate load voltage.This paper presents a mathematical model for leading series voltage injection to mitigate sags thereby achieving the improvement of the utility power factor as well as power sharing between the DVR and utility.The power sharing will be as per requirement to compensate the sags considering the available distributed generation(DG).The approach of mitigating voltage sags using the concept of leading series voltage injection is suitable for those locations where phase shift in the voltage will not cause any problem.The MATLAB/SIMULINK SimPowerSystem toolbox has been used to obtain simulation results to verify the proposed mathematical model.展开更多
Problems in power quality such as temporary drops in grid voltage and flickers have been caught attention with the increasing capacity of the new energy grid-connected systems, such as photovoltaic(PV) and photovoltai...Problems in power quality such as temporary drops in grid voltage and flickers have been caught attention with the increasing capacity of the new energy grid-connected systems, such as photovoltaic(PV) and photovoltaic storage. To solve these problems, a dynamic voltage restorer(DVR) for fault ride-through of photovoltaic energy storage systems is presented. We select the appropriate DVR topology and compensation strategy for PV energy storage systems which are used as energy supply equipment for DVR. It proves to be energy-saving and solves the instability of photovoltaic output effectively. The intelligent algorithm that optimized the controller parameter of dynamic voltage restorer is used and the effectiveness of the controller strategy proposed has been assessed by time-domain simulations in the MATLAB/Simulink platform.展开更多
This paper offers a systematic literature review of real-time detection and classification of Power Quality Disturbances(PQDs).A particular focus is given to voltage sags and notches,as voltage sags cause huge economi...This paper offers a systematic literature review of real-time detection and classification of Power Quality Disturbances(PQDs).A particular focus is given to voltage sags and notches,as voltage sags cause huge economic losses while research on voltage notches is still very incipient.A systematic method based on scientometrics,text similarity and the analytic hierarchy process is proposed to structure the review and select the most relevant literature.A biblio-metric analysis is then performed on the bibliographic data of the literature to identify relevant statistics such as the evolution of publications over time,top publishing countries,and the distribution by relevant topics.A set of articles is subsequently selected to be critically analyzed.The critical review is structured in steps for real-time detection and classification of PQDs,namely,input data preparation,preprocessing,transformation,feature extraction,feature selec-tion,detection,classification,and characterization.Aspects associated with the type of disturbance(s)addressed in the literature are also explored throughout the review,including the perspectives of those studies aimed at multiple PQDs,or specifically focused on voltage sags or voltage notches.The real-time performance of the reviewed tools is also examined.Finally,unsolved issues are discussed,and prospects are highlighted.展开更多
文摘The booming electronics itself carries an impact on power quality. Superconducting Magnetic Energy Storage (SMES) is proposed to enhance power quality in three-phase systems under various loads. This paper aimed to compensate the voltage sags under various faults in the grid systems. The SMES is selected as an energy storage unit to improve the capability of voltage sag compensation. Optimized Dual Fuzzy Flow (ODFF) logic controller is designed to prevent the voltage sag time during excessive phase voltage variation. Hence the proposed controller strategy reduces the total harmonic distortion during various fault conditions. To regulate the contribution of active power, the least possible value is improved using ODFF. The depth of voltage sags compensation is achieved by the over modulation and an iterative loop is designed in the control block. While protecting sensitive loads from voltage disturbances, and sags initiated by the power system, the proposed configuration is advantageous for an industrial implementation. It is found that the proposed method can result in more than 50% additional sag support time when compared with the previous methods such as PI and PSO. Utilizing MATLAB Simulink, compensation of sag and minimization of THD is established, and the simulation tests are performed to evaluate the performance of the proposed control method.
基金This work was supported in part by the National Natural Science Foundation of China under Grant51307050。
文摘Voltage sag is one of the most common power quality disturbances in industry,which causes huge inrush currents in stator windings of induction motors,and adversely impacts the motor secure operation.This paper firstly introduces a 2D Time-Stepping multi-slice finite element method(2D T-S multi-slice FEM)which is used for calculating the magnetic field distribution in induction motors under different sag events.Then the paper deduces the transient analytical expression of stator inrush current based on the classical theory of AC motors and presents a separation method for the positive,negative and zero sequence values based on instantaneous currents.With this method,the paper studies the influences of voltage sag amplitude,phase-angle jump and initial phase angle on the stator positive-and negative-sequence peak currents of 5.5 kW and 55 kW induction motors.This paper further proposes a motor protection method under voltage sag condition with the stator negative-sequence peak currents as the protection threshold,so that the protection false trip can be avoided effectively.Finally,the calculation and analysis results are validated by the comparison of calculated and measured stator peak value of the 5.5 kW induction motor.
基金the financial support from the Universiti Kebangsaan Malaysia under the research grant UKM-DLP-2011-059
文摘An alternative method was introduced for voltage sag source location based on S and TT transformed disturbance powers. It is done to avoid the wrong and inconclusive detection of conventional disturbance power method proposed in the literature. Unlike in the case of the traditional method, the proposed method first transforms the recorded voltage and current during the sag event to some special features before calculating the new version of disturbance powers. The effectiveness of the proposed method has been verified through simulation and actual data from an industrial power system. The results show that the presented method can correctly detect the location of voltage sag source.
基金Project(DIP-2012-30)supported by the Universiti Kebangsaan,Malaysia
文摘A method for improving the level of reliability of distribution systems is presented by employing an integrated voltage sag mitigation method that comprises a two-staged strategy,namely,distribution network reconfiguration(DNR)followed by DSTATCOM placement.Initially,an optimal DNR is applied to reduce the propagated voltage sags during the test period.The second stage involves optimal placement of the DSTATCOM to assist the already reconfigured network.The gravitational search algorithm is used in the process of optimal DNR and in placing DSTATCOM.Reliability assessment is performed using the well-known indices.The simulation results show that the proposed method is efficient and feasible for improving the level of system reliability.
基金supported by the twelfth five-year National Mega-projects of Science and Technology (2011BAA01B03)
文摘Unified power quality conditioner(UPQC)holds the capability of solving power quality problems,especially shows good performance in the voltage sag compensation. In this paper, a compensation strategy based on simultaneous reactive power injection for UPQC(namely UPQC-SRI) is proposed to address the issue of voltage sag. The proposed UPQC-SRI determines the injection angle of compensation voltage with consideration of optimal configuration of UPQC current-carrying.Moreover, the compensation strategy also considers the current-carrying limit of UPQC, and then the zero active power injection region of UPQC-SRI(also called UPQCSRI region) is obtained. Under the conditions which exceed the UPQC-SRI region, the limit value of shunt current is determined by this proposed strategy. Finally, the proposed strategy and the corresponding algorithm are verified under the PSCAD/EMTDC platform. The result indicates the proposed UPQC-SRI strategy in this paper can provide more persistent voltage sag compensation than the previous strategies for the sensitive load.
基金supported by National Nature Science Foundation under Grant 51477070,and the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD).
文摘Introduction:This paper uses a dynamic voltage restorer(DVR)to improve the voltage quality from voltage sags.It is difficult to satisfy various of compensation quality and time of the voltage sag by using single compensation method.Furthermore,high-power consumption of the phase jump compensation increases the size and cost of a dynamic voltage restorer(DVR).Methods&Results:In order to improve the compensating efficiency of DVR,an optimized compensation strategy is proposed for voltage sag of micro-grid caused by interconnection and sensitive loads.The proposed compensation strategy increases the supporting time for long voltage sags.Discussion:Firstly,the power flow and the maximum compensation time of DVR are analyzed using three basic compensation strategies.Then,the phase jump is corrected by pre-sag compensation.And a quadratic transition curve,which involves the injected voltage phases of pre-sag strategy and minimum energy strategy,is used to transform pre-sag compensation to minimum energy compensation of DVR.Conclusions:The transition utilizes the storage system to reduce the rate of discharge.As a result,the proposed strategy increases the supporting time for long voltage sags.The analytical study shows that the presented method significantly increases compensation time of DVR.The simulation results performed by MATLAB/SIMULINK also confirm the effectiveness of the proposed method.
基金This work was supported by China Southern Power Grid(No.GZHKJXM20170141).
文摘The impact of voltage sag on sensitive devices is related to the time when the sag occurs.However,the point-on-wave of a sag is uncertain.Therefore,this paper presents a nov-el approach to evaluate the voltage sag severity considering a random point-on-wave.First,the uncertainty of equipment malfunction is revealed.Second,under a given residual voltage,the relationship between the point-on-wave and the duration that the device can withstand is described with a fitting curve.Third,a voltage sag probabilistic index is proposed to describe the severity.The evaluation procedure is also presented.Finally,three types of releasers are tested and analyzed to determine the effectiveness of the proposed method.The evaluation method can help instruct electrical engineers establish more well-grounded sag mitigation proposals.
基金The National Science and Technology Sup-port Project (No.2007BAA12B03)
文摘Control strategy affects directly the working performances of dynamic voltage regulator (DVR). One-cycle control is an effective nonlinear signal modulation control method. In this paper, a new one-cycle control scheme for DVR was proposed in single phase supply system. On the basis of principle analysis, the corresponding one-cycle control model for DVR was built up, which is characterized by simple control circuits, good control performance, and high control precision. As an example, a control model for single-phase DVR was simulated by using Matlab/Simulink and SimPowerSystem. The results show that the load voltage could be compensated quickly at the points of supply voltage stepping down and up, and the relative error was less than 4% in the whole voltage sag process. Both theory analysis and simulation results show that the new one-cycle control scheme for DVR is effective.
文摘The modular multilevel converter (MMC) is a highly modular, easy to expand; the output voltage waveform is good, especially suitable for application in high voltage power system. This article first introduces the circuit topology and principle of MMC, and the main technical characteristics of MMC. And according to the relationship between the drop power voltage and the load power factor, proposed three working modes of the minimum energy compensation strategy. It is shown that MMC has good application prospect in future medium or high- voltage high power applications, especially be one of candidates for HVDC system application.
文摘Power quality is one of the major concerns among consumers and electric utility companies. CUPS (custom power systems) devices are used to improve the quality of power and enhance the reliability of the power supply in the distribution networks. The DVR (dynamic voltage restorer) is an important CUPS device used to mitigate voltage sag/swell and imbalances. Various control techniques have been implemented to control the DVR, among which the PID (proportional-integral-derivative) controller is dominant because of its model independent property and its error driven technique. In this paper, a new controller based on the ADRC (active disturbance rejection control) concept is developed, and its performance is compared to that of the PID controller. The model of the DVR and its ADRC and PID controllers were developed under the MATLAB (matrix laboratory)/Simulink environment. The simulation results demonstrated the effectiveness of the ADRC over the PID controller.
文摘The inter-line dynamic voltage restorer (IDVR) consists of several voltage source inverters connected to different independent distribution feeders with common dc bus. When one of the inverters compensates for voltage sag that appears in its feeder (voltage control mode), the other inverters pump the required power into the dc bus (power control mode). Each inverter will have both voltage and power controllers; only one controller is in use during the abnormal conditions according to its feeder state. The voltage controller uses one of the dynamic voltage restoration techniques. In this paper, the in-phase technique is applied and two types of loads are considered (constant impedance and three phase induction motor). Since the voltage restoration process may need real power injection into the distribution system, the power controller injects this power via voltage injection. This voltage injection is simulated by voltage drop across series virtual impedance. A new scheme is proposed to select the impedance value. The impedance value is selected such that the power consumed by this impedance represents the required power to be transferred without perturbing the load voltage. The performance of this system is also studied during voltage swell. A scheme for operation of multi-feeder IDVR system is proposed in this paper. Simulation results substantiate the proposed concept.
文摘This paper proposes about a powerful control mechanism of UPQC (Unified Power Quality Conditioner) work on voltage source inverter which can effectively compensate source current harmonics and also mitigate all voltage collapse such as dip, swell, voltage unbalances and harmonics. The consolidation of series and parallel active power filters sharing mutual DC bus capacitor forms UPQC. PI (Proportional Integral) controller is mainly used in order to maintain continual DC voltage along with the hysteresis current controller. The parallel and series power filters were designed using 3-phase voltage source inverter. The reference signals for shunt and series active power filters were obtained by Synchronous Reference Frame (SRF) theory and Power Reactive (PQ) theory respectively. By using these theories, reference signals were obtained which was fed to the controllers for generating switching pulses for parallel and series active filters. The UPQC dynamic performance is obtained through testing terms like the compensation of voltage, current harmonics and all voltage distortion associated with 3-phase 3-wire power system which is simulated using MATLAB-Simulink software.
基金Science and Technology Project of State Grid Corporation of China,Scale application and benefit evaluation of typical power substitution technology considering the influence of power quality(52182018000H).
文摘With the implementation of electric energy alternatives,the large-scale application of electric energy substitution represented by air-source heat pumps has replaced traditional coal-fired heating,which is beneficial for the environment and alleviates air pollution.However,the large-scale application of airsource heat pumps has brought power quality problems such as voltage sags,harmonic pollution,and three-phase imbalance to the distribution network.This paper studies the fixed-frequency and variablefrequency air-source heat pump,introduces its working principle,analyzes the mechanism of its power quality problem.Moreover,the paper establishes a simulation model for the fixed-frequency heat pump and variable-frequency heat pump to connect to the distribution network.This research mainly studies the impact of large-scale fixed-frequency heat pumps on the depth of voltage sags in the distribution network and the impact of large-scale variable-frequency heat pumps on the harmonic content of the distribution network under different penetration rates and uses measured data to verify the reliability of the simulation results.This paper uses experimental data for the first time to verify the real power quality problems of large-scale heat pumps,which can provide a reference for determining the power quality standards for heat pumps connected to the power grid.At the same time,it can also provide a reference for the power quality management of the distribution network that is actually connected to electric heating.
文摘This paper presents an analysis of the electric power flows in a hot rolling mill plant using a power quality analyzer and developing simulation models with Matlab-Simulink. The model inputs have been taken from process data by the process computer of the plant. Data from different rolling campaigns have been analysed. A STATCOM (static synchronous compensator) with a control strategy based on voltage oriented control with d-q coordinates is used as solution to improve the reactive compensation as well as to minimize the voltage fluctuations and sags effect. The overall electric model has been simulated with the STATCOM to check the improvement in the voltage stability and the consumption.
文摘The experimental results by the simulated PV (photovoltaic) system for understanding the cause of disconnection when instantaneous voltage sag occurs are reported in this study. Moreover, it is understood that the PCS with the voltage phase jump detection method which is one of the main causes of the disconnection. We modeled it in the simulation. When fault occurs, even though the residual voltage is more than 20% and the voltage sag time is within 1.0 s, the PCS disconnected by the voltage phase jump detection was confirmed in the simulation results. Ifa large number of PV systems are interconnected in the power system, this study is verified through the simulation that the interaction caused by the disconnection which generated by the voltage phase jump detection. This study is proposed threshold limit value of islanding detection. The validity of proposed method was verified through the simulation in this study.
文摘In recent years, a rapid decrease in the cost of various energy storage technologies and their integration into grid becomes a reality with the advent of smart grid. The Dynamic Voltage Restorer (DVR) is a custom power device that has an excellent dynamic capability used to provide voltage sag, swell compensation in distribution systems. Among the energy storage devices, Ultra-Capacitors (UCAP) have ideal characteristics such as high power and low energy density essential for the compensation of voltage sag and swell, which require high power for short interval of time. This paper presents an integration of rechargeable UCAP with DVR. This UCAP-DVR presents a modular, flexible system configuration that will have an active power capability and also provide deep, extended mitigation for power quality problems. The DVR is integrated into UCAP via bidirectional DC-DC converter which supports a rigid dc-link voltage for DVR and also helps in compensating temporary voltage sag and swell. FUZZY LOGIC Controller is used to enhance the performance of UCAP-DVR. The simulation model for the proposed system has been developed in MAT-LAB and the performance over conventional DVR is compared with the results obtained.
基金This work was partly supported by National Natural Science Foundation of China(No.61903296)Key Project of Natural Science Basic Research Plan in Shaanxi Province of China(No.2019ZDLGY18-03)+1 种基金Thousand Talents Plan of Shaanxi Province for Young Professionals,Project of Shaanxi Science and Technology(No.2019JQ-329)Doctoral Scientific Research Foundation of Xi’an University of Technology(No.103-451116012).
文摘Accurate sag source location and precise sag type recognition are both essential to verifying the responsible party for the sag and taking countermeasures to improve power quality.In this paper,an attention-based independently recurrent neural network(IndRNN)for sag source location and sag type recognition in sparsely monitored power system is proposed.Specially,the given inputs are voltage waveforms collected by limited meters in sparsely monitored power system,and the desired outputs simultaneously contain the following information:the located lines where sag occurs;the corresponding sag types,including motor starting,transformer energizing and short circuit;and the fault phase for short circuit.In essence,the responsibility of the proposed method is to automatically establish a nonlinear function that relates the given inputs to the desired outputs with categorization labels as few as possible.A favorable feature of the proposed method is that it can be realized without system parameters or models.The proposed method is validated by IEEE 30-bus system and a real 134-bus system.Experimental results demonstrate that the accuracy of sag source location is higher than 99%for all lines,and the accuracy of sag type recognition is also higher than 99%for various sag sources including motor starting,transformer energizing and 7 different types of short circuits.Furthermore,a comparison among different monitor placements for the proposed method is conducted,which illustrates that the observability of power networks should be ensured to achieve satisfactory performance.
基金Project(No. UET/ASR&TD-251/2006)supported by the Higher Education Commission of Pakistan
文摘The major aim of power quality(PQ) enhancing techniques is to maintain a specified voltage magnitude at a desired frequency for sensitive loads irrespective of faults on the power distribution network.The dynamic voltage restorer(DVR) is a device used to mitigate voltage sags to regulate load voltage.This paper presents a mathematical model for leading series voltage injection to mitigate sags thereby achieving the improvement of the utility power factor as well as power sharing between the DVR and utility.The power sharing will be as per requirement to compensate the sags considering the available distributed generation(DG).The approach of mitigating voltage sags using the concept of leading series voltage injection is suitable for those locations where phase shift in the voltage will not cause any problem.The MATLAB/SIMULINK SimPowerSystem toolbox has been used to obtain simulation results to verify the proposed mathematical model.
基金Supported by the National Natural Science Foundation of China(61603242)。
文摘Problems in power quality such as temporary drops in grid voltage and flickers have been caught attention with the increasing capacity of the new energy grid-connected systems, such as photovoltaic(PV) and photovoltaic storage. To solve these problems, a dynamic voltage restorer(DVR) for fault ride-through of photovoltaic energy storage systems is presented. We select the appropriate DVR topology and compensation strategy for PV energy storage systems which are used as energy supply equipment for DVR. It proves to be energy-saving and solves the instability of photovoltaic output effectively. The intelligent algorithm that optimized the controller parameter of dynamic voltage restorer is used and the effectiveness of the controller strategy proposed has been assessed by time-domain simulations in the MATLAB/Simulink platform.
文摘This paper offers a systematic literature review of real-time detection and classification of Power Quality Disturbances(PQDs).A particular focus is given to voltage sags and notches,as voltage sags cause huge economic losses while research on voltage notches is still very incipient.A systematic method based on scientometrics,text similarity and the analytic hierarchy process is proposed to structure the review and select the most relevant literature.A biblio-metric analysis is then performed on the bibliographic data of the literature to identify relevant statistics such as the evolution of publications over time,top publishing countries,and the distribution by relevant topics.A set of articles is subsequently selected to be critically analyzed.The critical review is structured in steps for real-time detection and classification of PQDs,namely,input data preparation,preprocessing,transformation,feature extraction,feature selec-tion,detection,classification,and characterization.Aspects associated with the type of disturbance(s)addressed in the literature are also explored throughout the review,including the perspectives of those studies aimed at multiple PQDs,or specifically focused on voltage sags or voltage notches.The real-time performance of the reviewed tools is also examined.Finally,unsolved issues are discussed,and prospects are highlighted.