Ngo Khoa - Academia.edu (original) (raw)

Papers by Ngo Khoa

International Journal of Electrical and Electronic Engineering & Telecommunications

Electric transmission lines play a very essential role in transmitting power energy from generati... more Electric transmission lines play a very essential role in transmitting power energy from generation centers to consumption regions. They can be exposed to fault occurrences due to various reasons, such as lightning strikes, malfunction of components, and human errors. Since fault is unpredictable, a fast fault location method is required to minimize the impact of fault in power systems. This paper presents a research work for comparing the performance of the impedance-based fault location methods, in which the impedance parameter of the faulted line section is calculated as a measure of the distance to the fault. To evaluate the capability of the methods for correctly detecting and locating the fault locations, comprehensive simulation results are carried out. This computation is based on modeling and simulating a three-phase 220kV overhead transmission line in the Matlab/Simulink software. Short circuits which occur in various fault resistances and locations along the transmission ...

International Journal of Electrical and Electronic Engineering & Telecommunications, 2022

This paper presents an architecture of the Doubly-Fed Induction Generator based on Wind Energy Co... more This paper presents an architecture of the Doubly-Fed Induction Generator based on Wind Energy Conversion System (DFIG-WECS) to study with the Low Voltage Ride Through (LVRT) capability. The proposed architecture consists of three main parts namely the wind turbine, electric generator, control systems. The wind turbine and gearbox are modeled by a servo motor driven by using an inverter system. The electric generator uses the Wound Rotor Induction Generator (WRIG). The control system composes of the rotor-side converter (RSC) and the grid-side converter (GSC). The integration of the digital signal processor (DSP) with the Simulink/Matlab software of the vector control scheme is implemented to control both RSC and GSC. Besides, to protect the overcurrent of the generator’s rotor and overvoltage of the DC-link, the crowbar and chopper circuits and the logical scheme between the crowbar and the RSC are also proposed. To approve the control algorithms implemented in DSP as hardware in t...

Journal of Electrical Systems, 2018

Voltage sag event is one of the most important power quality disturbances in power systems. It ca... more Voltage sag event is one of the most important power quality disturbances in power systems. It can have affect on voltage quality and sensitive equipment in power systems. Detecting voltage sag events in power systems is a vital role in operating systems, therefore, this paper proposes an algorithm based on extended Kalman filter (EKF) for characterizing and detecting the parameters of voltage sag events accurately. A status-space modeling of voltage sag signals is defined to model voltage sag signal according to status-space modeling of EKF. The parameters of voltage sag events are estimated using the proposed method including voltage magnitude, estimation error, starting and ending times, duration time of the event. Matlab software is used to generate database of voltage sag waveforms modeled by a mathematical equation and then the waveforms are used to evaluate the proposed method. The simulation results of the proposed method are also compared with the simulation results of the ...

Advances in Engineering Research and Application, 2018

This study focuses on setting up a simulation program using Matlab/Simulink for a simplified vibr... more This study focuses on setting up a simulation program using Matlab/Simulink for a simplified vibrational model of a horizontal washing machine with 2 degrees of freedom. A reliable experiment was carried out to define the orbit of the tub's vibration in symmetry plane that consists of the suspension system. The comparison between experimental and simulation results is used to analyze and evaluate the reliability and application scope of the model.

Advances in Engineering Research and Application, 2018

This paper focuses on constructing a Matlab/Simulink program of vibration model with 2 DOF horizo... more This paper focuses on constructing a Matlab/Simulink program of vibration model with 2 DOF horizontal washing machine. The key point of this paper is using a strong nonlinear friction force - velocity (F-V) relationship of dampers which is obtained from experiment as an input for the simulation. The suitability and high reliability of the model were proved by comparing simulation and experimental results. The model was used to study the effect of damper configurations on the vibration characteristics of horizontal washing machines and then to propose several suitable damper configurations.

Vietnam Journal of Mechanics, 2001

In this paper the exact moisture concentration function m(z, t) is used to compute the hygroscopi... more In this paper the exact moisture concentration function m(z, t) is used to compute the hygroscopic residual stresses in laminated composites. The governing equations were established by using a full higher-order displacement theory. Hygroscopically induced residual stresses in thick graphite-epoxy composite laminates: Cross-ply [0/90] 8 based on this approach were compared with those obtained by assumption: the moisture concentration m is a constant in all plies through the laminates thickness

Archives of Electrical Engineering, 2021

This paper proposes an advanced Internet of Things (IoT) system for measuring, monitoring, and re... more This paper proposes an advanced Internet of Things (IoT) system for measuring, monitoring, and recording some power quality (PQ) parameters. The proposed system is designed and developed for both hardware and software. For the hardware unit, three PZEM-004T modules with non-invasive current transformer (CT) sensors are used to measure the PQ parameters and an Arduino WeMos D1 R1 ESP8266 microcontroller is used to receive data from the sensors and send this data to the server via the internet. For the software unit, an algorithm using Matlab software is developed to send measurement data to the ThingSpeak cloud. The proposed system can monitor and analyse the PQ parameters including frequency, root mean square (RMS) voltage, RMS current, active power, and the power factor of a low-voltage load in real-time. These PQ parameters can be stored on the ThingSpeak cloud during the monitoring period; hence the standard deviation in statistics of the voltage and frequency is applied to analy...

For voltage-source-converter based high-voltage-direct-current (VSC-HVDC) transmission systems, f... more For voltage-source-converter based high-voltage-direct-current (VSC-HVDC) transmission systems, fault ride-through (FRT) capability is a very important grid requirement in order to enhance its operational availability under an alternating current (AC) grid fault condition. Voltage sags during a short-circuit fault in power transmission lines can lead to fluctuations in the direct current (DC) link voltage of converter systems, and may induce reversed power flow and even trip a VSC-HVDC transmission system. A practical method is developed in this paper for investigating FRT capability of VSC-HVDC transmission system characteristics during a voltage sag event using experimental results from Smart Grid Laboratory. Symmetrical and asymmetrical voltage sag events with different remaining voltages are applied to an AC grid that lasts with a variable duration. The experimental waveforms of the two converter systems are recorded and analyzed in order to evaluate the FRT capability of VSC-HV...

Engineering, Technology & Applied Science Research, 2019

In this paper, an experimental system based on Arduino Uno microcontroller board was developed fo... more In this paper, an experimental system based on Arduino Uno microcontroller board was developed for measuring electrical quantities and protecting overvoltage and undervoltage conditions in a single-phase power supply. The main components are described in detail, including the hardware and software to build the system in which an Arduino Uno platform is implemented as a vital microcontroller to read voltage and current measurement from a voltage sensor (ZMPT101B) and a current sensor (ACS712) respectively. In addition, the Arduino is also used to send all measurement to a PC through a serial port for monitoring the measured data graphically. The proposed method for designing the software uses the root mean square (RMS) method for measuring electrical quantities and then the RMS voltage measurement is compared with the minimum voltage and the maximum voltage to switch on or switch off the load. The monitoring GUI is designed with the use of the free and open-source Telemetry Viewer v0...

Engineering, Technology & Applied Science Research, 2018

The impact of thyristor controlled series capacitor (TCSC) on distance protection relays in trans... more The impact of thyristor controlled series capacitor (TCSC) on distance protection relays in transmission lines is analyzed in this paper. Voltage and current data are measured and collected at the relay locations to calculate the apparent impedance seen by distance protection relays in the different operating modes of the TCSC connected to the line. Short-circuit faults which occur at different locations on the power transmission line are considered in order to locate the fault for the purpose of evaluating the impact of TCSC on the distance protection relay. Matlab/Simulink simulation software is used to model the power transmission line with two sources at the two ends. Voltage source, transmission line, TCSC, voltage and current measurement, and discrete Fourier transform (DFT) blocks are integrated into the model. Simulation results show the impact of TCSC on the distance protection relay and determine the apparent impedance and fault location in the line.

Energies, 2020

The detection, mitigation, and classification of power quality (PQ) disturbances have been issues... more The detection, mitigation, and classification of power quality (PQ) disturbances have been issues of interest in the power system field. This paper proposes an approach to detect and classify various types of PQ disturbances based on the Stockwell transform (ST) and decision tree (DT) methods. At first, the ST is developed based on the moving, localizing, and scalable Gaussian window to detect five statistical features of PQ disturbances such as the high frequency of oscillatory transient, distinction between stationary and non-stationary, the voltage amplitude oscillation around an average value, the existence of harmonics in a disturbance signal, and the root mean square voltage at the internal period of sag, swell or interruption. Then, these features are classified into nine types, such as normal, sag, swell, interruption, harmonic, flicker, oscillatory transient, harmonic voltage sag, and harmonic voltage swell by using the DT algorithm that is based on a set of rules with the ...

Energies, 2018

The flexible alternating current transmission systems (FACTS) have been widely used in modern pow... more The flexible alternating current transmission systems (FACTS) have been widely used in modern power systems. Because of the presence of the FACTS devices, distance relays in transmission lines may inaccurately locate fault locations. Therefore, it is significant to find a mechanism for locating fault in transmission lines connected to FACTS in which a static var compensator (SVC) is investigated in this work. Based on the development of a phasor measurement unit (PMU) with global positioning system (GPS), this paper proposes a new method for calculating apparent impedance seen by the distance relay location while a short-circuit fault occurs in a transmission line connected the SVC to the midpoint of the line. According to the method, sampled voltage and current measurement at the relay and SVC locations are synchronized using PMUs and the synchronized measurements are then used to calculate a new apparent impedance and to locate the fault location in the line. The method in this pa...

International Journal of Electrical and Computer Engineering (IJECE), 2017

This paper focuses on analyzing and evaluating impact of a Static Var Compensator (SVC) on the me... more This paper focuses on analyzing and evaluating impact of a Static Var Compensator (SVC) on the measured impedance at distance protection relay location on power transmission lines. The measured impedance at the relay location when a fault occurs on the line is determined by using voltage and current signals from voltage and current transformers at the relay and the type of fault occurred on the line. The MHO characteristic is applied to analyze impact of SVC on the distance protection relay. Based on the theory, the authors in this paper develop a simulation program on Matlab/Simulink software to analyze impact of SVC on the distance protection relay. In the power system model, it is supposed that the SVC is located at mid-point of the transmission line to study impact of SVC on the distance relay. The simulation results show that SVC will impact on the measured impedance at the relay when the fault occurs after the location of the SVC on the power transmission line.

International Journal of Electronics and Electrical Engineering, 2016

In the coming years, the flexibility of distribution network will be required more due to the imp... more In the coming years, the flexibility of distribution network will be required more due to the implementation of distributed generation of renewable energy sources such as wind, solar, biomass, etc. The distributed generations are connected to the power grid in order to contribute to supplying energy for the loads. Thus the power flow direction and fault direction at the relays will be also changed. Therefore, using directional overcurrent protection relay is necessary to isolate the fault quickly and exactly. This paper proposes a novel method based on linear adaptive neural network which is used in directional overcurrent protection relay. The proposed method has the advantages compared with the fast Fourier transform method in signal processing. It can estimate the amplitude and phase angle of voltage and current signals accuracy after each updated sample. In addition, the proposed method is verified on the distribution network with/without distributed generation which is modeled on Matlab/Simulink software. The simulation results show that the proposed method accurately detect the direction at the relay when the fault occurs at different locations on the network. 

International Review of Electrical Engineering (IREE), 2016

This paper proposes a method to monitor, detect and classify voltage disturbances including volta... more This paper proposes a method to monitor, detect and classify voltage disturbances including voltage sag, voltage swell, voltage interruption, and long duration voltage variations. The detail coefficient in discrete wavelet transform is used to extract the start and end times of the voltage disturbance. The decomposed level of multi-resolution analysis in discrete wavelet transform is calculated according to the sampling frequency of the voltage signal for determining the approximation coefficient that only contains the fundamental frequency band. Then an adaptive linear neural network is used to estimate the voltage magnitude from the approximation coefficient. Finally, the disturbance will be classified into groups of voltage disturbances based on the characteristics according to the rules in IEEE Std. 1159-2009. The voltage waveforms based on theoretical signal models and actual voltage waveforms which recorded by power quality monitoring equipment are applied to evaluate the proposed method. The simulation results show that the proposed method can detect and classify voltage disturbances better than traditional methods based on root mean square and conventional adaptive linear neural network techniques.

2015 IEEE 11th International Conference on Power Electronics and Drive Systems, 2015

This paper presents a configuration and a control strategy for dynamic voltage restorer (DVR). In... more This paper presents a configuration and a control strategy for dynamic voltage restorer (DVR). In order to compensate the voltage of each phase separately, a closed-loop PI control law in the d-q reference frame is proposed. The proposed method provides a fast response and effective sag compensation capabilities. In addition, in order to detect voltage sag, a linear Kalman filter is employed to estimate three-phase voltages. By using Kalman filter, the voltage sag can be detected faster than other conventional methods. Therefore DVR can compensate voltage sag quickly and accurately. The obtained results that are simulated in Matlab/ Simulink indicate that the proposed method can mitigate the balanced and unbalanced voltage sag types efficiently in the distribution networks.

Vietnam Journal of Mechanics, 2012

A new C 1 rectangular element is proposed and the finite element formulation based on Reddy's hig... more A new C 1 rectangular element is proposed and the finite element formulation based on Reddy's higher-order shear deformation plate theory is developed. Although the plate theory is quite attractive but it could not be exploited as expected in finite-element analysis. This is due to the dificulties associated with satisfaction of inter-elemental continuity requirement and satisfy zero shear stress boundary conditions of the plate theory. In this paper, the proposed element is developed where Reddy's plate theory is successfully implemented. It has nine nodes and each node contains 7 degrees of freedom. The performance of the element is tested with different numerical examples, which show its precision and range of applicability.

International Journal of Electrical and Electronic Engineering & Telecommunications

Electric transmission lines play a very essential role in transmitting power energy from generati... more Electric transmission lines play a very essential role in transmitting power energy from generation centers to consumption regions. They can be exposed to fault occurrences due to various reasons, such as lightning strikes, malfunction of components, and human errors. Since fault is unpredictable, a fast fault location method is required to minimize the impact of fault in power systems. This paper presents a research work for comparing the performance of the impedance-based fault location methods, in which the impedance parameter of the faulted line section is calculated as a measure of the distance to the fault. To evaluate the capability of the methods for correctly detecting and locating the fault locations, comprehensive simulation results are carried out. This computation is based on modeling and simulating a three-phase 220kV overhead transmission line in the Matlab/Simulink software. Short circuits which occur in various fault resistances and locations along the transmission ...

International Journal of Electrical and Electronic Engineering & Telecommunications, 2022

This paper presents an architecture of the Doubly-Fed Induction Generator based on Wind Energy Co... more This paper presents an architecture of the Doubly-Fed Induction Generator based on Wind Energy Conversion System (DFIG-WECS) to study with the Low Voltage Ride Through (LVRT) capability. The proposed architecture consists of three main parts namely the wind turbine, electric generator, control systems. The wind turbine and gearbox are modeled by a servo motor driven by using an inverter system. The electric generator uses the Wound Rotor Induction Generator (WRIG). The control system composes of the rotor-side converter (RSC) and the grid-side converter (GSC). The integration of the digital signal processor (DSP) with the Simulink/Matlab software of the vector control scheme is implemented to control both RSC and GSC. Besides, to protect the overcurrent of the generator’s rotor and overvoltage of the DC-link, the crowbar and chopper circuits and the logical scheme between the crowbar and the RSC are also proposed. To approve the control algorithms implemented in DSP as hardware in t...

Journal of Electrical Systems, 2018

Voltage sag event is one of the most important power quality disturbances in power systems. It ca... more Voltage sag event is one of the most important power quality disturbances in power systems. It can have affect on voltage quality and sensitive equipment in power systems. Detecting voltage sag events in power systems is a vital role in operating systems, therefore, this paper proposes an algorithm based on extended Kalman filter (EKF) for characterizing and detecting the parameters of voltage sag events accurately. A status-space modeling of voltage sag signals is defined to model voltage sag signal according to status-space modeling of EKF. The parameters of voltage sag events are estimated using the proposed method including voltage magnitude, estimation error, starting and ending times, duration time of the event. Matlab software is used to generate database of voltage sag waveforms modeled by a mathematical equation and then the waveforms are used to evaluate the proposed method. The simulation results of the proposed method are also compared with the simulation results of the ...

Advances in Engineering Research and Application, 2018

This study focuses on setting up a simulation program using Matlab/Simulink for a simplified vibr... more This study focuses on setting up a simulation program using Matlab/Simulink for a simplified vibrational model of a horizontal washing machine with 2 degrees of freedom. A reliable experiment was carried out to define the orbit of the tub's vibration in symmetry plane that consists of the suspension system. The comparison between experimental and simulation results is used to analyze and evaluate the reliability and application scope of the model.

Advances in Engineering Research and Application, 2018

This paper focuses on constructing a Matlab/Simulink program of vibration model with 2 DOF horizo... more This paper focuses on constructing a Matlab/Simulink program of vibration model with 2 DOF horizontal washing machine. The key point of this paper is using a strong nonlinear friction force - velocity (F-V) relationship of dampers which is obtained from experiment as an input for the simulation. The suitability and high reliability of the model were proved by comparing simulation and experimental results. The model was used to study the effect of damper configurations on the vibration characteristics of horizontal washing machines and then to propose several suitable damper configurations.

Vietnam Journal of Mechanics, 2001

In this paper the exact moisture concentration function m(z, t) is used to compute the hygroscopi... more In this paper the exact moisture concentration function m(z, t) is used to compute the hygroscopic residual stresses in laminated composites. The governing equations were established by using a full higher-order displacement theory. Hygroscopically induced residual stresses in thick graphite-epoxy composite laminates: Cross-ply [0/90] 8 based on this approach were compared with those obtained by assumption: the moisture concentration m is a constant in all plies through the laminates thickness

Archives of Electrical Engineering, 2021

This paper proposes an advanced Internet of Things (IoT) system for measuring, monitoring, and re... more This paper proposes an advanced Internet of Things (IoT) system for measuring, monitoring, and recording some power quality (PQ) parameters. The proposed system is designed and developed for both hardware and software. For the hardware unit, three PZEM-004T modules with non-invasive current transformer (CT) sensors are used to measure the PQ parameters and an Arduino WeMos D1 R1 ESP8266 microcontroller is used to receive data from the sensors and send this data to the server via the internet. For the software unit, an algorithm using Matlab software is developed to send measurement data to the ThingSpeak cloud. The proposed system can monitor and analyse the PQ parameters including frequency, root mean square (RMS) voltage, RMS current, active power, and the power factor of a low-voltage load in real-time. These PQ parameters can be stored on the ThingSpeak cloud during the monitoring period; hence the standard deviation in statistics of the voltage and frequency is applied to analy...

For voltage-source-converter based high-voltage-direct-current (VSC-HVDC) transmission systems, f... more For voltage-source-converter based high-voltage-direct-current (VSC-HVDC) transmission systems, fault ride-through (FRT) capability is a very important grid requirement in order to enhance its operational availability under an alternating current (AC) grid fault condition. Voltage sags during a short-circuit fault in power transmission lines can lead to fluctuations in the direct current (DC) link voltage of converter systems, and may induce reversed power flow and even trip a VSC-HVDC transmission system. A practical method is developed in this paper for investigating FRT capability of VSC-HVDC transmission system characteristics during a voltage sag event using experimental results from Smart Grid Laboratory. Symmetrical and asymmetrical voltage sag events with different remaining voltages are applied to an AC grid that lasts with a variable duration. The experimental waveforms of the two converter systems are recorded and analyzed in order to evaluate the FRT capability of VSC-HV...

Engineering, Technology & Applied Science Research, 2019

In this paper, an experimental system based on Arduino Uno microcontroller board was developed fo... more In this paper, an experimental system based on Arduino Uno microcontroller board was developed for measuring electrical quantities and protecting overvoltage and undervoltage conditions in a single-phase power supply. The main components are described in detail, including the hardware and software to build the system in which an Arduino Uno platform is implemented as a vital microcontroller to read voltage and current measurement from a voltage sensor (ZMPT101B) and a current sensor (ACS712) respectively. In addition, the Arduino is also used to send all measurement to a PC through a serial port for monitoring the measured data graphically. The proposed method for designing the software uses the root mean square (RMS) method for measuring electrical quantities and then the RMS voltage measurement is compared with the minimum voltage and the maximum voltage to switch on or switch off the load. The monitoring GUI is designed with the use of the free and open-source Telemetry Viewer v0...

Engineering, Technology & Applied Science Research, 2018

The impact of thyristor controlled series capacitor (TCSC) on distance protection relays in trans... more The impact of thyristor controlled series capacitor (TCSC) on distance protection relays in transmission lines is analyzed in this paper. Voltage and current data are measured and collected at the relay locations to calculate the apparent impedance seen by distance protection relays in the different operating modes of the TCSC connected to the line. Short-circuit faults which occur at different locations on the power transmission line are considered in order to locate the fault for the purpose of evaluating the impact of TCSC on the distance protection relay. Matlab/Simulink simulation software is used to model the power transmission line with two sources at the two ends. Voltage source, transmission line, TCSC, voltage and current measurement, and discrete Fourier transform (DFT) blocks are integrated into the model. Simulation results show the impact of TCSC on the distance protection relay and determine the apparent impedance and fault location in the line.

Energies, 2020

The detection, mitigation, and classification of power quality (PQ) disturbances have been issues... more The detection, mitigation, and classification of power quality (PQ) disturbances have been issues of interest in the power system field. This paper proposes an approach to detect and classify various types of PQ disturbances based on the Stockwell transform (ST) and decision tree (DT) methods. At first, the ST is developed based on the moving, localizing, and scalable Gaussian window to detect five statistical features of PQ disturbances such as the high frequency of oscillatory transient, distinction between stationary and non-stationary, the voltage amplitude oscillation around an average value, the existence of harmonics in a disturbance signal, and the root mean square voltage at the internal period of sag, swell or interruption. Then, these features are classified into nine types, such as normal, sag, swell, interruption, harmonic, flicker, oscillatory transient, harmonic voltage sag, and harmonic voltage swell by using the DT algorithm that is based on a set of rules with the ...

Energies, 2018

The flexible alternating current transmission systems (FACTS) have been widely used in modern pow... more The flexible alternating current transmission systems (FACTS) have been widely used in modern power systems. Because of the presence of the FACTS devices, distance relays in transmission lines may inaccurately locate fault locations. Therefore, it is significant to find a mechanism for locating fault in transmission lines connected to FACTS in which a static var compensator (SVC) is investigated in this work. Based on the development of a phasor measurement unit (PMU) with global positioning system (GPS), this paper proposes a new method for calculating apparent impedance seen by the distance relay location while a short-circuit fault occurs in a transmission line connected the SVC to the midpoint of the line. According to the method, sampled voltage and current measurement at the relay and SVC locations are synchronized using PMUs and the synchronized measurements are then used to calculate a new apparent impedance and to locate the fault location in the line. The method in this pa...

International Journal of Electrical and Computer Engineering (IJECE), 2017

This paper focuses on analyzing and evaluating impact of a Static Var Compensator (SVC) on the me... more This paper focuses on analyzing and evaluating impact of a Static Var Compensator (SVC) on the measured impedance at distance protection relay location on power transmission lines. The measured impedance at the relay location when a fault occurs on the line is determined by using voltage and current signals from voltage and current transformers at the relay and the type of fault occurred on the line. The MHO characteristic is applied to analyze impact of SVC on the distance protection relay. Based on the theory, the authors in this paper develop a simulation program on Matlab/Simulink software to analyze impact of SVC on the distance protection relay. In the power system model, it is supposed that the SVC is located at mid-point of the transmission line to study impact of SVC on the distance relay. The simulation results show that SVC will impact on the measured impedance at the relay when the fault occurs after the location of the SVC on the power transmission line.

International Journal of Electronics and Electrical Engineering, 2016

In the coming years, the flexibility of distribution network will be required more due to the imp... more In the coming years, the flexibility of distribution network will be required more due to the implementation of distributed generation of renewable energy sources such as wind, solar, biomass, etc. The distributed generations are connected to the power grid in order to contribute to supplying energy for the loads. Thus the power flow direction and fault direction at the relays will be also changed. Therefore, using directional overcurrent protection relay is necessary to isolate the fault quickly and exactly. This paper proposes a novel method based on linear adaptive neural network which is used in directional overcurrent protection relay. The proposed method has the advantages compared with the fast Fourier transform method in signal processing. It can estimate the amplitude and phase angle of voltage and current signals accuracy after each updated sample. In addition, the proposed method is verified on the distribution network with/without distributed generation which is modeled on Matlab/Simulink software. The simulation results show that the proposed method accurately detect the direction at the relay when the fault occurs at different locations on the network. 

International Review of Electrical Engineering (IREE), 2016

This paper proposes a method to monitor, detect and classify voltage disturbances including volta... more This paper proposes a method to monitor, detect and classify voltage disturbances including voltage sag, voltage swell, voltage interruption, and long duration voltage variations. The detail coefficient in discrete wavelet transform is used to extract the start and end times of the voltage disturbance. The decomposed level of multi-resolution analysis in discrete wavelet transform is calculated according to the sampling frequency of the voltage signal for determining the approximation coefficient that only contains the fundamental frequency band. Then an adaptive linear neural network is used to estimate the voltage magnitude from the approximation coefficient. Finally, the disturbance will be classified into groups of voltage disturbances based on the characteristics according to the rules in IEEE Std. 1159-2009. The voltage waveforms based on theoretical signal models and actual voltage waveforms which recorded by power quality monitoring equipment are applied to evaluate the proposed method. The simulation results show that the proposed method can detect and classify voltage disturbances better than traditional methods based on root mean square and conventional adaptive linear neural network techniques.

2015 IEEE 11th International Conference on Power Electronics and Drive Systems, 2015

This paper presents a configuration and a control strategy for dynamic voltage restorer (DVR). In... more This paper presents a configuration and a control strategy for dynamic voltage restorer (DVR). In order to compensate the voltage of each phase separately, a closed-loop PI control law in the d-q reference frame is proposed. The proposed method provides a fast response and effective sag compensation capabilities. In addition, in order to detect voltage sag, a linear Kalman filter is employed to estimate three-phase voltages. By using Kalman filter, the voltage sag can be detected faster than other conventional methods. Therefore DVR can compensate voltage sag quickly and accurately. The obtained results that are simulated in Matlab/ Simulink indicate that the proposed method can mitigate the balanced and unbalanced voltage sag types efficiently in the distribution networks.

Vietnam Journal of Mechanics, 2012

A new C 1 rectangular element is proposed and the finite element formulation based on Reddy's hig... more A new C 1 rectangular element is proposed and the finite element formulation based on Reddy's higher-order shear deformation plate theory is developed. Although the plate theory is quite attractive but it could not be exploited as expected in finite-element analysis. This is due to the dificulties associated with satisfaction of inter-elemental continuity requirement and satisfy zero shear stress boundary conditions of the plate theory. In this paper, the proposed element is developed where Reddy's plate theory is successfully implemented. It has nine nodes and each node contains 7 degrees of freedom. The performance of the element is tested with different numerical examples, which show its precision and range of applicability.