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Mohsen Akbari

K.N.Toosi University of Technology, Electrical Engineering, Alumnus

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Mohsen Akbari received his Ph.D. degree in power electronics engineering from K. N. Toosi University of Technology, Tehran, Iran. Also, from 2017 to 2018 (about 1 year), he was a visiting Ph.D. researcher with the Department of Energy Technology at Aalborg University, Aalborg, Denmark. His current research interests include multiphysics modeling, thermal management, packaging, and reliability of power semiconductor devices.
Supervisors: Mohammad Tavakoli Bina, Francesco Iannuzzzo, Masoud Aliakbar Golkar, Seyed Masoud Moghaddas Tafreshi, and Reza Shariatinasab
Phone: +989045140407
Address: Tehran, Iran

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Papers by Mohsen Akbari

Failure Modes and Effects Analysis ( FMEA ) for Power Transformers

The Failure Modes and Effects Analysis (FMEA) technique has been shown to be an effective way of ... more The Failure Modes and Effects Analysis (FMEA) technique has been shown to be an effective way of improving reliability, increasingly using in different fields of power grids. Due to the economic value and importance of the power transformers in a power grid, FMEA technique is proposed and studied for them in this paper. The output of this analysis could be graphical charts and matrices to sort the most critical components, failure modes and causes. This sorting will contribute to identify and take the most effective maintenance actions. Also, another output (this table output is a traditional output in FMEA) which is a worksheet lists common failure modes together with their failure causes, failure effects and a common index used to measure failure seriousness, usually risk priority number (RPN). Also, in this table the corrective actions should be proposed to reduce failures RPN. Keywords—power transformer; FMEA; failure mode; failure cause; failure effect; corrective action; risk ...

Enhancement of Thermo-mechanical Behavior of IGBT Modules through Engineered Threshold Voltages

In this paper, a purposely-imbalanced current density distribution in insulated-gate bipolar tran... more In this paper, a purposely-imbalanced current density distribution in insulated-gate bipolar transistor (IGBT) chips is introduced to reduce the surface temperature inhomogeneity of standard chips technology. The idea is implemented by modifying the gate threshold voltage across the active chip area, to counteract the uneven temperature distribution of a standard IGBT chip. Coupled thermomechanical analysis realized by finite element method (FEM) is used for validating the engineered IGBT chip via comparing different layouts.

Non-uniform Temperature Distribution Implications on Thermal Analysis Accuracy of Si IGBTs and SiC MOSFETs

2018 24rd International Workshop on Thermal Investigations of ICs and Systems (THERMINIC), Sep 1, 2018

Being the power loss and temperature distribution in power-electronics semiconductor dies influen... more Being the power loss and temperature distribution in power-electronics semiconductor dies influenced by one another, this paper demonstrates that neglecting such an effect can result in significant errors in electro-thermal simulations and mistaken calculation of junction temperatures. Two case studies on different semiconductor technologies, namely Silicon Insulated-Gate Bipolar Transistors (IGBTs) and Silicon Carbide Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs), are presented to corroborate the paper findings. Resultant temperature distributions are obtained by a proposed flowchart, which accepts the corresponding power dissipation input from MATLAB environment and employs a finite element based analysis implemented in COMSOL Multiphysics environment.

Thermal modeling of wire-bonded power modules considering non-uniform temperature and electric current interactions

Microelectronics Reliability, 2018

To assess power devices' reliability, it is crucial to have a relatively accurate thermal approac... more To assess power devices' reliability, it is crucial to have a relatively accurate thermal approach which provides valid temperature estimates. In this paper, for two commonly used Si IGBT and SiC MOSFET power modules, the electric current-induced effects on bond wires and the correlation between the non-uniform temperature distribution and electrical conductivity of the sensitive constituent materials are studied. In addition, a more realistic active area of the modules is defined by excluding inactive regions, i.e., the gate area, gate runners, and termination ring. Also, the electric current distribution among parallel bond wires attached to the dies' metalization pads is investigated. Comparisons made between an approach which includes all the above aspects with a conventional one where uniform heat is injected into semiconductor dies, although showing acceptable error in Si IGBTs, result in a very significant difference in SiC MOSFETs.

Model Predictive Control of STATCOM for Grid Voltage Regulation

Renewable Energy and Power Quality Journal, 2017

In this paper, a predictive control method known as FS-MPC is raised to adjust the grid voltage b... more In this paper, a predictive control method known as FS-MPC is raised to adjust the grid voltage by STATCOM. The FS-MPC control strategy is easy to implement that considers nonlinearities and limitations as well. In this way, the system model is used to predict the current behavior in the next sampling period for each possible switching mode. The STATCOM is simulated using the FS-MPC control method by MATLAB SIMULINK, and compared to conventional PI-controller accompanied with the PWM. The results of simulations represent considerable improvement in the performance of the FS-MPC control method for adjusting the grid voltage variations.

Controller designing to improve the voltage and frequency stability of a hybrid AC/DC micro-grid

22nd International Conference and Exhibition on Electricity Distribution (CIRED 2013), 2013

In this paper, the voltage and frequency control of a proposed hybrid AC/DC Micro-Grid is studied... more In this paper, the voltage and frequency control of a proposed hybrid AC/DC Micro-Grid is studied. The main objective of this study is to develop the PI, self-tuning fuzzy and wavelet controllers and compare their performances through the study of the voltage and frequency control of the Micro-Grid under disturbances. First, only PI controllers based Micro-Grid is analyzed by MatLab/Simulink during the load and generation uncertainties to show their good control performances. Then, self-tuning fuzzy controllers are follow to show a superior robustness and efficiency compared to the PI controllers during the islanding event. Finally, the wavelet controllers are studied to show and verify a much more ability, precision and robustness than the PI and even the fuzzy controllers to quickly restore and stabilize the Micro-Grid during events such as the islanding.

Wavelet-Based Multi-Resolution Voltage Controller in a Hybrid AC/DC Microgrid

In this paper, a hybrid AC/DCmicrogrid is studied. Furthermore, different control strategies are ... more In this paper, a hybrid AC/DCmicrogrid is studied. Furthermore, different control strategies are defined for most of converters in the islanded and grid-connected modes of microgrid to control the voltage of the DC and AC buses. To have a stable operation, converters controller is also coordinated. The main objective of this paper is to design a wavelet-based multi-resolution PI (MRPI) controller for the voltage control of the hybrid microgrid under large disturbances of the study system. The proposed controller is based on the discrete wavelet transform (DWT) of the error signal between actual and command voltages. Results will show more accurate performance of MRPI controller than the conventional PI controller. Streszczenie. W niniejszej pracy, badana jest hybrydowa sieć AC/DC microgrid. Głównym celem niniejszej pracy jest zaprojektowanie falkowej metody sterowania opartej na wielorozdzielczym sterowniku PID (MRPID) sterujący m siecią microgrid w obecności zaburzeń układu i niepewności. Proponowany sterownik bazuje na dyskretnej transformaty falkowej (DWT) sygnału błędu pomiędzy napięciem rzeczywistym a żądanym. Wyniki wykazały dokładniejsze sterowanie kontrolera MRPID w porównaniu z konwencjonalnym regulatorem PI. (Sterowanie napięciem w sieci microgrid z wykorzystaniem transformaty falkowej)

An Extended Multilayer Thermal Model for Multichip IGBT Modules Considering Thermal Aging

IEEE Access, 2021

An accurate and real-time knowledge of temperatures in insulated-gate bipolar transistor modules ... more An accurate and real-time knowledge of temperatures in insulated-gate bipolar transistor modules is crucial for reliability analysis and thermal management of power electronic converters. For this purpose, this paper establishes an integrated thermal equivalent circuit model comprising self-heating thermal impedances and cross-heating thermal impedances to provide a temperature profile of the junction and solder joints during various operations and in the case of thermal aging. The thermal resistance and capacitance parameters of the thermal impedances are characterized in terms of different electro-thermal operating conditions and solder joints aging conditions with the help of three-dimensional finite element simulations. Also, the effect of the heatsink, which brings an uneven heat transfer coefficient distribution at the module baseplate, is investigated and modeled into the thermal impedances. The introduced thermal model can work even if the conditions change simultaneously. The accuracy of the model is verified by experiments and finite element simulations, all of which agree with negligible error unlike thermal models given in the datasheet and fixed-parameter thermal models.

Harmonic Analysis of Power Systems in Order to Network Conversion

International Review on Modelling and Simulations (IREMOS), 2011

Conversion of 3-phase single-circuit (3PSC) to 3-phase double-circuit (3PDC) and 6-phase single-c... more Conversion of 3-phase single-circuit (3PSC) to 3-phase double-circuit (3PDC) and 6-phase single-circuit (6PSC) transmission line is a well known method to increase the power transfer capability of the network. The constraints using to decide on conversion type are usually network total loss and desirable voltage limits; while the harmonic effects are omitted. However, harmonics lead to undesirable power quality and increase total loss of the network. Thereby, in order to obtain the accurate result to adopt an optimal scheme for network conversion, harmonics should also be considered. In this paper a harmonic analysis due to the conversion of 3PSC to 3PDC and 6PSC network is performed. The analysis is applied to a real study system by conversion of the entire and just one of the existing lines of the network, separately. The results show that, when harmonic effects are considered or omitted, the criteria needed to make a decision on the options existed for network conversion could change. Due to the obtained results, telephone influence factor (TIF) of currents and total harmonic distortion (THD) of voltages are dependent on conversion type together with the harmonic sources of the network. However, in 6PSC conversion compared to 3PDC conversion type, the number of resonances is increased and propagation of high frequency disturbances is decreased.

A Multi-Layer RC Thermal Model for Power Modules Adaptable to Different Operating Conditions and Aging

2018 20th European Conference on Power Electronics and Applications (EPE'18 ECCE Europe), 2018

Semiconductor devices are often the most vulnerable components of power electronics converters am... more Semiconductor devices are often the most vulnerable components of power electronics converters among which thermal failures are the most likely ones. Thus, more accurate but straightforward thermal models are needed to efficiently do actions such as lifetime prediction, thermal management, etc. This paper presents a Foster-type equivalent transient thermal model developed through finite element simulations for a commercial Si IGBT power module. Such thermal models can easily merge into circuit simulation programs and even can be employed as real-time temperature estimators. However, fixed thermal models may give large errors in different operating conditions. In addition, they become unable to satisfactorily estimate temperatures over time, because of the thermal aging phenomenon. Thus, in this study, the thermal model of the power module is developed to be adapted to different boundary conditions-ambient temperature, and cooling system-as well as thermal aging of solder joints, whi...

A novel wavelet-neural network method for fault location analysis on transmission lines

2012 16th IEEE Mediterranean Electrotechnical Conference, 2012

This paper presents a technique, based on discrete wavelet transform (DWT) and back-propagation n... more This paper presents a technique, based on discrete wavelet transform (DWT) and back-propagation neural network (BPNN), to find the fault location on single circuit transmission lines. The proposed method has been applied to IEEE 9-bus test system. In order to go through this, MATLAB was used to apply DWT on the signal of fault currents of all the existed generators. The Daubechies Four (db4) mother wavelet is employed to decompose the high-frequency component of fault signals. The norm of detail coefficients of five decomposition levels for all fault current signals was selected as input pattern for the training process of a BPNN. The obtained results show that trained BPNN can be used as a proper tool to detect the location as well as the type of the occurred faults on the system, with a reasonable accuracy.

An Extended Multilayer Thermal Model for Multichip IGBT Modules Considering Thermal Aging

IEEE Access, 2021

An accurate and real-time knowledge of temperatures in insulated-gate bipolar transistor modules ... more An accurate and real-time knowledge of temperatures in insulated-gate bipolar transistor modules is crucial for reliability analysis and thermal management of power electronic converters. For this purpose, this paper establishes an integrated thermal equivalent circuit model comprising self-heating thermal impedances and cross-heating thermal impedances to provide a temperature profile of the junction and solder joints during various operations and in the case of thermal aging. The thermal resistance and capacitance parameters of the thermal impedances are characterized in terms of different electro-thermal operating conditions and solder joints aging conditions with the help of three-dimensional finite element simulations. Also, the effect of the heatsink, which brings an uneven heat transfer coefficient distribution at the module baseplate, is investigated and modeled into the thermal impedances. The introduced thermal model can work even if the conditions change simultaneously. The accuracy of the model is verified by experiments and finite element simulations, all of which agree with negligible error unlike thermal models given in the datasheet and fixed-parameter thermal models.

Enhancement of Thermo-mechanical Behavior of IGBT Modules through Engineered Threshold Voltages

2019 21st European Conference on Power Electronics and Applications (EPE '19 ECCE Europe), 2019

In this paper, a purposely-imbalanced current density distribution in insulated-gate bipolar tran... more In this paper, a purposely-imbalanced current density distribution in insulated-gate bipolar transistor (IGBT) chips is introduced to reduce the surface temperature inhomogeneity of standard chips technology. The idea is implemented by modifying the gate threshold voltage across the active chip area, to counteract the uneven temperature distribution of a standard IGBT chip. Coupled thermomechanical analysis realized by finite element method (FEM) is used for validating the engineered IGBT chip via comparing different layouts.

Non-uniform Temperature Distribution Implications on Thermal Analysis Accuracy of Si IGBTs and SiC MOSFETs

24th International Workshop on Thermal Investigations of ICs and Systems (THERMINIC), 2018

Being the power loss and temperature distribution in power-electronics semiconductor dies influen... more Being the power loss and temperature distribution in power-electronics semiconductor dies influenced by one another, this paper demonstrates that neglecting such an effect can result in significant errors in electro-thermal simulations and mistaken calculation of junction temperatures. Two case studies on different semiconductor technologies, namely Silicon Insulated-Gate Bipolar Transistors (IGBTs) and Silicon Carbide Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs), are presented to corroborate the paper findings. Resultant temperature distributions are obtained by a proposed flowchart, which accepts the corresponding power dissipation input from MATLAB environment and employs a finite element based analysis implemented in COMSOL Multiphysics environment.

Thermal modeling of wire-bonded power modules considering non-uniform temperature and electric current interactions

Microelectronics Reliability, 2018

To assess power devices' reliability, it is crucial to have a relatively accurate thermal approac... more To assess power devices' reliability, it is crucial to have a relatively accurate thermal approach which provides valid temperature estimates. In this paper, a commercial Si IGBT and SiC MOSFET power modules are investigated. Also, the electric current-induced effects on bond wires and the correlation between the non-uniform temperature distribution and electrical conductivity of the sensitive constituent materials are studied. A more realistic active area of the die is defined by excluding inactive regions, i.e., the gate area, gate runners, and termination ring. Also, the electric current distribution among parallel bond wires attached to the dies' meta-lization pads is investigated. A comparison between an approach which includes all the above aspects with a conventional one where a thermal power with the same total value, but unifrom, is injected into the semiconductor dies is made, While an acceptable error is found for Si IGBTs, a very significant difference is observed in SiC MOSFETs.

A Multi-Layer RC Thermal Model for Power Modules Adaptable to Different Operating Conditions and Aging

20th European Conference on Power Electronics and Applications (EPE'18 ECCE Europe), 2018

Semiconductor devices are often the most vulnerable components of power electronics converters am... more Semiconductor devices are often the most vulnerable components of power electronics converters among which thermal failures are the most likely ones. Thus, more accurate but straightforward thermal models are needed to efficiently do actions such as lifetime prediction, thermal management, etc. This paper presents a Foster-type equivalent transient thermal model developed through finite element simulations for a commercial Si IGBT power module. Such thermal models can easily merge into circuit simulation programs and even can be employed as real-time temperature estimators. However, fixed thermal models may give large errors in different operating conditions. In addition, they become unable to satisfactorily estimate temperatures over time, because of the thermal aging phenomenon. Thus, in this study, the thermal model of the power module is developed to be adapted to different boundary conditions - ambient temperature, and cooling system – as well as thermal aging of solder joints, which is the most common failure in the power modules. Also, the thermal model features the effect of power loss, and the cross-coupling effect among nearby semiconductor dies. Comparisons with FEM verify the performance of the studied thermal model.

New Islanding Detection Technique for DG Using Discrete Wavelet Transform

IEEE International Conference on Power and Energy, 2011

Islanding phenomenon is a problem for Distributed Generator (DG) based networks leading to troubl... more Islanding phenomenon is a problem for Distributed Generator (DG) based networks leading to troubles in voltage and frequency control and other power quality issues. This paper describes the development of a method based on Discrete Wavelet Transform (DWT), in order to detect islanding for DGs. This method detects the islanding state only by evaluating the terminal current of DGs. Hence, different types of current signal in the case of fault occurrence, load and capacitor switching and motor starting have been investigated. In order to increase the accuracy of the wavelet analysis, the proposed algorithm is executed for each type of current signals using different types of mother wavelets, decomposition levels, length of data window and moving size of window to decide on the best assumption of each parameter. The results of the study show that the proposed method can detect the islanding state within a time less than one third of a cycle with a good accuracy.

Voltage Stability Analysis in Conversion of Double Three-Phase to Six-Phase Transmission Line

IEEE International Conference on Power and Energy, 2010

In recent years, problems regarding the voltage stability have been of vital importance at EHV an... more In recent years, problems regarding the voltage stability have been of vital importance at EHV and UHV level because of its sensitivity to active and reactive power changes. Beside, conversion of three-Phase Double-Circuit (3PDC) to six-Phase Single-Circuit (6PSC) line is known as a well method to increase the power transfer capability. The voltage stability problem has received little attention in case of 6PSC systems. In this paper, an investigation of voltage stability has been carried out in conversion of an existing 3PDC to a 6PSC transmission line considering conversion transformers reactance. The results show that by this conversion, improvement in power transfer capacity is gained for long 6PSC lines, but a 3PDC line has the better performs from reactive power view for voltage stability and the minimum line length at which the power transfer capability is limited by voltage stability concern is dramatically decreased in 6PSC line. Moreover, the reactance increase of conversion transformers worsens the aforementioned problems. A comparison of 3PDC and 6PSC systems presented in the paper and other economical and practical factors can be studied for planning, development and design of future transmission network.

Smart Grid in Iran: Driving Factors, Evolution, Challenges and Possible Solutions

10th International Conference on Environment and Electrical Engineering, 2011

Due to the remarkable development of technology and economy, the resilient power system is emergi... more Due to the remarkable development of technology and economy, the resilient power system is emerging as a key element which inevitably leads us towards the Smart Grid. This smart grid should be able to bring new abilities such as high reliability, self-healing, energy efficiency, price response, peak load reduction, and distribution automation. This paper gives a comprehensive comparison of the existing grid with the future grid and as a result, an overview of essential requirements for the implementation of a smart grid in Iran is obtained. The presses of establishing the smart grid in Iran together with analysis of its roadmap in this country are discussed later. The challenges concerning with the implementation of this concept along with their possible solutions are finally addressed in the power grid of Iran.

Feasibility and Impact of Using Six-Phase Line in a Specific Distribution and Sub-Transmission System

TENCON 2011 - 2011 IEEE Region 10 Conference, 2011

Power loss issue is one of the most significant issues encountered in electrical industry and it ... more Power loss issue is one of the most significant issues encountered in electrical industry and it is essential to note. System design is essentially to ensure that the increased electricity demand could be meeting by power system development, so that it becomes technically a suitable and economical system. Distribution system has a particular importance in electrification due to: 1) near perfectly to the consumers 2) high investment cost. On the other hand, about 67% of power grid loss is related to the distribution system. Beside, conversion of 3-Phase Double-Circuit (3PDC) to 6-Phase Single-Circuit (6PSC) line is known as a well method to increase the power transfer capability of existing ROWs. Thus, in this paper, an investigation of conversion of existing 3-Phase Single-Circuit (3PSC) lines to the 3PDC to 6PSC lines is studied and compared. It is found that with the same transmitted power in the 3PDC and 6PSC states, using the 6PSC line in suitable places of sub-transmission and distribution systems will dramatically result in decreased loss and improved voltage regulation. In all the cases, test power system is assumed as a balanced system.

Failure Modes and Effects Analysis ( FMEA ) for Power Transformers

The Failure Modes and Effects Analysis (FMEA) technique has been shown to be an effective way of ... more The Failure Modes and Effects Analysis (FMEA) technique has been shown to be an effective way of improving reliability, increasingly using in different fields of power grids. Due to the economic value and importance of the power transformers in a power grid, FMEA technique is proposed and studied for them in this paper. The output of this analysis could be graphical charts and matrices to sort the most critical components, failure modes and causes. This sorting will contribute to identify and take the most effective maintenance actions. Also, another output (this table output is a traditional output in FMEA) which is a worksheet lists common failure modes together with their failure causes, failure effects and a common index used to measure failure seriousness, usually risk priority number (RPN). Also, in this table the corrective actions should be proposed to reduce failures RPN. Keywords—power transformer; FMEA; failure mode; failure cause; failure effect; corrective action; risk ...

Enhancement of Thermo-mechanical Behavior of IGBT Modules through Engineered Threshold Voltages

In this paper, a purposely-imbalanced current density distribution in insulated-gate bipolar tran... more In this paper, a purposely-imbalanced current density distribution in insulated-gate bipolar transistor (IGBT) chips is introduced to reduce the surface temperature inhomogeneity of standard chips technology. The idea is implemented by modifying the gate threshold voltage across the active chip area, to counteract the uneven temperature distribution of a standard IGBT chip. Coupled thermomechanical analysis realized by finite element method (FEM) is used for validating the engineered IGBT chip via comparing different layouts.

Non-uniform Temperature Distribution Implications on Thermal Analysis Accuracy of Si IGBTs and SiC MOSFETs

2018 24rd International Workshop on Thermal Investigations of ICs and Systems (THERMINIC), Sep 1, 2018

Being the power loss and temperature distribution in power-electronics semiconductor dies influen... more Being the power loss and temperature distribution in power-electronics semiconductor dies influenced by one another, this paper demonstrates that neglecting such an effect can result in significant errors in electro-thermal simulations and mistaken calculation of junction temperatures. Two case studies on different semiconductor technologies, namely Silicon Insulated-Gate Bipolar Transistors (IGBTs) and Silicon Carbide Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs), are presented to corroborate the paper findings. Resultant temperature distributions are obtained by a proposed flowchart, which accepts the corresponding power dissipation input from MATLAB environment and employs a finite element based analysis implemented in COMSOL Multiphysics environment.

Thermal modeling of wire-bonded power modules considering non-uniform temperature and electric current interactions

Microelectronics Reliability, 2018

To assess power devices' reliability, it is crucial to have a relatively accurate thermal approac... more To assess power devices' reliability, it is crucial to have a relatively accurate thermal approach which provides valid temperature estimates. In this paper, for two commonly used Si IGBT and SiC MOSFET power modules, the electric current-induced effects on bond wires and the correlation between the non-uniform temperature distribution and electrical conductivity of the sensitive constituent materials are studied. In addition, a more realistic active area of the modules is defined by excluding inactive regions, i.e., the gate area, gate runners, and termination ring. Also, the electric current distribution among parallel bond wires attached to the dies' metalization pads is investigated. Comparisons made between an approach which includes all the above aspects with a conventional one where uniform heat is injected into semiconductor dies, although showing acceptable error in Si IGBTs, result in a very significant difference in SiC MOSFETs.

Model Predictive Control of STATCOM for Grid Voltage Regulation

Renewable Energy and Power Quality Journal, 2017

In this paper, a predictive control method known as FS-MPC is raised to adjust the grid voltage b... more In this paper, a predictive control method known as FS-MPC is raised to adjust the grid voltage by STATCOM. The FS-MPC control strategy is easy to implement that considers nonlinearities and limitations as well. In this way, the system model is used to predict the current behavior in the next sampling period for each possible switching mode. The STATCOM is simulated using the FS-MPC control method by MATLAB SIMULINK, and compared to conventional PI-controller accompanied with the PWM. The results of simulations represent considerable improvement in the performance of the FS-MPC control method for adjusting the grid voltage variations.

Controller designing to improve the voltage and frequency stability of a hybrid AC/DC micro-grid

22nd International Conference and Exhibition on Electricity Distribution (CIRED 2013), 2013

In this paper, the voltage and frequency control of a proposed hybrid AC/DC Micro-Grid is studied... more In this paper, the voltage and frequency control of a proposed hybrid AC/DC Micro-Grid is studied. The main objective of this study is to develop the PI, self-tuning fuzzy and wavelet controllers and compare their performances through the study of the voltage and frequency control of the Micro-Grid under disturbances. First, only PI controllers based Micro-Grid is analyzed by MatLab/Simulink during the load and generation uncertainties to show their good control performances. Then, self-tuning fuzzy controllers are follow to show a superior robustness and efficiency compared to the PI controllers during the islanding event. Finally, the wavelet controllers are studied to show and verify a much more ability, precision and robustness than the PI and even the fuzzy controllers to quickly restore and stabilize the Micro-Grid during events such as the islanding.

Wavelet-Based Multi-Resolution Voltage Controller in a Hybrid AC/DC Microgrid

In this paper, a hybrid AC/DCmicrogrid is studied. Furthermore, different control strategies are ... more In this paper, a hybrid AC/DCmicrogrid is studied. Furthermore, different control strategies are defined for most of converters in the islanded and grid-connected modes of microgrid to control the voltage of the DC and AC buses. To have a stable operation, converters controller is also coordinated. The main objective of this paper is to design a wavelet-based multi-resolution PI (MRPI) controller for the voltage control of the hybrid microgrid under large disturbances of the study system. The proposed controller is based on the discrete wavelet transform (DWT) of the error signal between actual and command voltages. Results will show more accurate performance of MRPI controller than the conventional PI controller. Streszczenie. W niniejszej pracy, badana jest hybrydowa sieć AC/DC microgrid. Głównym celem niniejszej pracy jest zaprojektowanie falkowej metody sterowania opartej na wielorozdzielczym sterowniku PID (MRPID) sterujący m siecią microgrid w obecności zaburzeń układu i niepewności. Proponowany sterownik bazuje na dyskretnej transformaty falkowej (DWT) sygnału błędu pomiędzy napięciem rzeczywistym a żądanym. Wyniki wykazały dokładniejsze sterowanie kontrolera MRPID w porównaniu z konwencjonalnym regulatorem PI. (Sterowanie napięciem w sieci microgrid z wykorzystaniem transformaty falkowej)

An Extended Multilayer Thermal Model for Multichip IGBT Modules Considering Thermal Aging

IEEE Access, 2021

An accurate and real-time knowledge of temperatures in insulated-gate bipolar transistor modules ... more An accurate and real-time knowledge of temperatures in insulated-gate bipolar transistor modules is crucial for reliability analysis and thermal management of power electronic converters. For this purpose, this paper establishes an integrated thermal equivalent circuit model comprising self-heating thermal impedances and cross-heating thermal impedances to provide a temperature profile of the junction and solder joints during various operations and in the case of thermal aging. The thermal resistance and capacitance parameters of the thermal impedances are characterized in terms of different electro-thermal operating conditions and solder joints aging conditions with the help of three-dimensional finite element simulations. Also, the effect of the heatsink, which brings an uneven heat transfer coefficient distribution at the module baseplate, is investigated and modeled into the thermal impedances. The introduced thermal model can work even if the conditions change simultaneously. The accuracy of the model is verified by experiments and finite element simulations, all of which agree with negligible error unlike thermal models given in the datasheet and fixed-parameter thermal models.

Harmonic Analysis of Power Systems in Order to Network Conversion

International Review on Modelling and Simulations (IREMOS), 2011

Conversion of 3-phase single-circuit (3PSC) to 3-phase double-circuit (3PDC) and 6-phase single-c... more Conversion of 3-phase single-circuit (3PSC) to 3-phase double-circuit (3PDC) and 6-phase single-circuit (6PSC) transmission line is a well known method to increase the power transfer capability of the network. The constraints using to decide on conversion type are usually network total loss and desirable voltage limits; while the harmonic effects are omitted. However, harmonics lead to undesirable power quality and increase total loss of the network. Thereby, in order to obtain the accurate result to adopt an optimal scheme for network conversion, harmonics should also be considered. In this paper a harmonic analysis due to the conversion of 3PSC to 3PDC and 6PSC network is performed. The analysis is applied to a real study system by conversion of the entire and just one of the existing lines of the network, separately. The results show that, when harmonic effects are considered or omitted, the criteria needed to make a decision on the options existed for network conversion could change. Due to the obtained results, telephone influence factor (TIF) of currents and total harmonic distortion (THD) of voltages are dependent on conversion type together with the harmonic sources of the network. However, in 6PSC conversion compared to 3PDC conversion type, the number of resonances is increased and propagation of high frequency disturbances is decreased.

A Multi-Layer RC Thermal Model for Power Modules Adaptable to Different Operating Conditions and Aging

2018 20th European Conference on Power Electronics and Applications (EPE'18 ECCE Europe), 2018

Semiconductor devices are often the most vulnerable components of power electronics converters am... more Semiconductor devices are often the most vulnerable components of power electronics converters among which thermal failures are the most likely ones. Thus, more accurate but straightforward thermal models are needed to efficiently do actions such as lifetime prediction, thermal management, etc. This paper presents a Foster-type equivalent transient thermal model developed through finite element simulations for a commercial Si IGBT power module. Such thermal models can easily merge into circuit simulation programs and even can be employed as real-time temperature estimators. However, fixed thermal models may give large errors in different operating conditions. In addition, they become unable to satisfactorily estimate temperatures over time, because of the thermal aging phenomenon. Thus, in this study, the thermal model of the power module is developed to be adapted to different boundary conditions-ambient temperature, and cooling system-as well as thermal aging of solder joints, whi...

A novel wavelet-neural network method for fault location analysis on transmission lines

2012 16th IEEE Mediterranean Electrotechnical Conference, 2012

This paper presents a technique, based on discrete wavelet transform (DWT) and back-propagation n... more This paper presents a technique, based on discrete wavelet transform (DWT) and back-propagation neural network (BPNN), to find the fault location on single circuit transmission lines. The proposed method has been applied to IEEE 9-bus test system. In order to go through this, MATLAB was used to apply DWT on the signal of fault currents of all the existed generators. The Daubechies Four (db4) mother wavelet is employed to decompose the high-frequency component of fault signals. The norm of detail coefficients of five decomposition levels for all fault current signals was selected as input pattern for the training process of a BPNN. The obtained results show that trained BPNN can be used as a proper tool to detect the location as well as the type of the occurred faults on the system, with a reasonable accuracy.

An Extended Multilayer Thermal Model for Multichip IGBT Modules Considering Thermal Aging

IEEE Access, 2021

An accurate and real-time knowledge of temperatures in insulated-gate bipolar transistor modules ... more An accurate and real-time knowledge of temperatures in insulated-gate bipolar transistor modules is crucial for reliability analysis and thermal management of power electronic converters. For this purpose, this paper establishes an integrated thermal equivalent circuit model comprising self-heating thermal impedances and cross-heating thermal impedances to provide a temperature profile of the junction and solder joints during various operations and in the case of thermal aging. The thermal resistance and capacitance parameters of the thermal impedances are characterized in terms of different electro-thermal operating conditions and solder joints aging conditions with the help of three-dimensional finite element simulations. Also, the effect of the heatsink, which brings an uneven heat transfer coefficient distribution at the module baseplate, is investigated and modeled into the thermal impedances. The introduced thermal model can work even if the conditions change simultaneously. The accuracy of the model is verified by experiments and finite element simulations, all of which agree with negligible error unlike thermal models given in the datasheet and fixed-parameter thermal models.

Enhancement of Thermo-mechanical Behavior of IGBT Modules through Engineered Threshold Voltages

2019 21st European Conference on Power Electronics and Applications (EPE '19 ECCE Europe), 2019

In this paper, a purposely-imbalanced current density distribution in insulated-gate bipolar tran... more In this paper, a purposely-imbalanced current density distribution in insulated-gate bipolar transistor (IGBT) chips is introduced to reduce the surface temperature inhomogeneity of standard chips technology. The idea is implemented by modifying the gate threshold voltage across the active chip area, to counteract the uneven temperature distribution of a standard IGBT chip. Coupled thermomechanical analysis realized by finite element method (FEM) is used for validating the engineered IGBT chip via comparing different layouts.

Non-uniform Temperature Distribution Implications on Thermal Analysis Accuracy of Si IGBTs and SiC MOSFETs

24th International Workshop on Thermal Investigations of ICs and Systems (THERMINIC), 2018

Being the power loss and temperature distribution in power-electronics semiconductor dies influen... more Being the power loss and temperature distribution in power-electronics semiconductor dies influenced by one another, this paper demonstrates that neglecting such an effect can result in significant errors in electro-thermal simulations and mistaken calculation of junction temperatures. Two case studies on different semiconductor technologies, namely Silicon Insulated-Gate Bipolar Transistors (IGBTs) and Silicon Carbide Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs), are presented to corroborate the paper findings. Resultant temperature distributions are obtained by a proposed flowchart, which accepts the corresponding power dissipation input from MATLAB environment and employs a finite element based analysis implemented in COMSOL Multiphysics environment.

Thermal modeling of wire-bonded power modules considering non-uniform temperature and electric current interactions

Microelectronics Reliability, 2018

To assess power devices' reliability, it is crucial to have a relatively accurate thermal approac... more To assess power devices' reliability, it is crucial to have a relatively accurate thermal approach which provides valid temperature estimates. In this paper, a commercial Si IGBT and SiC MOSFET power modules are investigated. Also, the electric current-induced effects on bond wires and the correlation between the non-uniform temperature distribution and electrical conductivity of the sensitive constituent materials are studied. A more realistic active area of the die is defined by excluding inactive regions, i.e., the gate area, gate runners, and termination ring. Also, the electric current distribution among parallel bond wires attached to the dies' meta-lization pads is investigated. A comparison between an approach which includes all the above aspects with a conventional one where a thermal power with the same total value, but unifrom, is injected into the semiconductor dies is made, While an acceptable error is found for Si IGBTs, a very significant difference is observed in SiC MOSFETs.

A Multi-Layer RC Thermal Model for Power Modules Adaptable to Different Operating Conditions and Aging

20th European Conference on Power Electronics and Applications (EPE'18 ECCE Europe), 2018

Semiconductor devices are often the most vulnerable components of power electronics converters am... more Semiconductor devices are often the most vulnerable components of power electronics converters among which thermal failures are the most likely ones. Thus, more accurate but straightforward thermal models are needed to efficiently do actions such as lifetime prediction, thermal management, etc. This paper presents a Foster-type equivalent transient thermal model developed through finite element simulations for a commercial Si IGBT power module. Such thermal models can easily merge into circuit simulation programs and even can be employed as real-time temperature estimators. However, fixed thermal models may give large errors in different operating conditions. In addition, they become unable to satisfactorily estimate temperatures over time, because of the thermal aging phenomenon. Thus, in this study, the thermal model of the power module is developed to be adapted to different boundary conditions - ambient temperature, and cooling system – as well as thermal aging of solder joints, which is the most common failure in the power modules. Also, the thermal model features the effect of power loss, and the cross-coupling effect among nearby semiconductor dies. Comparisons with FEM verify the performance of the studied thermal model.

New Islanding Detection Technique for DG Using Discrete Wavelet Transform

IEEE International Conference on Power and Energy, 2011

Islanding phenomenon is a problem for Distributed Generator (DG) based networks leading to troubl... more Islanding phenomenon is a problem for Distributed Generator (DG) based networks leading to troubles in voltage and frequency control and other power quality issues. This paper describes the development of a method based on Discrete Wavelet Transform (DWT), in order to detect islanding for DGs. This method detects the islanding state only by evaluating the terminal current of DGs. Hence, different types of current signal in the case of fault occurrence, load and capacitor switching and motor starting have been investigated. In order to increase the accuracy of the wavelet analysis, the proposed algorithm is executed for each type of current signals using different types of mother wavelets, decomposition levels, length of data window and moving size of window to decide on the best assumption of each parameter. The results of the study show that the proposed method can detect the islanding state within a time less than one third of a cycle with a good accuracy.

Voltage Stability Analysis in Conversion of Double Three-Phase to Six-Phase Transmission Line

IEEE International Conference on Power and Energy, 2010

In recent years, problems regarding the voltage stability have been of vital importance at EHV an... more In recent years, problems regarding the voltage stability have been of vital importance at EHV and UHV level because of its sensitivity to active and reactive power changes. Beside, conversion of three-Phase Double-Circuit (3PDC) to six-Phase Single-Circuit (6PSC) line is known as a well method to increase the power transfer capability. The voltage stability problem has received little attention in case of 6PSC systems. In this paper, an investigation of voltage stability has been carried out in conversion of an existing 3PDC to a 6PSC transmission line considering conversion transformers reactance. The results show that by this conversion, improvement in power transfer capacity is gained for long 6PSC lines, but a 3PDC line has the better performs from reactive power view for voltage stability and the minimum line length at which the power transfer capability is limited by voltage stability concern is dramatically decreased in 6PSC line. Moreover, the reactance increase of conversion transformers worsens the aforementioned problems. A comparison of 3PDC and 6PSC systems presented in the paper and other economical and practical factors can be studied for planning, development and design of future transmission network.

Smart Grid in Iran: Driving Factors, Evolution, Challenges and Possible Solutions

10th International Conference on Environment and Electrical Engineering, 2011

Due to the remarkable development of technology and economy, the resilient power system is emergi... more Due to the remarkable development of technology and economy, the resilient power system is emerging as a key element which inevitably leads us towards the Smart Grid. This smart grid should be able to bring new abilities such as high reliability, self-healing, energy efficiency, price response, peak load reduction, and distribution automation. This paper gives a comprehensive comparison of the existing grid with the future grid and as a result, an overview of essential requirements for the implementation of a smart grid in Iran is obtained. The presses of establishing the smart grid in Iran together with analysis of its roadmap in this country are discussed later. The challenges concerning with the implementation of this concept along with their possible solutions are finally addressed in the power grid of Iran.

Feasibility and Impact of Using Six-Phase Line in a Specific Distribution and Sub-Transmission System

TENCON 2011 - 2011 IEEE Region 10 Conference, 2011

Power loss issue is one of the most significant issues encountered in electrical industry and it ... more Power loss issue is one of the most significant issues encountered in electrical industry and it is essential to note. System design is essentially to ensure that the increased electricity demand could be meeting by power system development, so that it becomes technically a suitable and economical system. Distribution system has a particular importance in electrification due to: 1) near perfectly to the consumers 2) high investment cost. On the other hand, about 67% of power grid loss is related to the distribution system. Beside, conversion of 3-Phase Double-Circuit (3PDC) to 6-Phase Single-Circuit (6PSC) line is known as a well method to increase the power transfer capability of existing ROWs. Thus, in this paper, an investigation of conversion of existing 3-Phase Single-Circuit (3PSC) lines to the 3PDC to 6PSC lines is studied and compared. It is found that with the same transmitted power in the 3PDC and 6PSC states, using the 6PSC line in suitable places of sub-transmission and distribution systems will dramatically result in decreased loss and improved voltage regulation. In all the cases, test power system is assumed as a balanced system.