Fast Envelope Estimation Technique for Monitoring Voltage Fluctuations

Marei, Mostafa I.,Shatshat, Ramadan El The Korean Institute of Electrical Engineers 2007 Journal of Electrical Engineering & Technology Vol.2 No.4

Voltage quality problems such as voltage sag, swell, flicker, undervoltage, and overvoltage have been of great concern for both utilities and customers over the last decade. In this paper, a new approach based on the $H_{\infty}$ algorithm to monitor voltage disturbances is presented. The key idea of this approach is to estimate the amplitude of the fundamental component of distorted and noisy voltage waveform instantaneously, and then the information can be extracted from the estimated envelope to identify and classify different voltage related power quality problems. The $H_{\infty}$ algorithm is characterized by a fast tracking, unlike that of existing techniques. The $H_{\infty}$ algorithm outperforms the Kalman Filter (KF) by its fast convergence and robust tracking performance against non-Gaussian noise. The paper investigates the effects of various types of noise on the performance of the $H_{\infty}$ algorithm. Digital simulation results confirm the validity and accuracy of the proposed method. The proposed $H_{\infty}$ algorithm is examined by tracking the flicker produced by a resistance welder simulated in the PSCAD/EMTDC package.

Fast Envelope Estimation Technique for Monitoring Voltage Fluctuations

Mostafa I. Marei,Ramadan El Shatshat 대한전기학회 2007 Journal of Electrical Engineering & Technology Vol.2 No.4

Voltage quality problems such as voltage sag, swell, flicker, undervoltage, and overvoltage have been of great concern for both utilities and customers over the last decade. In this paper, a new approach based on the H∞ algorithm to monitor voltage disturbances is presented. The key idea of this approach is to estimate the amplitude of the fundamental component of distorted and noisy voltage waveform instantaneously, and then the information can be extracted from the estimated envelope to identify and classify different voltage related power quality problems. The H∞ algorithm is characterized by a fast tracking, unlike that of existing techniques. The H∞ algorithm outperforms the Kalman Filter (KF) by its fast convergence and robust tracking performance against non-Gaussian noise. The paper investigates the effects of various types of noise on the performance of the H∞ algorithm. Digital simulation results confirm the validity and accuracy of the proposed method. The proposed H∞ algorithm is examined by tracking the flicker produced by a resistance welder simulated in the PSCAD/EMTDC package.

A Fault Tolerant Control Technique for Hybrid Modular Multi-Level Converters with Fault Detection Capability

Abdelsalam, Mahmoud,Marei, Mostafa Ibrahim,Diab, Hatem Yassin,Tennakoon, Sarath B. The Korean Institute of Power Electronics 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.2

In addition to its modular nature, a Hybrid Modular Multilevel Converter (HMMC) assembled from half-bridge and full-bridge sub-modules, is able to block DC faults with a minimum number of switching devices, which makes it attractive for high power applications. This paper introduces a control strategy based on the Root-Least Square (RLS) algorithm to estimate the capacitor voltages instead of using direct measurements. This action eliminates the need for voltage transducers in the HMMC sub-modules and the associated communication link with the central controller. In addition to capacitor voltage balancing and suppression of circulating currents, a fault tolerant control unit (FTCU) is integrated into the proposed strategy to modify the parameters of the HMMC controller. On advantage of the proposed FTCU is that it does not need extra components. Furthermore, a fault detection unit is adapted by utilizing a hybrid estimation scheme to detect sub-module faults. The behavior of the suggested technique is assessed using PSCAD offline simulations. In addition, it is validated using a real-time digital simulator connected to a real time controller under various normal and fault conditions. The proposed strategy shows robust performance in terms of accuracy and time response since it succeeds in stabilizing the HMMC under faults.

New Soft Rough Set Approximations

Shawkat Alkhazaleh,Emad A. Marei 한국지능시스템학회 2021 INTERNATIONAL JOURNAL of FUZZY LOGIC and INTELLIGE Vol.21 No.2

The soft rough set model was introduced by Fing in 2011 and can be considered as a generalized rough set model, in which an interesting connection was established between two mathematical approaches to vagueness: rough sets and soft sets. It was also shown that Pawlak’s rough set model can be viewed as a special case of soft rough sets. There are two problems with this model in using this concept in real-life applications. The first problem is that some soft rough sets are not contained in their upper approximations, which contradicts Pawlak’s thoughts. The second problem is that the boundary region of any considered set, in the soft rough set model, must be decreased to make it possible to take a true decision of any application problem. In this study, the soft rough set model is modified to solve these problems. The basic properties of the modified approximations are introduced and supported with propositions and illustrative examples. Modified concepts can be viewed as a general mathematical model for qualitative and quantitative real-life problems. A comparison between the suggested approach to soft rough sets and the traditional soft rough set model is provided.

A Fault Tolerant Control Technique for Hybrid Modular Multi-Level Converters with Fault Detection Capability

Mahmoud Abdelsalam,Mostafa Ibrahim Marei,Hatem Yassin Diab,Sarath B. Tennakoon 전력전자학회 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.2

In addition to its modular nature, a Hybrid Modular Multilevel Converter (HMMC) assembled from half-bridge and full-bridge sub-modules, is able to block DC faults with a minimum number of switching devices, which makes it attractive for high power applications. This paper introduces a control strategy based on the Root-Least Square (RLS) algorithm to estimate the capacitor voltages instead of using direct measurements. This action eliminates the need for voltage transducers in the HMMC sub-modules and the associated communication link with the central controller. In addition to capacitor voltage balancing and suppression of circulating currents, a fault tolerant control unit (FTCU) is integrated into the proposed strategy to modify the parameters of the HMMC controller. On advantage of the proposed FTCU is that it does not need extra components. Furthermore, a fault detection unit is adapted by utilizing a hybrid estimation scheme to detect sub-module faults. The behavior of the suggested technique is assessed using PSCAD offline simulations. In addition, it is validated using a real-time digital simulator connected to a real time controller under various normal and fault conditions. The proposed strategy shows robust performance in terms of accuracy and time response since it succeeds in stabilizing the HMMC under faults.

The Predictive Value of Enhanced Liver Fibrosis (ELF) Score for the Patient with Hepatocellular Carcinoma after Liver Resection

( Munseok Choi ),( Alshandder Marei Hussein ),( Dai Hoon Han ),( Gi Hong Choi ),( Jin Sub Choi ) 대한간학회 2021 춘·추계 학술대회 (KASL) Vol.2021 No.1

The predictive value of enhanced liver fibrosis (ELF) score for the patient with hepatocellular carcinoma after liver resection

Munseok CHOI,Alshandeer Marei HUSSAIN,Dai Hoon HAN,Gi Hong CHOI,Jin Sub CHOI 한국간담췌외과학회 2021 Annals of hepato-biliary-pancreatic surgery Vol.25 No.-

Reduced Switch Count Topology of Current Flow Control Apparatus for MTDC Grids

Diab, Hatem Yassin,Marei, Mostafa Ibrahim,Tennakoon, Sarath B. The Korean Institute of Power Electronics 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.5

The increasing demand for high voltage DC grids resulting from the continuous installation of offshore wind farms in the North Sea has led to the concept of multi-terminal direct current (MTDC) grids, which face some challenges. Power (current) flow control is a challenge that must be addressed to realize a reliable operation of MTDC grids. This paper presents a reduced switch count topology of a current flow controller (CFC) for power flow and current limiting applications in MTDC grids. A simple control system based on hysteresis band current control is proposed for the CFC. The theory of operation and control of the CFC are demonstrated. The key features of the proposed controller, including cable current balancing, cable current limiting, and current nulling, are illustrated. An MTDC grid is simulated using MATLAB/SIMULINK software to evaluate the steady state and dynamic performance of the proposed CFC topology. Furthermore, a low power prototype is built for a CFC to experimentally validate its performance using rapid control prototyping. Simulation and experimental studies indicate the fast dynamic response and precise results of the proposed topology. Furthermore, the proposed controller offers a real solution for power flow challenges in MTDC grids.

Modeling of a Four-Quadrant Switched Reluctance Motor Drive on EMTDC/PSCAD

El-Samahy, Ismael,Marei, Mostafa I.,El-Saadany, Ehab F. The Korean Institute of Electrical Engineers 2008 Journal of Electrical Engineering & Technology Vol.3 No.1

This paper introduces a complete package for SRM drive on Power System Computer-Aided Design/Electromagnetic Transients (PSCAD/EMTDC). A three-phase SRM drive is modeled and simulated on PSCAD. The motor is modeled using an accurate nonlinear analytical model that takes into consideration the machine nonlinearities. A current control algorithm is applied for torque ripple minimization to achieve a smooth output torque which is necessary for high performance applications. The motor drive is tested for four-quadrant operations. The modeled SRM is capable of operating as a motor or generator during clockwise and counterclockwise motions. The proposed package helps in understanding the operational principles of switched reluctance motors, investigating the dynamic characteristics of SRM drives, and achieving a high performance dynamic control task.

Reduced Switch Count Topology of Current Flow Control Apparatus for MTDC Grids

Hatem Yassin Diab,Mostafa Ibrahim Marei,Sarath B. Tennakoon 전력전자학회 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.5

The increasing demand for high voltage DC grids resulting from the continuous installation of offshore wind farms in the North Sea has led to the concept of multi-terminal direct current (MTDC) grids, which face some challenges. Power (current) flow control is a challenge that must be addressed to realize a reliable operation of MTDC grids. This paper presents a reduced switch count topology of a current flow controller (CFC) for power flow and current limiting applications in MTDC grids. A simple control system based on hysteresis band current control is proposed for the CFC. The theory of operation and control of the CFC are demonstrated. The key features of the proposed controller, including cable current balancing, cable current limiting, and current nulling, are illustrated. An MTDC grid is simulated using MATLAB/SIMULINK software to evaluate the steady state and dynamic performance of the proposed CFC topology. Furthermore, a low power prototype is built for a CFC to experimentally validate its performance using rapid control prototyping. Simulation and experimental studies indicate the fast dynamic response and precise results of the proposed topology. Furthermore, the proposed controller offers a real solution for power flow challenges in MTDC grids.