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.

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.

Impact of COVID-19 Pandemic on Graduates Seeking Jobs

El-Boghdadi, Hatem M.,Noor, Fazal,Mahmoud, Mostafa International Journal of Computer ScienceNetwork S 2021 International journal of computer science and netw Vol.21 No.1

The appearance of COVID-19 virus has affected many aspects of our life. These include and not limited to social, financial and economic changes. One of the most important impacts is the economic effects. Many countries have taken actions to continue the teaching process through online teaching platforms. The students are expected to graduate during the next few semesters with certificates that include some online-completed courses and their graduation certificates are called mixed certificates. This paper considers graduation mixed certificates with some online courses and its impact on graduates seeking jobs. First, we study how well the mixed certificates are accepted by job market. In other words, how different companies, organizations and even governmental entities would accept such certificates when hiring. We study the perception of job market for such certificates for different learning fields. Secondly, we study how well the online courses are accepted by the students keeping in mind that these students are used to traditional face to face teaching. Finally, we paper our results and recommendations according to the collected data from the surveys. Some of the results show that about 60% of companies don't have policies to encourage hiring graduates with mixed certificates. Also, colleges are almost divided evenly between preferring face to face and preferring online teaching.

Progressive Collapse Assessment of Multistory Reinforced Concrete Structures Subjected To Seismic Actions

Ahmed Elshaer,Hatem Mostafa,Hamed Salem 대한토목학회 2017 KSCE JOURNAL OF CIVIL ENGINEERING Vol.21 No.1

Progressive collapse is a catastrophic partial or total failure of a structure that mostly occurs when a structure loses a primary component like a column. Some international standards have started to consider progressive collapse resistance in various approaches. In this study, the ‘Unified Facilities Criterion’ guidelines were used in assessing the structure; these guidelines represent one of the codes that discuss progressive collapse using sophisticated approaches. Three-dimensional nonlinear dynamic analyses using the ‘Applied Element Method’ were performed for a structure that lost a column during a seismic action. A parametric study was made to investigate the effect of different parameters on progressive collapse. In this study, a primary structural component was assumed lost during an earthquake. The studied parameters were the location of the removed column in plan, the level of the removed column, the case of loading, and the consideration of the slabs. For the study cases, it was concluded that the buildings designed according to the Egyptian code satisfies the progressive collapse requirements stated by ‘Unified Facilities Criteria’ (UFC) guidelines requirements with a safety factor of 1.97. Also, it was found that losing a column during a seismic action is more critical for progressive collapse than under gravity load. Finally, this study elaborated the importance of considering the slab in progressive collapse analysis of multistory buildings in order to include the significant catenary action developed by the slabs.

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.

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.