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Improvement of Inverter-based AC Microgrids Protection Against Short Circuit
, Ph.D. Dissertation Sharif University of Technology ; Mokhtari, Hossein (Supervisor) ; Blaabjerg, Frede (Co-Supervisor)
Abstract
Inverter-based distributed generations (IBDGs) have gained special interest in the electricity supply chain due to the advancements in power electronics technology. Power electronic inverters provide high-efficiency energy conversion with full controllability over a wide operating range, and ancillary services such as reactive power support and active filtering. Considering the voltage and frequency control capability of power inverters, supplying inverter-based micro-grid (IBMG) loads is now pissible. Despite the significant opportunities associated with such sources, they introduce new challenges that should be addressed properly. Reliable and accurate protection against short circuit...
Decentrilized Power Management in AC-DC Hybrid Microgirds
, Ph.D. Dissertation Sharif University of Technology ; Mokhtari, Hossein (Supervisor) ; Blaabjerg, Frede (Co-Advisor)
Abstract
Proliferation of Distributed Generations (DGs) introduces higher reliability, stability, and quality as well as lower power losses and operational costs to the power systems. Integrating smart-grid and microgrid technologies to the power systems will further improve the overall performance of the system. Moreover, DC microgrids create an infrastructure to supply DC loads by DC sources such as photovoltaic arrays, fuel cell modules, as well as storages, which in case, increases the energy conversion efficiency. Operating DC microgrids together with AC microgrids, therefore, will form a new distrib-ution system called hybrid AC/DC systems, in which the DC side is dynamically decoupled from the...
Improving Power Management System in All-Electric Ships
, Ph.D. Dissertation Sharif University of Technology ; Parniani, Mostafa (Supervisor) ; Blaabjerg, Frede (Co-Supervisor)
Abstract
Development of the electric propulsion system and its applications in all-electric ships (AES) has made proper operating approaches for their power system more essential than ever. The proposed solutions should lower the design cost, operation cost, and greenhouse gas emission while increasing the reliability and power quality of the vessel. Because of abrupt changes in propellers consumption power, it is critical to consider the hydrodynamic phenomena and examine the propulsion system torque variations in the power management system at the design stage.In this dissertation, considering the importance of evaluating the operation methods in different operating conditions, such as sea waves or...
Hierarchical power sharing control in DC microgrids
, Article Microgrid: Advanced Control Methods and Renewable Energy System Integration ; 2016 , Pages 63-100 ; 9780081012628 (ISBN) ; Mokhtari, H ; Blaabjerg, F ; Sharif University of Technology
Elsevier Inc
2016
Abstract
Because of the advances in power electronics, DC-based power systems, have been used in industrial applications such as data centers [. 18], space applications [. 10], aircraft [. 12], offshore wind farms, electric vehicles [. 56], DC home systems [. 5, 20], and high-voltage DC transmission systems. To provide such sensitive loads with more reliability, efficiency, and controllability for future power systems, AC microgrid and more recently DC microgrid and smart-grid technologies have been employed [. 5-9].To obtain stable and optimal operation in DC power systems (microgrids), proper load sharing among different energy units and acceptable voltage regulation across the microgrid is...
Autonomous power management in LVDC microgrids based on a superimposed frequency droop
, Article IEEE Transactions on Power Electronics ; 2017 ; 08858993 (ISSN) ; Mokhtari, H ; Blaabjerg, F ; Sharif University of Technology
2017
Abstract
In this paper a novel droop approach for autonomous power management in low voltage dc microgrids based on a master-slave concept is presented. Conventional voltage-based droop approaches suffer from poor power sharing due to line resistance effects on a virtual resistance, which is solved a by introducing a communication system to increase the current sharing accuracy. In this paper, a virtual frequency is superimposed by the master units, and slave units determine their output power according to the corresponding frequency-based droop characteristics. Unlike the voltage-droop methods, the proposed virtual frequency-droop approach can be applied for proportional power management among the...
Autonomous power management in LVDC microgrids based on a superimposed frequency droop
, Article IEEE Transactions on Power Electronics ; Volume 33, Issue 6 , 2018 , Pages 5341-5350 ; 08858993 (ISSN) ; Mokhtari, H ; Blaabjerg, F ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2018
Abstract
In this paper, a novel droop approach for autonomous power management in low voltage DC (LVDC) microgrids based on a master-slave concept is presented. Conventional voltage-based droop approaches suffer from poor power sharing due to line resistance effects on a virtual resistance, which is solved by introducing a communication system to increase the current sharing accuracy. In this paper, a virtual frequency is superimposed by the master units, and slave units determine their output power according to the corresponding frequency-based droop characteristics. Unlike the voltage-droop methods, the proposed virtual frequency-droop approach can be applied for proportional power management among...
Autonomous operation of a hybrid AC/DC microgrid with multiple interlinking converters
, Article IEEE Transactions on Smart Grid ; Volume 9, Issue 6 , 2018 , Pages 6480-6488 ; 19493053 (ISSN) ; Mokhtari, H ; Blaabjerg, F ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2018
Abstract
Applying conventional dc-voltage-based droop approaches for hybrid ac/dc microgrids interconnected by a single interlinking converter (IC) can properly manage the power flow among ac and dc subgrids. However, due to the effect of line resistances, these approaches may create a circulating power as well as overstressing the ICs in the case of employing multiple ICs for interconnecting the ac and dc subgrids. This paper proposes an autonomous power sharing approach for hybrid microgrids interconnected through multiple ICs by introducing a superimposed frequency in the dc subgrid. Hence, a suitable droop approach is presented to manage the power among the dc and ac sources as well as ICs. The...
Decentralized load sharing in a low-voltage direct current microgrid with an adaptive droop approach based on a superimposed frequency
, Article IEEE Journal of Emerging and Selected Topics in Power Electronics ; Volume 5, Issue 3 , 2017 , Pages 1205-1215 ; 21686777 (ISSN) ; Mokhtari, H ; Blaabjerg, F ; Sharif University of Technology
2017
Abstract
Conventional droop methods for load sharing control in low-voltage direct current microgrids suffer from poor power sharing and voltage regulation, especially in the case when operating many dc sources with long feeders. Hence, the communication-based approaches are employed to improve the load sharing accuracy and voltage regulation. To avoid using such an infrastructure and the corresponding effects on the reliability and stability, an adaptive droop controller based on a superimposed frequency is proposed in this paper. Load sharing accuracy is improved by adapting the droop gains utilizing an introduced ac power. The secondary controller locally estimates and compensates the voltage drop...
Fault detection and protection strategy for islanded inverter-based microgrids
, Article IEEE Journal of Emerging and Selected Topics in Power Electronics ; 2019 ; 21686777 (ISSN) ; Mokhtari, H ; Blaabjerg, F ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2019
Abstract
This paper proposes a fault detection and protection strategy for islanded inverter-based microgrids (IBMGs). Reliable and accurate protection is one of the main challenges in the proliferation of modern microgrids (MGs). Considering the limited fault current of the voltage-frequency controlled inverter-based distributed energy resources (VF-IBDERs), the protection is more challenging in islanded IBMGs. In this regard, the control scheme of VF-IBDER with a current limiting strategy plays an important role. Due to the limited fault currents close to the converter nominal current, the conventional fault detection methods do not work properly. In addition, bi-directional fault currents worsen...
Fault detection and protection strategy for islanded inverter-based microgrids
, Article IEEE Journal of Emerging and Selected Topics in Power Electronics ; 2019 ; 21686777 (ISSN) ; Mokhtari, H ; Blaabjerg, F ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2019
Abstract
This paper proposes a fault detection and protection strategy for islanded inverter-based microgrids (IBMGs). Reliable and accurate protection is one of the main challenges in the proliferation of modern microgrids (MGs). Considering the limited fault current of the voltage-frequency controlled inverter-based distributed energy resources (VF-IBDERs), the protection is more challenging in islanded IBMGs. In this regard, the control scheme of VF-IBDER with a current limiting strategy plays an important role. Due to the limited fault currents close to the converter nominal current, the conventional fault detection methods do not work properly. In addition, bi-directional fault currents worsen...
Reliability evaluation in microgrids with non-exponential failure rates of power units
, Article IEEE Systems Journal ; Volume 14, Issue 2 , 2020 , Pages 2861-2872 ; Fotuhi Firuzabad, M ; Blaabjerg, F ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2020
Abstract
This article explores the impacts of non-exponentially distributed failures on reliability of microgrids. Failure rate of some components such as power electronic converters is not constant, while they play a major role in microgrids. Consequently, their failure characteristics will affect the microgrid reliability. Hence, the conventional reliability evaluation approaches based on mean time to failure may introduce inaccurate inputs for decision making in planning and operation of microgrids. In this article, different approaches are employed for evaluating the reliability of microgrids with non-constant failure rates. The obtained results indicate that the system reliability remarkably...
Active damping of torsional vibrations due to the sub-harmonic instability on a synchronous generator
, Article 20th European Conference on Power Electronics and Applications, EPE 2018 ECCE Europe, 17 September 2018 through 21 September 2018 ; 2018 ; 9789075815283 (ISBN) ; Azizi, A ; Mokhtari, H ; Blaabjerg, F ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2018
Abstract
Sub-harmonic stability issues due to the interaction between a load-commutated motor drive and a synchronous turbo-generator train in a Liquefied Natural Gas (LNG) station are studied in this paper. The sub-harmonic current injected by motor drives may excite the mechanical torsional modes of turbogenerator train. In this paper, the electro-mechanical interaction phenomenon is investigated and an active damper is proposed to absorb the sub-harmonic currents of motor drives and increase the damping of the electro-mechanical system. Simulations and experiments validate the instability problem and effectiveness of the proposed solution. © 2018 EPE Association
Decentralized droop control in DC microgrids based on a frequency injection approach
, Article IEEE Transactions on Smart Grid ; Volume 10, Issue 6 , 2019 , Pages 6782-6791 ; 19493053 (ISSN) ; Davari, P ; Mokhtari, H ; Blaabjerg, F ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2019
Abstract
Power sharing control among grid forming dc sources employing a conventional voltage droop approach meets inaccurate load sharing and unacceptable voltage regulation performance. Thereby, communication-based secondary and supervisory controllers have been presented to overcome the aforementioned issues. Furthermore, with the aim of eliminating communication system, frequency-based droop approaches have been introduced for low-voltage dc grids where the frequency of the superimposed ac signal onto the dc voltage is proportional to the output power. However, in reality, dc grid structures can be applied to medium and high voltage applications with different X/R ratios. This paper generalizes...
Modeling in-and-out-of-water impact on all-electric ship power system considering propeller submergence in waves
, Article 2021 IEEE Transportation Electrification Conference and Expo, ITEC 2021, 21 June 2021 through 25 June 2021 ; 2021 , Pages 533-538 ; 9781728175836 (ISBN) ; Peyghami, S ; Parniani, M ; Blaabjerg, F ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2021
Abstract
Despite the advantages of employing an electric propulsion system in All-Electric Ships (AES), additional power fluctuation sources have emerged in the ship power system as a result. Since the propellers are the primary power consumers in the AES, these fluctuations may significantly affect its power system power quality. Thus, for optimal performance of the ship power system, these fluctuations need to be rigorously investigated at the design level of vessels. Waves collision is one of the critical conditions where propellers inject power fluctuations into the ship power system. Therefore, a comprehensive model is essential to analyze the propellers in-and-out-of-water effect on the ship...
An open-water efficiency based speed change strategy with propeller lifespan enhancement in all-electric ships
, Article IEEE Access ; Volume 9 , 2021 , Pages 22595-22604 ; 21693536 (ISSN) ; Peyghami, S ; Parniani, M ; Blaabjerg, F ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2021
Abstract
In recent years, utilizing the electrical propulsion system in the marine industry has become widely popular. Control of the propeller has been a high-priority design challenge in this industry. One of the essential issues in propeller control is the speed control of the ships. A suitable control strategy for the propeller should be economically-efficient while ensuring stability, reliability, and power quality of the ship's power system. This article proposes an improved propeller control strategy for increasing/decreasing the ship's speed. This scheme consists of two strategies: a maximum acceleration strategy and an efficient operation strategy. The maximum acceleration strategy aims to...
Enhanced frequency droop method for decentralized power sharing control in DC microgrids
, Article IEEE Journal of Emerging and Selected Topics in Power Electronics ; Volume 9, Issue 2 , 2021 , Pages 1290-1301 ; 21686777 (ISSN) ; Peyghami, S ; Mokhtari, H ; Blaabjerg, F ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2021
Abstract
This article proposes two novel approaches to improve the superimposed frequency droop scheme for the control of dc microgrids (MGs). Conventional voltage-based control strategies suffer from issues such as undesirable voltage regulations, poor power sharing among the sources, and negative effects of line resistances on the equivalent droop characteristics. To overcome these challenges, a superimposed frequency droop scheme has been introduced. However, this method suffers from three major issues: 1) instability in terms of load variation, which is due to the location of system dominant poles; 2) limitation in system loading due to the limitation in the transferred reactive power; and 3)...
A comprehensive theoretical approach for analysing manoeuvring effects on ships by integrating hydrodynamics and power system
, Article IET Electrical Systems in Transportation ; Volume 12, Issue 2 , 2022 , Pages 89-101 ; 20429738 (ISSN) ; Peyghami, S ; Parniani, M ; Blaabjerg, F ; Sharif University of Technology
John Wiley and Sons Inc
2022
Abstract
Ship motions affect the propulsion system, which causes fluctuations in the power system. Mutually, the power system variations impact the ship velocity by generating speed changes in the propeller. Therefore, interconnecting the ship hydrodynamic and power system has paramount importance in designing and analysing an all-electric ship (AES). The lack of an integrated model that can be evaluated in various operating conditions, such as manoeuvring, is evident. This paper explores the required perceptions for the power system and hydrodynamic analysis of an AES. Then, an integrated theoretical model comprising both the ship motion and power system is proposed. In addition to providing an...
Power management strategies based on propellers speed control in waves for mitigating power fluctuations of ships
, Article IEEE Transactions on Transportation Electrification ; Volume 8, Issue 3 , 2022 , Pages 3247-3260 ; 23327782 (ISSN) ; Peyghami, S ; Parniani, M ; Blaabjerg, F ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2022
Abstract
This article proposes two novel power management strategies (PMSs) to enhance the electrical power quality in twin-screw all-electric ships (AESs) during vessel-wave encountering. Soothing PMS (SPMS) focuses on mitigating power fluctuations of the propulsion system since it has significant impacts on the power system in extreme conditions. For this purpose, the PMS modifies propellers' speed based on the in-and-out-of-water effect loss factor (LF) in wave collisions. This method does not require typical equipment, such as energy storage systems (ESSs), to moderate the variations. Hence, it decreases the ESS demand capacity and maintenance costs at the design and operation levels. An...
Analysis of all-electric ship motions impact on PV system output power in waves
, Article 2022 IEEE Transportation Electrification Conference and Expo, ITEC 2022, 15 June 2022 through 17 June 2022 ; 2022 , Pages 450-455 ; 9781665405607 (ISBN) ; Parniani, M ; Blaabjerg, F ; Peyghami, S ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2022
Abstract
Waves encountering can cause significant ship motions and affect the photovoltaic power generation capacity in All-Electric Ships (AES) during extreme conditions. In this paper, a comprehensive strategy is proposed to examine the impact of modern vessels' movements on the PV system output and the ship power quality during various operating scenarios. The proposed theoretical model-based technique determines ship angles in a wave collision and assesses sun-related angles concerning the vessel motions. Based on the panel angles, the solar irradiance and the PV system power variations can be derived. The developed method can simultaneously evaluate the effect of ship motions on the photovoltaic...
Health monitoring of output capacitor in boost converters based on dissipation factor
, Article IEEE Transactions on Power Electronics ; Volume 38, Issue 10 , 2023 , Pages 12355-12358 ; 08858993 (ISSN) ; Peyghami, S ; Mokhtari, H ; Blaabjerg, F ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2023
Abstract
The purpose of this letter is to present a simple technique for monitoring the health status of the output capacitor of a boost converter. The majority of previous studies have measured an electrolytic capacitor equivalent series resistance or capacitance to track its health condition. However, this letter suggests a new approach based on the accurate measurement of the dissipation factor. The effectiveness of the proposed method is verified through experimental tests. According to the results, the dissipation factor is measured with a maximum error of 4%. © 1986-2012 IEEE