Mohamed Dahidah, Georgios Konstantinou, Vassilios G. Agelidis,
This study presents a novel formulation of multilevel selective harmonic elimination pulse width modulation (MSHE-PWM) technique with optimised DC voltage levels suitable for high-power voltage source converter-based applications. The study reformulates the problem in a way in which the levels of the DC voltage sources are made variables within certain constraints. Therefore the degrees of freedom for specifying the cost function are increased when compared to the existing family of selective harmonic ...
Tópico(s): Advanced DC-DC Converters
2012 - Institution of Engineering and Technology | IET Power Electronics
Sridhar R. Pulikanti, Georgios Konstantinou, Vassilios G. Agelidis,
A generalised n-level flying capacitor (FC)-based active-neutral-point-clamped (ANPC) voltage source converter is discussed in this study. The converter is based on the arrangement of a three-level ANPC cell and a number of two-level cells creating an n-level line-to-neutral voltage waveform. The converter is operated under a phase-shifted carrier (PSC) pulse-width modulation (PWM) technique. The mathematical model for the DC-link capacitors' voltage behaviour of the three-phase converter is also presented. ...
Tópico(s): Advanced DC-DC Converters
2012 - Institution of Engineering and Technology | IET Power Electronics
Sridhar R. Pulikanti, Georgios Konstantinou, Vassilios G. Agelidis,
This paper presents the hybrid seven-level cascaded active neutral-point-clamped (ANPC)-based multilevel converter. The converter topology is the cascaded connection of a three-level ANPC converter and an H-bridge per phase. The voltage of the H-bridge is actively maintained to the required level through selection of the switching states of the converter. The topology is operated under selective harmonic elimination pulsewidth modulation (SHE-PWM), maintaining the switching frequency of the converter ...
Tópico(s): Silicon Carbide Semiconductor Technologies
2012 - Institute of Electrical and Electronics Engineers | IEEE Transactions on Industrial Electronics
Sridhar R. Pulikanti, Georgios Konstantinou, Vassilios G. Agelidis,
This paper presents a dc-link voltage ripple compensation method for flying-capacitor (FC)-based active neutral-point-clamped multilevel converters operating under selective harmonic elimination pulsewidth modulation. The method is based on feedforward modification of the modulation index according to the ripple on the dc-link voltage, effectively altering the switching control functions. The low-order harmonics in the output due to the presence of the dc-link ripple are eliminated. In addition, ...
Tópico(s): Silicon Carbide Semiconductor Technologies
2012 - Institute of Electrical and Electronics Engineers | IEEE Transactions on Power Delivery
Mohamed Dahidah, Georgios Konstantinou, Vassilios G. Agelidis,
Selective harmonic elimination pulse width modulation (SHE-PWM) offers tight control of the harmonic spectrum of a given voltage and/or current waveform generated by a power electronics converter. Owing to its formulation and focus on elimination of low-order harmonics, it is highly beneficial for high-power converters operating with low switching frequencies. Over the last decade, the application of SHE-PWM has been extended to include multilevel converters. This paper provides a comprehensive review ...
Tópico(s): Silicon Carbide Semiconductor Technologies
2014 - Institute of Electrical and Electronics Engineers | IEEE Transactions on Power Electronics
Josep Pou, Salvador Ceballos, Georgios Konstantinou, Vassilios G. Agelidis, Ricard Picas, Jordi Zaragoza,
This paper studies different circulating current references for the modular multilevel converter. The circulating current references are obtained from the instantaneous values of the output current and modulation signal of the phase leg. Therefore, the determination of the amplitude and phase of the output current is not needed, which is a significant improvement compared to other methods such as those based on injecting specific harmonics in the circulating currents. Among the different methods ...
Tópico(s): Silicon Carbide Semiconductor Technologies
2014 - Institute of Electrical and Electronics Engineers | IEEE Transactions on Industrial Electronics
Georgios Konstantinou, Vassilios G. Agelidis, Josep Pou,
This letter defines selective harmonic elimination pulse width modulation (SHE-PWM) formulations for single-phase, interleaved converters. Through precalculated solutions, interleaved converters work at the same operating point while eliminating multiple low-order harmonics. It is shown that multiple continuous solutions can be acquired for three-level interleaved waveforms. Extending the method to multiple levels further complicates the problem and reduces both the number and continuity of the solutions. ...
Tópico(s): Microgrid Control and Optimization
2014 - Institute of Electrical and Electronics Engineers | IEEE Transactions on Power Electronics
Ricard Picas, Salvador Ceballos, Josep Pou, Jordi Zaragoza, Georgios Konstantinou, Vassilios G. Agelidis,
In this paper, a new discontinuous modulation technique is presented for the operation of the modular multilevel converter (MMC). The modulation technique is based on adding a zero sequence to the original modulation signals so that the MMC arms are clamped to the upper or lower terminals of the dc-link bus. The clamping intervals are controlled according to the absolute value of the output current to minimize the switching losses of the MMC. A significant reduction in the capacitor voltage ripples ...
Tópico(s): High-Voltage Power Transmission Systems
2014 - Institute of Electrical and Electronics Engineers | IEEE Transactions on Power Electronics
Georgios Konstantinou, Vassilios G. Agelidis,
This paper analyzes the half-wave symmetrical two-level SHE-PWM, proposes two formulations of the SHE-PWM waveform with multiple solutions and evaluates the solutions for different cases of eliminated harmonics. Previous work on SHE-PWM focused on algorithms for calculating the solutions and only considered the quarter-wave symmetry in the formulation. In this paper two different formulations to the problem are considered and solutions for a number of eliminated harmonics are presented. The different ...
Tópico(s): Multilevel Inverters and Converters
2013 - Elsevier BV | Electric Power Systems Research
Christopher D. Townsend, Yifan Yu, Georgios Konstantinou, Vassilios G. Agelidis,
The cascaded H-bridge (CHB) topology is ideal for implementing large-scale converters for photovoltaic (PV) applications. The improved quality of output voltage waveforms, high efficiency due to transformer-less connection, and ability to employ multiple instances of a maximum power point tracking (MPPT) algorithm are just some advantages. An important disadvantage is the required over-rating to ensure balanced three-phase currents at times of unequal PV generation. Unequal generation occurs due to ...
Tópico(s): HVDC Systems and Fault Protection
2015 - Institute of Electrical and Electronics Engineers | IEEE Transactions on Power Electronics
Kyriakos Anastasiadis, Polychronis Antonitsis, Christos Asteriou, Helena Argiriadou, Apostolos Deliopoulos, Dimitrios Konstantinou, Vassilios Grosomanidis, Paschalis Tossios,
Abstract Minimal invasive extracorporeal circulation (MiECC) has initiated important new efforts within science and technology towards a more physiologic perfusion. In this study, we aim to investigate the learning curve of our center regarding MiECC. We studied a series of 150 consecutive patients who underwent elective coronary artery bypass grafting by the same surgical team during the initial phase of MiECC application. Patients were randomly assigned into two groups. Group A ( n = 75) included patients ...
Tópico(s): Cardiac Ischemia and Reperfusion
2016 - Wiley | Artificial Organs
Mohamed Dahidah, Georgios Konstantinou, Nikolas Flourentzou, Vassilios G. Agelidis,
Selective harmonic elimination pulse-width modulation (SHE-PWM) techniques offer a tight control of the harmonic spectrum of a given voltage waveform generated by a power electronic converter along with a low number of switching transitions. These optimal switching transitions can be calculated through Fourier theory, and for a number of years quarter-wave and half-wave symmetries have been assumed when formulating the problem. It is shown recently that symmetry requirements can be relaxed as a constraint. ...
Tópico(s): Silicon Carbide Semiconductor Technologies
2010 - Institution of Engineering and Technology | IET Power Electronics
Georgios Konstantinou, Mohamed Dahidah, Vassilios G. Agelidis,
A detailed analysis of a seven-level selective harmonic elimination pulse-width modulation method suitable for multilevel DC–AC converters is presented in this study. Solution trajectories that cover the normal range of modulation indices typical for the operation of multilevel inverters are documented. The properties and characteristics of these solutions with regard to the distribution of switching instants (angles) to the levels of the waveform are also reported. Selected simulation and experimental ...
Tópico(s): Silicon Carbide Semiconductor Technologies
2011 - Institution of Engineering and Technology | IET Power Electronics
Gabriel J. Capella, Josep Pou, Salvador Ceballos, Georgios Konstantinou, Jordi Zaragoza, Vassilios G. Agelidis,
This letter presents a novel implementation of pulse width modulation that improves the quality of the line-to-line output voltages in interleaved multiphase voltage-source inverters (VSIs). In multiphase VSIs with n interleaved parallel-connected legs, the best single-phase output voltage is achieved when the carriers are evenly phase shifted. However, switching among nonadjacent levels can be observed at regular intervals in the line-to-line voltages, causing bad harmonic performance. With the ...
Tópico(s): Silicon Carbide Semiconductor Technologies
2014 - Institute of Electrical and Electronics Engineers | IEEE Transactions on Power Electronics
Georgios Konstantinou, Mihai Ciobotaru, Vassilios G. Agelidis,
The modular multilevel converter (MMC) is the state-of-the-art for multilevel converter topologies. This study presents the operation of the MMC using the multilevel selective harmonic elimination pulse-width modulation (MSHE-PWM) technique. MSHE-PWM offers tight control of the low-order harmonics and the lowest switching frequency for the power semiconductors among all modulation techniques. A comprehensive analysis of the modulation methods for the MMC leads to two different modulation patterns ...
Tópico(s): Silicon Carbide Semiconductor Technologies
2013 - Institution of Engineering and Technology | IET Power Electronics
Yifan Yu, Georgios Konstantinou, Branislav Hredzak, Vassilios G. Agelidis,
A cascaded H-bridge (CHB) converter is one of the viable options for next-generation large-scale photovoltaic (PV) power conversion. Owing to the increased number of components involved, converter reliability and fault-tolerant control are important issues. A CHB converter must also manage unequal power generation among bridges, which is inherent in PV applications because of unequal solar irradiance and/or module temperatures. This paper proposes a fault-tolerant strategy, which maintains balanced ...
Tópico(s): Silicon Carbide Semiconductor Technologies
2015 - Institute of Electrical and Electronics Engineers | IEEE Transactions on Industrial Electronics
Rosheila Darus, Josep Pou, Georgios Konstantinou, Salvador Ceballos, Vassilios G. Agelidis,
Control of the circulating currents in a modular multilevel converter (MMC) is an integral part of its operation as the circulating currents have a significant impact on the rating of the power devices, losses and also capacitor voltage ripples. This study proposes two methods to control the circulating currents in the phase-legs of the MMC to their minimum dc value through elimination of the low-order harmonic components in the circulating current. The first method acts directly on the ac harmonics ...
Tópico(s): Silicon Carbide Semiconductor Technologies
2015 - Institution of Engineering and Technology | IET Power Electronics
Yifan Yu, Georgios Konstantinou, Branislav Hredzak, Vassilios G. Agelidis,
Multilevel cascaded H-bridge converters are promising candidates for large-scale photovoltaic power plants. They allow direct connection to medium-voltage distribution networks without the presence of bulky line frequency power transformers. Owing to the stochastically variable nature of irradiance level, ambient temperature, and other factors, power levels in the three phases are expected to be unequal. The power imbalance condition creates unexpected problems with this topology, which was initially ...
Tópico(s): Silicon Carbide Semiconductor Technologies
2015 - Institute of Electrical and Electronics Engineers | IEEE Transactions on Power Electronics
Yifan Yu, Georgios Konstantinou, Branislav Hredzak, Vassilios G. Agelidis,
Multilevel-cascaded H-bridge converters are promising candidates for next generation photovoltaic power converters. They feature reduced switching losses and higher conversion efficiency with modular structure; characteristics vital for large-scale photovoltaic power plants. However, the stochastically-variable nature of irradiance levels and ambient temperatures affects the normal operation of this topology, because power levels in the three phases can be unequal. The existing zero sequence injection ...
Tópico(s): Silicon Carbide Semiconductor Technologies
2015 - Institute of Electrical and Electronics Engineers | IEEE Transactions on Power Electronics
Harith R. Wickramasinghe, Georgios Konstantinou, Josep Pou, Vassilios G. Agelidis,
Estimation-based indirect dc-voltage control in MMCs interacts with circulating current control methods. This paper proposes an estimation-based indirect dc-voltage control method for MMC-HVDC systems and analyzes its performance compared to alternative estimations. The interactions between estimation-based indirect dc-voltage control and circulating current control methods, active/reactive power regulation are also investigated. The proposed method delivers similar performance to measurement-based ...
Tópico(s): High-Voltage Power Transmission Systems
2017 - Institute of Electrical and Electronics Engineers | IEEE Transactions on Power Systems
Yifan Yu, Georgios Konstantinou, Christopher D. Townsend, Vassilios G. Agelidis,
Photovoltaic (PV) power generation levels in the three phases of a multilevel cascaded H-bridge (CHB) converter can be significantly unbalanced, owing to different irradiance levels and ambient temperatures over a large-scale solar PV power plant. Injection of a zero-sequence voltage is required to maintain three-phase balanced grid currents with unbalanced power generation. This study theoretically compares power balance capabilities of various zero-sequence injection methods based on two metrics ...
Tópico(s): Microgrid Control and Optimization
2016 - Institution of Engineering and Technology | IET Renewable Power Generation
Rosheila Darus, Josep Pou, Georgios Konstantinou, Salvador Ceballos, Ricard Picas, Vassilios G. Agelidis,
This paper introduces a low complexity implementation of the voltage balancing algorithm aiming to reduce the switching frequency of the power devices in modular multilevel converters (MMCs). The proposed algorithm features a relatively simple implementation without any conditional execution requirements and is easily expandable regardless of the number of submodules (SMs). Two modulation techniques are evaluated, namely the staircase modulation and the phase-disposition pulse width modulation (PD- ...
Tópico(s): High-Voltage Power Transmission Systems
2014 - Institute of Electrical and Electronics Engineers | IEEE Transactions on Power Electronics
Georgios Konstantinou, Josep Pou, Salvador Ceballos, Vassilios G. Agelidis,
The modular multilevel converter (MMC) is based on the cascaded connection of identical submodules (SMs) enabling additional redundancies. This paper proposes the configuration of the MMC topology with redundant SMs and demonstrates the effects of active redundancies. The proposed configuration decreases the switching frequency per SM while reducing the SM capacitor voltage ripples. An analytical model for determining the SM capacitor voltage ripple and voltage dynamics is derived. The results from ...
Tópico(s): High-Voltage Power Transmission Systems
2013 - Institute of Electrical and Electronics Engineers | IEEE Transactions on Power Delivery
Ricardo P. Aguilera, Pablo Acuna, Pablo Lezana, Georgios Konstantinou, Bin Wu, Steffen Bernet, Vassilios G. Agelidis,
In this study, a model predictive control (MPC) strategy that combines finite-control-set MPC with selective harmonic elimination (SHE) modulation pattern in its formulation is proposed to govern multilevel power converters. Based on a desired operating point for the system state (converter current reference), an associated predefined SHE voltage pattern is obtained as a required steady-state control input reference. Then, the cost function is formulated with the inclusion of both system state and ...
Tópico(s): Advanced DC-DC Converters
2016 - Institute of Electrical and Electronics Engineers | IEEE Transactions on Power Electronics
Dimitrios Konstantinou, Georgios Efthimiadis, Vassilios Vassilikos, Stylianos Paraskevaidis, Efstathios D. Pagourelias, Barry J. Maron, Haralambos Karvounis,
Sudden cardiac death (SCD) may complicate hypertrophic cardiomyopathy (HCM) natural course. Patient selection for implantable cardioverter defibrillator (ICD) therapy in the primary prevention setting is still a challenge.Thirty-seven HCM patients with a primary prevention ICD were included. All patients underwent preimplantation SCD risk assessment and semi-annual device interrogation during follow-up. Primary end point was the time to first appropriate ICD intervention including antitachycardia pacing ...
Tópico(s): Cardiac Arrhythmias and Treatments
2016 - Lippincott Williams & Wilkins | Journal of Cardiovascular Medicine
Ricardo P. Aguilera, Pablo Acuna, Yifan Yu, Georgios Konstantinou, Christopher D. Townsend, Bin Wu, Vassilios G. Agelidis,
This paper presents a predictive control strategy for grid-connected cascaded H-bridge (CHB) converters under unbalanced power generation among each converter phase. The proposed controller belongs to the finite-control-set model predictive control (FCS-MPC) family and is designed to extract unbalanced power from each CHB converter phase while providing balanced power to the grid. The key novelty of this strategy lies in the way the unbalanced power generation among the phases is explicitly considered ...
Tópico(s): Advanced DC-DC Converters
2016 - Institute of Electrical and Electronics Engineers | IEEE Transactions on Industrial Electronics
Μαρία Αντωνοπούλου, Vassilios Papadopoulos, Ioannis Konstantinou,
Abstract BACKGROUND: TiO 2 heterogeneous photocatalysis should be optimized before application for the removal of pollutants in treated wastewaters. The response surface methodology (RSM) and artificial neural networks (ANNs) were applied to model and optimize the photocatalytic degradation of total phenolic (TPh) compounds in real secondary and tertiary treated municipal wastewaters. RESULTS: RSM was developed by considering a central composite design (CCD) with three input variables, i.e. TiO 2 mass, ...
Tópico(s): Advanced oxidation water treatment
2012 - Wiley | Journal of Chemical Technology & Biotechnology
Nikolaos Stamatis, Dimitra Hela, Vassilios Triantafyllidis, Ioannis Konstantinou,
A three‐year monitoring survey (March 2005–February 2008) was conducted to investigate, on monthly basis, the presence of thirty pesticides belonging to various categories and metabolites, in Acheloos River (Western Greece), one of the most important water resources in Greece. Six sampling stations along the river were established. Water analyses were performed using solid‐phase extraction combined with gas chromatography with flame thermionic detector and mass spectrometry. Statistical analysis using ...
Tópico(s): Pesticide Residue Analysis and Safety
2013 - Hindawi Publishing Corporation | The Scientific World JOURNAL
Yifan Yu, Georgios Konstantinou, Christopher D. Townsend, Ricardo P. Aguilera, Vassilios G. Agelidis,
The cascaded H-bridge (CHB) converter is becoming a promising candidate for use in next generation large-scale photovoltaic (PV) power plants. However, solar power generation in the three converter phase-legs can be significantly unbalanced, especially in a large geographically-dispersed plant. The power imbalance between the three phases defines a limit for the injection of balanced three-phase currents to the grid. This paper quantifies the performance of, and experimentally confirms, the recently ...
Tópico(s): Silicon Carbide Semiconductor Technologies
2016 - Institute of Electrical and Electronics Engineers | IEEE Transactions on Industrial Electronics
Dimitrios Mikroulis, Vassilios Didilis, Fotios Konstantinou, Kosmas Tsakiridis, George Vretzakis, Georgios Bougioukas,
The prophylactic effect of amiodarone on atrial fibrillation after coronary bypass grafting with extracorporeal circulation was compared with that of diltiazem in two groups of 60 patients each. Patients were monitored continuously for 8 days. The incidence of atrial fibrillation was recorded retrospectively in a control group of 60 patients who received our standard prophylactic regimen of an oral beta blocker. The incidence of postoperative atrial fibrillation was not significantly different in ...
Tópico(s): Cardiac pacing and defibrillation studies
2005 - SAGE Publishing | Asian Cardiovascular and Thoracic Annals