Nicholas A Vovos- Professor
- Professor (Full) at University of Patras
Nicholas A Vovos
- Professor
- Professor (Full) at University of Patras
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92
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Introduction
Professor N. A. Vovos has been a member of the department of Electrical and Computer Engineering at Patras University since 1981 and he was Head of the department in the time period 2003-2007 and deputy Head in period 2001-2003. His main fields of interest are: analysis, control and protection of HVDC systems, flexible AC transmission systems (FACTS) and Custom Power (CP) devices, dynamic simulation and interaction study of AC/DC systems including FACTS and CP devices.
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Publications (92)
In this paper the harmonic cancellation performance of a power converter, supplied by Photovoltaic (PV) arrays, is investigated. The power converter consists of a dc-dc buck-boost converter connected in series with a full-bridge polarity swapping inverter. Due to specific way of converter’s operation, ripples are caused to PV’s output voltage. Cons...
Fuel-cell-based power generation is a promising DG technology, gaining popularity in residential applications due to its cleanliness, portability and suitability for electricity and heat generation. It also features as a great choice for remote isolated residences for covering the water needs. This paper presents an experimental study of a Proton E...
This work presents a method of current harmonic reduction in a distorted distribution system. In order to evaluate the proposed method a grid with high-order current harmonics is assumed. The reduction of current distortion is feasible due to the pulse modulation of an active filter, which consists of a buck-boost converter connected back-to-back t...
This paper proposes a new computational intel ligence-based control strategy, to enhance the low voltage ride-through capability of grid-connected wind turbines (WTs) with doubly fed induction generators (DFIGs). Grid codes world-wide require that WTs should supply reactive power to the grid during and after the fault, in order to support the grid...
This paper presents a control method of Renewable Energy Sources (RES) to reduce the harmonic content of the distribution system to which are connected, such as a Microgrid. By this method the RES is acting as a Power Conditioner and its supplying system consists of a buck-boost converter connected back-to-back to a polarity swapping inverter. A RE...
This paper presents a control method of Renewable Energy Sources (RES) to reduce the harmonic content of the distribution system to which are connected, such as a Microgrid. By this method the RES is acting as a Power Conditioner and its supplying system consists of a buck-boost converter connected back-to-back to a polarity swapping inverter. A RE...
Based on the principle of the regulating transformer booster, a new voltage regulator is described which selects parts of the supply-voltage waveform by means of phase-controlled thyristor switches and thus provides fast and variable voltage boost. Two different types of control are investigated and their performance is analysed with different type...
Στο βιβλίο αυτό παρουσιάζεται η ανάλυση απλών ηλεκτρικών κυκλωμάτων στη μόνιμη ημιτονοειδή κατάσταση λειτουργίας. Δημιουργεί ένα βασικό υπόβαθρο γνώσεων για την αποτελεσματικότερη κατανόηση των θεμάτων που πραγματεύεται η ανάλυση Συστημάτων Ηλεκτρικής Ενέργειας και περιλαμβάνει τις απολύτως απαραίτητες γνώσεις για τον Ηλεκτρολόγο Μηχανικό.
Η ύλη το...
Περιέχει όλες τα προβλήματα & Λύσεις που περιέχονται στο βιβλίο Έλεγχος και Ευστάθεια Συστημάτων Ηλεκτρικής Ενέργειας
Περιέχει όλες τα προβλήματα & Λύσεις που περιέχονται στο βιβλίο Ανάλυση Συστημάτων Ηλεκτρικής Ενέργειας
Storage devices are introduced in microgrids in order to secure their power quality, power regularity and offer ancillary services in a transient period. In the transition period of a low voltage microgrid, from the connected mode of operation to the islanded mode of operation, the power unbalance can be partly covered by the inertia energy of the...
In order to integrate different distributed generations (DGs) into a microgrid connected to a weak distribution grid, this paper proposes local controllers based in fuzzy logic. The integration of the DGs is achieved through the ≪plug and play- procedure. The understudy microgrid includes an hybrid fuel cell-battery system and a Doubly Fed Inductio...
This paper proposes a fuzzy based local control for a hybrid fuel cell-battery system in order to integrate distributed generation (DG) into the distribution grid. Either the grid is connected to the mean voltage side or working in islanded mode, the proposed system offers ancillary services. The performance of the system is evaluated when the grid...
In order to integrate a proton exchange membrane type (PEM) fuel cell system (FCS) to a distribution system, this paper proposes a local controller for providing primary frequency control and local bus voltage support. The FCS has been designed to operate in the distribution system either this is connected to the mean voltage side or it is disconne...
Η αυξανόμενη εξάρτηση της σύγχρονης κοινωνίας από την ηλεκτρική ενέργεια οδήγησε στα σημερινά πολύπλοκα και εκτεταμένα Συστήματα Ηλεκτρικής Ενέργειας (ΣΗΕ). Με τη σημερινή οργάνωση της ζωής μας και η συντομότερη διακοπή της λειτουργίας των ΣΗΕ προκαλεί τρομακτική αναστάτωση στις δραστηριότητές μας, λόγω του μεγάλου πλήθους των ηλεκτρικών συσκευών π...
This paper presents different discrete control strategies for a variable speed pitch-controlled wind turbine (WT) which supplies an autonomous system in cooperation with a small hydro power unit. The WT consists of a synchronous generator (SG) with two three-phase stator windings displaced by 300, so as the torque distortions due to the wind fluctu...
Στο βιβλίο αυτό περιλαμβάνεται η ύλη του μαθήματος «Εισαγωγή στα Συστήματα Ηλεκτρικής Ενέργειας» που διδάσκεται στους φοιτητές του Γ' έτους σπουδών του Τμήματος Ηλεκτρολόγων Μηχανικών και Τεχνολογίας Υπολογιστών του Πανεπιστημίου Πατρών.
Παρόλο που το μάθημα είναι εισαγωγικό και απευθύνεται σε όλους τους φοιτητές του τμήματος ανεξαρτήτως κύκλου σπ...
Σκοπός του παρόντος βιβλίου είναι να διερευνήσει τη λειτουργία των Συστημάτων Ηλεκτρικής Ενέργειας (ΣΗΕ) υπό την επίδραση διαταραχών. Καλύπτει την ύλη του μαθήματος «Έλεγχος και Ευστάθεια ΣΗΕ», που διδάσκεται στους φοιτητές του Τμήματος Ηλεκτρολόγων Μηχανικών και Τεχνολογίας Υπολογιστών της Πολυτεχνικής Σχολής του Πανεπιστημίου Πατρών. Η λειτουργία...
Το βιβλίο αυτό καλύπτει την ύλη του μαθήματος «Ανάλυση Συστημάτων Ηλεκτρικής Ενέργειας» που διδάσκεται στους φοιτητές του Δ' έτους του κύκλου σπουδών Συστημάτων Ηλεκτρικής Ενέργειας του Τμήματος Ηλεκτρολόγων Μηχανικών και Τεχνολογίας Υπολογιστών του Πανεπιστημίου Πατρών. Το βιβλίο πραγματεύεται όλο εκείνο το υλικό που είναι απαραίτητο για να δημιου...
This paper studies the issue of the fault ride-through capability of a wind farm of induction generators, which is connected to an AC grid through an HVDC link based on voltage sourced converters (VSCs). National grid codes require that wind turbines should stay connected to the power system during and after short-circuit faults. In the latest lite...
This paper presents a control strategy for a variable-speed pitch-controlled wind turbine (WT) generation scheme for the supply of an autonomous system with no energy storage units. The synchronous generator includes two three-phase stator windings displaced by 30deg that are connected to the transformer load through two dc links with voltage sourc...
Power System Stabilizers (PSS) superimposed to the basic control system of an HVDC link supplying a weak AC system, in order to enhance its frequency regulation action, are proposed. To decrease the AC voltage sensitivity at the inverter side, the basic control system of the HVDC link is proposed to operate with the rectifier under Minimum Ignition...
This paper presents a computationally efficient technique for digital simulation of slip energy recovery induction motor drives. A machine model that significantly simplifies the machine equations, by eliminating the dependence of the inductance matrix on the ever-changing rotor angle, is used. Combining this model with a flexible technique to repr...
This paper studies the behavior of a high-voltage direct current link based on voltage-source converters, which feeds a weak ac network with power produced from an offshore wind farm (WF) of induction generators. Its control system, which is based on adaptive fuzzy controllers, manages to offer very satisfactory performance, without the need for a...
New technologies based on the development of new high-power switches, transistors and thyristors made it possible to implement Voltage Source Converters with Pulse Width Modulation, and other types of converters for usage in power systems. They now provide the opportunity to introduce power electronics applications in distribution systems too. The...
An HVDC link based on VSCs with a special control system is proposed in this paper, for the connection of a Wind Farm (WF) with induction generators to an ac grid. The proposed control system, based on fuzzy logic, is on-line tuned in order to be self-adapted according to the operating conditions. In this way, it combines maximum wind power acquisi...
This paper analyses the control strategy and performance of an HVDC link based on VSCs, which is controlled using fuzzy logic. The system can feed a weak or even "dead" network under fluctuations and big variations of the input power. The fuzzy-logic-based control of the system helps to optimize the efficiency of the link under these disturbances.
A specific wind turbine (WT) generation scheme is used and a control strategy is studied, not only to increase the efficiency of the WT but also to limit the influence on the alternating current (AC) distribution grid. The system is a variable-speed wind-energy conversion scheme, including a synchronous generator with two three-phase stator winding...
Σκοπός του βιβλίου είναι να διερευνήσει τη λειτουργία των Συστημάτων Ηλεκτρικής Ενέργειας (ΣΗΕ) υπό την επίδραση διαταραχών. Καλύπτει την ύλη των μαθημάτων «Ανάλυση ΣΗΕ ΙΙ» και «Έλεγχος και Ευστάθεια ΣΗΕ», που διδάσκονται στους φοιτητές του Τμήματος Ηλεκτρολόγων Μηχανικών και Τεχνολογίας Υπολογιστών της Πολυτεχνικής Σχολής του Πανεπιστημίου Πατρών....
A three level control system for a variable speed wind energy
conversion scheme (VSWECS) supplying a weak AC power system is
presented. The objective of the control strategy is to maximize energy
capture and simultaneously to support the voltage of the bus where the
VSWECS is connected. Using an insulated gate bipolar transistor (IGBT)
inverter, bo...
The capability of controllable shunt and series compensators to
modulate the real power flow in integrated AC/DC systems has been
investigated and compared. The linearized state space equations of the
system have been included in a load flow program and the change of the
real power flow per change of the reactive or both active and reactive
power i...
A variable speed wind turbine (VSWT) conversion system with the appropriate control system is proposed. The system has been designed for connection to small power grids since voltage support and good electric power quality at its connection point were from the primary specifications. Below rated wind speed maximum capture of the wind power is achie...
A method for fast digital simulation of induction motor drive systems based on a simple numerical algorithm is proposed. An efficient technique is used for the automatic formulation of the power electronic circuit which is based on the fundamental loop matrix modification. A discrete-time model of the induction machine, which can be directly interf...
The dynamics of a 30 kW autonomous wind turbine (WT) driving a
synchronous generator (SG) which supplies two reverse osmosis (RO)
desalination units and a dump load are examined. The controlled dump
load enables the control of electrical disturbances but the highly
resonant, non-linear dynamic system determines the mechanical and
electrical stresse...
In this paper a comparison is made between the conventional shunt
compensator (Static Var Compensator, SVC) providing only reactive power
modulation and the GTO-based advanced compensator (Static Condenser,
STATCON) providing both active and reactive power modulation, regarding
their effectiveness in damping power oscillations. Based on small
purtu...
This paper presents a method for formulating the dynamic model of inverter-fed induction motor drive systems. An efficient model for the machine, which eliminates the time-varying terms of the inductance matrix, is used. This model has the additional advantage that can be directly interfaced with the inverter switching circuit, which is simulated i...
A pilot 30 kW autonomous wind turbine generator (WTG) supplying a reverse osmosis (RO) desalination unit has been designed and constructed by a consortium of Greek manufacturers, research Institutes and three departments of the University of Patras. The basic design specifications were simplicity for maximum reliability, minimum maintenance require...
A 30KW Wind Turbine, designed and constructed by Greek manufacturers and Research Institutions, is combined with a modular Reverse Osmosis Desalination Plant, in order to:
(1) obtain transfer of technology in the design and construction of all parts of the wind Turbine / Desalination system, with special care to critical components, such as:
(1.a)...
The design of a centralized suboptimal static controller for HVDC links connected to load systems without AC generators, using the projective control technique, is presented. Frequency and voltage variations at the inverter side are the inputs of the static controller, while the modulation of the DC current settings and the constant extinction angl...
The design process of centralized suboptimal low order dynamic controllers for HVDC links supplying weak AC power systems, using the projective control technique, is presented. The controllers are simple and easily super imposed to the classical control system of the HVDC links. They exploit the possibility of simultaneous control of active and rea...
A new method for simulating three phase bridge converters in a flexible and computationally efficient manner is presented. Exploiting the structure of the converter circuit and using a modular modelling technique the state equations of the converter are obtained effectively. The resulting dynamic model simulates successfully a wide range of convert...
The theoretical basis of a flexible and computationally efficient
method for transient simulation of integrated AC/DC systems of any
desired configuration is described. Using a modular modelling technique
in conjunction with a modified state-variable approach, the state
equations of the various components are formulated and solved separately
at the...
A modelling approach for the detailed dynamic simulation of multiterminal HVDC systems embedded in a conventional AC network is presented. This approach utilizes a decomposition technique to construct separately the state equations of properly defined subsystems, which are linked using automatically created algebraic equations of the state variable...
A new converter equivalent circuit suitable for dynamic simulation of multiterminal HVDC systems with multibridge converters is presented. Using this circuit all possible operating modes of the converter can be analyzed by means of one topological matrix only. It is shown that the proposed converter equivalent circuit increases the flexibility of t...
A new method is presented for the analysis of power systems including static convertors. The basic feature of the proposed method is that the state equations of each component of a power system can be written separately by considering fictitious sources at their terminals. The values of these sources are calculated from a general algebraic connecti...
Active power modulation has been successfully used to improve the dynamic performance of interconnected AC/DC systems. This, however, results in uncoordinated reactive power modulation which, in the case of weak systems, reduces the effectiveness of the method. The paper presents the basic design of a DC link controller which, in the presence of ma...
A control system which utilizes the inherent capability of dc transmission for fast electronic modulation of the active and reactive power of the convertors has been theoretically developed. The objective of this modulation controller is the improvement of the transient stability of the interconnected ac systems in the presence of major disturbance...
One of the problems of DC links is that, in the case of severe AC faults at the inverter side due to successive commutation failures, their operation is interrupted and they are unable to assist the integrated AC¿DC system to recover. This is particularly true in the case of weak systems. The paper develops the theory and design of a control syste...
This paper develops a mathematical model for the dynamic simulation of ac-dc systems. The basic features of the proposed model are: All the subsystems and components of a realistic HVDC scheme are included in the model. The power system components are modelled using the exact differential equations derived from their three phase equivalent networks...
A power system consisting of two control areas is simulated in this paper. The two areas are interconnected via two parallel ac tie lines and as an alternative, the interconnection via an ac line and a parallel dc link is examined. The two system configurations are subjected to the same disturbances and faults and their responses are compared and a...
This paper presents a method for the damping of power swings in the ac lines interconnecting two power systems, utilising the fast electronic power flow control characteristics of a parallel dc link. The basic principle of the method is that the dc link is operated in order to maintain constant active power flow in the ac tie lines and constant rea...
Abstract: Based on the principle of the regulating transformer booster, a new voltage regulator is described which selects parts of the supply-voltage waveform by means of phase-controlled thyristor switches and thus provides fast and variable voltage boost. Two different types of control are investigated and their performance is analysed with diff...
