Improved control strategy of DFIG-based wind turbines using direct torque and direct power control techniques

This paper presents different control strategies for a variable-speed wind energy conversion system (WECS), based on a doubly fed induction generator. Direct Torque Control (DTC) with Space-Vector Modulation is used on the rotor side converter. This control method is known to reduce the fluctuations of the torque and flux at low speeds in contrast to the classical DTC, where the frequency of switching is uncontrollable. The reference for torque is obtained from the maximum power point tracking technique of the wind turbine. For the grid-side converter, a fuzzy direct power control is proposed for the control of the instantaneous active and reactive power. Simulation results of the WECS are presented to compare the performance of the proposed and classical control approaches.Peer reviewedFinal Accepted Versio

Fuzzy Risk Graph Model for Determining Safety Integrity Level

The risk graph is one of the most popular methods used to determine the safety integrity level for safety instrumented functions. However, conventional risk graph as described in the IEC 61508 standard is subjective and suffers from an interpretation problem of risk parameters. Thus, it can lead to inconsistent outcomes that may result in conservative SIL's. To overcome this difficulty, a modified risk graph using fuzzy rule-based system is proposed. This novel version of risk graph uses fuzzy scales to assess risk parameters, and calibration may be made by varying risk parameter values. Furthermore, the outcomes which are numerical values of risk reduction factor (the inverse of the probability of failure on demand) can be compared directly with those given by quantitative and semiquantitative methods such as fault tree analysis (FTA), quantitative risk assessment (QRA), and layers of protection analysis (LOPA)

Transfinite interpolation for well-definition in error analysis in solid modelling

Abstract. An overall approach to the problem of error analysis in the context of solid modelling, analogous to the standard forward/backward error analysis of Numerical Analysis, was described in a recent paper by Hoffmann and Stewart. An important subproblem within this overall approach is the well-definition of the sets specified by inconsistent data. These inconsistencies may come from the use of finite-precision real-number arithmetic, from the use of low-degree curves to approximate boundaries, or from terminating an infinite convergent (subdivision) process after only a finite number of steps. An earlier paper, by Andersson and the present authors, showed how to resolve this problem of well-definition, in the context of standard trimmed-NURBS representations, by using the Whitney Extension Theorem. In this paper we will show how an analogous approach can be used in the context of trimmed surfaces based on combined-subdivision representations, such as those proposed by Litke, Levin and Schröder. A further component of the problem of well-definition is ensuring that adjacent patches in a representation do not have extraneous intersections. (Here, ‘extraneous intersections ’ refers to intersections, between two patches forming part of the boundary, other than prescribed intersections along a common edge or at a common vertex.) The paper also describes the derivation of a bound for normal vectors that can be used for this purpose. This bound is relevant both in the case of trimmed-NURBS representations, and in the case of combined subdivision with trimming.

On-line losses minimization of induction motor vector control

Conventional field-orientated Induction motor drives operate at rated flux even at low load. To improve the efficiency of the existing motor it is important to regulate the flux of the motor in the desired operating range. In this paper a loss model controller (LMC) based on the real coded genetic algorithm is proposed, it has the straightforward goal of maximizing the efficiency for each given load torque. In order to give more accuracy to the motor model and the LMC a series model of the motor which consider the iron losses as a resistance connected in series with the mutual inductance is considered. Digital computer simulation demonstrates the effectiveness of the proposed algorithm and also simulation results have confirmed that this algorithm yields the optimal efficiency

Dyskretne przybliżenia równania Hamiltona-Jacobiego dla zadania sterowania optymalnego układem różniczkowo-algebraicznym

This paper discusses the numerical resolution of the Hamilton-Jacobi-Bellman equation associated with optimal control problem when the state equation is of algebraic differential type. We discuss two numerical schemes. The first reduces to the standard framework, while the second does not suppose any knowledge of the Jacobian of the data. We obtain some error estimates, and display numerical results obtained on a simple test problem.Artykuł rozpatruje rozwiązanie numeryczne równania Hamiltona-Jacobiego-Bellmana, związanego z zagadnieniem sterowania optymalnego w przypadku, gdy równanie stanu jest algebraiczno-różniczkowe. Rozważane są dwie procedury numeryczne. Pierwsza z nich sprowadza się do postępowania standardowego, podczas gdy druga nie zakłada znajomości Jakobianu danych. Otrzymano pewne oceny błędu, a na końcu artykułu pokazano wyniki numeryczne dla prostego zadania testowego

Дослідження оптимального складу ванни на зародження та ріст тонких плівок сплаву Ni-Fe

Тонкі плівки сплаву Ni-Fe є однією з найстаріших тем в області електрохімії, оскільки вони демонструють низку фізичних властивостей, що призводить до їх широкого використання в різних додатках. У статті було вивчено вплив складу ванни та прикладного потенціалу на тонкі плівки сплаву Ni-Fe. Тонкі плівки Ni-Fe електроосаджували на мідні підкладки при pH приблизно 3, і експерименти проводили при кімнатній температурі. Час осадження дорівнював 10 хв для всіх нанесених зразків, прикладеного потенціалу (– 1,35 В; 1 В) і складу ванни (0,005; 0,075 і 0,1 М). Експерименти проводилися з використанням електрохімічних методів, таких як циклічна вольтамперометрія (CV), а хроноамперометрію використовували для розробки електролітичних сплавів типу Ni-Fe з урахуванням явища росту зародків. Ми продемонстрували, що фактично концентрація електроліту майже не впливає на тип нуклеації, але її вплив виявляється в лінійності кривої. Коефіцієнт дифузії та густина нуклеації для миттєвої нуклеації та швидкість нуклеації для прогресивної нуклеації також були оцінені, а реакція осадження тонкої плівки Ni-Fe показала нуклеацію та ріст (3D) під контролем дифузії. Проростання Ni-Fe є важким на поверхнях мідної підкладки за низьких перенапруг, і максимальний час зменшується зі збільшенням перенапруг.Ni-Fe alloy thin films are one of the oldest topics within the framework of electrochemistry because they exhibit a range of physical properties that lead to their widespread use in a variety of applications. In this study, the effects of bath composition and applied potential on Ni-Fe alloy thin films were investigated. Ni-Fe thin films were electrodeposited on copper substrates at a pH of approximately 3, and the experiments were performed at room temperature. The deposition time was equal to 10 min for all deposited samples and the applied potential (– 1.35 V, 1 V) and bath composition (0.0.05, 0.075 and 0.1 M). The experiments were performed using electrochemical techniques such as cyclic voltammetry (CV), and an electrochemical method called chronoamperometry was used to develop electrolytic alloys of the Ni-Fe type by considering the nucleation growth phenomenon. We demonstrated in fact, the concentration of the electrolyte had almost no effect on the type of nucleation, but its effect appeared in the linearity of the curve. The diffusion coefficient and nucleation density for instantaneous nucleation and the nucleation rate for progressive nucleation were also evaluated and the Ni-Fe thin film deposition reaction showed nucleation and growth (3D) under diffusion control. Germination of Ni-Fe is difficult on copper substrate surfaces for low overpotentials, and the maximum time decreases with increasing overpotentials

Error analysis for operations in solid modeling in the presence of uncertainty

Abstract. The problem of maintaining consistent representations of solids, in computer-aided design, and of giving rigorous proofs of error bounds for operations such as regularized Boolean intersection, has been widely studied for at least two decades. One of the major difficulties is that the representations used in practice are not only in error, they are fundamentally inconsistent. Such inconsistency is one of the main bottlenecks in downstream applications. This paper provides a framework for error analysis in the context of solid modeling, in the case where the data is represented using the standard representational method, and where the data may be uncertain. Included are discussions of ill-condition, error measurement, stability of algorithms, inconsistency of defining data, and the question of when we should invoke methods outside the scope of numerical analysis. A solution to the inconsistency problem is proposed and supported by theorems: it is based on the use of Whitney extension to define sets, called QuasiNURBS sets, which are viewed as realizations of the inconsistent data provided to the numerical method. A detailed example illustrating the problem of regularized Boolean intersection is also given

FAULT DETECTION AND DIAGNOSIS ON A PWM INVERTER BY DIFFERENT TECHNIQUES

This paper investigates the use of different techniques for fault detection in voltage-fed asynchronous machine drive systems. With the proposed techniques it is possible to detect and identify the power switch in which the fault has occurred. A diagnosis system which uses only the input variables of the drive is presented. It is based on the analysis of the current-vector trajectory, of the instantaneous frequency in faulty mode, and the evaluation of machine state variables which are processed due to the machine control algorithm. With this algorithm a fast an reliable fault detection can be realized. Furthermore limited drive operation in case of a fault mode will be discussed. All obtained results are based on computer simulation. These knowledge based methods have been test in simulation