Analysis of optimized multilevel matrix converter for DFIG based wind energy conversion system

Wind power generation is an increasing trend worldwide. Multilevel converters in this regard are playing an essential role in high power system applications due to various features. In this paper, multi-objective optimization based multilevel matrix converter (MOMMC) is proposed for wind energy conversion system. The assessment of feasibility through the discussion of two objectives: reliability and cost have been considered in this study. Initially, the model of the two objectives is assessed against redundancy configuration and power loss. Then a multi-objective function is defined for achieving low cost and high reliability. The optimal topology for the matrix multi-level converter is determined using the membership function, and the solution is selected from the Pareto-optimal set. The reliability and cost analysis of the proposed MOMMC is performed. Simulation is carried out for the proposed multi-objective optimization based multilevel matrix converter using the PSIM software. To establish the validity of the proposed method, two different cases: 1) fixed and 2) variable speed of 9 MW doubly-fed induction generator-based wind energy system are considered. The results show the superiority of the proposed method over the others.

Fault detection in wind turbine's doubly fed induction generators

El següent treball final de grau té com a objectiu proporcionar una manera d'identificar fallades en aerogeneradors basats en generadors d'inducció doblement alimentats (DFIG, per les seves sigles en anglès), un dels tipus de generadors més utilitzats actualment en el camp dels aerogeneradors de mida industrial. A causa de les severes condicions en les quals operen els aerogeneradors DFIG, la detecció de fallades és un tema de gran preocupació i importància. L'enfocament proposat simula l'aerogenerador utilitzant el programari MATLAB/Simulink, una eina molt comuna per a modelar sistemes dinàmics. L'aerogenerador, inclosos els convertidors del costat del rotor i l'estator a més del sistema de control del DFIG, es modelen amb precisió en el model de simulació. El model de generador utilitzat per a la simulació s'ha modificat per a simular amb major precisió el comportament de l'aerogenerador. L'enfocament que ha pres el treball consisteix a combinar mètodes d'aprenentatge automàtic i tècniques de processament de senyals per a trobar errors en el convertidor del costat del rotor i l'estator, a més de la xarxa. L'anàlisi wavelet s'utilitza per a examinar els senyals del DFIG amb la finalitat d'identificar les característiques indicadores de fallades. A continuació, les característiques recopilades s'utilitzen per a entrenar classificadors d'aprenentatge automàtic com Support Vector Machines (SVM), K-Nearest Neighbors (KNN) i Arbres de Decisió per a trobar errors en el DFIG. Per a avaluar la tècnica proposada, es realitzen simulacions amb diversos tipus de fallades, com a curtcircuits i baixades i de tensió. L'estudi ofereix una eina pràctica perquè els operadors d'aerogeneradors i enginyers puguin trobar defectes del DFIG i evitin llargs períodes d'inactivitat, que poden resultar costosos.El siguiente trabajo final de grado tiene como objetivo proporcionar una forma de identificar fallos en aerogeneradores basados en generadores de inducción doblemente alimentados (DFIG, por sus siglas en inglés), uno de los tipos de aerogeneradores más utilizados actualmente en el campo de los aerogeneradores de tamaño industrial. Debido a las severas condiciones en las que operan los aerogeneradores DFIG, la detección de fallos es un tema de gran preocupación e importancia. El enfoque propuesto simula el aerogenerador utilizando el software MATLAB/Simulink, una herramienta muy común para modelar sistemas dinámicos. El aerogenerador, incluidos los convertidores del lado del rotor y estator además del sistema de control del DFIG, se modelan con precisión en el modelo de simulación. El enfoque que ha tomado el trabajo consiste en combinar métodos de aprendizaje automático y técnicas de procesamiento de señales para encontrar errores en el convertidor del lado del rotor, estator y en la red. El análisis wavelet se utiliza para examinar las señales del DFIG con el fin de identificar las características indicadoras de fallos. A continuación, las características recopiladas se utilizan para entrenar clasificadores de aprendizaje automático como Support Vector Machines (SVM), K-Nearest Neighbors (KNN) y Árboles de Decisión para encontrar errores en el DFIG. Para evaluar la técnica propuesta, se realizan simulaciones con varios tipos de fallos, como cortocircuitos y subidas y bajadas de tensión. El estudio ofrece una herramienta práctica para que los operadores de aerogeneradores e ingenieros puedan encontrar defectos en el DFIG y eviten largos periodos de inactividad, que podrían resultar costosos.The following bachelor’s thesis has the objective of providing a way to identify faults in doubly fed induction generators (DFIG) based wind turbines, one of the most widely used types of wind turbines in the field of industrial-sized wind turbines currently. Due to the severe conditions that DFIG wind turbines are operating in, fault detection becomes a topic of big concern. The suggested approach simulates the wind turbine using MATLAB/Simulink software, a very common and well-liked tool for modelling dynamic systems. The wind turbine, including the rotor-side and stator-side converters and the control system for the DFIG, are all precisely modelled in the simulation model. The approach studied combines machine learning methods and signal processing techniques to find errors in the rotor-side, stator-side and grid. Wavelet analysis is used to examine the DFIG signals in order to identify fault-indicating characteristics. The collected characteristics are then used to train machine learning classifiers like Support Vector Machines (SVM), K-Nearest Neighbours (KNN) and Decision Trees to find errors in the DFIG. Simulations with several fault types, such as short circuits and voltage rise and drop are used to assess the suggested technique. The study offers a practical tool for wind turbine staff and engineers to find DFIG defects and prevent long periods of downtime, which could be expensive

Optimized servo-speed control of wind turbine coupled to doubly fed induction generator

Optimal control of any variable speed wind turbine needs maximum power point tracking (MPPT) coupled to doubly fed induction generator (DFIG) for better power generation. This paper offers a novel direct power servo-speed control of wind turbine. This latter is based on DFIG optimal hysteresis MPPT inverter current control combined with space voltage modulation (SVM) inverter voltage technique, thus providing a stable and continuous energy flow to power grid. In this design, the asynchronous machine stator is directly connected to the grid. Bidirectional power converter, acting as frequency converter, is rotor circuit located. Rectifier supplies rotor windings with voltages and reference frequency resulting from control procedure of the power exchange between the stator and grid. Inverter is directly controlled by means of SVM technique to maintain direct current (DC) bus voltage constant. Simulation results show that the proposed configuration improves power converters efficiency due that rotor circuit needs less power than stator circuit which is injected into the grid

Source Grid Interface of Wind Energy Systems

Wind power is one of the most developed and rapidly growing renewable energy sources. Through extensive literature review this thesis synthesizes the existing knowledge of wind energy systems to offer useful information to developers of such systems. Any prototyping should be preceded by theoretical analysis and computer simulations, foundations for which are provided here. The thesis is devoted to an in-depth analysis of wind energy generators, system configurations, power converters, control schemes and dynamic and steady state performance of practical wind energy conversion systems (WECS). Attention is mainly focused on interfacing squirrel cage Induction generators (SCIG) and doubly-fed induction generators (DFIG) with the power network to capture optimal power, provide controllable active and reactive power and minimize network harmonics using the two-level converter, as a power electronic converter. Control of active and reactive power, frequency and voltage are indispensable for stability of the grid. This thesis focuses on two main control techniques, field oriented control (FOC) and direct torque control (DTC) for the SCIG. The dynamic model of induction generator is non-linear and hence for all types of control, the flux and the torque have to be decoupled for maintaining linearity between input and output for achieving high dynamic performance. FOC is used for decoupled control for rotor flux and electromagnetic torque . The stator current is decomposed into flux and torque producing components and they both are controlled independently. FOC uses three feedback control loops generate gating signals for the converter. DTC also achieves high dynamic performance by decoupling of rotor flux and electromagnetic torque without the intermediate current loops. DTC asks for the estimation of stator flux and torque and like FOC has 2 branches which have flux and torque comparators. The errors between the set and the estimated value are used to drive the inverters. The two methods are valid for both steady and transient state. Their validity is confirmed by simulating the systems on MATLAB/Simulink platform and comparing them the results obtained by hand calculations. Further DFIG’s are introduced. The dynamic model is developed using the machines equivalent circuit and is expressed in the stationary, rotor and the synchronous reference frames for evaluating the performance of the machine. The stator of the DFIG is directly interfaced to the grid and by controlling the rotor voltage by a two level back-to-back converter the grid synchronization and power control is maintained. The DTC and the direct power control (DPC) methods are used to control the rotor side (RSC) and the grid side converter (GSC). The RSC generates the 3-ph voltages of variable frequency in order to control the generator torque and the reactive power exchanged between the stator and the grid. The GSC exchanges active power with the grid injected by the RSC with a constant frequency. The steady and transient behavior of the machine is investigated through simulations

Induction Motors

AC motors play a major role in modern industrial applications. Squirrel-cage induction motors (SCIMs) are probably the most frequently used when compared to other AC motors because of their low cost, ruggedness, and low maintenance. The material presented in this book is organized into four sections, covering the applications and structural properties of induction motors (IMs), fault detection and diagnostics, control strategies, and the more recently developed topology based on the multiphase (more than three phases) induction motors. This material should be of specific interest to engineers and researchers who are engaged in the modeling, design, and implementation of control algorithms applied to induction motors and, more generally, to readers broadly interested in nonlinear control, health condition monitoring, and fault diagnosis

Converter fault diagnosis and post-fault operation of a doubly-fed induction generator for a wind turbine

Wind energy has become one of the most important alternative energy resources because of the global warming crisis. Wind turbines are often erected off-shore because of favourable wind conditions, requiring lower towers than on-shore. The doubly-fed induction generator is one of the most widely used generators with wind turbines. In such a wind turbine the power converters are less robust than the generator and other mechanical parts. If any switch failure occurs in the converters, the wind turbine may be seriously damaged and have to stop. Therefore, converter health monitoring and fault diagnosis are important to improve system reliability. Moreover, to avoid shutting down the wind turbine, converter fault diagnosis may permit a change in control strategy and/or reconfigure the power converters to permit post-fault operation. This research focuses on switch fault diagnosis and post-fault operation for the converters of the doubly-fed induction generator. The effects of an open-switch fault and a short-circuit switch fault are analysed. Several existing open-switch fault diagnosis methods are examined but are found to be unsuitable for the doubly-fed induction generator. The causes of false alarms with these methods are investigated. A proposed diagnosis method, with false alarm suppression, has the fault detection capability equivalent to the best of the existing methods, but improves system reliability. After any open-switch fault is detected, reconfiguration to a four-switch topology is activated to avoid shutting down the system. Short-circuit switch faults are also investigated. Possible methods to deal with this fault are discussed and demonstrated in simulation. Operating the doubly-fed induction generator as a squirrel cage generator with aerodynamic power control of turbine blades is suggested if this fault occurs in the machine-side converter, while constant dc voltage control is suitable for a short-circuit switch fault in the grid-side converter.Wind energy has become one of the most important alternative energy resources because of the global warming crisis. Wind turbines are often erected off-shore because of favourable wind conditions, requiring lower towers than on-shore. The doubly-fed induction generator is one of the most widely used generators with wind turbines. In such a wind turbine the power converters are less robust than the generator and other mechanical parts. If any switch failure occurs in the converters, the wind turbine may be seriously damaged and have to stop. Therefore, converter health monitoring and fault diagnosis are important to improve system reliability. Moreover, to avoid shutting down the wind turbine, converter fault diagnosis may permit a change in control strategy and/or reconfigure the power converters to permit post-fault operation. This research focuses on switch fault diagnosis and post-fault operation for the converters of the doubly-fed induction generator. The effects of an open-switch fault and a short-circuit switch fault are analysed. Several existing open-switch fault diagnosis methods are examined but are found to be unsuitable for the doubly-fed induction generator. The causes of false alarms with these methods are investigated. A proposed diagnosis method, with false alarm suppression, has the fault detection capability equivalent to the best of the existing methods, but improves system reliability. After any open-switch fault is detected, reconfiguration to a four-switch topology is activated to avoid shutting down the system. Short-circuit switch faults are also investigated. Possible methods to deal with this fault are discussed and demonstrated in simulation. Operating the doubly-fed induction generator as a squirrel cage generator with aerodynamic power control of turbine blades is suggested if this fault occurs in the machine-side converter, while constant dc voltage control is suitable for a short-circuit switch fault in the grid-side converter

A Review of Control Techniques for Wind Energy Conversion System

Wind energy is the most efficient and advanced form of renewable energy (RE) in recent decades, and an effective controller is required to regulate the power generated by wind energy. This study provides an overview of state-of-the-art control strategies for wind energy conversion systems (WECS). Studies on the pitch angle controller, the maximum power point tracking (MPPT) controller, the machine side controller (MSC), and the grid side controller (GSC) are reviewed and discussed. Related works are analyzed, including evolution, software used, input and output parameters, specifications, merits, and limitations of different control techniques. The analysis shows that better performance can be obtained by the adaptive and soft-computing based pitch angle controller and MPPT controller, the field-oriented control for MSC, and the voltage-oriented control for GSC. This study provides an appropriate benchmark for further wind energy research

Control Method for the Wind Turbine Driven by Doubly Fed Induction Generator Under the Unbalanced Operating Conditions

This thesis illustrates the principle and the behavior for doubly fed electric machines used in variable speed wind power systems under the balanced and unbalanced operating conditions. A generalized control method for complete stator pulsating power elimination and harmonic elimination in grid currents with adjustable power factor of a doubly fed induction generator under the unbalanced operating conditions is proposed. The theoretical analysis of this proposed control method is presented and then demonstrated by the simulation in Powersim®. The grid ride-through-fault ability by using the proposed method is also teste