Theoretical analysis of control properties for the brushless doubly fed reluctance machine

Presents the fundamental theory, modelling aspects and operating/control principles of the BDFRM. This emerging machine technology is being regarded by academic and industrial communities as a prospective brushless candidate for wind turbine generators (especially off-shore installations) and large pump drives where it can offer reliable, maintenance-free, operation and competitive performance at low cost due to the use of a smaller inverter. The results in the paper are the outcomes of a joint research project (Australian Research Council - ARC funded) of the author

Comparison of doubly-fed induction generator and brushless doubly-fed reluctance generator for wind energy applications

Phd ThesisThe Doubly-fed Induction Generator (DFIG) is the dominant technology for variable-speed wind power generation due in part to its cost-effective partially-rated power converter. However, the maintenance requirements and potential failure of brushes and slip rings is a significant disadvantage of DFIG. This has led to increased interest in brushless doubly-fed generators. In this thesis a Brushless Doubly-Fed Reluctance Generator (BDFRG) is compared with DFIG from a control performance point of view. To compare the performance of the two generators a flexible 7.5kW test facility has been constructed. Initially, a classical cascade vector controller is applied to both generators. This controller is based on the stator voltage field orientation method with an inner rotor (secondary stator) current control loop and an outer active and reactive power control loop. The dynamic and steady state performance of two generators are examined experimentally. The results confirm that the BDFRG has a slower dynamic response when compared to the DFIG due to the larger and variable inductance. Finally a sensorless Direct Power Control (DPC) scheme is applied to both the DFIG and BDFRG. The performance of this scheme is demonstrated with both simulation and experimental results.Engineering and Physical Sciences Research Council (EPSRC) and Overseas Researcher Scholarship (ORS

Modeling and control of brushless doubly-fed bar cage induction machines

Thesis (MEng)--Stellenbosch University, 2022.ENGLISH ABSTRACT: In recent years the requirement for more sustainable sources of energy has increased sig nificantly, with wind energy growing increasingly as a renewable source. Many countries are investing greatly in sustainable growth by going completely renewable. Countries like Iceland had an annual consumption of 60.8 TWh in 2019, of which 79% was produced by renewable energy sources. For this growth to be sustainable, more efficient and eco nomic sources of renewable energy will be required. The Brushless Doubly Fed Induction Generator (BDFIG) has become a focus point due to its variable speed capability and brushless technology. The direct-current-link (DC-link voltage) in the BDFIG systems’ back to back con verter allow for bidirectional power flow of the control winding’s power. Making effective control of the DC-link voltage a necessity. Due to the presence of switching elements in the back-to-back converter, there are harmonics introduced into the utility network. To mitigate this low pass filters such as inductance capacitance (LCL) and resistive inductive (RL) filters are often used. Currently, BDFIGs are not used in sizable wind farms. This is mostly due to their complexity when compared to standard doubly fed induction generators (DFIG’s) and permanent magnet synchronous generators (PMSGs). Thus far they have mostly been used in islanding applications. In this mode of operation they must be controlled to provide stable voltages at constant frequency with varying load conditions and changing wind speeds. To compete with DFIG’s which are already in the market, the BDFIG has a few disadvantages due to its slightly more complex structure, higher cost and larger dimensions. In this thesis, the power control of the grid-connected BDFIG systems in wind turbine applications are presented. Additionally the control of these machines as motors are also investigated and performed. An experimental machine consisting of a bar cage rotor is modeled in detail and controlled in simulation and by experimentation. DC-link volt age control is analyzed whereby the grid-side converter is controlled as a voltage source converter. Vector control is used in all control solutions, with reductions in control com plexity made and analyzed for the control winding side of the machine to reduce cost and improve robustness while maintaining responsiveness and accuracy.AFRIKAANSE OPSOMMING: In die laaste paar jaar het die aanvraag vir meer volhoubare energiebronne aansienlik toegeneem, veral wanneer daar gekyk word na wind energie as energiebron. Baie lande is al klaar besig om grootliks in hernubare energie te belê. Ysland, byvoorbeeld, het ’n jaarlikse verbruik van 60.8 TWh in 2019 gehad, waarvan 79% van die energie geproduseer was deur hernubare bronne. Vir die groei om volhoubaar te wees word meer effektiewe en ekonomiese hernubare energiebronne benodig. Die Brusellose Dubbel Gevoerde Induksie Generator (BDGIG) het, as gevolg van die masjien se veranderlike spoed vermoë en brusellose tegnologie, n fokus punt in die navorsingsveld geword. Die direkte stroom (DS) skakel spanning in die BDGIG sisteme se rug-aan-rug omskakelaar laat tweerigting krag vloei van die beheer winding se krag toe. Dus is effektiewe beheer van die DS-skakel se spanning nodig. As gevolg van die wisselings elemente wat in rug-aan-rug omskakelaars voorkom, kan daar harmonieke in die krag netwerk geïnduseer word. Om hierdie te versag word laag deurlaat filters, soos LCL en RL filters, gereeld gebruik. Tans word BDGIG nie op groot wind plase gebruik nie. Dit is meestal as gevolg van die kompleksiteit daarvan wanneer dit met standaard DGIGe en permanente magneet sinkroon masjinee (PMSMe) vergelyk word. Tot dusver is dit meestal vir eiland wyse toepassing gebruik. In hierdie wyse van werking moet hulle beheer word om stabiele spanning teen n konstante frekwensie met afwisselende lading kondisies en veranderende wind spoed te kan bied. Dit is moeilik vir die BDGIG om met DGIGe wat klaar in die mark is te kompeteer aangesien dit nadele soos n meer komplekse struktuur, hoër kostes en groter dimensies het. In dié tesis word die krag beheer van die krag-netwerk-gekoppelde BDGIG sisteme in wind turbine toepassing voorgestel. Verder word die beheer van die masjiene as motors nagevors en uitgevoer. n Eksperimentele masjien, wat bestaan uit n staafhok rotor, is in detail ontwerp en beheer in simulasie sowel as deur eksperimentering. DC-skakel spanning beheer is ook geanaliseer waardeur die krag-netwerk omskakelaar as spanning bron beheer word. Vektor beheer word in alle kontrole oplossings gebruik, met vermindering in beheer kompleksiteit wat plaasvind en ’n analise van die beheer winding kant van die masjien wat verminderde koste en verbeterde robuustheid vertoon terwyl dit responsiwiteit en akkuraatheid volhou.Master

Vector control of brushless doubly-fed induction machines based on highly efficient nonlinear controllers

Recent advancement in design and control of brushless doubly-fed induction machine (BDFIM) has substantially improved its performance. In this article, two high efficient vector control schemes are proposed for the BDFIM drive based on Lyapunov nonlinear techniques. The first scheme aims for speed control with a one-level structure without an inner loop controller, and the rotor speed error is delivered to a backstepping speed controller. The second scheme has a two-level structure with a backstepping controller and a model reference controller for torque and speed control, respectively. To enhance the performance, the proposed control schemes are based on a novel maximum torque per Ampere (MTPA) control strategy, and their stability is proven by Lyapunov control theory. The proposed controllers are validated experimentally on a 3-kW prototype D132-BDFIM by a TMS320F2833 microcontroller synchronized with a personal computer, and show superior performance over optimal proportional-integral controllers under changing reference speed and load torque

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

Brushless Doubly-Fed Reluctance Machines for Aerospace Electrical Power Generation Systems

This thesis describes a programme of research encompassing the design, optimisation and experimental testing of a brushless doubly fed reluctance machine (BDFRM) for use as an aerospace electrical generator, specifically a direct line connected generator, to widen the input shaft speed beyond the normal constraints imposed by the 360-800Hz specification for a variable-frequency AC aerospace network. BDFRMs offer the functionality of frequency correction, via a control winding, and have the advantage of using a robust reluctance rotor. A partially-rated control winding converter can, in principle, be used to provide the slip power required. A further advantage of the BDFRM is the inherent fail-safe nature of these machines, with the output voltage collapsing as soon as the control winding current has been removed. A synchronous reluctance machine was studied as a means of providing a baseline for the BDFRM performance, including a comparison of the effect of scaling on power density. A large number of time-stepped finite element simulations were undertaken to explore BDFRM performance, in particular, the influence of magnetic saturation in limiting the achievable power density and in compromising power quality. Detailed optimisation of a BDFRM was undertaken, including systematic mechanical design of the rotor for high speed operation. This analysis illustrates the significant compromises in machine electromagnetic performance which result from the need to accommodate mechanical stress. The scope for employing small amounts of permanent magnet material in the rotors of both synchronous reluctance machines and BDFRMs, to improve the machine performance at the lower end of the current density range, was investigated. Following detailed optimisation, a demonstrator machine was manufactured, which includes a skewed rotor. The performance of this machine was measured at a number of test points to verify predictions of output power, voltage and voltage harmonics

Analysis of the integration of two DFIGs with rotating power electronics for wind energy application. Analisi sull'integrazione di due generatori DFIG con elettronica di potenza su rotore per generazione eolica

Questa tesi descrive l'analisi effettuata su una nuova topologia di doubly-fed-induction-generator per la generazione di potenza elettrica da eolico, nella quale due generatori sono connessi in parallelo condividendo lo stesso albero, entrambi contribuendo alla generazione di potenza verso la rete elettric

Development of a scaled doubly-fed induction generator for assessment of wind power integration issues

Years of experience have been dedicated to the advancement of thermal power plant technology, and in the last decade the investigation has focused on the wind energy conversion system (WECS). Wind energy will play an important role in the future of the energy market, due to the changing climate and the fossil fuel crisis. Initially, wind energy was intended to cover a small portion of the energy market, but in the long term it should compete with conventional fossil fuel power generation. The movement of the power system towards this new phenomena has to be investigated before the wind energy share increases in the network. Therefore, the wind energy integration issues serve as an interesting topic for authors to improve the perception of integration, distribution, variability and power flow issues. Several simulation models have been introduced in order to resolve this issue, however, the variety in types of wind turbines and the network policies result in these models having limited accuracy or being developed for specific issues. The micro-machine is introduced in order to overcome the challenges of simulation models and the costs involved in field tests. In the past, the grid integration issue of large turbo-alternators was solved by the micro-machines. A variety of tests are possible with the micro-machines and they also increase the flexibility of the system. The increased accuracy as well as the ability to carry out real-time analysis and compare actual field test data are strengths worth utilizing. This project involves the designing and the prototyping of a scaled doubly-fed induction generator (micro-DFIG). The machine is also analysed and tested. The scaling of the micro-machine is achieved by means of a dimensional analysis, which is a mathematical method that allows machines and systems to be downscaled by establishing laws of similitude between the reference model and its scaled model. MATLAB/SIMULINK, Maxwell and Solid Work are employed to achieve the objectives of this project