A new sensorless speed control scheme for doubly-fed reluctance generators

This paper presents the development and experimental validation of a novel angular velocity observer-based field-oriented control algorithm for a promising low-cost brushless doubly fed reluctance generator (BDFRG) in wind power applications. The BDFRG has been receiving increasing attention because of the use of partially rated power electronics, the high reliability of brushless design, and competitive performance to its popular slip-ring counterpart, the doubly fed induction generator. The controller viability has been demonstrated on a BDFRG laboratory test facility for emulation of variable speed and loading conditions of wind turbines or pump drives

Magnetic field modelling of machine and multiple machine systems using dynamic reluctance mesh modelling

This thesis concerns the modified and improved, time-stepping, dynamic reluctance mesh (DRM) modelling technique for machines and its application to multiple machine systems with their control algorithms. Improvements are suggested which enable the stable solution of the resulting complex non-linear equations. The concept of finite element (FE) derived, overlap-curves has been introduced to facilitate the evaluation of the air-gap reluctances linking the teeth on the rotor to those on the stator providing good model accuracy and efficient computation. Motivated industrially, the aim of the work is to develop a fast and effective simulation tool principally for evaluating salient pole generator system designs including the generator, exciter and the automatic voltage regulator (AVR). The objective is to provide a modelling system capable of examining the detail of machine operation including saturation of main and leakage flux paths, slotting and space harmonics of the windings. Solutions are obtained in a sufficiently short computational time to facilitate efficient iterative design procedures in an industrial design office. The DRM modelling technique for electrical machines has been shown in this thesis to be a fast and efficient tool for electrical machine simulation. Predicted results for specific machine and system designs have been compared with FE solutions and with experimental results showing, that for engineering purposes, the technique yields excellent accuracy. The DRM method has a great advantage in multiple machine simulations. This is because magnetic field calculations are limited to evaluating only the most important information so saving computation time. A brushless generating system including the excitation system and control scheme has been modelled. Additionally a cascaded, doubly fed induction generator for wind generator applications has also been modelled. These different applications for the dynamic reluctance mesh method have proved that this approach yields an excellent machine and machine-system evaluation and design tool

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

Transient stability enhancement of a gridconnected wind farm using an adaptive neurofuzzy controlled-flywheel energy storage system

With the rapid growth of the wind energy systems in the past years and their interconnection with the existing power system networks, it has become very significant to analyse and enhance the transient stability of the wind energy conversion systems connected to the grid. This study investigates the transient stability enhancement of a grid-connected wind farm using doubly-fed induction machine-based flywheel energy storage system. A cascaded adaptive neuro-fuzzy controller (ANFC) is introduced to control the insulated gate bipolar transistor switches-based frequency converter to enhance the transient stability of the grid-connected wind farm. The performance of the proposed control strategy is analysed under a severe symmetrical fault condition on both a single-machine infinite bus model and the IEEE-39 bus New England test system. The transient performance of the system is investigated by comparing the results of the system using the proposed ANFCs with that of the black-box optimisation technique-based proportional-integral controllers. The validity of the system is verified by the simulation results which are carried out using PSCAD/EMTDC environment