An improved rotor speed observer for standalone brushless doubly-fed induction generator under unbalanced and nonlinear loads

The conventional control methods for brushless doubly-fed induction generator (BDFIG) normally employ mechanical sensors to acquire the information of rotor speed, which brings many disadvantages in the cost, complexity, reliability, and so on. This paper presents an improved rotor speed observer (RSO) for the sensorless operation of a standalone BDFIG, which is based on the power winding (PW) voltage and control winding (CW) current. In order to eliminate the impact of unbalanced and nonlinear loads on the RSO, second-order generalized integrators (SOGIs) and low-pass filters (LPFs) are introduced to pre-filter the PW voltage and CW current, respectively. Through comprehensive parameter design, the response speed of the improved RSO will be not lower than that of the basic RSO with ensuring the filtering effect of these additional filters. In addition, the proposed RSO is independent to machine parameters except the pole pairs. Comprehensive experiments are conducted and results verify the proposed improved RSO applied to the standalone BDFIG. Also, the applicability of the proposed RSO on another dual-electrical-port machine, DFIG, is confirmed by simulation results

Fractional kVA Rating PWM Converter Doubly Fed Variable Speed Electric Generator Systems:An Overview in 2020

Variable speed generator systems (VSGs) are at work in the now 600 GW installed wind power plants (parks). Also, they are used as vehicular and on ground stand-alone generators. VSGs imply full kVA rating PWM converters in permanent magnet (PM) or in electrically excited synchronous or in cage rotor inductance generators. But, to reduce cost in absence of PMs at a reasonable initial cost (weight) and efficiency, the fractional kVA PWM converter doubly fed induction generators (DFIG) cover now about 50% of all installed power in wind generators. The present paper reviews recent progress in DFIG and various forms of brushless DFGs (doubly fed generators) characterized in terms of topology, design, performance and advanced control for healthy and faulty load conditions in the hope of inspiring new, hopefully ground breakings, progress for wind and hydro energy conversion and in vehicular and on the ground stand-alone generator applications

Improved vector control methods for brushless double fed induction generator during inductive load and fault conditions

A Brushless Double-Fed Induction Generator (BDFIG) has shown tremendous success in wind turbines due to its robust brushless design, less maintenance, smooth operation, and variable speed characteristics. These generators are composed of two back-to-back voltage source converters, a Grid Side Converter (GSC) and a Rotor Side Converter (RSC). Existing control techniques use a “trial and error” method that results in a poor dynamic response in machine parameters during the absence of load. The RSC control is used for reactive current control during the inductive load insertion. However, it is more suitable for stabilizing steady-state behaviour, but it suffers from slow response and introduces a double fundamental frequency component to the Point of Common Coupling (PCC) voltage. In addition, generally, a Low Voltage Ride Through (LVRT) fault is detected using a hysteresis comparison of the power winding voltage. The LVRT capability is provided by using fixed reference values to control the winding current. This approach results in an erroneous response, sub-optimal control of voltage drops at PCC, and false alarms during transient conditions. This thesis aims to solve the mentioned issues by using an improved vector control method. Internal Model Control (IMC) based Proportional-Integral (PI) gains calculation is used for GSC and RSC. These are controlled to enhance the transient response and power quality during no-load, inductive load, and fault conditions. Firstly, a GSC-based vector control method is proposed to suppress the PCC voltage fluctuations when a large inductive load is suddenly connected. The proposed technique is based on an analytical model of the transient behaviour of the voltage drop at the PCC. To block a double fundamental frequency component as a result of reactive current compensation, a notch filter is designed. Secondly, an RSC-based vector control method is proposed using an analytical model of the voltage drop caused by a short circuit. Moreover, using a fuzzy logic controller, the proposed technique employs the voltage frequency in addition to the power winding voltage magnitude to detect LVRT conditions. The analytical model helps in reducing the power winding voltage drop while the fuzzy logic controller leads to better response and faster detection of faults. However, the reference value for reactive current compensation is analysed using an analytical model of the voltage drop at the PCC in the event of a short-circuit fault. The results obtained from MATLAB/Simulink show that the GSC-based vector control method technique can effectively reduce about 10% voltage drop at PCCs. Total Harmonics Distortion (THD) is improved to 22.3% by notch filter in comparison with an existing technique such as instantaneous reactive power theory. The RSC-based vector control method can achieve up to 11% voltage drop reduction and improve the THD by 12% compared to recent synchronous control and flux tracking methods

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

New synchronous machine rotor design for easy insertion of excitation coils based on surrogate optimisation

The thesis reviews the development of traditional synchronous machine design and point out one problem with the manufacture of wound rotor synchronous machines. Install and repair process of the rotor windings can be considered labor-costly and time-consuming in synchronous machine design. The conclusion indicates a new winding method would be helpful for not only the new machines but also for rewound machines. A new rotor design for the easy insertion and repair of the rotor windings is then introduced. This new asymmetrical rotor shows good potentials for reducing the maintenance and repair costs of synchronous machines, making it suitable for manufacturers within the mass production markets such as gen-sets, steam turbines, wind power generators. Simulation results from 2-D finite element analysis and experimental results from testing a 27.5 kVA prototype machine have verified the performance of the new rotor. The results show that the asymmetrical machine’s electromagnetic performance is worse than traditional design and need to be optimised. The shape of the rotor is then optimised based on novel surrogate method in order to achieve the lowest power loss under the maximum power output. This method combines surrogate optimistaion with finite element method. It significantly reduces the time cost of the optimization process and can be applied with very complicated geometry design of the rotor. The performance of the new rotor is examined in 2-D finite element software and validated by experiments. After optimisation, the efficiency of the new rotor can reach the same level of the traditional rotor in electromagnetic performance in addition to its easy insertion and repair feature

Studies in Electrical Machines & Wind Turbines associated with developing Reliable Power Generation

The publications listed in date order in this document are offered for the Degree of Doctor of Science in Durham University and have been selected from the author’s full publication list. The papers in this thesis constitute a continuum of original work in fundamental and applied electrical science, spanning 30 years, deployed on real industrial problems, making a significant contribution to conventional and renewable energy power generation. This is the basis of a claim of high distinction, constituting an original and substantial contribution to engineering science

Renewable Energy

Renewable Energy is energy generated from natural resources - such as sunlight, wind, rain, tides and geothermal heat - which are naturally replenished. In 2008, about 18% of global final energy consumption came from renewables, with 13% coming from traditional biomass, such as wood burning. Hydroelectricity was the next largest renewable source, providing 3% (15% of global electricity generation), followed by solar hot water/heating, which contributed with 1.3%. Modern technologies, such as geothermal energy, wind power, solar power, and ocean energy together provided some 0.8% of final energy consumption. The book provides a forum for dissemination and exchange of up - to - date scientific information on theoretical, generic and applied areas of knowledge. The topics deal with new devices and circuits for energy systems, photovoltaic and solar thermal, wind energy systems, tidal and wave energy, fuel cell systems, bio energy and geo-energy, sustainable energy resources and systems, energy storage systems, energy market management and economics, off-grid isolated energy systems, energy in transportation systems, energy resources for portable electronics, intelligent energy power transmission, distribution and inter - connectors, energy efficient utilization, environmental issues, energy harvesting, nanotechnology in energy, policy issues on renewable energy, building design, power electronics in energy conversion, new materials for energy resources, and RF and magnetic field energy devices

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