A Novel Algorithm for Rotor Speed Estimation of DFIGs Using Machine Active Power based MRAS Observer

This paper presents a new algorithm based on Model Reference Adaptive System (MRAS) and its stability analysis for sensorless control of Doubly-Fed Induction Generators (DFIGs). The reference and adjustable models of the suggested observer are based on the active power of the machine. A hysteresis block is used in the structure of the adaptation mechanism, and the stability analysis is performed based on sliding mode conditions. Simulation and practical results show appropriate operation and speed tracking of the observer with regard to obtained stability conditions

Performance comparisons of doubly-fed machines

This research project aims at evaluating a conversion system based on the emerging Brushless Doubly Fed Reluctance Machine (BDFRM) through a comparative experimental study with a traditional and well established slip-ring counterpart, the Doubly Fed Induction Machine (DFIM). One of the main objectives is to establish whether this alternative machine is worthy of industrial consideration in variable speed applications with limited speed ranges (e.g. wind turbines, pump-like drives etc.) in terms of control, reliability, efficiency and power factor performance as major criteria. Such kind of work has not been reported in the open-literature to date and represents the main contribution of the project being undertaken. A conventional and widely used parameter-independent vector control (VC) scheme has been selected for the operation of both the machines using a shaft-position sensor. The VC algorithm has been simulated and implemented in real-time on state-of-the-art eZdsp development platform based on the TMS320F28335 Digital Signal Controller (DSC). The control code has been derived from a programme written in C++ using the corresponding compiler, the Code Composer Studio (CCS). Comprehensive computer simulations have been done in Matlab/Simulink using the parameters obtained by off-line testing of the DFIM and BDFRM prototypes, which have been built in the same stator frame for comparison purposes. The simulation results have been experimentally verified on two identical test rigs where a commercial 4-quadrant cage induction machine V/f drive has been used as a prime mover or load for either the DFIM or the BDFRM subject to their operating mode. The preliminary experimental results on two small-scale prototypes have shown that the BDFRM can achieve competitive performance to the similarly rated DFIM and as such should warrant further investigation and increasing interests of both academic and industrial communities as a potential large-scale wind generator or a pump drive

Position/speed sensor-less control of wind energy conversion systems based on Rotor-Tied Doubly-Fed induction generator systems

Thesis (PhD)--Stellenbosch University, 2019.ENGLISH ABSTRACT: The doubly-fed induction generator (DFIG) is amongst the most popular wind turbine generator in South Africa. This is partly due to the fact that its backtoback power converters are partially rated. More precisely, they are rated at 30% of the generator rated power. A new DFIG topology has been proposed recently. That is the rotor-tied doubly-fed induction generator (RDFIG). In this topology, the rotor side is connected to the grid while the stator side is connected to the power converter. It has been shown that this topology holds the advantage of higher effeciency compared to the standard DFIG topology. High accuracy in all the measurements is required for the optimum operations of wind energy conversion systems (WECSs). The measurement of the rotor position/speed is amongst the most important measurements when it comes to implement any control system for the WECS. The conventional method of measuring the rotor position/speed is to use an electronic/mechanical sensor (encoder or resolver). This measurement involves the use of long cables and in a harsh environment, this can lead to faulty operations of the WECS. In this thesis, several slip speed estimators for sensor-less control of RDFIGbased WECSs are developed and implemented. The proposed slip speed estimators are based on the association of different sliding mode observers and the PLL estimator. The association of the PLL estimator improves the estimation performance by reducing the noise created by the sliding control control functions. Also, the proposed PLL estimator helps in avoiding a phase shift of π in super-synchronous operating conditions. In addition, in this thesis, several sliding mode observers were developed in order to improve the estimation performance. The proposed sliding mode observers were satisfactory for all the operating conditions of the RDFIG-based WECSs. The robustness of the proposed slip speed estimators is validated experimentally under various operating conditions. A 5.5-kW custom-designed gridconnected RDFIG test-bench based on a National Instrument (NI) PXIe-8115 controller is used. The proposed slip speed estimators solve the problem linked to the failure of the electromechanical sensors. The overall sensor-less control strategy provides an alternative to the sensor-based control of the RDFIGs. Also, the proposed sensor-less vector control strategy can be used as a back-up in case the electromechanical sensor fails.AFRIKAANSE OPSOMMING: Die dubbelgevoerde induksiegenerator (DFIG) is een van die gewildste windturbinegenerators in Suid-Afrika. Dit is deels as gevolg van die laer kapasiteit omsetters wat die DFIG benodig. 'n Nuwe DFIG-topologie is onlangs voorgestel: Die rotorgebonde DFIG (RDFIG). In dié topologie word die masjien se rotor aan die netwerk gekoppel en die stator aan laer kapasiteit omsetters. Dit is bewys dat hierdie topologie 'n hoër masjieneffektiwiteit het in vergelyking met die standaard-DFIG. Hoë akkuraatheid van metings word vereis vir die optimale beheer van windenergie-omsettingstelsels (WECS). Die meting van die rotorposisie en - spoed is van die belangrikste metings wanneer dit kom by die beheerstelsel van 'n WECS. Die konvensionele metode van rotorposisie- en rotorspoedmeting is deur middel van 'n kodeerder. Dié meting behels die gebruik van lang kabels in 'n fel omgewing, wat kan lei tot die foutiewe werking van die stelsel. In hierdie verhandeling word verskeie glipspoedafskatters vir die sensorlose beheer van 'n RDFIG-gebaseerde WECS ontwikkel en geïmplimenteer. Die voorgestelde glipspoedafskatter is gebaseer op die assosiasie van verskillende glymodus-observeerders en 'n PLL-afskatter. Die assosiasie van die PPLafskatter verbeter die afskattingprestasie deur die geruis van die glymodusbeheerstelsels te verminder. Die voorgestelde PPL-afskatter help ook om 'n faseskuif van π te vermy tydens super-sinchroonoperasie. In hierdie verhandeling word verskeie glymodusobserveerders ontwikkel om die afskattingsprestasie te verbeter. Die voorgestelde glymode-observeerders presteer bevredigend vir alle toestande van die RDFIC-gebaseerde WECS. Die kragtigheid van die voorgestelde glipspoedafskatters se geldigheid word onder verskeie toestande eksperimenteel getoets en bewys. 'n 5.5 kW netwerkgekoppelde RDFIG toetsbank gebaseer op 'n National Instrument PXIe-8115-beheerder word gebruik. Die probleem van gefaalde elektromeganiese sensors word deur die voorgestelde glipspoedafskatters opgelos. Die sensorlose beheerstrategie gee ook 'n alternatief vir tradisionele sensor-gebaseerde beheer van die RDFIG's.Master

Performance analysis of doubly-fed induction generator (DFIG)- based wind turbine with sensored and sensorless vector control

PhD ThesisConventional energy sources are limited and pollute the environment. Therefore more attention has been paid to utilizing renewable energy resources. Wind energy is the fastest growing and most promising renewable energy source due to its economically viability. Wind turbine generator systems (WTGSs) are being widely manufactured and their number is rising dramatically day by day. There are different generator technologies adopted in wind turbine generator systems, but the most promising type of wind turbine for the future market is investigated in the present study, namely the doubly-fed induction generator wind turbine (DFIG). This has distinct advantages, such as cost effectiveness, efficiency, less acoustic noise, and reliability and in addition this machine can operate either in grid-connected or standalone mode. This investigation considers the analysis, modeling, control, rotor position estimation and impact of grid disturbances in DFIG systems in order to optimally extract power from wind and to accurately predict performance. In this study, the dynamic performance evaluation of the DFIG system is depicted the power quantities (active and reactive power) are succeed to track its command signals. This means that the decouple controllers able to regulating the impact of coupling effect in the tracking of command signals that verify the robust of the PI rotor active power even in disturbance condition. One of the main objectives of this study is to investigate the comparative estimation analysis of DFIG-based wind turbines with two types of PI vector control using PWM. The first is indirect sensor vector control and the other type includes two schemes using model reference adaptive system (MRAS) estimators to validate the ability to detect rotor position when the generator is connected to the grid. The results for the DFIG-based on reactive power MRAS (QRMRAS) are compared with those of the rotor current-based MRAS (RCMRAS) and the former scheme proved to be better and less sensitive to parameter deviations, its required few mathematical computations and was more accurate. During the set of tests using MATLAB®/SMULINK® in adjusting the error between the reference and adaptive models, the estimated rotor position can be obtained with the objective of achieving accurate rotor position information, which is usually measured by rotary encoders or resolvers. The use of these encoders will conventionally lead to increased cost, size, weight, and wiring ii complexity and reduced the mechanical robustness and reliability of the overall DFIG drive systems. However the use of rotor position estimation represents a backup function in sensor vector control systems when sensor failure occurs. The behavioral response of the DFIG-based wind turbine system to grid disturbances is analyzed and simulated with the proposed control strategies and protection scheme in order to maintain the connection to the network during grid faults. Moreover, the use of the null active and reactive reference set scheme control strategy, which modifies the vector control in the rotor side converter (RSC) contributes to limiting the over-current in the rotor windings and over-voltage in the DC bus during voltage dips, which can improve the Low Voltage Ride-through (LVRT) ability of the DFIG-based wind turbine system.my home country of Iraq and its Ministry of Planning for providing a scholarship for my study

Grid fault ride through for wind turbine doubly-fed induction generators

EngD ThesisWind farms must contribute to the stability and reliability of the transmission grid, if they are to form a robust component of the electrical network. This includes providing grid support during grid faults, or voltage dips. Transmission system grid codes require wind farms to remain connected during specified voltage dips, and to supply active and reactive power into the network. Doubly-fed induction generator (DFIG) technology is presently dominant in the growing global market for wind power generation, due to the combination of variable-speed operation and a cost-effective partially-rated power converter. However, the DFIG is sensitive to dips in supply voltage. Without specific protection to 'ride through' grid faults a DFIG risks damage to its power converter due to over-current and/or overvoltage. Conventional converter protection via a sustained period of rotor-crowbar closed-circuit leads to poor power output and sustained suppression of the stator voltages. This thesis presents a detailed understanding of wind turbine DFIG grid fault response, including flux linkage behaviour and magnetic drag effects. A flexible 7.5kW test facility is used to validate the description of fault response and evaluate techniques for improving fault ride-through performance. A minimum threshold rotor crowbar method is presented, successfully diverting transient over-currents and restoring good power control within 45ms of both fault initiation and clearance. Crowbar application periods were reduced to 11-16ms. A study of the maximum crowbar resistance suggests that this method can be used with high-power DFIG turbines. Alternatively, a DC-link brake method is shown to protect the power converter and quench the transient rotor currents, allowing control to be resumed; albeit requiring 100ms to restore good control. A VAr-support control scheme reveals a 14% stator voltage increase in fault tests: reducing the step-voltage impact at fault clearance and potentially assisting the fault response of other local equipment.EPSR

High Performance Control Techniques for Multiphase eDrives

L'abstract è presente nell'allegato / the abstract is in the attachmen

Grid fault ride through for wind turbine doubly-fed induction generators

Wind farms must contribute to the stability and reliability of the transmission grid, if they are to form a robust component of the electrical network. This includes providing grid support during grid faults, or voltage dips. Transmission system grid codes require wind farms to remain connected during specified voltage dips, and to supply active and reactive power into the network. Doubly-fed induction generator (DFIG) technology is presently dominant in the growing global market for wind power generation, due to the combination of variable-speed operation and a cost-effective partially-rated power converter. However, the DFIG is sensitive to dips in supply voltage. Without specific protection to 'ride through' grid faults a DFIG risks damage to its power converter due to over-current and/or overvoltage. Conventional converter protection via a sustained period of rotor-crowbar closed-circuit leads to poor power output and sustained suppression of the stator voltages. This thesis presents a detailed understanding of wind turbine DFIG grid fault response, including flux linkage behaviour and magnetic drag effects. A flexible 7.5kW test facility is used to validate the description of fault response and evaluate techniques for improving fault ride-through performance. A minimum threshold rotor crowbar method is presented, successfully diverting transient over-currents and restoring good power control within 45ms of both fault initiation and clearance. Crowbar application periods were reduced to 11-16ms. A study of the maximum crowbar resistance suggests that this method can be used with high-power DFIG turbines. Alternatively, a DC-link brake method is shown to protect the power converter and quench the transient rotor currents, allowing control to be resumed; albeit requiring 100ms to restore good control. A VAr-support control scheme reveals a 14% stator voltage increase in fault tests: reducing the step-voltage impact at fault clearance and potentially assisting the fault response of other local equipment.EThOS - Electronic Theses Online ServiceEPSRCGBUnited Kingdo

Coordinated control of wind power and energy storage

Nowadays, wind power has become one of the fastest growing sources of electricity in the world. Due to the inherent variability and uncertainty, wind power integration into the grid brings challenges for power systems, particularly when the wind power penetration level is high. The challenges exist in many aspects, such as reliability, power quality and stability. With the rapid development of energy storage technology, the application of Energy Storage System (ESS) is considered as an effective solution to handle the aforementioned challenges. The main objective of this study is to investigate the coordinated control of wind power and ESS. Due to the different technical characteristics, such as power and energy density, ESS can play different roles either in generation-side, grid-side or demand side. This thesis focuses on the following two scenarios:• Scenario 1: As a part of wind farm, the ESS plays a generation-side role which aims to improve the grid-friendliness of the wind farm. • Scenario 2: As a part of microgrid, the ESS is used to efficiently accommodate the wind power fluctuation.Around the main objective, the relevant research fields including the wind turbine modeling and control, wind farm modeling and control, planning of ESS are also studied in this thesis. The implementation and validation of the International Electrotechnical Commission (IEC) generic Type 1A are presented in this thesis. It is shown that the implemented IEC generic Type 1 models in PowerFactory (PF) can represent the relevant dynamics during normal operation and fault conditions. The model against measurements validation was carried out to verify the implemented wind turbine generator model. For the wind turbine control strategy, the L1 adaptive controller for Maximum Power Point Tracking (MPPT) of a small variable speed Wind Energy Conversion System (WECS) is developed. It showed good tracking performance towards the optimum Tip Speed Ratio (TSR) and robustness with fast adaptation to uncertainties and disturbances. For the wind farm control, the optimal active power control based on Distributed Model Predictive Control (D-MPC) is proposed. With the developed D-MPC, most of computation tasks are distributed to the local D-MPCs equipped at each actuator (wind turbine or ESS). This control structure is independent from the scale of the wind farm. The algorithms for optimal siting and sizing of ESS in the grid with a significant penetration of wind power are studied and implemented in a test network. For the point of view the grid operator, the optimal sizing and siting of ESS are analyzed, which enhance the controllability and derive the global benefit of the whole grid