Rotor Side Converter Research Articles

«Пряме» векторне управління асинхронною машиною подвійного живлення

Побудова регульованого електропривода на базі асинхронної машини подвійного живлення є досить актуальною задачею, оскільки дозволяє управляти великими потоками електроенергії при високих енергетичних показниках. У таких відомих системах електропривода є досить складна система управління ними, оскільки передбачає використовування перетворювачів координат (прямі-зворотні) та наявність нелінійних зв’язків між каналами управління, це погіршує надійність таких систем. У роботі пропонується«пряме» векторне керування асинхронною машиною подвійного живлення без використання перетворювачів координат. Струми ротора запропоновано примусово формувати повністю керованим перетворювачем частоти, щоб зробити його активним та синфазним фазній е.р.с ротора. Перетворювач включається у роторне коло. Для схемної реалізації у якості перетворювачаобраний перетворювач частоти з ланкою постійної напруги з релейним керуванням. Вхідний випрямляч якого є активний випрямляч. Крім того перетворювач забезпечує електромагнітну сумісність з мережею живлення, та задовольняє вимогам, які зазначені в стандартах, на якість струму мережі. Представлена модель асинхронної машини подвійного живлення з традиційною системою керуванням з використанням перетворювачів координат «прямі-зворотні».Проведено порівняння математичної моделі при традиційному векторному керуванні та моделі з «прямим» векторним керуванням за допомогою Matlab. Отримані осцилограми роботи з запропонованим керуванням, вони демонструють наростання швидкості в машині подвійного живлення, при цьому струми з мережі синусоїдальні та співпадають за фазою зі своїми напругами, а пуск електропривода супроводжується віддачою енергії ротора через перетворювач до мережі.Результати показують, що електропривод формує раціональну динаміку без перерегулювання координат.

Modified Control Technique of DFIG for Power Quality Improvement

In this paper, a modified control technique for doubly fed induction generator (DFIG) is presented to improve its power quality by controlling (minimizing) grid current harmonics. The problems of harmonics injection in grid current, especially due to the presence of nonlinear loads, are very crucial. The proposed control technique can transfer the power from grid to DFIG and vice versa and can also control the DC link voltage (Vdc ) against wide variations in wind speeds. The maximum power point tracking (MPPT) is used in rotor side converter (RSC) to control the power flow through the DFIG. The MPPT extracts the maximum electromagnetic torque Tem from wind energy even during wide variations in wind speeds. A comparison of hysteresis current control (HCC) and space vector pulse width modulation (SVPWM) techniques for harmonic mitigation is presented considering all wind speeds. Also, the control technique for RSC and GSC is discussed in detail in this paper. Finally, the performance of the modified control technique to improve DFIG power quality is checked with the help of MATLAB/SIMULINK software considering 2.6 MW DFIG connected to a power grid.

Maximum power production operation of doubly fed induction generator wind turbine using adaptive neural network and conventional controllers

Production of maximum power based on control of the Rotor Side Converter (RSC) of Doubly Fed Induction Generator (DFIG) wind turbine direct axis current is necessary to accomplish fast reaching to the maximum power point and protect the working parts in RSC from high overshoot in the current. An assessment study between adaptive Neural Network (NN) and conventional Proportional Integral (PI) controllers for control of the RSC direct axis current is introduced in this study. NN controller-based Levenberg-Marquardt backpropagation (LMBP) is designed and is trained to mainly control RSC direct axis current. Also, RSC direct axis current is extracted based on PI controller which used to control the speed of DFIG according to the optimum tip speed ratio obtained by genetic algorithm. The simulation results show that the RSC based NN controller is better than RSC-based conventional speed regulator in protecting RSC parts from high overshoot in the current.

An improved control of grid integrated doubly fed induction generator

This study proposes a vector control approach (VCA) for a doubly fed induction generator (DFIG)-based wind energy conversion system (WECS) connected to the grid. Regarding the configuration of the system, the stator of the induction machine is connected directly to the power grid and the rotor is connected to the power grid via a back-to-back converter. The control schemes are presented, including the rotor side converter (RSC) control, grid side converter (GSC) converter and the pitch angle control. The RSC is used to implement maximum power point tracking (MPPT). The GSC regulates reactive and real power flow to the power network. Besides, it regulates the DC bus voltage and the AC side power-factor. The controller system's abilities are tested via simulations performed with MATLAB/Simulink. A complete simulation model is developed for the control of the active and reactive powers of the DFIG under varying wind conditions and system responses of open loop control are compared with those of closed loop control for different grid voltage conditions.

Understanding the Origin of SSR in Series-Compensated DFIG-Based Wind Farms: Analysis Techniques and Tuning

This paper is dedicated to presenting control-tuning methodologies for the rotor-side converter (RSC) and grid-side converter (GSC) of series-compensated DFIG-based wind farms (WF) and to determining the origin of subsynchronous resonance (SSR). Unlike conventional approaches to re-tuning controller gains to achieve desirable performance, these methodologies only consider the mathematical models of the states variables to be controlled. A PI cascade topology is used to control the RSC and GSC. An inner loop is required for current control and an outer loop for voltage control. Special consideration is taken for tuning the RSC because this converter is coupled with the mechanical variables as mechanical rotor speed of the DFIG. Compared with standard tuning, a better system behavior during a resonance condition is achieved with the proposed tuning methodology. Regarding the analysis of the SSR origin, the modal impedance (MI) technique is used as a tool to study SSR issues; its advantages compared to the driving point impedance technique are highlighted. In this context, the small-signal-stability (SSS) analysis is performed to evaluate the overall system. With the combination of MI and SSS, the phenomena of induction generator effect, torque interaction, and torque amplification are analyzed. As a result, the modes involved in the SSR phenomenon are identified and a discrimination procedure is described to determine the origin of the SSR.

A Common Capacitor Based Three Level STATCOM and Design of DFIG Converter for a Zero-Voltage Fault Ride-Through Capability

To meet the augmented load power demand, the doubly-fed induction generator (DFIG) based wind electrical power conversion system (WECS) is a better alternative. Further, to enhance the power flow capability and raise security margin in the power system, the STATCOM type FACTS devices can be adopted as an external reactive power source. In this paper, a three-level STATCOM coordinates the system with its dc terminal voltage is connected to the common back-to-back converters. Hence, a lookup table-based control scheme in the outer control loops is adopted in the Rotor Side Converter (RSC) and the grid side converter (GSC) of DFIG to improve power flow transfer and better dynamic as well as transient stability. Moreover, the DC capacitor bank of the STATCOM and DFIG converters connected to a common dc point. The main objectives of the work are to improve voltage mitigation, operation of DFIG during symmetrical and asymmetrical faults, and limit surge currents. The DFIG parameters like winding currents, torque, rotor speed are examined at 50%, 80% and 100% comparing with earlier works. Further, we studied the DFIG system performance at 30%, 60%, and 80% symmetrical voltage dip. Zero-voltage fault ride through is investigated with proposed technique under symmetrical and asymmetrical LG fault for super-synchronous (1.2 p.u.) speed and sub-synchronous (0.8 p.u.) rotor speed. Finally, the DFIG system performance is studied with different phases to ground faults with and without a three-level STATCOM.

Design and control of autonomous hybrid wind solar system with DFIG supplying three-phase four-wire loads

Evaluation of an autonomous hybrid wind solar system energy system feeding into three-phase, four-line loads and an array of batteries. It contains doubly fed induction generator, photovoltaic system and two voltage source converters, i.e., grid side converter (GSC) and rotor side converter (RSC) connected back-to-back at DC-link and are provided with an algorithm for maximum power point tracking. The grid voltage-oriented control algorithm is to maintain a steady DC bus voltage for the GSC and to balance the reactive power at the power grid even the divergence in frequency and voltage can be regulated with this novel approach. The stator voltage-orientated vector control is implemented in the RSC control strategy, effective controlling of active and reactive power at the stator. Model is implemented in MATLAB/Simulink and is presented in different scenarios, e.g., solar irradiation, differing wind velocity, dynamic and unbalanced nonlinear loads with low THD value less than 4%.

Contribution of Variable Speed Wind Turbine Generator based on DFIG using ADRC and RST Controllers to Frequency Regulation

In the interconnected power systems, there must always be a balance between the amount of electricity produced and the amount of electricity consumed in order to keep the grid frequency stable and nearby to its nominal value. Therefore, any change in consumption can lead to imbalance, instability, load shedding and system frequency disturbances. With the increase of wind energy penetration level in the electrical network, it has become necessary to make wind generators participate in frequency regulation. The fundamental objective of this research paper is to investigate the ability of wind turbine at variable speed equipped with doubly fed induction generator (DFIG) to contribute in the grid frequency regulation. For the purpose of the contribution in the frequency regulation, the wind turbine system must inject a supplementary power support into the electrical network. To do that, two control strategies are adopted: the first one is the synthetic inertia control which uses the kinetic energy reserved and stocked in the turbine and generator rotors of the wind system. The second one is the droop frequency control which includes the deloading method that allows to the VSWT to create a certain reserve active power. Then, each of these control techniques is implemented and their performances are evaluated in case of frequency variation. Moreover, the control structure that uses the combination of these two techniques is also implemented and studied. The active disturbance rejection control strategy (ADRC), the classical PI controller and the polynomial RST controller have been adopted to command the rotor side converter (RSC) of the DFIG which allows it to provide, in case of frequency fault, a support for the power system into the grid by adjusting the rotor speed. The performance of these controllers are tested and compared and the simulation is performed by MATLAB/Simulink simulation software.

A Sub-Synchronous Oscillation Suppression Strategy for Doubly Fed Wind Power Generation System

During the power transmission of doubly-fed induction generator (DFIG), due to the influence of series compensating capacitance and long-distance transmission, DFIG is prone to sub-synchronous oscillation, which damages the stability of the system. By establishing the mathematical model of DFIG system, the cause of sub-synchronous oscillation and its influence on the control strategy of DFIG system are discussed. In order to solve the problem of performance degradation of traditional phase-locked loop (PLL) under sub-synchronous oscillation, an improved PLL is proposed to replace the traditional PLL. Aiming at the problem that the control of rotor side converter(RSC) and grid side converter(GSC) in doubly-fed wind power generation system under sub-synchronous oscillation is disturbed by harmonic signals, a control method of adding a quasi resonant controller in the control link of RSC and GSC to suppress sub-synchronous oscillation is proposed, and the feasibility of the method is verified by simulation and experiment. Finally, based on the research process of RSC direct resonance control, the sub-synchronous oscillation suppression strategy based on harmonic current extraction is proposed for the frequency adaptability of the quasi resonant controller. The actual performance of the sub-synchronous oscillation suppression strategy is verified through simulation and experiment. The experimental results show that the strategy is effective.

Performance optimization of doubly-fed induction generator (DFIG) equipped variable-speed wind energy turbines by using three-level converter with adaptive fuzzy PI control system

The present paper aims at optimizing the performance of a Doubly Fed Induction Generator (DFIG) equipped variable-speed wind energy turbine in utility grid-connected mode. Since maximum power extraction and output power quality improvement are considered the main challenges for enormous scale variable-speed wind turbines to meet the worldwide demand for clean energy, this work has two contributions; the first concerns the use of the three-level converters to upgrade the output power quality of the wind energy turbine through reducing the total harmonic distortion (THD) of the currents delivered to the power grid, whereas the second contribution intends to design an adaptive proportional-integral (PI) control system for the rotor side converter (RSC) control. The proposed adaptive PI control system is designed by combining the intelligent and adaptive nature of fuzzy logic control (FLC) and the simpleness of the PI controller framework to effectively optimize the DFIG wind energy turbine performance. In the proposed control system, the PI controller's gains are adjusted in real-time by a supervisory system based on FLC according to the wind turbine running conditions. The adopted control scheme to controlling the RSC comprises two cascaded regulation loops for reaching the maximum power point tracking (MPPT), that intends to extract obtainable maximum power of the wind energy turbine. The internal regulation loop is applied to control the rotor current while the external regulation loop is employed to regulate the generator speed. To prove the efficiency of the three-level converter and performance of the proposed control system, simulation studies were performed utilizing MATLAB/Simulink software. The obtained results through simulation clearly show that research paper purposes are achieved and the performance optimization of the wind turbine is well done.

Black-Start Capability of DFIG Wind Turbines Through a Grid-Forming Control Based on the Rotor Flux Orientation

The increasing penetration of renewable energies in the power system is demanding new services from wind farms. In particular, system operators are concerned about system restoration after a black-out and new grid codes are under consideration that demand the participation of wind farms in the restoration process. Black start requires the wind farms to be capable of controlling voltage and frequency in an isolated grid. This paper proposes the use of a novel grid forming control for doubly fed induction generators (DFIG) for restoring the system after a black-out. The proposed grid forming control uses the rotor flux orientation principle, that allows to generate an internal electromotive force for controlling in this way the terminal voltage and frequency. Then, it is demonstrated that the rotor flux magnitude and frequency can be controlled by means of the rotor voltage applied the rotor side converter of the DFIG. The paper also proposes a wind turbine control system for balancing the power demanded by the load at the wind turbine mechanical system. Black start capability of the proposed control system has been validated through a comprehensive simulation. The simulated system consists of a wind farm with two DFIG-based wind turbines connected in parallel to a point of common coupling that supplies an induction motor through a feeder. Also, the synchronization of the isolated system to a main grid has been simulated, demonstrating the ability of the proposed control system for successfully completing the restoration process.

Active and Reactive Powers Control of DFIG Based WECS Using PI Controller and Artificial Neural Network Based Controller

The purpose of this study is to improve the control performance of a Doubly Fed Induction Generator (DFIG) in a Wind Energy Conversion System (WECS) by using both of the conventional Proportional-Integral (PI) controllers and an Artificial Neural Network (ANN) based controllers. The rotor-side converter (RSC) voltages are controlled using a stator flux oriented control (FOC) to achieve an independent control of the active and reactive powers, exchanged between the stator of the DFIG and the power grid. Afterward, the PI controllers of the FOC are replaced with two ANN based controllers. A Maximum Power Point Tracking (MPPT) control strategy is necessary in order to extract the maximum power from the of wind energy system. A simulation model was carried out in MATLAB environment under different scenarios. The obtained results demonstrate the efficiency of the proposed ANN control strategy.

Control & Design for FOPID Based Line-Side Converter of the Brushless Doubly-Fed Induction Generator

This paper deals with the operation of doubly fed induction generator (DFIG) with an integrated active filter capabilities using grid-side converter (GSC). The main contribution of this work lies in the control of GSC for supplying harmonics in addition to its slip power transfer. The rotor-side converter (RSC) is used for attaining maximum power extraction and to supply required reactive power to DFIG. This wind energy conversion system (WECS) works as a static compensator (STATCOM) for supplying harmonics even when the wind turbine is in shutdown condition. Control algorithms of both GSC and RSC are presented in detail. The proposed DFIG-based WECS is simulated using MATLAB/Simulink.

Measurement based parameters estimation of large scale wind farm dynamic equivalent model

For the past few decades, the drastic increase in the installed capacity of wind farms (WFs) has necessitated a computationally efficient dynamic equivalent model of a WF, which can be used for accurate power network simulations. Various doubly-fed induction generators (DFIGs) with sophisticated power control, rotor, and grid side converter control based models for wind turbine (WT) exist in the literature. However, these models are computationally burdensome and restrict their application for modeling large WFs. Thus, an equivalent DFIG based model of a WF, with the rotor circuit modeled as a constant current source, is proposed in this paper. The proposed model is simple and computationally efficient as no rotor measurements are required, and voltage and current measurements at the point of common coupling (PCC) of the WF are used in extended Kalman filter (EKF) to evaluate the dynamic parameters of the equivalent DFIG. A Ybus based reduction is also proposed for the equivalent collector system’s impedance. Simulation results on a test WF in MATLAB Simulink and DIgSILENT prove the proposed model’s efficacy over the existing equivalent models for different operating conditions like wake effect and contingencies in the interconnected power system network.

Cuckoo search algorithm based for tunning both PI and FOPID controllers for the DFIG-Wind energy conversion system

Wind Energy has received great attention in this century. It influences the new power systems, adding new challenges to the power system expansion problem. Nowadays, double feed induction generator (DFIG) wind turbines are used majorly in wind farms, due to their advantages over other types. Therefore, the analysis of the system using this type has become very important. In this paper, a wind turbine modelling was introduced with suggested controllers, in order to enhance the system response, with respect to both pitch control and maximum output power. Cuckoo search algorithm (CSA), a meta-heuristic optimization technique, was implemented to determine the gains of a proportional-integral (PI) controller and fractional order proportional-integral-derivative (FOPID) controller to optimize the system, which considered three control loops: pitch, rotor-side converter, and grid-side converter control loop. Simulation results were determined using MATLAB/Simulink. The comparative analysis of the results showed that the PI Controller gave the simplest and the best response in case of the pitch and rotor-side control loops while the FOPID was the best when applied to the grid-side control loop. Based on the results and discussion, 
 a suggestion of using a compination of each controller was introduced.

Performance improvement of DPC in DFIGs during unbalanced grid voltage based on extended power theory

Doubly fed induction generator (DFIG) control process is more complex in the calculations under voltage unbalance condition because of the power oscillations, and the conventional controllers cannot maintain the system in a stable and smooth condition. In this paper, a flexible method is presented to control the DFIG based on an improved extended power theory on the direct power control platform. The proposed method can simultaneously improve electromagnetic torque oscillations, reduce total harmonic distortion (THD) of stator currents and eliminate active or reactive power oscillations by controller of rotor side converter. The main control system relations based on an analytical process are presented. The improved extended power theory method has made the proposed control independent from decomposition of the positive and negative sequence components which provides ease of the calculation and better performance accuracy. Compared to the conventional extended theory, the proposed method is capable to reduce the torque oscillations, reduction of the stator current THD, and eliminating the powers oscillations of the DFIG. Also, In order to maintain the appropriate dynamic response, a switching table is presented according to the proposed method. The simulation results are clearly confirmed that the proposed method improves the DFIG performance in view of the oscillations under the voltage unbalance conditions.

Power Quality Improvement in Grid Connected DFIG-Wind System using ANFIS

This paper proposes a concept of ANFIS based DFIG controller to variable speed wind turbine system for power smoothening. Power fluctuations due to the unpredictable nature of the wind are eliminated by introducing battery energy storage system in the dc link between two back-to-back connected voltage source converters. The design of BESS is presented for feeding regulated power to the grid irrespective of the wind speeds. The control algorithm of the grid-side converter is implemented with ANFIS for feeding regulated power to the grid. Rotor-side converter is controlled for achieving MPPT and unity power factor operation at the stator terminals. And also to improve the efficiency of WECS an MPPT controller is proposed in this paper. The ANFIS based DFIG system is to be implement in MATLAB.

Thermal Performance Improvement in Multi-Megawatt Power Converters Serving to Asynchronous Hydro Generators Operating Around Synchronous Speed

In multi-MW three-level neutral point clamped back-to-back (3L-NPC) power converters, power semiconductor devices are considered as most vulnerable components due to its thermo-mechanical fatigue stress. Particularly, rotor side converter (RSC) in doubly fed induction machine (DFIM) experiences high thermal stress during its operation around synchronous speed. It degrades the performance of power converter and reduces the lifetime availability of the drive. In practice, stabilization of temperature fluctuation across each power semiconductor device improves the efficiency and reliability of power converter. With respect to this prime aim, this paper proposes a carrier-based active thermal control method to regulate temperature fluctuation across power semiconductor devices in a multi-MW (5 x 5 MW) 3L-NPC power converters serving to a 250 MW asynchronous hydro-generating unit. To test the proposed active thermal control method, different operating conditions of a 250 MW DFIM hydro-generating unit (to be commissioned in Tehri pumped storage plant, India) are examined in MATLAB/PLECS environment. The designed active thermal control method effectively regulates mean junction temperature and temperature fluctuation of power semiconductor devices within a safe operating limit. The practical feasibility and adoptability of proposed active thermal control is examined through a 2.2-kW DFIM laboratory prototype.

Improved Current Controlled Doubly Fed Induction Generator Model with Grid Integration Under Sub and Super Synchronous Conditions

This paper presents the development and experimental verification of the mathematical model of wind turbine and Doubly Fed Induction Generator (DFIG) using the current control and voltage estimation method between the DC link. The rotor of the induction generator (IG) is rotated with the wind turbine at a specific speed. The DFIG is directly coupled with a grid station and the synchronization between DFIG and the grid station is controlled by setting two converters: Machine Side Converter (MSC) implemented with the rotor side and Grid Side Converter (GSC) implemented with the grid. PI controllers have been utilized in the control loops and the parametric range is extracted to maximize the mechanical power transferred to the IG rotor. The model is tested under three conditions DFIG running at super synchronous speed, synchronous speed, and under synchronous speed using MATLAB Simulink. In the end, the same model is also tested through a series of experiments using lab modules. The results show that the proposed model is much simplified and accurate as compared to previous versions available in the literature.

Mutual Inductance Estimation Based Sensorless Adaptive Variance Controller for Doubly Fed Induction Generator

This article presents a novel robust adaptive speed control architecture that allows doubly fed induction generator (DFIG) to operate independently of any speed sensors or position encoders. The proposed speed sensorless control based on modified minimum variance adaptive control based speed observer makes the system robust to machine parameter variations and sensor malfunctions. The observer is formulated using a rotor current based reference adaptive system. To ensure robustness to current sensor failure, a modified adaptive rotor side converter control loop is proposed. The online identification for the adaptive control logic is based on the recursive least square estimation technique while the adaptive control law is based on an extended version of the minimum variance control algorithm. To ensure improved dynamic performance for the proposed control, a modification for the terminal voltage control loop is proposed. The reactive power reference for the vector control loop is calculated considering the rotor current component responsible for reactive power generation. The performance of the proposed control architecture is validated on a 1.5 MW DFIG modeled in MATLAB/Simulink and experimentally verified on hardware.