Power Quality Enhancement of DFIG Based Wind Energy System Using Priority Control Strategies

A. BOUZEKRI T. ALLAOUI, M. DENAI, 'Power Quality Enhancement of DFIG Based Wind Energy System Using Priority Control Strategies', Journal of Electrical Engineering, Vol. 15 (4): 139-145, 2015.The integration of intermittent renewable energy sources into the electric grid presents some challenges in terms of power quality issues, voltage regulation and stability. Power quality relates to those factors which affect the variability of the voltage level and distortion of the voltage and current waveforms which can cause severe adverse effects to the electric grid. The paper focuses on the design and evaluation of a priority control strategy for improving the quality of energy of a grid-connected variable speed Doubly Fed Induction Generator (DFIG) wind energy conversion system. The aim of priority control is to manage the priority among three different controls: active stator power control; reactive stator power control and harmonic rotor current control by using the active shunt filter with SRF method harmonic compensation, and to have a high performance and robustness; an adaptive-fuzzy PI control are including for currents rotor control. The simulation model was developed in Matlab/Simulink environment. The results show that the proposed control scheme can effectively reduce the Total Harmonic Distortion (THD) in the grid currents.Peer reviewedFinal Published versio

Using Feedback Control to Control Rotor Flux and Torque of the DFIG-Based Wind Power System

Direct torque control (DТС) is a method of controlling electrical machines that are widely used, and this is due to its simplicity and ease of use. However, this method has several issues, such as torque, rotor flux, and current fluctuations. To overcome these shortcomings and improve the characteristics and robustness of the DTC strategy of the doubly-fed induction generator (DFIG), a new DTC scheme based on the feedback control method (FCM) and space vector modulation (SVM) is proposed. In the proposed DTC technique, a proportional-integral controller based on feedback control theory is used to control and regulate the torque and rotor flux of the DFIG. On the other hand, the SVM technique is used to control the rotor side converter (RSC) to obtain a high-quality current. The simulation result shows that the proposed DTC technique has the advantages of faster dynamics and reduced harmonic distortion of current compared to the ‎conventional technique.

Mitigation of Harmonics and Inter-Harmonics with LVRT and HVRT Enhancement in Grid-Connected Wind Energy Systems Using Genetic Algorithm-Optimized PWM and Fuzzy Adaptive PID Control

© 2021 Author(s). This is the accepted manuscript version of an article which has been published in final form at https://doi.org/10.1063/5.0015579The growing installed wind capacity over the last decade has led many energy regulators to define specific grid codes for wind energy generation systems connecting to the electricity grid. These requirements impose strict laws regarding the Low Voltage Ride Though (LVRT) and High Voltage Ride Though (HVRT) capabilities of wind turbines during voltage disturbances. The main aim of this paper is to propose LVRT and HVRT strategies that allow wind systems to remain connected during severe grid voltage disturbances. Power quality issues associated with harmonics and inter-harmonics are also discussed and a control scheme for the grid-side converter is proposed to make the Wind Energy Conversion System insensitive to external disturbances and parametric variations. The Selective Harmonic Elimination Pulse Width Modulation technique based on Genetic Algorithm optimization is employed to overcome over-modulation problems, reduce the amplitudes of harmonics, and thus reduce the Total Harmonic Distortion in the current and voltage waveforms. Furthermore, to compensate for the fluctuations of the wind speed due to turbulence at the blades of the turbine, a fuzzy Proportional-Integral-Derivative controller with adaptive gains is proposed to control the converter on the generator side.Peer reviewedFinal Accepted Versio

Model predictive control of a doubly fed induction generator.

Masters Degree. University of KwaZulu- Natal, Durban.The world is currently is energy despair. For years, the world has relied on fossil fuels as the main energy source to produce electricity. At the start, this worked well as there was an abundance. However, due to the increase in population, urbanisation and the birth of many industries, this fuel source has been put under strain. Furthermore, the harmful emissions from the use of fossil fuels has been a great contributor to the destruction of our precious ozone layer. This in turn has gradually increased the harmful effects of global warming on Earth. The need for clean, reliable sources of energy has increased over time, and in a few years, it is expected to be the only source of energy utilized in the production of electrical energy. The research undertaken in this project involves the control of the doubly fed induction generator, which is used in wind energy conversion systems. Commonly termed DFIG, this generator has gained worldwide popularity and is used in majority of wind energy conversion systems. It provides direct grid connection and uses only a partially rated converter. However, the conventional control methods used in the control of the DFIG are either difficult to implement or inefficient. Some require complex tuning of proportional-integral controllers while some produce distorted results. The aim of this research was to investigate and evaluate the application of model predictive control to the control of the DFIG. There exist various different control strategies for the control of the DFIG. This research involved implementing all of the different control strategies via conventional methods and then via the use of model predictive control. Despite there being various methods to implement model predictive control, due to its simplicity and strong suitability, finite control set model predictive control was used in this research. Each of the control strategies implemented both conventionally and via model predictive control were thoroughly analysed in terms of the steady state response, dynamic response and quality of stator current. A comparison between the corresponding control methods is also presented

Comparison between unipolar and bipolar single phase grid-connected inverters for PV applications

An inverter is essential for the interfacing of photovoltaic panels with the AC network. There are many possible inverter topologies and inverter switching schemes and each one will have its own relative advantages and disadvantages. Efficiency and output current distortion are two important factors governing the choice of inverter system. In this paper, it is argued that current controlled inverters offer significant advantages from the point of view of minimisation of current distortion. Two inverter switching strategies are explored in detail. These are the unipolar current controlled inverter and the bipolar current controlled inverter. With respect to low frequency distortion, previously published works provide theoretical arguments in favour of bipolar switching. On the other hand it has also been argued that the unipolar switched inverter offers reduced switching losses and generates less EMI. On efficiency grounds, it appears that the unipolar switched inverter has an advantage. However, experimental results presented in this paper show that the level of low frequency current distortion in the unipolar switched inverter is such that it can only comply with Australian Standard 4777.2 above a minimum output current. On the other hand it is shown that at the same current levels bipolar switching results in reduced low frequency harmonics

Comparison between unipolar and bipolar single phase grid-connected inverters for PV applications

An inverter is essential for the interfacing of photovoltaic panels with the AC network. There are many possible inverter topologies and inverter switching schemes and each one will have its own relative advantages and disadvantages. Efficiency and output current distortion are two important factors governing the choice of inverter system. In this paper, it is argued that current controlled inverters offer significant advantages from the point of view of minimisation of current distortion. Two inverter switching strategies are explored in detail. These are the unipolar current controlled inverter and the bipolar current controlled inverter. With respect to low frequency distortion, previously published works provide theoretical arguments in favour of bipolar switching. On the other hand it has also been argued that the unipolar switched inverter offers reduced switching losses and generates less EMI. On efficiency grounds, it appears that the unipolar switched inverter has an advantage. However, experimental results presented in this paper show that the level of low frequency current distortion in the unipolar switched inverter is such that it can only comply with Australian Standard 4777.2 above a minimum output current. On the other hand it is shown that at the same current levels bipolar switching results in reduced low frequency harmonics

Power Quality Enhancement in Electricity Grids with Wind Energy Using Multicell Converters and Energy Storage

In recent years, the wind power industry is experiencing a rapid growth and more wind farms with larger size wind turbines are being connected to the power system. While this contributes to the overall security of electricity supply, large-scale deployment of wind energy into the grid also presents many technical challenges. Most of these challenges are one way or another, related to the variability and intermittent nature of wind and affect the power quality of the distribution grid. Power quality relates to factors that cause variations in the voltage level and frequency as well as distortion in the voltage and current waveforms due to wind variability which produces both harmonics and inter-harmonics. The main motivation behind work is to propose a new topology of the static AC/DC/AC multicell converter to improve the power quality in grid-connected wind energy conversion systems. Serial switching cells have the ability to achieve a high power with lower-size components and improve the voltage waveforms at the input and output of the converter by increasing the number of cells. Furthermore, a battery energy storage system is included and a power management strategy is designed to ensure the continuity of power supply and consequently the autonomy of the proposed system. The simulation results are presented for a 149.2 kW wind turbine induction generator system and the results obtained demonstrate the reduced harmonics, improved transient response, and reference tracking of the voltage output of the wind energy conversion system.Peer reviewedFinal Accepted Versio

A new robust control using adaptive fuzzy sliding mode control for a DFIG supplied by a 19-level inverter with less number of switches

This article presents the powers control of a variable speed wind turbine based on a doubly fed induction generator (DFIG) because of their advantages in terms of economy and control. The considered system consists of a DFIG whose stator is connected directly to the electrical network and its rotor is supplied by a 19-level inverter with less number of switches for minimize the harmonics absorbed by the DFIG, reducing switching frequency, high power electronic applications because of their ability to generate a very good quality of waveforms, and their low voltage stress across the power devices. In order to control independently active and reactive powers provided by the stator side of the DFIG to the grid and ensure high performance and a better execution, three types of robust controllers have been studied and compared in terms of power reference tracking, response to sudden speed variations, sensitivity to perturbations and robustness against machine parameters variations.В статье описывается управление мощностью ветряной турбины переменной скорости на основе асинхронного генератора двойного питания ввиду их преимуществ с точки зрения экономичности и управления. Рассматриваемая система состоит из асинхронного генератора двойного питания, статор которого подключен непосредственно к электрической сети, а его ротор питается от 19-уровневого инвертора с меньшим количеством коммутаторов для минимизации гармоник, поглощаемых генератором, уменьшая частоту переключения, и устройств силовой электроники вследствие их способности генерировать высокое качество сигналов и низкого уровня напряжения на них. Чтобы независимо управлять активной и реактивной мощностью, подаваемой стороной статора указанного генератора в сеть, и обеспечивать высокую производительность и лучшее конструктивное исполнение, изучены и сопоставлены три типа робастных контроллеров с точки зрения отслеживания мощности, реакции на внезапное изменение скорости, чувствительности к возмущениям и устойчивости к изменениям параметров машины

A Linear Parameter Varying Controller for Grid-tied Converters under Unbalanced Voltage Network Conditions

This thesis focuses on the development and practical assessment of a contemporary Linear Parameter Varying (LPV) controller for grid-tied converters. The increasing popularity of renewable energy resources necessitates intelligent power converters to interface with utility network. The proposed control methodology can effectively regulate converter powers/currents under highly unbalanced voltage conditions. The methodology can be easily applied to rotating electrical machines that have similar dynamic models. A LPV model of grid-tied converter with filters are derived in synchronous positive and negative rotating frames and a detailed controller design procedure is then carried out using Matrix Linear Inequality technique. The proposed controller uses network frequency as a reference and it has the capability to handle the system frequency variations. Off-line controller design stage is computed by Matlab software while on-line controller calculations are dealt by a Digital Signal Processor (DSP). The highly distorted voltage at the point of common coupling between Voltage Source Inverter (VSI) and utility network may degrade the outputs of the phase locked loop (PLL) module and overall controller performance. An enhanced version of PLL technique is proposed to overcome the voltage distortions and a significant reduction of Total Harmonic Distortion has been recorded. The harmonic issue is successfully treated further with an additional harmonic observer supporting the main controller. To verify the proposed control approach, studies are carried out using Matlab/SIMULINK platform with the code-based simulation. This simulation method can ensure the results close to a real DSP system and enables the user to transfer the simulation studies effectively to the experimental setup without major modifications. A prototype of a three phase VSI with a DSP controller is then investigated using dSPACE DS1104 development board. Experimental results from this system validate the proposed control technique and its benefits