525 research outputs found
Small-Signal Modelling and Analysis of Doubly-Fed Induction Generators in Wind Power Applications
The worldwide demand for more diverse and greener energy supply has had a significant
impact on the development of wind energy in the last decades. From 2 GW in 1990,
the global installed capacity has now reached about 100 GW and is estimated to grow to
1000 GW by 2025. As wind power penetration increases, it is important to investigate its
effect on the power system. Among the various technologies available for wind energy
conversion, the doubly-fed induction generator (DFIG) is one of the preferred solutions
because it offers the advantages of reduced mechanical stress and optimised power capture
thanks to variable speed operation. This work presents the small-signal modelling and
analysis of the DFIG for power system stability studies.
This thesis starts by reviewing the mathematical models of wind turbines with DFIG
convenient for power system studies. Different approaches proposed in the literature for
the modelling of the turbine, drive-train, generator, rotor converter and external power
system are discussed. It is shown that the flexibility of the drive train should be represented
by a two-mass model in the presence of a gearbox.
In the analysis part, the steady-state behaviour of the DFIG is examined. Comparison
is made with the conventional synchronous generators (SG) and squirrel-cage induction
generators to highlight the differences between the machines. The initialisation of the
DFIG dynamic variables and other operating quantities is then discussed. Various methods
are briefly reviewed and a step-by-step procedure is suggested to avoid the iterative
computations in initial condition mentioned in the literature.
The dynamical behaviour of the DFIG is studied with eigenvalue analysis. Modal
analysis is performed for both open-loop and closed-loop situations. The effect of parameters
and operating point variations on small signal stability is observed. For the
open-loop DFIG, conditions on machine parameters are obtained to ensure stability of
the system. For the closed-loop DFIG, it is shown that the generator electrical transients
may be neglected once the converter controls are properly tuned. A tuning procedure is
proposed and conditions on proportional gains are obtained for stable electrical dynamics. Finally, small-signal analysis of a multi-machine system with both SG and DFIG is
performed. It is shown that there is no common mode to the two types of generators.
The result confirms that the DFIG does not introduce negative damping to the system,
however it is also shown that the overall effect of the DFIG on the power system stability
depends on several structural factors and a general statement as to whether it improves or
detriorates the oscillatory stability of a system can not be made
High-Order Sliding Mode Control of DFIG-Based Marine Current Turbine
This work is supported by Brest Métropole Océane (BMO) and the European Social Fund (ESF). It is also supported by the GDR SEEDS CNRS N°2994 under the Internal Project HYDROLE. It is done within the framework of the Marine Renewable Energy Commission of the Brittany Maritime Cluster (PÎle Mer Bretagne).International audienceThis paper deals with the speed control of a variable speed DFIG-based marine current turbine. Indeed, to increase the generated power and therefore the efficiency of a marine current turbine, a nonlinear controller has been proposed. DFIG has been already considered for similar applications particularly wind turbine systems using mainly PI controllers. However, such kinds of controllers do not adequately handle some of tidal resource characteristics such as turbulence and swell effects. Indeed, these may decrease marine current turbine performances. Moreover, DFIG parameter variations should be accounted for. Therefore, a robust nonlinear control strategy, namely high-order sliding mode control, is proposed. This control strategy relies on the resource and the marine turbine models that were validated by experimental data. The sensitivity of the proposed control strategy is analyzed regarding the swell effect as it is considered as the most disturbing one for the resource model. Tidal current data from the Raz de Sein (Brittany, France) are used to run simulations of a 7.5-kW prototype over various flow regimes. Simulation results are presented and fully analyzed
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
Grid Strength Assessment Trough Q-V Modal Analysis and Maximum Loadability of a Wind-Dominated Power System Using P-Q Regions
Climate change is a menace to the existence of the world and policymakers are trying totackle this phenomenon by deploying large-scale wind farms into their grids. Among them, wind energy shows a promising future to substitute the traditional power plants. However, the deployment of these wind farms into the grid is not a panacea that does not pose any challenges to the grid operators. Keeping the power system voltage stable while considering the strength of the transmission grid is among the major challenges facing by the transmission system operators. Amid normal operation and fault conditions, wind farms should help the grid in reactive power supply according to the grid codes to ride through the fault. In doing so, during fault conditions or heavy loading conditions, the voltage of the power system will not deteriorate. A wind farm, most of the time, is incapable to meet the grid codes requirements without reactive power support. For the compensation of the reactive power deficit, FACTS devices are extensively used. The most popular FACTS devices used by electric utilities are, STATCOM, SVC, SSSC, TCSC, and UPFC. In this work, attention is given to the amelioration of transient stability in wind-dominated power systems via STATCOM and SSSC. Furthermore, a systematic approach to locate large wind power plants to an existing transmission grid is developed by combining the QV-modal analysis, Q-V curves, and P-Q method. The steady-state voltage stability at different wind power penetration levels is investigated while considering the weakest and the strongest region of the power system. The P-Q region method is used to size the wind farm in each scenario. The reliability of the system is verified from the worst contingencies with the wind farm connected at the most vulnerable bus of the system in reactive power capability. The system considered for testing is the modified IEEE 14 bus system
The control of power electronic converters for grid code compliance in wind energy generation systems
This research report reviews some of the latest control schemes for the power
electronic converters found in modern variable speed wind turbines in order to
comply with various grid codes. Various control schemes, in order to comply with
low voltage ride-through requirements, active and reactive power control and
frequency control, are presented. The report first investigates the South African
grid code requirements for wind energy generation, and then makes a comparison
to grid codes of countries with significant penetration levels and vast experience
in wind energy generation. This is followed by a review of the state of the art in
fixed and variable speed wind turbine technologies. The research revealed that
Type 3 generators offer significant advantages over others but suffer due to grid
faults. Various active control schemes for fault ride-through were researched and
the method of increasing the rotor speed to accommodate the power imbalance
was found to be the most popular. It was found that Type 4 generators offer the
best fault ride-through capabilities due to their full scale converters. The research
will assist power system operators to develop appropriate and effective grid codes
to enable a stable and reliable power system. The research will also provide
turbine manufacturers and independent power producers with a comprehensive
view on grid codes and relate them to the associated turbine technologies
Low Voltage Capability of Generator for Frequency Regulation of Wind Energy System
For the extraction of wind energy through a doubly fed induction generator (DFIG), low voltage is major particular essential controlled by the transmission structure executive. Under a structure issue condition, DFIG should remain with respect to the lattice for a particular least period and deal open power support on a case-by-case basis by the Transmission framework administrator. A pleasant control plot involving gear course of action through a superconducting resistance type issue current limiter (R-SFCL) and programming plan based on the rotor reference current direction control system (RRCOCS) with transient voltage control (TVC), is proposed in this paper to address the Low voltage essential. The results got by the proposed procedure are differentiated and RRCOCS and RRCOCS-TVC
Improved Wind Turbine Control Strategies for Maximizing Power Output and Minimizing Power Flicker
For reducing the cost of energy (COE) for wind power, controls techniques are important for enhancing energy yield, reducing structural load and improving power quality. This thesis presents the control strategies studies for wind turbine both from the perspectives of both maximizing power output and reducing power flicker and structural load,
First, a self-optimizing robust control scheme is developed with the objective of maximizing the power output of a variable speed wind turbine with doubly-fed induction generator (DFIG) operated in Region 2. Wind power generation can be divided into two stages: conversion from aerodynamic power to rotor (mechanical) power and conversion from rotor power to the electrical (grid) power. In this work, the maximization of power generation is achieved by a two-loop control structure in which the power control for each stage has intrinsic synergy. The outer loop is an Extremum Seeking Control (ESC) based generator torque regulation via the rotor power feedback. The ESC can search for the optimal torque constant to maximize the rotor power without wind measurement or accurate knowledge of power map. The inner loop is a vector-control based scheme that can both regulate the generator torque requested by the ESC and also maximize the conversion from the rotor power to grid power. In particular, an â controller is synthesized for maximizing, with performance specifications defined based upon the spectrum of the rotor power obtained by the ESC. Also, the controller is designed to be robust against the variations of some generator parameters. The proposed control strategy is validated via simulation study based on the synergy of several software packages including the TurbSim and FAST developed by NREL, Simulink and SimPowerSystems.
Then, a bumpless transfer scheme is proposed for inter-region controller switching scheme in order to reduce the power fluctuation and structural load under fluctuating wind conditions. This study considers the division of Region 2, Region 2.5 and Region 3 in the neighborhood of the rated wind speed. When wind, varies around the rated wind speed, the switching of control can lead to significant fluctuation in power and voltage supply, as well as structural loading. To smooth the switch and improve the tracking, two different bumpless transfer methods, Conditioning and Linear Quadratic techniques, are employed for different inter-region switching situations. The conditioning bumpless transfer approach adopted for switching between Region 2 maximum power capture controls to Region 2.5 rotor speed regulation via generator torque. For the switch between Region 2.5 and Region 3, the generator torque windup at rated value and pitch controller become online to limit the load of wind turbine. LQ technique is posed to reduce the discontinuity at the switch between torque controller and pitch controller by using an extra compensator. The flicker emission of the turbine during the switching is calculated to evaluate power fluctuation. The simulation results demonstrated the effectiveness of the proposed scheme of inter-region switching, with significant reduction of power flicker as well as the damage equivalent load
LVRT and HVRT control strategies of doubly- fed induction generator
The Doubly Fed Induction Generator (DFIG) has a high sensitivity to the Grid Faults (GFs), which can cause many problems on the power quality and the production continuity. Actually, the grid connection requirements impose strict laws to respect to Low Voltage Ride Through (LVRT), High Voltage Ride Through (HVRT), and grid support capacities following the Grid Codes (GCs). In fact, when detecting voltage fault, Wind Turbines (WTs) should stay in connection with the grid in order to hold a safe and stable operation. The main objective of this work is to propose LVRT and HVRT strategies able to retain WTs connected to the grid during severe grid voltage faults. The proposed approach is a hybrid method combining two methods (active and passive methods): The first aim is to develop the control of DFIG, while the second is applied for severe voltage faults using hardware protection circuits
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