Intelligent Control of DFIG Using Sensorless Speed Estimation and Lookup Table-Based MPPT Algorithm to Overcome Wind and Grid Disturbances

This aim of this paper is to design controller for Doubly Fed Induction Generator (DFIG) converters and MPPT for turbine and a sensor-less rotor speed estimation to maintain equilibrium in rotor speed, generator torque, and stator and rotor voltages. It is also aimed to meet desired reference real and reactive power during the turbulences like sudden change in reactive power or voltage with concurrently changing wind speed. The turbine blade angle changes with variations in wind speed and direction of wind flow and improves the coefficient of power extracted from turbine using MPPT. Rotor side converter (RSC) helps to achieve optimal real and reactive power from generator, which keeps rotor to rotate at optimal speed and to vary current flow from rotor and stator terminals. Rotor speed is estimated using stator and rotor flux estimation algorithm. Parameters like tip speed ratio; coefficient of power, stator and rotor voltage, current, real, reactive power; rotor speed and electromagnetic torque are studied using MATLAB simulation. The performance of DFIG is compared when there is in wind speed change only; alter in reactive power and variation in grid voltage individually along with variation in wind speed.

<p>Doubly Fed Induction Generator (DFIG) needs to get adopted to change in wind speeds with sudden change in reactive power or grid terminal voltage as it is required for maintaining synchronism and stability as per modern grid rules. This paper proposes a controller for DFIG converters and optimal tip speed ratio based maximum power point tracking (MPPT) for turbine to maintain equilibrium in rotor speed, generator torque, and stator and rotor voltages and also to meet desired reference real power during the turbulences like sudden change in reactive power or voltage with concurrently changing wind speed. The performance of DFIG is compared when there is change in wind speed only, changes in reactive power and variation in grid voltage along with variation in wind speed.</p>

<p>Doubly Fed Induction Generator (DFIG) needs to get adopted to change in wind speeds with sudden change in reactive power or grid terminal voltage as it is required for maintaining synchronism and stability as per modern grid rules. This paper proposes a controller for DFIG converters and optimal tip speed ratio based maximum power point tracking (MPPT) for turbine to maintain equilibrium in rotor speed, generator torque, and stator and rotor voltages and also to meet desired reference real power during the turbulences like sudden change in reactive power or voltage with concurrently changing wind speed. The performance of DFIG is compared when there is change in wind speed only, changes in reactive power and variation in grid voltage along with variation in wind speed.</p>

In this paper, a comparative study between voltage oriented control (VOC) and frequency coordinated control (FCC) of grid connected doubly fed induction generator (DFIG) is presented. The two method controls are deeply done on DFIG converter sides, grid side converter (GSC), and rotor side converter (RSC). The VOC method permanently maintains the DFIG reactive power to zero values to achieve stable voltage. This control is implemented by regulating the rotor direct axis reference current in RSC using grid reactive power. On the other hand, the FCC has employed the active power obtaining from the system frequency deviation to control the rotor quadrature axis reference current in the RSC. The GSC is the same in two studies, and its applied vector controlled method. The comparison study between the two methods is conducted at a steady and dynamic state under constant and variable wind speeds. The simulation results are carried out by using PSCAD/EMTDC electromagnetic transient program to validate the comparison study between two methods control of DFIG. The outcomes of the simulation show that the VOC is very convenient when the DFIG operated at transient mode and variable wind speeds while the FCC is feasible and effective for steady-state mode applications. Furthermore, the FCC method has an ability to reduce the active and reactive powers ripples as well as decreasing torque harmonics. Both of two methods had fewer transient recovery values of output parameters, which ensure safety dynamic response of DFIG and power system. This study contributes significantly to choose the suitable control of the DFIG converters according to electrical grid operation conditions. In addition, if a joint control has been applied to these two methods, the wind power gained strong and flexible control of the frequency and voltage for different operating conditions.

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.

Rapid reactive power control for Doubly Fed Induction Generator (DFIG) is necessary for stable operation during voltage control and grid fault conditions. This paper examines the performance of DFIG under three cases viz., i) generator speed, ii) reactive power demand from grid and iii) wind speed. Based on the above disturbances, the system performance is analyzed by considering the parameters like rotor speed, generator torque, stator and rotor voltages and powers. It is also aims to explain DFIG as a vital dynamic reactive power source without the use of any additional external reactive power devices. The simulation results illustrate the efficacy and robustness of torque, speed and stator reactive power control for DFIG system by the proposed methodology. The torque surges are minimum even there is sudden change in wind speed, torque ripples and speed surges are not there when there is sudden change in wind speed.

This paper presents the power outputs control and DC-link voltage regulation of the Doubly Fed Induction Generator (DFIG) for the variable speed Wind Energy Conversion System (WECS). The DFIG control structure consists of the two four quadrant IGBT PWM converters are connected in AC-DC-AC in order to control the power outputs of the DFIG. The dynamic behavior of DFIG is modeled in the Stator Flux Orientation (SFO) related to the Rotor Side Converter (RSC) and Grid Side Converter (GSC) control strategies. The RSC controls the power flow (the active and reactive power) from the stator of the DFIG to the grid by controlling the rotor currents of the DFIG. The GSC ensures the regulation of the DC-link voltage to the desired value by controlling the grid currents. In this paper, is realized with a conventional PI controller based on SFO vector control, which gives the super-synchronous operation of the DFIG. This control strategy not only improves the efficiency but also maintains almost unity power factor to the grid. The proposed control scheme is simulated and investigated for variations in wind speed and under small disturbance. The effectiveness of the proposed method is verified by developing the simulation model of 1.5 MW in MATLAB-SIMULINK-2013.

The integration of renewable energy sources, particularly wind power, into the electrical grid has gained significant attention in current years. The Doubly Fed Induction Generator (DFIG) is a mostly used generator in modern wind turbine systems due to its advantages such as improved efficiency, variable speed operation, and enhanced grid stability. However, the performance of a DFIG is highly influenced by the variable wind speed conditions it operates under. This paper presents a comprehensive modelling approach for a DFIG system considering variable wind speeds. The proposed model incorporates the dynamic characteristics of the wind turbine and DFIG components, such as the mechanical system, electrical circuits, and control strategies. The wind speed profile is taken into account, enabling the analysis of the DFIG system's behaviors under different operating conditions. The model is developed using mathematical equations and simulation techniques to accurately represent the interactions between the wind turbine, DFIG, and the grid. Various control strategies, including the rotor-side and grid-side converters, are implemented to optimize the power extraction, enhance grid stability, and mitigate potential issues such as grid faults and voltage variations. The MATLAB simulated results show the effectiveness of this proposed model is captured by the dynamic behaviors of the DFIG system with variable wind speeds. The model provides valuable insights into the system's behaviors, enabling the evaluation of performance metrics such as power output, rotor speed, and control responses. Moreover, the model can be utilized for analyzing the impact of different wind speed profiles, investigating the effectiveness of control strategies, and optimizing the design and operation of DFIG-based wind turbine systems. Overall, the developed model offers a reliable tool for understanding and analyzing the performance of DFIG systems under variable wind speed conditions. It can aid in the development of advanced control algorithms, grid integration studies, and decision-making processes for wind power generation projects.

The rapidly increasing energy demand is compelling the humankind for an alternative source of electrical energy generation and that leads to one thought, which is nothing but employing renewable energy generation. The incorporation of renewable energy generation into the existing grid system overlooks at some of the technical challenges and difficulties. The modern wind power plants use the methodology of Doubly Fed Induction Generator (DFIG) based Wind Turbine Generator (WTG). This framework focuses on the performance of a new control mechanism incorporated with grid fused DFIG based WTG. The fuzzy-based Rotor Side Converter (RSC) is developed to achieve maximum power delivery from DFIG using slip frequency control mechanism. To assist the slip frequency control, the PI-based Grid Side Converter (GSC) of DFIG is also proposed to maintain constant DC link voltage under grid voltage variations. The efficacy of the controller is validated using MATLAB/Simulink for the different operating conditions such as varying wind speed, grid voltage variations, etc. A unique feature of the controller is that it adapts to variations in wind velocities for achieving Maximum power output. The laboratory prototype model of RSC and GSC converter controller is developed and the hardware setup along with the results are examined.

Summary This paper presents a simplified voltage control of paralleling doubly fed induction generators (DFIGs) connected to the grid by using static Var compensator (SVC). The DFIG converters are based on a voltage source converter in the grid side converter (GSC) and current source converter in the rotor side converter (RSC). The GSC is employed to work like static synchronous compensator (STATCOM) to provide precise control to maintain the DC link voltage under control. The RSC is oriented to control real and reactive powers of the DFIG. Instead of adding two SVCs in every DFIG bus it connects only one SVC in the point of common coupling of the generators to enhance the voltage stability at a steady state and dynamic operation by decreasing the reactive power hence to increase the voltage amplitude. The comprehensive simulations are carried out using PSCAD/EMTDC program. The results show that the SVC has improved voltage stability and promote the system transient response by compensating reactive power. Furthermore, this study has presented the possibility of using one SVC with low capacity based on the SVC characteristics adjusted only by choosing a suitable transformer rating. Moreover, the system model simulation was tested at steady state and dynamic mode during constant and random wind speeds. Using one SVC with low capacity leads to decrease power dissipation, and this directly reduced the power cost. Copyright © 2014 John Wiley & Sons, Ltd.

This article presents the sharing of reactive power between two converters of a doubly fed induction generator (DFIG) based wind energy conversion system interacting with the grid. The rotor side converter (RSC) control of DFIG is designed for sharing of reactive power at below rated wind speeds, which essentially reduces the amount of rotor winding copper loss. However, at rated wind speed, the RSC control is designed to maintain the unity power factor at stator terminals and to extract rated power without exceeding its rating. Further, the reduction in rotor winding copper loss due to reactive power distribution is demonstrated with an example. Moreover, the grid side converter (GSC) control is designed to feed regulated power flow to the grid along with reactive power support to DFIG and to the load connected at point of common coupling. Moreover, the GSC control is designed to compensate load unbalance and load harmonics. The battery energy storage connected at dc link of back-to-back converters, is used for maintaining the regulated grid power flow regardless of wind speed variation. The system is modeled and its performance is simulated under change in grid reference active power, varying wind speed, sharing of reactive power, and unbalanced nonlinear load using SimPowerSystems toolbox of MATLAB. Finally, a prototype is developed to verify the system steady state and dynamic performance. Moreover, system voltages and currents are found sinusoidal and balanced, and their total harmonic distortions are as per the IEEE 519 standard.

Grid-connected doubly-fed induction generator (DFIG) based wind energy conversion system (WECS) is widely used in harnessing wind power. The paper attempts to characterize a 15-kW grid-connected DFIG based WECS operating under variable speed and loading conditions. Back to back converter topologies are utilized consisting of rotor side converter (RSC) and grid side converter (GSC) controlled in the synchronous reference frame coordinates. The design, modeling, and control of various system components are deliberated. The interaction of the grid with the proposed DFIG-WECS is analyzed where the regulation of the machine active power is achieved through the control of RSC. The current quality, voltage regulation is achieved by the control of GSC. Case studies involving constant wind speed, variable wind speed, and variable loading are undertaken for the characterization analysis. The performance characterizations of the entire system is validated in Matlab/Simulink simulation environment where the critical performance parameters like DC link voltage, generator torque, DFIG stator current, active and reactive power delivered by the DFIG to the grid, PCC side voltage/ current profile and the PCC current Total harmonic distortion (THD) are rigorously monitored, presented and discussed for each case studies.

This paper proposes a reactive power coordination control scheme combines doubly fed induction generator (DFIG) with static synchronous compensator (STATCOM) on the basis of considering the limited reactive power of DFIG. It takes the voltage stability of point of common coupling (PCC) as the target to determine the required reactive power value, which is a priority to select DFIG to compensate reactive power, and the surplus reactive power demand is supplemented by STATCOM. The reactive power regulation of DFIG needs to be realized by controlling the rotor side converter (RSC) and the grid side converter (GSC), and the reactive power command value of DFIG is distributed between the RSC and the GSC according to the maximum reactive power capacity. This method not only can make full use of the reactive power regulation of DFIG itself, but also can reduce the capacity of reactive power compensation device. Simulation results based on Matlab/Simulink verify the effectiveness and superiority of the proposed scheme.

Low-frequency oscillations are a primary issue for integrating a renewable source into the grid. The objective of this study was to find sensitive parameters that cause low-frequency oscillations and design a Twin Delayed Deep Deterministic Policy Gradient (TD3) agent controller to damp the oscillations without requiring an accurate system model. In this work, a Q-learning (QL)-based model-free wind speed DFIG was designed on the rotor-side converter (RSC), and a QL-based model-free DC-link voltage regulator was designed on the grid-side converter (GSC) to enhance the stability of the system. In the next step, the TD3 agent was trained to learn the system dynamics by replacing the inner current controllers of the RSC, which replaced the QL-based model. In the first stage, the conventional PSS and Proportional–Integral (PI) controllers were introduced to both the RSC and GSC. Then, the system was trained to become model-free by replacing the PSS and the PI controller with a QL algorithm under very small wind speed variations. In the second stage, the QL algorithm was replaced with the TD3 agent by introducing large variations in wind speed. The results reveal that the TD3 agent can sustain the stability of the DFIG system under large variations in wind speed without assuming a detailed control structure beforehand, while QL-based controllers can stabilize the doubly fed induction generator (DFIG)-equipped wind energy conversion system (WECS) under small variations in wind speed.

Improved dynamic modelling of DFIG driven wind turbine with algorithm for optimal sharing of reactive power between converters