Generator-based Wind Energy Conversion System Research Articles

Enhancement of Low Voltage Ride Through Capability of Doubly Fed Induction Generator Based Wind Turbine Using Fuzzy Logic Controller

Combined impact of environmental issues and policies of utilities has led to generation of clean and sustainable energy. Solar and wind energies are prominent and can provide bulk amount of electrical energy. Vast number of resources and more electrical energy density are attractive features of wind energy. Generation of bulk amount of wind energy especially offshore wind energy is attracting utilities to incline towards wind energy. Variable speed wind energy conversion systems employing Doubly fed induction generators offers several advantages such as maximum power generation and independent control of active and reactive powers. Doubly fed induction generator-based wind energy system became the first choice of power system operators due to its low-cost power electronic convertors. Stringent grid codes adopted by various countries made Low voltage ride through a serious problem for electric utilities as well as DFIG manufacturers. Many researchers tried to address the problem of low voltage ride through. In initial stages, crowbar circuits were used. Later Low voltage ride through was addressed using additional hardware such as STATCOM. Artificial intelligent controllers were used to minimize the effect of ride through. A comprehensive review, of different issues allied with low voltage ride through of doubly fed induction generator-based wind energy conversion system is presented in this article.

Maximum power extraction framework using robust fractional-order feedback linearization control and GM-CPSO for PMSG-based WECS

The most important issue in the use of wind energy conversion systems is to ensure maximum power extraction in terms of efficiency. Therefore, maximum power point tracking algorithms are as important as the maximum power point tracking controller. In this study, maximum power extraction frameworks operating the state-of-the-art optimization methods are presented for permanent magnet synchronous generator–based wind energy conversion system. These frameworks consist of a Gauss map–based chaotic particle swarm optimization and a hybrid maximum power point tracking approach that combines feedback linearization technique with fractional-order calculus. The feedback linearization control strategy can fully decouple and linearize the original state variables of the nonlinear system and thus provide an optimal controller crossing wide-range operating conditions. The objective is to maintain the tip speed ratio at its optimal value, which implies the use of a rotational speed loop. The method is based on the feedback linearization technique and the fractional control theory. Gauss map–based chaotic particle swarm optimization, which is a remarkable and recent optimization technique, is utilized to achieve optimum coefficients to efficiently ensure the maximum power point tracking operation in here. A simulation study is carried out on a 3-kW wind energy conversion system to show the effectiveness of the proposed control scheme.

Improved control strategy for Cuk converter assisted wind‐driven SEIG for DC nanogrid

In this study, the current mode control strategy for a Cuk converter assisted self-excited induction generator-based wind energy conversion system (WECS) for DC nanogrid is proposed. The sliding mode controller (SMC) is a non-linear controller and, is preferred because of good static and dynamic response for input -output disturbance rejections. However, the knowledge of all the state variables is required, which increases the number of sensors and control complexity. To reduce the number of sensors, reduced-order SMC (ROSMC) can be implemented. Conventionally design of the voltage loop in ROSMC does not consider the uncertainty of the control parameter. However, the accuracy of the control signal generated by the ROSMC also depends on how accurately the reference current is generated. Therefore, a genetic algorithm tuned PI controller is proposed to generate the ripple-free reference current. Artificial intelligence assisted ROSMC (AIROSMC) is proposed because of its advantages over SMC, which are a reduced number of sensors, improved dynamic response and easy implementation. The extensive simulation study is carried in MATLAB\Simulink for comparative analysis of fixed frequency SMC, two variable SMC, ROSMC, and AIROSMC. The harmonic spectrum analysis is carried out to justify the selection of DBR instead of the controlled rectifier.

Voltage stability assessment and enhancement of power grid with increasing wind energy penetration

This paper presents the voltage stability assessment of power system with increasing wind energy penetration. The effects of increasing Doubly-Fed Induction Generator-based Wind Energy Conversion System (DFIG-WECS) penetration in the power system have been investigated in this work. Active Power-Voltage (PV) analysis was employed to determine the voltage stability limits in terms of the maximum loadability limit within which stable operation of the grid can be guaranteed as the wind energy penetration increases. The analyses in this work were carried out both for normal and contingency operations of the grid. IEEE 14-bus test system was used as the study case. Simulations were carried out using DigSilent PowerFactory software and results analyses were done using MATLAB. Furthermore, the effects of integrating DFIG-WECS on the loading of essential power system equipment are investigated. The results show that the maximum loadability limit of the study system increases with increasing DFIG-WECS power penetration up to 100%. However, the overloading effects on critical transmission lines presents a definitive limit to the allowable practical penetration level, which is determined to be 28.06%. This limit can be improved to 29.88%, 46.3% and 52.23% by Thyristor-Controlled Series Capacitor (TCSC) application on Line 9–14, upgrading Line 9–14 to double circuit, and upgrading both Line 9–14 and Line 13–14 to double circuit respectively. Thus, effective line enhancement and reactive power compensation strategy such as those offered by FACTS devices are required for a voltage-stable operation of the grid with increasing wind energy penetration.

Overall Adaptive Controller Design of PMSG Under Whole Wind Speed Range: A Perturbation Compensation Based Approach

This paper proposes an adaptive overall control strategy of the permanent magnet synchronous generator-based wind energy conversion system (WECS) in the whole wind speed range. For the machine side, the maximum power point tracking (MPPT) operation is realized by stator current and mechanical rotation speed control under below-rated wind speeds. Under above-rated wind speeds, the extracted wind power is limited via pitch control. For the grid side, the reactive and active power injected into grid is regulated by DC-Link voltage and grid current control loop. In addition, under grid voltage dips, the pitch control is employed for limiting grid current and maintaining the DC-Link voltage around its rated value. The fault ride-through capability (FRTC) can be enhanced. The overall control strategy is based on perturbation estimation technique. A designed observer is used for estimating the perturbation term including all system nonlinearities, uncertainties and disturbances, so as to compensate the real perturbation. Then, an adaptive control for the original nonlinear system can be realized. The effectiveness of the proposed overall control strategy is verified by applying the strategy to a 2-MW WECS in MATLAB/Simulink. The results show that, compared with the feedback linearizing control (FLC) strategy and conventional vector control (VC) strategy, the proposed perturbation observer based adaptive control (PO-AC) strategy realizes the control objectives without knowing full state information and accurate system model, and improves the robustness of the WECS parameter uncertainties and FRTC.

Efficiency Analysis of Vienna Rectifier-Based Grid interface Systems for Low-Power PM WECS

Losses of power semiconductor switching devices used in grid-connected wind energy conversion systems (WECSs) are regarded as one of the main issues to be considered when comparing different types of grid interface systems (GISs). This loss is more highlighted for low-power applications, because it directly affects the reliability and efficiency of the system. Recently, a GIS using Vienna rectifier (VR) as generator-side converter is investigated for a permanent magnet synchronous generator-based WECS. Due to its cost advantage, this reduced switch count rectifier is specifically attractive for low-power applications. In this study, the analytical relations for switching and conduction losses of a VR-based GIS are derived and compared to conventional back-to-back systems. As for the grid-side converter, two types of inverters, conventional six-switch inverter and B4 inverter, are considered and the efficiency of GIS is investigated analytically. In order to derive the loss equations for VR, a new current PWM method is presented explaining the formulas required for its implementation. Finding the relations for switching loss and efficiency, different GISs are compared and the most efficient ones are determined for different ratings. The GISs are also simulated, and their switching power losses for different operating points are shown.

Direct driven wind energy conversion system connected to load using variable frequency transformer

This paper proposes a variable frequency transformer for wind energy conversion systems using permanent magnet synchronous generator. It is a doubled-fed wound round induction machine which transfers the power between asynchronous networks. Typical permanent magnet synchronous generator-based wind energy conversion systems with back-to-back converters produces harmonics which creates power quality problems.The above problem can be overcome using the variable frequency transformer between permanent magnet synchronous generator and load. This design does not employ any power electronic converter for wind energy conversion system and harmonics can be diminished using the variable frequency transformer. In this paper, the PMSG is connected through variable frequency transformer for different wind speeds. The results are endorsed using MATLAB/SIMULINK.

Grid Ancillary Services From Doubly Fed Induction Generator-Based Wind Energy Conversion System: A Review

Modern electrical grids face serious challenges to maintain healthy operational conditions. The nominal voltage and frequency, for instance, are affected by huge load changes and renewable energy integration. Renewable energy conversion systems are traditionally installed to provide active power. Fortunately, advanced renewable energy conversion systems have the ability to provide other facilities such as reactive power control and harmonic mitigation. In fact, recent grid codes obligate renewable energy systems to serve other duties such as generating reactive power rather than just simply supply active power, participate in fault ride through, for instance. This paper presents a comprehensive study on the doubly fed induction generator (DFIG)-based wind energy conversion system (WECS), which provides ancillary services to the grid along with performing its regular duties. These services include reactive power control, voltage ride through, power quality improvement, frequency control, and power oscillation damping. The literature survey and comparative studies show that the DFIG-based WECS has the ability to support electrical grid during normal and transient conditions, and it can also help in the large-scale renewable energy penetration to the power grid. The effect of different industrial and nonlinear controllers on DFIG performance in extracting grid ancillary services is highlighted.

A new combined actuator fault estimation and accommodation for linear parameter varying system subject to simultaneous and multiple faults: an LMIs approach

This paper proposes a novel fuzzy observer scheme-based active fuzzy fault-tolerant tracking control (FFTTC) combined with a parallel distributed compensation control law for a linear parameter varying system subject to actuator faults and noise measurement. This system consists of a doubly fed induction generator-based wind energy conversion system described by a Takagi–Sugeno fuzzy model. The developed scheme is able to force system states to track their desired reference signal in finite time and obtain a better dynamic response and performance. A fuzzy state observer is also developed to simultaneously estimate the generator states and the actuator faults. Based on the obtained online fault estimation information, the FFTTC will be reconfigured to compensate for the fault impact. The closed-loop stability is established based on a Lyapunov function. Sufficient conditions are formulated for the existence of fuzzy fault-tolerant control parameters in the form of linear matrix inequalities (LMIs), which can be easily solved by means of a standard YALMIP toolbox. The fuzzy observer and fuzzy fault-tolerant tracking control gains can be computed based on the solutions of a set of LMIs. Computer simulations were performed using the MATLAB/Simulink environment to highlight the performance and robustness of the proposed design procedure with respect to actuator fault occurrences.

Active disturbance rejection based MPPT control for wind energy conversion system under uncertain wind velocity changes

The tip speed ratio regulation based maximum power point tracking (MPPT) control for the wind energy conversion system (WECS) is studied in this paper. Challenges imposed by uncertain changes in wind velocity and unmodelled system dynamics are considered. A first order active disturbance rejection controller (ADRC) is designed to tackle this problem. Based on the platform of the high-power (2-MW) rigid-drive-train squirrel-cage induction generator-based wind energy conversion system (WECS), a simulation study is carried out by comparing with the performance of a well-tuned published PI (proportional–integral) speed controller, and the results show that the proposed first order ADRC controller exhibits better tracking performance and adaptability for uncertain wind velocity changes. There are only two controller parameters, namely, ωo and ωc, to tune, and control adaptability can be held without parameters resetting or extractable mechanical power reducing, proving the effectiveness of the proposed ADRC approach for the WECS MPPT problem.

Passivity‐based linear feedback control of permanent magnetic synchronous generator‐based wind energy conversion system: design and analysis

This study designs a passivity-based linear feedback control scheme of a permanent magnetic synchronous generator-based wind energy conversion system, which attempts to achieve a maximum power point tracking (MPPT) at generator-side voltage source converter (VSC) and enhance fault ride-through (FRT) capability at grid-side VSC simultaneously. A storage function is constructed based on the passivity theory, in which the actual role of each term is meticulously investigated while the beneficial ones are remained so as to significantly improve the transient responses. Then, an auxiliary input is employed in the form of linear feedback control to ensure a desired tracking error convergence. Moreover, the closed-loop system stability is thoroughly analysed, together with a detailed physical interpretation of the storage function. Three case studies are undertaken including step change of wind speed, stochastic wind speed variation, and FRT. Simulation results verify that the proposed approach can effectively achieve MPPT and dramatically improve the FRT capability under various operation conditions against that of vector control and feedback linearisation control.

A sliding mode controller-based STATCOM for voltage profile improvement of micro-grids

PurposeThe purpose of this paper is to evaluate the suitability and robustness of sliding mode controller (SMC) for maintaining flat voltage profile at the load bus of two different micro-grid systems using STATCOM.Design/methodology/approachTwo micro-grid systems are dynamically modelled and simulated using MATLAB/Simulink. The first micro-grid has a single diesel engine-driven synchronous generator. The second micro-grid has one diesel engine-driven synchronous generator and a doubly fed induction generator-based wind energy conversion system. The STATCOM is connected to the load bus in both the micro-grids. SMC is used for the control of STATCOM for voltage profile improvement of micro-grid. The performance of SMC-based STATCOM is analysed and compared with the performance of conventional PI controller-based STATCOM.FindingsThe SMCs are more suited for STATCOM control as these are more immune to load disturbances even with the presence of wind energy generators. The voltage deviations and the steady state errors in voltage are less with SMC. Although SMC introduces a bit of steady state error in the dc link voltage of the STATCOM, it is much less than the settling limit of 2 per cent, which is quite acceptable. SMC proves to be better than conventional PI controllers in both the proposed models of micro-grid.Originality/valueDesign of a robust first-order SMC for a STATCOM is used for voltage profile improvement in two different micro-grid systems.

Robust nonlinear control via feedback linearization and Lyapunov theory for permanent magnet synchronous generator- based wind energy conversion system

In this paper, the method for the nonlinear control design of a permanent magnet synchronous generator based-wind energy conversion system (WECS) is proposed in order to obtain robustness against disturbances and harvest a maximum power from a typical stochastic wind environment. The technique overcomes both the problem of nonlinearity and the uncertainty of the parameter compared to such classical control designs based on traditional control techniques. The method is based on the differential geometric feedback linearization technique (DGT) and the Lyapunov theory. The results obtained show the effectiveness and performance of the proposed approach.

Power Curve Based-Fuzzy Wind Speed Estimation in Wind Energy Conversion Systems

Availability of wind speed information is of great importance for maximization of wind energy extraction in wind energy conversion systems. The wind speed is commonly obtained from a direct measurement employing a number of anemometers installed surrounding the wind turbine. In this paper a sensorless fuzzy wind speed estimator is proposed. The estimator is easy to build without any training or optimization. It works based on the fuzzy logic principles heuristically inferred from the typical wind turbine power curve. The wind speed estimation using the proposed estimator was simulated during the operation of a squirrel-cage induction generator-based wind energy conversion system. The performance of the proposed estimator was verified by the well estimated wind speed obtained under the wind speed variation.

A Robust Control Strategy Research on PMSG-Based WECS Considering the Uncertainties

This paper proposes a robust control strategy for the uncertainties of permanent magnet synchronous generator-based wind energy conversion system, based on state feedback. Meanwhile, the detailed design and analysis process of this robust controller also have been presented. Compared with the conventional control, the new method with a better robustness can not only make the whole closed-loop system stable but also reduce the major harmonics and total harmonic distortion of currents and ripples of torque. And then, we set up a detailed 2 MW simulation test platform based on MATLAB/SIMULINK/SimPowerSysterms. The simulation results verify the effectiveness and correctness of the algorithm.

Maximum power point tracking for the permanent magnet synchronous generator‐based WECS by using the discrete‐time integral sliding mode controller with a chattering‐free reaching law

In this study, a single sensor-based maximum power point tracking (MPPT) algorithm is presented for permanent magnet synchronous generator-based wind energy conversion system (WECS). The MPPT method used in this study uses only the wind speed sensor to generate the reference point required for the maximum power. A discrete-time controller is proposed to bring the system to the reference point determined by the MPPT algorithm. The designed MPPT controller consisting of a new discrete-time reaching-law approach and a discrete-time integral sliding mode control (SMC). The designed discrete-time SMC-based controller is implemented by using an Acorn RISC Machine (ARM)-based LM4F120 microcontroller, and its performance is examined on a WECS emulator prepared in the laboratory. The results got from the real-time studies prove that the proposed controller has the satisfactory performance to bring the system to the MPP. The performance of the proposed controller is also compared with the conventional sliding mode controller and perturb and observe method. The obtained results proved that the proposed controller has a better performance than the other controllers in terms of the settling time and output voltage's ripple.

Reliability and performance improvement of double-fed induction generator-based wind energy conversion system

The aim of this paper is to present a new coordination control between active crowbar and PV-STATCOM to enhance the performance and the reliability of grid connected double-fed induction generator (DFIG)-based wind farm under grid disturbance. A new technique to detect the fault is also presented. It is based on monitoring the rotor voltages and currents of the DFIG by using the symmetrical components approach. A modified control scheme of the solar farm converter is adopted to operate as STATCOM in the presence of a disturbance. The proposed control scheme is simulated under MATLAB/Simulink platform to verify its efficiency.

Reliability and performance improvement of double-fed induction generator-based wind energy conversion system

Reliability and performance improvement of double-fed induction generator-based wind energy conversion system

Robust Sliding Mode Control of Permanent Magnet Synchronous Generator-Based Wind Energy Conversion Systems

The subject of this paper pertains to sliding mode control and its application in nonlinear electrical power systems as seen in wind energy conversion systems. Due to the robustness in dealing with unmodeled system dynamics, sliding mode control has been widely used in electrical power system applications. This paper presents first and high order sliding mode control schemes for permanent magnet synchronous generator-based wind energy conversion systems. The application of these methods for control using dynamic models of the d-axis and q-axis currents, as well as those of the high speed shaft rotational speed show a high level of efficiency in power extraction from a varying wind resource. Computer simulation results have shown the efficacy of the proposed sliding mode control approaches.

Grid voltage local regulation by a doubly fed induction generator–based wind turbine

Voltage regulation at point of common coupling using a doubly fed induction generator–based wind energy conversion system is achieved through reactive power control. Wind energy conversion system produces reactive power when the voltage is less than grid nominal voltage and it consumes it in the opposite case. In this article, a method to achieve this goal is proposed. It consists of controlling the reference value of the vector control system in order to affect the wind energy conversion system reactive power output. Two situations have been simulated. Sudden voltage increase and decrease were applied to the control system. Satisfying results have been obtained since the voltage at point of common coupling has been restored back to its initial value.