Modeling Of Wind Energy Conversion System Research Articles

Sampled-data observer design for sensorless control of wind energy conversion system with PMSG

This paper presents a nonlinear observer for a variable-speed wind energy conversion system (WECS) utilizing a permanent magnet synchronous generator (PMSG). The study addresses the design of high-gain sampled-data observers based on the nonlinear WECS model, supported by formal convergence analysis. An essential aspect of this observer design is the incorporation of a time-varying gain, significantly enhancing system performance. Convergence of estimation errors is demonstrated using the input-to-state stability method. Simulation of the proposed observer is conducted using the MATLAB-Simulink tool. The obtained results are presented and analyzed to showcase the overall effectiveness of the proposed system.

An improved sliding mode control for reduction of harmonic currents in grid system connected with a wind turbine equipped by a doubly-fed induction generator

Introduction. The implementation of renewable energy resources into the electrical grid has increased significantly in recent years. Wind power is one of the existing resources. Presently, power electronics has become an indispensable tool in wind power plants. Problem. However the associated control usually has an impact on increasing the harmonic distortion, especially on the output voltage. Goal. This paper proposes a new sliding mode control strategy, applied on a rotor-side of a doubly-fed induction generator. The main goal is to meet the electrical power requirements, while responding to the power quality issues. Methodology. The wind energy conversion system must be able to not only track the maximum power point of the wind energy, but also to mitigate the harmonic currents caused by the non-linear loads. To achieve this goal, the power converters are driven by the proposed sliding mode control strategy. The corresponding two gains of the sliding surface are well selected using a particle swarm optimization algorithm. The particle swarm optimization algorithm solves a constrained optimization problem whose fitness function is a prior formulated as the sum of two mean square error criterions. The first criterion presents the tracking dynamic of the reference active power while the second one presents the tracking dynamic of the reference reactive power. The novelty lies in the implementation of the particle swarm optimization algorithm in conventional sliding mode control strategy, in which the proposed-improved sliding mode control strategy is developed. The wind energy conversion system control uses the principal of the vector oriented control to decouple the control of the active power from that of the reactive power. Results. The improved sliding mode control strategy is applied to control separately theses powers in the presence of non-linear loads. The energy assessment of this strategy is analysed using the wind energy conversion system model based on SimPower software. Originality. The obtained simulation results confirm the superiority of the proposed-improved sliding mode control strategy in terms of reference tracking dynamics and suppression of harmonic currents.

A Complete Impedance Model of a PMSG-Based Wind Energy Conversion System and Its Effect On the Stability Analysis of MMC-HVDC Connected Offshore Wind Farms

Impedance modeling of a permanent magnet synchronous generator (PMSG)-based wind energy conversion system (WECS) usually ignores the machine-side dynamics, instead, the machine-side system is simplified as a constant power source, while merely keeping the detailed grid-side converter model. This simplification is mainly based upon the intuition that the dc-bus capacitor is large enough so that the machine- and grid-side dynamics can be decoupled. However, the simplification probably does not hold in practice since there is always a tendency to minimize the capacitor size to achieve a smaller package for installation. Therefore, the machine-side system should not be ignored, otherwise maybe leading to error for stability analysis. To address this issue, this paper developed a complete ac-side impedance model of the PMSG-based WECS. Then, impact factors about the coupling characteristics between machine- and grid-side systems of the PMSG-based WECS are discussed. Finally, a case study of sub/super synchronous oscillation is carried out on a practical offshore wind farm integrated with a modular multilevel converter based high-voltage dc (MMC-HVDC) transmission system in China. The results show that ignoring the machine-side system would lead to an optimistic stability judgement, which confirms the necessity of the complete model of PMSG-based WECS. Furthermore, the system can be stabilized by either changing the couplings between machine- and grid-side systems of PMSG-based WECS or implementing active damping in the wind farm side MMC.

A modified sliding mode controller for a permanent magnet synchronous generator-based wind turbine system

To enhance the control and stability of the wind energy conversion system (WECS) based on direct drive permanent magnet synchronous generator (PMSG), this artefact presents a modified sliding mode control approach. A detailed time domain dynamic model of PMSG-based WECS integrated to infinite bus is also presented in terms of d-q reference frame. In order to compensate the general limitations with regard to various control strategies, a proportional integral (PI) type sliding surface-based fast sliding mode control is executed for the above. A current control strategy has been suggested for real and reactive power control keeping voltage under the desired limit. To justify the superior performance of the proposed controller in terms of robustness, reliability and accuracy compared to PI controller, the control strategy is validated through MATLAB simulation, when the system is subjected to diverse operating conditions like wind speed and system parameter variations.

A modified sliding mode controller for a permanent magnet synchronous generator-based wind turbine system

To enhance the control and stability of the wind energy conversion system (WECS) based on direct drive permanent magnet synchronous generator (PMSG), this artefact presents a modified sliding mode control approach. A detailed time domain dynamic model of PMSG-based WECS integrated to infinite bus is also presented in terms of d-q reference frame. In order to compensate the general limitations with regard to various control strategies, a proportional integral (PI) type sliding surface-based fast sliding mode control is executed for the above. A current control strategy has been suggested for real and reactive power control keeping voltage under the desired limit. To justify the superior performance of the proposed controller in terms of robustness, reliability and accuracy compared to PI controller, the control strategy is validated through MATLAB simulation, when the system is subjected to diverse operating conditions like wind speed and system parameter variations.

Comparative study of back-stepping controller and super twisting sliding mode controller for indirect power control of wind generator

This paper presents the application nonlinear control to regulate the rotor currents and control the active and reactive powers generated by the Doubly Fed Induction Generator used in the Wind Energy Conversion System (WECS). The proposed control strategies are based on Lyapunov stability theory and include back-stepping control (BSC) and super-twisting sliding mode control. The overall WECS model and control scheme are developed in MATLAB/Simulink and the simulation results have shown that the BSC leads to superior performance and improved transient response as compared to the STSMC controller.

Dynamic performance enhancement for wind energy conversion system using Moth-Flame Optimization based blade pitch controller

Moth-Flame Optimization (MFO) technique has recently been explored to develop a novel algorithm for distributed optimization and control. In this paper, the MFO-based design of blade pitch controllers (BPCs) is proposed for wind energy conversion system (WECS) to enhance the damping of oscillations in the output power and voltage. The simple Proportional-Integral-Differential (PID) is used to realize the advantage of the proposed hybrid referential integrity MFO technique. The proposed blade pitch controllers are termed as BPC-PID (MFO). Single wind turbine system, equipped with BPC-PID (MFO), is considered to accomplish this study. The suggested WECS model considers small as well as large scale uncertainties. MFO is utilized to search for optimal controller parameters by minimizing a candidate time-domain based objective function. The performance of the proposed controller has been compared to those of the conventional PID controller based on Zeigler Nichols and simplex algorithm and the PID controller optimized by genetic algorithms (GA), to demonstrate the superior efficiency of the MFO-based BPC-PID. Simulation results emphasis on the better performance of the proposed BPC-PID (MFO) compared to conventional and GA-based BPC-PID controllers over a wide range of operating conditions and control system parameters uncertainties.

Further results on robust H∞ control design for uncertain time-delay systems with actuator delay: application to PMSG machine

ABSTRACTThe problem of robust state-feedback control design for a class of uncertain systems with two different time delays in the state vector and the input signal is investigated in this paper. The main feature of the paper is to develop a robust controller, which ensures the robust asymptotic stability of the system as well as the desired performance. By constructing a Lyapunov–Krasovskii functional, some sufficient conditions for the existence of the state-feedback controller is derived in terms of linear matrix inequalities. Numerical examples such as a wind energy conversion system model based on a permanent magnet synchronous generator model are provided to illustrate the effectiveness of the proposed method.

An internal model control for enhanced grid-connection of direct-driven PMSG-based wind generators

For Wind Energy Conversion Systems (WECS) based on Permanent Magnet Synchronous Generators (PMSG) with back-to-back converters, some strategies have been employed aiming safe and reliable grid-connection, among them the grid-side control in coordination with the braking chopper. Conventionally, the grid-side control is of the Proportional-Integral (PI) type, however, due to the presence of cross-coupling terms between the dq currents delivered to the grid, PI does not ensure null steady-state error resulting in an inappropriate power delivery. Moreover, during voltage sags at the connection point, the chopper turning on is often commanded based on the DC-link voltage increase, however, a more suitable trigger signal should be based on the current delivered to the grid. Seeking to improve the grid-connection issue, in this work a new control is presented, which is based on Internal Model State Feedback Control (IMSFC) in order to eliminate dq current steady-state error and whose the control design is achieved through Linear Quadratic Regulator (LQR). Besides, the chopper trigger signal is based on the current delivered to the grid, ensuring safe Low-Voltage Ride-Through (LVRT). The proposed control and the conventional PI have been discretized and implemented to interact with a suitable model of grid-connected PMSG WECS in MatLab/Simulink. The proposed control performance has overcome the conventional both for steady-state and low-voltage conditions.

Intelligent Open Switch Fault Detection for Power Converter in Wind Energy System

ABSTRACTThis paper proposes a simple and fast fuzzy logic-based open switch fault detection method for rotor side converter (RSC) in doubly fed induction generator (DFIG) wind turbine system. In the proposed scheme, only the mean values of the three-phase rotor currents are used to identify the power switch in which the open-circuit fault has occurred.The wind energy conversion system model developed for the design and evaluation of the proposed fault detection technique including three principal controls. the first control ensure the regulation of the electromagnetic torque and the reactive stator power (named Rotor Side Converter (RSC) control), the second regulates the DC-link voltage at the desired level (named Grid Side Converter (GSC) control) and in order to achieve maximum power at any wind speed condition a maximum power point tracking (MPPT) control strategy has been used. The simulation model was developed in MATLAB/Simulink environment. The results show that the proposed fault detection scheme is able to rapidly and effectively identify open switch faults among other fault types in a time less than one period.

ENGLISH

3 ABSTRACT: In modern wind turbines, the energy conversion process uses the basic aerodynamic force of lift to produce a net positive torque on a rotating shaft, resulting first in the production of mechanical power and then its conversion to electricity in a generator. Wind turbines, unlike most other turbines, can produce power only in response to the wind that is available at the time. The output of a wind turbine is thus inherently fluctuating with the wind and can't be directly dispatched for a purpose. Apart from this, the output depends on individual components like rotor dimension, transmission shaft, gear box and alternator. Since the wind turbine is relatively large, expensive, and Wind Energy Conversion System (WECS) is complex, it is not convenient to do research on actual wind farm. Therefore, WECS model development for steady and dynamic state analysis and design has been research issue in recent years. This paper presents a new block-based approach for WECS dynamic modeling. The blocks (modules) developed by Aalborg University - Denmark, RISO national laboratory based on Kaimal Spectra have been customized, updated and integrated into MATLAB/SIMULINK platform and then utilized to simulate performance of 5kW WECS. In addition to the developed block sets, in this paper, a proportional-integral controller is designed to control the turbine pitch and integrated with the simulation models. The simulation result demonstrates that the model output is in agreement with what is expected. The system has advantages like: research cost reduction, ease in application and control, flexibility and completeness for analysis in MATLAB/SIMULINK environment. The system can be used for assessment of power quality and design of wind turbine system for grid connection.

Filter-Based Fault Diagnosis of Wind Energy Conversion Systems Subject to Sensor Faults

The operational reliability of wind energy conversion systems (WECSs) has attracted a lot of attention recently. This paper is concerned with sensor fault detection (FD) and isolation problems for variable-speed WECSs by using a novel filtering method. A physical model of WECS with typical sensor faults is first built. Due to the non-Gaussianity of both wind speed and measurement noises in WECSs, an improved entropy optimization criterion is then established to design the filter for WECSs. Different from previous entropy-filtering results, the generalized density evolution equation (GDEE) is adopted to reveal the relationship among the estimation error, non-Gaussian noises, and the filter gain. The sensors FD and isolation algorithms are then obtained by evaluating the decision rule based on the residual signals generated by the filter. Finally, simulation results show that the sensor faults in WECSs can be detected and isolated effectively by using the proposed method.

Design of PI Controller in Pitch Control of Wind Turbine: A Comparison of PSO and PS Algorithm

In wind energy conversion system (WECS) at wind speed above rated, the pitch angle is controlled to keep the generated output fixed so also the speed and the frequency. The model is built as a discrete model of WECS connected to Grid including a Line to Ground (LG) fault in Grid. A Proportional-Integral (PI) controller with gain K p and K i is used in pitch angle control loop. The proportional gain K p and integral gain K i are tuned through Particle Swarm Optimization (PSO) and Pattern Search (PS) algorithms. A comparison of two different objective functions with its weight adjustment is presented. The performances of the algorithms in designing the optimal controller are compared. The analysis indicates the superiority of PSO over PS and takes less time to achieve the minimum error criteria. The controller designed using PSO minimizing the proposed objective function has better settling time as regards wind turbine speed response, compared to the other. The control action is validated in real time using OPAL-RT taking different cases of random wind speed, gust and gust with random wind speed and Line to Ground fault.

Comparative Study of PI, RST, Sliding Mode and Fuzzy Supervisory Controllers for DFIG based Wind Energy Conversion System

This work aims to present a comparative study of four controllers for Double Fed Induction Generator (DFIG) based Wind Energy Conversion System (WECS). The DFIG is directly connected to the grid and driven by the rotor through an AC/DC/AC converter. A model was developed for each component (Turbine, DFIG and Rectifier-Filter-Inverter) of the wind system. The PWM control method is applied to the inverter to drive the DFIG from the rotor circuit. To ensure high performance and better enforcement of DFIG, a direct vector control strategy of active and reactive power of the stator has been developed. The synthesis of conventional PI controller and advanced RST, Sliding Mode (SM) and Fuzzy Supervisory (FS) controllers is performed. The system’s performance has been tested and compared according to reference tracking, robustness, and disturbance rejection. A set of simulation studies are carried-out on a WECS model to prove the effectiveness of the proposed controllers design.

Modeling and Control of Standalone Direct-Driven PMSG WECS for Grid Compatibility at Varying Wind Speeds

Wind energy is one of the most available and exploitable forms of renewable energy. Variable speed PMSG based Wind Energy Conversion System (WECS) offers many advantages compared to the fixed speed squirrel cage induction generators such as improved stator output operation at better power factor, no maintenance cost for gear box (as it is direct-driven) reduction in weight and losses, higher efficiency and ability to run at low speeds. The elimination of the gear box and brushes can enhance the efficiency of wind turbine by 10%. In this paper a Permanent Magnet Synchronous Generator (PMSG) is modeled whose stator is connected to the constant single phase load (in place of grid) through AC/DC thyristors based rectifier followed by capacitor (dc-link) and DC/DC converter control. Overall arrangement provides constant output to connected load if applied with proper controlling techniques. Hence this proposed wind generation system design can be extended for grid connection also via DC/AC inverter control. Results are simulated and verified in MATLAB/Simulink platform at constant rated (12m/s) and varying (stepped) wind speed for smooth and constant output voltage. DOI: http://dx.doi.org/10.11591/telkomnika.v13i3.7097

Sensorless wind energy conversion system maximum power point tracking using Takagi–Sugeno fuzzy cerebellar model articulation control

In this paper, we propose a sensorless wind energy conversion system (WECS) maximum wind power point tracking using Takagi–Sugeno fuzzy cerebellar model articulation control (T-S CMAC). The main objective of the WECS is to achieve maximum power transfer under various wind speeds without actual measurement of the wind velocity. We first represent the WECS, which uses a permanent magnet synchronous generator (PMSG), as a nonlinear dynamical model. To carry out the T-S CMAC design, we rewrite the WECS model as a T-S fuzzy representation. The T-S CMAC design is inspired by the architectural similarity of the T-S fuzzy control and CMAC where accordingly the PDC design control gains and weighting parameter are augmented into a single vector. The advantages of this approach are 3-fold: (i) increases accuracy of CMAC initial weights – we assign the initial weights of CMAC using the control gains solved by the LMIs from the PDC design; (ii) introduces adaptive ability in LMI-based design – the CMAC design allows time-varying parameters in the system; and (iii) relaxes assumption on system uncertainty – we drop the assumption that a strict upper bound on system uncertainty is known. Numerical simulations under various wind speeds show exponential convergence results which further verify the theoretical derivations.

Comparative Study of PI, RST, Sliding Mode and Fuzzy Supervisory Controllers for DFIG based Wind Energy Conversion System

This work aims to present a comparative study of four controllers for Double Fed Induction Generator (DFIG) based Wind Energy Conversion System (WECS). The DFIG is directly connected to the grid and driven by the rotor through an AC/DC/AC converter. A model was developed for each component (Turbine, DFIG and Rectifier-Filter-Inverter) of the wind system. The PWM control method is applied to the inverter to drive the DFIG from the rotor circuit. To ensure high performance and better enforcement of DFIG, a direct vector control strategy of active and reactive power of the stator has been developed. The synthesis of conventional PI controller and advanced RST, Sliding Mode (SM) and Fuzzy Supervisory (FS) controllers is performed. The system’s performance has been tested and compared according to reference tracking, robustness, and disturbance rejection. A set of simulation studies are carried-out on a WECS model to prove the effectiveness of the proposed controllers design.

Wind energy resource, wind energy conversion system modelling and integration: a survey

In this paper, critical review of various work done in the areas of wind energy resource, modelling of wind energy conversion system (WECS) and issues regarding wind power integration into the grid are presented with the aim of examining the development, progress, achievements and direction of research. Some of the findings show that every site is unique; therefore, no generic conclusion can be drawn with regards to wind characteristics and the wind power potential of locations. The study also reveals that there is no single model of WECS. The model to be adopted will depend on the problem to be solved. This paper is useful in providing background details for wind turbine designers, researchers and practical engineers who are new in the field of wind energy.

AC Losses of a Grid-Connected Superconducting Wind Turbine Generator

We present a numerical method to estimate the steady-state AC losses of a superconducting wind turbine generator connected to the grid through its AC/DC/AC converter. We use a multiscale simulation with unidirectional couplings between a lumped-parameter wind energy conversion system model, a finite element machine model, and a finite element HTS tape model. The estimation include effects linked to the generator space harmonics, the exciter control, and the AC/DC/AC converter PWM and control. As the superconducting coil is made of several thousand of HTS tapes, we evaluate AC losses for a fraction of them and we interpolate the results to the others. The steady-state AC losses of a 10 MW class generator are estimated to be under 60 W.

Modeling of small wind turbines based on PMSG with diode bridge for sensorless maximum power tracking

The Permanent Magnet Synchronous Generator (PMSG) with diode bridge is frequently used in small Wind Energy Conversion Systems (WECS). This configuration is robust and cheap, and therefore suitable for small WECS. In order to achieve Maximum Power Point Tracking (MPPT) with no mechanical sensors, it is possible to impose the relationship between the DC voltage and the DC current on the optimum operating points. However, this relationship is difficult to calculate theoretically since the whole system is involved. In fact, as there is no model of the whole system in the literature, the optimum curve IL∗(Vdc) is obtained with experimental tests or simulations. This paper develops an accurate model of the whole WECS, thereby making it possible to relate the electrical variables to the mechanical ones. With this model, it is possible to calculate the optimum curve IL∗(Vdc) from commonly-known system parameters and to control the system from the DC side. Experimental results validate the theoretical analysis and show that maximum power is extracted for actual wind speed profiles.