Variable-speed Wind Energy Conversion Systems Research Articles

Optimal Estimation and Tracking Control for Variable-speed Wind Turbine with PMSG

Designing an optimal tracking controller and system observer is a nonlinear problem in the variable-speed wind energy conversion system (WECS). In this paper, an adjusted feedforward and feedback optimal controller with extended Kalman filter (EKF) is introduced to estimate and control the permanent magnet synchronous generator (PMSG) for the maximum power point tracking (MPPT) with several disturbances of the wind speed. An augmented model of wind turbine and PMSG is expanded, and then the parameters of the optimal controller and estimator are obtained. The dynamic stability of the closed-loop system with feedback-feedforward controller (FFC), EKF and speed controller are analyzed. To compare the dynamic performance of EKF and FFC with the conventional controllers, numerical results are demonstrated with the disturbances of the wind speed and faults in power grid.

Variable structure power control under different operating conditions of PM synchronous generator wind farm connected to electrical network

The enlarged penetration of wind power into electrical network brings challenges to control strategies of variable speed wind energy conversion systems (VS-WECS). In this study, a nonlinear control scheme for wind farm system (WFS) is proposed. The control technique is realised using variable structure sliding mode control (VSSMC). The generator side rectifiers control is used to keep the generator rotor velocities at an optimal value obtained from the maximum power point tracking (MPPT) algorithm to maximise the total extracted power. The grid-side inverter injects the generated power into the AC network, regulates DC-link voltage and it is used to achieve unity power factor. The simulation results demonstrate the effectiveness of the proposed VSSMC strategy in different scenarios, and their advantages are shown in comparison with a conventional proportional integral (PI) control approach under grid fault conditions and the possible presence of uncertainties.

A grid-connected variable-speed wind generator driving a fuzzy-controlled PMSG and associated to a flywheel energy storage system

In this paper, we propose a variable speed-wind energy conversion system based on a permanent magnetic synchronous generator (PMSG). A complete system model with multiple controllers is proposed and simulated. Two controllers are proposed and examined for regulating the current from the PMSG, the first is a simple PI controller and the second uses a fuzzy component to improve the tracking performance. A flywheel energy storage system (FESS) is associated to the proposed variable speed wind generator (VSWG). The FESS is linked at the DC bus stage in order to regulate the power supplied to the grid. In simple terms, if the generated power exceeds the demand, the excess is stored by the FESS for use when a shortage occurs. In this scenario, the VSWG is controlled to capture the maximum wind energy by means of the maximum power point tracking (MPPT) method. To maintain this operation as the turbine speed increases above the rated speed, we implement a pitch angle controller. The FESS is based on a squirrel-cage induction machine (IM) coupled to a flywheel. A controlled grid converter allows for the exchange of active and reactive powers with the grid. A proportional integral (PI) based grid connection is proposed that controls the current and voltage amplitudes as well as the frequency passed onto the grid. The aim of the converter control is to achieve a decoupled active and reactive power control suitable for operation at a unitary power factor. The dynamic model of the proposed system is simulated using the Matlab–Simulink package. The obtained results are presented and discussed to illustrate the performance of the overall proposed system.

Energy efficient control of a stand-alone wind energy conversion system with AC current harmonics compensation

This paper presents a new energy-efficient control strategy for a variable-speed wind energy conversion system (WECS). The considered WECS is designed for dc load supply and battery charging in stand-alone applications. The batteries are charged through a three-phase full-bridge power converter. The WECS contains a vector-controlled self-excited induction generator (SEIG) coupled to a wind turbine (WT) for electric power generation on the ac side. The control algorithm proposed in this paper includes three separate optimizations: two fuzzy-logic-based optimizations, which ensure that maximum energy is extracted from both the WT and the SEIG, respectively, at all operating conditions, and also the optimization of phase current harmonics through adaptive hysteresis control. In addition, a recently developed algorithm for real-time loss calculation of a hysteresis-driven power converter is utilized to quantitatively assess the power converter losses with respect to different hysteresis bandwidth settings. The performance of the proposed control algorithm is experimentally evaluated and compared with two competing algorithms which do not involve current harmonics compensation, whereas one of them also does not involve optimization of the SEIG output power. This enables evaluation of the gain in system performance due to the introduced optimizations. The evaluation and comparison are made over a wide range of wind speeds, both in steady state and under transient conditions, by using a 1.5 kW experimental setup with the DS1103 controller board (dSPACE).

Symbiotic organisms search algorithm‐based optimal control strategy for efficient operation of variable‐speed wind generators

The penetration rate of grid-tied wind turbine generator systems (WTGSs) into the existing electricity networks is rapidly increasing worldwide. Huge efforts are exerted for improving the characteristics of variable-speed wind energy conversion systems. This study exhibits a novel symbiotic organisms search algorithm (SOSA)-based optimal control strategy for achieving efficient operation of a grid-connected WTGS. The optimal control strategy relies on proportional–integral (PI) controllers, which are properly fine-tuned using the SOSA. The simulation-based optimisation method is considered in the optimisation process, where the integration of the square error criterion is selected as a fitness function. To obtain realistic performances, practical wind speed data extracted from the Zaafarana power plant in Egypt are used in the analyses. The efficacy of the SOSA-based optimal PI control strategy is compared with that realized using the grey wolf optimiser algorithm (GWOA)-based PI control scheme, considering network disturbances. The feasibility of the proposed control strategy is validated using the simulation studies, which are implemented using MATLAB/Simulink software. Notably, the proposed SOSA-based optimal control strategy is considered to be a precise means of improving the behaviour of grid-tied WTGSs.

Design of Z Source Inverter based VSWECS with Improved PWM Control

With rapid development in Wind Energy Conversion Systems (WECS), various methods have been used to increase power generation from wind. In order to reach voltage gain as maximum in a variable speed WECS, an improved PWM method through varying shoot through time for Impedance source inverter is implemented in this paper. For a given modulation index, the correlation of voltage gain with capacitor voltage, and the device stress are analyzed in detail. For ‘various shoot through time ,the simulation results of voltage across capacitor, current through inductor ,output current and output voltage are obtained by using Simpower system tool in MATLAB/ Simulink and compared. The results have been confirmed for the developed experimental model.

Sliding mode type‐2 neuro‐fuzzy power control of grid‐connected DFIG for wind energy conversion system

This study presents an adaptive sliding mode type-2 neuro-fuzzy controller for power control of doubly fed induction generators (DFIGs). DFIG-based wind turbine system is variable-speed constant-frequency wind energy conversion system. In this proposed control scheme, in order to enhance its performance, sliding mode control (SMC) theory is used for online training the parameters of type-2 fuzzy system membership functions. To regulate the antecedent and consequent part parameters, the SMC adaptive technique is used according to the controller inputs. These inputs are active and reactive power errors and their time derivative, which applied to the structure of T2NF system. The proposed controller employs an interval type-2 fuzzy system because of the uncertainties of the wind speed and variation in parameters in the wind power conversion system. The simulations carried out for a DFIG-based 1.5 MW wind turbine. The results of simulation are compared with the classical proportional-integral controller to confirm the effectiveness of this control scheme. This comparison is carried out between the cut-in and rated region wind speeds. The results of simulation show that the proposed control scheme has better performance to track the peak power and is more robust to machine parameter variations.

Modified P&O MPPT algorithm for optimal power extraction of five-phase PMSG based wind generation system

In this study, the maximum power point tracking (MPPT) performance is investigated based on variable-speed wind energy conversion system below the rated wind speed. The proposed modified perturb and observe (MPO) MPPT enhances the initial speed-tracking accuracy and eliminates the oscillations level. The MPO employs four sectors operation using a variable-speed step sizes by comparing the new suggesting curve with the P–ω curve. The system is described as a large-scale five-phase permanent magnet synchronous generator (PMSG) which is grid connected through a back-to-back converter (BTBC) and Dc-link capacitor. The field-oriented control (FOC) is applied in the machine-side converter (MSC) to extract the optimal generated power using the proposed MPPT algorithm. Moreover, the voltage-oriented control (VOC) is applied in the grid-side converter (GSC) to regulate the Dc-link voltage and inject active power with unity power factor. The simulation results depict the superior performance of the MPO over the conventional P&O. The performance of the proposed control scheme is validated using MATLAB/SIMULINK program.

Fuzzy Logic Based Robust DVC Design of PWM Rectifier Connected to a PMSG WECS under wind/load Disturbance Conditions

Permanent Magnet Generator has been widely used in Variable-Speed Wind Energy Conversion System (VSWECS). Fuzzy Logic Control (FLC) of the generator side converter has the ability to have good regulation of the DC-link voltage to meet the requirements necessary to achieve optimal system operation, regardless of the disturbances caused by the characteristics of the drive train or some changes into the DC-load. The main focus of this paper is to present a model for a three-phase voltage source space vector pulse width modulation (SVPWM) rectifier which is connected to a PMSG in a wind turbine system, where a direct voltage control (DVC) using FLC based on voltage orientation strategy is used to control the mentioned rectifier. The control algorithm employs a fuzzy logic controller to effectively achieve a smooth control of DC-link voltage under wind/load perturbation conditions. Some simulation results, using Matlab/Simulink, are presented to show the effectiveness of the SVPWM rectifier Connected to a PMSG WECS with the proposed control strategy.

Efficient Direct-Model Predictive Control With Discrete-Time Integral Action for PMSGs

This paper presents an efficient direct-model predictive control (EDMPC) technique for surface-mounted permanent-magnet synchronous generators (PMSGs) in variable-speed wind energy conversion systems. The proposed control technique is based on directly computing the reference voltage vector (VV) from the demanded currents using a deadbeat (DB) function. Then, a discrete-time integral action (DTIA) is added to this DB function to enhance the robustness of the proposed EDMPC scheme against variations of the machine parameters and to achieve a good steady-state response. The proposed DTIA is simple and easy to implement. Finally, according to the location of this reference VV, two evaluations of the quality function are only required. Accordingly, the proposed EDMPC technique with DTIA overcomes the following drawbacks of the conventional direct-model predictive control (DMPC): high calculation burden, sensitivity to parameters mismatches, and non-zero steady-state error. The performance of the proposed EDMPC technique with DTIA has been experimentally investigated and compared with that of the EDMPC with time delay control approach and with the performance of the convention DMPC using a $\text{14.5}\,\text{kW}$ PMSG.

Intelligent tuned PID controller for wind energy conversion system with permanent magnet synchronous generator and AC-DC-AC converters

This paper presents the intelligent tuned PID controller-based Single Ended Primary Inductor Converter (SEPIC) for Maximum Power Point Tracking (MPPT) operation of Wind Energy Conversion System (WECS). As the voltage and frequency of the Permanent Magnet Synchronous Generator (PMSG) varies with the wind speed changes, Intelligent controlled SEPIC is utilized to maintain the constant DC link voltage. The intelligent tuned PID controller combines the advantages of both conventional and soft controllers. The 1.5MW variable speed WECS (VSWECS) with AC-DC-AC converter is developed using MATLAB/Simulink software. PMSG delivers a load/utility grid through an uncontrolled diode rectifier, intelligent controlled SEPIC and three phase inverter. The real time implementation of the proposed system is done by the DSP processor MSP430F5529. The performance of the SEPIC is tested in both simulation and experiment at different wind speed conditions. The performance of the proposed Intelligent MPPT control of SEPIC are compared with the conventional PID controller. Intelligent tuning of PID controller such as Fuzzy-PID, and ANFIS-PID is implemented in the proposed system and results are compared. The simulation and experimental results reveals that the proposed ANFIS method provide improved performance than the conventional PID method in terms of power quality.

A novel approach for coordinated operation of variable speed wind energy conversion in smart grid applications

In smart grid applications, the high penetration level of wind energy requires precise coordination of wind energy conversion systems (WECS) with the existing grid. In this paper, a variable speed WECS using Squirrel-Cage Induction Generator (SCIG) is modeled and analyzed under fault conditions. The converters and their controllers are so designed that the complete system works in coordination and the turbine remains operative even under fault conditions. A droop controller regulates the torque and generator speed to limit power generation during faults, thereby preventing a shutdown of the wind turbine. A dual current controller is designed for individual control of positive and negative sequence currents to eliminate the double frequency oscillations that arise at the DC-link voltage during unsymmetrical faults. With the proposed controller, rise in DC link voltage and generator speed is limited to a bounded value of 1.2 pu whereas the fault current is limited to 1.5 pu.

Optimal power extraction control schemes for five-phase PMSG based wind generation systems

This paper presents a variable speed -wind energy conversion system (VS-WECS) based on a large-scale grid-connected five-phase permanent magnet synchronous generator (PMSG). This work studies control techniques for five-phase PMSG, where back-to-back converters (BTBC) are employed on the machine and the grid side converters. Two control loops are employed to control the machine side converter (MSC) in order to attain the optimum power at any wind speed. The outer control loop is applied to adjust the rotor speed while the inner control loop is employed to regulate the generator current. On the other hand, the grid side converter (GSC) employs two control loops; the outer loop controls the DC-link voltage while the inner one regulates the grid current. Moreover, the maximum power point tracking (MPPT) and pitch angle control schemes are utilized to obtain the optimal power during different environmental conditions. The proposed integral sliding mode controller (ISMC) is employed to regulate the rotor speed of the five-phase PMSG to track the reference speed at different wind speed. The proposed ISMC considers the limitations of the conventional PI controller and the dynamic system disturbance, especially in the large wind turbine inertia. Furthermore, the proposed ISMC stability is examined using Lyapunov’s stability function. The performance of the proposed ISMC is compared to a conventional PI controller, the study shows the superior performance of the ISMC. The overall WECS efficiency is improved using the proposed ISMC to 92.45% compared to the PI controller which is 88.12%. The effectiveness of the proposed control scheme is carried out through simulation results using MATLAB/SIMULINK.

PMSG‐based VS‐WECS for constant active power delivery to standalone load using direct matrix converter‐based SST with BESS

This study presents a simplified control algorithm for constant active power delivery to a weak-grid/standalone load from a variable speed-wind energy conversion system (VS-WECS). The proposed system consists of a permanent magnet synchronous generator (PMSG)-based WECS connected to a weak-grid/standalone through a direct matrix converter-based solid-state transformer (SST) along with a bidirectional buck–boost battery energy storage system (BESS). The power from the WECS is processed through the SST using Venturini-based control algorithm together with the voltage-oriented control scheme. This scheme effectively regulates active and reactive power as well as voltage gain of the SST. Wind turbines maximum power point tracking power curves are used to set reference for active power. While the reference for reactive power is taken as zero. The bidirectional buck–boost-based BESS is used to smoothen the power generated by the PMSG-based VS-WECS. It absorbs the surplus power from the WECS during over generating period and delivers power back under power shortage period. To validate the performances of the proposed scheme, extensive simulation has been performed and exclusive hardware built by dSPACE1104 using MATLAB/Simulink.

Variable step size P&O MPPT algorithm for optimal power extraction of multi-phase PMSG based wind generation system

To eradicate limitations of conventional fixed step-size perturb and observe (P&O) maximum power point tracking (MPPT) based on the variable speed - wind energy conversion system (VS-WECS), this article proposes a fast and an efficient MPPT modular sectors algorithm. The variable-step perturb and observe (VS-PO) MPPT algorithm is implemented to divide the power-speed (P-ω) curve into modular sectors each with specific step-size. The modular sectors are established by comparing a special synthesized ratio, that associates with the theoretical power, with a specified ratio corresponding the required power accuracy. Hence, the proper step-size is selected according to the operating sector location. For the sectors near the maximum power point (MPP), a small step-size is applied. Otherwise, a large step-size is used. To calculate the theoretical power, a wind speed estimation algorithm is utilized for evaluating the wind speed. The system configuration involves a 1.5 MW five-phase permanent magnet synchronous generator (PMSG), and a back-to-back frequency converter with the dc-link capacitor for the grid integration. The simulation results illustrate the VS-PO superiority over both the conventional P&O (CPO) and modified P&O (MPO) techniques. The VS-PO improves the initial speed tracking and minimizes the steady state oscillations. The performance of the proposed control schemes is validated using MATLAB/SIMULINK environment.

A Simple and Robust Sensorless Control Based on Stator Current Vector for PMSG Wind Power Systems

This paper proposes a novel sensorless control based on the stator current vector for permanent-magnet synchronous generators in variable-speed wind energy conversion systems. In the proposed method, the rotor angle and speed are estimated indirectly from the stator currents, where only the stator inductance is required regardless of the stator resistance. In addition, the proposed method uses one current control loop to regulate the stator current magnitude, rather than two current control loops. To eliminate the current measurement noise, the second-order generalized integrator (SOGI) with a frequency-locked loop (FLL) is utilized, which can improve the estimation performance. The proposed sensorless control method with the SOGI-FLL is simple and easy to implement while achieving a fast and accurate estimation performance of the rotor angle and speed. The feasibility of the proposed method has been verified by simulation and experimental results.

High-order sliding mode control for variable speed PMSG wind turbine based disturbance observer

This paper introduces a model-based control system for variable speed wind energy conversion system (VSWECS)-based permanent magnet synchronous generator (PMSG). Comparing to traditional wind turbines operating methods, these variable speed systems have the advantages of increasing the energy capture and reducing the mechanical stress. In order to exploit this latest advantage, a high order sliding mode (HOSM) control strategy has been developed to enhance system performances, ensure the maximum power point tracking (MPPT) and track the generator reference speed. Moreover, for the WT system, the turbine torque is considered as an immeasurable disturbance. Therefore, using a modified disturbance observer will allow direct tracking of the maximum power point. The stability analysis of the system has been proved using the Lyapunov theory. Finally, simulation results have been presented to verify the proposed approach efficiency.

High-order sliding mode control for variable speed PMSG-wind turbine-based disturbance observer

This paper introduces a model-based control system for variable speed wind energy conversion system (VSWECS)-based permanent magnet synchronous generator (PMSG). Comparing to traditional wind turbines operating methods, these variable speed systems have the advantages of increasing the energy capture and reducing the mechanical stress. In order to exploit this latest advantage, a high order sliding mode (HOSM) control strategy has been developed to enhance system performances, ensure the maximum power point tracking (MPPT) and track the generator reference speed. Moreover, for the WT system, the turbine torque is considered as an immeasurable disturbance. Therefore, using a modified disturbance observer will allow direct tracking of the maximum power point. The stability analysis of the system has been proved using the Lyapunov theory. Finally, simulation results have been presented to verify the proposed approach efficiency.

Modeling and Robust Control of a Grid Connected Direct Driven PMSG Wind Turbine By ADRC

In this paper, we present the modeling and control of a grid connected Variable Speed Wind Energy Conversion System (VS-WECS) based on a Direct Driven Permanent Magnet Synchronous Generator (DD-PMSG). A new robust control has been proposed and utilized to operate the wind turbine so as to extract the maximum power from the wind energy and to ensure a unit power factor. This control is known as the Active Disturbance Rejection Control (ADRC) and it is based on the Extended State Observer (ESO). It consists in controlling, through the stator currents, the machine side converter in order to adapt the rotational speed of the generator to the different wind speed profiles (Maximum Power Point Tracking MPPT). In addition, it ensures the control of the DC bus voltage and the exchange of active and reactive powers between the wind turbine and the electrical power grid. In order to evaluate the performance of the proposed control a series of simulations are made under the MATLAB/SIMULINK environment. The results obtained by simulation show that the proposed strategy is efficient in terms of stability and precision as well as for the robustness with regard to the internal disturbances when variying the parameters of the machine.

Enhanced radial fuzzy wavelet neural network with sliding mode control for a switched reluctance wind turbine distributed generation system

ABSTRACTIn this article, an Enhanced Radial Fuzzy Wavelet Neural Network with Sliding Mode (RFWNNSM) and hill-climb searching (HCS) maximum power point tracking (MPPT) strategy are proposed for a switched reluctance generator (SRG) in a variable-speed wind energy conversion system (WECS). The implemented MPPT control is an HCS algorithm that does not require the knowledge of turbine or generator characteristics. However, this study proposes a simple optimal DC-Link voltage search type HCS control, and therefore a faster convergence to MPPT is achieved. A high-performance online training Enhanced Radial Fuzzy Wavelet Neural Network (RFWNN) using a back-propagation learning algorithm with a sliding mode regulating controller is designed for an SRG. The MPPT strategy locates the system operation points along the maximum power curves based on the DC-Link voltage of the inverter, thus avoiding the need to detect the generator speed.