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

The battery charging control within wind turbine applications is the most important challenge in standalone exploitation mode because of the random nature of wind energy and irregular use of electricity. Within this problematic, this paper deals with monitoring and control of a permanent magnet synchronous generator voltage for battery charging. In the proposed topology, the output direct drive PMSG is linked to the battery through a vector-controlled pulse modulated (PWM) rectifier. Most wind energy conversion systems are based on precise knowledge of the wind speed, which makes the adjustment of the charge voltage relatively complicated, and degrades the powers captured with erroneous measurements of this wind speed. In this context, all the efforts of this work are meant to simplify and improve the dynamic performance of the system. The technique used in this work is devoid of wind measurement. By neglecting different losses, the approach adopted leads us to the reference electromagnetic torque, assuming that the wind speed and consequently the rotational speed of the turbine vary slowly in steady state. Using the load current and voltage measures, the proposed controllers calculate permanently the power reference that corresponds to the fixed battery voltage. A vector control approach is adopted to achieve decoupled power control on the supply side power converter by generating the direct and quadrature control voltages. These voltages are necessary to generate the corresponding duty cycles of the PWM active switching devices. Hence, the PWM rectifier maintains the battery voltage at a fixed value by balancing both the rectifier output current and the load input current. To activate the vector control, two dynamic controllers are designed, simulated, and compared. The first controller is based on simple PI regulators. Meanwhile, the second one, which is a sliding mode technique, is applied to control the battery voltage. In order to assess the effectiveness of the used techniques, simulation models have been subjected to critical conditions of changing in speed and load. Simulation results revealed a poor accuracy of the first technique during transients and its close correlation under load disturbance. Whereas the sliding mode controller has high precision and strong robustness in steady state and during transient phases. The system simulation is performed using MATLAB/SIMULINK.

Wind energy conversion systems present several sources of disturbances and uncertainties due to nonlinear and complex dynamics. These phenomena can negatively impact the expected behavior of the controlled system and, consequently, lead to a decrease in maximum power extraction. This study focuses on designing a novel fractional-order control method for permanent magnet synchronous generator-based wind turbine systems. To improve the control performance in the presence of external disturbances and parametric variations, the proposed approach combines the robust super-twisting sliding mode technique with adaptive Type-3 fuzzy logic systems. Resulting from the evolution of Type-2 fuzzy logic systems, the interval Type-3 provides better approximation capabilities, especially in the presence of a higher degree of uncertainties. Combined with the super-twisting algorithm, fuzzy systems are used both to approximate unknown nonlinear functions and to replace discontinuous control laws. The system stability is ensured by the extended fractional Lyapunov criterion. Furthermore, a new lemma is proposed to demonstrate the finite time convergence. A comparative study including other well-known control techniques is presented to validate the effectiveness of the proposed approach.

In this work unlike the usual grid side converter, the machine side converter is considered to control the dc-link voltage of a permanent magnet synchronous generator-based wind turbine generator. For this purpose, a discrete real-time laboratory test-rig is prepared for real-time application of the system. In the real-time test-rig, 5-kVA permanent magnet synchronous servo motor is driven by Unidrive SP variable frequency drive to emulate a standalone wind energy conversion system; GUASCH converter as a machine side converter and for implementing the designed PI controllers using pole placement technique combined with a symmetrical optimum criterion for real-time control of the dc-link voltage transient changes, Texas instrument TMS320F28069 digital signal processor discrete real-time microcontroller control card in a GUASCH board are used. Moreover, a simulation model of the system is prepared in MATLAB Simulink user-defined function blocks considering the dynamic mathematical equations of every part in the system. Achieved simulation and real-time test-rig results show that the designed dc-link voltage control of the system works properly at different transient load changes connected to the standalone WTG and dc voltage reference value changes. Moreover, the simulation results are properly validated by the real-time test-rig results and the PI controller designed using pole placement technique combined with a symmetrical optimum criterion method was ideal.

This paper presents a non-linear Sliding Mode Control (SMC) strategy based on continuous switching law for large-power (10MW) Permanent Magnet Synchronous Generator (PMSG) based Wind-Energy Conversion System (WECS). The WECS model consists of a wind turbine, PMSG, rectifier fed boost converter, PWM inverter and the filter. The controller is used to maintain the DC-link voltage constant and to generate controlled active and reactive power for grid. For verification of validity of proposed control scheme and model, the proposed system's dynamic model is simulated in MATLAB/Simulink. SMC has the promising features of: fast switching, insensitivity to parameter uncertainty, disturbance rejection quality, and more robustness than the conventional linear controllers. The proposed continuous control compelled the states trajectories of the system onto the surface in error space (sliding surface) for the system behavior to obtain design specifications. Simulation results demonstrate that the proposed SMC is effective and gives superior performance than conventionally tuned PI controller.

This paper presents comprehensive modelling ofWind Energy Conversion System (WECS) based on interfacing a Permanent Magnet Synchronous Generator (PMSG) to the utility grid by using the direct AC/AC matrix converter. To estimate the wind velocity and extracts the maximum power at all wind velocities Wind speed estimation control technique is presented based on sliding mode control. Sliding mode controller has many advantages such as fast transient response and robustness against system parametric variations and unknown external disturbances. The matrix converter controls the maximum power point tracking MPPT by adjusting the PMSG terminal frequency, and hence, the shaft speed. In addition, the matrix converter controls the grid injected current to be in-phase with the grid voltage for the unity power factor. Space Vector Modulation is used to generate the PWM signals of the matrix converter switches. The system dynamic performance is investigated using Matlab/Simulink.

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

Purpose This study proposes a modified sliding mode control technique having a proportional plus integral (PI) sliding surface aided by auxiliary control applied to a wind turbine driven permanent magnet synchronous generator. This paper aims to realize real and reactive power control, keeping the voltage under the desired limit during transients. Design/methodology/approach First, a PI sliding surface type sliding mode control (PISMC) is formulated, which is capable of dragging the system to the desired state and stability. Then a saturation function-based auxiliary controller is incorporated with PISMC to enhance its performance during wind speed and system parameter variations. Findings The proposed controller can tackle the problems faced while using a PI controller and the conventional sliding mode controller (CSMC) such as lack of robustness and requirement of unnecessary large control signals to overcome the parametric uncertainties and problem of chattering. Originality/value To justify the superior performance of the proposed controller in terms of robustness, reliability and accuracy a comparative study is done with the CSMC and PI controllers. The simulations are performed using MATLAB.

Wind energy has recently become the most cost-effective and environmentally friendly amongst other renewable energy resources. However, since wind resource is intermittent in nature, the wind power output is inconsistent. Therefore, a control system needs to be implemented to ensure that maximum power is extracted from the wind resource at a wide range of wind speeds to optimize the performance of the wind turbine. This paper deals with the control of the rotor speed of a 2MW direct-driven permanent magnet synchronous generator to perform maximum power point tracking (MPPT). Vector-oriented control technique is used to control the machine-side converter and the types of controllers used are the phase-lead, phase-lag and lead-lag compensators. The proposed wind energy conversion system was implemented in PSIM software and the control system modelling has been carried out in MATLAB using bode plots and step-response curves. The overall system's performance analysis and validation were carried out by simulation. The results obtained show that the MPPT controller enabled the power generated by the WT to closely track pre-determined optimal power curves. This shows that MPPT was ensured when the wind speed was less than the wind turbine's rated wind speed.

Conventional wind energy conversion systems (WECS) typically employ rotor side synchronous frame current control strategies to regulate the active/reactive power supplied by the WECS generator. Such strategies require accurate information regarding the rotor position and speed in order to set the dq frame reference currents and to perform the necessary frame transformations. This information can be obtained using a rotor speed sensor (i.e. a shaft encoder) or via a sensor-less strategy in which a dynamic machine model and stator current measurements are used to estimate the true rotor position. This paper now presents an alternative approach to control the active/reactive power supplied by the WECS permanent magnet synchronous generator (PMSG). The proposed strategy uses the three phase converter modulation commands to identify the phase and frequency of the PMSG stator terminal voltages. This enables the direct regulation of the real and reactive power extracted at the PMSG terminal voltages using a stationary frame Proportional + Resonant (PR) stator current regulation strategy, without requiring precise knowledge of the rotor position. Maximum power point tracking (MPPT) functions are realized using the measured PMSG terminal voltage frequency to form an estimate of the rotor speed. The result is a simple robust WECS control strategy that rapidly and accurately tracks rotor speed changes caused by wind speed variations. Detailed simulation and experimental results obtained for a scaled laboratory prototype system are presented to validate the proposed strategy.

A new predictive control strategy for improving operating performance of a permanent magnet synchronous generator-based wind energy and superconducting magnetic energy storage hybrid system integrated with grid

Conventional fossil fuels such as coal, oil and natural gas are being reduced and become more and more a source of serious undesirable effects on the environment. Wind power is playing a major role in the effort to augment the share of renewable energy sources in the world energy mix with a continuously increasing penetration into the grid. Wind turbine generators can be divided into two basic categories: fixed speed and variable speed. Variable-speed wind energy systems are presently favored than fixed-speed wind turbines thanks to their higher wind power extraction, improved efficiency, reactive power support and voltage control. This study addresses the problem of control of Wind Energy Conversion System (WECS) in variable speed. To this end, two simultaneous control objectives, namely the maximization of the energy conversion efficiency based on Squirrel Cage Induction Generator (SCIG) wind turbine and the regulation of the active and reactive power feed to the grid, to guarantee Unit Power Factor (UPF), have been established. To deal with the complexity and nonlinearity of the system, the sliding mode control is adopted. Indeed, this technique provides an efficient tool for controller design and presents attractive features such as robustness to parametric uncertainties of the different components of the system. In this way, sliding-mode control laws are developed using Lyapunov stability analysis, to guarantee the reaching and sustaining of sliding mode and stability of the system control. Evaluation of the reliability and performance of the proposed sliding mode control approach has been established on a 3MW three-blade wind turbine. Simulation results demonstrate that the proposed control strategy is effective in terms of MPPT control strategy, active and reactive power tracking trajectories and robustness against system parameter variations.

Augmenting effectiveness of control loops of a PMSG (permanent magnet synchronous generator) based wind energy conversion system by a virtually adaptive PI (proportional integral) controller

This paper presents a novel control strategy employing the artificial neural network-based direct torque control (DTC) strategy and direct power control (DPC) strategy for permanent magnet synchronous generator (PMSG)-based wind energy conversion system (WECS). The Aeolos 3 kW wind system ratings are considered in this paper for real time system validation. The proposed control strategy combines artificial neural network (ANN)-based DTC as machine side control (MSC) strategy and ANN-based DPC as grid side control (GSC) strategy in order to track the maximum power and to regulate the active power, respectively. To generate the switching pulse for the converter in generator side and grid side, a neural network-based technique is employed. Furthermore, the DC link voltage is optimised using the GSC topology. The proposed controller provides a stable voltage and power which is an effective solution for grid integration and constant power flow from the generator system to the grid system. The proposed coordinate control strategy is validated using MATLAB/Simulink software to analysis the working condition. The experimental test bench is implemented using dSPACE to study the real time analysis of the proposed control strategy.

Wind energy conversion systems (WECSs), which are based on permanent magnet synchronous generators (PMSG), typically have a wide range of operating speed. The variations in the generator speed lead to significant deviations in the frequency of the electrical output power. Typically, in this type of WECSs, the power converter needs to control the phase of the current with respect to the phase of the back EMF. Thus, the control system should perform reactive power control over a wide range of frequencies. In order to operate over a wide range of frequencies, advanced synchronizing algorithms are required to generate precise references for reactive power control. In this paper, a three phase reactive power control scheme based on adaptive proportional-resonant (APR) controller is presented. The APR controller adaptively adjusts the coefficients of the digital controller based on the terminal voltages of the machine. This algorithm not only provides wide bandwidth operation of the PR-controller but also helps compensate the harmonic currents injected into the machine. The theoretical analysis of the proposed closed-loop control scheme, which is given in this paper, is supported by simulation and experimental results.

In this paper, various control strategies for Doubly Fed Induction Generators (DFIG) in Wind Energy Conversion Systems (WECS) are compared. Because of their high energy efficiency and variable speed operation, DFIGs are widely used in modern WECS; therefore, improving their control techniques is crucial to enhancing system performance and dependability. The study looks at a number of well-known control techniques, including Generalized Predictive Control (GPC), Sliding Mode Control (SMC), and Proportional-Integral (PI) control. Each strategy is analyzed based on key performance metrics such as power capture efficiency, dynamic response, robustness to wind speed variations, and Total Harmonic Distortion (THD) in the generated power. The study offers comparative findings that highlight the advantages and disadvantages of every control strategy in a variety of operational situations. Findings indicate that while traditional PI control offers simplicity and satisfactory performance under steady-state conditions, advanced strategies like SMC and GPC demonstrate superior adaptability and robustness under dynamic and uncertain wind scenarios. The impact of control strategies on THD is also discussed. For DFIGbased WECS, this study provides valuable insights to inform the design and selection of control strategies, aiming to guide future research and practical implementations towards more efficient and resilient renewable energy solutions.