Grid-connected Wind Energy Conversion System Research Articles

Three-Phase Grid-Connected WECS With Mechanical Power Control

This paper presents a grid-connected wind energy conversion system (WECS) based on a permanent magnet synchronous generator (PMSG) operating with variable speed. Considering that the wind has intrinsic intermittent nature, it is desirable to maximize the extracted energy, as a maximum power point tracking (MPPT) strategy is described for this purpose. Otherwise, the MPPT algorithm is disabled to maintain the rated power condition and avoid damage to the PMSG, as an external mechanical power control loop associated to active stall is introduced in this work, whose power extraction characteristic is similar to that obtained with pitch control. The WECS employs a bridgeless boost rectifier, which provides power factor correction using self-control strategy, with the advantages of reduced conduction losses, simplified drive circuitry for the active switches, and high input power factor without the need to use multipliers in the control system and impose a sinusoidal reference to the input current unlike average current mode control. Connection with the power grid occurs through a three-phase full-bridge inverter, as experimental results on a 6-kW prototype are presented and discussed in detail in order to validate the proposed approach.

Combined parameters selection of a proportional integral plus resonant controller for harmonics compensation in a wind energy conversion system

This paper introduces the use of the Naslin polynomial technique in order to tune a proportional integral resonant (PIR) controller for the rotor-side converter of a grid-connected wind energy conversion system (WECS), which is based on a back-to-back converter and a doubly fed induction generator (DFIG). The objective of the proportional integral part of the PIR controller is to control the active and reactive power of the rotor-side converter, while the resonant part of the PIR controller deals with the stator current harmonics of the generator due to grid voltage distortions. Most papers that use PIR controllers for WECS often carry out the separated tuning of the PI part and then the tuning of the resonant part without any guide. In this paper, the tuning of the PIR controller as a single controller is proposed taking into account the mathematical base of the Naslin polynomial technique. The case of study is a WECS based on a 50 HP DFIG, and the considered grid voltage harmonics are the fifth and seventh. Simulations were implemented to evaluate the compensation of the current harmonics with the selected PIR controller values.

Augmented grey wolf optimizer for grid-connected PMSG-based wind energy conversion systems

The grey wolf optimizer (GWO) is a new meta-heuristic algorithm inspired from the leadership and prey searching, encircling, and hunting of the grey wolves’ community. The GWO algorithm has the advantages of simplicity (less control parameters), flexibility, and globalism. In this paper, a simple and efficient augmentation for the GWO (AGWO) algorithm is proposed for better hunting performance. The AGWO algorithm focuses on increasing the possibility of the exploration process over the exploitation process by modifying the behavior of the control parameter (a) and position updating. The AGWO is suitable to the low number of search agents such as the electric power system application. The proposed AGWO algorithm is verified using twenty-three benchmark test functions and is applied to the grid-connected permanent magnet synchronous generator driven by variable speed wind turbine (PMSG-VSWT). The obtained results of the AGWO algorithm are compared with the results of the original GWO and other algorithms. The comparisons verified that the proposed AGWO is significantly augmented the performance of the original GWO algorithm without affecting its simplicity and easy implementation.

Classical vector, first-order sliding-mode and high-order sliding-mode control for a grid-connected variable-speed wind energy conversion system: A comparative study

This article proposes a comparative study between different control strategies of a wind energy conversion system. It aims to guarantee a robust control strategy which gives a good performance despite the external disturbances. Studied system comprises a wind turbine, a permanent magnet synchronous generator, and two converters linked by a DC bus. The whole is connected to the grid through a resistor–inductor filter. A classical vector control based on proportional–integral controller is applied to our system. Owing to the sensitivity of this control against external disturbances, a control strategy using first-order sliding mode has been proposed. This strategy provides good performance, such as insensitivity to non-linearity of system. Yet, the theory of first sliding mode has faced the problem of chattering, which proved to be a major drawback. To overcome this problem, a control strategy using sliding mode of higher order was implemented on the basis of the super-twisting algorithm.

Multivariable control of a grid-connected wind energy conversion system with power quality enhancement

This paper proposes the design of a multivariable robust control strategy for a variable-speed WECS based on a SCIG. Optimal speed control of the SCIG is achieved by a conventional PI controller combined with a MPPT strategy. DTC-SVM technique based on a simple Clarke transformation is used to control the generator-side three-level converter in the variable speed WECS. The flow of real and reactive power between the inverter and the grid is controlled via the grid real and reactive currents and the DC link voltage using multivariable H $$_{\infty }$$ control. The overall WECS and control scheme are developed in Matlab/Simulink and the performance of the proposed control strategy is evaluated via a set of simulation scenarios replicating various operating conditions of the WECS such as variable wind speed and asymmetric single grid faults. The power quality of the WECS system under H $$_{\infty }$$ control control approach is assessed and the results show a significant improvement in the total harmonic distorsion as compared to that achieved with a classical PI control.

The Performance of a Digital Interconnection Protection for Grid-Connected WECSs

This paper develops and experimentally tests the performance of a digital interconnection protection for grid-connected wind energy conversion systems (WECSs). The developed protection is constructed by two frequency frames to process voltages and currents measured at the point-of-common-coupling (PCC). The first frequency frame is set to process the $d-q$ -axis components of the instantaneous $3\phi$ apparent powers ( $s_{d}$ and $s_{q}$ ) determined at PCC. This processing of $s_{d}$ and $s_{q}$ aims to extract their high-frequency subband contents in order to detect the islanding condition. The second frequency frame is set to extract the high-frequency contents (magnitudes and phases) present in the $3\phi$ currents flowing through PCC. These high-frequency contents provide signature information for detecting faults occurring on either side of PCC. The multiframe digital interconnection protection is implemented for performance evaluation on two different WECSs operated in grid connection. Performance results show accurate and reliable detection and identification of the islanding condition and faults occurring on either side of PCC. In addition, performance results show that the multiframe digital interconnection protection has minor sensitivity to the type, structure, ratings, and levels of power delivery to the host grid.

Recent Advances in the Design, Modeling, and Control of Multiphase Machines—Part I

The main objective of this two-part state-of-the-art paper called “Recent Advances in the Design, Modeling, and Control of Multiphase Machines” is to present latest contributions in the multiphase machines' field. The first part of this paper focuses on the recent progress in the design, modeling, and control, whereas the drive is in healthy operation. This second part presents relevant contributions in two not analyzed fields. The first is in relation with the use of the additional degrees of freedom of multiphase machines and the exploitation of their fault-tolerant capabilities without adding extra hardware. The second one analyzes multiphase generation, particularly in grid-connected wind energy conversion systems and stand-alone applications. Recent progresses are shown and open challenges and future research directions are discussed.

A small-scale standalone wind energy conversion system featuring SCIG, CSI and a novel storage integration scheme

In this paper, a small-scale standalone wind energy conversion system composed of a squirrel-cage induction generator, a buck converter and a current-source inverter is proposed, as an attractive renewable energy solution for off-grid communities. Geared squirrel-cage induction generators are well-known for their robustness, simplicity, light weight and low cost. Current-source inverters, even though mainly used in medium-voltage, high power applications, and proposed for megawatt-level grid-connected wind energy conversion systems, offer potential benefits in small-scale off-grid wind energy conversion systems that are yet to be investigated and evaluated against those of commonly-used voltage-source inverters. In the proposed system, the generator's shaft speed is controlled by a buck converter to extract maximum available wind power in normal mode of operation, and the wind power is dumped when it is not possible to absorb maximum available power by the storage system and the load. A novel scheme for integration of a battery energy storage system is proposed and an effective power management algorithm is employed to maintain the supply-demand power balance through direct control of dc-link current. A systematic approach for the dc-link inductor design is presented. The feasibility of the proposed system and its performance under variable wind and load conditions are analyzed and demonstrated through simulation.

Power Control in Grid-Connected Wind Energy System Using Diode-Clamped Multilevel Inverter

ABSTRACTThis paper presents dynamic modelling and control of real and reactive power in grid-connected variable speed wind energy conversion system using diode-clamped multilevel inverter (DCMLI). A modified five-level DCMLI is used for power control, which eliminates the requirement of transformer and improves the quality of controlled output voltage. It is shown that the system is dynamically stable and is able to control the real and reactive power independently, and provides harmonic compensation within standard limits. The voltage balancing across the capacitors of the five-level diode-clamped inverter is obtained using external balancing circuits. The performance of the proposed control method is tested under variable wind speed, sudden load changes, and under single-phase and three-phase faults. Simulation studies PSCAD/EMTDC verifies the proposed control method.

Robust fractional-order control of PMSG-based WECS

This paper presents some novel fractional-order nonlinear sliding mode controllers for maximum power extraction of a grid-connected wind energy conversion system. Two similar fractional-order controllers with nonlinear sliding manifolds are proposed for generator-side and grid-side converters. The main role of the generator-side controller is regulating the mechanical speed of wind turbine to follow an optimum speed. On the other hand, the grid-side controller main goal is governing the active and reactive power by tuning DC-link voltage. Practical stability of both controllers is achieved by fractional-order nonlinear stability theorems. Comparative simulations are presented to show the effectiveness of the proposed controllers.

Flexible Arrangement of Static Converters for Grid-Connected Wind Energy Conversion Systems

This paper presents a new flexible arrangement of static converters for grid-connected wind energy conversion systems (WECS). The proposed arrangement uses three-phase voltage-fed back-to-back mass-produced power converter modules with reconfiguration switches. The main features of the proposed flexible arrangement are as follows: 1) expanded reactive power capability limits; 2) high efficiency, mainly under low wind conditions where the active power is reduced; and 3) low current harmonic content. In addition, a detailed description of the operating modes, as well as of the grid, generator, and circulating current controller design, are given. Finally, experimental results support the theoretical development, and demonstrate the good performance and flexibility of the proposed arrangement.

Coordinated Controller Design of Grid-connected Variable-speed Wind Energy Conversion System with Model-based Predictive Control Using Response Surface Methodology

This paper presents an optimum design procedure for the coordinated tuning of machine side converter (MSC) and grid side converter (GSC) controllers of grid connected permanent magnet synchronous generator (PMSG). Model based predictive controller (MBPC) is used to control the MSC. MBPC based speed control design consists of two steps. A linearized state space model is employed to predict the future output (rotor speed). An optimal control law is derived by minimizing a quadratic performance index that considers the control effort and the difference between the predicted rotor speed and the reference rotor speed. A proportional-integral (PI) controller is used to control the GSC. The MSC and GSC controller parameters are determined by simultaneously optimizing the controller performance indices. The coordinated controller design is carried out in two steps. The analytical expression that relates the performance indices and the controller parameters is arrived using response surface methodology (RSM). The determination of controller parameters is posed as a constrained multi-objective optimization problem and solved employing NSGA-II (non-dominated sorted genetic algorithm II). The proposed methodology is tested on a sample power system with PMSG based WECS (Wind Energy Conversion System). Simulation results demonstrate the effectiveness of the proposed methodology.

Wavelet based Power Quality Monitoring in Grid Connected Wind Energy Conversion System

Recently renewable energy resources especially wind power integration has been far increased in the electric power distribution system. To utilize wind power more effectively, wind energy conversion system is interfaced to grid through power electronics interfaces. In this paper, monitoring of various power quality disturbances at the point of common coupling in grid connected wind energy conversion system have been done. Discrete wavelet transform and wavelet energy function are used for detection of power quality disturbances. The grid connected wind energy conversion system is simulated in MATLAB environment. Power quality disturbances such as voltage sag, voltage swell, interruption and harmonics are investigated. A new diagnostic method in which signal is processed using discrete wavelet transform and wavelet energy function is proposed. Simulation results show the usefulness of the proposed method to find out the power quality disturbances in grid-connected wind energy conversion system accurately and quickly. Voltage signal extracted directly at the point of common coupling is used for detection of power quality disturbances.

Performance of PI controller for control of active and reactive power in DFIG operating in a grid-connected variable speed wind energy conversion system

Due to several factors, wind energy becomes an essential type of electricity generation. The share of this type of energy in the network is becoming increasingly important. The objective of this work is to present the modeling and control strategy of a grid connected wind power generation scheme using a doubly fed induction generator (DFIG) driven by the rotor. This paper is to present the complete modeling and simulation of a wind turbine driven DFIG in the second mode of operating (the wind turbine pitch control is deactivated). It will introduce the vector control, which makes it possible to control independently the active and reactive power exchanged between the stator of the generator and the grid, based on vector control concept (with stator flux or voltage orientation) with classical PI controllers. Various simulation tests are conducted to observe the system behavior and evaluate the performance of the control for some optimization criteria (energy efficiency and the robustness of the control). It is also interesting to play on the quality of electric power by controlling the reactive power exchanged with the grid, which will facilitate making a local correction of power factor.

A power conversion system for PMSG-based WECS operating with fully-controlled current-source converters

We propose a new power conversion system for a permanent magnet synchronous generator (PMSG) based grid-connected wind energy conversion system (WECS) operating with fully-controlled back-to-back current-source converters. On the generator side, two independent current-source rectifiers (CSRs) with space-vector pulse width modulation (SVPWM) are employed to regulate and stabilize DC-link currents. Between DC-link and the electrical grid, a direct-type three-phase five-level current-source inverter (CSI) is inserted as a buffer to regulate real and reactive power fed to the grid and thus adjusts the grid side power-factor. We also present a current-based maximum power point tracking (MPPT) scheme, which helps the generator extract the maximum power through closed-loop regulation of the generator speed. By applying the multilevel modulation and control strategies to the grid-side five-level CSI, a multilevel output current waveform with less distortion is produced, and the bulk requirement of the output capacitor filter to eliminate the harmonic current is reduced. All the proposed concepts are verified by simulation models built in a PSIM environment.

Control of a grid-connected direct-drive wind energy conversion system

This paper investigates the current control for a grid-connected direct-drive wind energy conversion system (DDWECS) with a permanent magnet synchronous generator (PMSG), which utilizes a back-to-back pulse width modulation (PWM) converter. For the machine-side, the controller adopts a current vector control method based on the rotating reference frame (RRF) and the maximum power extraction (MPE) is realised through the tip speed ratio (TSR) method. For the grid-side, a novel controller is proposed for the first time to be successfully used for the DDWECS, which combining a proportional complex integral (PCI) current inner loop based on stationary reference frame (SRF) for regulating the grid-side current with a dc voltage outer loop for stabilizing the dc bus voltage and compare with the proportional resonant (PR) controller. A system simulation model is established by using the Matlab/Simulink to simulate the performance of the DDWECS and a prototype system has been build and tested to verify the validity of the developed control methods for both machine-side and grid-side and the excellent performance of the DDWECS.

Fault Ride Through in Grid-connected WECS Using FACTS

This paper discusses the effectiveness of installing two types of FACTS devices, namely STATCOM and DVR to enhance the fault ride through (FRT) capability of a doubly fed induction generator (DFIG) applied in wind energy conversion systems (WECS). The response of the DFIG to a 3-phase ground fault is investigated with each of these devices. Comparing the stator and rotor voltages, stator and rotor currents, active and reactive power, of the two investigated systems is presented. PI controllers are employed to allow the rotor speed to follow the turbine speed and to adjust the applied rotor voltage magnitude and phase angle according to the wind turbine speed for maximum power tracking. This is achieved by controlling the two PWM converters connected between the rotor circuit and the electrical grid. Results showed a better FRT when using the STATCOM device with the DFIG.

Power Quality Improvement Strategy for Wind Energy Conversion System

Wind energy is one of the world's fastest growing energy technologies, as wind is an intermittent renewable source, the wind source extracted by a wind turbine is therefore not constant. For this reason, the fluctuation of wind power results in fluctuated power output from wind turbine generator. From the point of view of utilities, due to the fluctuation of generator output, it’s not appropriate for the generator to be directly connected to the power grid. In order to achieve the condition that the generator output power is suitable for grid-connection, it is necessary to use a controller to manage the output produced by the wind turbine generator. This paper proposes a novel control scheme of a three-phase grid-connected wind energy conversion system to improve the power quality of WECS. The WECS model consists of a permanent magnet generator and the electronic power conditioning system is composed of full bridge rectifier, close loop boost converter, three phase inverter. Wind generation is being increasingly connected at distribution level due to increasing load demand. The inverter is controlled to perform following function 1) power converter to inject power generated from WECS to the grid, and 2) shunt APF to compensate current unbalance, load current harmonics, load reactive power demand Validation of the proposed system is verified through MATLAB/Simulink simulation.

Energy Management and Power Control for a Grid-Connected PMSG Wind Energy Conversion System with Extra Function of Harmonic Elimination for Local Nonlinear Loads

Wind energy conversion maximum power extracting along with power quality issues both play a crucial role in the power systems. This paper demonstrates the feasibility of using a new controlling method for simultaneously performing the maximum power point tracking and decreasing grid current total harmonic distortion (THD) as an extra function in wind energy conversion using permanent magnet synchronous generator (PMSG). While enhancing the grid power quality using proposed method, an improved maximum power point tracking (MPPT) algorithm based on optimum torque controlling is employed. Resorting this improved algorithm increases MPPT efficiency to be higher than 97% in all operation modes. In this study, a PMSG wind energy conversion with nominal power of 20 KW at wind speed of 9 m/s is considered for simulation. This system is connected to the local nonlinear load and the grid. Simulation results including MPPT dynamic and steady state behaviors in three different wind speeds and THD analyzing in presence and absence of harmonic elimination extra function show impressive benefits of the proposed method.

Arranjo Flexível De Conversores Estáticos Para Sistemas De Conversão De Energia Eólica Conectados À Rede


 Este artigo apresenta um arranjo flexível de conversores estáticos para sistemas de conversão de energia eólica (WECS), conectados à rede. O arranjo flexível proposto utiliza módulos conversores trifásicos back-to-back com interruptores auxiliares de reconfiguração. As principais características do arranjo flexível proposto são: (i) expansão dos limites de capabilidade de potência reativa, (ii) alta eficiência, principalmente para condições de baixa velocidade do vento em que a potência ativa é reduzida e (iii) baixo conteúdo harmônico das correntes de saída. Além disso, uma descrição detalhada dos modos de operação, definição das referências de potência, bem como os controladores das correntes do lado da rede, do lado do gerador e correntes circulantes são apresentados. Finalmente, resultados experimentais demonstram o bom desempenho e flexibilidade do arranjo proposto.