Grid-connected Wind Energy Conversion System Research Articles

Development of a Grid-Connected Wind Generation System With a Modified PLL Structure

This paper presents the development of a single-phase grid-connected wind energy conversion system (WECS) that uses a modified PLL. The WECS development is based on the use of the low cost 30 MIPS Digital Signal controller (DSC) dsPIC30f3011. The modified single-phase PLL is based on the PQ theory, where a lag structure based on an integrator is proposed instead of a conventional lag structure. The voltage source inverter (VSI) is driven by a Space Vector Pulse Width Modulation (SVPWM). The maximum power transfer is achieved by using a Maximum Power Point Tracking (MPPT) algorithm based on the steepest ascent method. The tasks related to the SVPWM algorithm, the PLL, the MPPT algorithm, and the monitoring of the DC voltage were successfully implemented in the DSC.

Dynamic Model and Control of DFIG Wind Energy Systems Based on Power Transfer Matrix

This paper presents a power transfer matrix model and multivariable control method for a doubly-fed induction generator (DFIG) wind energy system. The power transfer matrix model uses instantaneous real/reactive power components as the system state variables. It is shown that using the power transfer matrix model improves the robustness of controllers as the power waveforms are independent of a <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> frame of reference. The sequential loop closing technique is used to design the controllers based on the linearized model of the wind energy system. The designed controller includes six compensators for capturing the maximum wind power and supplying the required reactive power to the DFIG. A power/current limiting scheme is also presented to protect power converters during a fault. The validity and performance of the proposed modeling and control approaches are investigated using a study system consisting of a grid-connected DFIG wind energy conversion system. This investigation uses the time-domain simulation of the study system to: 1) validate the presented model and its assumptions, 2) show the tracking and disturbance rejection capabilities of the designed control system, and 3) test the robustness of the designed controller to the uncertainties of the model parameters.

Intelligent speed sensorless maximum power point tracking control for wind generation system

A sensorless vector-control strategy for an induction generator (IG) operating in a grid-connected variable speed wind energy conversion system is presented. The sensorless control is based on a model reference adaptive system (MRAS) observer for estimating the rotational speed. An on-line training recurrent neural network (RNN) controller using back-propagation learning algorithm with particle swarm optimization (PSO) is designed to allow the rotational speed adjustment for power regulation. The node connecting weights of the RNN are trained online by back-propagation (BP) methodology. The PSO is adopted to adjust the learning rates in the BP process to improve the learning capability. The proposed output maximization control is achieved without mechanical sensors such as wind speed or position sensor, and the new control system will deliver maximum electric power with light weight, high efficiency, and high reliability. The concept has been developed and analyzed using a turbine directly driven IG.

Analysis and Test of Diode Rectifier Solutions in Grid-Connected Wind Energy Conversion Systems Employing Modular Permanent-Magnet Synchronous Generators

This paper deals with the ac-dc interface conversion in grid-connected wind energy conversion systems based on modular permanent-magnet synchronous generators. In particular, some solutions based on diode rectifiers are extensively analyzed as for the waveforms, the efficiency, and the torque ripple, by considering several connections, which are allowed by the inherent modularity of the considered generators. Rectifier schemes with a high number of pulses can be easily realized without using special shifter transformers so that these solutions can be attractive for low- and medium-power applications.

Multivariable 2-sliding mode control for a wind energy system based on a double fed induction generator

The purpose of this paper is to present a control strategy using Multiple Input/Multiple Output (MIMO) Second Order Sliding Modes (SOSM) for a grid-connected variable-speed Wind Energy Conversion System (WECS). The latter is based on a Double Fed Induction Generator (DFIG) in a bidirectional configuration with slip power recovery. Its points of operation can be electronically controlled and, with them, two independent control objectives can be stated. Thus, a control is designed to maximize the energy captured from the wind and to regulate the stator reactive power, contributing to the compensation of the power factor according to grid requirements.The proposed technique can be applied to nonlinear MIMO systems and allows to make a separate design for each component of the controller. For these designs the Super-Twisting algorithm is employed in this work, which possesses excellent properties regarding simplicity of implementation and online operation, and robustness against uncertainties and external disturbances.Finally, representative simulation results are presented and analyzed.

Sensorless Vector Control of Induction Generators for Variable-Speed Wind Turbines Using Micro-2407

A sensorless vector-control strategy for an induction generator in a grid-connected wind energy conversion system is presented. The sensorless control system is based on a model reference adaptive system (MRAS) to estimate the rotational speed. In order to tune the MRAS observer and compensate for the parameter variation and uncertainties, a separate estimation of the speed is obtained from the rotor slot harmonics using an algorithm for spectral analysis. This algorithm can track fast dynamic changes in the rotational speed, with high accuracy. Two back to back pulse width modulated (PWM) inverters are used to interface the induction generator with the grid. The front-end converter is also vector controlled. The dc link voltage is regulated using a PI fuzzy controller. The proposed sensorless control strategy has been experimentally verified on a 2.5-kW experimentally set up with an induction generator driven by a wind turbine emulator. The emulation of the wind turbine is performed using a novel strategy that allows the emulation of high-order wind turbine models, preserving all of the dynamic characteristics. The experimental results show the high level of performance obtained with the proposed sensorless vector-control method.

A PWM Multilevel Current-Source Inverter Used for Grid-Connected Wind Energy Conversion System

This paper proposes a grid-connected wind energy conversion system (WECS) based on a PWM multilevel currentsource inverter (MCSI) topology. The topology used here is derived from the multilevel voltage-source inverter (MVSI) by dual conversion, this allows the wealth of existing knowledge relating to the operations, modulations and control strategies of multilevel VSI to be immediately applied to such multilevel CSI. The topology are supplied with two independent DC current-sources, 2n+1 current levels are obtained at the output. In the proposed control scheme, DC-link current controller is used to regulate and stabilize dc link current, output power factor controller is used to independently control the real power or reactive power, and unity power factor is easily achieved at grid side. Validation of models, control and steady-state and transient performances of a WECS based on 5-level CSI is carried out in the MATLAB/Simulink environment.

Optimal Design of a Direct-Drive Permanent Magnet Synchronous Generator for Small-Scale Wind Energy Conversion Systems

This paper presents an optimal design of a direct-drive permanent magnet synchronous generator for a smallscale wind energy conversion system. An analytical model of a small-scale grid-connected wind energy conversion system is presented, and the effects of generator design parameters on the payback period of the system are investigated. An optimization procedure based on genetic algorithm method is then employed to optimize four design parameters of the generator for use in a region with relatively low wind-speed. The aim of optimization is minimizing the payback period of the initial investment on wind energy conversion systems for residential applications. This makes the use of these systems more economical and appealing. Finite element method is employed to evaluate the performance of the optimized generator. The results obtained from finite element analysis are close to those achieved by analytical model.

Mitigation of Voltage Dips and Swells in Grid-connected Wind Energy Conversion Systems

This paper investigates two methods for mitigation of voltage dips and voltage swells in a grid to which a wind energy conversion system (WECS) is connected. The two mitigation methods are the dynamic voltage restorer (DVR) and the static synchronous compensator (STATCOM). The wind energy system employs permanent magnet synchronous generator (PMSG). It is well known that the voltage dips affect the PMSG adversely, leading to unlimited increase in its speed. Hence, quick voltage dip mitigation is required. The responses of both DVR and STATCOM to voltage dips as well as voltage swells are investigated and compared. The control algorithms employed with each device are presented. The need for applying additional filters to suppress harmonic contents of each system (the system employing DVR and that employing STATCOM) is studied. Also, the active and reactive power behaviors in each system during and after fault recovery are investigated. The simulation results compared for voltage dips and voltage swells show the less harmonic contents for the system employing the DVR. However, the response of the two systems to faults is comparable.

Efficiency Comparison of Power Electronic Converters Used in Grid-Connected Permanent-Magnet Wind Energy Conversion System Based on Semiconductors Power Losses

An efficiency comparison of power converters is presented for a permanent magnet generator based grid-connected wind energy conversion system. The power converters examined are: the intermediate boost converter (IBC), the intermediate buck-boost converter (IBBC), the back-to-back converter (BBC) and the matrix converter (MC). The aim is to determine which power electronic converter yields the highest efficiency in terms of power losses of the semiconductor devices with the varying wind speeds. In view of this, a furled wind turbine model is developed that generates power for different wind speeds. Afterwards, a relation between the wind speed and power loss is established to evaluate the efficiency of the power electronic converters for discrete wind speeds. The power loss model presented in this paper has taken into account the conduction and switching losses of the semiconductor devices within each converter. Simulation results are presented showing the power loss characteristics with the variation in wind speeds. Finally, with regard to the global efficiency for the power electronic converters of the considered wind speed regime, the IBC is found to be the most favourable choice considering the typical wind conditions encountered by a wind energy conversion system operating at the kWatt level.

Development of High-Performance Grid-Connected Wind Energy Conversion System for Optimum Utilization of Variable Speed Wind Turbines

This paper presents an improvement technique for the power quality of the electrical part of a wind generation system with a self-excited induction generator (SEIG) which aims to optimize the utilization of wind power injected into weak grids. To realize this goal, an uncontrolled rectifier-digitally controlled inverter system is proposed. The advantage of the proposed system is its simplicity due to fewer controlled switches which leads to less control complexity. It also provides full control of active and reactive power injected into the grid using a voltage source inverter (VSI) as a dynamic volt ampere reactive (VAR) compensator. A voltage oriented control (VOC) scheme is presented in order to control the energy to be injected into the grid. In an attempt to minimize the harmonics in the inverter current and voltage and to avoid poor power quality of the wind energy conversion system (WECS), an <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> filter is inserted between VOC VSI and the grid. The proposed technique is implemented by a digital signal processor (DSP TMS320F240) to verify the validity of the proposed model and show its practical superiority in renewable energy applications.

Analytical and Experimental Evaluation of a WECS Based on a Cage Induction Generator Fed by a Matrix Converter

In this paper, the control of a grid-connected wind energy conversion system (WECS), based on an induction machine fed by a matrix converter (MC), is presented. The MC is controlled using a space vector modulation algorithm with zero displacement factor at the input. Stability issues related to the operation of the WECS for the whole power and speed range are fully analyzed in this paper, using a simplified small-signal model. The implementation of a model reference adaptive system (MRAS) observer, for sensorless control of the proposed WECS, is also presented in this paper. The MRAS observer is implemented using the output voltage demand, avoiding the use of voltage transducers to measure the machine voltage. From the speed estimated by the MRAS observer, the electrical torque of the induction generator is regulated in order to drive the WECS to the operating point where the aerodynamic efficiency is maximized. Experimental results obtained with a 2.5-kW prototype are presented and fully discussed in this paper.

Study on the Multiple Voltage Source Inverter for Grid-Connected Large-Scale Wind Energy Conversion System

This paper proposes a novel grid-connected multiple voltage source inverter (VSI) for large-scale wind energy conversion system (WECS) applications. Firstly, the typical configuration, operation principle and mathematical modeling of the direct-drive grid-connected WECS are analyzed in brief. Then, a suitable topology of the grid-connected multiple VSI composed of two six-pulse inverters, two separate zig-zag transformers and a dc-link capacitor is presented. In order to reduce numbers of commutations and to increase dc-link voltage utilization ratio of the proposed grid-connected multiple VSI, a quasi twelve-pulse phase-shift PAM switching strategy is demonstrated. Finally, a simulation test system is set up by using MATLAB/SIMULINK, and the results of simulation validate the effectiveness of the proposed grid-connected multiple VSI.

Design of intelligent controllers for wind generation system with sensorless maximum wind energy control

This paper presents the design of an on-line training recurrent fuzzy neural network (RFNN) controller with a high-performance model reference adaptive system (MRAS) observer for the sensorless control of a induction generator (IG). The modified particle swarm optimization (MPSO) is adopted in this study to adapt the learning rates in the back-propagation process of the RFNN to improve the learning capability. By using the proposed RFNN controller with MPSO, the IG system can work for stand-alone power application effectively. The proposed output maximization control is achieved without mechanical sensors such as the wind speed or position sensor, and the new control system will deliver maximum electric power with light weight, high efficiency, and high reliability. The estimation of the rotor speed is based on the MRAS control theory. A sensorless vector-control strategy for an IG operating in a grid-connected variable speed wind energy conversion system can be achieved.

Stability Analysis of a Wind Energy Conversion System Based on a Doubly Fed Induction Generator Fed by a Matrix Converter

In this paper, the performance of a grid-connected wind energy conversion system (WECS), based on a doubly fed induction generator (DFIG) fed by a matrix converter (MC), is presented. The MC replaces the back-to-back converters conventionally used to control a DFIG. The MC is operated with close-to-unity power factor at the grid side. Stability issues related to the operation of the MC in the proposed WECS are discussed. A small signal model is used to investigate the dynamic performance of the two control arrangements discussed in this paper. Experimental results, obtained with a 4-kW prototype, are presented and fully discussed in this paper. The performance of the system for variable speed generation is verified using the emulation of a variable speed wind turbine implemented with a digitally controlled dc machine.

05/02253 A sensorless variable structure control of induction motor drives

A sensorless vector-control strategy for an induction generator (IG) operating in a grid-connected variable speed wind energy conversion system is presented. The sensorless control is based on a model reference adaptive system (MRAS) observer for estimating the rotational speed. An on-line training recurrent neural network (RNN) controller using back-propagation learning algorithm with particle swarm optimization (PSO) is designed to allow the rotational speed adjustment for power regulation. The node connecting weights of the RNN are trained online by back-propagation (BP) methodology. The PSO is adopted to adjust the learning rates in the BP process to improve the learning capability. The proposed output maximization control is achieved without mechanical sensors such as wind speed or position sensor, and the new control system will deliver maximum electric power with light weight, high efficiency, and high reliability. The concept has been developed and analyzed using a turbine directly driven IG.

계통연계 풍력발전시스템의 최대출력제어를 위한 신경회로망 제어기에 관한 연구

This paper presents a neural network controller of a grid-connected wind energy conversion system for extracting maximum power from wind and a power controller to transfer the maximum power extracted into a utility grid. It discusses the modeling and simulation of the wind energy conversion system with the controllers, which consists of an induction generator, a transformer, a link of a rectifier, and an inverter. The paper describes tile drive train model, induction generator model and grid-interface model for dynamics analysis. Maximum power extraction is achieved by controlling the pitch angle of the rotor blades by a neural network controller. Pitch control method is mechanically complicated, but the control performance is better than that of the stall regulation. The simulation results performed on MATLAB show the variation of the generator torque, the generator rotor speed, the pitch angle, and real/reactive power injected into the grid, etc. Based on the simulation results, the effectiveness of the proposed controllers is verified.

Sensorless Vector Control of Induction Machines for Variable-Speed Wind Energy Applications

A sensorless vector-control strategy for an induction generator in a grid-connected wind energy conversion system is presented. The sensorless control system is based on a model reference adaptive system (MRAS) observer to estimate the rotational speed. In order to tune the MRAS observer and compensate for the parameter variation and uncertainties, a separate estimation of the speed is obtained from the rotor slot harmonics using an algorithm for spectral analysis. This algorithm can track fast dynamic changes in the rotational speed, with high accuracy. Two back-to-back pulse-width-modulated (PWM) inverters are used to interface the induction generator with the grid. The front-end converter is also vector controlled. The dc link voltage is regulated using a PI fuzzy controller. The proposed sensorless control strategy has been experimentally verified on a 2.5-kW experimental set up with an induction generator driven by a wind turbine emulator. The emulation of the wind turbine is performed using a novel strategy that allows the emulation of high-order wind turbine models, preserving all of the dynamic characteristics. The experimental results show the high level of performance obtained with the proposed sensorless vector-control method.

Stochastic analysis and simulation of grid-connected wind energy conversion system

An increasing presence of renewable energy forms, due to environmental and socio-economic reasons, in the electric power industry necessitates an assessment of the impact of these sources, on a conventional electric utility. This assessment incorporates stochastic theory to investigate the security and stability of a wind energy conversion system (WECS) on an electrical utility to quantify the limits of such a system's operation. This paper presents a model that captures the uncertainties in the system load at the wind generator bus, a method that approximates the randomness experienced by the system. Future dynamic models in development will capture noise due to wind effects. A simple model of a grid-connected WECS is presented. An index of reliability is also determined known as the mean first passage time (MFPT), the time taken for the system to leave its stability region.