Small Wind Energy Conversion Systems Research Articles

Power Quality impact of a small wind energy conversion system connected to the LV grid

This research work is devoted to the study of the Power Quality (PQ) impact of small wind energy conversion systems (SWECS) connected to the low voltage grid. A common coupling point (CCP) has been monitored using a PQ meter that fulfils the standard IEC 61000-4-30 class A. The PQ survey has been conducted with and without the SWECS and the results were compared with the limits defined by the standard EN 50160

A single current sensor based adaptive step size MPPT control of a small scale variable speed wind energy conversion system

Due to the limited size and lower environmental impact, a small-scale wind energy conversion system (WECS) is a promising alternative for remote locations and residential areas where installing large wind turbines is not feasible. This system employs a permanent magnet synchronous generator (PMSG) as a variable speed wind generator due to its advantages such as high torque density, gearless, and require no external excitation, etc. This article proposes a single load current sensor-based adaptive step size (LCAS) maximum power point extraction (MPPT) method which utilizes the load current information to track the maximum power. This method does not require rotor speed information and knowledge of the turbine parameters. Also, this article uses a simple and cost-effective switch mode rectifier topology (AC–DC and DC–DC boost converters) for the PMSG-based variable speed WECS. The proposed method is validated in a 1.5 kW test rig using an OPAL-RT digital signal controller and also compared with various fixed step size (FSS) MPPT algorithms at various operating conditions. Extensive experimental work has been carried out for the LCAS MPPT method that confirms the tracking efficiency is better and tracking speed is faster along with the improved steady state as well as transient performance.

Contribution to Improve Magnetic Performance and Torque Ripple Reduction of the Low-Speed DSPM Machine

This article deals with the performance improvement of a toothed pole variable reluctance machine excited by permanent magnets housed in the stator yoke. The objective was to reduce the electromagnetic torque ripples caused by the structure geometry and by the supply technique. The machine was designed to meet the specifications of a small wind energy conversion system. The proposed solution improved the electromagnetic design of the new structure in order to minimize the variation of the reluctance. This improvement was obtained by action on the geometry of the structure (the location of the permanent magnets), by action on the stator and rotor tooth pitch, and by the application of an indirect control strategy called torque sharing function. The PSO optimization algorithm was applied in the first part for the optimization of the machine’s global parameters to maximize torque density and then, in the second part, for the research of the optimum tooth pitch parameters to minimize torque ripple. Static and dynamic performances were obtained using 2D-FEM and MATLAB/Simulink software. The results reveal that by action on the stator/rotor tooth pitch, the ripple torque was reduced by about 53%, and by approximately 76% with the used command technique.

Experimental and Numerical Investigation of the Effect of Blades Number on the Dynamic Response of a Small Horizontal-Axis Wind Turbine

The new energy scenario is rising a strong interest towards the distributed production from renewable sources; among them, wind seems to be one of the most interesting and at the same time critical due to the challenges of the conversion technology. Operation of small wind energy conversion systems is generally very complex due the extremely variable regime of operation and the high turbulent wind, so that a deep knowledge of the dynamic response of such devices is crucial not only for optimising their performances but also to make them comfortable to be used in residential areas. For these reasons, the present work is focused on analysing the effect in changing the number of blades on a small horizontal axis wind turbine through an experimental campaign in the wind tunnel. The turbine dynamics has been characterised running some “wind ramp” tests and analysing the rotor capability in following the wind as well the vibrations transmitted by the turbine during the operation. Results demonstrate that a higher number of blades, despite a small decrease of performance, can make the machine more efficient in operating at low wind regimes. At the same time, a higher number of blades can make the rotor efficient even at lower speed of rotation, thus limiting the risks of having high magnitude vibrations.

Small scale wind & solar photovoltaic energy conversion system for DC microgrid applications

The rise in demand for electrical energy throughout the globe gives a significant rise in new power generating sources. The Wind and Solar Photovoltaic energy sources are the most propitious power generating sources among them. Nowadays, these sources play an important role to form a Micro Grid with the incorporation of conventional grid and energy storage facilities. This article comprises of the simulations analysis for Wind Energy Conversion System and Photovoltaic Energy System incorporated with DC load for the applications of DC Microgrid. The mathematical model of the WECS and PVES are incorporated and proposed with the Gain Scheduled Proportional Integral controller is proposed in the paper. The WECS and PVES are simulated with interfacing units for the DC load. The results are obtained for Ahmedabad, Gujarat, India for the input solar insolation and wind speed data. The materials used in small wind energy conversion systems and photovoltaic energy systems are discussed for microgrid applications. The performance for the WECS and PVES is analyzed for change in wind speed and change in solar insolation. The incorporation of GSPI controller provides stable results to maintain the voltage regulation. The results are stable over an extensive range under the unpredictable atmospheric conditions the dynamic scheduling is proposed.

Rüzgâr Enerjisi Dönüşüm Sistemlerinde bir DC-DC Güç Dönüştürücüsünün Denetimli Öğrenme Destekli Kontrolü

Over the last decades, to adopt high penetration of renewable energy sources (RESs) in electrical energy systems, distributed energy resources (DERs) have become prominent. Due to easy attainability status of small wind turbines (WTs), wind energy conversion systems (WECSs) are feasible applications for small customers, especially in windy areas. The next decade is likely to witness a considerable rise in DERs. In this context, WECSs are preferred broadly, thus harvesting wind energy into electrical energy effectively is a substantial issue. WTs can be got involved in the grid-connected or autonomous mode with a variety of topologies. In this paper, we examine to control of DC-DC boost converter of a WECS with the help of artificial intelligence (AI)-aided PI controller based on supervised learning method. Regarding the proposed method, artificial neural networks (ANNs) as a subset of AI are utilized. To test and ensure the applicability of the proposed control method, a small WECS with a permanent magnet synchronous generator (PMSG) connected a DC bus was implemented in MATLAB/Simulink environment. The proposed ANN scheme has reached a high accuracy rate with an overall mean squared error (MSE) equal to 7.4e-08. The results present that dynamic response and less complexity with a high accuracy rate have been obtained under study. The main target of this study is to reduce the number of sensors in the control layer. Thus, a cost-effective and more reliable structure is obtained with fewer sensor requirements.

An MPPT Control of a PMSG-Based WECS with Disturbance Compensation and Wind Speed Estimation

The paper presents simulation research on a variable structure control scheme of a small variable-speed fixed-pitch wind energy conversion system (WECS) with a three-phase permanent magnet synchronous generator (PMSG) in variable wind conditions. The WECS is connected to a power grid through two back-to-back voltage source converters (VSCs) with a DC link. The presented control algorithm is based on feedforward compensation of the wind turbine aerodynamic torque estimated using a linear disturbance observer (DOB). The torque estimate is employed to determine the effective wind speed, required for setting the reference angular speed, using numerical zero search of a nonlinear function. The simulation model, built in the Matlab/Simulink environment using the Simscape Electrical toolbox, includes the field-oriented control of the PMSG via the machine VSC, performed by cascaded angular velocity and current/torque PI controllers, as well as synchronization with the grid and the reactive power control via the grid VSC. The presented results are focused on the performance of the proposed control in the maximum power point tracking (MPPT) operating region of the WECS for various wind speed profiles.

A Controller for Optimum Electrical Power Extraction from a Small Grid-Interconnected Wind Turbine

Currently, wind power is the fastest-growing means of electricity generation in the world. To obtain the maximum efficiency from the wind energy conversion system, it is important that the control strategy design is carried out in the best possible way. In fact, besides regulating the frequency and output voltage of the electrical signal, these strategies should also extract energy from wind power at the maximum level of efficiency. With advances in micro-controllers and electronic components, the design and implementation of efficient controllers are steadily improving. This paper presents a maximum power point tracking controller scheme for a small wind energy conversion system with a variable speed permanent magnet synchronous generator. With the controller, the system extracts optimum possible power from the wind speed reaching the wind turbine and feeds it to the grid at constant voltage and frequency based on the AC–DC–AC conversion system. A MATLAB/SimPowerSystems environment was used to carry out the simulations of the system. Simulation results were analyzed under variable wind speed and load conditions, exhibiting the performance of the proposed controller. It was observed that the controllers can extract maximum power and regulate the voltage and frequency under such variable conditions. Extensive results are included in the paper.

Step-Down Switched-Inductor Hybrid DC-DC Converter for Small Power Wind Energy Conversion Systems With Hybrid Storage

This work is focused on a step-down switched-inductor hybrid dc-dc converter (SIHDC) integrated in a small power wind energy conversion system (WECS). The converter has two roles, to maintain the wind turbine at the maximum power point by controlling the electric generator loading, and to charge a high power density supercapacitor, which is part of a hybrid storage unit that also contains rechargeable batteries. The paper points out the steady-state analysis of the converter in continuous and discontinuous current modes, specific for this application. The stability investigation is presented in detail, including the influence of the electrical generator. The parameterized small-signal transfer function of the control variable derived in this paper can be used to quickly obtain the information needed to evaluate the stability of any similar WECS. A current controller was designed to achieve a stable operation in continuous current mode, and afterwards the stability was checked for discontinuous current mode. A 5kW step-down SIHDC prototype was built and extensively tested, both in laboratory, by using a wind turbine emulator, and in a small power (5kW) WECS industrial platform. Experimental results obtained under real operating conditions confirm the theoretical analysis and laboratory tests, showing that SIHDC converter is a valid solution for low power wind energy conversion systems.

Quantitative Feedback Theory design of robust MPPT controller for Small Wind Energy Conversion Systems: Design, analysis and experimental study

This paper addresses the design of a robust Maximum Power Point Tracking (MPPT) controller for a small wind energy conversion system fed by a Permanent Magnet Synchronous Generator (PMSG). The proposed MPPT controls the generator rectified voltage instead of the rotational speed avoiding the need for a mechanical sensor. Traditionally, this control problem is performed using a Proportional Integrator (PI) controller optimised at a specific operating point. However, the PI controller does not guarantee the promising transient performance under changing operating conditions. In this work, the Quantitative Feedback Theory (QFT) has been applied to synthesis a robust DC-voltage controller to ensure a robust stability and tracking specifications for all operating points. The performance of the designed controller has been compared with the classical PI controller experimentally on laboratory benchmark. The experimental results prove that the proposed controller outperforms the conventional PI controller reducing the overshoot between 26.67% and 82.53% and the response time between 36.36% and 71.33%, reducing by the way the mechanical stress on the PMSG under a turbulent wind speed profile. In addition, the extracted electrical energy using the proposed controller over 90 s of a typical wind speed profile is 1.7015% higher.

Combined control of stand-alone energy conversion scheme for distributed sources: Development and performance analysis

This paper has addressed the variable speed and constant frequency (VSCF) generation from the uncontrolled prime mover-based scheme for a stand-alone system. The small and medium scale wind energy conversion systems, usually dealing with this uncontrolled nature of prime movers, has been handled by the scheme, in this paper. The distributed generation unit (DGU) has considered a squirrel cage induction generator (SCIG) and a back to back converter in its structure. The DGU is developed with a load voltage control, including the filter elements, for the load side voltage source converter (LVSC) and a three-stage control for the generator side voltage source converter (GVSC). This combined controller for the DGU enables it to operate under both input and output side variations. Further, the controller is able to supply constant voltage at a constant frequency throughout the operation. The developed control is successfully implemented in the simulation environment, and the performance of the system is analyzed thoroughly. The variations, considered here are the d-axis component of load voltage, load impedance, dc- link voltage, and the prime mover speed. The performance of the control is verified experimentally with a prototype in reduced power scale in real-time. The results in both environments are found to be satisfactory.

Algorithm for the Performance Evaluation of Three Selected Wind Energy Conversion Systems (WECS) for Electricity Generation in Minna, Nigeria

Most of the wind energy conversion systems are failing in many developing countries such as Nigeria due to poor and un-appropriate site selection. Ten years (2001-2010) daily average wind speed data measured at 10m height for Minna (9.6°N, 6.6°E and 251m) were obtained from Nigerian Meteorological Agency (NIMET) and the characteristics of the three small scale wind energy conversion systems with power rating of 1, 1.5 and 3.0 kW obtained from the manufacturers websites were used in this study for the performance evaluation of three selected wind energy conversion system (WECS). The performance of the selected WECS were compared using the capacity factors obtained for the turbines from the algorithms developed, that combine the daily average wind speed and standard deviation for the location with the selected turbines characteristics provided by the manufacturers. The annual energy output for the WECS were found to be 1.37MWh, 1.23MWh and 2.53MWh with corresponding capacity factor of 18.8%, 11.2% and 8.4% respectively from e3001 (1kW), Ge-Power System 1.5SL (1.5kW) and Gv-3kW (3.0 kW). The e30001 (1kW) was observed to performed better with capacity factor of 18.8% as against 11.2% and 8.4% for Ge-Power system 1.5SL (1.5kW) and Gv-3kW (3.0 kW) respectively for Minna location.

Experimental and Numerical Vibrational Analysis of a Horizontal-Axis Micro-Wind Turbine

Micro-wind turbines are energy conversion technologies strongly affected by fatigue, as a result of their size and the variability of loads, induced by the unsteady wind conditions, and modulated by a very high rotational speed. This work is devoted to the experimental and numerical characterization of the aeroelastic behavior of a test-case horizontal-axis wind turbine (HAWT) with a 2 m rotor diameter and a maximum power production of 3 kW. The experimental studies have been conducted at the wind tunnel of the University of Perugia and consisted of accelerometer measurements at the tower and the tail fin. The numerical setup was the Fatigue, Aerodynamics, Structures, and Turbulence (FAST) code for aeroelastic simulations, which was fed as input with the same wind conditions employed in the wind tunnel tests. The experimental and numerical analyses were coupled with the perspective of establishing a reciprocal feedback, and this has been accomplished. On one hand, the numerical model is important for interpreting the measured spectrum of tower oscillations and, for example, inspires the detection of a mass unbalance at the blades. On the other hand, the measurements inspire the question of how to interpret the interaction between the blades and the tower. The experimental spectrum of tail fin vibrations indicates that secondary elements, in terms of weight, can also transmit to the tower, giving meaningful contributions to the vibration spectra. Therefore, an integrated numerical and experimental approach is not only valuable but is also unavoidable, to fully characterize the dynamics of small wind-energy conversion systems.

Applications of small-scale, stand-alone wind energy conversion systems in rural Cross River State, Nigeria

The study presents the wind energy potential (WEP) for six locations in Cross River State, Nigeria. The objective of the study was to assess the WEP of the selected sites for electricity generation, using small size wind energy conversion systems (WECs). The wind data were measured at 10 m height and ranged from 4 to 10 years. Additionally, the data were evaluated using the two-parameter Weibull function. Results obtained show that annual mean wind speed, vm, and Weibull parameters k and c range from 3.21 to 4.55 m/s, 3.32 to 6.69 and 2.99 to 5.40 m/s, in that order. The cost per kWh of energy for the selected WECs fluctuated between 0.0626 ≤ COE ≤ 0.1375 USD/kWh, while the avoidable CO2 emissions exist between 0.64 and 38.21 tons/year. However, the probable savings made from diesel was not greater than 14,524.94 litres/year for the locations with high WEP for small-scale stand-alone applications.

Small Scale Wind Generation System: Part II – A Novel Quasi-Z-Source Inverter and FRG-QZSI-Micro Grid Interface

<p>This paper proposes modelling, analysis and control of a small scale wind energy conversion system employing a direct driven Flux Reversal Generator (FRG) connected to the micro grid through a quasi-Z-source inverter (QZSI). This entire research is made up of two major parts viz., FRG and QZSI. In the part I report of this research work, the role of FRG has been thoroughly modelled and verified. In this part II, the modelling and analysis of QZSI for this purpose is presented. In addition, the modified space vector PWM (SVPWM) technique is proposed in this paper to satisfy the shoot-through characteristic of QZSI, which is a novel. The interface of FRG and QZSI to inject power in to micro grid has been finally presented. The simulation results are validated with the analytical results. Section I discusses the open loop control of QZSI. The mathematical modelling of QZSI for this purpose is given and analytically validated. This flowed by section II in which the proposed SVPWM is presented. The procedure to obtain triggering pulses using this proposed modulation technique is discussed. Section III presents closed loop control strategies for QZSI. Section IV presents the micro grid<br />inte face and power injection.</p>

Small Scale Wind Generation System: Part I – Experimental Verification Of Flux Reversal Generator Block

<p>This research work, titled Small Scale Wind Generation System, reported in part I and part II, proposes modeling, analysis and control of a small scale wind energy conversion system employing a direct driven Flux Reversal Generator (FRG) connected to the micro grid through a Quasi-Z-Source Inverter (QZSI). The application of QZSI using FRG to feed micro grid is proposed for the first time in this research work. The QZSI can realize buck/boost, inversion and power conditioning in a single stage with improved reliability. Also it features a wide range of voltage gain which is suitable for applications in wind systems, due to the fact that the wind generator output varies widely with wind velocity. In addition, the modified Space Vector PWM (SVPWM) technique is proposed in this paper to satisfy the shoot-through characteristic of QZSI. This also adds to the contribution of this research work. In this part I of this full research, modelling of the small scale FRG for wind system using Finite Element Analysis (FEA) is presented. The major parameter of FRG viz, voltage, current, torque and power are analyzed, validated and then represented in d-q model. The simulation results are validated with the analytical results. An experimental set-up to run the full procedure reported in this paper. These results form the basis for part II of this research work.</p>

DC-Link Control Filtering Options for Torque Ripple Reduction in Low-Power Wind Turbines

Small wind energy conversion systems (WECSs) are becoming an attractive option for distributed energy generation. WECSs use permanent-magnet synchronous generators (PMSGs) directly coupled to the wind turbine and connected to the grid through a single-phase grid-tie converter. The loading produced on the dc link is characterized by large ripple currents at twice the grid frequency. These ripple currents are reflected through the dc bus into the PMSG, causing increased heating and ripple torque. In this paper, the PMSG inverter is used to control the dc-link voltage. In order to avoid reflecting the ripple currents into the PMSG, the feedback dc-link voltage is passed through a filter. The Butterworth filters, notch filters, antiresonant filter (ARF) and moving average filter (MAF) are considered. For a fair comparison, formulas are provided to tune the filter parameters so that dc-link voltage control will achieve the selected bandwidth. The different filtering options produce different levels of torque ripple reduction. The notch filter, ARF, and MAF obtain the best results and there is a tradeoff between the filter implementation complexity, bandwidth, overshoot, and the torque ripple reduction. Simulations and experiments using a 2.5-kW PMSG turbine generator validate the proposals.

Design of an efficient small wind-energy conversion system with an adaptive sensorless MPPT strategy

This paper presents an original method for the sensorless Maximum Power Point Tracking (MPPT) of a small power wind turbine using a permanent magnet synchronous generator (PMSG) to supply a DC load. This method does neither require to measure the wind speed nor to know the turbine parameters. After a presentation of the energy conversion chain (wind turbine and PMSG), we first derive an analysis of its energy efficiency. This analysis shows that the highest power at the output of the turbine and the highest power supplied to the load are not obtained at the same rotor speed. This clearly shows the interest to maximize the power supplied to the load rather than to track the maximum power at the output of the turbine deduced from its theoretical power coefficient Cp, and the interest to use an active three-phase rectifier combined with a field oriented control of the PMSG. We then describe the proposed MPPT process and the speed estimator used to design a sensorless MPPT. Simulation results demonstrate the feasibility of the proposed approach.

New control strategy for fast-efficient maximum power point tracking without mechanical sensors applied to small wind energy conversion system

This paper proposes a new Perturb and Observe (P&O) Maximum Power Point Tracking (MPPT) algorithm for Small Wind Energy Conversion Systems to overcome the rapidity-efficiency trade-off and wrong behavior problems of the conventional P&O technique. The proposed algorithm works in two separate modes. The first mode is activated when the wind speed changes slowly. Under a rapid change of the wind speed, the second mode is switched to avoid the divergence of the system. The proposed algorithm requires only the measurement of the dc-link voltage and the dc current to realize the MPPT control, so no rotor speed measurement is needed, reducing the complexity of the overall system. The performance and the validity of the new MPPT algorithm have been proved by both simulation and experimental results.

Implementation of a new maximum power point tracking control strategy for small wind energy conversion systems without mechanical sensors

This paper proposes a modified perturbation and observation maximum power point tracking algorithm for small wind energy conversion systems to overcome the problems of the conventional perturbation and observation technique, namely rapidity/efficiency trade-off and the divergence from peak power under a fast variation of the wind speed. Two modes of operation are used by this algorithm, the normal perturbation and observation mode and the predictive mode. The normal perturbation and observation mode with small step-size is switched under a slow wind speed variation to track the true maximum power point with fewer fluctuations in steady state. When a rapid change of wind speed is detected, the algorithm tracks the new maximum power point in two phases: in the first stage, the algorithm switches to the predictive mode in which the step-size is auto-adjusted according to the distance between the operating point and the estimated optimum point to move the operating point near to the maximum power point rapidly, and then the normal perturbation and observation mode is used to track the true peak power in the second stage. The dc-link voltage variation is used to detect rapid wind changes. The proposed algorithm does not require either knowledge of system parameters or of mechanical sensors.The experimental results confirm that the proposed algorithm has a better performance in terms of dynamic response and efficiency compared with the conventional perturbation and observation algorithm.