Small-scale Wind Energy Conversion System Research Articles

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.

Analytical Design Methodology for Wind Power Permanent Magnet Synchronous Generators

In this paper a novel analytical design methodology for wind power permanent magnet synchronous generators is presented. This kind of electric generator plays a major role in small-scale wind energy conversion systems up to 10 kW. The proposed diameter-cubed sizing equation is based both on the generator requirements, imposed by the application, and the design parameters that rely on the designer criteria. The magnetic field waveforms of both the permanent magnets field and the armature field are considered from the first moment through the winding factors, as well as the slots effects given by the Carter factor. The analytical model of the permanent magnet synchronous generator is validated with the finite element method, showing good agreement, both with no load and under load. As the generator is unsaturated, the main source of divergence between the analytical and the finite element model are the iron losses, due to the nonuniform magnetic field distribution.

Adaptive Maximum Power Point Tracking Control Algorithm for Wind Energy Conversion Systems

For small-scale wind energy conversion systems (WECSs), an adaptive maximum power point tracking (MPPT) algorithm is presented in this paper to increase wind energy harvesting. For its adaptability across a wide range of WECSs and quick tracking of maximum power point, the proposed algorithm combines the computational behavior of hill climb search, tip speed ratio, and power signal feedback control algorithms. Using buck–boost-featured single-ended primary inductor converters, the proposed MPPT algorithm is implemented in this paper to extract maximum power from the entire wind velocity profile. A laboratory-scaled dc motor drive-based WECS emulator is used to test the proposed algorithm. The in-lab experimental setup's control schemes are carried out with the help of a 32-bit floating point digital signal controller called TMS320F28335. The experimental results demonstrate that the proposed algorithm's tracking capability is effective and efficient in both sudden and gradual wind conditions.

Fuzzy model based multivariable predictive control design for rapid and efficient speed-sensorless maximum power extraction of renewable wind generators

Introduction. A wind energy conversion system needs a maximum power point tracking algorithm. In the literature, several works have interested in the search for a maximum power point wind energy conversion system. Generally, their goals are to optimize the mechanical rotation or the generator torque and the direct current or the duty cycle switchers. The power output of a wind energy conversion system depends on the accuracy of the maximum power tracking controller, as wind speed changes constantly throughout the day. Maximum power point tracking systems that do not require mechanical sensors to measure the wind speed offer several advantages over systems using mechanical sensors. The novelty. The proposed work introduces an intelligent maximum power point tracking technique based on a fuzzy model and multivariable predictive controller to extract the maximum energy for a small-scale wind energy conversion system coupled to the electrical network. The suggested algorithm does not need the measurement of the wind velocity or the knowledge of turbine parameters. Purpose. Building an intelligent maximum power point tracking algorithm that does not use mechanical sensors to measure the wind speed and extracts the maximum possible power from the wind generator, and is simple and easy to implement. Methods. In this control approach, a fuzzy system is mainly utilized to generate the reference DC-current corresponding to the maximum power point based on the changes in the DC-power and the rectified DC-voltage. In contrast, the fuzzy model-based multivariable predictive regulator follows the resultant reference current with minimum steady-state error. The significant issues of the suggested maximum power point tracking method, such as the detailed design process and implementation of the two controllers, have been thoroughly investigated and presented. The considered maximum power point tracking approach has been applied to a wind system driving a 5 kW permanent magnet synchronous generator in variable speed mode through the simulation tests. Practical value. A practical implementation has been executed on a 5 kW test bench consisting of a dSPACEds1104 controller board, permanent magnet synchronous generator, and DC-motor drives to confirm the simulation results. Comparative experimental results under varying wind speed have confirmed the achievable significant performance enhancements on the maximum wind energy generation and overall system response by using the suggested control method compared with a traditional proportional integral maximum power point tracking controller.

Efficiency improvement and reliability evaluation of small-scale PMSG-based wind energy conversion system using back-to-back T-type converter

Utilization of small-scale wind energy conversion systems (WECS) has been grown in recent years. Permanent magnet synchronous generator due to lack of slip rings is a suitable alternative for induction generators to be used in these systems. However, these generators use full power converters which means higher power losses. In this paper, an ultra-efficient three-level converter, called T-type converter, is used in a back-to-back configuration as power electronic interface for PMSG-based small-scale WECS. Then, simulations are carried out to evaluate the efficiency of the system and compare it to conventional two- and three-level back-to-back configurations. Meanwhile, thermal analysis is carried out to investigate the thermal loading of different switching components of the converter. Data given by this analysis can be further used to evaluate system reliability. Therefore, system reliability is calculated and compared to conventional two- and three-level converter systems.

Experimental investigation of power generation in a microgrid hybrid network

The hybrid integration of small-scale wind and solar energy conversion systems can be used for on- and off-grid applications. This paper investigates a stand-alone off-grid application of a hybrid small-scale wind turbine and photovoltaic (PV) cell microgrid to supply houses in rural Iraq far from the utility grid. Experimental investigations were performed to measure wind speed and solar radiation, as well as the DC voltage in the rectifier section of a small-scale permanent magnet synchronous generator (PMSG) wind turbine and the DC voltage in a PV cell for 24 hours. The results showed that using a small-scale hybrid wind and solar generating system for off-grid applications in Iraq is possible if the components are equipped with proper charge controllers that perform maximum power point tracking (MPPT) during wind speed and solar radiation fluctuations.

Holistic Design of Small-scale Stand-alone Wind Energy Conversion Systems Using Locally Manufactured Small Wind Turbines

A holistic and multi-disciplinary design approach is developed for small-scale stand-alone wind energy conversion systems (WECS) using locally manufactured small wind turbines (LMSWTs), with the aim of reducing capital and maintenance costs while increasing the annual energy production and energy utilization of such systems. Various subsystems are analysed and modelled, using both sequential and integrated design approaches, such as the rotor, including the airfoil and blade geometries, the axial flux permanent magnet generator including economic, thermal and structural aspects of the stator and rotor geometry, the furling system and the electrical system, including the power transmission cables and the battery bank. The holistic design approach is then applied to a 2.4m rotor diameter LMSWT and the complete WECS is dimensioned. Finally, the designed low cost system is compared to a high cost system using a maximum power point converter, with satisfactory results especially for low wind speeds around the mean wind speed of the site. It is thus concluded that a holistic and multi-disciplinary design approach to small-scale stand-alone WECS using LMSWTs, can lower the cost of energy for rural electrification applications by reducing capital costs, while sustaining the system’s efficiency and annual energy production in low wind speed regions.

MPPT Control of PMSG Based Small-Scale Wind Energy Conversion System Connected to DC-Bus

Abstract While the use of renewable energy systems in electric power generation is increasing more and more, wind energy conversion systems (WECS) receive considerable attention among these. Thanks to the ability of power generation in all wind speed range by controlling the rotor speed, Variable Speed WECSs are more preferred than fixed speed WECSs. When considering small-scale applications in variable speed WECS, Permanent Magnet Synchronous Generator (PMSG) based WECS structures are focus of the interest due to their advantages such as high efficiency and low maintenance costs. The generator must be operated at an optimum speed to obtain maximum power from the WECS. Moreover, different Maximum Power Point Tracking (MPPT) methods can be used to control and determine optimal operating speed. In this paper, WECS configuration consists of PMSG, uncontrolled rectifier, DC link capacitor, DC-DC boost converter and DC-Bus. Capturing the maximum power from WECS and supplying the DC-Bus is performed via tip speed ratio and PI control (TSR-PI) based MPPT method. Moreover, two wind speed profiles having constant and instant changes are created to test the performance of the proposed method. For comparison purposes, perturbation & observation (P&O) based MPPT method is also carried out in here. According to obtained results from this study performed in Matlab/Simulink environment, it is verified that TSR-PI based MPPT method ensures higher power and efficiency for these wind speed profiles by means of a more successful generator speed tracking.

Wind Energy Potential for Small-scale WEC Systems in Port Elizabeth

South Africa is the highest emitter of greenhouse gases in the continent, and 18th in the world. Electricity generation in South Africa is heavily dependent on fossil fuels for its energy needs. Hence, it is a necessity to shift to renewable energy sources for electricity production in order to mitigate carbon emissions. This paper discusses the potential for electricity generation through small-scale wind energy conversion (WEC) systems in Port Elizabeth that is considered to be South Africa’s windiest city. A wind energy study was conducted through analyses of the local weather data. The study shows that Port Elizabeth has an annual wind power density of 138 W/m2. The area studied has great wind power potential, especially for small-scale wind energy production. The Weibull method has been applied to predict wind power potential in Port Elizabeth, South Africa. Furthermore, the Weibull method was applied to model the probability function of the wind speed due to its user friendliness and flexibility.

Passivity-Based Control of Switched Reluctance-Based Wind System Supplying Constant Power Load

This paper presents a passivity-based control (PBC) scheme for the switched reluctance generator (SRG) in small-scale wind energy conversion systems for dc microgrid applications. The main objective is to stabilize the output voltage in case the system supplies constant power loads (CPLs) and operates with maximum power point tracking (MPPT). Stability improvement and dc-link ripple reduction in the presence of CPLs is achieved using system-level modeling of SRG-based dc microgrid through the Euler-Lagrange system (ELS) from the viewpoint of the machine physical structure. Compared with other control methods, the proposed MPPT method based on passivity-based speed controller employs the back electromotive force (EMF) in the generation process as a position-dependent voltage source to overcome the major challenge of SRG complicated uncertain dynamic model. To deal with the time-varying inductance and back EMF of SRG, an adaptation mechanism is incorporated in the proposed adaptive PBC and the control design is constructed by using the Lyapunov theorem where the closed-loop stability is ensured. The effectiveness of the proposed method in avoiding instability effects of SRG and CPL with voltage ripple reduction and precise wind turbine speed tracking is investigated with simulation results and validated with experimental by using a four-phase, 8/6 SRG drive system.

A Control Approach for a Small-Scale PMSG-Based WECS in the Whole Wind Speed Range

In this paper, an overall power control strategy is proposed for control of a fixed-pitch small-scale wind energy conversion system operating at both underrated and overrated wind speeds. At underrated wind speeds, the dynamical behavior of the rotor is considered, and the optimal reference torque is generated without the need of wind speed sensors through a robust variable structure observer with the aim of maximum power point tracking. At overrated wind speed, the flux-weakening strategy is invoked to let the machine exploit maximum electrical torque under given current and voltage constraints. As a new approach, the optimal reference flux magnitude together with a reference torque angle is provided by online numerically solving an optimization problem in the whole wind speed range. Moreover, a space-vector-modulation -based direct torque control (SVM-DTC) is used to track the provided references for flux magnitude and torque angle. In particular, the SVM-DTC is composed of a reference voltage vector calculator providing a desired voltage vector. The effectiveness of the proposed overall power control strategy is verified not only by applying the strategy to a commercial 10-kW wind turbine simulated in MATLAB/Simulink, but also by experimental results derived from a developed laboratory setup.

Type-2 Fuzzy Logic Predictive Control of a Grid Connected Wind Power Systems with Integrated Active Power Filter Capabilities

This paper proposes a real-time implementation of an optimal operation of a double stage grid connected wind power system incorporating an active power filter (APF). The system is used to supply the nonlinear loads with harmonics and reactive power compensation. On the generator side, a new adaptive neuro fuzzy inference system (ANFIS) based maximum power point tracking (MPPT) control is proposed to track the maximum wind power point regardless of wind speed fluctuations. Whereas on the grid side, a modified predictive current control (PCC) algorithm is used to control the APF, and allow to ensure both compensating harmonic currents and injecting the generated power into the grid. Also a type 2 fuzzy logic controller is used to control the DC-link capacitor in order to improve the dynamic response of the APF, and to ensure a well-smoothed DC-Link capacitor voltage. The gained benefits from these proposed control algorithms are the main contribution in this work. The proposed control scheme is implemented on a small-scale wind energy conversion system (WECS) controlled by a dSPACE 1104 card. Experimental results show that the proposed T2FLC maintains the DC-Link capacitor voltage within the limit for injecting the power into the grid. In addition, the PCC of the APF guarantees a flexible settlement of real power exchanges from the WECS to the grid with a high power factor operation.

Experimental analysis of impact of maximum power point tracking methods on energy efficiency for small‐scale wind energy conversion system

The power control of small-scale wind energy conversion system is usually limited by the sluggish mechanical dynamic. Aiming at highlighting this phenomenon, this article introduces a small-scale wind energy conversion system using the permanent magnet synchronous machine as generator to validate different combinations of control strategy resulting from four different maximum power point tracking (MPPT) methods with hysteresis control: one indirect MPPT method based on a look-up table and three direct methods based on perturb and observe relationship. Following two ideal wind speed profiles, a real rapid wind speed profile and using a test bench emulating a small-scale wind turbine, the MPPT methods are compared and analysed based on experimental results. The indirect method operates with the best MPPT performances for all three wind speed profiles while requiring accurate knowledge of the controlled system. The direct methods operate with low MPPT performance under rapid variation of wind speed and the superiority of variable step size is not significant since the dynamic process of the perturbation strongly weakens the effect of MPPT algorithm.

Overall power control strategy for small‐scale WECS incorporating flux weakening operation

This study presents an overall power control strategy for control of fixed-pitch small-scale wind energy conversion system (WECS). The overall power control strategy is designed in such a way that the WECS efficiently operates for both underrated and overrated wind speeds. At underrated wind speeds, maximum power point tracking is achieved through a proportional–integral (PI) mechanical torque controller while no wind speed sensor is required. The PI mechanical torque controller together with a high-gain observer, estimating mechanical torque, generates the reference electrical torque. At overrated wind speed, the control strategy limits the generated power to rated power of generator via an anti-windup algorithm. In this case, the flux weakening strategy then is invoked. The optimal (reference) flux magnitude is provided by off-line numerically solving an optimisation problem. An space-vector modulation (SVM)-based direct-torque control (DTC) is used to track the electrical torque and flux references. In particular, the SVM-DTC is composed of a reference voltage vector calculator providing a desired voltage vector. The effectiveness of the proposed overall power control strategy is verified by applying the strategy to a commercial 10 kW wind turbine simulated in MATLAB/Simulink.

Adaptive Maximum Power Point Tracking Control Algorithm for Wind Energy Conversion Systems

This paper presents an adaptive maximum power point tracking (MPPT) algorithm for small-scale wind energy conversion systems (WECSs) to harvest more energy from turbulent wind. The proposed algorithm combines the computational behavior of hill climb search, tip speed ratio, and power signal feedback control algorithms for its adaptability over wide range of WECSs and fast tracking of maximum power point. In this paper, the proposed MPPT algorithm is implemented by using buck–boost featured single-ended primary inductor converter to extract maximum power from full range of wind velocity profile. Evaluation of the proposed algorithm is done on a laboratory-scaled dc motor drive-based WECS emulator. TMS320F28335, 32-bit floating point digital signal controller, is used to execute the control schemes of the in-lab experimental setup. Experimental results show that tracking capability of the proposed algorithm under sudden and gradual fluctuating wind conditions is efficient and effective.

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.

Analytical Evaluation of Surface-Mounted PMSG Performances Connected to a Diode Rectifier

This paper analyzes some operational issues of three-phase surface-mounted permanent magnet synchronous generators (PMSGs) connected to a diode rectifier. This simple configuration coupled to a single-switch dc–dc converter is used in small-scale wind energy conversion systems, as well as in energy harvesting systems, to reduce costs. The diode rectifier causes an intrinsic limit for the maximum convertible power, which is related to the load impedance matching, and additional joule losses due to the distorted currents. By using an analytical steady-state model of the rectifier and of the PMSG, this paper discusses how to achieve two particularly meaningful operating conditions characterized respectively by the maximum power transfer and the maximum power per ampere. The theory is validated by simulation and test results on a prototype.

An adapted blockage factor correlation approach in wind tunnel experiments of a Savonius-style wind turbine

An investigation into the blockage correction effects in wind tunnel experiments of a small-scale wind energy conversion system in an open type test section is carried out. The energy conversion system includes a Savonius-style wind turbine (SSWT) and a power measurement assembly. As the available correlations for the closed type test sections may not be appropriate for the open test section under dynamic loading conditions, new correlations are adapted for the blockage correction factors with free stream wind speed, turbine rotational speed and variable load applied to the turbine to quantify the energy conversion coefficients more precisely. These are obtained for a blockage ratio of 21.16% through a comparison of present experimental data with those of established experimental data under dynamic loading conditions. Further, the accuracy of the adapted correlations is substantiated into the experiments with smaller blockage ratios of 16% and 12.25%. The relationships of the tip speed ratios and blockage ratios with the blockage correction factor are also discussed. Using these correlations, this study provides evidence of increase of blockage correction in the range 1–10% with the increase of both tip speed ratio and blockage ratio. The results also indicate that for blockage ratios approaching 10 and tip speed ratios below 0.5, the blockage effects are almost negligible in the open type test sections.

AN ENHANCED MPPT TECHNIQUE FOR SMALL-SCALE WIND ENERGY CONVERSION SYSTEMS

This paper proposes an enhanced Maximum Power Point Technique (MPPT) based on Artificial Neural Network (ANN) for small-scale wind energy conversion systems using Permanent Magnet synchronous Generators (PMSGs). The conventional MPPT technique which used a Perturb and observes (P&O) method is compared with the proposed ANN method. For this, MATLAB/Simulink is used to simulate both the conventional P&O method and the proposed ANN method. The proposed ANN uses the dc- link voltage and duty cycle as the control variables for MPPT. The advantages of the proposed MPPT are low system cost, increase reliability, less mechanical stress of the generator and no need for shaft speed sensing. Moreover the conversion efficiency of the proposed ANN method is increased while comparing with the conventional P&O method.

New Overall Control Strategy for Small-Scale WECS in MPPT and Stall Regions With Mode Transfer Control

This paper presents a new overall control strategy for small-scale wind energy conversion systems (WECS). The purpose of the proposed strategy is to utilize a maximum power point tracking control (MPPT) to maximize the captured energy when the wind speeds are below the rated speed. For high wind speed region; two stall controllers are developed: The constant speed stall controller which will limit the rotational speed of the generator to its rated value, and the constant power stall controller, which will regulate the captured power to be within the system rating. For the MPPT control, a modified perturb and observe (P&O) algorithm is utilized, where the dc side current is used as a perturbation variable and the dc-link voltage slope information is used to enhance the tracking speed and stability of the algorithm. For the speed and power regulation operation during high wind speeds, the system is controlled in the stall region to limit the rotational speed and the power of the generator. A stabilizing control loop is proposed to compensate for the stall region instability. A new mode transfer control strategy is developed to effectively control the transition between different modes of operation while ensuring the system stability without using any preknowledge of the system parameters. A 1 kW hardware prototype is developed and tested to validate the proposed new control strategy.