Control of a switched reluctance generator for variable-speed wind energy applications

This paper presents a novel control system for the operation of a switched reluctance generator (SRG) driven by a variable speed wind turbine. The SRG is controlled to drive a wind energy conversion system (WECS) to the point of maximum aerodynamic efficiency using closed loop control of the power output. In the medium and low speed range, the SRG phase current is regulated using pulsewidth-modulation (PWM) control of the magnetizing voltage. For high speeds the generator is controlled using a single pulse mode. In order to interface the SRG to the grid (or ac load) a voltage-source PWM inverter is used. A 2.5-kW experimental prototype has been constructed. Wind turbine characteristics are emulated using a cage induction machine drive. The performance of the system has been tested over the whole speed range using wind profiles and power impacts. Experimental results are presented confirming the system performance.     

On-line designed hybrid controller with adaptive observer for variable-speed wind generation system

This paper presents a wind-driven induction generator system with a hybrid controller, which combines the advantages of the integral–proportional and the sliding mode controllers. The proposed controller is designed to adjust the turbine speed to extract maximum power from the wind. The integral–proportional speed controller can be designed on-line according to the estimated rotor parameters, and the observed disturbance torque is feed-forward to increase the robustness of the system. The designed integral switching surface with integral–proportional due to on-line tuning produced a new sliding surface to implement the control, and can ensure the robustness under noisy environment. The rotor inertia constant, friction constant, and the disturbed mechanical torque of the induction generator are estimated by a proposed adaptive observer, which is composed of the recursive least square algorithm and a torque observer.     

Comparative study of power converter topologies and control strategies for the harmonic performance of variable-speed wind turbine generator systems

Power converters play a vital role in the integration of wind power into the electrical grid. Variable-speed wind turbine generator systems have a considerable interest of application for grid connection at constant frequency. In this paper, comprehensive simulation studies are carried out with three power converter topologies: matrix, two-level and multilevel. A fractional-order control strategy is studied for the variable-speed operation of wind turbine generator systems. The studies are in order to compare power converter topologies and control strategies. The studies reveal that the multilevel converter and the proposed fractional-order control strategy enable an improvement in the power quality, in comparison with the other power converters using a classical integer-order control strategy.     

Probabilistic load flow with detailed wind generator models considering correlated wind generation and correlated loads

The enhancement in the penetration of intermittent generation necessitates the need to include uncertain behaviour in the conventional power flow programs. In this paper, four different wind generation models have been incorporated in probabilistic load flow for calculating the probability distribution of the reactive power consumed by the wind generators for three different scenarios; i) uncorrelated wind and uncorrelated loads ii) uncorrelated wind and correlated loads and iii) correlated wind and correlated loads The above mentioned scenarios have been implemented in probabilistic load flow using point estimate method in the IEEE-118 bus test system and accuracy of the results have been validated by comparing these results with those obtained by Monte Carlo simulation studies.     

Optimal design of linear switched reluctance motor for sea wave power generation

The switchless reluctance motor’s non-permanent magnet structure design ensures its high reliability in the marine environment; thus, it is a feasible solution for the generator of a sea wave power generation system. However, the corresponding thrust density and efficiency remain insufficient. This study focused on a new type of flat linear switched reluctance motor(LSRM), using the finite element software to establish a structural model, and optimized the design with the goal of improving the e...     

The impact of land use constraints in multi-objective energy-noise wind farm layout optimization

Recently the environmental impact of onshore wind farms is receiving major attention from both governments and wind farm designers. As land is more extensively exploited for wind farms, it is more likely for wind turbines to be in proximity with human dwellings, infrastructure (e.g. roads, transmission lines), and natural habitats (e.g. rivers, lakes, forests). This proximity makes significant portions of land unusable for the designers, introducing a set of land-use constraints. In this study, we conduct a constrained and continuous-variable multi-objective optimization that considers energy and noise as its objective functions, based on Jensen's wake model and the ISO-9613-2 noise standard. A stochastic evolutionary algorithm (NSGA-II) solves the optimization problem, while the land-use constraints are handled with static and dynamic penalty functions. Results of this study illustrate the effect of constraint severity and spatial distribution of unusable land on the trade-off between energy generation and noise production.     

A review of power converter topologies for wind generators

Wind energy conversion systems have become a focal point in the research of renewable energy sources. This is in no small part due to the rapid advances in the size of wind generators as well as the development of power electronics and their applicability in wind energy extraction. This paper provides a comprehensive review of past and present converter topologies applicable to permanent magnet generators, induction generators, synchronous generators and doubly fed induction generators. The many different generator–converter combinations are compared on the basis of topology, cost, efficiency, power consumption and control complexity. The features of each generator–converter configuration are considered in the context of wind turbine systems.     

Power regulation in pitch-controlled variable-speed WECS above rated wind speed

In medium to large scale wind energy conversion systems (WECS), the control of the pitch angle of the blades is an usual method for power regulation above rated wind speed. However, limitations of the pitch actuator have a marked influence on the regulation performance. In variable-speed mode, the control of the generator torque is able to reduce the effects of the pitch actuator limitations. Nevertheless, in this case the system is multiple-input multiple-output (MIMO) and then the control design results more complex. In this situation advance control techniques, such as optimal control, are an interesting option for a systematic controller design. This work analyzes variable-pitch power regulation above rated wind speed in the context of optimal control. The analysis is approached from a new point of view in order to establish a clear connection between the choice of the optimization criteria and the compromise between power regulation and pitch actuator limitations.     

Performance evaluation of pairing between sites and wind turbines

This paper presents a simple method for determination of pairing between sites and wind generators. It requires six parameters to describe the matching between turbine models and site characteristics, and the energy output performance can thus be easily estimated and used as the index of pairing effectiveness. To describe a Weibull model of wind speed distribution, the shape parameter and the scale parameter are necessarily required. Besides, four other parameters are chosen to specify the characteristics of the power curve of a wind generator: the cut-in speed, the rated speed, the cut-off speed and the nominal power. By combining these six parameters, the average power output of some particular wind turbine at a specific site can be practically and quickly approximated as a reference for turbine siting consideration. An example is also shown to demonstrate the utilization of the proposed method to choose between a group of wind sites and a list of commercial wind turbines.     

Effect of wind energy system performance on optimal renewable energy model-an analysis

The Optimal Renewable Energy Model (OREM) has been developed to determine the optimum level of renewable energy sources utilisation in India for the year 2020–21. The model aims at minimising costefficiency ratio and determines the optimum allocation of different renewable energy sources for various end-uses. The extent of social acceptance level, potential limit, demand and reliability will decide the renewable energy distribution pattern and are hence used as constraints in the model. In this paper, the performance and reliability of wind energy system and its effects on OREM model has been analysed. The demonstration windfarm (4 MW) which is situated in Muppandal, a village in the southern part of India, has been selected for the study. The windfarm has 20 wind turbine machines of 200 KW capacity. The average technical availability, real availability and capacity factor have been analysed from 1991 to 1995 and they are found to be 94.1%, 76.4% and 25.5% respectively. The reliability factor of wind energy system is found to be 0.5 at 10,000 hours. The OREM model is analysed considering the above said factors for wind energy system, solar energy system and biomass energy systems. The model selects wind energy for pumping end-use to an extent of 0.3153×10¹⁵ KJ.     

Model simplification and optimization of a passive wind turbine generator

In this paper, the design of a “low cost full passive structure” of wind turbine system without active electronic part (power and control) is investigated. The efficiency of such device can be obtained only if the design parameters are mutually adapted through an optimization design approach. For this purpose, sizing and simulating models are developed to characterize the behavior and the efficiency of the wind turbine system. A model simplification approach is presented, allowing the reduction of computational times and the investigation of multiple Pareto-optimal solutions with a multiobjective genetic algorithm. Results show that the optimized wind turbine configurations are capable of matching very closely the behavior of active wind turbine systems which operate at optimal wind powers by using a MPPT control device.     

Optimal placement of wind turbines in a wind park using Monte Carlo simulation

In the present study, a novel procedure is introduced for the optimal placement and arrangement of wind turbines in a wind park. In this approach a statistical and mathematical method is used, which is called ‘Monte Carlo simulation method’. The optimization is made by the mean of maximum energy production and minimum cost installation criteria. As a test case, a square site is subdivided into 100 square cells that can be possible turbine locations and as a result, the program presents us the optimal arrangement of the wind turbines in the wind park, based on the Monte Carlo simulation method. The results of this study are compared to the results of previous studies that handle the same issue.     

Review of 600–2500 kW sized wind turbines and optimization of hub height for maximum wind energy yield realization

The percent increase in energy production with corresponding increase in hub-height for wind energy conversion system (WECS) from different manufacturers was compared in this study. It was seen that an increase of 10 m in hub-height from 40 to 50 m resulted in an increase of 3.17% in energy production for wind turbines from Nordex, while a change of 3.48% from Vestas, and so on. The overall mean increase in energy production was found to be 2.92% while changing the hub-height from 40 to 50 m. Further increase of 10 m in hub-height from 50 to 60 m, showed an increase of 7.55%, 7.90%, 7.88%, 8.25%, 8.14% and 7.75% for WECS from Nordex, Vestas, DeWind, GE, Bonus and Enercon respectively. The overall mean increase in energy production was found to be 7.91% for this change of hub-height from 50 to 60 m. Similarly, an increase of 3.02% in energy production was obtained for an additional of 10 m increase in hub-height i.e. from 70 to 80 m. On the average the maximum increase in energy production of 7.91% was obtained while changing hub-height from 50 to 60 m.     

Transient analysis of variable-speed wind turbines at wind speed disturbances and a pitch control malfunction

As wind power generation undergoes rapid growth, new technical challenges emerge: dynamic stability and power quality. The influence of wind speed disturbances and a pitch control malfunction on the quality of the energy injected into the electric grid is studied for variable-speed wind turbines with different power-electronic converter topologies. Additionally, a new control strategy is proposed for the variable-speed operation of wind turbines with permanent magnet synchronous generators. The performance of disturbance attenuation and system robustness is ascertained. Simulation results are presented and conclusions are duly drawn.     

Developing the dual system of wind chiller integrated with wind generator

The successfully developed wind chiller in our CCT Lab. directly uses wind force to drive refrigeration system and hence reduces two times energy conversions between mechanical and electrical energies. The wind chiller needs high wind speed for its effective work due to the large working torque is required by the compressor. For the purpose of enlarging the applied wind field by the wind machine, this work aims to develop a dual system of wind chiller integrated with wind generator. The integrated wind generator can use the wind energy which cannot effectively drive the compressor. Therefore, the new developed dual system can apply larger range of the wind field and further increase the total working efficiency of the wind machine. A programmable logic controller (PLC) is applied in this wind forced dual system to select the wind chiller or the wind generator separately in terms of the rotational speed of the wind machine. In this work, the wind chiller is switched on while the accelerated rotational speed reaches 80 rpm and off while the decelerated rotational speed reaches 60 rpm. The integrated wind generator is switched on while the decelerated rotational speed reaches 60 rpm and off while the decelerated rotational speed reaches 40 rpm. The two apparatuses in the dual system always work separately. The results show that there is ca. 18.5% increment of effective working efficiency which is captured by the wind generator.     

Potential wind power generation in the State of Kuwait

The wind characteristics of six locations in the State of Kuwait have been assessed. The annual average wind speed for the considered sites ranged from 3.7 to 5.5 m/s and a mean wind power density from 80 to 167 W/m² at standard height of 10 m. The Weibull parameters and power density of each station have been determined using Weibull distribution. The wind data at heights 15, 20, 25 and 30 m were obtained by extrapolation of the 10 m data using the Power-Law. The potential wind energy at different heights was estimated using Weibull parameters. Maximum power density is found at 30 m height which varies between 130 and 275 W/m² with 70% increase from the standard height indicating fairly potential wind energy especially in the northern part of the country. The highest potential wind power was found during the summer season which is the peak demand season of electricity in Kuwait.     

Overview of worldwide wind generation

An summary of the growth in wind energy generation worldwide.     

Adaptive back-stepping control for a permanent magnet synchronous generator wind energy conversion system

The maximize energy captured from the wind of a grid-connected variable speed Wind Energy Conversion System (WECS) based on a Permanent Magnet Synchronous Generator (PMSG) is investigated in this paper. An adaptive back-stepping control scheme is applied to achieve maximum power point tracking in the coefficient of maximum power. The features of the proposed control scheme are that it deals with the random nature of wind speed, the uncertainties and external perturbations the acting on WECS effectively, where the bounds of the perturbations are not known in advance. At the same time, a proof of the convergence of the closed-loop system under the proposed controller is derived using the Lyapunov stability theory. Finally, simulations are conducted to illustrate the effectiveness of the proposed approach.     

Investigation of wind shear coefficients and their effect on electrical energy generation

Wind measurements are generally performed below wind turbine hub heights due to higher measurement and tower costs. In order to obtain the wind speed at the hub height of the turbine, the measurements are extrapolated, assuming that the wind shear is constant. This assumption may result in some critical errors between the estimated and actual energy outputs. In this paper wind data collected in Bal?kesir from October 2008 to September 2009, has been used to show the effects of wind shear coefficient on energy production. Results of the study showed that, the difference between wind energy production using extrapolated wind data and energy production using measured wind data at hub height may be up to 49.6%.