Stand-alone Wind Energy Conversion System Research Articles

Hybrid Wind–Battery System for a Stand-Alone Wind Energy Conversion System

Hybrid Wind–Battery System for a Stand-Alone Wind Energy Conversion System

Design and Development of a Wind Turbine Emulator for Analyzing the Performance of Stand-alone Wind Energy Conversion System

<p>This paper describes the design and development of a Wind Turbine Emulator (WTE), which can be used to analyze and assess the performance of Wind Energy Conversion System (WECS). The mathematical modeling of the WTE has been done using MATLAB/Simulink platform. A separately excited DC motor is deployed in order to reproduce the speed/torque, replacing the real wind turbine rotor. The half-bridge DC-DC power converter is developed to run the DC motor in a controlled fashion. Two PI controllers viz speed and current controller are employed which guarantee that the DC motor is following the theoretical (reference) rotational speed of the turbine rotor. A user interface is created in ControlDesk Next Generation, through which the input parameters of the WTE can be altered in real time and the instantaneous effect can be observed by analyzing the output parameters. The designed system offers wide range flexibility and provides a friendly environment in which wind speed and turbine parameters can be altered easily. Hence, offering user to conduct research on variable wind speeds. The DS1104 R&D controller board is employed for implementation of the developed Simulink model. The system design, the model used, and obtained results are presented in this paper. </p>

Intelligent Neural Network-Based Controller for Single-Phase Wind Energy Conversion System Using Two Winding Self-Excited Induction Generator

This paper deals with a single-phase standalone wind energy conversion system using a two winding self-excited induction generator (SEIG). The proposed controller consists of a two leg voltage source converter (VSC) and a battery energy storage system (BESS) connected at its dc bus. The VSC-BESS system is controlled using an intelligent neural network-based control (INNBC) algorithm with a dynamic learning rate, depending upon the rate of change of load current to achieve an excellent dynamic as well as steady-state response of the system. The proposed control algorithm is implemented in real time using a digital signal processor. Simulated and experimental steady state and dynamic performances of proposed SEIG are presented with the proposed controller using the INNBC algorithm. The system voltage and frequency are maintained constant in all types of steady-state and dynamic loading conditions.

Static Voltage and Frequency Regulation of Standalone Wind Energy Conversion System

Background/Objective: This paper presents regulation of Self Excited Induction Generator (SEIG) as asynchronous generator in standalone mode for wind energy conversion system (WECS). Methods/Statistical Analysis: The proposed controller consists of Voltage Source Converter (VSC) having bidirectional active & reactive power flow control, integrated with Battery Storage Unit (BSU), connected in shunt. It compensates for variable reactive power with variable active power. Rating of induction machine has been obtained by short circuit test, open circuit test and synchronous speed test. Findings: SEIG have relative advantage over conventional synchronous generator. However, vo1ltage and frequency regulation are among prime challenges in its practical application as standalone generator. Voltage and frequency of SEIG depends upon speed of rotor, shunt capacitor and load. A suitable control scheme needs to be developed to ensure minimum variation in voltage and frequency for variable input and electrical load. Voltage regulation has been achieved by adjusting reactive power provided by static compensator consisting of inductor a VSC and dc bus capacitor. Conclusion/Improvement: The simulation results show that voltage and frequency of SEIG-WECS have negligible variation for resistive, reactive, balanced, unbalanced and nonlinear load under varying wind speed and consumer load. It eliminates harmonic contents and balances the connected electrical load.

Experimental Implementation of Doubly Fed Induction Generator-Based Standalone Wind Energy Conversion System

This paper presents the advantages of integrating battery energy storage system (BESS) with doubly fed induction generator (DFIG)-based standalone wind energy conversion system (SWECS). A comparison between DFIG-based SWECS with and without BESS is presented in this paper. Control strategies for both rotor-side converter (RSC) and load-side converter (LSC) are presented for regulating voltage and frequency for variable-speed DFIG-based SWECS. By integrating BESS, this proposed standalone DFIG is able to extract maximum power. A prototype of this DFIG-based SWECS is developed using a digital signal processor (DSP)-dSPACE-DS1103. This standalone DFIG is tested under nonlinear and dynamic loads in both the cases. Dynamic performance of proposed standalone DFIG is also verified for variable wind speeds.

Direct Voltage Control of Dual-Stator Brushless Doubly Fed Induction Generator for Stand-Alone Wind Energy Conversion Systems

This paper presents a dual-stator brushless doubly fed induction generator-based stand-alone wind energy conversion system (DSBDFIG-SA-WECS). With the advantages of compact structure, high reliability, and low cost, the DSBDFIG-SA-WECS shows great potential in wind energy applications. Based on the traditional stator-flux-oriented control (SFOC), an improved direct voltage control (DVC) is proposed for stand-alone operation. Performance analysis is carried out to evaluate SFOC and DVC in the aspects of control objects, orientation, feedback, and parameters involved. The DVC method is simple, robust, and cost-effective with the outer stator current sensors eliminated, and there are no extra parameters involved that the control performance can be enhanced. Fair comparisons are made in simulation to demonstrate better performance of the proposed DVC, and the effectiveness of DVC is further validated by experiment under variable speed condition.

Terminal voltage build-up and control of a DFIG based stand-alone wind energy conversion system

The paper presents the voltage build-up process and the terminal voltage control of a doubly-fed induction generator (DFIG) driven by a pitch controlled wind turbine for the supply of autonomous system without any auxiliary source. A control strategy for the complete system including voltage build-up phase is developed with a view to provide as well as possible the required power for load. Indirect stator flux-oriented vector control is proposed to keep the stator voltage constant by means of a back-to-back converter connected to the rotor side, while the management system is supported by the pitch angle and the load shedding controllers. A novel scheme for voltage build-up is presented, which requires no additional hardware support, and physical interpretation of how self-excitation can occur from residual magnetism in the machine core is examined. A reliable start-up process is accomplished by using an appropriate voltage reference ramp which enables minimizing energy loss during the starting. The proposed system is modeled and simulated using Matlab/Simulink software program to examine the dynamic characteristics of the system with proposed control strategy. Dynamic simulation results for different transient conditions demonstrate the effectiveness of the proposed control strategy.

Modeling and control of a permanent magnet synchronous generator dedicated to standalone wind energy conversion system

The interest for the use of renewable energies has increased, because of the increasing concerns of the environmental problems. Among renewable energies, wind energy is now widely used. Wind turbines based on an asynchronous generator with a wound rotor present the inconvenience of requiring a system of rings and brooms and a multiplier, inferring significant costs of maintenance. To limit these inconveniences, certain manufacturers developed wind turbines based on synchronous machines with large number of pairs of poles coupled directly with the turbine, avoiding using the multiplier. If the generator is equipped with permanent magnets, the system of rings and brooms is eliminated. The control of the permanent magnet synchronous generator (PMSG) can be affected with the implementation of various techniques of control. This paper presented a new approach mainly based on the control strategy of power production system based on the PMSG. In fact, a mathematical model that simulates the Matlab chain was established with the introduction of control techniques, such as direct control of the torque (DTC) to control the load side converter (LSC), the control of the speed of the turbine and the DC-bus voltage ensured by PI regulators. To show the performance of the correctors used, some simulation results of the system were presented and analyzed.

Performance Evaluation of Fixed-speed and Variable-speed Stand-alone Wind Energy Conversion Systems

This article deals with the performance evaluation of fixed-speed and variable-speed stand-alone wind energy conversion systems using an isolated asynchronous generator. A voltage and frequency controller for an isolated asynchronous generator based variable-speed stand-alone wind energy conversion system is investigated using two back-to-back connected voltage source converters and a battery energy storage system. A three-leg insulated-gate bipolar transistor based voltage source converter is used at the machine side for variable-voltage–variable-frequency energy conversion, and a four-leg insulated-gate bipolar transistor based voltage source converter is used between the load terminals and intermediate DC link for feeding regulated voltage and frequency supply. A voltage and frequency controller for an isolated asynchronous generator based fixed-speed stand-alone wind energy conversion system is also designed and modeled using a four-leg voltage source converter and battery energy storage system. A detailed performance evaluation is made between fixed-speed and variable-speed stand-alone wind energy conversion systems using wind data obtained for Jakhau (Gujarat) situated in India.

Improved control scheme of stand-alone DFIG-based wind energy conversion system with battery energy storage system

An improved control scheme for stand-alone DFIG-based wind energy conversion system is proposed. The intermediate DC-link of back-to-back PWM converter is supported with a battery energy storage system to smooth the fluctuation of power caused by the variation of wind speed and loads. A three-phase four-leg converter is employed as the Stator-Side Converter (SSC) to provide a path for the zero-sequence current. Based on the modified topology, the stator voltage of DFIG is directly controlled by the SSC. And the rotor speed of DFIG is regulated by the rotor-side converter for maximum power point tracking. Modified repetitive controllers incorporated with the state-feedback controllers are adopted for the SSC to ensure the desirable stator voltage even under the unbalanced loads or non-linear loads conditions. The proposal avoids the complicated operation of the harmonic extraction, and the positive- and negative-sequence current decomposition, which is verified by the simulation results.

Improved control scheme of stand-alone DFIG-based wind energy conversion system with battery energy storage system

Improved control scheme of stand-alone DFIG-based wind energy conversion system with battery energy storage system

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.

Load Voltage and Frequency Regulation in PMSG based Standalone Wind Energy Conversion System

Stand alone variable speed wind energy conversion system with PMSG is proposed in this paper. Two back to back VSCs are connected to interface PMSG with load. Constant voltage in DC link between two VSCs can be maintained constant by using a battery energy storage system (BESS). BESS is efficient to maintain load voltage and frequency to be regulated during variable wind speed conditions. MPPT based vector controlling is used to control generator side converter to maintain unity power factor at PMSG which improves generated power and efficiency. Load side converter is controlled to maintain regulated voltage and frequency at load side. Simulations are performed using MATLAB/SIMULINK to check effectiveness of control strategies. Performance is checked with increase in wind speed; decrease in wind speed and with unbalanced/non linear loads.

A new synchronous generator based wind energy conversion system feeding an isolated load through variable frequency transformer

This paper aims to explore the possibility of synchronous generator (SG) based wind energy generation system feeding an isolated load using a latest power transmission technology i.e. variable frequency transformer (VFT). The proposed configuration does not employ any power electronics based interface as in conventional SG based stand-alone wind energy conversion systems (SWECS). For analysis, the simulation models of proposed configuration as well as conventional configuration have been developed under MATLAB-Simulink environment. A series of studies on power fed from the SG to the different loads at various SG input speeds has been carried out with the developed models. Further to analyze the effectiveness of the proposed method; the efficiency, total harmonic distortion (THD) of output voltage and THD of output current of the proposed method have been compared with those of the conventional method. From obtained results, it is observed that the proposed method is simple and does not produce harmonics. Moreover to validate the proposed scheme, an experimental analysis has been carried out. Further, the cost analysis of both systems has also been carried out. From the cost analysis, it is observed that the proposed system is cheaper than the conventional system.

Comparison of PV Supported DVR and DSTATCOM with Multiple Feeders in Stand Alone WECS by Mitigating Power Quality Problems

In this paper standalone WECS (Wind Energy Conversion System) is taken in which PV supported DVR (Dynamic Voltage Restorer) or D-STATCOM (Distribution Static Synchronous Compensation) is connected to mitigate power quality problems such as voltage sag, swell, unbalance and harmonics, which are created by both source and as well as due to other feeders disturbances. DFIG (Doubly Fed Induction Generator) is used as a generator to generate three phase supply from the wind source to the load. PV (Photo Voltaic) is used as a DC source for the VSI (Voltage Source Inverter). SRFT (Synchronous Reference Frame Theory) is used for the generating reference voltages. HC (Hysteresis controller) is used to generate pulse signal for the VSI of DVR or D-STATCOM. These voltages, when injected in line by a series or shunt transformer can regulate the voltage at the load terminals against any power quality problems. Thus the protection of the loads can be achieved economically using the DVR or D-STATCOM. Simulation results are carried out by MATLAB/Simulink to verify the performance of the proposed method.

Voltage and frequency controllers for standalone wind energy conversion systems

This study presents the design, development and comprehensive analysis of voltage and frequency controllers (VFCs) for standalone wind energy conversion systems (SWECSs). An isolated asynchronous generator, a synchronous generator (SG) and a permanent magnet SG are used with these SWECSs. These VFCs are developed with three-phase generators driven through a wind turbine to feed three-phase and single-phase loads. A battery energy storage system is used invariably with each system configuration to facilitate load leveling under change in wind speeds and consumer loads. The performance of VFCs are demonstrated to validate its operation as a load leveler, load balancer, phase balancer, neutral current compensator and an active filter along with a VFC.

Asynchronous Generator With Battery Storage for Standalone Wind Energy Conversion System

This paper deals with the implementation of a voltage and frequency controller (VFC) for an isolated asynchronous generator (IAG)-based stand-alone wind energy conversion system (SWECS) with a battery energy storage system (BESS) feeding three-phase four-wire loads. The control algorithm for VFC is based on a low-pass filter (LPF) for estimation of reference source currents. The VFC is realized using a voltage source converter (VSC) with a BESS at its dc bus and a nonisolated T-connected transformer to feed three-phase four-wire consumer loads. Test results are presented to demonstrate the performance of a proposed VFC for an IAG in the wind power generation.

Wind Energy Conversion System for Rural Application

This paper presents the use of induction generator with suitable control strategy for use as standalone wind energy conversion system. This may find application in remote rural areas where extension of 11 kV feeder may not be feasible due to physical terrain and where drawing of line may not be economically viable if loads are dispersed over wide area. This Induction machine is driven from a prim em over which is usually a wind turbine. The stator terminals of the induction machine is connected to a voltage source converter. The voltage source converter (VSC) is a three level diode clamped VSC. The terminals of the converter are connected to a capacitor and a battery. The battery is initially charged to 12 V and provides initial magnetisation for the Induction Generator. The terminals of the stator are also connected to an induction motor represented by RL load. Control strategy has been developed to keep the DC voltage constant irrespective of variation of load and rotor speeds. The total harmonic distortion in the line voltage of the induction machine is ensured to be within limits by employing three level converter. The proposed system is mathematically modelled using SIMULINK/MATLAB. The simulated results validate the theory studied.

Real-time replication of a stand-alone wind energy conversion system: Error analysis

This paper provides adequate information about the problem of real-time replicating in laboratory conditions. The dynamic behavior of stand-alone low-power wind energy conversion systems (WECS) in response to the wind speed variations and also to the electrical load variations is replicated. The investigated system consists of a variable-speed wind turbine based on a permanent-magnet synchronous generator (PMSG), a diode bridge rectifier, a DC–DC step-down converter and a wide range DC load. Because of reduced noise level and better steady-state accuracy, a speed-driven hardware-in-the-loop physical WECS simulator has been used to accomplish this task. Its significant drawback – that is, a reduced bandwidth – has been significantly alleviated by using an enhanced software simulator structure which uses a feed-forward compensation of the inherent physical disturbance produced by the generator torque variations. Both time-domain experimental results and a thorough frequency-domain error analysis show good replication performance in the frequency range of variation of both wind speed and electrical load.

Nonlinear Modeling and Simulation of a Four-phase Switched Reluctance Generator for Wind Energy Applications

Abstrac t—Thesubject of this paper is a modeling method of switched reluctance generator (SRG) based on the nonlinear inductance model and electromagnetic field finite element analysis (FEA) to be used in wind energy applications. SRG and its behavior, modeling and Simulations results are presented. It was analyzed the characteristics of the SRG under different conditions. The nonlinear inductance model allows us to develop a control strategy that gives high performance controller with a closed loop was designed on PI controller. I. INTRODUCT ION The rapid depletion of fossil fuels has necessitated the need for the utilization of non-conventional energy sources. Among these renewable energies widely used around the world in the last years, wind energy conversion system seems to be very interesting, it is clean energy source suitable for rural areas and the stand alone wind energy conversion system in rural areas must be characterized by economic and maintenance free operation. Doubly fed induction generator (DFIG) suffers from limited rotor converter rating and has problems with over currents during voltage dips and the multistage gearbox that the DFIG must incorporate is unreliable and expensive. The direct coupled variable speed generators for these systems obviate the need for gear box which is the most unreliable and maintenance intensive component in the system. Permanent Magnet Synchronous Generator or Field Wound Synchronous Generator in standalone wind energy conversion systems eliminate the unreliability associated with gear box drive trains through direct coupled variable speed operation and even though permanent magnet machines will have a better torque density than the field wound version, the presence of permanent magnets will make assembly more difficult (1). In the Field Wound Synchronous Generator, the brushes required to excite the field winding demand maintenance at regular intervals. The variable speed direct drive synchronous generator shortfalls fr om cost, size, weight, energy yield and requirement of a converter. Although Permanent magnet generators exhibit low losses, lower weight, better torque density and perhaps low cost with the disadvantage that the excitation cannot be controlled while axial flux permanent magnet generators are heavier and more expensive than radial flux counterparts. To overcome the beyond mentioned obstacles Switched Reluctance Generator (SRG) is being considered as the generator of choice in standalone wind energy conversion