Variable Speed Wind Generation System Research Articles

Model Reference Adaptive System with Finite-Set for Encoderless Control of PMSGs in Micro-Grid Systems

In micro-grid systems, wind turbines are essential power generation sources. The direct-driven surface-mounted permanent-magnet synchronous generators (SMPMSGs) in variable-speed wind generation systems (VS-WGSs) are promising due to their high efficiency/power density and the avoidance of using a gearbox, i.e., regular maintenance and noise are averted. Usually, the main goal of the control system for SMPMSGs is to extract the maximum available power from the wind turbine. To do so, the rotor position/speed of the SMPMSG must be known. Those signals are obtained by the help of an incremental encoder or speed transducer. However, the system reliability is remarkably reduced due to the high failure rate of these mechanical sensors. To avoid this problem, this paper presents a model reference adaptive system with finite-set (MRAS-FS) observer for encoderless control of SMPMSGs in VS-WGSs. The motif of the presented MRAS-FS observer is taken from the direct-model predictive control (DMPC) principle, where a certain number of rotor position angles are utilized to estimate the stator flux of the SMPMSG. Subsequently, a new optimization criterion (also called quality or cost function) is formulated to select the best rotor position angle based on minimizing the error between the estimated and reference value of the stator flux. Accordingly, the traditional fixed-gain proportional-integral regulator generally employed in the classical MRAS observers is not needed. The proposed MRAS-FS observer is validated experimentally, and its estimation response has been compared with the conventional MRAS observer under different conditions. In addition to that, the robustness of the MRAS-FS observer is tested at mismatches in the parameters of the SMPMSG.

Salp swarm algorithm-based TS-FLCs for MPPT and fault ride-through capability enhancement of wind generators

This article presents an optimum design of Takagi–Sugeno fuzzy logic controllers (TS-FLCs) to enhance capability of fault ride-through (FRT) and the maximal power point tracking (MPPT) of the grid-tied wind farms. To obtain the optimum TS-FLCs, salp-swarm-algorithm (SSA) applied to minimize the sum of integral squared-error (ISE) function, where the variables of the cost function are the factors of Gaussian membership functions and the control rules of eight TS-FLCs. After that, the optimized TS-FLCs are applied to control the grid-tied variable-speed wind generator system, which is simulated using PSCAD/EMTDC. Thus, the transient and dynamic responses revealed that the optimum TS-FLCs have better stability margins than the optimum proportional–integral (PI) controllers. Furthermore, a realistic variable wind speed measured data are implemented to test the robustness of the MPPT based on the optimal TS-FLCs to extract more power than the MPPT based on optimal PI controllers.

Implementación del Algoritmo Sünter-Clare en un Convertidor Matricial 3x3

This paper presents the direct and easy way to implement digitally a Sünter-Clare modulation algorithm for a 7.5 KVA, three-wires, matrix converter. This modulation algorithm is used to calculate 3x3 matrix converter duty cycles to produce constant output voltage and frequency signals. The Sünter-Clare modulation algorithm recalculates switching patterns and switching times every sampling period in order to compensate the input voltage and frequency variations. This algorithm is defined in terms of the three-phase input and the output reference voltages at each sampling instant and is convenient for closed loop operations when the input voltage and frequency are variable in time as in the variable speed wind generation system. The experimental control setup is comprised of a field programmable gate array board, a digital signal processor and a graphics interface board.

PENERAPAN DOUBLY-FED INDUCTION GENERATOR (DFIG) UNTUK PEMBANGKIT LISTRIK TENAGA ANGIN

Wind energy has become one of the most important and promising sources of renewable energy, which demands additional transmission capacity and better means of maintaining system reliability. The evolution of technology related to wind systems industry leaded to the development of a generation of variable speed wind turbines that present many advantages compared to the fixed speed wind turbines. These wind energy conversion systems are connected to the grid through Voltage Source Converters (VSC) to make variable speed operation possible. The studied system here is a variable speed wind generation system based on Doubly Fed Induction Generator (DFIG). The rotor side converter (RSC) usually provides active and reactive power control of the machine while the grid-side converter (GSC) keeps the voltage of the DC-link constant. The additional freedom of reactive power generation by the GSC is usually not used due to the fact that it is more preferable to do so using the RSC. However, within the available current capacity the GSC can be controlled to participate in reactive power generation in steady state as well as during low voltage periods. The GSC can supply the required reactive current very quickly while the RSC passes the current through the machine resulting in a delay. Both converters can be temporarily overloaded, so the DFIG is able to provide a considerable contribution to grid voltage support during short circuit periods. This report deals with the introduction of DFIG, AC/DC/AC converter control and finally the SIMULINK/MATLAB simulation for isolated Induction generator as well as for grid connected Doubly Fed Induction Generator and corresponding results and waveforms are displayed.

Standalone micro grid power quality improvement using inertia and power reserves of the wind generation systems

This paper proposes two controllers for employing part of variable speed wind generation systems kinetic energy in supporting the standalone MG frequency. The first controller acts similar to the frequency droop control, while the second controller emulates both the inertia response and the frequency droop control simultaneously. The MG frequency dropped only to 49.9 Hz with employing the proposed controllers compared with 49.68 Hz without employing the proposed controllers. Also, the injected active power from the storage device dropped from 20 kW to only 3 kW after employing the proposed controllers. In addition, the reactive power capability of the Double Fed Induction Generator (DFIG) wind generation system has been employed to maintain the standalone MG bus voltage at acceptable level. If there are fixed speed wind generation systems in the standalone MG, this paper proposed using the pitch angle controller to employ a suitable wind turbine power reserve in MG frequency supporting during the standalone mode. Results proved the effectiveness of the proposed controllers in improvement the MG overall performance during and subsequent the islanding occurrence.

Approach for performance optimization of switched reluctance generator in variable-speed wind generation system

In this paper, algorithms are proposed to get optimal parameters of a switched reluctance generator (SRG) when applied in variable speed wind generation systems. The driver’s parameters affect power generated, torque ripples, iron losses, and electric losses. Therefore, the optimal values of the drive activation must be defined for SRG’s operation in a wide speed range. Thus, knowing the operating points of the wind turbine (speed and power), algorithms that perform dynamic simulations of the operation at low and high speed were developed. Driver’s parameters of the SRG are obtained through cost functions, which are defined such that the balance between torque ripples, iron losses, and electric losses are maintained. With simulations results, the cost functions were minimized to get SRG’s optimal firing angles according to the operating speed. Simulation and experimental tests were performed emulating a wind turbine system. The results confirmed the efficiency of the methodology proposed in this paper.

Voltage regulation of a stand-alone self-excited induction generator using STATCON with one cycle control technique for wind energy conversion system

ABSTRACTThis paper presents the simple voltage regulation scheme using a three-phase static VAr compensator (STATCON) for a stand-alone self-excited induction generator (SEIG) that uses variable-speed wind generation system. Most of the loads are inductive and need an equal amount of leading VArs, which is generated by the STATCON and injected at point of common coupling instantaneously. The one cycle control technique is considered and modified to implement for VAr compensation of SEIG voltage regulation. To emphasis the controller characteristics, a STATCON is designed for a 3-Ø, 0.75 kW, 415 V, 1.8 A Induction Machine and tested in simulation using MATLAB/SIMULINK software.

Comparison among series compensators for transient stability enhancement of doubly fed induction generator based variable speed wind turbines

This study investigates the effects of series compensators, such as the dynamic voltage restorer (DVR), series dynamic braking resistor, thyristor switched series capacitor, and the high temperature superconducting fault current limiter (SFCL), in enhancing the transient stability of a doubly fed induction machine based variable speed wind generator system. The tested system consists of a 9 MW doubly fed induction generator based wind farm connected to an infinite bus through two step-up transformers and a double run transmission lines. A three-phase-to-ground (3LG) fault and a single-line-to-ground fault (1LG) were applied to one of the lines to demonstrate the transient stability enhancement ability of the series devices. A performance comparison among the four series compensators is made based on responses of active/reactive power, terminal voltage, rotor speed, dc link voltage, and current variations. Simulations were carried out in the MATLAB/Simulink environment. Simulation results show that all series devices can improve the transient stability, however, the SFCL is the most efficient in terms of active power, rotor speed stability and fault current suppression, and the DVR seems to have a better performance than the SFCL in terms of voltage and reactive power.

Optimal Control of an Autonomous Variable-speed Wind Generation System Based on a Bacterial Foraging Optimization Technique

—A developed control strategy for an isolated wind generation unit is presented. The proposed system mainly consists of an induction generator driven by a wind turbine, synchronous machine, consumer load, discrete dump load, and gate turn-off thyristor based power electronics converter. Two control loops are used in this study. The first regulates the load bus voltage based on the excitation control of the synchronous machine. The second simultaneously controls the dump load to absorb excessive power generation, in turn regulating the frequency of the proposed power system. Two optimization techniques based on the bacterial foraging algorithm and genetic algorithm are used to tune the proposed control parameters. The proposed system is tested for turbulent change in wind speed and step change in consumer load. The complete system is modeled and simulated using a MATLAB/Simulink software package (The MathWorks, Natick, Massachusetts, USA). The performance of the optimized control system is compared with the conventional proportional-integral-derivative control system. The simulation results show that the optimized control system has good performance, with less settling time and less overshoot compared to the case of a conventional proportional-integral-derivative controller.

Full-Scale Modeling, Control, and Analysis of Grid-Connected Wind Turbine Induction Generators With Back-to-Back AC/DC/AC Converters

A model-based dynamic analysis of a variable-speed wind generator system consisting of an induction generator connected to the grid through a full power frequency converter is conducted. To this end, a nonlinear modeling of the entire system is used in a manner that permits a novel controller design with common structure for both the generator- and grid-side converters. The proposed controller, acting directly on the duty-ratio inputs of the converters, ensures the boundedness of the duty-ratio signals in the permitted range although its structure is independent from the system parameters and open to different control objectives. Therefore, maximum power point tracking and power factor correction are easily implemented. Furthermore, the controller is proven to guarantee stability of the whole system under field- or near-field-oriented conditions without needing any flux measurement or estimation. Hence, the main contribution established by this approach is that a rigorous stability analysis taking into account the generator, converters, dc link, and controller dynamics is presented on the basis of a complete system modeling and controller design approach. The theoretical analysis and controller effectiveness are confirmed via extended simulation results for a commercial size 2-MW induction generator operating under varied wind speed conditions and are further validated on a similar system with real-time results.

Optimal control for variable-speed wind generation systems using General Regression Neural Network

An induction generator (IG) speed drive with the application of an optimal controller and a proposed General Regression Neural Network (GRNN) controller is introduced in this paper. Grid connected wind energy conversion system (WECS) present interesting control demands, due to the intrinsic nonlinear characteristic of wind mills and electric generators. The GRNN with adaptive ant colony optimization (AACO) torque compensation is feed-forward to increase the robustness of the wind driven induction generator system. An optimal control loop for the wind power system is designed. The optimality of the whole system is defined in relation with the trade-off between the wind energy conversion maximization and the minimization of the induction generator torque variation that is responsible for the frequency fluctuations. This is achieved by using a combined optimization criterion, resulting in a LQ tracking problem with an infinite horizon and a measurable exogenous variable (wind speed). The proposed controller is designed to drive the turbine speed to extract maximum power from the wind and adjust to the power regulation.

A Variable Speed Wind Generation System Based on Doubly Fed Induction Generator

Wind energy has become one of the most important and promising sources of renewable energy, which demands additional transmission capacity and better means of maintaining system reliability. The evolution of technology related to wind systems industry leaded to the development of a generation of variable speed wind turbines that present many advantages compared to the fixed speed wind turbines. These wind energy conversion systems are connected to the grid through Voltage Source Converters (VSC) to make variable speed operation possible. The studied system here is a variable speed wind generation system based on Doubly Fed Induction Generator (DFIG). The rotor side converter (RSC) usually provides active and reactive power control of the machine while the grid-side converter (GSC) keeps the voltage of the DC-link constant. The additional freedom of reactive power generation by the GSC is usually not used due to the fact that it is more preferable to do so using the RSC. However, within the available current capacity the GSC can be controlled to participate in reactive power generation in steady state as well as during low voltage periods. The GSC can supply the required reactive current very quickly while the RSC passes the current through the machine resulting in a delay. Both converters can be temporarily overloaded, so the DFIG is able to provide a considerable contribution to grid voltage support during short circuit periods. This report deals with the introduction of DFIG,AC/DC/AC converter control and finally the SIMULINK/MATLAB simulation for isolated Induction generator as well as for grid connected Doubly Fed Induction Generator and corresponding results and waveforms are displayed.

Sliding mode control-based active power control for wind farm with variable speed wind generation system

Active power control in wind farm, implemented with hierarchical structure (including the central wind farm active power control system and the control system of variable speed wind generation system), has significantly improved the wind-farm-generated power. However, the interaction between the control system of variable speed wind generation system and the central wind farm active power control system has not been considered in the control system design of both sides. The wind generation system with active power control in wind farm, as a high-order nonlinear large-scale system, will not only autonomous operating with maximum power capture, but also being demanded to regulate power output according to the power set points ordered by the central wind farm active power control system. Therefore, robust active power control of wind farm is clearly necessary. In this article, sliding mode is used to design the active power control system for wind farm, which makes the output power of wind farm track the active power order from the power grid operator asymptotically. Particularly, the control system of the variable speed wind generation system is designed with cascaded structure: the input of the internal rotational speed control loop of the wind generation system is controlled by the external power loop which tracks the specified power set point. Then, based on the dynamic model of wind farm, the central wind farm active power control system is designed to control the total output power of wind farm by using the sliding mode control method. Furthermore, in order to ensure the given power set point is within the regulation capability of the wind generation system, the proportional distribution strategy is utilized to specify the power set point according to the available output power of each wind generation system, which is quantified by ultra-short term power prediction model. The proposed approach is illustrated by implementing it to the active power control of a wind-farm model in simulation. The simulation results demonstrate that the proposed method outperforms the method based on proportional-integral control.

Modeling and Control of Wind Power Conversion System With a Flywheel Energy Storage System and Compensation of Reactive Power

In this paper, a control of a variable speed wind generator (VSWG) system based on a doubly fed induction machine connected to the network associated to a flywheel energy storage system (FESS) is considered. The maximum power point tracking (MPPT) method, the independent control power of generator, the grid connection, and the control of flywheel energy storage system are studied. The flywheel energy storage system consists of a power electronic converter supplying a squirrel-cage induction machine coupled to a flywheel. This study investigates also, the possibility to compensate the reactive power. In order to validate the control method and to show the performances of the proposed system, its model is simulated for different operating points.

Synchronization of DFIG output voltage to utility grid in wind power system

This paper presents a new synchronization algorithm for grid connection of a doubly fed induction generator (DFIG) in a variable speed wind generation system. Stator flux-oriented vector control for back-to-back PWM converters in the DFIG rotor circuit is used for synchronization process. By controlling the rotor d-axis current, the magnitude of the stator EMF is adjusted to be equal to the grid voltage. PLL circuit is used to compensate for the phase shift between the stator EMF and the grid voltage. By controlling the turbine pitch angle, the generator speed is determined to adjust the stator frequency to be equal to the grid. The experimental results show a smooth synchronization and fast dynamic responses. Compared to the existing DFIG synchronization algorithms, the proposed method gives fast starting and can take only 2 cycles to be performed and has satisfactory performance and better robustness than existing methods.

Modeling and application of permanent magnet synchronous generator (PMSG) based variable speed wind generation system

n the early development of wind energy, the majority of wind turbines were operated at constant speed. Recently, the number of variable-speed wind turbines installed in wind farms has increased and more wind turbine manufacturers are making variable-speed wind turbines. In this paper, maximum power control of wind turbine and permanent magnet synchronous generator connected with two back to back voltage source converters to grid are studied. Machine currents are controlled by indirect vector control method. In this method, generator side converter controls the maximum excitation (air gap flux) by machine's d-axis current and controls generator torque by machine's q-axis current. Permanent magnet synchronous generator (PMSG) speed is controlled by tip speed ratio upon the wind speed variations to generate the maximum output power. Grid side converter regulates the DC link voltage and injective active power by d-axis current and regulates the injective reactive power by q-axis current using simple control method P-Q. Simulation results depict that the proposed method operates properly. Key words: Wind turbine, permanent magnet synchronous generator, maximum power control, superconductive inductor.

Fault ride-through capability enhancement of doubly-fed induction wind generators

Recent fault ride-through (FRT) requirements have proven problematic for variable-speed wind generation systems. A particular problem regarding to doubly-fed induction generators (DFIGs) is that standard proportional integral (PI) current controllers, designed with very limited control bandwidth, cannot eliminate rotor current oscillations that occur during a grid fault. As a consequence, the current in the rotor-side converter can exceed the safety limits of semiconductor switches, which potentially leads to converter failure. This study introduces a hybrid current controller to enhance the FRT capability of DFIGs through keeping the rotor current below the safety limits. The proposed current controller includes two switching strategies: the standard PI current controller for normal operating conditions and a vector-based hysteresis current controller (with very fast transient response) for overcurrent protection during grid faults. Simulation studies are carried out to demonstrate the effectiveness of the proposed hybrid current controller under various symmetrical and asymmetrical voltage sag conditions.

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

Abstract 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.

Designing optimal controllers for doubly fed induction generators using a genetic algorithm

This work presents a design procedure based on evolutionary computation, more specifically on a genetic algorithm combined with the formal pole placement project, to obtain optimal controllers to the rotor-side converter of doubly fed induction generators (DFIGs), in variable-speed wind generation systems connected to the electrical grid. With this procedure it is intended to improve the global system dynamic behaviour during and after the fault period, also increasing the transient stability margin of the power system and the fault ride-through capability. The control action of the DFIG converters is accomplished by proportional and integral controllers, whose gains' adjustment is not a trivial task, because of the high complexity of the system. The results obtained confirm the efficiency of the proposed control design procedure.

Variable Speed Wind Power Generation System Using Direct Torque Control Suited for Maximum Power Control within Voltage and Current Limitations of Converter

This paper proposes a variable speed wind generation system using a direct torque controlled interior permanent magnet synchronous generator. The proposed system has no wind speed and generator position sensors, and thus, it is considered that the proposed system has cost and reliability advantages. The proposed direct torque control (DTC) system in wind power generation has several advantages over conventional current control. First, DTC is well suited for the maximum power point tracking (MPPT) control that is implemented by controlling the generator torque. Second, the method of flux-weakening to maintain the terminal voltage at the limiting value of the converter is simple. Finally, a novel method is proposed for torque limiting, which makes it easy to maintain the armature current at the limiting value. The proposed method accomplishes current limiting using the reactive torque, which is calculated as the inner product of the flux and current. This does not require generator parameters such as magnet flux and inductances. Experimental results demonstrate the effectiveness of the proposed system using a wind turbine emulator instead of the actual wind turbine.