Variable Speed Doubly-fed Induction Generator Research Articles

Improved Hydroturbine Control and Future Prospects of Variable Speed Hydropower Plant

Hydroturbine control system (HTCS) is a nonlinear, nonminimum phase system comprising of speed/frequency sensors, hydraulic servo motors, wicket gates, gate position feedback mechanism, and proportional integral derivative (PID) controller (governor). Governor controls the guide vane opening (GVO) corresponding to the input (speed/frequency). Nowadays, HTCS becomes more intricate insight of variable speed doubly-fed induction generator for compensating wide variation in water head. Hence, robust control techniques are necessary for the optimal utilization of hydropower potential. In this article, a brief review of HTCS is given and a complimentary sliding-mode controller (CSMC) is designed for GVO serving a 250 MW hydrogenerating unit. The CSMC control law is derived and the stability is verified through the Lyapunov function. Simulation is carried out through the MatLab Simulink environment for a 250 MW HTCS. Then, the performance of CSMC for GVO and its influence on the generator characteristics are analyzed and compared with the traditional PID controller. The simulation results demonstrate the efficacy of the controller during the startup process, subsynchronous, and super synchronous mode of operations. It is inferred that the proposed CSMC has three times faster settling time than that of the traditional PID controller. Experimental validation is carried out with a scaled-down laboratory prototype. Furthermore, future scope and design challenges associated with the hydropower control system are illustrated.

Power fuzzy adaptive control for wind turbine

In recent years, wind energy has become one of the most promising renewable energy sources. The doubly-fed induction generator (DFIG) is currently the most common type of generator used in wind farms. This paper describes an approach for the independent control of the active and reactive power of the variable-speed DFIG. This paper deals with the control of the active and reactive powers in a DFIG designed for a wind system. The simulation model including a 7 KW - DFIG driven by a wind turbine, a PWM inverter and the proposed control strategy are developed and implemented using Matlab Simulink.

Modeling, simulation and control of a doubly-fed induction generator for wind energy conversion systems

In recent years, wind energy has become one of the most promising renewable energy sources. Various wind turbine concepts with different generator topologies have been developed to convert this abundant energy into electric power. The doubly-fed induction generator (DFIG) is currently the most common type of generator used in wind farms. Usually the DFIG generator is a wound rotor induction machine, where the stator circuit is directly connected to grid while the rotor’s winding is connected to the grid via a three-phase converter. This paper describes an approach for the independent control of the active and reactive powers of the variable-speed DFIG. The simulation model including a 1.5 MW-DFIG driven by a wind turbine, a PWM back-to-back inverter and the proposed control strategy are developed and implemented using MATLAB/Simulink/SimPowerSystems environment.

Stability Enhancement of Small-Scale Power Grid with Renewable Power Sources by Variable Speed Diesel Power Plant*

This paper proposes a power control method to improve a stability of a small-scale power grid with renewable energy sources. In an isolated small- scale power grid such as an island, diesel power plant is main power source which has an environmental burden and expensive running cost due to high priced fossil fuel. Thus, expanding installation of the renewable energy sources such as a wind power is strongly desirable. Such fluctuating energy sources, however, harm power quality of the small-scale power grid, and in addition, conventional power plant in the small-scale power grid cannot, in general, stabilize the grid system with such fluctuating power sources. In this study, Variable Speed Doubly-Fed Induction Generator (VS-DFIG) is proposed to be in-stalled at a diesel power plant instead of a conventional Fixed Speed Synchronous Generator (FS-SG), because quick control of a power balance in the small-scale power grid can be achieved by using the inertial energy of VS-DFIG. In addition, utilization of a Battery Energy Storage System (BESS) is also considered to assist cooperatively the VS-DFIG control. As a result of the simulation analysis by using the proposed method, it is verified that frequency fluctuations due to renewable energy source can be effectively reduced by quick power control of the VS-DFIG compared to the conventional FS-SG, and further control ability can be obtained by utilizing BESS. Moreover, the transient stability of a small-scale power grid during a grid fault can also be enhanced.

Direct torque control improvement of a variable speed DFIG based on a fuzzy inference system

In this paper, a fuzzy direct torque control (DTC) for a variable speed doubly fed induction generator (DFIG) based wind turbine is investigated. The DTC has been widely applied to doubly fed induction machines in recent years due to the high performances that it provides in comparison with the classical field oriented control. Meanwhile, it has a major drawback that is the significant torque and flux undulations generated by the hysteresis band controllers. To overcome this problem, the improvement of this technique by removing these controllers is proposed in this paper. The proposed control technique is based on replacing the hysteresis controllers by a fuzzy inference system which will have the same inputs as these controllers plus the sector angle determination so that the look-up table can be replaced by a fuzzy rule-base matrix. The simulation was performed in MATLAB/SIMULINK, and the results obtained make it possible to evaluate the performance of the proposed technique over the classical one.

Modeling of Wind Power Plant with Doubly-Fed Induction Generato

This paper presents the modeling and simulation of wind turbine driven by doubly-fed induction generator which feeds ac power to the distribution network. A stator flux oriented vector control is used for the variable speed doubly-fed induction generator operation. By controlling the generator excitation current the amplitude of the stator EMF is adjusted equal to the amplitude of the grid voltage. To set the generator frequency equal to the grid one, the turbine pitch angle controller accelerates the turbine/generator until it reaches the synchronous speed. The system is modeled and simulated in the Matlab Simulink environment in such a way that it can be suited for modeling of all types of induction generator configurations. The model makes use of rotor reference frame using dynamic vector approach for machine model. The system is also simulated when a fault occurs in 25 kV grid of distribution system. The results of a single line to ground fault and a symmetrical three-phase ground fault is analyzed. The results show that the wind energy conversion system can normally operate in fault conditions.

A New Robust Decoupled Control of the Stator Active and Reactive Currents for Grid-Connected Doubly-Fed Induction Generators

This paper addresses the grid-connected variable speed doubly-fed induction generator, and proposes a new decoupled control to replace the conventional decoupled active and reactive powers (P-Q) control. The proposed decoupled control is based on decoupling the stator active and reactive currents, in contrast with the conventional decoupled P-Q control, which is based on decoupling the stator active and reactive powers by forcing the stator d- or q-voltage to zero. The proposed decoupled control has all the advantages of the conventional decoupled P-Q control such as constant switching frequency and robustness against slip angle inaccuracy, and it has some additional advantages: The proposed control requires less machine parameters; for the controller design, it requires the stator-to-rotor turns ratio only; for the online calculation, it does not requires any machine parameter. The proposed decoupled control is more flexible and robust since the control is independent of the grid voltage orientation. It is robust against variation in the grid voltage amplitude. Several experiments are carried out using a 1.1 kW doubly-fed induction generator (DFIG), and the results support the proposed decoupled control and demonstrate some of its advantages.

Voltage stability enhancement using an adaptive hysteresis controlled variable speed wind turbine driven EESG with MPPT

This paper investigates the enhancement in voltage stability achieved while connecting a variable speed wind turbine (VSWT) driven electrically excited synchronous generator (EESG) into power systems. The wind energy conversion system (WECS) uses an AC-DC-AC converter system with an uncontrolled rectifier, maximum power point tracking (MPPT) controlled dc-dc boost converter and adaptive hysteresis controlled voltage source converter (VSC). The MPPT controller senses the rectified voltage (VDC) and traces the maximum power point to effectively maximize the output power. With MPPT and adaptive hysteresis band current control in VSC, the DC link voltage is maintained constant under variable wind speeds and transient grid currents.The effectiveness of the proposed WECS in enhancing voltage stability is analysed on a standard IEEE 5 bus system, which includes examining the voltage magnitude, voltage collapse and reactive power injected by the systems. Simulation results show that the proposed WECS has the potential to improve the long-term voltage stability of the grid by injecting reactive power. The performance of this scheme is compared with a fixed speed squirrel cage induction generator (SCIG), a variable speed doubly-fed induction generator (DFIG) and a variable speed permanent magnet synchronous generator (PMSG).

Stabilisation of grid connected wind farms using doubly-fed induction generators with FACTS controllers

The impact of the wind generation on the power systems is no longer negligible if high penetration levels are going to be achieved. It is very important to boost the transfer capability of the transmission system while improving the utilisation of transmission assets to accommodate high penetration of wind power on the network. Hence, more sophisticated control schemes using advanced power electronic-based flexible AC transmission system (FACTS) controllers are required which will enhance voltage security and voltage stability control. This paper presents the impact of FACTS controllers on the dynamic stability of power systems connected with wind energy conversion systems. The wind farm model considered is a variable speed doubly-fed induction generator model. The dynamic simulation results yield information on 1 the impact of faults and wind speed changes on the performance of DFIG-based induction generators 2 the change in controllable parameters of the FACTS controllers following the faults and wind speed changes 3 transient rating of the FACTS controllers for enhancement of rotor speed stability of induction generators and angle stability of synchronous generators.

High-Order Sliding Mode Control of a Marine Current Turbine Driven Doubly-Fed Induction Generator

This paper deals with the speed control of a variable speed doubly-fed induction generator (DFIG)-based marine current turbine (MCT). To increase the generated power and therefore the efficiency of an MCT, a nonlinear controller has been proposed. DFIG has been already considered for similar applications, particularly wind turbine systems using mainly proportional-integral (PI) controllers. However, such kinds of controllers do not adequately handle some tidal resource characteristics such as turbulence and swell effects. These may decrease MCT performances. Moreover, DFIG parameter variations should be accounted for. Therefore, a robust nonlinear control strategy, namely high-order sliding mode (HOSM) control, is proposed. This control strategy relies on the resource and the marine turbine models that were validated by experimental data. The sensitivity of the proposed control strategy is analyzed regarding the swell effect as it is considered as the most disturbing one for the resource model. Tidal current data from the Raz de Sein (Brittany, France) are used to run simulations of a 7.5-kW prototype over various flow regimes. Simulation results are presented and fully analyzed.

Modeling and Control of a Doubly-Fed Induction Generator (DFIG) Wind Power Generation System for Real-time Simulations

This paper presents a study of a DFIG wind power generation system for real-time simulations. For real-time simulations, the Real-Time Digital Simulator (RTDS) and its user friendly interface simulation software RSCAD are used. A 2.2MW grid-connected variable speed DFIG wind power generation system is modeled and analyzed in this study. The stator-flux oriented vector control scheme is applied to the stator/rotor side converter control, and the back-to-back PWM converters are implemented for the decoupled control. The real-wind speed signal extracted by an anemometer is used for a realistic, reliable and accurate simulation analysis. Block diagrams, a mathematical presentation of the DFIG and a control scheme of the stator/rotor-side are introduced. Real-time simulation cases are carried out and analyzed for the validity of this work.

Fault ride-through capability of DFIG wind turbines

This paper concentrates on the fault ride-through capability of doubly fed induction generator (DFIG) wind turbines. The main attention in the paper is, therefore, drawn to the control of the DFIG wind turbine and of its power converter and to the ability to protect itself without disconnection during grid faults. The paper provides also an overview on the interaction between variable-speed DFIG wind turbines and the power system subjected to disturbances, such as short circuit faults. The dynamic model of DFIG wind turbine includes models for both mechanical components as well as for all electrical components, controllers and for the protection device of DFIG necessary during grid faults. The viewpoint of the paper is to carry out different simulations to provide insight and understanding of the grid fault impact on both DFIG wind turbines and on the power system itself. The dynamic behaviour of DFIG wind turbines during grid faults is simulated and assessed by using a transmission power system generic model developed and delivered by the Danish Transmission System Operator Energinet.dk in the power system simulation toolbox PowerFactory DIgSILENT. The data for the wind turbines are not linked to a specific manufacturer, but are representative for the turbine and generator type used in variable-speed DFIG wind turbines with pitch control.