DFIG Based Wind Turbine System For Clemson Micro-grid

As an important part of the smart grid, the micro-grid interfaces with distributed energy sources, loads and control devices. A doubly fed induction generator (DFIG) based wind turbine (WT) is the main power source of the presented project. The DFIG system is connected to the three phase AC grid via back-to-back power converter and an LCL filter. Decoupled q-d control strategies are investigated for the DFIG system. Matlab/Simulink results will show the performance of the proposed system. Hardware validation results are also presented and discussed. As a rapidly increasing research interest area the dc micro-grid has been extensively investigated. A topology is proposed to connect the DFIG based WT system to a dc link using a diode bridge and a three phase power converter. The rotor side of the DFIG is connected to the dc link through a converter while the stator is connecting to a three phase diode bridge with the dc side connected to a dc link. The control method is developed to regulate the stator frequency and the d-q axis voltage of the diode bridge to operate the DFIG at a desired stator frequency and generate the required power. Undesired harmonics in the three phase system will lead to excessive THD, a decrease the power quality and an increase the power loss of the system. An novel methods to compensate the current harmonics by controlling the power converter of the DFIG system is also proposed. With the DFIG connected to the three phase AC gird, the focus has been put into a scenario: a nonlinear load connected to the same node of the DFIG point of common coupling (PCC) to the gird, to draw the harmonics to the system. In the proposed dc link system, the diode bridge will introduce harmonics to the stator current of the DFIG. In both cases, the selected low-order harmonics are detected and calculated by a multiple reference frame estimator. The control methods of how to regulate the harmonics are developed for both the grid-side converter and the rotor-side converter based on multiple reference frame theory. A hybrid state observer for speed-sensorless motor drives of induction machines is also proposed. The hybrid observer comprises of a Luenberger observer and a sliding mode observer. For a conventional induction motor with shorted rotor, the stator currents and rotor flux linkages are estimating following a Luenberger observer. While, for a DFIG the similar approach will apply to the stator currents and rotor currents. The rotor speed is estimated using a sliding mode observer. The combination of two observers takes advantage of both approaches. The Luenberger observer is easy to realize and the computational burden is small. The sliding mode observer is known for its robustness with respect to model parameter errors and it will also provide a fast convergence rate. The chattering of the sliding mode observer is addressed by applying a boundary layer

Improved control strategy of DFIG-based wind turbines using direct torque and direct power control techniques

This paper presents different control strategies for a variable-speed wind energy conversion system (WECS), based on a doubly fed induction generator. Direct Torque Control (DTC) with Space-Vector Modulation is used on the rotor side converter. This control method is known to reduce the fluctuations of the torque and flux at low speeds in contrast to the classical DTC, where the frequency of switching is uncontrollable. The reference for torque is obtained from the maximum power point tracking technique of the wind turbine. For the grid-side converter, a fuzzy direct power control is proposed for the control of the instantaneous active and reactive power. Simulation results of the WECS are presented to compare the performance of the proposed and classical control approaches.Peer reviewedFinal Accepted Versio

Performance Analysis of Doubly Fed Induction Generator Using Vector Control Technique

There are many solar power and wind stations installed in the power system for environmental and economic reasons. In fact, wind energy is inexpensive and the safetest among all sources of renewable energy, it has been recognized that variable speed wind turbine based on the doubly fed induction generator. It is the most effective with less cost and high power yield. This paper has chosen doubly fed induction generator for a comprehensive study of modelling, performance and analysing. DFIG wind turbine has to operate below and above synchronous speed which requires smooth transition mode change for reliable operation to be controlled to provide stability for the power system. Hence its performance depends on the generator itself and the converter operation and control system. This paper presents completed mathematical model of DFIG with its AC/DC/AC converter driven by DC machine. The rotor is considered fed by a voltage source converter whereas the stator is connected to the grid directly. The capacity of the wind power generation is 1.5MW. The voltage rating and frequency for this system are 575V, 50Hz .This paper show detailed model of DFIG

The control of power electronic converters for grid code compliance in wind energy generation systems

This research report reviews some of the latest control schemes for the power electronic converters found in modern variable speed wind turbines in order to comply with various grid codes. Various control schemes, in order to comply with low voltage ride-through requirements, active and reactive power control and frequency control, are presented. The report first investigates the South African grid code requirements for wind energy generation, and then makes a comparison to grid codes of countries with significant penetration levels and vast experience in wind energy generation. This is followed by a review of the state of the art in fixed and variable speed wind turbine technologies. The research revealed that Type 3 generators offer significant advantages over others but suffer due to grid faults. Various active control schemes for fault ride-through were researched and the method of increasing the rotor speed to accommodate the power imbalance was found to be the most popular. It was found that Type 4 generators offer the best fault ride-through capabilities due to their full scale converters. The research will assist power system operators to develop appropriate and effective grid codes to enable a stable and reliable power system. The research will also provide turbine manufacturers and independent power producers with a comprehensive view on grid codes and relate them to the associated turbine technologies