Doubly Fed Induction Generator Grid Research Articles

A sensorless control strategy for automatic start‐up and grid‐synchronization of doubly fed induction generator in wind energy conversion system

SummaryIn a wind energy conversion system (WECS) based on a doubly fed induction generator (DFIG), a fast and smooth automatic synchronization of the DFIG with the utility grid is always desirable. Additionally, elimination of the need for a speed encoder makes the synchronization process much more reliable. This paper proposes a modified voltage controller‐based automatic grid‐synchronization strategy for the DFIG‐WECS using a rotor‐current‐dependent model‐reference‐adaptive‐system (MRAS) for rotor‐speed/position estimation. A V/f control‐based starting strategy is used to start the DFIG. An improved decoupled DFIG stator voltage controller is proposed to enhance the transient response during the DFIG grid synchronization. The modified controller is implemented in a grid‐voltage‐oriented reference frame to synchronize the DFIG‐stator with the grid. A robust modified MRAS with higher noise immunity and reduced machine parameter dependency is used to estimate the rotor‐speed/position during synchronization control. To validate the performance of the proposed strategy, a DFIG‐based WECS is modeled and simulated using an OPAL‐RT real‐time simulator, where a motor‐generator setup is modeled to have an equivalent WECS configuration. As compared with the latest reported work, this approach reduces the synchronization time by 16.99% while ensuring a smooth synchronization with no stator inrush‐current, even without any speed/position encoder.

Embeddable parallel digital image of doubly-fed induction generator

Due to the complexity of the structure of doubly-fed induction generator (DFIG), it is difficult to conduct real-time simulation. For this reason, this paper designs an embeddable parallel digital image IP of DFIG based on field programmable logic array (FPGA) to realize efficient electromagnetic simulation of DFIG. First, this paper proposes a virtual capacitor equivalent method for induction machine equivalent “T” circuit decoupling; Secondly, based on the principle of data independence and parallelism within the time step, a parallel algorithm for the internal components of DFIG is proposed; Finally, the FPGA-DFIG digital image constructed in this paper is connected to the RT-LAB/power grid, and hardware experiments are carried out under three working conditions: steady state, voltage sag and DC side fault. The experimental results are compared with the simulation results of DFIG grid connected system built in MATLAB/Simulink environment to verify the effectiveness and rapidity of the methods and models proposed in this paper.

Analysis of SSO in DFIG grid with series compensation

Doubly fed induction generator (DFIG) has become the most widely used type of wind power generation due to its superior technical performance. Series compensation technology is widely used in large-scale and long-distance wind power transmission system because of its high cost performance and significant improvement of transmission capacity. However, it may cause subsynchronous oscillation (SSO). This paper first introduces the definition and harm of subsynchronous oscillation, and then analyzes the advantages and disadvantages of series compensation technology, as well as the mechanism and suppression measures of subsynchronous oscillation of DFIG connected system through series compensation. Through modeling and simulation analysis, the suppression effect of additional subsynchronous damping controller (SSDC) on subsynchronous oscillation of DFIG control system is verified.

The Relevance of Doubly – Fed Induction Generator (DFIG) in Modelling and Simulation of a Grid Connected Wind Turbine System

The need for clean and stable electricity has given rise to renewable energy globally. Currently, Wind Energy generation is one the leading renewable energy sources and DFIG-based wind turbine are invariably the best approach to generate a multi-megawatts power at variable speed with less fluctuation in output power, ability to control its generated active and reactive power with minimal cost. This paper presents a model of a grid connected DFIG based Wind Turbine system for variable- speed where the speed range requirements are small, the overall system simulated using MATLAB/SIMULINK and the results shows the behaviour of DFIG with this type of control system and the numerous advantages in terms of cost reduction and the potential to build economically at multi-megawatt power system, as a result, DFIG grid connected wind turbine is essential.

Study on DFIG Dissipation Energy Model and Low-Frequency Oscillation Mechanism Considering the Effect of PLL

Considering the dynamic characteristics of phase-locked loop (PLL), the effect of interaction between doubly fed induction generator (DFIG) and power grid on system low-frequency oscillation is revealed from the perspective of dissipation energy. First, the dynamic energy model of DFIG with PLL is derived, and the component that varies nonperiodically is extracted and defined as the dissipation energy. Second, the dissipation energy is decomposed into the free dissipation energy and DFIG-grid coupled dissipation energy. On this basis, the free dissipation intensity and coupled dissipation intensity are defined, which, respectively, characterize the immanent damping of DFIG and the DFIG-grid interaction degree. Thus, the contribution degree of DFIG to electromechanical oscillation is quantified for evaluation, and the mechanism of interaction between DFIG and power grid is further revealed. Finally, hardware-in-the-loop simulation tests with real-time digital simulator of the IEEE 10-machine 39-bus system verify that when the oscillation frequency of PLL is close to electromechanical oscillation frequency, strong coupling and resonance exist between DFIG and grid, and negative dissipation effect on the oscillation of DFIG will result. Thus, DFIG, as an oscillator, continuously injects dynamic energy to the grid, causing the system to oscillate to instability.

Distributed Consensus for Output Power Regulation of DFIGs With On-Site Energy Storage

This paper proposes a novel distributed control architecture for output power regulation of doubly fed induction generator (DFIG) based wind turbines (WTs) with on-site battery energy storage systems (BESSs). The proposed distributed control architecture receives information from adjacent WTs+BESSs to control the DFIG's grid side converter (GSC) and the storage unit for output active/reactive power regulation and energy management purposes. The proposed method guarantees the equal active power sharing and energy management of WTs+BESSs in various wind speed conditions. A distributed controller is also designed to respond to the reactive power demand and share the reactive load demand between the GSC and BESS controllers based on their capacities. Furthermore, a controller is designed to account for the communication delays caused by the communication systems based on the IEEE standards. The proposed method is tested on the modified IEEE 14-bus power system with 10 WTs+BESSs.

Model-Based Predictive Rotor Current Control for Grid Synchronization of a DFIG Driven by an Indirect Matrix Converter

A novel predictive rotor current control scheme for a doubly fed induction generator (DFIG) is implemented to perform the DFIG grid synchronization with a fast dynamic response. With this control strategy applied to an experimental setup, the rotor currents swiftly follow the necessary reference for grid synchronization in the range ±30% of the generator rated shaft speed. The DFIG and converter discrete models are used to predict the behavior of the rotor currents. By minimizing the error between the references and the predictive rotor currents for each of the valid states of the converter, the best-suited switching state is selected and applied at the next sampling time. To validate the feasibility of implementing this approach, simulations and experiments were carried out for various shaft speed profiles.