High Efficiency Double–Fed Induction Generator Applied to Wind Power Generator Technical Analyses

High efficiency Double-Fed Induction Generator applies new power electronic technology, and utilizes vector control to fix the magnetic direction of the stator to the vertical axis. Adjusting the input current of rotor via an inverter can separately control the cross axis and vertical axis current of real power and reactive power of a generator. Traditionally, rotating speed affects frequency and the output is unstable. This study concentrates on high efficiency Double-Fed Induction Generators and Traditional Generators from mathematic model to derive and control the characteristics simulation and comparison than get an output of high efficiency Double-Fed Industrial Generators. This study utilizes the simulation software MATLAB/Simulink to simulate the response characteristics of vector control of a Double-Fed Industrial Generator. The operating and control functions are better than those of a traditional generator.

An analytic electromagnetic calculation method for performance evolution of doubly fed induction generators for wind turbines

An analytic electromagnetic calculation method for doubly fed induction generator(DFIG) in wind turbine system was presented. Based on the operation principles, steady state equivalent circuit and basic equations of DFIG, the modeling for electromagnetic calculation of DFIG was proposed. The electromagnetic calculation of DFIG was divided into three steps: the magnetic flux calculation, parameters derivation and performance checks. For each step, the detailed numeric calculation formulas were all derived. Combining the calculation formulas, the whole electromagnetic calculation procedure was established, which consisted of three iterative calculation loops, including magnetic saturation coefficient, electromotive force and total output power. All of the electromagnetic and performance data of DIFG can be calculated conveniently by the established calculation procedure, which can be used to evaluate the new designed machine. A 1.5 MW DFIG designed by the proposed procedure was built, for which the whole type tests including no-load test, load test and temperature rising test were carried out. The test results have shown that the DFIG satisfies technical requirements and the test data fit well with the calculation results which prove the correctness of the presented calculation method.

Effects of Wind Turbines Equipped with Doubly-fed Induction Generators on Distance Protection

Nowadays wind energy is the fastest growing renewable energy resource in the world.The problems of integrating wind farms are caused by changes of wind speed during a day.Moreover,the behaviors of wind turbines equipped with doubly-fed induction generators differ fundamentally from synchronous generators.Therefore,more considerations are needed to analyze the performances of the distance protection relays.The protection of a wind farm with distance relay is inspected.By changing the conditions of the wind farm,the characteristics of the distance relay are studied.

A New Approach to Calculate Parameters of Induction Generator with Double Windings

The accuracy prediction for the performance of an induction generator depends much on the parameters of the equivalent circuit. This paper presented a new way for calculating these parameters of induction generator with double windings. The method is based on 2D time-dependent magnetic field coupled with electric circuit. An application example of a 12-phase self-excited induction generator (SEIG) was provided to demonstrate the effectiveness of the presented approach. Some of the calculated results show good coincidence with the experiment values.

Reactive Current Allocation and Control Strategies Improvement of Low Voltage Ride Though for Doubly Fed Induction Wind Turbine Generation System

为满足风电机组低电压穿越（low voltage ride through,LVRT）的测试要求及其电气模型一致性评估需要,提出考虑向电网注入无功电流的双馈风电机组LVRT的控制策略。在阐述风电机组LVRT测试要求及控制原理的基础上,推导双馈发电机（doubly fed induction generator,DFIG）定子侧及网侧变流器输出无功电流极限表达式,研究电网电压跌落深度和发电机总输出有功功率对其无功电流极限值的影响规律,进而提出DFIG在LVRT期间的无功电流分配算法和改进的有功、无功功率控制策略。最后,以某实际2 MW双馈风电机组为例,分别对风速为5和12 m/s、电网电压对称跌落至20%和50%工况下的LVRT运行性能进行仿真比较和样机测试。与传统LVRT控制方法的对比表明,所提改进控制策略能更好地满足风电机组LVRT的测试要求。样机测试结果进一步证明了改进控制策略和仿真模型的有效性。

Steady State Analysis of a Doubly Fed Induction Generator

In this paper, we present the steady state analysis of a double-fed induction generator (DFIG) adopted for wind power generation. The three-phase induction machine connected to the network, to work as a generator for wind farms, is excited on the rotor circuit by a slip-frequency current injected to the rotor, from an exciter mounted on the same shaft of the machine. The resulting rotating magnetic field rotates at synchronous speed;as such the generated power has a constant frequency independent of the shaft speed. Effects of the excitation voltage magnitude and phase angle on the active and reactive power are studied, when the machine runs at constant speed. It has been shown that by controlling the excitation voltage magnitude and phase angle would control the mode of operation of the machine;motor mode or generator mode. Furthermore, the effects of the shaft speed on the active and reactive power at constant excitation voltage magnitude and constant phase angle are also investigated.

A Novel Grid Synchronization Control of Doubly-fed Induction Generator

The dynamic performance of doubly-fed induction generator(DFIG) before and after connection is analyzed based on corresponding mathematical models and transfer functions in decoupled vector control.The parameter tuning methods of rotor current regulator before and after connection are given.To reach same dynamic performance the parameters should take different values and be switched before and after connection.However on one hand the closing moment of stator contactor is difficult to get as the feedback signal is usually twenty millisecond delay or so.The delay in parameter switching will affect rotor current and torque dynamics during the delayed period after connection. On the other hand parameter switching is troublesome.Hence a synchronization control strategy without parameter switching is proposed and analyzed in detail,which has linear rising exciting current to avoid current overshooting. The dynamic performance of the proposed strategy is analyzed in frequency domain and implemented on a DFIG experimental platform subsequently.The proposed synchronization strategy is validated by experimental results.

Control of Doubly Fed Induction Generator under Unbalanced Voltages for Reduction of Torque Pulsation

The unbalanced voltages cause negative effects on the doubly fed induction generator （DFIG） sucn as torque pulsation,and increased stator current. Based on the symmetrical component theory, the torque pulsation is the consequence of the interaction of stator and rotor currents of different sequences. This paper presents a control technique to reduce the effect of unbalanced voltages on the DFIG in wind energy conversion systems. The negative sequence stator voltage is derived from the unbalanced three phase stator voltages. The compensated rotor voltage in terms of the derived negative sequence stator voltage and slip which minimizes the negative stator and rotor currents is proposed. The results from the simulation of control system with steady state model and dynamic model of the DFIG show that additional control loop with compensated voltage can significantly reduce torque and reactive power pulsations.

Dynamic Couplingand Cooperative Control for Multi-paralleled Doubly Fed Induction Generator Wind Farms during Symmetrical Low Voltage Ride-through in a Weak Grid

In multi-fed grid-connected systems,there are complex dynamic interactions between different pieces of equipment.Particularly in situations of weak-grid faults,the dynamic coupling between equipment becomes more pronounced.This may cause the system to experience small-signal instability during the fault steady-state.In this paper,multi-paralleled doubly fed induction generator(DFIG)-based wind farms(WFs)are taken as an example to study the dynamic coupling within a multi-fed system during fault steady-state of symmetrical low voltage ride-through(LVRT)in a weak grid.The analysis reveals that the dynamic coupling between WFs will introduce a damping shift to each WF.This inevitably affects the system’s dynamic stability and brings the risk of small-signal instability during fault steady-state in LVRT scenarios.Increasing the distance to fault location and fault severity will exacerbate the dynamic coupling between WFs.Because of the dynamic coupling,adjusting the control state of one WF will affect the stability of the remaining WFs in the system.Hence,a cooperative control strategy for multi-paralleled DFIG WFs is proposed to improve dynamic stability during LVRT.The analysis and the effectiveness of the proposed control strategy are verified by modal analysis and simu-lation.

Robust Optimal Framework for Doubly Fed Induction Generator with Uncertain Dynamics

A robust optimal framework is designed herein to mitigate the oscillatory dynamics in a doubly fed induction generator(DFIG)even in the presence of network disturbances and input variation.To address uncertain dynamics,herein,a novel transformation formula is developed for a wind energy conversion system.An unscented Kalman filter is applied to estimate the un-measured internal states of the wind energy conversion system using terminal measurements.The detailed convergence and stability analyses of the presented framework are investigated to validate its effectiveness.Additionally,comparative modal analyses are carried out to demonstrate the improvement in the damping of critical low-frequency oscillatory modes using the presented framework.The simulation results demonstrate satisfactory performance under various operating scenarios,such as increasing and decreasing wind speed and varying the terminal voltage.The comparative performance is demonstrated to validate the effectiveness of the presented framework over that of the state-of-the-art frameworks.

A Long-Range Generalized Predictive Control Algorithm for a DFIG Based Wind Energy System

This paper presents a new Long-range generalized predictive controller in the synchronous reference frame for a wind energy system doubly-fed induction generator based. This controller uses the state space equations that consider the rotor current and voltage as state and control variables, to execute the predictive control action. Therefore, the model of the plant must be transformed into two discrete transference functions, by means of an auto-regressive moving average model, in order to attain a discrete and decoupled controller, which makes it possible to treat it as two independent single-input single-output systems instead of a magnetic coupled multiple-input multiple-output system. For achieving that, a direct power control strategy is used, based on the past and future rotor currents and voltages estimation. The algorithm evaluates the rotor current predictors for a defined prediction horizon and computes the new rotor voltages that must be injected to controlling the stator active and reactive powers. To evaluate the controller performance, some simulations were made using Matlab/Simulink. Experimental tests were carried out with a small-scale prototype assuming normal operating conditions with constant and variable wind speed profiles. Finally, some conclusions respect to the dynamic performance of this new controller are summarized.

Analysis on Effect of Parameters of Different Wind Generator on Power Grid Transient Stability

To analyze the factors which affecting transient stability of power system, the dynamic model of doubly-fed induction generator and direct-drive PM synchronous generator has been built using PSCAD. Impact of different wind farm integration on grid typically in China has been presented. The influence of the variations of transient reactance, negative sequence reactance and rotary inertia on critical clearing time of power system transient stability is analyzed by time-domain simulation. Mixture operation of DFIG and PMSG to optimize the stability of system has been analyzed firstly. The digital simulation results show that doubly-fed induction wind turbines is a better choice to meet the requirement of system instability due to large wind farm integration in comparison with direct-drive PM synchronous wind turbines. With a rather large rotary inertia, the proper ratio of direct-drive PM synchronous wind turbines used in wind farm could be comprehensive planning by optimized the stability of system. Analysis of this paper should be provided as academic reference for improving design of wind farm system.

Research on multi-time scale doubly-fed wind turbine test system based on FPGA+CPU heterogeneous calculation

As the proportion of renewable energy increases, the interaction between renewable energy devices and the grid continues to enhance. Therefore, the renewable energy dynamic test in a power system has become more and more important. Traditional dynamic simulation systems and digital-analog hybrid simulation systems are difficult to compromise on the economy, flexibility and accuracy. A multi-time scale test system of doubly fed induction generator based on FPGA+ CPU heterogeneous calculation is proposed in this paper. The proposed test system is based on the ADPSS simulation platform. The power circuit part of the test system is setup up using the EMT(electromagnetic transient simulation) simulation, and the control part uses the actual physical devices. In order to realize the close-loop testing for the physical devices, the power circuit must be simulated in real-time. This paper proposes a multi-time scale simulation algorithm, in which the decoupling component divides the power circuit into a large time scale system and a small time scale system in order to reduce computing effort. This paper also proposes the FPGA+CPU heterogeneous computing architecture for implementing this multitime scale simulation. In FPGA, there is a complete small time-scale EMT engine, which support the flexibly circuit modeling with any topology. Finally, the test system is connected to an DFIG controller based on Labview to verify the feasibility of the test system.

Small Signal Stability Analysis of DFIG Fed Wind Power System Using a Robust Fuzzy Logic Controller

This paper focuses on the small signal stability analysis of Doubly-Fed Induction Generator (DFIG) fed wind power system under three modes of operation. The system stability is affected by the influence of electromechanical oscillations, which can be damped using Power System Stabilizer (PSS). A detailed modeling of DFIG fed wind system including controller has been carried out. The damping controller is designed using fuzzy logic to damp the oscillatory modes for stability. The robust performance of the system with controllers has been evaluated using eigen value analysis and time domain simulations under various disturbances and wind speeds. The effectiveness of the proposed fuzzy based PSS is compared with the performance of conventional PSS implemented in the wind system.

Robust nonlinear controller design of wind turbine with doubly fed induction generator by using Hamiltonian energy approach

Based on Hamiltonian energy theory, this paper proposes a robust nonlinear controller for the wind turbine with doubly fed induction generator （DFIG）, such that the closed-loop system can achieve its stability. Furthermore, in the presence of disturbances, the closed-loop system is finite-gain L2 stable by the Hamiltonian controller. The Hamiltonian energy approach provides us a physical insight and gives a new way to the controller design. The simulation results illustrate that the proposed method is effective and has its advantage.

WIND POWER IMPACT ON TRANSIENT FAULT BEHAVIOR IN ELECTRICAL POWER GRID USING DOUBLY FED INDUCTION GENERATOR

The amount of electrical energy produced by wind mills is constantly increasing.Nowadays detailed analyzes considering the impact of wind energy integration on the transmission system are required.The goal of this study is to investigate the dynamic response of a wind turbine with doubly fed induction generator connected to the power system during grid disturbance.The current and future wind power situation is modeled as two cases and a transient fault is simulated.In order to analyze the impact of wind energy integration in electrical power grid,a power system model has been developed,integrated with wind turbine using doubly fed induction generator and transient analysis are performed.Here,an attempt has been made to compare the impact,in terms of voltages,currents,total harmonic distortion,etc.,of adding wind turbines into electrical power grid.

适应并离网模式切换的DFIG电磁暂态仿真建模

目前,常用的商业仿真软件中的双馈式感应发电机(double-fed Induction Generator,DFIG)模型通常不支持离网运行模式,难以实现风力发电系统由离网到并网的全过程电磁暂态仿真,对电力系统仿真分析工作带来极大不便。研究适应并离网模式切换的DFIG电磁暂态仿真建模方法。基于模块化思想分别对风力机、异步电机、变流器以及断路器进行建模,在系统组装形成DFIG风力发电系统电磁暂态仿真模型。提出了适应并离网模式切换的DFIG受控源等效电路模型和离散时间域实现方法,通过设计状态变量矩阵元素的截取和扩充算法实现了模型在并离网模式下的无缝衔接。在MATLAB/Simulink中搭建DFIG发电系统模型对所提方法和模型进行验证,仿真结果表明,所提建模方法能够很好地支持DFIG离网运行模式,实现DFIG由离网到并网的全过程电磁暂态仿真。

基于硬件在环仿真的DFIG并网系统开环模式谐振风险及验证

开环模式谐振理论是阐释风电并网引起的电力系统振荡机理的研究成果,其中基于平均模型的离线时域仿真结果可信度存疑。为提升开环模式谐振的工程指导可靠度,首先基于硬件在环仿真,组建了用于验证开环模式谐振的半实物实验平台;其次建立双馈风电场并网系统的小信号模型,提出开环模式分析通用方法评估系统振荡风险;最后以两个算例进行了开环模式谐振现象的分析与实验。得到结论:硬件在环仿真的结果符合开环模式分析的结果,在开环模式谐振条件下,系统稳定性下降。留数法可以较为准确地预测系统闭环模式,系统参数的合理整定可以减小开环模式谐振带来的影响。

计及风力发电机转速安全约束的DFIG一次调频模型预测控制策略

针对传统方法控制双馈感应发电机(DFIG)的调频效果过于依赖参数整定的问题,该文提出了一种基于模型预测控制(MPC),计及转速安全约束的风力发电机参与一次调频控制策略。该方法结合风力发电机动力学模型与频率响应模型建立预测模型,通过线性回归方法变参考值将风力发电机转速的稳定性纳入考虑。相较于虚拟惯性控制等方法将系统频率偏差与转子动能直接关联,该文方法通过建立全新的预测模型,实时统筹考虑整个系统的状态信息,无需反复调整参数,在考虑转速安全性的同时兼顾全局性能。最后,通过实际算例分析验证了该文调频策略的有效性以及相对现有方法的优越性。