Dual-negative-objective Coordinated Control of Brushless Doubly Fed Induction Generator under Unbalanced Grid Voltage

This article proposes a dual-negative-objective coordinated control strategy for brushless doubly fed induction generator(BDFIG)based wind power generation system under unbalanced grid voltage.To alleviate the mechanical stress and impaction on rotating shaft,the negative control objective(NCO)of machine side converter(MSC)is set to suppress the ripple of electromagnetic torque.While the NCO of grid side converter(GSC)is selected to suppress the oscillation of total output active power or the unbalanced degree of total output current for BDFIG generation system.In comparison with traditional single converter control scheme of the MSC or GSC,dual NCOs can be satisfied at the same time due to the enlarged freedom degree in the proposed improved coordinated control system for back-toback converters.The effectiveness of proposed control strategy is validated by simulation and experimental results on a dual-cagerotor BDFIG(DCR-BDFIG)prototype.

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 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.

A novel transient rotor current control scheme of a doubly-fed induction generator equipped with superconducting magnetic energy storage for voltage and frequency support

A novel transient rotor current control scheme is proposed in this paper for a doubly-fed induction generator（DFIG）equipped with a superconducting magnetic energy storage（SMES） device to enhance its transient voltage and frequency support capacity during grid faults. The SMES connected to the DC-link capacitor of the DFIG is controlled to regulate the transient dc-link voltage so that the whole capacity of the grid side converter（GSC） is dedicated to injecting reactive power to the grid for the transient voltage support. However, the rotor-side converter（RSC） has different control tasks for different periods of the grid fault. Firstly, for Period I, the RSC injects the demagnetizing current to ensure the controllability of the rotor voltage. Then, since the dc stator flux degenerates rapidly in Period II, the required demagnetizing current is low in Period II and the RSC uses the spare capacity to additionally generate the reactive（priority） and active current so that the transient voltage capability is corroborated and the DFIG also positively responds to the system frequency dynamic at the earliest time. Finally, a small amount of demagnetizing current is provided after the fault clearance. Most of the RSC capacity is used to inject the active current to further support the frequency recovery of the system. Simulations are carried out on a simple power system with a wind farm. Comparisons with other commonly used control methods are performed to validate the proposed control method.

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.

A Gain Scheduled Method for Speed Control of Wind Driven Doubly Fed Induction Generator

This paper proposes a gain scheduled control method for a doubly fed induction generator driven by a wind turbine. The purpose is to design a variable speed control system so as to extract the maximum power in the region below the rated wind speed. Gain scheduled control approach is applied in order to achieve high performance over a wide range of wind speed. A double loop configuration is adopted. In the inner loop, the rotor speed is used as the scheduling parameter, while a function of wind and rotor speed is used as the scheduling parameter in the outer loop. It is verified in simulations that a high tracking performance has been achieved.

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.

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。

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.Index Terms—Optimal control,power system,renew-able energy sources,wind energy conversion system,doubly fed induction generator.

基于SSO多扰动输入机理分析的DFIG-GSC功率振荡抑制策略研究

电网次同步振荡(SSO)已成为桎梏新能源发展的主要问题之一,针对SSO下双馈感应发电机(DFIG)中网侧变流器(GSC)的功率振荡问题展开研究。首先,建立SSO对GSC的多扰动输入数学模型,探究不同扰动输入的性质以及其对GSC系统的影响,明确了针对物理量扰动以及信号扰动分别采用补偿与滤除两种不同的抑制方法。其次,针对锁相环(PLL)输出误差经过坐标变换产生耦合振荡的问题,建立PLL输出误差角度的频域数学模型,并通过设计一种改进PLL消除其输出误差对GSC的信号扰动影响。同时,设计一种准谐振控制器的自适应算法,并提出基于自适应准谐振控制器的DFIG-GSC功率振荡抑制策略,消除SSO对GSC的物理扰动影响;最后,通过搭建具有SSO模拟环境的DFIG实验平台,验证本文所提控制策略的有效性。

基于改进型Super-twisting的双馈感应发电机直接功率控制

为提高双馈感应发电机(DFIG)直接功率控制的鲁棒性和抗干扰能力,提出一种改进型超螺旋滑模(STSMC)的直接功率控制(DPC)。首先,建立参数摄动下的DFIG最大功率捕获模型和定子磁场定向的双馈感应发电机模型;然后,将非奇异快速终端滑模面(NFTSM)与一种改进型超螺旋(Super-twisting)优化算法结合,设计DFIG直接功率控制器(IST-NFTSMC)。其中所设计的非奇异滑模面能有效避免传统滑模控制(SMC)的奇异现象,且改进超螺旋控制律能有效削弱NFTSMC抖振,提高功率控制精度;最后,通过仿真和实验,与PI控制和传统SMC控制相比,该控制能削弱DFIG功率与电流抖振问题,加快其收敛速度,提高DFIG直接功率控制稳态精度。

基于LESO的DFIG-GSC反馈线性化直接功率控制

为了提高双馈风力发电机网侧变换器(DFIG-GSC)这个强耦合非线性系统的性能,提出了一种反馈线性化直接功率控制策略。首先在αβ坐标系下建立以有功功率、无功功率为变量的DFIG-GSC的数学模型,针对模型中的强耦合项采用反馈线性化进行解耦,得到其线性模型,再结合滑模控制理论设计出功率内环的控制律。由于功率内环控制律中未建模部分和不确定因素会对控制效果产生影响,采用线性扩张状态观测器对其进行观测并对其控制量进行修正。同时电压外环采用滑模控制来提高直流侧电压的响应速度。最后搭建仿真模型与传统PI控制以及直接功率控制进行比较,验证了所提控制策略的合理性和有效性。

基于VMD-CNN-BiLSTM的轴承故障多级分类识别

双馈风力发电机(DFIG)作为风能发电领域的关键设备之一,保障其稳定运行显得尤为重要。针对DFIG轴承故障的多级分类问题,提出了一种基于参数优化的变分模式分解-卷积神经网络-双向长短期记忆(VMD-CNN-BiLSTM)故障诊断模型。首先,采用改进的麻雀优化算法——鱼鹰-柯西-麻雀搜索算法(OCSSA)对变分模态分解(VMD)的惩罚因子、模态分量进行了优化,OCSSA算法是将鱼鹰算法和柯西变异策略与麻雀算法进行了融合,形成了一种新的优化算法,该算法利用强大的参数搜索能力获取了更精确的频率特征;然后,利用卷积神经网络(CNN)提取了信号的时域和频域特征,并对特征进行了融合;最后,利用双向长短期记忆网络(BiLSTM)学习了故障的序列模式,完成了故障的多级分类任务。研究结果表明:基于OCSSA算法优化的VMD-CNN-BiLSTM模型在多级轴承故障识别方面表现出明显的优势,平均识别准确率可达98.36%,与CNN-LSTM、CNN-BiLSTM和VMD-BiLSTM模型进行对比,该模型具有更卓越的故障诊断性能、出色的泛化能力和快速的计算速度。这一结果充分验证了该模型在双馈风力发电机轴承故障的多级分类识别任务上的有效性,且适用于在线监测和智能诊断,为实现高效、可靠的风能发电提供了重要的实际应用价值。

基于GA-FC的双馈风机调频优化策略

双馈风机通过附加虚拟惯性控制和下垂控制参与电力系统调频,但固定的控制系数无法发挥风机实际调频潜力。针对这一问题,提出了一种将遗传算法和模糊控制(GA-FC)相结合的变系数风机调频优化控制策略。首先,为提高调频时功率支撑能力,分析了超速减载控制,对不同风速下减载率进行拟合;然后,参考其他文献虚拟惯性控制系数整定结果,对下垂控制系数进行整定,再通过GA-FC实现动态调整控制系数,实时挖掘风机实际调频能力;最后,在MATLAB/Simulink搭建仿真模型,对所提策略进行验证。结果表明所提策略能够有效提升系统频率支撑。

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.

Robust control based on the Lyapunov theory of a grid-connected doubly fed induction generator

This paper discusses the robust control of a grid-connected doubly-fed induction generator （DFIG） controlled by vector control using a nonlinear feedback linearization strategy in order to ameliorate the performances of the control and to govern the developed stator active and reactive power in a linear and decoupled manner, in which an optimal operation of the DFIG in subsynchronous operation is given, as well as the control stator power flow with the possibility of keeping stator power factor at a unity. The use of the state-all-flux induction machine model gives place to a simpler control model. So, to achieve this objective, the Lyapunov approach is used associated with a sliding mode control to guarantee the global asymptotical stability and the robustness of the parametric variations.

Robust direct power control based on the Lyapunov theory of a grid-connected brushless doubly fed induction generator

This paper deals with robust direct power control of a grid-connected bmshless doubly-fed induction generator（BDFIG）. Using a nonlinear feedback lineariza- tion strategy, an attempt is made to improve the desired performances by controlling the generated stator active and reactive power in a linear and decoupled manner. There- fore, to achieve this objective, the Lyapunov approach is used associated with a sliding mode control to guarantee the global asymptotical stability. Thus, an optimal operation of the BDFIG in sub-synchronous operation is obtained as well as the stator power flows with the possibility of keeping stator power factor at a unity. The proposed method is tested with the Matlab/Simulink software. Simulation results illustrate the performances and the feasibility of the designed control.

Doubly-fed induction generator drive based WECS using fuzzy logic controller

The purpose of this paper is to improve the control performance of the variable speed, constant frequency doubly-fed induction generator in the wind turbine generation system by using fuzzy logic controllers. The control of the rotor-side converter is realized by stator flux oriented control, whereas the control of the grid-side converter is performed by a control strategy based on grid voltage orientation to maintain the DC-link voltage stability. An intelligent fuzzy inference system is proposed as an alternative of the conventional proportional and integral （PI） controller to overcome any disturbance, such as fast wind speed variation, short grid voltage fault, parameter variations and so on. Five fuzzy logic controllers are used in the rotor side converter （RSC） for maximum power point tracking （MPPT） algorithm, active and reactive power control loops, and another two fuzzy logic controllers for direct and quadratic rotor currents components control loops. The performances have been tested on 1.5 MW doubly-fed induction generator （DFIG） in a Matlab/Simulink software environment.