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。

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 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.

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

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.

计及低电压穿越及故障全过程动态的双馈风电场等值方法

在分析双馈感应发电机(DFIG)故障各阶段动态的基础上,提出了一种计及低电压穿越控制的双馈风电场等值方法。首先,讨论了低电压穿越控制策略,给出了含双馈风电场的电力系统故障稳态潮流计算方法。在考虑电压暂态过程的条件下,分析了外部系统短路故障后DFIG转子电流的变化机理,指出电压跌落深度及风电功率是影响短路电流的主要因素,可根据动作分界线判断撬棒是否动作。然后,根据初始风速及撬棒状态将风电场中的DFIG分为3群,并对等值DFIG及集电网络进行聚合。为提高等值模型在恢复阶段的精度,根据故障稳态电压对双馈风电场功率恢复曲线进行预估,并在此基础上对等值DFIG恢复速率进行分段修正。最后,对含双馈风电场的算例系统进行了等值计算。仿真结果表明,等值模型较好地保持了原系统在故障各阶段的动态,在保持较高精度的前提下有效简化了系统,提高了计算速度。

基于传递函数分析的双馈风力发电系统动态建模方法研究

以双馈风力发电系统(doubly-fed induction generator based wind energy conversion system,DFIG-based WECS)为例,利用小信号分析法推导出由风机、双质量块传动链构成的动力与传动系统通用传递函数方程。动力与传动系统传递函数的零极点位置、稳定性与系统参数及系统运行工作点相关。该传递函数可进一步分解为扭转分量和非扭转分量。传动链参数仅对扭转分量造成影响。在此基础上,建立了考虑动力传动、电机、变流器、控制等环节的风力发电系统传递函数模型。模型综合了各环节参数,可直观反映系统参数对系统响应的影响,有助于深入了解系统动态行为。算例及时域仿真结果证明了所提出传递函数模型的准确性和高效性,可为系统参数设计研究提供理论依据。

含双馈机组风电场备用电缆位置和容量优化方法

链状结构风电场中电缆故障后,故障串部分风电机组将被迫停运。在两串末端增加备用电缆,可以为故障下游风电机组提供输电通道,但对非故障串电缆容量要求较大,利用率低。文章提出一种备用电缆位置和容量优化方法。首先定义最小路矩阵,评估随机风速/电缆故障时风电场输出。根据备用电缆位置对风电场分区。提出有限容量模型解决故障串输电优先性顺序,以确定备用电缆最佳位置。然后引入双馈感应发电机(doubly-fed induction generator,DFIG)稳态约束,采用主从分裂算法,求解风电场潮流。以利用率和成本为目标,提出备用电缆容量的优化模型。最后给出算例分析结果,验证所提方法的有效性。

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。

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.

风电制氢系统阻抗建模及振荡特性分析

由于风电机组与主网呈现远距离逆向分布特点,高度电力电子化的风电就地制氢系统与电网互联时将存在振荡失稳的风险。对此,通过建立风电制氢系统的阻抗模型分析了其与电网互联时的振荡特性。首先,建立了考虑电解槽动静态电气特性的阻抗模型,并在此基础上采用双傅里叶变换,建立了包含电力电子变换器在内的电解水制氢设备阻抗模型;随后,结合风电机组的阻抗特性,分析了电网短路比以及制氢设备运行工况对风电制氢系统稳定性的影响。接着,对制氢设备控制参数进行了灵敏度分析,为提升系统稳定性的参数优化方案提供了指导;最后,构建了时域仿真模型,对所得结论进行验证。

考虑撬棒与直流卸荷协同保护动作特性的双馈风电场通用等值建模方法

低电压穿越(low voltage ride through,LVRT)期间撬棒(Crowbar)保护和直流卸荷(Chopper)保护的工作状态均对双馈风电机组(doubly fed induction generator,DFIG)的暂态响应特性有重要影响。传统等值方法往往只能识别与表征撬棒保护动作情况及其暂态特性,对于目前普遍的硬件协同保护场景而言,将造成等值误差,进而难以从电网侧准确描述风电接入后的动态特性及作用规律,在高比例风电场景下这样的误差将被放大,严重时可能会对电力系统安全稳定分析造成影响。因此,该文充分考虑双馈感应风机(doubly fed induction generator,DFIG)低电压穿越控制策略,揭示风机低电压穿越下两种保护协同动作特性,提出一种双馈型风电场通用等值方法,通过MATLAB/Simulink验证理论分析的正确性,并与仅考虑Crowbar保护的等值方法对比,说明所提等值建模方法的准确性。

风电场柔直送出系统联接变故障特性分析及差动保护方案

联接变是衔接交直流系统的桥梁,对其故障特性的分析是构建保护方案的重要基础。然而,双馈风电经柔直送出系统中整流侧联接变发生故障时,机侧短路电流呈现出频偏和弱馈故障特性,而阀侧短路电流不仅含有大量谐波,在不同的控制策略下还存在幅值差异、相角差异,甚至会出现断流的情况。如此复杂的故障特性给联接变的差动保护正确动作带来十分严峻的挑战。为此,该文以联接变阀侧发生最为常见的单相接地故障为例,分析双馈风电场柔直送出系统联接变风电场侧及阀侧短路电流故障特性及致使差动保护性能降低的原因。在此基础上,提出分别利用形态学滤波分解及同步挤压小波变换对换变流两侧电流进行处理,并以处理后的两侧电流轨迹图斜率为判据,对区内外故障和涌流进行识别的保护方案。最后,基于PSCAD/EMTDC的仿真结果表明:所提出的方案能很好地对风电联接变区内外故障和涌流进行识别,在不同影响因素条件下该方案也具有良好的适用性。

一种基于虚拟阻尼绕组的双馈电机灭磁方法

针对电网故障引发的双馈电机磁链阻尼振荡问题,提出一种基于虚拟阻尼绕组的灭磁控制方法。首先根据双馈电机的电磁关系分析了在电网故障下定子磁链的动态变化过程。在此基础上建立了双馈电机矢量控制的数学模型。通过MATLAB软件进行仿真实验,对比分析了改进与常规控制策略下,电压跌落和电压骤升后定子磁链d轴分量与定子磁链q轴分量的变化波形。改进的灭磁方法可有效对抗磁链的振荡冲击,提升了双馈风力发电机在电网故障下的运行性能。

基于空间多分量极对数磁场耦合的FSCW双馈感应电机电磁及损耗特性分析

分数槽集中绕组(FSCW)感应电机中存在大量非主导极对数谐波,导致其转矩脉动及铁心损耗较大。针对此问题,以一台定子15槽、转子18槽的FSCW双馈感应电机为研究对象,对该类电机的转矩特性和铁心损耗特性进行了研究。首先,介绍了FSCW双馈感应电机的结构及工作原理,推导了其在双馈工况下的定子电流方程;其次,通过绕组函数法及匝数函数法求解了特定极槽配合下定转子前n次谐波自感和互感之和;然后,基于虚位移法对电磁转矩进行理论计算,并将理论计算结果与有限元仿真结果以及试验测量结果进行对比分析;最后,对不同工况下的转矩特性及铁心损耗特性进行了分析,得到了不同转差率下的电磁转矩脉动频率和铁心损耗的变化规律,即转矩脉动频率随转差率减小而增大,铁心损耗随转差率的减小而降低。

不同运行方式的大规模新能源接入电网后的调频特性研究

给出了双馈风力发电机(doubly-fed induction generator,DFIG)参与电网调频的基本数学模型,推导出了大规模风电接入电网后,在不同运行方式(如惯性控制或者最大功率跟踪)下风电功率的渗透率、可调频风电机组所占比例以及风电机组的频率调节系数等与风电利用率之间的关系,提出了不同运行方式的风电机组参与电网调频的控制策略。以南方某片区电网为例,分析了风速改变及负荷变化的情况下风电功率注入比例对接入电网调频的影响特征,验证了可调频新能源发电对电网调频作用的有效性。将可调频风电机组接入4机2区域的电网模型,给出风电注入比例不同情况下所需要的可调频风机所占比例最小值及电网对新能源的综合承载能力。仿真结果表明,大规模风电场参与调频时应尽可能使运行在额定风速附近的机组参与调频,从而最大程度确保电网的频率偏差变小,维持频率在安全运行范围内。