双馈异步发电机变速风力发电机组闪变研究资源-CSDN文库

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Abstract —— Grid connected wind turbines may produce flicker during continuous operation. This paper presents a simulation model of a MW-level variable speed wind turbine with a doubly fed induction generator developed in the simulation tool of PSCAD/EMTDC. Flicker emission of variable speed wind turbines with doubly fed induction generators is investigated during continuous operation, and the dependence of flicker emission on mean wind speed, wind turbulence intensity, short circuit capacity of grid and grid impedance angle are analyzed. A comparison is done with the fixed speed wind turbine, which leads to a conclusion that the factors mentioned above have different influences on flicker emission compared with that in the case of the fixed speed wind turbine. Flicker mitigation is realized by output reactive power control of the variable speed wind turbine with doubly fed induction generator. Simulation results show the wind turbine output reactive power control provides an effective means for flicker mitigation regardless of mean wind speed, turbulence intensity and short circuit capacity ratio. 双馈异步发电机在变速风力发电机组中的应用与闪变问题随着全球风能发电的迅速发展，风力发电并网对电力质量的影响日益受到关注。其中，一个关键的电力质量问题是“闪变”（flicker）。闪变是指由于光源亮度或光谱分布随时间波动引起的一种视觉不稳定感，可能导致用户不适甚至投诉。对于高比例风能并网的电力系统，闪变限制了风力发电机组的进一步整合。本研究基于2005年896期《IEEE Transactions on Energy Conversion》上的一篇论文，深入探讨了采用双馈异步发电机（DFIG）的变速风力发电机组在连续运行时产生的闪变问题。该研究利用PSCAD/EMTDC仿真工具构建了一个兆瓦级变速风力发电系统的模型，以分析闪变现象及其影响因素。研究表明，闪变的产生与平均风速、风切变强度、电网短路容量以及电网阻抗角等因素密切相关。通过对比固定速度风力发电机组，发现这些因素对变速风力发电机组的闪变影响与固定速度机组有所不同。具体来说： 1. 平均风速：随着风速的变化，风力发电机的输出功率波动，从而影响到电网电压的稳定性，进而产生闪变。 2. 风切变强度：风切变是指风速在空间或时间上的不均匀性，它增加了风力发电机输出功率的不稳定性，可能加剧闪变。 3. 电网短路容量：电网的短路容量影响风力发电机组并网后电压的稳定程度，短路容量越大，通常对闪变的抑制效果越好。 4. 电网阻抗角：阻抗角影响电网的无功功率平衡，从而影响闪变水平。为了解决这一问题，论文提出采用双馈异步发电机的输出无功功率控制策略进行闪变缓解。仿真结果显示，无论平均风速、风切变强度还是短路容量比如何，这种控制策略都能有效地降低闪变，提高了电力系统的稳定性。双馈异步发电机的优势在于能够独立控制其有功和无功功率输出，因此可以主动调节以减少对电网的闪变影响。这种控制策略的实施，不仅有助于改善风电场的电力质量，还有助于促进风能的大规模并网，推动可再生能源的广泛应用。理解并控制变速风力发电机组的闪变是提高风能并网系统电力质量的关键，而双馈异步发电机的无功功率控制技术为此提供了有效手段。随着风能技术的不断进步，类似的解决方案将有助于实现更清洁、更可靠的电力供应。

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896 IEEE TRANSACTIONS ON ENERGY CONVERSION, VOL. 20, NO. 4, DECEMBER 2005

Flicker Study on Variable Speed Wind Turbines

With Doubly Fed Induction Generators

Tao Sun, Zhe Chen, Senior Member, IEEE, and Frede Blaabjerg, Fellow, IEEE

Abstract—Grid connected wind turbines may produce ﬂicker

during continuous operation. This paper presents a simulation

model of a MW-level variable speed wind turbine with a doubly

fed induction generator developed in the simulation tool of

PSCAD/EMTDC. Flicker emission of variable speed wind tur-

bines with doubly fed induction generators is investigated during

continuous operation, and the dependence of ﬂicker emission on

mean wind speed, wind turbulence intensity, short circuit capacity

of grid and grid impedance angle are analyzed. A comparison is

done with the ﬁxed speed wind turbine, which leads to a conclu-

sion that the factors mentioned above have different inﬂuences on

ﬂicker emission compared with that in the case of the ﬁxed speed

wind turbine. Flicker mitigation is realized by output reactive

power control of the variable speed wind turbine with doubly fed

induction generator. Simulation results show the wind turbine

output reactive power control provides an effective means for

ﬂicker mitigation regardless of mean wind speed, turbulence

intensity and short circuit capacity ratio.

Index Terms—Doubly fed induction generator, ﬂicker, variable

speed wind turbine.

I. INTRODUCTION

N RECENT years wind power generation has experienced

a very fast development in the whole world. As the wind

power penetration into the grid is increasing quickly, the in-

ﬂuence of wind turbines on the power quality is becoming an

important issue. One of the important power quality aspects is

ﬂicker.

Flicker is deﬁned as “an impression of unsteadiness of visual

sensation induced by a light stimulus, whose luminance or

spectral distribution ﬂuctuates with time” [1], which can cause

consumer annoyance and complaint. Furthermore, ﬂicker can

become a limiting factor for integrating wind turbines into

weak grids, and even into relatively strong grids where the

wind power penetration levels are high.

Flicker is induced by voltage ﬂuctuations, which are caused

by load ﬂow changes in the grid. Grid connected wind turbines

may have considerable ﬂuctuations in output power, which

depend on the wind power generation technology applied. The

Manuscript received October 28, 2003; revised June 19, 2004. Paper no. TEC-

00311-2003.

T. Sun is with the Institute of Energy Technology, Aalborg University, Aal-

borg DK-9220, Denmark. He is also with North China Electric Power Univer-

sity, Baoding 071003, China, and China Electric Power Research Institute, Bei-

jing 100085, China (e-mail: tsu@iet.auc.dk).

Z. Chen is with the Institute of Energy Technology, Aalborg University, Aal-

borg DK-9220, Denmark, on leave from De Montfort University, Leicester LE1

9BH, U.K. (e-mail: zch@iet.aau.dk).

F. Blaabjerg is with the Institute of Energy Technology, Aalborg University,

Aalborg DK-9220, Denmark (e-mail: fbl@iet.aau.dk).

Digital Object Identiﬁer 10.1109/TEC.2005.847993

ﬂicker emission produced by grid connected wind turbines

during continuous operation is mainly caused by ﬂuctuations

in the output power due to wind speed variations, the wind

gradient and the tower shadow effect [2].

As a consequence of the combination of wind speed varia-

tions, the wind gradient and the tower shadow effect, an output

power drop will appear three times per revolution for a three-

bladed wind turbine. This frequency is normally referred to as

the

frequency. For ﬁxed speed wind turbines with induction

generators, power pulsations up to 20% of the average power at

the frequency of

will be generated [3].

There are numerous of factors that affect ﬂicker emission

of grid-connected wind turbines during continuous operation,

such as wind characteristics (e.g. mean wind speed, turbulence

intensity) and grid conditions (e.g. short circuit capacity, grid

impedance angle, load type) [2], [4]–[7]. The type of wind tur-

bine also has inﬂuence on ﬂicker emission. Variable speed wind

turbines have shown better performance related to ﬂicker emis-

sion in comparison with ﬁxed speed wind turbines [2], [4]. The

reason is that variable speed operation of the rotor has the ad-

vantage that the faster power variations are not transmitted to

the grid but are smoothed by the ﬂywheel action of the rotor.

Although the variable speed wind turbine produces lower

ﬂicker levels, the ﬂicker study becomes necessary and imper-

ative as the wind power penetration level increases quickly.

Variable speed wind turbines with doubly fed induction gener-

ators, the most popular installed variable speed wind turbines

worldwide [8], [9] are the main research topic in this paper.

In this paper, a simulation model of a MW-level variable

speed wind turbine with a doubly fed induction generator

developed in PSCAD/EMTDC [10], [11] is presented, and the

control schemes of the wind turbine are described. Based on

the wind turbine model, ﬂicker emission of variable speed wind

turbines with doubly fed induction generators is investigated

during continuous operation. The factors that affect ﬂicker

emission of wind turbines, such as wind characteristics (mean

speed, turbulence intensity) and grid conditions (short circuit

capacity, grid impedance angle) are analyzed. Compared with

that in the case of the ﬁxed speed wind turbine, the factors

mentioned above have different inﬂuences on ﬂicker emission

of the variable speed wind turbine with doubly fed induction

generator. Flicker mitigation is realized by output reactive

power control of the variable speed wind turbine with doubly

fed induction generator.

II. W

IND TURBINE MODEL

The wind turbine considered here applies a doubly fed

induction generator, using a back-to-back PWM voltage source

Authorized licensed use limited to: Jiangsu University. Downloaded on February 24,2021 at 05:37:02 UTC from IEEE Xplore. Restrictions apply.

SUN et al.: FLICKER STUDY ON VARIABLE SPEED WIND TURBINES WITH DOUBLY FED INDUCTION GENERATORS 897

Fig. 1. Block diagram of a grid connected wind turbine with a doubly fed induction generator.

converter in the rotor circuit. Variable speed operation of the

wind turbine can be realized by appropriate adjustment of the

rotor speed and pitch angle.

A complete wind turbine model includes the wind speed

model, the aerodynamic model of the wind turbine, the me-

chanical model of the transmission system and models of the

electrical components, namely the induction generator, PWM

voltage source converters, transformer, and the control and

supervisory system. Fig. 1 illustrates the main components of

a grid connected wind turbine.

The simulation model of the wind turbine is developed in

the dedicated power system analysis tool, PSCAD/EMTDC.

The grid model and the electrical components of the wind

turbine are built with standard electrical component models

from PSCAD/EMTDC library. The models of the wind speed

and the aerodynamic, mechanical and control components of

the wind turbine are built with custom components developed

in PSCAD/EMTDC.

Wind simulation plays an important task in wind turbine

modeling, particularly for dynamic interaction analysis between

wind farms and the power system to which they are connected.

A wind model has been developed to support such studies [12],

[13], which is applied in this paper. The structure of the wind

model is built into two steps: The ﬁrst step of the wind model

is the park scale wind model, which simulates the wind speed

in hub height at each wind turbine, taking into account the

park scale coherence; The second step of the wind model is the

rotor wind model, which includes the inﬂuence of rotational

sampling and the integration along the wind turbine blades as

the blades rotates. The rotor wind model provides an equivalent

wind speed for each wind turbine, which is conveniently used

as input to a simpliﬁed aerodynamic model of the wind turbine.

A simpliﬁed aerodynamic model is normally used when the

electrical behavior of the wind turbine is the main interest of the

study. The relation between the wind speed and aerodynamic

torque may be described by the following equation:

(1)

where

is the aerodynamic torque extracted from the wind

[Nm],

the air density , the wind turbine rotor radius

[m],

the equivalent wind speed [m/s], the pitch angle of the

rotor [deg],

the tip speed ratio, where is the

wind turbine rotor speed [rad/s],

the aerodynamic efﬁciency

of the rotor.

As for the mechanical model, emphasis is put on the parts of

the dynamic structure of the wind turbine that contribute to the

interaction with the grid. Therefore, only the drive train is con-

sidered, while the other parts of the wind turbine structure, e.g.

tower and ﬂap bending modes, are neglected. When modeling

the drive train, it is a common practice to neglect the dynamics

of the mechanical parts, as their responses are considerably slow

in comparison to the fast electrical ones, especially for machines

with great inertia. The rotational system may therefore be mod-

eled by a single equation of motion

(2)

where

is the wind turbine mechanical inertia plus gener-

ator mechanical inertia

kg m , generator electromagnetic

torque [Nm], and

friction coefﬁcient [Nm/rad].

PSCAD/EMTDC software library provides dedicated model

of the wound rotor induction generator. In this paper the wound

rotor induction generator model with detailed description of the

stator and rotor direct and quadrature axis currents (or ﬂux link-

ages) and the rotor speed is applied.

For a detailed PWM voltage source converter model, the

power electronic components should be switched on and off

at a high frequency [several kilohertz (kHz) or higher], which

requires a very small simulation time step to well represent

the PWM waveforms. The simulation speed is thus fairly slow.

Therefore, the detailed PWM voltage source converter model is

unsuitable for ﬂicker calculation that requires a long simulation

time. Since the study interest is not concentrated on the switches

of the PWM converter, an average model without switches is

used so that the simulation can be carried out with a larger time

step resulting in a simulation speed improvement [14].

III. C

ONTROL SCHEMES

For a variable speed wind turbine with a doubly fed induction

machine, it is possible to control the load torque at the gener-

ator directly, so that the speed of the turbine rotor can be varied

Authorized licensed use limited to: Jiangsu University. Downloaded on February 24,2021 at 05:37:02 UTC from IEEE Xplore. Restrictions apply.

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