Analysis of SSR in DFIG Based Wind Farms - A Toturial

8/9/2019 Analysis of SSR in DFIG Based Wind Farms - A Toturial

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Presenter:

Hossein A. Mohammadpour

[email protected]

February 2014Grid-Connected

AdvancedPower ElectronicsSystems GRAPES

Supervised by :

Prof. Enrico Santi

[email protected]
mailto:[email protected]:[email protected]:[email protected]:[email protected]


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1. H. A. Mohammadpour , E. Santi, Modeling and control of gate - controlled series capacitor interfaced with aDFIG- based wind farm, IEEE Transactions on Industrial Electronics, DOI:10.1109 /TIE.2014.2347007, Availableon-line: 12 August 2014.

2. H. A. Mohammadpour , E. Santi, Sub -synchronous resonance analysis in DFIG-based wind farms: definitionsand problem identification - Part I, IEEE Energy Conversion Congress and Exposition (ECCE) 2014, pp. 1 - 8,14 - 18 September, Pittsburgh, PA , USA.

3. H. A. Mohammadpour , E. Santi, Sub -synchronous resonance analysis in DFIG-based wind farms: mitigationmethods - TCSC, GCSC, and DFIG controllers - Part II, IEEE Energy Conversion Congress and Exposition (ECCE),pp. 1 - 8, 14 - 18 September, Pittsburgh, PA , USA.

4. H. A. Mohammadpour, Y. J. Shin, E. Santi,SSR analysis of a DFIG-based wind farm interfaced with a gate-controlled series capacitor, IEEE Twenty -Ninth Annual Applied Power Electronics Conference and Exposition(APEC) 2014, pp. 3110 - 3117, 16 - 20 March, Fort Worth, TX, USA.

5. H. A. Mohammadpour , E. Santi, Sub -synchronous resonance mitigation in wind farms using gate-controlledseries capacitor, IEEE 4th International Symposium on Power Electronics for Distributed Generation Systems(PEDG) 2013, pp. 1 - 6, 8 - 11 July, Rogers, AR, USA.

Please ask for full paper at [email protected] , if you do not have

access to the paper.s Please do not hesitate to ask any questionregarding this presentation.Thanks you.Hossein


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Offshorewind farm

Long HVACtransmission line Inf. bus

Fixed series capacitor

Maximum transmittable power is reduced by transmission line reactance.Indeed, the longer the line, the less maximum transmittable power.

Series compensation is the most economical way to increase maximumtransmissible power of a transmission line.


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Fixed series capacitor

Sub-synchronous resonance(SSR) may appears in thesystem and make the systemunstable.

But:


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ControlSeries FACTS

A well-designed FACTScontroller can damp the SSRand stabilize the wind farm.


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Gate-controlledseries capacitor (GCSC)

1. A SSR damping controller is used to stabilize the wind farm.2. Eigenvalue analysis approach is used to design the SSRDC.3. Residue-based analysis is used to find the optimum input control signal (ICS)

to SSRDC.4. Root-locus approach is used to compute SSRDC gain.5. PSCAD /EMTDC is used to validate the approach.


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Introduction to Wind FarmsSeries Compensation Basics and FACTS Devices

Modeling of Series Compensated DFIG Studied Power System Basics: Small-Signal Stability and abc to dq Transformation Mathematical Modeling and Implementation in Matlab/Simulink

Sub-Synchronous Resonance (SSR) Definition and Basics Eigenvalue Analysis of DFIG Detailed Time-Domain Simulation in PSCAD/EMTDC

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Gate-Controlled Series Capacitor (GCSC) Basic Structure Power Scheduling Controller (PSC) SSR Damping Controller (SSRDC)

SSR Damping Controller (SSRDC) Design Residue-Based Analysis for Optimal Input Selection to SSRDC Rotor speed, line current, and voltage across GCSC Root-Locus Diagram for Computing SSRDC Gain

Detailed Time-Domain Simulation in PSCADConclusion and Future Work

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Advantages :No air pollutionNo greenhouse gassesDoes not pollute water with mercury

No water needed for operations

Disadvantages:Intermittent source of power

Only when the wind blows (night? day?)Transmission constraints Offshore wind farms are far away from customers Need long transmission lines

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Offshore Wind Farms vs Onshore Wind Farms:Much biggerFurther distance from customersRequire a reliable transmission lines with high voltage

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Studies show that HVAC option is technically feasible for distances larger

than 250 km provided that capacitive series compensation is used.

Transmission Line Options:High voltage DC (HVDC)

High voltage AC (HVAC)

Expensive


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Type A: ConventionalInduction

Generator (fixed speed)

Type B: Wound-Rotor InductionGenerator w/variable Rotor

Resistance

Type C: Doubly-Fed InductionGenerator (variable speed)

Type D: Full-Converter Interface

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Introduction to Wind Farms

Series Compensation Basics and FACTS Devices



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The most economical way to increase the transmittable powerDisadvantage:

It can increase the risk of sub-synchronous resonance (SSR)

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Definition:Alternating current transmission systems incorporating powerelectronics-based and other static controllers to enhancecontrollability and increase power transfer capability.

Advantages of FACTS DevicesTransient stability improvementInter-area oscillation damping

Greater flexibility in power networkDeliver the optimum power

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Sub-synchronous resonance mitigation


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Static VARCompensator - SVC

Thyristor ControlledSeries Compensator - TCSC

Gate ControlledSeries Compensator - TCSC

Unified Power FlowController (UPFC)

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Solid State SeriesCompensator - SSSC

Static SynchronousCompensator - StatCom


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Introduction to Wind Farms

Series Compensation Basics and FACTS Devices


Sub-Synchronous Resonance (SSR)

Definition and Basics Eigenvalue Analysis of DFIG Detailed Time-Domain Simulation in PSCAD/EMTDC

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100 MW wind farm is aggregation of 2 MW x 50 DFIG wind turbines

Wind turbine aerodynamicsand a 3rd order two-mass

shaft system

A 4th order series compensatedtransmission line model6th order induction

generator model

An 8th order rotor andgenerator side converter

controllers

A 1st order DC link model

The entire system is of 22nd order

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Any dynamic system can be expressed by a set of n first

order nonlinear ordinary differential equations

For small disturbances, the differential equations can be

linearized around operating points and can be expressed in

state-space form.

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Stationary circuit variables referred to a synchronously rotating reference frame.

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Typical abc-to-dq transformation


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RSC real power

GSC real power

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Matlab/Simulink Model

A first order DC-link model


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Maximum Power Point Tracking (MPPT)

The aim of the GSC and RSC are to enable theDFIG to work on the MPPT curve.

Rotor-side converter (RSC) controllers

Grid-side converter (GSC) controllers

MPPT is used in order to achieve highefficiency in the DFIG wind farm.

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A 6 th order induction generator model


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A 4 th order transmission line model


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A 3 rd order mechanical system model


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Equivalent circuit of system under sub-synchronous frequency

= + + : The entire reactance seen from

infinite bus : Frequency corresponding to rotorspeed

andIf

sum of resistancesof the armatureand the network

< 0

>

Then there will be a negativeresistance at the sub-synchronous

frequency, and the sub-synchronouscurrent will increase with time.

This phenomenon is called induction generator effect (IGE).IGE is the major problem in wind farms.

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Wind

speed

( / )

Mode 1

SSR Mode Mode 2

Sup-SR Mode Mode 3

Shaft Mode

Mode 4

Elec. Mech. Mode

7 . . 5.3126 640.1460 1.0405 5.9975 18.4753 95.5005

8 0.7958 106.4835 6.1834 642.3497 1.5952 5.7523 7.3302 64.5295

9 4.0322 107.0110 7.1346 645.3255 3.2322 4.6631 2.4978 31.2250

( ) Mode 1

SSR Mode Mode 2

Sup-SR Mode Mode 3

Shaft Mode Mode 4

Elec. Mech. Mode

50 5.3908 179.2258 4.9224 572.6882 0.9432 6.0249 4.8676 97.6290

75 . . 5.2066 617.1976 0.9221 5.9992 9.9111 99.9693

90 . . 5.3126 640.1460 1.0405 5.9975 18.4753 95.5005

I. High series compensation, e.g. 90 , and different wind speeds

II. Low wind speed, e.g. 7 m/s, and different series compensation levels

IGE-SSR in DFIG is affected by:Wind speed

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At lower wind speed, i.e. 7 m/s, even at a very realistic compensation level, i.e. 75%,the DFIG wind farm is unstable due to SSR Mode.

Time-domain simulation confirms the eigenvalue analysis.

Electric Torque

Rotor Speed

Terminal Voltage

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At higher wind speed, i.e. 9 m/s, even at a very high compensation level, i.e. 90%, theDFIG wind farm is still stable

Electric Torque

Rotor Speed

Terminal Voltage

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Considered signals:

a) Rotor speedb) Line currentc) Voltage across GCSC

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For a complex root , the residue is a complex number, which can beconsidered as a vector having a certain direction.

, Right and left eigenvectors

In a root locus diagram, is representation of the direction and magnitudeof the closed loop eigenvalue , which leaves the pole .

Basics:


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The above equations show that residue influences closed-loop systemroot, by determining the direction and magnitude of it.

Suppose dynamics of all eigenvalues are ignored, except one specific eigenvalue, .

If the magnitude of the residue is large enough, then a smaller gain isneeded for the feedback control system

= =


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This will increase the difficulty of thecontroller design.

The reason is that a simpleproportional controller chosen toincrease damping of the SSR mode willdecrease the damping of the SupSRmode.

The residue magnitude ofthe SSR mode is small.

A larger gain is needed forthe feedback control.

The residues of the SSR andSupSR modes are in an opposite direction.


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However, since the residues of the SSRand SupSR modes in this case point inopposite directions, stabilizing the SSRmode via a feedback gain will decreasethe SupSR mode damping.

The residue magnitude ofthe SSR mode is large.

A smaller gain is needed forthe feedback control.


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The SSR and SupSR modes are in the same

directions. This make the design of thefeedback control simple so that a smallgain will be enough to force both the SSRand SupSR modes to move to the left andmake the system stable.

The residue magnitude of

the SSR mode is large.

A smaller gain is needed forthe feedback control.


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Destabilizing the SupSR mode, while stabilizing the SSR mode.

SSR Mode

SupSR Mode

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All system modes could be stabilized using GCSC voltage as ICS.

SSR Mode

SupSR Mode

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Super-synchronous oscillations

Electric Torque Terminal Voltage

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1. Time-domain simulation verifies the designed controller.2. A well-designed GCSC can damp the oscillation.3. Voltage across the GCSC is an optimal input control signal to SSRDC.


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The GCSC can stabilize the SSR mode.

A control system design procedure is presented for GCSC.

Rotor speed, line current, and cap. Voltage tested as ICS to SSRDC block.

The best signal as ICS to SSRDC block is voltage across series capacitor.

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Supported by NSF I/U CRC forGrid-Connected Advanced Power Electronics Systems

(GRAPES)


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Analysis of SSR in DFIG Based Wind Farms - A Toturial

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Transcript of Analysis of SSR in DFIG Based Wind Farms - A Toturial