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IEEE PES IBR SSO

Controller interaction of wind farm and STATCOM

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Presenter: Li Bao, University of South Florida

August 4^th, 2021

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Collaborators:

Miao Zhang, Lingling Fan, Zhixin Miao

Motivation

How the controller of STATCOM interacts with wind farm?

1. Demonstration
1. With PI controller.
2. Without PI controller.
2. Open-loop control analysis
• Linear model extraction.
• Root locus analysis.
• Validation.

System Model

EMT testbed structure of a type-4 wind farm with reactive power devices.

STATCOM control structure.

Type-4 Wind farm in weak grid (no STATCOM)

PCC voltage of wind farm.

Transmission line impedance X_g is given a step change from 0.2 pu at 5 second to emulate a parallel line tripping events.

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Different PI controller parameters are compared under the event of tripping line.

Q from STATCOM

STATCOM: reactive power control

Increasing PI parameters, the system may have better stability performance.

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STATCOM: constant firing angle control

If the controller is disable, and input angle is set a constant to ensure output Q be zero. The system is still stable.

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Harmonic injection

Measurement

tf(f_i)=i_q(f_i)/α(f_i)

If the angle α is input and i_q is output, by using harmonic injection and vector fitting, the linear model can be extracted as:

System linear model

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Root locus analysis

With the linear model, the root locus is shown as:

If the gain is 1.91, the simulation results are:

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2.75 Hz.

Root locus analysis

If the gain is 0.63, the system will be unstable:

Wind farm results

FFT for V_PCC

Concluding remarks

• PI controller parameters of STATCOM have impact on system stability performance.

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• Without PI controller, the system becomes stable.

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• By using harmonic injection method and vector fitting, the linear model of the system can be extracted.

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• Root locus analysis is validated by EMT results.

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