Analysis of Sub-synchronous Frequency Interactions in Power Systems Using TGSSR

Team: Prof. Udaya Annakkage (U of M / TGS) Chandana Karawita (TGS) Hiranya Suriyaarachchi (U of M / TGS) Dan Kell (TGS)

IEEE PES Winnipeg Section Luncheon Meeting - January 2012

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Presented by: Chandana Karawita, TransGrid Solutions

Outline

Introduction to TGSSR Applications

Generator-turbine - series capacitor SSR Generator-turbine – HVDC torsional

interactions Generator-turbine – VSC torsional

interactions Wind plant - series capacitor SSR

Applicability in Modern Power Systems 2

Introduction to TGSSR

Dynamic phasor based small signal stability assessment. Not another small signal stability program meant for

electromechanical oscillation analysis Network dynamics are modelled using dynamic

phasors. Generator stator dynamics are modeled. Models are accurate up to the frequency at which the

system harmonics and the frequency dependency of network components can be ignored.

Main focus is on sub-synchronous frequency range.

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Introduction to TGSSR

Input

• Read PSS/E raw data • Read Dynamic data

Process-1

• Create linearized models of dynamic devices • Combine with dynamic phasor network model

Output

• Save A and B matrices (ΔẊ=A ΔX + B ΔU) to text files • Save state and input data to text files

Process

Process-2

• Eigen analysis of A matrix • Small signal time domain simulations

Output

• Eigen values and vectors, participation factors • Polar plots, frequency responses

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Introduction to TGSSR

Present Capabilities Synchronous generator models including

exciters, governors, stabilizers (PSS) and multi-mass turbine units.

Single and double cage induction generator/motor models.

Network components – Tx lines, two and three winding transformers, series capacitors and zero impedance lines.

Static and dynamic load models. 5

Introduction to TGSSR

Present Capabilities Monopole and Bipole HVDC models

including detailed controllers and DC transmission system.

Monopole and Bipole VSC models. SVC and STATCOM models – Detailed and

PSS/E type. Wind plant models (DFIG type) The models have been validated against PSCAD

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Introduction to TGSSR

Applications Generator-turbine – Series capacitor sub-

synchronous resonances. Generator-turbine – HVDC torsional interactions. Wind turbine – Series capacitor sub-synchronous

resonances. HVDC control interactions and DC resonance

issues. Multi-in-feed HVDC interactions.

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Introduction to TGSSR

Applications All other sub-synchronous frequency

interactions in power systems (Interactions of FACTS devices, Network resonances etc.)

Controller tuning and sub-synchronous damping controller design.

Analysis of Eigen properties to determine the locations for damping controllers.

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Introduction to TGSSR

Largest System Analyzed Manitoba Hydro System

More than 400 buses About 100 current injection devices Bipoles 1, 2 and 3 (proposed) About 5000 state variables

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Applications – Generator-Series Cap SSR

Series cap – generator electrical resonance (self excitation)

Network (series cap-gen) interaction with torsional oscillations.

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Applications – Generator-Series Cap SSR

A network mode interacts with a torsional mode.

SSI occurs when Network mode is close to one of the torsional modes in frequency - weak resonance condition

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Applications – Generator-Series Cap SSR

A network mode interacts with a torsional mode.

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Applications – Generator-Series Cap SSR

When Network mode is close to 16 Hz torsional mode.

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Applications – Generator-HVDC Torsional Interactions

Torsional interactions occur when there is a lightly damped oscillatory mode in the HVDC system close to one of the torsional modes – weak resonance condition

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Applications – Generator-HVDC Torsional Interactions

Under normal operating conditions

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State participations in 16 Hz torsional mode

Generator HVDC AC Filters and Network

Applications – Generator-HVDC Torsional Interactions

Current controller gains were adjusted to create a oscillatory mode close to 16 Hz.

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State participations in 16 Hz torsional mode

Generator HVDC AC Filters and Network

Applications – Generator-HVDC Torsional Interactions

Sub-synchronous Damping Controller (SSDC) Design The torsional modes of nearby generators can be controlled

through a damping controller added to HVDC controllers. Current controller is the most effective location.

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Applications – Generator-VSC Torsional Interactions

It is believed that VSC systems provide positive damping to the torsional modes of nearby generators.

Our analysis showed that this is not always correct.

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Applications – Generator-VSC Torsional Interactions

0.00

0.05

0.10

0.15

0.20

0.25

12.0 14.0 16.0 18.0 20.0 22.0 24.0 26.0 28.0 30.0 32.0

Dam

ping

(%)

Controller Mode Frequency (Hz)

16.3 Hz Torsional Mode

0.0 2.0 4.0 6.0 8.0

10.0 12.0 14.0

12.0 14.0 16.0 18.0 20.0 22.0 24.0 26.0 28.0 30.0 32.0

Dam

ping

(%)

Controller Mode Frequency (Hz)

Controller Mode

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Applications – Generator-VSC Torsional Interactions

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When controller mode is at 16 Hz

When controller mode is at 18 Hz

Applications – Wind Generator – Series Cap SSR

Torsional oscillations are in low frequency range (<5Hz) – not possible to have torsional interactions.

The problem is identified as a Sub-Synchronous Resonance in the electrical system.

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Applications – Wind Generator – Series Cap SSR

Frequency scans with equivalent circuit (change in slip is calculated for each frequency)

Analysis shows sub-synchronous resonance (stable). Self excitation according to conventional definition is not present.

Dynamic behaviour of controllers and rotor voltage is not included.

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Applications – Wind Generator – Series Cap SSR

Damping of resonance is very sensitive to the rotor side converter controllers.

24.4 24.5 24.6 24.7 24.8 24.9 25 25.1 25.2 25.3-4

-3

-2

-1

0

1

2

3

4

5

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Frequency(Hz)

Dam

ping

(%)

Kpdr

KpqrKpqr=0.125

Kpqr=0.100

Kpqr=0.0875

Kpqr=0.075

Kpqr=0.0625

Kpqr=0.05

Kpqr=0.0375

Kpdr=Kpqr=0.025,Kpωr=30,KpQs=0.5

Kpdr=0.0625

Kpdr=0.05

Kpdr=0.0375

Kpdr=0.075

Kpdr=0.0875

Kpdr=0.100

Kpqr=0.125

1

1/(sTiQs)

1

1/(sTidr)

Qs,ref

QsIDr

IDr,ref VDr+ +- -1x 3x

KpdrKpQs

1

Kiωr/s

1

Kiqr/sωr,ref IQr

IQr,refVQr

+ +- -

ωr

2x 4xKpqrKpωr

Small signal analysis shows an electrical resonance in which the damping can be controlled through the rotor side converter controllers.

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Applicability in Modern Power Systems

A new era of power systems Most of the HVAC lines are series compensated. A large percentage of wind generation. Wide usage of HVDC and DC grids. Involvements of FACTS devices are high.

Possibilities of having sub-synchronous frequency interactions are high.

A systematic approach using time domain simulations and small signal stability is essential to identify and solve these problems.

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Publications

1. Chandana Karawita, D.H.R. Suriyaarachchi and U.D. Annakkage , “A Case Study on the Vulnerability of VSC HVDC Systems for Sub-synchronous Interactions with Generator-Turbine Units”, CIGRE SCB4 Colloquium 2011, Brisbane, Australia, October 2011

2. D.H.R. Suriyaarachchi, U.D. Annakkage and Chandana Karawita, A Procedure to Study Sub-synchronous Interactions of Wind Integrated Power Systems, submitted to review, ”, IEEE Transactions on Power Systems.

3. D. H. R. Suriyaarachchi, U. D. Annakkage, C. Karawita, D. Kell, R. Mendis, and R. Chopra, “Application of an SVC to Damp Sub-synchronous Interaction between Wind Farms and Series Compensated Transmission Lines, Accepted to present in IEEE PES meeting, 2012

4. Chandana Karawita, U. D. Annakkage, “A Hybrid Network Model for Small Signal Stability Analysis of Power Systems”, IEEE Transactions on Power Systems, Vol.25, No. 1, Feb. 2010

5. Chandana Karawita, U. D. Annakkage, “Multi-In-Feed HVDC Interaction Studies Using Small Signal Stability Assessment”, IEEE Transactions on Power Delivery, Vol.24, No. 2, April 2009

6. Chandana Karawita, U. D. Annakkage, “Control Block Diagram Representation of an HVDC System for Sub-Synchronous Frequency Interaction Studies” The 9th International Conference on AC and DC Power Transmission, Oct 2010.

7. Chandana Karawita, U. D. Annakkage, “HVDC-Generator Torsional Interaction Studies Using A Linearized Model with Dynamic Network Representation”, International Conference on Power Systems Transients (IPST), June 3-6 2009, Kyoto, Japan

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Questions

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