Sub-Synchronous Control Interactiontsdos.org/2019/media/presentation2019/Sub- Synchronous Control... · Sub-Synchronous Control Interaction Sub-Synchronous Control Interaction (SSCI):

DNV GL © 04 September 2019 SAFER, SMARTER, GREENERDNV GL ©

04 September 2019

Prepared by DNV GL- Power System Advisory

ENERGY

Sub-Synchronous Control Interaction

Overview of Modeling, Risk Assessment and Countermeasures

1

Farshid Salehi, Farshid.Salehi@dnvgl.com

&Mike Tabrizi,

Mike.Tabrizi@dnvgl.com

mailto:Farshid.Salehi@dnvgl.commailto:Mike.Tabrizi@dnvgl.com

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Agenda

▪Background & History

▪Modeling & Study Approach

▪SSI Countermeasures

–Detection Solutions

–Mitigation Solutions

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Background & History


Mohave Incident (1970)An example of Sub-synchronous Torsional Interaction

▪ Mohave generator: 1,580 MW coal-fired in

NV.

▪ Gradually growing vibration that eventually

fractured a shaft section.

▪ First investigations incorrectly determined

cause. After 2nd failure in 1971 cause was

identified as Sub-synchronous Resonance

interaction with nearby series capacitors.

▪ An electrical resonance at 30.5 Hz excited a

mechanical resonance at 30.1 Hz.

▪ Problem was resolved by reducing

compensation percentage and installing a

torsional relay.

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Example of Sub-synchronous Oscillations for Wind Farms

▪ ERCOT SSCI EVENT (2009, 2017)

▪ China SSCI EVENT (2012)

▪ Minnesota SSCI EVENT

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Fault Recorder, South Texas Event, 2009


Classification of Sub-Synchronous Interaction (SSI)

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Classification of Simple synchronous Interaction

A. E. Leon, J. A. Solsona, "Sub-synchronous interaction damping control for DFIG wind turbines," IEEE Trans. Power System, vol. 30, no. 1, pp. 419-428, Jan. 2015.


Induction Generation Effect

▪ A series compensated line has a natural frequency at 𝑓𝑠𝑠𝑟 = 𝑓𝑠 ൗ𝑋𝑐

𝑋𝐿,

▪ 𝑆𝑠𝑠𝑟 =𝑓𝑠𝑠𝑟−𝑓𝑟

𝑓𝑠𝑠𝑟

▪ Where, 𝑓𝑟 is the electrical frequency of rotor.

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Simplified Sub-Synchronous Equivalent Model of DFIG

L. Fan, R. Kavasseri, Z. L. Miao, C. Zhu, "Modeling of DFIG-based wind farms for SSR analysis," IEEE Trans. Power

Delivery, vol. 25, no. 4, pp. 2073-2082, Oct. 2010.



▪ Sub-Synchronous Control Interaction (SSCI): is the result of

energy exchange between power electronic control systems and

series compensated lines within a sub-synchronous frequency

range, usually 5-55Hz in a 60Hz synchronous frequency system.

– The SSCI is not related to the shaft system and torsional mode.

– This is purely electrical phenomena and builds up very fast.

– The frequency of oscillation is not fixed and varies under differentcontrol parameters and system operating conditions.

– The Phenomena has been documented for Wind farm, Solar plantand HVDC in radial condition with series compensated lines.

– Type 3 wind farms have the most penetration and are morevulnerable to SSCI.

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▪ In the rotor current control loop of the DFIG, the proportional gain of the PI

controller can be interpreted as a resistance term added to the rotor circuit [a],

[b]. Therefore, this proportional gain increases the negative equivalent resistance

of the rotor, resulting in a lower damping or instability at a sub-synchronous

resonant frequency. This aggravation of the Induction Generation Effect (IGE)

produced by the rotor current control loop is called SSCI [b].

▪ [a] Z.Miao,“Impedance-model-based SSR analysis for type3 wind generator and series-compensated network,” IEEE Trans. Energy Convers., vol. 27, no. 4, pp.

984–991, Dec. 2012.

▪ [b] A. E. Leon, "Integration of DFIG-based wind farms into series-compensated transmission systems," IEEE Trans. Sustainable Energy, vol. 7, no. 2, pp. 451-459,

Apr. 2016.

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Modelling & Analysis


Modeling techniques for SSI Analysis

▪Detail State Space modelling

𝑥∙ = 𝑓 𝑥, 𝑢 & 𝑦 = 𝑔(𝑥, 𝑢)

▪ Impedance modelling (Transfer function)

–This is analytical technique, 𝑍 𝑠 =𝑉(𝑠)

𝐼(𝑠)

▪Detail EMT modelling

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Applications of Detail State Space Model

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Performing SSI Screening

Evaluating the impact of different parameters and state on SSI mode (Sensitivity Analysis &

Participation factor)

Tuning of control parameters


DFIG Detailed State Space Modelling

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Block Diagram of Detailed DFIG Connected to Series Compensated Line


Detailed State Space Modelling & SSI vulnerability Assessment

▪ Detail Models can be utilized for following purposes:

– Quick SSI screening

– Evaluating the impact of different parameters on SSCI

– Tuning of control parameters

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Radial Test System


State Space Modelling–Transient Simulation and FFT for 70% Compensation

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Acti

ve P

ow

er (

MW

)R

eacti

ve P

ow

er (

Mvar)

Active & reactive power for 70% compensation FFT result for 70% compensation


State Space Modelling – Transient Simulation and FFT for 50% Compensation

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Acti

ve P

ow

er (

MW

)R

eacti

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er (

Mvar)




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Acti

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er (

MW

)R

eacti

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Mvar)




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Acti

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State Space Modelling – Eigen Value Analysis For Screening

▪ Utilizing detail model for Screening (through Eigen value Analysis)

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Compensation Level

(%)

Eigen Value

frequency (Hz)

FFT Results

SSI Frequency

(Hz)

10 55.68 55.66 4.32

30 52.7 52.73 7.3

50 50.74 50.78 9.26

70 49.17 49.8 10.83

EIGENVALUE ANALYSIS RESULTS


Applications of Impedance Modelling

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Evaluating the impact of different dynamic loops on SSI


Applications of EMT Modelling

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Performing Detailed EMT SSI Analysis


Risk Assessment & Study Approach: Situations With SSI Risk

▪ SSI Analysis for Generation Interconnection

– Topology Check

– Frequency Scan-Based Screening

– Detailed EMT Simulation

▪ Evaluating the Impact of Transmission Expansion Projects on SSI

risk

– Topology Check for nearby Generation

– Sub-synchronous damping Screening

– Detailed EMT Simulation

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SSI Analysis for Generation Interconnection: Topology Check

▪ Identifying N-X contingencies which results in radial conditions

between the proposed generation interconnection and nearby

series compensated lines.

▪ Contingency Rank criteria is defined by ISO.

– For Example: Based on the ERCOT protocol, a generation

resource is considered to be potentially at SSI risk if there is

contingency with outage count equal or less than 14 which

leads to radial connection between the generation and nearby

series compensated line.

▪ Graph theory based algorithm are proposed to automate the

detection of the radial contingencies.

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SSI Analysis for Generation Interconnection: Frequency Scan-Based Screening

▪ Frequency Scan: is Strong tool for SSI Screening

– Frequency scan provides the impedance characteristic of wind

farm and also the transmission system as function of frequency.

– Performing separate scan on plan side and wind farm side.

– Calculate cumulative resistance and reactance at POI to

comment on SSI vulnerability.

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Frequency Scan- Harmonic injection

1. Bring the scanned grid to steady-state condition through an equivalent source.

2. Inject a voltage at a frequency of interest, 𝑉𝑖𝑛𝑗(𝑓), between the equivalent

source and the terminals of the grid.

3. Measure the voltage, 𝑉𝑚𝑒𝑎𝑠, and current, 𝐼𝑚𝑒𝑎𝑠, at the terminals of the grid;

4. Apply the Fast-Fourier Transform (FFT) to both 𝑉𝑚𝑒𝑎𝑠 and 𝐼𝑚𝑒𝑎𝑠 to get 𝑉𝑚𝑒𝑎𝑠(𝑓) and

𝐼𝑚𝑒𝑎𝑠(𝑓) at the same frequency of the injected voltage 𝑉𝑖𝑛𝑗 𝑓 .

5. Calculate the impedance, 𝑍𝑚𝑒𝑎𝑠 𝑓 , as below:

▪ 𝑍𝑚𝑒𝑎𝑠 𝑓 =𝑉𝑚𝑒𝑎𝑠(𝑓)

𝐼𝑚𝑒𝑎𝑠(𝑓)

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Different Steps of frequency scan-based Screening

I. B. M. Matsuo, F. Salehi, L. Zhao, Y. Zhou and W. Lee, "An Optimized Frequency Scanning Tool for Sub-Synchronous Interaction Analysis of Non-Linear Devices," 2019 IEEE/IAS 55th Industrial and Commercial Power Systems Technical Conference (I&CPS), Calgary, AB, Canada, 2019, pp. 1-7.


Frequency Scan- Plant Side

▪ The objective of these scans is to measure the resistance and

reactance of the entire wind/solar project in the sub-synchronous

(


Frequency Scan- Grid Side

▪ The 2nd step in the screening study involves conducting detailed

frequency scans on the transmission system. These scans are

performed to identify the series resonant frequency of the

transmission system under various contingencies.

▪ For the transmission side, a sensitivity analysis with different

compensation levels and statuses of switch shunts should be

performed as follows:

– Different compensation levels of the transmission system

– Transmission system with all critical switch shunts in service

– Transmission system with all critical switch shunts out of service

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▪ Calculate cumulative resistance and reactance at POI

▪ Cumulative resistance at cross-over frequency (zero reactance) is the index of

SSI risk

▪ If cumulative resistance at cross-over frequency is negative or marginally

positive there is SSI risk

Frequency Scan - Cumulative Impedance

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EMT Simulation

The results of the frequency scan analysis will be evaluated in conjunction

with “N-x” outage counts for all contingencies to determine need for

detailed EMT simulations..

Below are the example of criteria:

▪ If a fully radial contingency has an outage count of “N-6” or less, detailed EMT

simulation-based studies will be conducted regardless of whether frequency scans

depict SSR risk.

▪ Detailed EMT simulations will be performed for all contingencies that have been

identified using the process outlined above. Following aspects will be accounted

for while performing EMT simulations:

– Fault location – near-by or remote fault vis-à-vis the proposed project/series

compensation location

– Fault type preceding the line outages – S-L-G or 3-Phase fault

– Status of switched shunts between the project POI and series compensated

lines of interest

– Presence of neighbouring renewable/conventional generation resources

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SSI Analysis for Transmission Expansion Project

▪ Transmission expansion projects could increase the risk and severity of

SSI in power grid mainly by virtue of changing system configuration,

consequently electrical distance.

▪ This section propose a method and tool to quantify the impact of

transmission expansion projects on SSI risk.

▪ Two indices were proposed to comment on the impact of Transmission

expansion project on SSI risk:

➢Outage count of radial contingencies

➢Sub-synchronous damping at resonant frequencies

▪ A graph-theory based SSI screening tool is developed to quantify the

outage count associated with all grid radial contingencies.

▪ Frequency scan is utilized to estimate sub-synchronous damping.

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Transmission Expansion: Outage count of radial contingencies

▪ Identifying all generation resources in vicinity of both end of

proposed project.

▪ Identifying N-X contingencies which results in radial connection

between generation resources and nearby series compensated

line before and after proposed line.

▪ Compare the outage counts to evaluate the risk of SSI

occurrence.

▪ A graph-theory based SSI screening tool is developed to

quantify the outage count associated with all grid radial

contingencies.

Ref: F. Salehi, P. Saraf, A. Brahman and M. A. Tabrizi, "Evaluating the Impacts of Transmission Expansion on

Sub-Synchronous Resonance Risk," 2019 IEEE Power & Energy Society General Meeting, Atlanta, GA, 2019

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Transmission Expansion: Sub-synchronous damping at resonant frequencies

▪ Perform frequency scans on the grid side for all contingencies of

interest to see how new line affects the grid sub-synchronous

resonance.

▪ Decrease in Sub-synchronous resonance resistance lead to less

damping and exacerbate the SSI condition.

▪ If the outage count and sub-synchronous resonant damping show

higher SSI risk for a specific generation resource, comprehensive

frequency scan based screening should be performed to comment

on SSR vulnerability.

Ref: F. Salehi, P. Saraf, A. Brahman and M. A. Tabrizi, "Evaluating the Impacts of Transmission Expansion on

Sub-Synchronous Resonance Risk," 2019 IEEE Power & Energy Society General Meeting, Atlanta, GA, 2019

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Reference for Example of evaluating the Impact of Transmission Expansion project on SSI Risk

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▪ For Further Details and example of SSR risk assessment for transmission

expansion project, please refer to below paper by DNV GL team which was

presented in IEEE PES General meeting Atlanta, 2019

F. Salehi, P. Saraf, A. Brahman and M. A. Tabrizi, "Evaluating the Impacts of

Transmission Expansion on Sub-Synchronous Resonance Risk," 2019 IEEE Power &

Energy Society General Meeting, Atlanta, GA, 2019


Discussion for Transmission Expansion project

▪ The proposed approach provides a detailed methodology for evaluating

the impact of transmission expansion projects on SSI risk through a two-

steps approach utilizing outage count index and sub-synchronous

damping index.

▪ The proposed methodology and developed tool were utilized on a portion

of ERCOT grid and it was demonstrated that transmission expansion

projects can have potential detrimental effects on SSR risk in the

system.

▪ In this case, the results of frequency scan indicate that proposed system

upgrades lead to more negative damping for all scenario of operation

and consequently exacerbate the SSR condition.

▪ Finally, the results were validated using detailed EMT simulations.

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Questions?

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SSI Countermeasure


Sub-Synchronous Oscillation- Countermeasures

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Classification of Sub-Synchronous Oscillation countermeasures


SSCI Detection- Motivation▪ The power system has recently become more susceptible to Sub-

Synchronous Interactions (SSI) due to the high penetration of

renewable resources and series-compensated lines.

▪ SSCI and IGE is a purely electrical and fast-growing phenomenon.

▪ Detection of SSI is challenge because of the nature of the signal.

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Example of SSCI signal (Voltage & Current)


Reference for The Proposed SSCI Detection Algorithm

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▪ The details of proposed SSCI detection algorithm can be find in below paper:

▪ F. Salehi, I. Brandao Machado Matsuo, A. Brahman, M. Aghazadeh Tabrizi and W.

Lee, "Sub-Synchronous Control Interaction Detection: A Real-Time Application,"

in IEEE Transactions on Power Delivery.

doi: 10.1109/TPWRD.2019.2930400

▪ https://ieeexplore.ieee.org/document/8770097

▪

https://ieeexplore.ieee.org/document/8770097


Mitigation of Sub-Synchronous Interaction using battery Storage

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Hybrid Wind & Storage

Portion of ERCOT Grid


Mitigation of Sub-Synchronous Interaction using battery Storage

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Simplified Scheme – Radial connection between the RE and SC


Battery Storage control System with Feed Forward addition of SSI Damping Controller

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Storage Control Loop


Simulation Results for Hybrid Mitigation Solution

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Without Hybrid Storage With Hybrid Storage


Questions?

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SAFER, SMARTER, GREENER

www.dnvgl.com

Thank You

47

Sub-Synchronous Control Interactiontsdos.org/2019/media/presentation2019/Sub- Synchronous Control... · Sub-Synchronous Control Interaction Sub-Synchronous Control Interaction (SSCI):

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