• Introduction

Motivation and Operational Issues

Research Objectives

• Mathematical Modelling of DFIM with Transmission line

DFIM and Back-to-Back Power Converter Modelling

Series Capacitive Compensation Transmission line

• Analysis and Damping of Sub-Synchronous Oscillations in a 250 MW DFIM Hydro Unit Connected to Series Compensated 765 kV Transmission Lines
• Impact of SSCI on a Large Rated Asynchronous Hydro Unit Connected to 765kV and 400kV Extra High Voltage Long Transmission Lines
• Investigation of DC-link Stabilization Through BESS for DFIM fed Hydropower Unit Under Grid Faults
• Conclusion

Conclusion, Recommendations and Future Scope

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1
1
IMPACT OF SUB SYNCHRONOUS OSCILLATION IN RENEWABLE SYSTEMS FOR POWER GRID
RESILIENCE-BATTERY MANAGEMENT SYSTEM AND
HIGH VOLTAGE BATTERIES
2
Outline
• Introduction
 Motivation and Operational Issues
 Research Objectives
• Mathematical Modelling of DFIM with Transmission line
 DFIM and Back-to-Back Power Converter Modelling
 Series Capacitive Compensation Transmission line
• Analysis and Damping of Sub-Synchronous Oscillations in a 250 MW DFIM Hydro Unit
Connected to Series Compensated 765 kV Transmission Lines
• Impact of SSCI on a Large Rated Asynchronous Hydro Unit Connected to 765kV and 400kV
Extra High Voltage Long Transmission Lines
• Investigation of DC-link Stabilization Through BESS for DFIM fed Hydropower Unit Under
Grid Faults
• Conclusion
 Conclusion, Recommendations and Future Scope
3
Need of Energy Storage Systems
INTRODUCTION
3
Indian Power Sector Scenario @ Dec 2017
( source : CEA)
Expected Indian Power Scenario @ May 2023
( source : CEA)
 Power demand during the day is 12 GW (@12.00
hours,22 Aug, 2017)
 The combined wind & solar power generation during
the day was scheduled as 3.04 GW (@12.00 hours).
 As per CERC-DSM, 15% of the RES power variation is
allowable from the actual generation. (i.e. 2.584 GW to
3.496 GW)
 Power generation reaches to 5.28 GW (@12.00
hours) (Power deviation 1.824 GW) results in
financial implications.
Case Scenario of Indian Grid System on 22-August-2017
 Expected installed capacity is 522.4 GW
 Expected installed capacity of wind & solar power is 160
GW.
 Power demand during the day is estimated as 208 GW
 The combined wind & solar power generation during
the day is varied from 20 GW to 80 GW.
 If 10% deviation is occurred from the schedule, it
reflects 2 GW to 8 GW power variation from the
schedule results in challenging the grid stability.
Expected Case Scenario of Indian Grid System @ 2023
4
Machines Serving to Hydro-Generating Applications
4
SYNCHRONOUS MACHINE
• Thyristor is usually used.
• Power converter voltage and current ratings are less.
• No real power flow via power converter.
• Easy to adopt converter redundancy in excitation system.
• External static frequency converter is required for starting of
pump turbine.
• Less affected by SSO.
• High frequency switching devices used in power converter.
• Power converter voltage and current ratings are high.
• Power converter is responsible for real and reactive power
control (bidirectional power flow).
• Rotor side power converters are used for starting of pump
turbine.
• More affected by SSO.
DOUBLY FED INDUCTION MACHINE
Phase shift
Excitation Transformer
Slip power
Grid
1
DFIM
250 MW
3300 V
11600 A
Power Converters (5 x 5 MW)
2400 A
2400 A
15.75 kV 15.75 kV / 420 kV
10191 A
15.75 kV / 3.3 kV
5
15.75 kV
916.4 A
(a) Synchronous Machine
(b) Doubly fed Induction Machine
INTRODUCTION
5
Benefits of
Variable
Speed
PSPP
Rapid
Frequency
Control
High Power
Discharge
Higher
Efficiency
at Part
Loads
Quick
Response
Grid
Stability
Voltage
Support
Tehri Dam
Fig. Variation in water head during a year
INTRODUCTION
Need of Variable Speed Operation in Hydro
6
Fig. Sustainable development goals
INTRODUCTION
UN Sustainable Development Goals
04/12/2023
2
7
Series Compensation
7
INTRODUCTION
Fig. Series compensation
Fig. Series compensated EHV lines Fig. On site series capacitor bank
Increases power flow by series capacitor decreases its total line impedance.
𝑃􀭖 =
𝑉􀯦𝑉􀯋
𝑋􀯅
si n 𝛿
𝑃􀭖 =
𝑉􀯦𝑉􀯋
𝑋􀯅 − 𝑋􀮼
𝑠𝑖 𝑛 𝛿
Reducing XL increases PR
VS VR
XS XL1 XL2
XC XR
A P B
8
Sub Synchronous Oscillations (SSO)- History
8
INTRODUCTION
• Occurs mainly in series capacitor compensated transmission
systems
• First experienced in 1970 resulting in shaft failure of units
at Mohave Plant in Southern California
• Not until the second failure in 1971 was the real cause of
failure recognized as SSO
• Problem was solved by reducing series compensation
a) Failure of rotor shaft due to SSO b) Graph of mechanical frequency
Fig. SSO at Mohave Plant
Fig. Shaft of 250MW DFIM system
9
SSO and its Classification
INTRODUCTION
Fig. SSO classification model
Sub Synchronous
Oscillation
Sub Synchronous
Resonance
Device Dependent Sub
Synchronous Oscillation
Sub Synchronous Control
Interaction
Sub Synchronous Torsional
Interaction
Self
Excitation
Shaft Torque
Amplification
Torsional
Interaction
Induction
Generator
Effect
DFIM SSR
DC Converter
Control
Interaction
Power System
Stabilizer Control
Interaction
Speed Governor
System Interaction
Converter-
Converter
Interaction
Converter-Grid
Interaction
Converter-
Generator
Interaction

 Interaction between the
synchronous generator
and series capacitor
 Interaction between the
power converter and
synchronous generation
 Interaction between the
power converters
 Interaction between the
power converters and
DFIM
 Interaction between the
DFIM and series capacitor
 Interaction between the
controller and
synchronous generator
 Interaction between the
power converter and
grid
 Interaction between the
power converter and
grid
10
Time line of SSO Events-By IEEE PES IBR SSO TASK Force
INTRODUCTION
Year Country Frequency Components Machines Transmission line
2007 Minnesota 9.44 Hz Type 3 WPP 345 kV
2009 South Texas 20 Hz Type 3 WPP 345 kV
2010 Oklahoma USA 13 Hz Variable Speed 138 kV
2011 Texas 6 Hz Type-4 WPP 345 kV
2011-14 Oregon 14 Hz Type-4 WPP 345 kV
2011-12 Oklahoma USA 6 Hz Variable Speed 138 kV
2012-13 North Chine 9 Hz WPP —
2014-15 China 30 Hz Type-4 WPP 750 kV
2015 Canada 20 Hz Hydro 44 kV
2016 Virginia 10 Hz Solar —
2017 China 37 Hz WPP 220 kV
2019 Great Britain 9 Hz WPP 230 kV
2021 Scotland 8 Hz WPP 230 kV
11
SSR Analysis Techniques
INTRODUCTION
Eigenvalue Analysis
Frequency Scan Screening
Transient Simulation Analysis
Impedance Based Analysis
12
SSR Analysis Techniques
INTRODUCTION
Eigenvalue Analysis
This EVA depends on linear theory and it has been proven as an exact
and precise approach for analyzing the SSO. Real part of Eigen value
shows damping coefficients and imaginary is frequency of resonance.
Frequency Scan Screening
In this method calculate apparent impedance from generator and
identify the potential risk of SSO.
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13
SSR Analysis Techniques
INTRODUCTION
Transient Simulation Analysis
It uses ETAP, EMTP-RV and PSCAD Software’s.
Impedance Based Analysis
The impedance model analysis is categorized as stationary frame
(phase domain) impedance model and synchronous frame (dq model)
impedance model.
14
Damping Methods of SSO
INTRODUCTION
1. Facts Devices
TCSC
GCSC
2. Power Electronic Controller using RSC and GSC
Varying level of series compensation
Variation in slip power
15
Converter Control as SSO Mitigation Technique
INTRODUCTION
Authors/Transaction
Papers
Year Techniques Discoveries
Ali et al 2010 Eigen value analysis & time
domain simulation
The simulation experimental analysis shows that if any
sensitive parameters of RSC are tuned properly ,then the
DFIG system can become immune to the SSCI for level of
series compensation.
Fatah D. et al 2011 Modal analysis The SSR mode damping can be increased by increasing the
speed of RMS voltage over series capacitor than that of
current.
Basmath H J et al 2015 Time domain analysis The GSC controller is designed with Supplementary SSR
damping control that has simpler proportional gain.
Li G Chen et al 2019 Modal analysis The short transmission line distance among 2 generators
should be reduced to penetrate high DFIG-based
generation. This process would reduce the SSR efficiently
Jiao Y. Li 2019 Eigenvalue analysis and
time-domain simulation
The controller has simpler compensator arrangement for
the providence of adequate damping of SSO.
16
Converter Control as SSO Mitigation Technique
INTRODUCTION
Authors/
Transaction Papers
Year Techniques Discoveries
Zang et al 2015 Eigenvalue analysis and Time
domain simulations
The system stability has been enhanced by combining
Two-degree-of-freedom (2DOF) control mechanism.
Gu K wun et al 2016 Impedance analysis The wind turbine should be operated at a lower
closed-loop bandwidth while detecting a SSCI
disorder.
Yang F et al 2009 Eigenvalue analysis and Time
domain analysis
The speed deviance damping signal can be used
develop a control system.
Ali MT et al 2017 Electrical damping analysis and
eigenvalue analysis
A partial feedback linearization approach is used in
the nonlinear damping controller for the reduction of
SSR.
Liu et al 2017 Impedance-model-based analysis
and time-domain simulations
sub synchronous notch filters (SNFs) has been
embedded into DFIG converter controllers for
suppressing SSR.
Mahalaxmi R et al 2019 State space model Tuning of Fuzzy Logic Controller in Rotor side
converter to damped the SSO.
Vijay Mohale and
Thanga Raj Chelliah
2022 Eigen value analysis and SSCI DFIM Converter controls with challenges in selection
of compensation devices : RSC Controller
17
Publications
Ph.D. Publications-IEEE IAS Annual Meeting
 Vijay Mohale and T. R. Chelliah, “Sub Synchronous Oscillation in Asynchronous
Generators Serving to Wind and Hydro Power Systems – A Review,” in IEEE
Industry Applications Society Annual Meeting (IAS), Canada 2021, pp. 1-7.
Ph.D. Publications-Journal
 Vijay Mohale, Sunny Sonandkar, Thanga Raj Chelliah, “Large asynchronous
hydro generating systems connected to TCSC compensated transmission lines
(Simulation with experimental validation): A review on SSO perspectives,
Electric Power Systems Research, Volume 219, 2023.
18
• Investigation of sub-synchronous oscillations in a 250 MW DFIM fed hydropower unit connected to
765 kV and 400 kV extra high voltage long transmission line.
• Design and development of a software based SSO mitigation control strategies in a 250 MW DFIM
unit with respect to different series capacitive compensation level.
• Design and development of a hardware based SSO mitigation technique on a 2.2 kW DFIM unit.
Objectives
INTRODUCTION
04/12/2023
4
19
DFIM Modelling
3
. .
2
a a
g g dg P V I
 

3
. .
2
a a
g g qg Q V I
 
 
DFIM Control ( Stator Flux Oriented Vector Control)
3
. .
2
a
a
m s
em qr
s s
L V
T p I
L 


 
2
3
2
a
a a
s m
s s dr
s s s
V L
Q V I
 L L

   
     
 
Electro-magnetic Torque,
Reactive Power (Stator side),
DC Link Voltage Control (Grid Voltage Oriented Vector Control)
Active Power (Rotor side),
Reactive Power (Rotor side),
Vbn = Vc1/3 [2Sbg1-Sag1-Scg1]+Vc2/3[2Sbg2-Sag2-Scg2]
Van = Vc1/3 [2Sag1-Sbg1-Scg1]+Vc2/3[2Sag2-Sbg2-Scg2]
Modulator (SPWM/SVM)
Control System
DFIM
(rotor winding)
Three Level VSC
Sag1
Sag2
Sbg1
Sbg2
Scg1
Scg2
Var
Vbr
Vcr
Vc1
Vc2
Vcn = Vc1/3 [2Scg1-Sag1-Sbg1]+Vc2/3[2Scg2-Sag2-Sbg2]
Fig. Simplified VSC Model
MODELLING
Vds
Vqr
Vdr
Vqs
Idr
Iqr
Ids
Iqs
q
d
Rs+jLs
r r Rs +jLs R +jL
Fig. Kroon’s Primitive Machine Model
20
Back-to-Back Converter Control System
Iqg Rf+ωsLfIdg
V*
dc
Vdc
+
–
+
–
Iqg
+
+
Σ PI Σ
I*
qg
PI Σ
Σ PI Σ PI Σ
Q*
g
Qg
+
–
+
–
+
+
I*
dg
Idg
θs
dq
abc
Idg Rf -ωsLfIqg
+
+
Vdg
Vqg
Feedback
Decoupling PWM
dq
abc
dq
abc
Vc g
Icg
PLL
Idg
Vdg
Vag Ia g
Vbg Ibg
Iqg
Vqg
Vdc
DC Link
GSC
Grid Supply
La
Lb
Lc
Fig. Grid Side Converter Control System.
Fig. Rotor Side Converter Control System.
MODELLING
21
Transmission line
Impedance Modeling of DFIM Connected With a Series Compensated Line
Resonance frequency is presented, Slip of synchronous frequency is expressed as,
The Total impedance
Fig. Represents the DFIM equivalent circuit of SSO frequency
MODELLING
𝑓􀯡 = 𝑓􀬴
𝑋􀯖
𝑋􀯟
𝑆 =
𝑓􀯡 − 𝑓􀯠
𝑓􀯡
Total line impedance for series compensated line is,
Ζ􀮊(𝑠) = 𝑍􀯅 (𝑠) + 𝑍􀮽􀮿􀯂􀯆(𝑠)
Ζ􀮊(𝑓) = 𝑅(𝑓) + 𝑗𝑋(𝑓)
𝑍􀯅 = 𝑠𝐿􀯅 + 𝑅􀯅 +
1
𝑠𝐶􀯅
22
Fig. Electrical Depiction of RSC and GSC serving to 250 MW DFIM Unit Fed to EHV Lines
MODELLING
Copyright by IIT Roorkee
23
Fig. Experimental schematic of 2.2 kW DFIM unit
Experimental Set-up
MODELLING
Copyright by IIT Roorkee
24
Publications
Ph.D. Publications- IEEE IAS Annual Meeting
 Vijay Mohale, T. R. Chelliah and Yogesh. V. Hote, “Modeling and Analysis of
Sub-Synchronous Oscillation in Large Rated DFIM Based Hydro Unit Fed to
Extra High Voltage Transmission Lines,” in IEEE Industry Applications Society
Annual Meeting (IAS), Detroit, MI, USA 2022, pp. 1-7.
Ph.D. Publications- Journal
 V. Mohale, T. R. Chelliah and Y. V. Hote, “Small Signal Stability Analysis of
Damping Controller for SSO Mitigation in a Large Rated Asynchronous Hydro
Unit,” in IEEE Transactions on Industry Applications , vol. 59, no. 4, pp. 4914-
4923, July-Aug. 2023.
04/12/2023
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25
SOFTWARE AND HARDWARE BASED DAMPING OF SUB SYNCHRONOUS
OSCILLATIONS FOR VARIABLE SPEED PUMPED STORAGE UNITS FED EXTRA HIGH
VOLTAGE TRANSMISSION LINES
 ANALYSIS AND DAMPING OF SSO
 IMPACT OF SSCI ON LARGE RATED HYDRO UNIT
 INVESTIGATION OF DC-LINK STABILIZATION THROUGH BESS
26
ANALYSIS AND DAMPING OF SSO
Fig. Typical schematic diagram of the 250 MW large scale DFIM drive with series compensated 765 kV extra
high voltage transmission line
Typical schematic diagram Copyright by IIT Roorkee
27
Fig. Hydro turbine controller
ANALYSIS AND DAMPING OF SSO
Proposed SSO topology
28
Fig. Rotor side converter controller
ANALYSIS AND DAMPING OF SSO
Proposed SSO topology
Fig. Grid side converter controller
29
Fig. Selection of proportional parameters in the RSC controllers using dampness optimization approach
ANALYSIS AND DAMPING OF SSO
SSCI Mitigation Method 1
30
Fig. SSCI damping controller block diagram for GSC
ANALYSIS AND DAMPING OF SSO
SSCI Mitigation Method 2
04/12/2023
6
31
Observations
• It is inferred that the oscillations of every DFIM
component is increased when compensation level is
keep increasing, and system goes into the unstable mode
when adding 75% compensation.
• In case of 50% compensation level, DFIM components
are in the oscillatory condition, however it does not
make big impact to the machine operation.
• But, when 75% series compensation level is added into
the system then all the system parameters oscillated
heavily and goes into the unstable mode.
Simulation Results – 250 MW DFIM
DFIM PARAMETERS AT VARIOUS SERIES COMPENSATION LEVEL
Fig. 250 MW DFIM Parameters at various series compensation level
32
Observations
• It is inferred that without mitigation methods the
oscillation is carried in the dc link voltage and make
the system into unstable mode if it is continuously
existence in the system.
• When comparing performance of both methods, SSCI
mitigation method 1 provides fast reduction in SSCI
infliction.
Simulation Results – 250 MW DFIM
INVESTIGATING THE SSCI INFLICTION WITH THE PRESENCE OF TWO
PROPOSED MITIGATION METHODS
Fig. Comparison of SSCI Mitigation method in 250 MW
DFIM fed hydropower unit
33
Fig. Experimental schematic of 2.2 kW DFIM unit
Experimental Set-up
ANALYSIS AND DAMPING OF SSO-CHAPTER
34
Observations
• It is inferred that more oscillations are occurred in
the DFIM system when adding series
compensation to the system.
• In case of SSCI mitigation methods, tuning of rotor
side converter controller approach is performed in
the experimentation and result is given.
Hardware Results – 2.2 kW DFIM
Fig. 2.2 kW DFIM parameters with the presence of 50%
series compensation
50% series compensation
ANALYSIS AND DAMPING OF SSO
35
Publications
 Vijay Mohale, T. R. Chelliah and Y. V. Hote, “Analysis and Damping of Sub-
Synchronous Oscillations in a 250 MW DFIM Hydro Unit Connected to Series
Compensated 765 kV Transmission Lines,” in IEEE Transactions on Industry
Applications, vol. 59, no. 2, pp. 2234-2245, March-April 2023.
Ph.D Publications-Journal
Ph.D Publications-Conference
 Vijay Mohale and T. R. Chelliah, “Analysis of Sub-Synchronous Oscillations in
Asynchronous Generator Serving to Hydropower Systems,” 2022 IEEE
International Conference on Power Electronics, Smart Grid, and Renewable
Energy (PESGRE), 2022, pp. 1-6.
36
Fig. Typical schematic diagram of the 250 MW large scale DFIM based hydro unit connected to series
compensated extra high voltage transmission lines.
Typical schematic diagram
IMPACT OF SSCI ON LARGE RATED HYDRO UNIT
Copyright by IIT Roorkee
04/12/2023
7
37
Fig. Hydro turbine controller
IMPACT OF SSCI ON LARGE RATED HYDRO UNIT
Proposed SSO topology
38
Fig. Rotor side converter controller
IMPACT OF SSCI ON LARGE RATED HYDRO UNIT
Proposed SSO topology
Fig. Grid side converter controller
39
Fig. Proposed SSCI mitigation method.
IMPACT OF SSCI ON LARGE RATED HYDRO UNIT
Proposed Mitigation Method
40
Observations
• Simulation study, both transmission lines (765 kV and 400
kV) are capable to withstand until 50% of the series
compensation.
• When analyzing 55% series compensation level, 250 MW
DFIM unit connected with 765 kV transmission line can
withstand this compensation level and after the tiny
transients
• DFIM unit connected with 400 kV transmission line suffer
with an oscillation.
• When applying 85% series compensation level applied to
transmission lines connected with DFIM goes to oscillations
and subsequently fell into an unstable mode.
Simulation Results – 250 MW DFIM and 400 kV TL
PERFORMANCE COMPARISON OF TRANSMISSION LINES (TL)
Fig. DFIM unit connected with 400 kV transmission line
41
Simulation Results – 250 MW DFIM and 765kV TL
PERFORMANCE COMPARISON OF TRANSMISSION LINES (TL)
Fig. DFIM unit connected with 765 kV transmission line
Observations
• When analyzing 55% series compensation level, 250 MW
DFIM unit connected with 765 kV transmission line can
withstand this compensation level and after the tiny transients.
• When applying 85% series compensation level into the DFIM,
both transmission lines connected with DFIM go through
oscillations in the parameters and subsequently fell into an
unstable mode.
• While analyzing the results between two transmission lines,
DFIM unit has connected with 765 kV transmission lines
provides better performance compared to the 400 kV
transmission line because 765kV has high X/R ratio than 400
kV transmission line.
42
Observations
• From the results it is inferred that 250 MW DFIM unit is
suffered with the series compensation level of 55%, and
85% when there is no SSCI mitigation method is
employed in the DFIM unit.
• When proposed SSCI mitigation method is active in the
DFIM unit, the parameters are not undergone an
oscillation even series compensation level is reached to
85%.
• During the operation, the rotor resistance value is
increased towards the grid resistance value when
increasing the series compensation level.
Simulation Results – 250 MW DFIM and 765kV TL
EFFECT OF PROPOSED SSCI MITIGATION
Fig. Effect of proposed SSCI Mitigation method in a 250
MW hydropower unit connected with 400 kV transmission
line.
04/12/2023
8
43
Observations
• To analyze the performance of the proposed
SSCI mitigation method, the proposed SSCI
mitigation method is employed in the DFIM
unit, and 40% and 70% series compensation
levels are applied.
Hardware Results – 2.2 kW DFIM
Fig. 2.2 kW DFIM parameters with the presence of 50%
series compensation
IMPACT OF SSCI ON LARGE RATED HYDRO UNIT
50% series compensation
Fig. Effect of proposed SSCI Mitigation method in a 2.2
kW DFIM
44
Publications
Ph.D Publications-Conference
 Vijay Mohale and T. R. Chelliah, “Impact of Series Compensated High Voltage
Transmission Lines in the Operation of DFIM Based Hydro Unit,” 2022 Second
International Conference on Power, Control and Computing Technologies
(ICPC2T), 2022, NIT Raipur pp. 1-6.
 Vijay Mohale, T. R. Chelliah and Yogesh. V. Hote, ” Design and Development of a
Scaled Prototype of a 250MW Hydrogenerator Fed 765 kV Transmission Lines
to Test Sub-Synchronous Oscillation in Power System Laboratory,” in 2023 IEEE
Industry Applications Society Annual Meeting (IAS), Nashville, Tennessee,
USA,2023. (Status- Accepted)
Ph.D. Publications- IEEE IAS Annual Meeting
45
Fig. Diagram of the 250 MW large scale DFIM drive with series compensated extra high voltage transmission line
Typical schematic diagram
INVESTIGATION OF DC-LINK STABILIZATION THROUGH BESS
Copyright by IIT Roorkee
46
Observations
• a) It is observed that converter protections (both DC chopper and crowbar protection) are not activated during this
period as shown in Fig,a (iv) because DC link voltage fluctuation is within the safety limits.
• b) To stabilize the variations in the DC link voltage, DC chopper protection is therefore activated. when the DClink
voltage exceeds 1.1 p.u. to stabiles the DC link voltage fluctuations.
• During the grid fault period, active power delivery of the DFIM is reduced to 0.4 p.u. from 0.9 p.u. as shown.
Simulation Results – 250 MW DFIM
DYNAMIC PERFORMANCE OF DFIM HYDROPOWER UNIT
Fig. Dynamic performance of 250 MW DFIM hydropower unit under various grid faults
47
Observations
• c) Because of the induced rotor EMF, the rotor current exceeds 3 p.u. of its rated value and activates the
crowbar protection, the converter unit is isolated from the DFIM unit, and the rotor winding short-circuits and
shuts down the DFIM unit.
• d) In this scenario, a 55% series capacitive compensation system is intentionally added to the 250 MW DFIM
unit to analyze the sub-synchronous oscillations. During this period, converter protections are not activated
because either DC link voltage or rotor current are not reaching their safety limits.
Simulation Results – 250 MW DFIM
DYNAMIC PERFORMANCE OF DFIM HYDROPOWER UNIT
Fig. Dynamic performance of 250 MW DFIM hydropower unit under various grid faults
48
Fig. Proposed SSCI mitigation method.
INVESTIGATION OF DC-LINK STABILIZATION THROUGH BESS
Proposed Mitigation Method
04/12/2023
9
49
Fig. Closed loop control of DFIM unit with BESS unit.
INVESTIGATION OF DC-LINK STABILIZATION THROUGH BESS
Proposed Closed loop Control
50
Observations
• The comparison results of with and without BESS unit
during 55% SSCI infliction is shown.
• The dc link voltage of the back-to-back power converter
and active power delivery of the DFIM unit are
considered for analyzing the proposed BESS unit in the
DFIM unit.
• From the results it is inferred that 250 MW DFIM unit is
suffered with the series compensation level of 55%,
when there is no BESS unit is employed in the DFIM
unit.
Simulation Results – 250 MW DFIM
PERFORMANCE OF 250 MW UNIT WITH BESS
Fig. Performance of 250 MW unit with BESS unit during
SSCI infliction
Copyright by IIT Roorkee
51
Fig. Experimental Test set-up
Experimental Set-up
INVESTIGATION OF DC-LINK STABILIZATION THROUGH BESS
Transmission Line Modal with Series Compensation
Current Measuring Clamp
DC Machine DFIM
Auto
Transformar
GSC
RSC
Power
Analyzer
PQA
BESS
MATLAB
Control Algorithm
dSPACE
Grid
DSO
Copyright by IIT Roorkee
52
Observations
• It is inferred that more oscillations occur in the DFIM
system when adding series compensation to the system.
• These oscillations will lead to challenges in the power
delivery from DFIM to the grid and DFIM goes into
unstable mode.
• Series compensation levels do not make the oscillations in
the DFIM parameters because BESS unit is activated once
the dc-link voltage get oscillated. Consequently, DFIM
does not go into the SSCI infliction at a higher level.
Hardware Results – 2.2 kW DFIM
Fig. Performance of 2.2 kW unit with BESS control
during SSCI infliction
INVESTIGATION OF DC-LINK STABILIZATION THROUGH BESS
53
Publications
 Vijay Mohale, T. R. Chelliah and Yogesh. V. Hote, “Investigation of DC-link
Stabilization Through BESS for DFIM fed Hydropower Unit Under Grid Faults,”
submitted to IEEE System Journal.
Ph.D Publications-Journal
Ph.D Publications-Conference
 Vijay Mohale and T. R. Chelliah, ” Mitigation of Sub-Synchronous Oscillation in
Variable Speed Pumped Storage Units Connected With 765 kV Double Circuit
Transmission Lines,” National Conference on ‘Energy Storage including Pumped
Storage – Opportunities and Challenges’ 4-5 November 2022, Shimla by Central
Board of Irrigation and Power (CBIP) New Delhi, 2022, pp. 1-6.
54
CONCLUSION
Summary
Main contributions of this research
 Comprehensive review of large rated variable speed hydro-generating unit were reviewed
in view of series compensation, and it operational challenges related to sub synchronous
oscillations are addressed.
 Analysis and investigation of the SSCI in the DFIM fed hydro power unit and provides the
SSCI mitigation methods for enhancing the power system stability in the presence of subsynchronous
oscillations.
 The various proposed techniques are tested for different compensation level to check the
stability of the DC-link voltage during oscillations in the power system.
 This research indicated that 765 kV transmission line has lesser SSCI infliction when
compared to the 400 kV transmission line due to the higher X/R ratio, specifically 765 kV
line has not suffered with the SSCI infliction with 55% series compensation level where
400 kV has SSCI infliction.
 In this study confirmed that the inclusion of BESS in back-to-back converter in the DFIM
unit has mitigated the SSCI infliction with the series capacitive compensated levels and
improved the fault ride through control of 250 MW DFIM unit.
 Experimental work is validated in the laboratory with a scaled down model of 2.2 kW
DFIM to check the stability of the rotor side converter in the DFIM with the proposed
SSCI mitigation method.
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55
CONCLUSION
Summary
Future Scope
 The response of hydraulic governor control systems at the time of SSO needs to be
analyzed with a special focus on electromechanical vibration.
 The open challenge for the practical and effective SSCI mitigation strategy is
simultaneous monitoring of basic and sub-synchronous frequency components. On the
other hand, the usage of the virtual rotor speed and the consequence of the VSC of input
control signal (ICS) would be considered as for investigation of SSCI mitigation.
 A single machine of 250 MW capacity is consider in this present study, but a hydropower
project has multiple generators. Analysis on entire hydropower plant i.e. multiple
generators and turbines with the help of Real-Time Digital Simulator (RTDS) shall
strengthen the present work.
 Adaptive control techniques shall be applied for understanding the effectiveness of BESS
unit in SSO mitigation application.
56
List of Publications
1. Vijay Mohale, T. R. Chelliah and Yogesh. V. Hote, “Control system to dampen SSO in
Variable Speed Pumped Storage Units Connected with Extra High Voltage Transmission
Lines,” (filed on 1st Dec 2022 no-202211069377-Granted).
INDIAN Patent
Ph.D Publications- Journal
1. Vijay Mohale, T. R. Chelliah and Y. V. Hote, “Analysis and Damping of Sub-Synchronous
Oscillations in a 250 MW DFIM Hydro Unit Connected to Series Compensated 765 kV
Transmission Lines,” in IEEE Transactions on Industry Applications, vol. 59, no. 2, pp.
2234-2245, March-April 2023.
2. V. Mohale, T. R. Chelliah and Y. V. Hote, “Small Signal Stability Analysis of Damping
Controller for SSO Mitigation in a Large Rated Asynchronous Hydro Unit,” in IEEE
Transactions on Industry Applications , vol. 59, no. 4, pp. 4914-4923, July-Aug. 2023.
3. Vijay Mohale, T. R. Chelliah and Yogesh. V. Hote, “Investigation of DC-link Stabilization
Through BESS for DFIM fed Hydropower Unit Under Grid Faults,” submitted to IEEE
Systems Journal. (Under Revision-R2)
57
List of Publications
4. Vijay Mohale, Sunny Sonandkar, Thanga Raj Chelliah, “Large asynchronous hydro
generating systems connected to TCSC compensated transmission lines (Simulation
with experimental validation): A review on SSO perspectives, Electric Power Systems
Research, Volume 219, 2023.
5. Mohale, Vijay, and Thanga Raj Chelliah. 2023. “Impact of Fixed/Variable Speed Hydro,
Wind, and Photovoltaic on Sub-Synchronous Torsional Oscillation—A Review”
Sustainability 15, no. 1: 113.
Ph.D Publications- Journal
58
List of Publications
Ph.D Publications- IEEE IAS Annual Meetings
1. Vijay Mohale and T. R. Chelliah, “Sub Synchronous Oscillation in Asynchronous
Generators Serving to Wind and Hydro Power Systems – A Review,” in 2021 IEEE
Industry Applications Society Annual Meeting (IAS), Canada 2021, pp. 1-7.
2. Vijay Mohale, T. R. Chelliah and Yogesh. V. Hote, ” Modeling and Analysis of Sub-
Synchronous Oscillation in Large Rated DFIM Based Hydro Unit Fed to Extra High
Voltage Transmission Lines,” in 2022 IEEE Industry Applications Society Annual
Meeting (IAS), Detroit, MI, USA 2022, pp. 1-6.
3. Vijay Mohale, T. R. Chelliah and Yogesh. V. Hote, ” Design and Development of a Scaled
Prototype of a 250MW Hydrogenerator Fed 765 kV Transmission Lines to Test Sub-
Synchronous Oscillation in Power System Laboratory,” in 2023 IEEE Industry
Applications Society Annual Meeting (IAS), Nashville, Tennessee, USA,2023. (Status-
Accepted).
59
List of Publications
Ph.D Publications- Conferences
1. Vijay Mohale and T. R. Chelliah, “Analysis of Sub-Synchronous Oscillations in
Asynchronous Generator Serving to Hydropower Systems,” 2022 IEEE International
Conference on Power Electronics, Smart Grid, and Renewable Energy (PESGRE),
2022, pp. 1-6.
2. Vijay Mohale and T. R. Chelliah, “Impact of Series Compensated High Voltage
Transmission Lines in the Operation of DFIM Based Hydro Unit,” 2022 Second
International Conference on Power, Control and Computing Technologies (ICPC2T),
2022, pp. 1-6.
3. Vijay Mohale and T. R. Chelliah, “Mitigation of Sub-Synchronous Oscillation in Variable
Speed Pumped Storage Units Connected With 765 kV Double Circuit Transmission
Lines,” National Conference on ‘Energy Storage including Pumped Storage –
Opportunities and Challenges’ 4-5 November 2022, Shimla by Central Board of
Irrigation and Power (CBIP) New Delhi, 2022, pp. 1-6.
4. Vijay Mohale and T. R. Chelliah “Impact of Sub-Synchronous Resonance on Torsional
Vibration of Large Rated Variable Speed Pumped Storage Unit,” IEEE Industrial
Electronics Society Annual On-Line Conference ONCON-2022, December 9-11, 2022.
pp. 1-6
60
List of Achievements
Awards
1. Best Poster Award at Institute Research Day, IIT Roorkee during March 13-
14, 2022.
2. CSIR travel support to attend 2022 IEEE IAS Annual Meeting (October 9-13,
2022; USA)
3. Shortlisted for best paper award in IEEE Industrial Electronics Society
Annual On-Line Conference ONCON-2022, December 9-11, 2022.
4. Recognized young professional from IEEE.
5. Recognized Senior Member from IEEE.
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250 MW DFIM Simulation Parameters
PARAMETERS OF TEST MACHINE 1 (250 MW DFIM)
Machine Parameters (26 poles, 230.77 rpm, 50 Hz)
Stator voltage 15750 V Rotor inductance 0.00507 H
Stator current 11250 A Stator leakage inductance 0.00038 H
Rotor voltage 3300 V Rotor leakage inductance 0.00052 H
Rotor current 11600 A Magnetizing inductance 0.00455 H
Stator resistance 0.00252 Ω Moment of Inertia 4.6 e6 kgm2
Rotor resistance 0.00104Ω Friction of coefficient 0.006kgm2/s
Stator inductance 0.00494 H Sampling Time 0.0001s
AC Excitation system for 250 MW DFIM
AC Excitation VSI Transformer
Nominal power 25 MVA Primary Voltage 15.75 kV
Secondary Voltage 5X 3AC 3050 V Grid Frequency 50 Hz
Vector Group Yd1 (-12 ⁰) d1 (-6⁰) d1 (0⁰) d1 (+6⁰) d1 (+12⁰)).
62
2.2 kW DFIM Experimental Set-up Parameters
Test Machine II
DFIM (2.2 kW, 4 poles, 50 Hz, 1500 rpm)
Stator
voltage
415 V Rotor inductance 306.82 mH
Stator
current
4.7 A
Stator leakage
inductance
24.87 mH
Rotor voltage 185 V
Rotor leakage
inductance
24.87 mH
Rotor
current
7.5 A
Magnetizing
inductance
281.96 mH
Stator
resistance
3.678 Ω Moment of Inertia
0.014
kgm2
Rotor
resistance
5.26 Ω
Friction of
coefficient
0.03kg
m2/s
Stator
inductance
306.82
mH
Sampling Time 0.001s
AC Excitation system for 2.2 kW DFIM
AC Excitation VSI Transformer
Nominal power 3 KVA
Primary
Voltage
3 AC 415
V
Secondary
Voltage
2X 3AC
185 V
Grid
Frequency
50 Hz
Vector Group YY (0⁰) Yd1 (+30⁰)
2 Channel-Three level VSI Back to Back Power module
Output Voltage
3 AC/ (0-
185) V
Frequency 0 to 70 Hz
Vdc
450 V
(4700 μF)
GSC/RSC 12-Pulse
GSC switching
Frequency
5 kHz
RSC
switching
Frequency
3 kHz
Semiconductor
Switch
SEMIKRON 2 IGBT
(SKM100GB12T4)
63
Transmission Line Parameters
Characteristics Ratings
765 kV 400 kV
Positive sequence resistance 2.0139 Ω 0.2221 Ω
Positive sequence system reactance 50.9779 Ω 4.661 Ω
Capacitive reactance for both the lines (0.05 to 0.85)
64
Acknowledgement
I thank to POSOCO and Power grid.
65
Thank you.
66
Series Compensation
𝑃􀬵 =
𝑉􀯦𝑉􀯋
𝑋􀯅
si n 𝛿
VR VS
XS XL1 XL2
XC XR
A P B
𝑃􀬶 =
𝑉􀯦𝑉􀯋
𝑋􀯅 − 𝑋􀮼
𝑠𝑖 𝑛 𝛿
𝑃􀬵
𝑃􀬶
=
𝑋􀯅
𝑋􀯅 − 𝑋􀮼
=
1
1 −
𝑋􀮼
𝑋􀯅
=
1
1 − 𝑘
𝑘 =
𝑋􀮼
𝑋􀯅
The factor k is known as a degree of compensation or compensation factor. Thus, per unit compensation is given by the
equation percentage
𝑘 =
𝑋􀮼
𝑋􀯅
𝑝𝑢 × 100%
The factor k is varies from 0.2 to 0.85 for 20% to 85% series compensation respectively.
Fig. Series compensation
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67
Selection of dc link capacitor in back-to-back converter
(250 MW DFIM)
SW Converter max(grid)
dc dc dc
T .P V
C= 1-
ΔV .V V
   
   
   
3.3×10-3×7.92x106x0.0667
C=
20×5000
 
 
 
VSI rating – 3.3 KV, 2400 A (Pconverter) = 7.92 MVA
DC Link Voltage (Vdc) = 5000 volts
Allowable ripple voltage (ΔVdc) = 0.4% = 20 volts
Switching frequency (fsw) = 300 Hz
Grid voltage (Vrms) = 3.3 kV
Value of DC link capacitance is calculated as,
C= 17433 μF ≈ 18000 μF
Reference: D. Xu, F. Blaabjerg, W. Chen, N.Zhu. Advanced Control of Doubly Fed Induction Generator For Wind Power
Systems. Wiley-IEEE Press, 2018.
68
Gain Values Used in PI controller
2.2 KW
RSC
Inner controller (Idr) = Kp – 0.8, Ki – 200
Inner controller (Iqr) = Kp – 0.8, Ki – 200
Speed controller (Iqr) = Kp – 0.017 , Ki – 0.09
Reactive Power controller (Idr) = Kp – 0.03 , Ki = 5
GSC
Inner controller (Idr) = Kp – 1, Ki – 45
Inner controller (Iqr) = Kp – 1, Ki – 45
DC voltage controller (Idr) = Kp – 6 , Ki – 175
Reactive Power controller (Iqr) = 1
69
Gain Values Used in PI controller
250 MW
RSC
Inner controller (Idr) = Kp – 100, Ki – 50
Inner controller (Iqr) = Kp – 650, Ki – 120
Speed controller (Iqr) = Kp – 950 , Ki – 250
Reactive Power controller (Idr) = Kp – 4 , Ki = 0.025
GSC
Inner controller (Idr) = Kp – 960, Ki – 450
Inner controller (Iqr) = Kp – 960, Ki – 450
DC voltage controller (Idr) = Kp – 1025 , Ki – 175
Reactive Power controller (Iqr) = 1