Wind Generators and Wind Farms: Connection to Weak GridsMohammadreza Arani

Outline

• Inertia and System Strength

• Interesting case of South Australia 2016 Black out

• Definition

• Solutions

• Frequency Regulating Wind Generator

• Virtual Inertia

• Droop

• Mechanical Tension

• Conclusion

July 1, 2021 | 2

Inertia and System Strength

July 1, 2021 | 3

South Australia 2016 Black-out

• What happened?

• Aftermath

July 1, 2021 | 4

© AEMO, 2017

“Sufficient inertia to slow

down the rate of change of

frequency and enable

automatic load shedding to

stabilise the island system in

the first few seconds”July 1, 2021 | 5

[1]

“Sufficient system strength to

control over voltages, ensure

correct operation of grid protection

systems, and ensure correct

operation of inverter-connected

facilities such as wind farms”

July 1, 2021 | 6

[1]

Inertia and System Strength - Definition

• P. C. Kundur [2]:

• “The ac system can be considered “weak” from two aspects:

• (a)

• (b)

July 1, 2021 | 7

Inertia and System Strength - Definition

• Australian Energy Market Operator:

• “AEMO sees system strength as the ability of the power system to

maintain and control the at any given location in the

power system, both during operation and following

a .”[3]

• “Contribution to the capability of the power system to resist changes

in by means of an from a generating unit,

network element or other equipment that is electro-magnetically coupled

with the power system and synchronised to the frequency of the power

system.”[4]

July 1, 2021 | 8

July 1, 2021 | 9

“Inertial responses provide a and injection of energy

to suppress rapid frequency deviations, the rate of change of

frequency .” [3]

© 2020 Australian Energy Market Operator Limited.

© AEMO, 2020

Inertia and System Strength - Solution

• Needed Inertia

• Methods:

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Implementing Frequency Regulation in Wind Generators

July 1, 2021 | 11

Virtual Inertia

• Concept

July 1, 2021 | 12

Power System Stability and Control,

Prabha Kundur, McGraw-Hill, 1994

Virtual Inertia

• Energy Source

July 1, 2021 | 13

Virtual Inertia

• Energy Source

July 1, 2021 | 14

Rotor Side ConverterGrid Side Converter

DFIG(a) (b)

PMSGGenerator Side

Converter

Grid Side

Converter

Virtual Inertia

July 1, 2021 | 15

Virtual Inertia

July 1, 2021 | 16

Virtual Inertia

July 1, 2021 | 17

Virtual Inertia

• Virtual Inertia vs. Synthetic Inertia

• NERC: “Synthetic inertia” is a term sometimes used for fast controlled

active power injection from wind generators in response to

after a large generation trip. This control is enabled by accessing stored

kinetic energy ( ) of the turbine, hence the term “synthetic inertia”;

however, the response is not and of the behavior is

fundamentally different from

[6]

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Mechanical Tensions

• Double-Mass Model and Soft Shaft

• Formula and Modeling

July 1, 2021 | 19

PMSGGenerator Side

Converter

Grid Side

Converter

AC Filter

Transformer

Microgrid/

Low Inertia

Grid

Mechanical Tensions

• Fatigue

July 1, 2021 | 20

.shaft shaftaT gT = +

Mechanical Tensions

• Double-Mass Model and Soft Shaft

July 1, 2021 | 21

0 1 2

0.02

0.03

0.04

Mvi

/M

| f|

ma

x [

pu

]

(a)

0 1 20

2

4

6

8

10

Mvi

/M

RO

CO

Pg

,ma

x [

pu

/se

c]

(c)

0 1 20.05

0.1

The ratio of virtual inertia to physical inertia (Mvi

/M)RO

CO

Fa

ve [

pu

/se

c]

(b)

Mechanical Tensions

• Double-Mass Model and Soft Shaft

July 1, 2021 | 22

0 1 20

0.2

0.4

0.6

0.8

1

Ratio of virtual inertia to physical inertia (Mvi

/M)

Ma

xim

um

To

rqu

e (

Tm

ax)

[pu

]

(a)

0 1 20

2

4

6

8

10

Mvi

/M

RO

CO

Tm

ax [

pu

/se

c]

(b)

Generator

Shaft

Turbine

Mechanical Tensions

• Double-Mass Model and Soft Shaft

• Mechanical Resonance – virtual inertia

July 1, 2021 | 23

-2 -1.8 -1.6 -1.4 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2

-10

-5

0

5

10

Real Axis

Imagin

ary

Axis

Mechanical Tensions

• Double-Mass Model and Soft Shaft

• Ramp Rate Limiter

July 1, 2021 | 24

0 0.5 1 1.5 2 2.5

0.25

0.3

0.35

0.4

0.45

0.5

Ratio of Virtual Inertia to Physical Inertia (Mvi

/M)

Maxi

mu

m F

requency

Devi

atio

n (

| f| m

ax)

[Hz] (a)

0 0.5 1 1.5 2 2.5

0.7

0.8

0.9

1

1.1

1.2

1.3

Ratio of Virtual Inertia to Physical Inertia (Mvi

/M)

RO

CO

Fave

[H

z/se

c]

(b)

No Limit

dp/dt=0.05pu/sec

dp/dt=0.10pu/sec

dp/dt=0.15pu/sec

dp/dt=0.20pu/sec

0 0.5 1 1.5 2 2.5

0.25

0.3

0.35

0.4

0.45

0.5

Ratio of Virtual Inertia to Physical Inertia (Mvi

/M)

Maxim

um

Fre

quency D

evia

tion (

| f| m

ax)

[Hz] (a)

0 0.5 1 1.5 2 2.5

0.7

0.8

0.9

1

1.1

1.2

1.3

Ratio of Virtual Inertia to Physical Inertia (Mvi

/M)

RO

CO

Fave

[H

z/s

ec]

(b)

No Limit

dp/dt=0.05pu/sec

dp/dt=0.10pu/sec

dp/dt=0.15pu/sec

dp/dt=0.20pu/sec

Conclusion

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Questions

July 1, 2021 | 26

References

• [1] Black System South Australia 28 September 2016, Australia Electricity Market Operator (AEMO), March 2017.

• [2] P. C. Kundur, Power System Stability And Control, McGraw Hill, 1994.

• [3] Power System Requirements, Australia Electricity Market Operator (AEMO), July 2020.

• [4] National Electricity Amendment (Managing the rate of change of power system frequency) Rule 2017 No.9, Australia Energy Market Commission (AEMC), 2017.

• [5] H. Gu, R. Yan and T. Saha, "Review of system strength and inertia requirements for the national electricity market of Australia," in CSEE Journal of Power and Energy Systems, vol. 5, no. 3, pp. 295-305, Sept. 2019.

• [6] Forward Looking Frequency Trends Technical Brief, North American Electricity Reliability Corporation (NERC), 2018.

• [7] Technical Requirements for the Connection of Generating Stations to the Hydro-Québec Transmission System, December 2016.

July 1, 2021 | 27

References

• [8] Mohammadreza F. M. Arani and Ehab El-Saadany, “Implementing virtual inertia in DFIG-based wind power generation,” IEEE Transaction on Power Systems, vol. 28, no. 2, pp. 1373-1384, May 2013.

• [9] Mohammadreza F. M. Arani and Yasser A.-I. Mohamed, “Analysis and impacts of implementing droop control in DFIGs on microgrid/weak-grid stability”, IEEE Transaction on Power Systems, vol. 30, no. 1, pp. 385-396, Jan. 2015.

• [10] Mohammadreza F. M. Arani and Yasser A.-I. Mohamed, “Dynamic Droop Control for Wind Turbines Participating in Primary Frequency Regulation in Microgrids”, IEEE Transaction on Smart Grid, vol. 9, no. 6, pp. 5742-5751, Nov. 2018.

• [11] Mohammadreza F. M. Arani and Yasser A.-I. Mohamed, “Analysis and Mitigation of Undesirable Impacts of Implementing Frequency Support Controllers in Wind Power Generation”, IEEE Transaction on Energy Conversion, vol. 31, no. 1, pp. 174-186, March 2016.

• [12] Mohammadreza F. M. Arani and Yasser Mohamed, “Analysis and Damping of Mechanical Resonance of Wind Power Generators Contributing to Frequency Regulation”, IEEE Transactions on Power Systems, vol. 32, no. 4, pp. 3195-3204, July 2017.

July 1, 2021 | 28