frequency control and inertia response schemes for the future power networks

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Tegucigalpa, Hondruas, July 2017

FREQUENCY CONTROL AND INERTIA RESPONSE SCHEMES FOR THE FUTURE POWER NETWORKS

Dr. Francisco M. Gonzalez-LongattLoughborough University, UK

26th July 2017 | CIMEQH | Tegucigalpa, Honduras

http://www.fglongatt.org/

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Future Electric Power Grid:

Smart-erGrid

Driving Forces and challenges


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What is an Electrical Power System?• An electric power system is a network of electrical

components used to supply, transmit and use electric power.

• Modern Power Systems are complex and interconnected

structures.

Where Does Complexity Come From?


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Power System Dynamic: Complexity

• There are hundreds of interacting elements such ad

generator with their controls, energy supply system and

controls, and that the mathematical representation of each

element generally involves many independent variables

described by set of high order, non linear differential

equations.

System

Dispatch

Load-Freq

Control

With

Economic

Allocation

Freq

Flows

Prime

Mover

System

a cont.

Gen

Excitation

Controls

Electrical

Network

Mach elect

powers a tie

line powers

as function

of angles,

voltages,

speeds a

network

loads and

impedances

Match

Sched

Supp

Cont

Regulation

Shaft

PWR

Tie-Line

Mach

Freq

Output

Electrical Power

Tie-Line

Out

Powers

Powers

Source: P.M. Anderson “Power System and control”

@fglongatt


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European Interconnection• Head Organization ENTSO-E

• 5 Regional Groups (RG) RGContinental Europe (former

UCTE)

• Regulation Zone Germany 4 TSO

• 41 TSO

• 34 European countries

• 532 million customers served

• 312,693km of transmission lines

• 3,174.2 TWh electricity transported

• 423,586 GWh of electricity exchange

between member TSOs

• 1,023,721 MW net generation

capacity connected to the grid.

(European Network of Transmission

System Operators for Electricity)

532 Million Customers

1,023,721 MW

@fglongatt


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North American Interconnection…

• Provides electricity to 334 million people;

• Total electricity demand of 830 gigawatts

• 340,000 kilometres of high-voltage transmission lines

• Represents more than US$1trillion worth of assets.

334 Million Customers

830,000 MW

North American Electric Reliability Corporation (NERC)

@fglongatt


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Uk Interconnection• National Grid

• Transmission System

1200 Circuits

14000km OHL

635km of underground cable

319 Substations

750 transformers

2743 circuit breakers

132kV, 275kV & 400kV

50Hz

Installed generation capacity:

≈ 100 GW bulk generation

embedded generation

Demand

≈ 60 GW Peak

20 GW minimum National grid

26 Million

Customers

~60 GW

339 TWh in 2014. @fglongatt


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Context: Overview of Drivers

@fglongatt

@fglongatt


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Penetration Renewable: Germany (1/3)

End of Year 2000

@fglongatt


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End of Year 2005

@fglongatt


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End of Year 2010


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Prof Francisco M. Gonzalez-Longatt PhD, [email protected] .Copyright © 2008-2015. 07-08 November 2016. Seville, Spain. 12/73Mov

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North Sea National Targets 2030 (1/4)

SKAGERRAK

IRISH SEA

ENGLISH CHANNEL

KATTEGAT

DENMARK

GERMANY

NETHERLANDS

BELGIUM

UNITED

KINGDOM

IRELAND

www.fglongatt.org.veFrancisco Gonzalez-Longatt, PhD

June 2012Coventry, UK

@fglongatt

Data source: EWEA

@fglongatt

mailto:[email protected]


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Context: Changes in GB

15% of energy from renewable

34% reduction in CO2 emission versus 1990

2020No renewable target

80% reduction in CO2 emission versus 1990

2050

% of end use energy ~20%Carbon intensity (kgCO2/MWh) ~200

% of end use energy ~50%Carbon intensity (kgCO2/MWh) ~5Electricity

1860 1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 2020 20402030 2050

Oil

Gas

Coal

Hydro

Nuclear

Solar

Wind

Geothermal

Biomass

CCS

Billio

n B

arr

els

of

Oil E

qu

iva

len

t p

er

ye

ar

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70


% of end use energy ~35%Carbon intensity (kgCO2/MWh) ~184Gas


% of end use energy ~40%Carbon intensity (kgCO2/MWh) ~247Oil

Data source: National Grid Gone Green scenario

fglongatt 2013



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Context: Where do we need to Change?

EVIM

Storage

PV

MTDC

AC

System

Wind Farm

The other half of the challenge lies in building the transport and distribution networks

As the low-emission economy evolves,building new generation technologiesis just half the challenge

@fglongatt

Gonzalez-Longatt, F. (2014). Frequency Control and

Inertial Response Schemes for the Future Power

Networks. Large Scale Renewable Power Generation. J.

Hossain and A. Mahmud, Springer Singapore: 193-

231.



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DC is a real option



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Smart DC Micro-grids

http://smgaznec.fglongatt.org/



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Frequency stability and control

Main concepts


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What is Electric Frequency (f)? (1/6)ENTSO-E

• The electric frequency in the network (the systemfrequency f) is a measure for the rotation speed of thesynchronised generators.

• By increase in the total demand the system frequency(speed of generators) will decrease, and by decrease in thedemand the system frequency will increase.

National Grid (UK)

What is frequency?

• System frequency is a continuously changing variable thatis determined and controlled by the second-by-second (realtime) balance between system demand and totalgeneration.

• If demand is greater than generation, the frequency fallswhile if generation is greater than demand, the frequencyrises.



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What is Inertia? (2/6)• It is the energy stored in generators because they

are rotating….

They continue to rotate

after the energy source is

removed

Large spinning machines provide

stored energy due to the rotating

mass of their rotor, driving

turbine shafts etc.

Engineers model this as a number

of rotating masses.

@fglongatt



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Power System Stability

Rotor angle

stabilityVoltage Stability

Transient

Stability

Short term Long-term

Large

Disturbance

Voltage

Stability

Small-Signal

Stability

Short term

Small-

Disturbance

Voltage Stability

Frequency

Stability

Short term Long term

Frequency Stability• IEEE-CIGRE classification (IEEE/CIGRE Joint Task Force

on Stability Terms and Definitions, “Definition and

Classification of Power System Stability”, IEEE Trans. Power

Systems and CIGRE Technical Brochure 231, 2003):



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Frequency Stability• “Frequency stability refers to the ability of a power

system to maintain steady frequency following a severe

system upset resulting in a significant imbalance

between generation and load.”

• Frequency stability analysis concentrates on studying the

overall system stability for sudden changes in the

generation-load balance.

@fglongatt



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General Picture of Frequency Stability (4/4)

Demand Supply

50

+-

Generated

Power

Sales PurchasesInter-Regional

Interchange

Load

Losses

Frequency

IncreaseDecrease

@fglongatt



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Frequency Response

• It is an automatic change in active power output or

demand in response to a frequency change.

• To maintain system frequency within statutory and

operational limits.

What is it?

Why we need it?

Demand: 47318MW17:05:00 GMTFrequency: 49.996Hz17:07:45 GMTSystem TransfersN.Ireland to Great Britain: -444MWFrance to Great Britain: -310MWNetherlands to GB: 0MW07/03/2011 17:00:00 GMT

North-South: 7567MWScot - Eng: 215MW07/03/2011 17:10:00 GMT

http://www.nationalgrid.com/uk/Electricity/Data/Realtime/Frequency/Freq60.htm

Real Time Frequency Data - Last 60 Minutes

National Grid has a license obligation to control frequency within the limits specified in the 'Electricity Supply Regulations', i.e. ±1% of nominal system frequency (50.00Hz) save in abnormal or exceptional circumstances.

@fglongatt



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Steady-State Frequency

Upper Statutory Limit

Upper Operational Limit

Lower Operational Limit

Lower Statutory Limit

Lowest ‘planned’ Limit

Demand disconnection starts

Demand Disconnection complete

52.0

50.5

50.2

49.8

49.5

49.0

48.8

47.0

50.0

~60% od REC

Demand shed in 9

blocks

49.6 Hz – Standing reserve on LF (1st)

49.5 Hz – Standing reserve on LF (2nd

)

50.4 Hz – Generator independent action

52.0 Hz – Generators start tripping

Standards

Obligations, Statutory, Code and Operational Standards@fglongatt



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Objective of Control

Maintain 3 frequency indices

1. ROCOF

2. Transient Frequency Nadir

3. Steady state Frequency

deviation1

2

3

maximum frequency gradient (df/dt) as observed by ROCOF (Rate-Of-Change-Of-Frequency)



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Frequency Control (1/4)

Frequency Control processes

Continous Service

Reserve

Occasional Service

Fre

qu

en

cy (

Hz) 10s 30s 60s Time 30 mins

Secundary (to 30 mins)

Primary

50.0

50.2

49.8

49.5

49.2



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Frequency Control Processes (2/4)

Continous Service

Reserve

Occasional Service

Fre

qu

en

cy (



Primary

50.0

50.2

49.8

49.5

49.2

INERTIAL RESPONSE: The speed of the

synchronous generators also reduces and some of the

kinetic energy stored in the rotating mass is released

as electrical energy. This is a fast response and

proportional to the rate of change of frequency.

Frequency Control Phases

@fglongatt



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Continuous

Service

Reserve

Occasional Service

Fre

qu

en

cy (



Primary

50.0

50.2

49.8

49.5

49.2

GOVERNOR ACTION: The automatic droop control

loop of the governor acts on the change in frequency

and opens the governor valve to increase the turbine’s

output.

This is a slower response and depends on the dead band

of the governor and time lag of the prime mover

Frequency Control Phases

@fglongatt



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• Primary Control: The action of turbine governors due to

frequency changes when reference values of regulators are

kept constant.

• Secondary Control: The restoration of the rated frequency

followed to the primary control action, but now at the

required increased value of power demand.

• Tertiary control: Objective depends on the organizational

structure of a given power system and the role that power

plants play in this structure.

Summary of Frequency Controllers



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Controllers Used for Frequency

Response in Wind Power

Generators• This section presents the main aspects to considers in Controllers

used on Wind Power Generators for Frequency Response.

@fglongatt


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Commercially Dominant Technologies• WT Technologies

GridIs

PFC

Us

Single cage

induction

generator

Gearbox

GridIsUs

PMSG

ac/dc dc/ac

DC

link

Ir

UrN

N

NN

S

S

S

S

GridIsUs

Double-fed

induction

generator

Gearbox

ac/dc dc/ac

DC

link

Ir Ic

Ur

Variable Speed

PMSG

Direct Drive

Variable Speed Induction

generator

Variable Speed

Double fed



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Releasing Kinetic Energy: Physical Inertia!!!

• The contribution of the system inertia of one load or

generator depend if the system frequency causes

change in its rotational speed and, then, its kinetic

energy.

Restorative power

smaller

smaller

T

1

N

i

i

H H

2

1

2

i smi

base

JH

S



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Net

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System Frequency Dynamic• During a system frequency disturbance the balance

between generation-demand is not reached, then the

system frequency will change at a rate initially determinate

by the total system inertia (HT).

Reserve

Occasional Service

Fre

qu

en

cy (


Primary

50.0

50.2

49.8

49.5

49.2

df

dt

2m e

n

H dfp p p

f dt



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The Problem• Increasing wind power Penetration.

• Wind turbines provide small or even no

response to frequency changes.

CLASSIC TECHNOLOGIES

Fixed Speed WTG • Squirrel cage induction generator

• Provides inertial response

• Slower than synchronous generator

Variable Speed WTG

• Utilise power electronics converters

• Synchronous WTG: No inertial response

• Doubly Fed Induction Generator WTG:

Negligible inertial response

0 1 2 3 4 5 6 7 8 9 10

Time [sec]0 1 2 3 4 5 6 7 8 9 10

Fre

qu

ency

[H

z]

0 1 2 3 4 5 6 7 8 9 10

0.5

1

Po

wer

[p

.u]

Time [sec]0 1 2 3 4 5 6 7 8 9 10

48.5

49

49.5

50

Synchronous Generator

Fixed Speed WTG

DFIG WTG

Full Converter WTG



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Control Layers

Controller

Wind

Externalturb set

P

meas A. Wind Turbine

Min MPT

turb

,1uP

*

,1uP

Min MPT

,2uP

*

,2uP

Min MPT

,3uP

*

,3uP

cmmP

,1

MPT

aP ,2

MPT

aP ,3

MPT

aP

1/ NPI

maxP

0

*

WFP

WFP PCC

B. Wind

Farm Level

Inertial Control

Control Signal from

AGC or Operator

sysf

Droop Controlf

Converter

1cK1cP

2cP

ciP

cnP

2cK

cnK

ciK

.

.

.

.

.

.

inP

WFP

P

refP

iK

s

1

iR

iB

Speed Governor,ref iP

AGC

f

Load Reference

Error

C. Power System

Level



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Inertial Control (1/2)

• Functions:

– For variable speed wind turbines.

– To reduce the maximum frequencychange rate.

– To increase the transient frequencynadir.

d

dtFiltersys 2H

measP,r ref

,r meas

rPI

MPPTPConterter

“Hidden” inertia emulation

2sys

in sys

dP H

dt

r

P

MPPT

21

2

sm

base

JH

S

refP

• Comparison with fixed speed wind

turbines and conventional generators:

– Releasing considerably larger kinetic

energy.

– Responding faster because of the PWM

technology

G. Ramtharan, J. B. Ekanayake, and N. Jenkins, "Frequency support from doubly fed induction generator wind turbines," lET Renew. Power Gener., vol. I, pp. 3-9,2007.

J. Ekanayake, and N. Jenkins, "Comparison of the response of doubly fed and fixed-speed induction generator wind turbines to changes in network frequency," IEEE Trans. Energy Convers., vol. 19, no. 4, pp.800--802, Dec. 2004.

J. Morren, S W. H. de Haan, W. L. Kling, and J. A. Ferreira, "Wind turbines emulating inertia and supporting primary frequency control,“ IEEE Trans. Power Syst., vol. 21, no. I, pp. 433-434, Feb. 2006.



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Inertial Control (2/2)

• Similar functions to “hidden” inertia emulation

– To compensate the power loss for a short period and save time for other slowergenerators to participate in the frequency control

measP,r ref

rPI

r

P

MPPT

refPConterter

,r meas

constPt

,0r

2

, 0 2 constr ref rt r

Pt

J 2 2

0

1 1

2 2const r rtP t J J

A. Teninge, C. Jecu, D. Roye, S. Bacha, J. Duval, and R Belhomme, "Contribution to frequency control through wind turbine inertial energy storage," lET Renew. Power Gener., vol. 3, pp. 358-370,2009



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Future Electric Power Grid:

Smart-erGrid

Smarter-Grid and Potential solutions


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Reference to the Concept• The term smart grid has been

in use since at least 2005,

when it appeared in the article

“Toward A Smart Grid” by

Amin and Wollenberg.

Smart Grids European

Technology Platformhttp://www.smartgrids.eu/

http://energy.gov/oe/technology-development/smart-grid

“Smart Grid / Department

of Energy”

https://www.gov.uk/government/policies/maintaining-uk-energy-security--

2/supporting-pages/future-electricity-networks

Department of Energy &

Climate Change and Ofgem


https://www.gov.uk/government/policies/maintaining-uk-energy-security--2/supporting-pages/future-electricity-networks

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Global Smart• A concept

Water

Transport

Gas ICT

Electricity ?


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Smarter Grid


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What it is?

WAN

People

Smart

Meters

Smart

Appliances

Data

concentrator

Applications

server

PMU PMU


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Power Systems and Smart Grid

Server

Satellite

PhoneWireless

Modem

Concentrator

Devices

Satellite

Dish

WAN

Internet

VP

Generation Transmission Substation Distribution Costumer

Integracion de renovables Wide-Area Monitoring

and ControlSubstation

Automation

AMI EV/PHEV

IntegrationAutomation

Smart grid integrates ITC and Power

Systems

DER

Integration

Condition

MonitoringAsset

Optimization

Workforce

Effectiveness


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Technologies for Energy Storage

1,339 Projects

186,224 GW

2015


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Storage in UK

Dinorwig

Power

Station

30 Projects

3255 MW


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Storage in UK (3/4)• Smarter Network Storage

The Smarter Network Storage (SNS) project aims to carry out a range of

technical and commercial innovation to tackle the challenges associated with the

low-carbon transition and facilitate the economic adoption of storage. It is

differentiated from other LCNF electrical storage projects by its demonstration of

storage across multiple parts of the electricity system, outside the boundaries of the

distribution network. By demonstrating this multi-purpose application of

6MW/10MWh of energy storage at Leighton Buzzard primary substation, the

project will explore the capabilities and value in alternative revenue streams for

storage, whilst deferring traditional network


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Storage in UK• Preliminary analysis in UK suggest an additional storage

could be installed in the range of 1GW - 29GW under certain

future scenarios by 2050, of which distribution storage is

estimated to dominate bulk storage, due to the savings from

avoided distribution network costs.

The Electricity Storage Network has warned

that delays in installing at least an additional

2GW of electricity storage by 2020 will

result in costs of £100m a year for

taxpayers and investors.

The alert came as DECC named the first

two winners of its £20m energy storage

competition with the ESN adding that failure

to act would also cause a loss of value

rising to £10bn a year by 2050.

http://renews.biz/53357/uk-urged-to-focus-on-storage/


http://renews.biz/53309/wind-storage-system-wins-3-6m/

http://renews.biz/53357/uk-urged-to-focus-on-storage/

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EV at Loughborough University

@fglongatt


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EV at Loughborough University• Electric Vehicles at Loughborough University


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Incentive For Electric Vehicles (EVs)


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UK Distribution Networks


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Government Incentives For Renewable Generation


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Smart Meter Installations In Domestic Properties• From the start of the Programme up until 31 March 2016,

large energy suppliers have reported installing an estimated

total of 2,606,200 smart meters across domestic properties in

Great Britain.

Smart meters will be fitted in 26 million

homes by 2020


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The UK Context for Distribution• Business regulated by

• Assets account for 50%+

of the value of GB

electricity networks.

• A significant part of the

assets installed during

the 1950s and 60s.

https://www.ofgem.gov.uk/

https://www.ofgem.gov.uk/electricity/distribution-networks/gb-electricity-distribution-networkhttp://www.energynetworks.org/info/faqs/electricity-distribution-map.html


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Smart Network and Low Carbon

Primary

Substation CB

CB

Secondary

Substation

Tie-switch

Bulk

Generation

MV Micro Grid

+

-

Local

control

Local control

Local

control

+

-

+

-

Massive penetration of renewable

Medium-scale renewable controllable

Full coordination between transmission and distribution

Local

control

Hierarchical

control

Distributed

Generation

Real-time monitoring and control

Local

controlCentralized network management Maximizing the assets utilizationMaximum renewable harvesting

Optimization forecasting

LV Micro Grid

Frequency response oepration


All

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Primary

Substation CB

CB

Secondary

Substation

Tie-switch

Bulk

Generation

+

-

+

-

IED: Intelligent Electronic Device

DMS: Distribution Management System

MEMS: Microgrid Energy Management System

SCADA: Supervisory Control And Data Acquisition

MV Microgrid

LV Microgrid

Communication link

DMS

SCADA

IED IED

IED

MEMS

MEMS

MEMS

MEMS

+

-

+

-

+

-

Electric Vehicle

Heat pump

Energy storage

Solar photovoltaic system

Wind Power


All

right

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201

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Primary

Substation CB

CB

Secondary

Substation

Tie-switch

MV Micro Grid

+

-

Local

control

Local control

Local

control

+

-

+

-

Massive penetration of renewable

Medium-scale renewable controllable

Full coordination between transmission and distribution

Local

control

Hierarchical

control

Distributed

Generation

Real-time monitoring and control

Local

controlCentralized network management Maximizing the assets utilizationMaximum renewable harvesting

Optimization forecasting

LV Micro Grid

Frequency response oepration


All

right

s re

serv

ed. N

o pa

rt o

f thi

s pu

blic

atio

n m

ay b

e re

prod

uced

or

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any

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201

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Reduced Inertia in the UK

http://www2.nationalgrid.com/UK/Industry-information/Future-of-Energy/System-Operability-Framework/


All

right

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Declining Short Circuit Levels in the UKAs the short circuit level decreases, the

size of the area affected by a voltage dip

will increase.

The effects of transmission voltage dips

are not only observable across the

transmission network, but are also

observable on distribution networks in the

vicinity of the fault (the effects are “3-

dimensional”).

The critical role that reactive

current injection plays in the

response of the network to a

voltage depression.

http://www2.nationalgrid.com/UK/Industry-information/Future-of-Energy/System-Operability-Framework/


All

right

s re

serv

ed. N

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rt o

f thi

s pu

blic

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e re

prod

uced

or

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form

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201

7. h

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Closing…

or Opening?


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right

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serv

ed. N

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f thi

s pu

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or

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201

7. h

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Questions and Answers

Dr Francisco Gonzalez-Longatt

[email protected]

Copyright Notice

The documents are created by Francisco M. Gonzalez-Longatt and contain copyrighted material, trademarks, and other proprietary information. All rights reserved. No part of the documents may be reproduced or

copied in any form or by any means - such as graphic, electronic, or mechanical, including photocopying, taping, or information storage and retrieval systems without the prior written permission of Francisco M.

Gonzalez-Longatt . The use of these documents by you, or anyone else authorized by you, is prohibited unless specifically permitted by Francisco M. Gonzalez-Longatt. You may not alter or remove any

trademark, copyright or other notice from the documents. The documents are provided “as is” and Francisco M. Gonzalez-Longatt shall not have any responsibility or liability whatsoever for the results of use of the

documents by you.

Thank you!



frequency control and inertia response schemes for the future power networks

Engineering