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Thursday 3 June 2021

Power System Stability in MicrogridsTechnical Topic Webinar

CRICOS Provider Number: 03567C | Higher Education Provider Number: 14008 | RTO Provider Number: 51971

Dr. Imtiaz MadniEIT Lecturer and Electrical Systems Engineer

Presented by

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Introduction – Dr. Imtiaz Madni


Dr. Imtiaz Madni comes from a solid technical background with a diverse working experience in the energy industry as an electrical system engineer and electrical project manager. He has a demonstrated history of working in the manufacturing, electrical systems, renewables, and higher education industries.

With a Ph.D. in Electrical and Electronics Engineering, Imtiaz has a background in generating innovative ideas and strategies to improve processes that provide a deeper understanding of multifaceted problems that companies encounter in their daily operations. Together with renowned scientists and high-end industry collaborators, Imtiaz is working on the energy transformation of Australia.

Before moving to Australia, he was working as a post-graduate researcher at the Chinese Academy of Sciences in China.

Find him at: https://www.linkedin.com/in/imtiaz-madni-a8aa652a

https://www.linkedin.com/in/imtiaz-madni-a8aa652a

1 Power System Stability Overview

2 Classification of Stability

3 Microgrids and Power Stability

4 Microgrids Control Technologies

5 Q & A

Agenda


Power System Stability Overview


• Power system is defined as a network of one or more generating units, loadsand power transmission lines including the associated equipment connectedto it.

• The stability of a power system is its ability to develop restoring forces equalto or greater than the disturbing forces to maintain the state of equilibrium.

• Power system stability problem gets more pronounced in case ofinterconnection of large power networks.

~

Generator LoadTransmission line

Power System Stability Overview


Power system stability is the ability of an electric power system, for a given initial

operating condition, to regain a state of operating equilibrium after being

subjected to a physical disturbance, with most system variables bounded so that

practically the entire system remains intact.

Classification of Stability


Classification is based on the following considerations:

• physical nature of the resulting instability

• size of the disturbance considered

• processes, and the time span involved

Voltage Stability in Power Systems


Time

Bus voltage

Upper limit

Lower limit

Nominal voltage

Bus voltageUpper limit

Lower limit

Nominal voltage

Disturbance

Ability to maintain voltages of every bus within desired limits

1) Under normal condition 2) After disturbances

Instability may cause voltage collapse

Time

Bus voltageUpper limit

Lower limit

Disturbance

Nominal voltage Voltage drops uncontrollably

Voltage Instability and Blackouts


U.S. and Canada, 2003 Tokyo, Japan, 1987 Sweden, 1983

Voltage instability in northern Ohio was akey factor in originating the 2003blackout

55 million people lost power for up tothree days, with an economic cost of $5-10B

Tokyo blackout in 1987 caused byvoltage instability

Loss of power to 2.8 millionhouseholds for 3 hours

Sweden experienced voltageinstability following a disturbance in1983

Led to a blackout affecting 4.5 millionpeople (southern half of country) for5.5 hours

How does the power system control voltage?

Voltage Control in Conventional Systems


• Voltage deviates from desired value when reactive power supplied bygenerator cannot meet demand at load

• Reactive power can be injected at a bus by switching on capacitor banks atload buses (incurs switching cost)

~

0 0.1 0.2 0.3 0.4 0.5 0.6 0.70

0.2

0.4

0.6

0.8

1

1.2

1.4

Reactive power demand at load bus, QL

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Voltage−reactive power characteristicsOperating point

~

New operating point

Generator LoadTransmission

lineCapacitor bank

Power demanded by load: Power = P + jQReal power Reactive power

What is a Microgrid?

CRICOS Provider Number: 03567C | Higher Education Provider Number: 14008 | RTO Provider Number: 51971 Source: Electrical Academia

Microgrid Bus Topologies


Microgrid Bus Topologies


Some examples of different power distribution architectures:

Ladder (analogous to breaker-and-a-half or Double breaker-double bus substation configurations)

Ring

Radial

Benefits of DER in a Microgrid


• Incorporate low cost solar, low emission DER

• Implement net-zero projects

• Reduce green house gases

Green Energy

Reliable Energy

• Ability to proactively “island “from utility

• Preserve critical loads

• Repurpose grid tied inverters for island mode operation

• Determine root cause of outages and restore power quickly

• Minimize energy costs through fuel switching and energy savings

• Harness combined heat and power, maximize incentives

• Prioritize critical loads

• Monetize energy flexibility with the grid

Efficiency & Optimization

Operating Modes of a Microgrid


❖ Non-isolated microgrids

• Grid-connected mode (“on-grid” mode)

• Island mode

• Mode transfer?

❖ Isolated microgrids

Non-Isolated Microgrid


Isolated Microgrid


Operation Requirements: Non-Isolated Microgrids


➢Control of the grid-connected mode • DER and other components follow the same requirements

as in the utility grid • Voltage and frequency response characteristics

➢Control of the island mode • Voltage: power quality ?

• Frequency: ✓At least one (or one group of) controllable DER to

provide frequency reference ✓ Load tracking, load management, load shedding ✓ Transient stability

Mode Transfer of Non-Isolated Microgrid


• Mode transferring from grid-connected mode to island mode can bedivided into two types: intentional islanding and unintentional islanding.

• The intentional islanding requires the microgrid to be disconnected fromthe utility grid seamlessly. When there is a fault in the utility grid whichcauses power quality to deteriorate beyond the predefined limit at POC,the microgrid is separated from the utility grid passively, and this is calledunintentional islanding.

• A microgrid may have black start capability, which is needed if the modetransferring fails.

Control of Non-Isolated Microgrid


❑ Control of the grid-connected mode• Microgrid response as a whole, as seen from the POC• Control of the active power flow to the utility grid• Control of the reactive power

− constant power factor λ;− reactive power as a function of active power Q(P);− fixed reactive power Qfix;− reactive power as a function of voltage Q(U);− reactive power as a function of active power and voltage at the

same time Q(P,U).

❑ Control of the internal resources in order to achieve those objectives

Control of Isolated Microgrid


• The ratio of electrical energy storage capacity to the total of other DER capacity inthe isolated microgrid could be much larger than that of the island mode;

• The desired power quality of the isolated microgrid could be different from thatof the island mode depending on the load demand requirements;

• The isolated microgrid works currently in a self-sustained and independent waybased on the load requirements, while the non-isolated microgrid only operatesin island mode in limited time duration;

• From the control point of view such as voltage and frequency control, strategiesmight be different even there are some common points;

• The frequency and voltage of the non-isolated microgrid in island mode should bemonitored all time in order to reconnect back to the utility grid;

Typical Configuration of a Microgrid

CRICOS Provider Number: 03567C | Higher Education Provider Number: 14008 | RTO Provider Number: 51971 IEEE

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Classification of Stability in a Microgrid

CRICOS Provider Number: 03567C | Higher Education Provider Number: 14008 | RTO Provider Number: 51971IEEE-PES Task Force on Microgrid StabilityIEEE Transactions on Power Systems, 2019

Classification of Stability in a Microgrid


Microgrid Test System for Dynamic Load Studies


IEEE-PES Task Force on Microgrid StabilityIEEE Transactions on Power Systems, 2019



Dynamic characteristics

of different load types

during a fault in a

microgrid:

(a) Static (ZIP) load

(b) DOL motor load

(c) VSD motor load.




Dynamic response of different load types during a 20% load switch event.




Virtual-inertia using a power electronic converter.

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Future Developments


Defining Future Business Models for Microgrids

Reliability in the face of extreme weather events

Increased autonomy,

interoperability & optimization

Environmental benefits of local

renewable generation

New local-cost management or

revenue opportunities

Future Developments

CRICOS Provider Number: 03567C | Higher Education Provider Number: 14008 | RTO Provider Number: 51971 Source: Energy Central

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