System of Interconnected Microgrids

Challenges and Solutions

Dr Farhad Shahnia

Overview

Microgrids

Importance of Microgrids to Australia

Microgrid Projects in WA

On-going Research Topics

A New Research Avenue :

System of Interconnected Microgrids

Application and Benefit

An Example

Research Questions to be Addressed

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Microgrid

Microgrids are defined as

interconnected networks of loads and resources (distributed energy resources-DERs)

can function in grid-connected or islanded modes

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Microgrids are a way for utilities to:

Reduce loss, emissions, cost of energy

Upgrade aging systems

Build sustainable futures

Importance of Microgrids to Australia

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Importance of Microgrids to Australia

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Importance of Microgrids to Australia

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Microgrid Projects in WA

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http://reneweconomy.com.au/w-plans-australias-biggest-solarstorage-micro-grid-onslow-39857/http://www.energymatters.com.au/renewable-news/renewables-microgrid-wa-em5793/https://onestepoffthegrid.com.au/p2p-energy-sharing-start-brings-brooklyn-microgrid-smarts-australia/http://www.energynetworks.com.au/news/energy-insider/what-could-customers-save-standalone-systems-microgrids

On-going Research Topics

Structure:

AC microgrids

DC microgrids

AC-DC microgrids

Energy Sources:

Inertial Sources

Converter-dominated microgrids

Control Techniques:

Decentralized

Centralized

Hierarchical

Distributed Control

Power Sharing among Sources:

Sharing based on source ratings

Sharing based on economics

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A New Research Avenue

New possibility:

Temporary Interconnection of Neighboring Islanded Microgrids

or

Microgrid Clusters

Considered possibilities:

Grid-connected microgrids

Islanded (isolated/standalone/off-grid)

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Application and Benefit

Application:

• Remote large towns with no access to a utility feeder

• Presence of two or more microgrid owners (operators) in the town

Importance (Benefit):

• Reducing load-shedding possibility due to unexpected overloading of the microgrid

• Reducing renewable energy curtailment due to unexpected excessive generation

• Improving the self-healing, reliability, and resiliency of the electrical system of remote town

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An example

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Research Questions to be Addressed

• Q-1: What are the criteria based on which the necessity of interconnection is defined?

• Q-2: How to select the most suitable neighboring microgrid?

• Q-3: What must be the suitable structure and topology of the microgrids to enable the coupling?

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• Q-4: How to synchronize the selected microgrids?

Research Questions to be Addressed

• Q-5: How to prevent an interconnection, which may cause instability for the system of coupled microgrids, after their interconnection?

• Q-7: How should the interconnected system operate?

• Q-6: When to isolate a system of coupled microgrids into its contributing microgrids?

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Q-1: Defining Criteria on the necessity of interconnection

Centralized Approach

• Active and reactive power generation of each source

Decentralized approach• A frequency-based technique

E Pashajavid, F Shahnia, A Ghosh (2017) Development of a self-healing strategy to enhance the overloading resilience of islanded microgrids, IEEE Trans Smart Grid 8(2):868-880

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Q-2: Selecting the suitable neighboring microgrid(s)?

Decision-Making

• Fast but not optimal

Optimization• Optimal but slow

A Arefi, F Shahnia (2017) Tertiary controller-based optimal voltage and frequency management technique for multi-microgrid systems of large remote towns, IEEE Trans Smart Grid in-pressF Shahnia, S Bourbour, A Ghosh (2017) Coupling neighboring microgrids for overload management based on dynamic multi-criteria decision-making, IEEE Trans Smart Grid 8(2):969-983

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Q-3: Suitable Structure and Topology

Planning Study

• Cost• Frequency of interconnection• One or more system of coupled micreogrids

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Power Exchange Highway:

• Three-phase ac link

• Single-phase ac link

• DC link

Interconnecting Switch:

• Conventional Circuit breaker

• Power electronics-based switch

• Back-to-back power converters

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Q-3: Suitable Structure and Topology

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Q-4: Synchronization

MG-N-1

MG-N

(a) MG-2

MG-k

MG-1

MG-N-1

(b) MG-2

MG-k

MG-1

MG-N

MG-N-1

(c) MG-2

MG-k

MG-1

MG-N

MG-N-1

(d) MG-2

MG-k

MG-1

MG-NMG-N-1

(e) MG-2

MG-k

MG-1

MG-N

MG Central

Controller

Network

Controller

OMT

Synchronization

Module

ISS

ISS

Controller

UPC, PDL

Selected

MGs

On/Off

Synchronize,

Close, DR

CC, DR

Synchronize,

Close, Open, DR

CC, DR

Open, DR

S Bourbour and F Shahnia (2016) A suitable mechanism for the interconnection phase of temporary coupling of adjacent microgrids,” IEEE PES Innovative Smart Grid Technologies Asian Conference (ISGT-Asia), Melbourne.

Q-5: Stability Analysis

Small-signal stability analysis

• Will the system of coupled microgrids become stable after

their interconnection?

Transient Analysis

• Will the overloaded microgrid become unstable before the

synchronization is achieved and they are coupled?

F Shahnia, A Arefi (2017) Eigenanalysis-based small signal stability of the system of coupled sustainable microgrids, Int Journal of Electrical Power & Energy Systems 91:42-60F Shahnia (2016) Stability and eigenanalysis of a sustainable remote area microgrid with a transforming structure, Sustainable Energy, Grids & Networks, 8:37-50 19

Q-6: Isolation of microgrids

Defining Criteria to detect

• Interconnection necessity has been alleviated.

• Generation/demand imbalance

• Faults

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Q-7: Dynamic Operation

Challenges:

• Level of allowed voltage and frequency variations

• Primary controllers of DERs fighting against each other

• Central controllers of microgrids fighting against each other

• Communication link failure

• Coordination of energy storages (e.g. batteries) with interconnection

• Power trade among interconnected microgrids

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*F Shahnia, R Chandrasena, S Rajakaruna, A Ghosh (2014) Primary control level of parallel distributed energy resources converters in system of multiple interconnected autonomous microgrids within self-healing networks, IET Gen. Trans. & Dist. 8(2):203-222E Pashajavid, F Shahnia, A Ghosh (2017) Provisional internal and external power exchange to support remote sustainable microgrids in the course of power deficiency, IET Gen. Trans. & Dist. 11(1):246-260T Mehr, A Ghosh, F Shahnia (2017) Cooperative control of battery energy storage systems in microgrids, Int Journal of Electrical Power & Energy Systems 87:109-120

Discussion