System of Interconnected Microgrids Challenges and Solutions Dr Farhad Shahnia
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