Disturbance Detection, Diagnosis and Protection

Project 1.3
Status Monitoring, Disturbance Detection, Diagnostics,
and Protection for Intelligent Microgrids
Dr Wilsun Xu
C. Jiang, H. Yazdanpa, Y. Tian & A. Pezol
Project 1 of 3: How to protect MG from short-circuit faults?
Problems faced by industry:
• Overcurrent protections are widely used in various facilities (basis of MG)
• DGs (distributed generators) create difficulties for over-current protections
• Can we find a method for DGs to work with the protection scheme?
Proposed solutions and innovations:
• Introduce the concept of fault current restriction for DGs
• Each DG can only produces a limited amount of short-circuit currents
• Develop current restriction schemes for 4 types of DGs
Potential benefits:
• Both utilities and DG owners are very interested in finding a simple
solution to the problem. This solution does not require changes to utility
• The results will lower the interconnection barrier for DGs
Project 2 of 3: How to monitor and diagnose MG conditions?
Problems faced by industry:
• Even with ICT, it is still costly and difficult to monitor loads in a MG
• Can we monitor the loads at locations where power sensors are not available?
• The information will help to characterize the load behaviors in a MG and
to support demand response and other energy-saving activities
Proposed solutions and innovations:
• Introduce the concept of micro-grid state estimator (MG-SE)
• The estimator uses measured voltages to estimate loads in a MG
• The proposed system could solve the sub-metering problem
Potential benefits:
• The problem is of significant interest to commercial facility owners
• The results will enable more energy-efficient activities in MG &
commercial buildings
Project 3 of 3: Home-based MG or “nano-grid”
Home area network
Future Smart Home
Energy generation:
Energy storage:
Energy consumption:
Solar & natural gas
Electric vehicle
Home appliances
Nano-grid is a system for managing the generation, storage, consumption
of energy in homes. It is build on the concepts of microgrid and home
area network.
• Home-based MG could be the future form of energy use in homes
• The results will facilitate the energy saving activities of home owners
Proj 1: Propose and confirm solutions for 2 types of DGs
Proj 2: Complete technical feasibility study
Proj 3: Complete review and formulate research strategy
Proj 1: Propose and confirm solutions for other DG types
Complete project
Proj 2: Complete research work
Proj 3: Establish blueprints for nano-grid with research results
Proj 1: Technology transfer
Proj 2: Complete demo & tech transfer, complete study on
sub-metering applications
Proj 3: Complete research work and tech transfer
2.1: Cost-benefit
2.3: Demand responses
1.1 Control & operation
1.2: Power management
1.4 Operational
strategies of MG
3.1: HAN
(Home area network)
3.3: Automation
Collaboration items - General
1. Establish MG test cases (steady-state, dynamics and transients)
2. Experimental facilities available for the network. Especially on how to access
BCIT facility
Collaboration items - Specific
1. Experimental studies of fault current restriction schemes
2. MG State estimator: formulation, algorithms and experimental studies
3. Nanogrid: a) MG expertise and HAN expertise
b) architecture consideration of nanogrid
c) Experimental facility
d) Implications to power systems (theme 1)
Project 1 Details: Fault current restriction strategy for DG
Every DG shall not contribute to fault current that is higher than k-times of its
normal operating current (k=1.2 to 1.5)
Synchronous generator
We propose crowbar control to limit excitation current
E xcite r
C on tr o l
C row bar
Period critical
to relay
Project 1 Details: Fault current restriction strategy for DG
Inverter-based generator
We propose a control that reduces inverter output when sag is detected
• In traditional control, during voltage sags, inverter current is increased
until it reaches the current threshold which is normally set to 1.3~2 Irated .
• In our control strategy, converter current is reduced in proportional to
severity of sag level
Operation during
low-impedance fault
Operation during
high-impedance fault
Project 2 Details: Micro-grid state estimator
Panel 1
Panel 2
Panel 3
The currents of Load 1-3 are not known, we may only
know the panel 1 current
If we know the voltages of buses X,Y and Z and the
network impedances, the currents can be estimated
The voltages are much easier to measure with the
help of distributed plug-in voltage sensors
Load-1 Load-2 Load-3
Traditional SE: estimate V using known I or S
Microgrid SE: estimate I using known V