in the micro-grid system we must prevent system from working on islanding mode, because in this situation the power generation of DGs is not proportional to consumption and finally lead to the oscillation frequency and voltage.

Please do not forget that currently a lot of work is put to use the islanding mode of operation purposely. With a sophisticated control algorithms and load shedding you could be able form a stable island, for some time.

For the instabilities, shouldn't they be more or less the same as in normal grid? At the end, smart or not, grid is about delivering the power and the physics behind it is the same. You still can have voltage collapses, frequency instabilities, oscillations etc. Only in 'smart' version of the grid you can have self-healing possibilities as in the internet network and you can more easily avoid this kind of problems.

Hossein @ : How can we prevent the system from island mode of operation.

Wojciech @: What kind of algorithms can be used and is there any possibility to reduce the instability problems like voltage collapses, frequency, etc

by using a plc line between DG and substation we can send a segnal to DG if this signal dos not arrive to DG it means that the connection between substation and DG has been discontinued and the generation of DG must be stop

The problem posed by Hossein Hosseini is a real problem to be tackled if the DG Generation is more or less than its local load,if the island operation is small and about the DG location and is being contemplated by us.

Work is going on,on different aspects off islanding. US Govt. and Spain have already done some work on it for their Systems.

P.S.

I do not know exactly what types of algorithm are used. I wasn't much involved in this type of studies. At the end of this paper https://www.selinc.com/workarea/downloadasset.aspx?id=6375 you can find short description of Adaptive Load-Shedding Scheme (ALSS). One of the first results when I googled for this is this article http://www.eeh.ee.ethz.ch/uploads/tx_ethpublications/pscc2011_mv.pdf

If you have access to IEEE databases, the recent edition of Power and Energy Magazine is devoted to topic of Microgrids, there you can find some information what is going on currently on this topic. http://ieeexplore.ieee.org/xpl/mostRecentIssue.jsp?punumber=8014

Nice description of various classifications of stability of power systems you can find in this article (also by Kundur) http://orbi.ulg.ac.be/bitstream/2268/3467/1/TaskForce_Paper_Definitions.pdf

Pisupati@: Is here any simple method to tackle those problems.

How can we reduce instability problems in practical ways...

When considering smartgrid what are problems would occur when comparing with existing grid other than instability problems

Could you please clarify, whether you want to know about instabilities in smart grids that occurs due to microgrids or instabilities in microgrids??? Although MGs are having lots of advantages, the higher penetration of MGs in a power grids can invite lots of instability issues...like voltage and frequency instabilities, low frequency power oscillations...etc. There is no well developed operational code for MGs. Independent control of MGs willtake the powergrids to instability, if MG penetration is more. In case of distributed generations (DGs), it can support grid stability with proper synchronous control.

Smart grids are supposed to act like self-healing grids. What exactly it mean? Routing power from one source to another in optimal conditions to ensure continuity and reliability of power? Is that one kind of problem we can deal with smart grids?

Smart grids are liable to instability, if the inductances and the power sources fulfil certain conditions. See attached paper that is to be published at ETG Congress in Germany.

Sorry, got the wrong button. Here is the attachment.

According to my experience, when you add smartness to the grid it creates some stability related issues in addition to what we normally observe in the typical power grid. The type of instability varies significantly depending on the form of Smart Grid that you consider.

If we consider the Smart Grid architecture that is based on Real Time Pricing (RTP), where the utility controls the tariff to indirectly control the demand, large increase in tariff could cause large reduction of demand hence resulting in significant reduction in tariff for the next interval. When the tariff is low the demand would increase, and if this chain reaction is not damped then the system could become unstable. This scenario is well studied and presented in the paper titled "Volatility of Power Grind Under Real Time Pricing" by Mardavij Roozbehani et.al from MIT.

If you consider more advance Smart Grid architectures like those insist on significant deployment of non-conventional renewable sources like wind and solar PV in the distribution network, then the fundamental problem arises from the intermittent and random nature of these sources. As intermittent fast changes in power flow from the transmission network would destabilize the network these fluctuations must be suppressed within the distribution network.

Moreover, the power flow in the negative direction would effect the voltage profile along the distribution feeder. Therefore the typical Load Tap Changing transformers would not be sufficient to maintain the voltage withing the tolerance limit.

These issues were analyzed and an optimization algorithm to overcome these issues is presented in my paper titled "Active and Reactive Power Balancing of Ubiquitous Power Network Considering Voltage Constrains".

https://www.researchgate.net/publication/258100562_Active_And_Reactive_Power_Balancing_Of_Ubiquitous_Power_Network_Considering_Voltage_Constraints?fulltextDialog=true&ev=prf_pub_xaddfulltext

Conference Paper Active And Reactive Power Balancing Of Ubiquitous Power Netw...

1. Stability Problem due to Consumers:

since local consumer behavior cannot be controlled, and perhaps is unknown in the

framework of indirect control, several stability issues could potentially complicate the balance of the grid, and the risk of instability is related to the specific behavior and strategyof consumers. Therefore, deeper analysis of main consumer types and behavior, and the consequences for stability should be considered.Refer Article,

Stability Concerns for Indirect Consumer Control in Smart Grids

Morten Juelsgaard, Palle Andersen and Rafael Wisniewski

Dept. of Automation and Control, University of Aalborg,

Email: {mju, pa, raf}@es.aau.dk

LINK:

http://kom.aau.dk/~mju/downloads/papers/ecc13/indirectSubOptUploadFinal.pdf

2. Cyber Security:

Cyber security becomes a priority concern as additional technologies connect to grid systems and provide more real-time data as well as two-way communications. The need exists to assess risks and vulnerabilities all along the communications chain from data sources to consumers, much of which is outside ISO control. There is little doubt that situations will emerge that require new security controls and monitoring to ensure that grid monitoring, operations and control systems are not compromised.

Refer Article: SMART GRID Roadmap and Architecture

December 2010

LINK:

http://www.smartgrid.epri.com/doc/cal%20iso%20roadmap_public.pdf

3. Transient Stability: Refer Article:

Impact of Distributed Generation on Smart Grid Transient Stability

Nur Asyik Hidayatullah, Zahir J. Paracha, Akhtar Kalam

School of Engineering and Science, Victoria University, Melbourne, Australia.

Email: [email protected], {zahir.paracha,

akhtar.kalam}@vu.edu.au

LINK:

www.scirp.org/journal/PaperDownload.aspx?paperID=4957

P.S.

Firstly the frequency instability.

Transient and voltage instability may also occur in all power systems.

Smart grid involves high penetration of intermittent, non-dispatch-able sources, so There could be instability in frequency due to real power imbalance. Also improper reactive power management may lead to voltage instability.