Hello Dr. Fosso,

Active distribution systems (both in grid connected and islanded) are probably the next big thing in the field of microgrids. At customer level we call them residential microgrids. The issues you have identified basically refer to the power quality but there may be other power management issues that we need to look into.

Under islanded mode:

1. Issues related to power management between phases can be looked into (how PV, battery or other droop units will manage power in a phase).

2. Sharing of power on optimal solution (based on load forecast, line losses, frequency deviation, power generated in a phase). This is intra-phase power management using some sort of PE based solution between phases.

3. Synchronization from islanded to grid connected mode.

Hello Dr. Fosso,

Active distribution systems (both in grid connected and islanded) are probably the next big thing in the field of microgrids. At customer level we call them residential microgrids. The issues you have identified basically refer to the power quality but there may be other power management issues that we need to look into.

Under islanded mode:

1. Issues related to power management between phases can be looked into (how PV, battery or other droop units will manage power in a phase).

2. Sharing of power on optimal solution (based on load forecast, line losses, frequency deviation, power generated in a phase). This is intra-phase power management using some sort of PE based solution between phases.

3. Synchronization from islanded to grid connected mode.

Dear Professor Olav Bjarte Fosso ,

Better demand-side management; greater energy efficiency; improved supply reliability; increase renewable energy generation like wind, solar, biomass etc.; increased customer choice; energy storage; smart appliances etc.

Dear sir

From the electrical view you are right. But I think this subject has many issues from the material and mechanical engineering. Such as:

Reduction the cost and improve the cost of photocell.

Storage system

Regards

M.A.Ehyaei

Dear Professor Dr. Fosso,

Future challenges for active distribution networks will be important issue in the power distribution, generation networks. Penetration of EVs, DGs and other power electronic converters will hamper the power quality. Shortage of fossil fuel initiates renewable energy integration. However, to stability issues will be engaged, energy efficiency & storage capacity need to be improved. In case of EVs, G2V and V2G technology with renewable energy will be an important task in near future.

Thank you all for valuable contributions! Yes I addressed the technical aspects with purpose. Looking at published papers, many seem to address my first item while I suspect the third to get significant importance. Wind farms all over the world have experienced instabilities probably because of non-linearity of models, harmonics and controller interactions. The cases may have similarities.

Please notice this my paper:

"Quadratic optimization method for a dual index combination of the penetration level and the dispersion factor of the distributed generation"

Marzieh Naghdi, Mohammad‐Agha Shafiyi, Mahmoud‐Reza Haghifam, International transactions on electrical eenergy system, first polished: 18 April 2018.

Maybe one of the bigger challenges is indicated in the IEEE paper from 2004? (Link below)

Article Harmonic Interaction Between a Large Number of Distributed P...

Many things can be controllable but with an uncertain number of relatively small units it be may become difficult to be protected. There will be many of these units in the distribution grids.

One of the man challenges of the microgrids is the constant power load CPLs, especially in DC microgrids. Since, the tightly regulated point of load converter at the DC microgrids behaves as the CPL, consumes a fixed amount of power creating negative incremental impedance at their input terminals. This impedance has destabilizing effect on the DC bus voltage of the DC microgrid.

Dear Prof. Fosso,

Couple of challenges:

1. Communication Networks will be key enablers for active power distribution networks. How do we design communication network architectures for control of microgrids/ or a cluster of microgrids?

(Our research group at Virginia Tech. has worked on Microgrid Communication Architecture: Conference Paper Construction of a microgrid communication network

2. Evolving policy/ regulatory structure for reliability and energy exchange via microgrids in an active distribution network. To that end:

2.a. If there are millions (possibly more) of micro-transactions are happening, which platforms will be available for monitoring and enabling such transactions?

Olav Bjarte Fosso I could recommend a good book on this exact topic:

"Integration of Distributed Generation in the Power Systems", by Math Bollen and Fainan Hassan, ISBN: 978-0-470-64337-2, IEEE Press.

Some key issues/challenges of increased distributed generation that are discussed therein are:

1. On the transmission level (Ch. 8)

a. Increased uncertainty due to fluctuation of renewable power sources

b. Passing weather front can lead to unavailability of large amount of generation

c. Behavior of small, novel generators during large disturbances is unknown

2. On the distribution level

a. Overload of feeders and transformers due to large amounts of production during periods of low consumption (Ch. 4)

b. Increased risk of overvoltages due to production at remote parts of a distribution feeder (Ch. 5)

c. Power quality can be negatively effected (Ch. 6)

d. Improper operation of the protection equipment (Ch. 7)

e.g., uncontrolled islanding

You can add a market issue. DSO Company should deal with planning processes, like balancing and automatic generation control. In addition, there is a different perspective for network loss calculation and prediction. Then the relations towards TSO will have major changes.

While the issues that you have listed are completely valid, I'd like to add something that relates to my field of research. One of the things that we find is that the power system planning and operations tools that we have and what the TSOs and DSOs use are often time not sufficient for the future electricity network. This could become a major challenge for the progress of renewable energy future, because even now we are dependent on modeling, simulation tools to understand power system behavior, predict plausible contingencies etc.

Dear Prof. Fosso,

Future challenging in active distribution networks (ADNs) are the control and reliability issues of the power electronics converters to fulfill the requirements of ADNs. the continuous increased functionalities and grid restrictions have added more stresses and issue for controlling their performance and availability.

Here are a reference paper for this issue,

M. Aly, E. M. Ahmed and M. Shoyama, "Thermal and Reliability Assessment for Wind Energy Systems With DSTATCOM Functionality in Resilient Microgrids," in IEEE Transactions on Sustainable Energy, vol. 8, no. 3, pp. 953-965, July 2017. doi: 10.1109/TSTE.2016.2635200

https://ieeexplore.ieee.org/abstract/document/7765095

I will add on Mokhtar answer " Future challenging in active distribution networks (ADNs) are the control and reliability issues of the power electronics converters to fulfill the requirements of ADNs " also the protection of such future ADNs and anti-islanding protection of DGs in the ADNs

The issue of downtime due to intermittent nature of wind and solar irradiance at higher penetration level

ancillary services