Direction of research: Distributed Optimal Power Flow

I have just read the following papers on distributed optimal power flow:

1. Kim BH, Baldick R. Coarse-grained distributed optimal power flow. IEEE Transactions on Power Systems. 1997:932-939.

This paper provides a distributed approach to optimal power flow based on an objective function. It involves splitting the network into a variety of regions each with its own set of buses and transmission lines. Regions which have a transmission line between them share variable values by using a dummy bus. The variables are then duplicated for that dummy bus and each region uses their version of the variables to solve their power flow. For each iteration, regions exchange their shared variables and update them until convergence is experienced.

The distributed equations involve using lagrangians to solve and update the shared variables. This paper provides some very good reasons for decentralised power flow and promising test results. As future work it suggests a number of possibilities which could be used. For example make use of previous iterations to avoid having to refactorise certain equations.

2. Baldick R, Kim BH, Chase C, Luo Y. A fast distributed implementation of optimal power flow. IEEE Transactions on Power Systems. 1999:858-864.

This paper is a fast implementation of [1] using techniques from:

3. Wu Y-C, Debs AS, Marsten RE. A direct nonlinear predictor-corrector primal-dual interior point algorithm for optimal power flows. IEEE Transactions on Power Systems. 1994:876-883.

This is one direction that my research is heading. I am very interested in distributed optimal power flow and how this can be used in conjunction with reducing overloaded lines within a network whilst minimising carbon emissions.

Need to get back into the habit of blogging!

I have been familiarising myself with a few techniques that are used in the paper "The use of constraint programming for the autonomous management of power flows":

• back tracking search - Search the tree by starting at the root and traversing in a depth first manner. At a particular node C, checks whether a valid solution can be computed from C, if not whole subtree is pruned. Obviously the hard part using a good approximation function that can calculate whether a valid solution exists.
• best first - explores the tree by expanding the most promising node chose according to a specific rule. A* search is an example.

I have implemented the DC power flow equations in matlab, they use considerably less code then the java implementation. Hopefully this matlab implementation will be used by CPLEX, a constraint optimisation solver, so that it can calculate the flow, however I am still working on expressing the problem in CPLEX language. 

In parallel to this I have been describing the model and the problem in mathematical terms, I have written a one page mathematical explanation of the constraints, the network and the variables defining their domains and bounds. This in theory will allow me to then translate it into any coding environment in order to implement it.

A selection of papers that I have read:

1. Dam KH van, Houwing M, Lukszo Z, Bouwmans I. Agent-based control of distributed electricity generation with micro combined heat and power: cross-sectoral learning for process and infrastructure engineers. Computers & Chemical Engineering. 2008;32(1-2):205-217. 

2. Taylor P, Xu T, McArthur S, et al., others. Integrating voltage control and power flow management in AuRA-NMS. In: SmartGrids for Distribution, 2008. IET-CIRED. CIRED Seminar.; 2008:1-4.

3. Pipattanasomporn M, Feroze H, Rahman S. Multi-agent systems in a distributed smart grid: Design and implementation. In: Power Systems Conference and Exposition (PSCE 2009).; 2009:1-8. 

4. Dolan MJ, Davidson EM, Ault GW, McDonald JR. Techniques for managing power flows in active distribution networks within thermal constraints. In: Electricity Distribution-Part 1, 2009. CIRED 2009. 20th International Conference and Exhibition on.; 2009:1-4.

I have implemented the same network as the one in the paper "The use of constraint programming for the autonomous management of power flows". However it does not specify any of the loads, and therefore I will not be able to recreate the exact experiments without them.

Next week I am putting the PhD on a one week hold to code full time on a project for BAE systems.

Back in Southampton

Back in Southampton now here is a summery of what I have been doing:
I have been focusing my attention on achieving a good understanding of how the electricity system works by reading a variety of books including 

1. Galvin R, Yeager K, Stuller J. Perfect power: how the microgrid revolution will unleash cleaner, greener, and more abundant energy. 1st ed. McGraw-Hill Professional; 2008.

2. Weedy BM, Cory BJ. Electric Power Systems. 4th ed. John Wiley & Sons; 2004.

3. Gonen T. Electric power distribution system engineering. 2nd ed. McGraw-Hill New York; 2007.

4. Chard FDLC. Electricity Supply: Transmission and Distribution. 1st ed. Longman Group Limited; 1976.

I have also been studying the paper:

1. Davidson EM, Dolan MJ, McArthur SDJ, Ault GW. The use of constraint programming for the autonomous management of power flows. In: 15th International Conference on Intelligent System Applications to Power Systems (ISAP 2009).; 2009:1-7.

with the intention of first recreating the results found in the paper and then applying a decentralised way to calculate power flow analysis. By the end of January the goal is to have a mathematical model of the various constraints and equations used and a set of experiments and results written up in a small two column style paper.

TODO this week

I have just had the second ORCHID meeting. In it we covered all the research people have been doing since the last meeting. I spoke only briefly about max-sum and the areas I have been researching. I have also attended a library training course where we learnt about all the different resources available to us at Southampton. TODO (This Week) : Read DPOP Paper "Distributed constraint optimization with structured resource constraints", read other max-sum papers, research funding opportunities for internships abroad, research variable clustering (GDL paper), research pseudotrees.

This week I have been mostly..

This week I have focused my attention on the max-sum algorithm. I have implemented it in java and have created a simple visualisation to show it trying to perform graph colouring. I am still having problems with the implementation as it doesn't seem to converge to the correct solution. It will often reach the correct solution, but if left running will then converge to all nodes coloured one particular colour. I make sure each variable to function message is normalised before it is sent out and I also randomly allocate a variable state preference to each agent before the algorithm is run. In cyclic graphs (which will always be present when using agents) the max-sum algorithm does not guarantee convergence to an optimal solution, or a solution at all therefore I wonder whether I should implement the termination constraints and see if this makes any difference.

Today I have been reading a number of papers:
"The contract net protocol: High-level communication and control in a distributed problem solver" - presents an algorithm for task execution in a decentralised way using agents. A Manager agent will request a task to be completed, agents submit offers to complete that task with various constraints, the manger agent chooses the best offer, the offers owner becomes a contract agent and completes the task. Note this is a simple algorithm and there is no counter offers allowed.

"Intelligent distributed autonomous power systems (IDAPS)" - Presents IDAPS "Intelligent distributed autonomous power system" which is a form of microgrid.

I also attended the first Energy meeting where we discussed the particular areas we are all working in. These meeting will allow us to go into detail about particular problems that we have, or in order to get people interested in collaborating in a particular area. These meeting differ from the ORCHID meetings in that they are specifically in the area of energy and not the wider area of agents.

Things went wrong

On Friday I accidentally deleted my code I had been working on last week. Although I hadn't written much of the actual max-sum code, I had all the nice functions in place that handled the message passing etc so is a bit of a bore to write again (it is good practise though) Over the weekend I read a paper "Decentralised Coordination of Mobile Sensors Using the Max-Sum Algorithm" here is my take on it:

Uses max-sum to monitor and predict the state of spatial phenomena using a team of mobile sensors. Identifies that some centralised solutions exist (Gaussian Processing) however not acceptable in this setting for security reasons as provides central point of failure. To coordinate sensors, want to choose a move that maximises the total value obtained by the agents. (i.e. the agents that are connected to eachother and thus their utilities depend on eachother). Straight forward max-sum is not suitable in this setting as computation of messages is a bottleneck. Therefore introduces two techniques that prune the size of the joint action space (i.e. Utility) 1. Action pruning algorithm: pre run before the max-sum, prunes states that can never be maximised 2. Joint action pruning algorithm: speeds up computation of the messages from function to variable, uses branch and bound. TODO: Continue coding the max-sum algorithm, go to a lecture at 14:00 on sustainable energy.

A and E

Last night I took one one of my mates to A and E, nothing serious. Since there was a long waiting time, it gave me an opportunity to read quite a bit of hot air. It seems that nuclear power is the future for us if we want to have a 'sustainable' energy consumption for the next 1000 years. There are obviously a lot of problems to overcome first before but it is not totally infeasible. Over the next decades we sill see a rising demand for electricity. This will be due because of a shift to cleaner energy. Electricity is a high grade form of energy which if generated in the right way can be very clean. Therefore a shift to the electrification of certain service such as public transport and heating will be experienced. The book talks about the joys of heat pumps compared to conventional gas fired boilers. They are much more efficient at producing energy (in the form of heat) then gas or combined heat and power (CHP) and thus should be used in the future to provide living spaces with heating (and in the summer with air conditioning) Therefore I will be researching ways in which these micro generators can be incorporated into microgrids.

BAE Systems Report

Today I read the BAE Systems report on smart grids, here is a summery:

This report gives a detailed overview of smart grids and there applications. It begins with defining what a smart grid is and what it consists of. It then goes on to define how it could be used to manage the electricity in a static or deployable army base.

It identifies three aspects of the system that it would implement: demand side management (DSM), supply side managment (SSM) and Network management (NM). DSM is concerned with understanding and manageing consumer power demands in order to minimise peak power across many different consumers.SSM is Resposible for ensuring there is sufficient electrical power available to meet the total real-time consumers electrical power requirements. Needs to balance the generating of power across different generators and facilities. Uses predicted power estimates. NM manages the transmission and distribution of electrical power from the electricity generators to the consumers. This report provides the advantages of using a smart gird to manage the electricy on an army base.

Reading this report gave me some interesting areas that I could look into:

power dispatch and scheduling
network load balancing

All in all I want to look at power flow management and how this could be achieved in a microgrid environment.

monday morning

Today I spent most of my time finishing off the reading of "factor graphs and the sum-product algorithm". Oli and I also went through some more examples for the power systems lectures. TODO (for tomorrow): Read the BAE systems report on Smart Grids, Make a gantt chart for time up until the 9 month report, Go through the last question for power systems analysis.

maths

Over the past few days I have been reading two papers that contain quite a bit of maths. I have been going over both papers trying to understand what is going on. It is slow progress for me. The second of the two papers "factor graphs and the sum-product algorithm" is easier to understand and get a grasp of. So far essentially what the algorithm does is to construct a factor graph from a particular problem (which contains functions and variables) and then compute each variable as a product of all the factors. This is essentially computing a functions as a product of local functions (which take less operations to compute). This is what I understand is going on. Other then this, I have been working through a number of power analysis problems consisting of load factors, peak power, cost for generation etc.

monday morning

This week I shall be focusing on a lot of reading, surprise surprise! I was given another book to read by my supervisor Gopal called Perfect Power which details "how the microgrid revolution will unleash cleaner greener, and more abundant energy". TODO: Finish reading the current paper, and read another, go to the 14:00 lecture on sustainable energy, read some hot air, look at notes on conventional generation techniques.

interesting stuff

Read a few papers today and had some possible ideas about what to investigate: one paper Coalition formation in transmission expansion planning uses coalition formation to determine the optimal number of transmission lines to add to an existing network in order to supply forecasted load. This same technique could be applied to mircorgenerators to determine how many should be added to the network and in what locations in order to meet various flows. This could be based on certain factors like average power output or efficiency or something. I also talked to Harry in the labs today, he suggested Power Matcher (which I already new about) and also IDAPS which I had forgotten about, so will look at the various papers produced on these implementations in due course.

interesting lecture

Had a lecture on power systems analysis today. It was quite interesting and gave me a few ideas of what could be done. For instance load factor (average power / peak power) could be taken into consideration when controlling a microgrid. The idea is that you want the load factor to be as close to 1 as possible, that way the fluctuations between supply and demand is reduced meaning that high cost generators, which allows peak demand to be satisfied, do not have to be used as much! This is difficult to achieve in a microgrid that contains alot of renewable generators and many loads, but this could be solved using agents. I am interested in this and will look into this area of agent based microgrid management. TODO: Print off some more papers to read, read one paper and make notes, explore load factor and load loss factor, read notes on power systems analysis, go to lecture at 12:00 (sustainable energy), read some hot air (for background knowledge).

computer set up

Finally set up the new computer, its a beastly quad core with 12 GB of RAM and two 22" monitors, veeeerrrry nice! TODO: Read two papers and make comments, download and print some of the papers suggested by Gopal, read some Hot Air.

induction

Today is the first part of my induction to the university and postgraduate research. It involves some talks by various important people and a tour of the university campus (in case I have forgotten where everything is :p) TODO: Other then that I am going to read two papers today, they are Multi-Agent Systems for Power Engineering Applications Part I and II (written by the IEEE Power Engineering Society's (PES) Intelligent System Subcommittee). These should give a great deal of background knowledge about how to apply agents to the smart grid environment. I will also be reading my daily dose of "Sustainable Energy - without the hot air" I suggest anyone and everyone to read this, available online http://www.withouthotair.com/

lectures

I have a couple of lectures today, one was at 9:00 (power systems) and the other is at 12:00 (sustainable energy). Both should provide a good background knowledge to the area of Smart grids and energy. TODO: Read and provide comments on two papers, go to the lecture at 12, read some more of hot air, hand in demonstrator form and hopefully set up the new pc.

tasks for the day

Got into the office about half an hour ago and have been getting ready to read all day. Got a selection of papers and a book on sustainable energy (without the hot air), so should be good! Hopefully the computer will come today so I can set up my working environment properly. Still, early days!