Microgrids, islanding, and energy storage
Meet Mohammad Mojdehi
I designed software . . . that provides an in-depth evaluation of the risk of islanding by modeling the distribution system and pinpointing the conditions that could cause islanding . . . With the software, I’m able to determine how to prevent an islanding situation.
Mohammad Mojdehi joined OBG in June. He’s a newly minted PhD in electrical engineering with a focus on power systems from Syracuse University. Mojdehi grew up in Iran, where he earned his master’s and undergraduate degrees, and has also lived in South Africa. The author of two books, he is also widely published in academic journals. He recently worked as an intern at National Grid examining methods for evaluating ways consumer located generation (Distributed Generation) impacts the grid.
Q: With microgrids growing in popularity, confusion exists about the true definition of a microgrid. Can you explain the difference between a microgrid and a smartgrid? What are the best power sources for microgrids?
A microgrid is a smartgrid on a small scale, in terms of electrical load and generation. A microgrid can take advantage of different DG (distributed generation) technologies, such as wind turbines and photovoltaic cells (PV). The more DGs interconnected in the microgrid, the more resiliency can be achieved. However, the intermittent nature of renewable resources makes the operation of the microgrid more difficult. Energy storage devices are necessary to smooth power generation of renewable resources.
Q: Part of your doctoral thesis and some of the work at National Grid dealt with the problem of “islanding.” Tell us about the software you’ve developed that helps evaluate the risks of islanding.
Islanding can be defined as a condition in which a DG remains energized in a localized area while the remainder of the electric power system loses power – a situation that can cause damaging surges and danger to linemen who might not realize that power is still present.
Islanding is a major barrier to the development of microgrids because it’s time consuming and expensive to evaluate.
The national standard requires a loss of grid connection to be detected by DGs within two seconds, leading to an immediate trip of the DGs from the electric power system. So before we can connect DGs, we must evaluate the risk of violating that requirement.
There are several over-simplified screening procedures currently used to evaluate the risk of islanding. I designed software, based on the MATLAB platform, that provides an in-depth evaluation of the risk of islanding by modeling the distribution system and pinpointing the conditions that could cause islanding.
I used the software I developed on four projects while working for National Grid. With the software, I’m able to determine how to prevent an islanding situation. An example of a solution is using a direct transfer trip – a signal sent from a substation to a microgrid – alerting it to disconnect.
Q: You have also studied the “social welfare” of microgrids. Can you explain this concept?
Social welfare is finding a solution which pleases all interested parties involved, such as the system operator, end-users, and all companies involved in producing and delivering electrical power. Environmental concerns, such as greenhouse gas emissions, are another interest. If we can find a solution for a power system that could lead us to maximize social welfare, we can provide a win-win.
Q: How have changes in the national energy market over the years, such as restructuring of the electricity market in the 1990s, affected the development of alternative sources of power?
Currently, electricity is being traded through different market structures. Those market structures have been designed in order to remove monopoly and its negative consequences. Supplying electric power through a market increases competition and efficiency. One way to improve efficiency and reliability is using DGs in power system planning and operation, especially DGs using renewable resources which may be more aligned with the needs of end users and avoid the requirements for building large central generation facilities.
Q: How does the reliability of power in the United States compare to other countries? What role do microgrids play in the concept of power resiliency?
During the last decade, smartgrid and microgrid concepts have been the center of attention in the U.S. electric sector. Environmental concerns, efficiency, sustainability, and resilience are the main motives for upgrading the current power system in the U.S.
However, we are behind Europe. It goes back to the history of oil prices. When the price jumped, Europe started talking about what to do. They are also more concerned about the environmental impact. For the U.S., the restructuring of the electric sector was the turning point. The need for efficiency prompted that - our aging infrastructure, the monopoly, the cost of electricity.
Today, we have a 10- to 15-year gap in training power engineers. Around 50 percent are going to retire within the next five years, and there are not enough to replace them.
Q: Energy storage relates to another area of your research: EVs, electric vehicles. Can you explain EVs’ connection to microgrids, and what the future looks like?
EVs must be charged in order to run. The power EVs demand adds a significant amount of load on the system from where they reside at night to where they are parked during the day. This brings up two issues: the need to generate more power and the need to transfer it to EV owners. Technology developed for the EVs can be used for a microgrid and support services for the larger integrated grid. Vehicle-To-Grid (V2G) services like frequency regulation utilize EV batteries to store power for the microgrid, and the charger/inverter for reactive power service.
The EV market is growing very fast. The main problem with EVs is the price of the battery. We are expecting the price to go lower and lower. In his 2011 State of the Union address, President Barack Obama set the goal for the U.S. to become the first country to have 1 million EVs on the road by 2015.
Q: On a personal note, why did you decide to work for OBG? And do you drive an EV?
OBG is a great company with a dynamic atmosphere. Working on different projects provides me an opportunity to implement and extend my knowledge. I am so grateful and blessed to work for OBG with smart and great people.
I cannot afford an EV now but hopefully soon I will buy a Tesla.