Next Generation Power System with D-FACTS

The ability to route products through a system is a key feature for productivity and efficiency. Trucks hauling goods can be routed and packets in communication networks can be routed. What about power flows in an electric grid? There are new technologies and modeling tools becoming available that are changing the fundamental assumptions about the ways power systems operate. The result is a next generation power system that looks like nothing you've ever seen before.

To the utility folks and engineers, and anyone with a circuits background, there is a common understanding that power flows can't be routed. Power flows through a systems according to the laws of physics: Kirchoff's voltage and current laws, Ohm's law, conservation of power, and others while redistribution of power flows is governed by network characteristics. These are all concepts that you may be familiar with that are commonly covered in undergraduate electrical engineering classes.

A consequence of these facts to the electric grid is that a transfer of power between two areas will impact flows on other lines in the system, potentially even lines which are far away. These unintended flows can restrict transmission capability since available transfer capability (ATC) is limited by the first line to reach its limits. In fact, a single overload can prevent many transfers from taking place. Therefore, the ability to effectively control power flow in a network can allow better network utilization by routing power away from overloaded facilities. Therein lies the opportunity.

Changing how power flows, without defying the laws of physics mentioned earlier, requires changing something physical about the system itself, and

PowerWorld and I are involved in a DOE ARPA-E project to do exactly that. We start with a piece of hardware called a distributed series reactor (DSR) made by Smart Wire Grid. Clamping these devices onto a transmission lines converts the line into a "Smart Wire" a distributed series reactor (DSR) with the ability to change its effective impedance. You can see more details from a talk Smart Wire Grid gave at the 2013 PowerWorld Client Conference in January.

Similar concepts are used by other devices, and you may be familiar with the Flexible AC Transmission System (FACTS) devices developed in the 1990s. The good news is that many technology improvements have occurred since then, allowing a revisit of power flow control solutions from a fresh perspective. We call DSRs and other distributed technologies Distributed-FACTS (D-FACTS). A simple use case for D-FACTS is to relieve local overloads. But this can also increase the amount of power that can be transferred per route and lower the cost of what's called generation redispatch. The net result of D-FACTS in the example below is that transfer was increased by 30%.

Conceptual demonstration of reduction in wind curtailment and 30% increase in transfer due to D-FACTS devices

D-FACTS devices incorporate into a smart grid as they can be set up to operate autonomously or communicate with other devices or the control center, allowing coordinated control. They have the unique ability to provide distributed support to locations in the system where support would be the most useful. By distributing the control capability, D-FACTS are also increase reliability. They can even serve as a platform for monitoring transmission assets.

Our role in all this is to model these devices and their control capability using PowerWorld software. We are also examining how much benefit these devices can provide and working to optimize their settings and placement to realize these benefits. As a result, our optimal power flow (OPF) tools can now determine the optimal dispatch of large numbers of D-FACTS located throughout the transmission system network. Check out a free tutorial with sample cases demonstrating these capabilities.

But changing the power flow control paradigm involves more than a few isolated efforts. The ARPA-E Green Electrical Network Integration (GENI) program is supporting several related projects, each focusing on different technologies that share the goal of improving power system resiliency and lowering costs through more flexible control. Participants in these complementary efforts served on a power flow control panel at the recent IEEE Innovative Smart Grid Technologies Conference. In my next post, I will talk about these efforts in more detail.