Traditional, centralized power grids where power is generated, transmitted and then distributed to users are fast becoming a thing of the past. Such systems are inefficient and vulnerable to attack. In addition, renewable energy sources, such as wind and solar, have led to more compact generators. For all these reasons, the future of power is power electronics-based microgrids.
A microgrid is exactly what it sounds like - a small grid. It consists of multiple distributed generators and loads and can work in both grid-connected- or autonomous- modes. Pictured above is a modular multi-level converter development platform being used at Lehigh University for testing renewable microgrid and shipboard power system elements.
Rather than a centralized system, multiple microgrids are likely to be the future of power, according to Wenxin Liu, assistant professor of electrical engineering at Lehigh University because they allow for more flexibility.
Power electronics techniques, says Liu, have significantly improved the flexibility, reliability and power density of microgrids. However, control of microgrids remains a challenge due to reduced inertia, increase uncertainties and a wide range of operating conditions.
Liu is working on novel concept: developing "LEGO-like" power electronic systems that are easily, and inexpensively customized. This involves developing advanced hardware to improve a system's capability and potential; in this case, through the development of modular power converters and advanced controller hardware for high-performance component-level and system-level applications.
It also involves advanced software design to unlock hardware potential, improve performance and lower cost.
Wenxin Liu, Assistant Professor in the Department of Electrical and Computer Engineering at Lehigh University.
"What I want is to develop something that is small, modular," says Liu. "If an application needs higher voltage, we can connect them in a series. If an application requires a higher current, we can connect them in parallel. If both, then we can connect them in a series and in parallel. So, we can customize it for different applications."
The goal says Liu, is to reduce the time and expense it takes to construct or customize equipment for a microgrid.
"With a modular system, if something is not working, we can just replace that part, reducing maintenance costs," says Liu. "Because we always have two priorities: first we want to make it work--and then we want to make it work better."
Though his work has numerous potential applications, Liu's concept is particular appealing to the U.S. Navy for whom maintenance, reliability and survivability are of the utmost important, since equipment must be able to survive under extreme conditions. The Office of Naval Research has supported Liu's research for several years, most recently awarding him a three-year grant for continued development of "LEGO-like" complex power electronic systems.
Renewable Microgrid and Shipboard Power System Test-bed
Microgrid research, according to Liu, is a multidisciplinary project requiring expertise in three main areas: power systems, which considers the whole system; power electronics, which looks at single components; and, controls, which studies model based algorithms.
"Hardware can only improve the potential--how it works depends on the software," says Liu. "My work integrates the study and development of both hardware and software. And, since this is a microgrid, not a large scale system, is possible to test it through hardware experimentation.
Liu's Smart Microgrid and Renewable Technology (SMRT) research lab is well equipped for advanced power and control studies. Major equipment include an OPAL-RT real-time simulator, two renewable microgrid testbeds, and two modular multi-level converters.
"My goal over the three years of the project, is to demonstrate the concept, designing the hardware and then enabling it with software," says Liu. "I hope to promote and materialize this idea of modular power electronics systems."
