Princeton Power Systems

Seeking a Clean Wave Form in Power Conversion Devices

Psomas - President & CEO

Princeton classmates Eric Limpaecher, Darren Hammell, and Mark Holveck started the company based on a technology invented by Limpaecher’s father.

If you stroll through the Forrestal Campus at Princeton University in New Jersey, you’ll probably encounter one company that seems to be taking over the place. Princeton Power Systems finds itself growing in huge leaps. CEO Darren Hammell tells me, “We have almost the whole building right now; we started out in a couple of offices. We have more people, and we need more space.”

Princeton Power Systems uses advanced power electronics technologies in developing power conversion devices for industrial and military applications and renewable electricity generation. That last one — renewable energy — has spurred their growth.

“If you look at our products, they basically convert electricity from one form to another, whether it’s from DC power to three-phase AC or maybe variable AC power coming out of a wind turbine to steady AC power,” Hammell explains. On a navy ship, power might be distributed at 440 hertz AC, but to run a motor, they have to convert it to 60 hertz AC. A wind turbine might output 30 hertz AC, and they convert that to 60 hertz to put it on the utility grid. “The building blocks of our products are the same for both those markets.”

Hammell boasts, “We’re about to release our first broadly applicable commercial product.” This is a commercial-scale grid-tied inverter for connecting solar arrays, wind turbines, and other generation sources to the electric grid, so users can sell their power back to the utility. It is designed for systems large enough to power a big-box store, vineyard, or other similar business.

Princeton Power Systems traces its roots back to 2001, when Hammell; Mark Holvek, their chief technology officer; and Eric Limpaecher, VP of engineering, were classmates at Princeton. Hammell majored in computer science engineering, Holveck in mechanical and aerospace engineering, and Limpaecher in electrical engineering. Working on projects involving high power electronic circuits, they entered the 2001 Princeton business plan contest their senior year. After winning first place, one of their electrical engineering professors, Ed Zschau, helped them perfect their idea and launch a company. They met with Greg Olson, a successful local Princeton entrepreneur, and he provided the first round of financing for the company.

“We got our start doing work with the Navy and other military groups, a lot of R&D work, and we bootstrapped ourselves using government financing programs.” Hammell recalls. “We knew we wanted to eventually commercialize our technology.”

The company’s products are based on a patented technology called AC-link invented by Rudy Limpaecher, father of Eric and an advisor to the team. Rudy has 30-plus years of experience in the power conversion field and a Ph.D. in Plasma Physics from UCLA. The young guys have invented several related technologies to refine AC-link.

Rather than use the usual insulated gate bipolar transistors to turn components on and off, this uses silicon-controlled rectifier switches, which comprise a simpler, more reliable, and less expensive way to create high-quality power at high efficiency. “It doesn’t look that much different from other three-phase power converters, but it has a unique control method,” Hammell says. “When we convert power, say from DC to AC, we get a clean wave form without having to apply a lot of filtering. Those filters tend to be very a heavy and expensive component of the system.”

A clean AC waveform matters to utilities; when you dump power onto their electric grid, they require that it meet strict standards. It also matters in the military because they have issues with EMI (electromagnetic interference). And in general, it has become increasingly important over time as sensitive digital equipment has proliferated.

Engineering Driven
Some 20 people populate the staff at Princeton Power Systems. According to Hammell, “We do all our engineering and light manufacturing in the same facility. We buy most of the subassemblies of our products from outside companies, like we have digital circuit boards, big inductors, capacitors, parts like that. We do the final assembly and testing of the products here in our facility.” He adds, “If you include me, we have 19 engineers. We’re very light on administrative and sales right now, something that will probably change. But we’ve traditionally been a very technical, engineering-focused company.”

Psomas - President & CEO

Now located on the Princeton University campus,
the growing company is moving to bigger quarters
down the road.

On the military side, they partner with large contractors like Northrop Grumman and General Dynamics Electric Boat and some of their subcontractors such as Beech Panels and Controls and R&T Technologies, companies building and maintaining ships. “On the commercial side, we partner with systems integrators, companies like World Water and Solar Technologies and EPV Solar. These companies design a large solar array and then purchase our equipment to get the whole system working,” Hammell relates. They work with Conergy and Powerlight on the solar side and wind turbine manufacturers like Marquist Wind Power and BlueGreen Pacific. Having generator and turbine technology, the latter need a way to get power onto the utility grid so they can sell it.

In explaining how they got into renewable energy, Hammell says they did their homework. “We had new technology that could provide advantages, and we thought that market would develop. Over the next couple years, 2001 to 2004, people started to take notice, energy prices were rising, so we focused even more effort on that side of the business. All of a sudden the solar business is booming, wind has been booming for a couple of years.”

In wind energy, Hammell says, “The market has grown from the large utility side, so most of the growth is in huge wind turbines. In the solar world, it’s more mom-and-pop shops, a much more fragmented market. A lot of people out there are installing projects, and the systems tend to be less integrated, so you’ll buy the solar panel from one company, the inverter from a different company, and maybe the racking system from a third company. So for us as a small high-tech company, there has been more opportunity in the solar markets in the past couple of years. At the same time, though, we’ve also seen recently a bunch of smaller wind turbine companies popping up and a new market created for these business-sized wind turbines.”

Combining the military and renewable energy arenas, Princeton Power Systems is developing power converters for the Army to use in Iraq and Afghanistan. They want to create microgrids that combine diesel gensets with solar arrays, wind turbines, and whatever power source is available, putting it all onto a common grid so they can optimize their field use.

With all this going on, it comes as no surprise the firm is busting at the seams. To remedy the situation, Hammell reports, “We’ll actually be moving soon to a place about two to three times this size before the end of the year, just down the road. We’re getting bigger. We’ve outgrown the space.”


Princeton Power Systems

Engineering and light manufacturing firm specializing in power conversion devices

Princeton, New Jersey


Types of engineers they use:
“It’s primarily electrical, mechanical, and software,” says CEO Darren Hammell. “When you get into these high-power electronic systems, a lot of the design becomes thermal issues, reliability of the product, the packaging. So mechanical guys are really valuable. And then we have software folks that develop control algorithms for the products and a simulations package, where we can simulate how the circuits are going to operate just using a proprietary software program.”

Outlook for hiring engineers:
“We started this year with 12 people, and we’re up to 20 now, and we plan to hire at least 4 to 5 more before the end of the year,” Hammell explains. “And then we plan to double in size next year, so we’ve got a strong demand currently for all types of engineers.”

What they look for in engineers:
“We’re looking at both entry level and master’s or Ph.D. level engineers.” A Ph.D. or master’s level in power electronics engineering is very valuable to us. A master’s level in mechanical or software is also very valuable,” Hammell relates.

“It’s very difficult to find engineers, especially in the U.S., with a background in power electronics. But we’ve had success taking mechanical engineers and electrical engineers and giving them a little training on the power electronics side so they can understand what we do and contribute.”

Contact for submitting resumes:
E-mail to

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