Driving a new generation of power plants

Variable frequency drive (VFD) technology supports versatile, reliable, low-cost power inverters for industry-leading supplier of fuel cell plants.

08/15/2013


Environmentally friendly: The liquid-cooled design of the Rockwell PowerFlex 700L VFD allows for a small footprint, making it easy to fit the drive into a sealed outdoor enclosure, which extends the life of the electrical equipment. Courtesy: Rockwell AutFuel cell technology is showing great promise as a potential answer to the world’s growing demand for cleaner, cheaper forms of energy.

As a power source, fuel cells, which essentially are electrochemical devices that combine fuel with oxygen to produce electricity and heat, offer many advantages when compared with both traditional fossil fuel power generators and renewable forms of energy.   

Fuel cells produce much cleaner, more efficient energy from the same fossil-based fuel. And because they don’t rely on unpredictable—and sometimes unavailable—power sources such as sunlight, wind, or water, fuel cells can offer a more reliable source of energy than the renewables. Companies that build fuel cell power plants also are conquering another issue that is leading to power shortages in much of the industrialized world: the difficulty of adding capacity to the power grid.

Fuel cell plants are being built at—or very close to—the locations at which the power is consumed, breaking the mold of reliance on centrally located plants that employ long strings of unsightly, and potentially dangerous, power lines to deliver energy to consumers.

The practice of locating fuel cell plants near the point of consumption is known as distributed generation, and one way to make the energy conversion process more efficient is through integration of variable frequency drive (VFD) technology.

FuelCell Energy Inc., of Danbury, Conn., builds three types of fuel-cell systems:

  • One that provides 300 kW of continuous power output
  • A second that produces 1.4 MW of continuous power
  • A third that generates 2.8 MW of continuous power.

 

 

The company says its 300 kW system is suitable for powering smaller commercial operations such as supermarkets or medium-sized hospitals. Gill’s Onions, a manufacturer of fresh-cut, packaged onions based in Oxnard, Calif., relies on two of these systems to run its entire operation.

Saving money, and the planet

Gill’s Onions also is demonstrating how fuel cell power can help save the environment while also saving money for energy users.

Gill’s takes freshly grown onions and packages them for sale to supermarkets, fast food chains, and manufacturers of food products ranging from salsa to spaghetti sauce. Its production process generates roughly 300,000 pounds of waste each day.

Since 2009, Gill’s has used the FuelCell Energy systems to convert 75% of that waste into enough energy to power its entire operation. The remaining 25% of the waste is sold as cattle feed.

Gill’s estimates that it saves $700,000 a year on power costs and another $400,000 per year in waste disposal costs.

FuelCell Energy’s 1.4 MW units can supply the power needs of large hotels, conventions centers, and similar facilities. The 2.8 MW units can support even larger operations such as universities and large manufacturing complexes.

FuelCell Energy also can offer customers even more power by combining several units to form a multi-megawatt fuel-cell park, which it is doing for utility companies. For example, the company has an ongoing project  in the  city of Bridgeport, Conn., in which 5 of its fuel cell systems will combine to form a 15 MW fuel-cell park providing electricity to the power to the local power grid. 

A critical step in delivering fuel cell power to consumers is converting the dc power generated by the fuel cells into the ac power that is standard for use on the power grid. That conversion is performed by a piece of equipment called a power inverter, and Rockwell Automation supplies the hardware and supporting technology that drives the power inverters in all of FuelCell Energy’s systems.

Generating power: Fuel cell power plants produce power through the formation of hydrogen from a fuel source—usually clean natural gas or renewable biogas. Courtesy: Rockwell Automation

A Rockwell Automation variable frequency drive (VFD) is a core piece of the power inverters that FuelCell Energy employs. FuelCell Energy selected Rockwell as its VFD supplier primarily because Rockwell’s drive technology met all of FuelCell’s power conversion needs. However, FuelCell also knew that Rockwell, as a well-established, global company, would be able to support FuelCell’s growing business, which includes building and installing power plants across North America and Europe.

As their partnership expanded, Rockwell and FuelCell decided it made sense to bring together engineering teams from the two companies to develop a drive that would meet FuelCell’s unique power-conversion needs.

Partnership

The fuel cell company has been using the standard VFDs for many years, said Michael Lisowski, vice president, supply chain, for FuelCell Energy. “As our power plants evolved and reached a stable design configuration and our installed base grew, it was time for both companies to jointly develop a power-conversion system design. The solution is the culmination of the diverse experience of both companies working in somewhat different industries, coming together with the common goal to release the best product possible.”

As a result of this collaboration, the system FuelCell Energy uses to convert fuel cell power from ac to dc is built around The Allen-Bradley PowerFlex 700L VFD. The standard VFD, has some characteristics that were particularly attractive to FuelCell Energy. Rockwell’s low-voltage drive team worked with FuelCell Energy to develop some additional support components to make the drive more robust and enable it to provide high-quality ac power in accordance with   and local guidelines.

“Liquid-cooled drives with their exceptional performance, efficiency, and reliability are now the core of the power conversion solution for FuelCell Energy power plants,” Lisowski said. “Our customers benefit from a high-quality and reliable product.”

A steady source: FuelCell Energy finds its new VFD solution remarkably reliable—enabling its plants to supply continuous power with minimal downtime. Courtesy: Rockwell Automation

Liquid-cooled VFDs can be built in smaller, tightly sealed enclosures because they don’t require extra components such as fans or heat exchangers to prevent the drive from overheating. “Temperature fluctuations are one of the main causes of semiconductor failure,” said Doug Weber, business development manager for Rockwell’s Voltage OEM Drive Team. “Liquid cooling alleviates that problem by keeping the semiconductors operating at a constant temperature.”

The tight seal on a liquid-cooled drive also keep air or other substances that might cause damage away from the drive, which lowers the amount of maintenance required for the drive and extends its useful life.

Custom enclosure

Rockwell also built a custom enclosure to provide additional protection for the drives installed in the FuelCell Energy power inverters.

“We worked with a sheet metal supplier to design an enclosure that was based on our experience with the outdoor enclosures that we have been providing for the oil and water pumping industries for a number of years,” said Brian Bosch, program manager for Rockwell’s low-voltage drives team. “It’s an outdoor-rated Type 3R enclosure, that’s essentially waterproof. We validated that through environmental testing. We also built a custom thermal chamber that fits around the enclosure to allow for temperature testing up to 50 C.”

Power Flow: This is the one-line diagram for FuelCell Energy’s 1.5 MW power plant. Courtesy: Rockwell AutomationLisowski said Rockwell’s positive impact on FuelCell Energy’s business has been wide ranging.

The team included “every aspect of engineering, production, testing, and support,” Lisowski said of the power inverter project. “The results were impressive. We were able to streamline the design and reduce parts count by a substantial margin.

“The size of the power conversion unit was reduced to give us a very high power density and decrease the overall plant size. The liquid cooling increased efficiency and reduced noise. The final design’s scalable and modular architecture allowed us to use a single production design building block to power two models of fuel cell power plant. This reduces the cost to our customers without sacrificing performance or reliability.”

- Edited by Sidney Hill, Jr., a CFE Media contributing content specialist, sidhilljr(at)gmail.com.

www.fuelcellenergy.com

http://ab.rockwellautomation.com/drives/low-voltage-ac-drives

This article is part of the Industrial Energy Management supplement for CFE Media publications. 

See the links at the bottom of this article to read other articles in this supplement.



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