Electrical Regeneration

In an environmentally perfect world, all energy used to create a process could be recaptured and used for another process or returned to the power grid. While today there are no machines that recapture 100% of their energy, electrical regeneration facilitates a significant amount of energy reuse.

RedViking, a powertrain test system manufacturer in Michigan, emphasizes electrical regeneration as the greenest alternative for a historically energy guzzling process – engine and powertrain testing. Many aerospace and vehicle manufacturers use test systems that lose 100% of their energy in the form of wasted heat.

Electrical regeneration test systems can capture most of that energy to be put back into the power grid or used to run the machine itself. In addition, electrical re-gen systems are less expensive to build, have lower operating costs, require less maintenance, and have greater reliability. When compared to traditional testing systems, these systems will pay for themselves over time.

The basic premise of electrical regeneration is to replace traditional energy-wasting braking methods with a method that produces electricity, which is then fed back into the machine or the local power grid. The commercial automotive industry has been an early adopter of this technology, where large numbers of electrical re-gen dynamometers are used to test engines and powertrain components.
 

From 20 Test Stands to 5

RedViking engineers are currently working with the Department of Defense (DOD) to replace more than 20 helicopter powertrain test stands. The existing test stands were built decades ago with single purpose functionality and have excessive energy consumption and costs.

An obvious project foundation is the creation of excellent test results with a reduction in taxpayer dollars. It is critical to have accurate, repeatable test data for the safety of U.S. troops, so software and controls design are vitally important. A streamlined testing process was designed where the test articles are prepared for test outside of the test stand, freeing up the stand for more frequent use and thus allowing helicopters to return to service more quickly. The test stands themselves are designed to accommodate more than one type of transmission or gearbox, which also contributes to greater availability of helicopters. In the end, five flexible test machines are able to replace the functionality of the 20 single-purpose machines.

Another critical design element to this project is energy savings. With improvements over the conventional fluid braking process, the estimated energy cost savings for one RedViking transmission test system at an Army helicopter repair center is approximately $500,000 per year.

As shown in the illustration, current helicopter transmission and gearbox test systems use traditional braking technology that results in wasted energy by converting power to lost heat.
 

Traditional Powertrain Testing

For the DOD helicopter flexible test systems project, RedViking’s electrical re-gen systems use a common DC bus architecture, which allows for only one AC to DC conversion in the motoring direction. The regenerative braking power goes straight to another inverter, which is motoring via the common DC bus link. This method eliminates two conversion points where energy would be lost and increases overall efficiency.

In addition, the common bus solution paired with the active front end (AFE) has the ability for power factor correction, further increasing the overall savings of a common bus system. All AFE drives allow for unity power factor and low total harmonic distortion (THD) that meets IEEE 519 harmonic standards, which allows the drive systems to improve the present power factor displacement in the customer’s facility.

Powertrain Testing

The energy savings on this project have exceeded expectations with six times the energy efficiency of the single-purpose helicopter test stands. It is estimated that a test on the Main Transmission Flexible Test System, while running at full capacity, will cost approximately $400 less per hour to operate than current systems.

The potential for energy savings is even greater with jet engine test centers, which can lose as much as 5.5 million kilowatt-hours of electricity during a typical year.
 

Traditional Jet Engine Testing Center

As with traditional powertrain testing, most jet engine test centers use liquid brake testing and the resulting energy is lost as dissipated heat.

In addition to wasting energy, there are other disadvantages to using liquid brake test systems. The high rate of energy conversion taking place inside the brake erodes the internal components, requiring them to be rebuilt and replaced. With these frequent maintenance activities impacting the system’s structure and alignment, test data accuracy and repeatability are jeopardized. In addition, the erosion process is sensitive to the quality of the incoming cooling water, which must be continually filtered and chemically treated, adding cost to the testing process.

By selecting an electrical re-gen engine test system, these disadvantages are avoided, and most of the test system’s energy can be fed back to the power grid in the form of electricity. This type of engine test cell technology is analogous to wind turbines, using essentially the same conversion equipment, switching gear, and energy management systems.When testing drivetrain components for rotary wing aircraft, fixed wing aircraft, and ground vehicles, electrical regeneration offers significant potential for energy savings.

RedViking
Plymouth, Mich.
www.redviking.com

RedViking is a subsidiary of Superior Controls, a member of the Control System Integrators Association (CSIA), a global non-profit professional association that seeks to advance the industry of control system integration for the success of members and their clients. For more information, visit www.controlsys.org.

About the author: Jason Stefanski is the controls and software manager for RedViking, and was instrumental in selecting electrical regeneration motors and drives for the Department of Defense project. He can be reached at 734.927.1460 or jstefanski@redviking.com.