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Variable Speed Generator Optimizes Turbine Design Energy Efficiency & Technology, October 20, 2009

Synchrotek, Inc. offers a line of standard and custom electric generators that feature variable speed input, which permits the power source to rotate at its optimal speed. This arrangement is ideal for alternate energy systems, like wind turbines, where the power source is not constant. The wind turbine or other source can be tuned for maximum energy capture and is not limited by a narrow generator speed range.

In a typical wind turbine application, the wind speed can vary over a considerable range. In non-optimal areas, much of the time wind speed is between 5 and 10 mph, while it goes into the more ideal 15 to 25 mph range only a few days of the year. When the turbine has to accommodate the narrow speed range of an induction generator or the fixed speed of a wound-rotor generator, it cannot be optimized to capture all available wind power. The broad speed range of a Synchrotek, Inc. generator permits the wind turbine designer to optimize blade profile and blade pitch control for maximum energy capture, independent of rotational speed. In other variable speed applications, like hydro and waste process energy recovery, this input speed flexibility makes the variable speed input system attractive.

These generator systems include a permanent magnet generator combined with an electronic inverter, making them more compact and efficient than wound-rotor or induction generators. There is no exciter, which saves space and power. The high frequency design permits short end windings on the stator for reduced winding losses and space, and also reduces requirements for output power filters. Because of the modest losses, cooling requirements can be reduced for even greater power and packaging savings.

Generators can produce significant usable power between 20 and 125 percent of rated speed. The four-quadrant inverter efficiently converts the electricity from the generator voltage and frequency ranges to standard voltage and frequency, typically 480 volt, 60 Hz, 3 phase. The system can also include a battery in the DC inverter buss for energy storage in a hybrid system. The latest design is rated at 100 kW. The systems are suitable for stand-alone applications or for feeding power into the grid. Custom sizes and features can be designed upon customer request.

For additional information, contact Synchrotek at info@synchrotek.net, 1-888-850-3085. Synchrotek, 610 Baeten Road, Green Bay, WI 54324.


The recommendations on the Power requirements for Army of the 21st century by the Science and Technology Initiative group addressed certain new technologies to overcome critical problem areas identified by the user community.

An in-line generator employing the Vehicle Engine Driven (VED) concept for HMMWV was one of the concepts that addresses the army’s needs. At present, a towed generator set weighing almost 2000 lbs. and adding an additional logistic problem as a result of being a towed unit supplies electric power. In contrast, an in-line generator driven by the vehicle engine (VED) reduces the weight of power unit to less than 250 lbs., eliminates the additional space required, reduces unit response time by having ready power available at all times on HMMWV. Additional advantages are extremely quiet operation and lower center of gravity for the vehicle.

Synchrotek Contribution:

As a result of successful verification of in-line generator concept in the army medium tactical 2.5 ton truck, Synchrotek was awarded a contract to develop a 10 kW generator for light tactical vehicle. Synchrotek has developed a vehicle driven (VED) in-line generator for HMMWV tactical vehicle under army research and development contract. Three units have been installed in the vehicles and have been subjected to tests by the army and they are approved. Following successful tests Synchrotek has been awarded a follow-on research contract to develop Power Electronics to extend the capability of the generator for all speeds of the vehicle.

Description of Generator:

The generator is rated at 10 kW, 120/208, three-phase. The generator is installed between the vehicle engine and the transmission and serves as a part of the drive shaft. It weighs 220 lbs. The size is 16” diameter and 10.5” long. The frame is bolted on to the 6.5 liter GM engine bell housing at one end, and to the housing of the Allison transmission at the other end. The shaft is direct-coupled to the crankshaft of the engine by bolts on the drive end and to through a flex plate coupling to the rotor of the transmission on the other end.
The generator a self-cooled totally enclosed unit capable of vehicle fording in flood condition. The generator frame has built-in coolant passages through which a dedicated coolant pump pumps ethylene-glycol coolant. The heat gathered by the coolant from the generator stator and rotor is delivered to a radiator located next to the vehicle’s radiator located under the hood in front of the vehicle. The vehicle’s main radiator fan cools the generator radiator. By having its own dedicated cooling system, the coolant is not contaminated by the main engine coolant system and does not require frequent maintenance. Also, by maintaining lower temperature of the coolant, the generator works at a higher efficiency.

Benefits of the In-Line Generator:

Due to its in-line configuration the concept has many advantages over conventional engine-driven gensets and Auxiliary Power Units (APU). A separate engine to drive the generator is eliminated and this removes all of the weight of the engine and accessories and fuel to be carried. The generator is designed to eliminate a 2300 kg MIL-STD 15 kW towed power unit, reducing power source weight by 90% and eliminating all of the towed power unit volume. As the generator is installed under the chassis of the vehicle, it does
not take up the useful space from the inside of the vehicles as APUs or other gen-sets do. The problem that is addressed here is to maximize the power output of an in-line synchronous generator in a package that will meet the far more severe and weight restrictions of the HMMWV and other light tactical vehicles. The overriding considerations demand that the in-line generator does not degrade the vehicle operability, mobility or reliability. In addition to having a readily available power from the vehicle unlike towed power units, the benefit of the in-line concept is in logistics, transportation, etc. For example a C-130 transport plane can carry twice as many HMMWVs fitted with in-line generators as those with towed power units. This cuts down the number of trips to be made in half. Being located under the chassis, the noise in the usable space inside the vehicle is totally eliminated. Among other benefits are the following:

  • Get units in position and on-line faster than towed units, thereby reducing the unit response time to be operational
  • Cost less for logistic support. By elimination of a towed unit.
  • Comparable in purchase cost to the 15 kW TQG units
  • Takes up no extra space and at the same time lowers the Center of Gravity of the vehicle enhancing the vehicle performance
  • Reduced noise due to totally enclosed structure.

Power On the Move (POM):

In order to obtain a frequency of 60 Hz, the generator has to run at a constant speed of 1200 rpm, which would restrict the capability of the system, whereby the vehicle will have to be parked and fuel throttle adjusted to an engine speed of 1200 rpm. The original intention of the research was to investigate the feasibility of the in-line concept. As the results proved successful and the concept appeared very attractive, a follow-on research contract was awarded to Synchrotek to develop a power electronics package (PEP), where by the capability of the generator was extended to the entire operating range of speed of the vehicle.  The PEP utilizes the variable Speed Constant Frequency (VSCF) technology developed by Synchrotek and applied to several engine-driven. It converts the variable frequency, variable voltage of the generator running at the speed of the vehicle’s engine to a precise power at constant voltage (120/208V) and constant frequency (60 Hz).

The PEP is a self-cooled solid state unit and weighs less than 40 lbs. The unit can be mounted anywhere inside the vehicle where there is airflow available. The unit, just as the generator is designed for vibration and shock loads for military application.

  Download PDF: 12-15-2009.pdf



For additional information, contact Synchrotek at info@synchrotek.net, 920.1888.850.3085  Synchrotek, 610 Baeten Road, Green Bay, WI 54304