U.S. Patent Received for Overvoltage Suppression Technique for Variable Frequency Drives Operating Reciprocating Loads

Waukegan, IL –- Yaskawa Electric America, Inc. announces the Overvoltage Suppression Technique for Variable Frequency Drives Operating Reciprocating Loads is approved for a United States Patent, No. 7,227,330 B2. The Inventors are Mahesh M. Swamy, Brian Geoffrey, Yoshiaki Yukihira and Mike Rucinski.

In many industrial applications there exists reciprocating loads that are driven by variable frequency drives (VFD). In such applications, during a certain portion of one complete load cycle, the load tends to accelerate the motor at speeds higher than that commanded by the VFD. Under such a condition, the VFD is required to absorb the regenerated energy. Typically, this is achieved by providing braking resistor and transistor units known as ‘braking units’. The braking units are sized according to the duty cycle and stored regenerative energy in the load. Sometimes, multiple braking units may need to be employed in a master-slave manner to accommodate large amounts of regenerated energy. Such methods, though acceptable in the industry at present, suffer from high costs, require large space to mount, and are inherently inefficient since the regenerated energy is dissipated as heat in the braking resistors.

The Overvoltage Suppression Technique for Variable Frequency Drives Operating Reciprocating Loads is unique in the sense that it takes the energy in the load during the motoring mode and uses it in the generating portion of the load cycle, thereby controlling the motor so that the motor does not behave like a generator.

The advantage of this concept is two fold. First, there is no need to use braking units, which translates to lower system and maintenance cost of up to 30%. Second, it makes the entire system more efficient since most of the stored energy is recovered and used up in the generating (downward stroke) portion of the load cycle.

Typical applications that benefit from this idea would be vibration tables, reciprocating pumps, presses, hammers, and beam pumps also known in the oil industry as pump-jacks. However, the idea is not restricted for use with only such loads and can be extended to include all types of loads that are cyclic in nature that have an overhauling characteristic in one portion of a load cycle and a motoring characteristic in the remaining portion of the load cycle.

Yaskawa Electric is the world’s largest producer of AC drives. The drives business of Yaskawa Electric America, Inc. operates from facilities in New Berlin, WI; Waukegan and Buffalo Grove, IL; Los Angeles, and offices throughout the Americas. For further information, browse our web site or contact Neil Koepke at 2121 Norman Drive South, Waukegan, IL 60085. Phone: (262) 754-2220 Fax: (847) 785-2730 Email: neil_koepke@yaskawa.com