In many industrial applications, variable frequency drives (VFD) drive reciprocating loads. During a certain portion in one complete cycle, the load tends to accelerate the motor at speeds higher than the VFD commands. Under such a condition, the VFD must absorb the regenerated energy. Typically, braking resistor and transistor units known as ‘braking units’ let this occur. 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. Although these methods are currently a standard in the industry, they are costly, require a large mounting space, and are inherently inefficient since the regenerated energy is dissipated as heat in the braking resistors.
Yaskawa Electric America, Inc. has solved this problem with its United States Patent Approved (No. 7,227,330 B2) Overvoltage Suppression Technique for Variable Frequency Drives Operating Reciprocating Loads. It is unique because it takes the energy in the load during the motoring mode and uses it in the generating portion of the load cycle. This controls the motor so that it does not behave like a generator.
Yaskawa Electric America, Inc.
2121 Norman Drive South
Waukegan, IL 60085
Tel: 800. YASKAWA
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Filed Under: Drives (servo) + amplifiers