Physics Produces Savings With Variable-Frequency Drives

“It’s [through] appliedphysics,” declares this manager of components sales with BoschRexroth Corp.’s (www.boschrexroth-us.com) Electric Drivesand Controls Group, Hoffman Estates, Ill.

Running the drives at different speeds, rather than continuously在满载时，会产生这些节省。VFD自动化电动机，explains Sharon James, application engineer with Rockwell Automation Inc.’s (www.rockwellautomation.com) Low Voltage DrivesGroup, in Mequeon, Minn. “So with a motor that used to run at60 Hertz across the line at full speed, a VFD automates that to
run at a speed of your choice.”

And that’s where applied physics—specifically, the AffinityLaws, which James says can be used with centrifugal fans andpumps used in about 80 percent to 85 percent of heating, ventilation and air conditioning (HVAC) systems—provides savings.The law describes how—based on speed—fans and pumps fol低一个可变扭矩量的轮廓：流量与速度成正比，torque is proportional to speed squared and horsepower is pro分区至速度立方体。因此，“从100降低速度percent to 80 percent actually cuts power in half,” James explains.“在任何系统中，这种[关系]将是这种情况。”

The physics-based energy savings in pumps and motors hasbeen the selling point for VFDs used in HVAC systems sincetheir inception. But what about savings and benefits elsewhere,in applications such as conveyors used in materials handling?James mentions reduced maintenance and multi-motor capa能力。“您可以在VFD上运行多个电动机。你是maximizing the system efficiency.”

在某些以非常低速度运行的系统中，可变频率drives can operate very smoothly, James points out. And those drivesoffer self-diagnosis and more reliability. They’re self-protective, too,he adds. “If there is a dip or surge in power, it protects itself throughbuilt-in software.”

Through their intelligence and flexibility, VFDs also extendthe life of the pumps and fans with which they’re associated.“The amount of power being output is the amount of power themotor is asking for,” James explains. “The [variable-speed] driveis intelligently monitoring the power demand.”

But even more savings through variable-frequency drives磁通量控制可能是可能的，这可以更好电动机控制扭矩。“而不是改变频率和voltage, the drive comes into the game,” Fischbach states. This控制，允许智能磁化或某些人称之为能量节能或睡眠模式可以使用国家电气来完成卡尔制造商组合ion or International ElectrotechnicalCommission induction motors, he says.

State of flux

“You control the torque and magnetic flux of a motor, independent of one another,” Fischbach explains about flux-vectorcontrol. Why is that an advantage? “You can reduce the flux insome applications, dependent on the load characteristics, whenyou don’t need a lot of torque on a motor shaft.” So, if an operaTor知道将运行某个配置文件，操作员can reduce the flux, based on that profile, he explains.

How does having a flux-vector-control VFD vs. a standardVFD translate into money in a company’s pockets? If the motoralways operates at full torque, there’s not much savings, Fisch-
bach indicates. “But if [there is] a lot of idle time or reduced loadtime, you might see 5 percent reduction in costs, but that’s application dependent.”

C. Kenna Amos,ckamosjr@earthlink.net， 是一个Automation World Contributing Editor