What is a Variable Frequency

Variable Frequency Drives, or VFDs, were introduced to the material handling industry in the late 80’s-early 90’s after the birth of low cost high speed power transistors. Variable frequency drives were designed to allow greater precision and control of single-speed and 2-speed motors.

Initially, they were only specified on the bridge and trolleys of high-speed Class D and Class E cranes. Today, they’re used to control every motorized motion on a crane—including the hoist, bridge, trolley, and even hook rotation in certain applications.

Just like the name implies, a VFD varies the frequency to an AC motor by creating a sinusoidal wave. By varying the voltage and frequency supplied to the motor, the drive “tricks” an AC motor into thinking it’s at synchronous speed, even when it’s not. This creates better and smoother motor controls and allows for adjustable speed controls and adjustable acceleration and deceleration ramps.

As the cost of these systems have come down, they’ve increased in popularity and today get specified into all types of crane systems—ranging from lower-duty package crane systems, all the way up to high capacity/high duty cycle process cranes.

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