Understanding Speed Controls – How VFDs Can Control AC Induction Motor?

Understanding Speed Controls – How VFDs Can Control AC Induction Motor

A variable frequency drive (VFD) is an electronic mechanism used to control the speed of an AC induction motor. Variable speed requirements for AC induction motors are fulfilled by a 3-phase motor, an inverter, or VFD. 

Depending on VFD and how it is installed, the variable frequency drive operates on a single or 3-phase input and the output matches the required voltage. Because the motors are generally designed with a single operating speed, VFD is required to alter and control the speed of the motor.

Understanding Variable Frequency Drive (VFD)

There is a significant layer of control between the input and output processes of variable frequency drive (VFD). The control panel works as an interface that turns AC input to DC and then puts it on AC output using a conversion called power width modulation (PWM). Since the output is well-controlled by VFD on a motor, the input doesn’t require to match the desired output.

VFDs and Single-Phase Input

It is necessary to have 3-phase input to operate a 3-phase motor with a variable frequency drive. VFD will facilitate single-phase current during the conversion stage. For doing this, input power is initially turned to DC using diodes and then turned to the desired output using diodes and capacitors that result in AC. 3 phase motor is attached to the output connectors on the VFD, wherein the input voltage isn’t a considerable factor.

VFDs and 3-Phase Input

When you are using a 3-phase input, the wiring needs to be processed through an inverter to produce DC. The mechanical function of VFD remains the same and output is controlled by VFD. In order to reduce complications and chances of errors, it is good to work with a 3-phase variable frequency drive manufacturer or AC motor speed control manufacturer to get the best assistance.

Speed Control Method for AC Induction Motors

Many industrial AC induction motors are 4 pole type, so the motor speed works in sync with input power supply frequency (Hz). A VFD controls the motor speed by using pulse width modulation to modify the power supply frequency. To use VFDs, you may require a 3-phase AC induction motor with an inverter having at least a continuous duty rating. The phase control motor exhibits less electrical noise as compared to VFD-driven motors, where VFDs run at a much faster rate.

For applications like polishing machines, dual conveyors, or stirring machines, frequent speed fluctuations can affect the final product due to load. If constant torque and speed control are necessary, connecting VFDs to a 3-phase motor is worth considering.

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