A variable frequency drive is an electric controller that runs an electric motor by changing the voltage and frequency provided to the electric machine. You can call VFD by these names as well; Variable speed drive, adjustable frequency drive, micro-drive, adjustable speed drive, AC drive, and inverter. It is used in machines that are small devices to large compressors. In industrial practice, approximately 25% of electrical energy is used by electrical motors which can be more energy-saving if variable frequency drive is used. It is made in many different low-medium voltages known as AC-AC and AC-DC displays.

The history of Variable Frequency Drives

Tesla first introduced the drive in 1888. However, AC device speed control needed to change some poles on the motor. Even after the widespread use of induction motor, changing its frequency was considered a difficult task, and engines couldn’t create a device with more than two speeds because of its physical development. By the 1980s, it became a reliable and economical source by calculating the rate of the inductor accurately.

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The types of Variable Frequency Drives

There are three types of Variable Frequency Drives.

  • Current Source Inversion (CSI) is used successfully in signal handling and technical electric implementations. It is the only power that has the capability of reviving the power or putting differently; they can soak up electrical flow back from the motor supply. It gives a virtuous overcorrect waveform but needs large, high-priced inductors in its construction.
  • Voltage Source Inversion (VSI) has a poor electric factor and cause motor gearing up to 6 Hz and do not regenerate. Hence, CSI and VSI are not widely used.
  • Pulse Width Modulation (PWM) is widely used in the electrical industry since it has outstanding input power factor without any motor gearing, low cost, and higher effectiveness. It uses a chain of voltage electric current of varying extents to encourage curved waves.

Heat, Power Losses, and Harmonics

Heat is the thing that needs to be addressed by a variable frequency drive manufacturer. Though, it’s a hugely efficient device, but makers have to produce the ideal components. Apart from heating, harmonics are significant concerns in VFDs. The asymmetry in the Sine waves is known as harmonics. The simplest and easiest way to mitigate this problem is to place a sine wave filter on either side of the VFD. Another method is to use capacitors because the harmonics travel through the capacitor base, ignoring other loads.

Variable Frequency Drive Benefits

Variable Frequency Drives run at a high power factor to provide a better life to the motor. It provides a speed control for processing, operating and other economic advantages hence, giving full load power to the fans and pumps. The additional benefit of VFD is that it provides the maximum output in a constant torque. It has some implementations on the power grid as well that is seen in wind turbines and some small hydroelectric generation projects connected to the power grid.

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