how does sinewave filter protect VFD and motor?

how does sinewave filter protect VFD and motor?

In order to understand the basics of sine wave filters, we first need to look at how motor drive systems work. Motors that operate on alternating current need special power supplies that deliver power to start and stop the motor smoothly. If the motor were to transition from full “off” to full “on” in a short period of time, it would put undue stress on the mechanical parts of the equipment. Instead, the power supply needs to start and stop the fan motor gradually. Likewise, once a motor is running, many applications require adjusting its speed and torque to accommodate different mechanical loads. VARIABLE FREQUENCY DRIVES (VFDS) provide a power supply that can offer gradual start/stop and variable speed/torque. By adjusting the frequency of current sent to a motor, a VFD controls its speed.

VARIABLE FREQUENCY DRIVE (VFD):

AC motors operate at their peak efficiency when they run on clean sinusoidal power. VFD’s, however, produce modulated square waves. The pulse width of these square waves are variable. This is known as PWM—pulse width modulation. VFDs can also control the amplitude of each square wave.Installing a sine wave filter between the VFD power source and the motor itself “smooths” the VFD pulse width modulated square wave signal and converts it into a nearly perfect sinusoidal power waveform. The VFD and sine wave filter combination allows the motor to run at continuously adjustable speeds and adaptable torque for varying mechanical loads. Running the motor without a sine wave filter causes several problems.

Powering a motor with square waves might, at first, sound like a poor idea. However, VFD’s maintain such fine control over the width and amplitude of the square waves that they take on the appearance (as viewed on an oscilloscope) of fairly good approximations of a sine wave. Yet even the most sophisticated VFD’s fail to match the purity of a true sine wave. Additionally, VFD’s introduce significant harmonic distortion that can damage the motor. That’s where sine wave filters come into the picture.

THE BENEFITS OF SINE WAVE FILTERS:

Installing a sine wave filter between the VFD power source and the motor itself “smooths” the VFD pulse width modulated square wave signal and converts it into a nearly perfect sinusoidal power waveform. The VFD and sine wave filter combination allows the motor to run at continuously adjustable speeds and adaptable torque for varying mechanical loads. Running the motor without a sine wave filter causes several problems.