SINE-WAVE FILTER

Sine-wave filters are designed to let only low frequencies pass. High frequencies are consequently shunted away which results in a sinusoidal phase to phase voltage waveform and sinusoidal current waveforms. With the sinusoidal waveforms the use of special frequency converter motors with reinforced insulation is no longer needed. The acoustic noise from the motor is also damped as a consequence of the sinusoidal wave condition. The sinewave filter also reduces insulation stress and bearing currents in the motor, thus leading to prolonged motor lifetime and longer periods between services. Sine-wave filters enable use of longer motor cables in applications where the motor is installed far from the frequency converter. As the filter does not act between motor phases and ground, it does not reduce leakage currents in the cables. They consist of inductors and capacitors in a low-pass filter arrangement.

Features and benefits

As described above, Sine-wave filters reduce motor insulation stress and eliminate switching acoustic noise from the motor. The motor losses are reduced because the motor is fed with a sinusoidal voltage. Moreover, the filter eliminates the pulse reflections in the motor cable thus reducing the losses in the frequency converter.

Advantages

? Protects the motor against voltage peaks hence prolongs the lifetime ? Reduces the losses in the motor

? Eliminates acoustic switching noise from the motor

? Reduces semiconductor losses in the drive with long motor cables

? Decreases electromagnetic emissions from motor cables by eliminating high frequency ringing in the cable

? Reduces electromagnetic interference from unscreened motor cables

? Reduces the bearing current thus prolonging the lifetime of the motor

VOLTAGE WAVEFORM WITHOUT FILTER:

VOLTAGE WAVEFORM WITH SINE-WAVE FILTER:

Credit for graphical images

DANFOSS

REAL TIME PHOTOGRAPH OF WAVEFORMS SINE WAVE FILTER

TEST RESULT

INPUT VOLTAGE THD WAVEFORM:

BEFORE FILTER AT 3KHZ SWITCHING:

AFTER FILTER VOLTAGE THD WAVEFORM

FOR WAVEFORMS