Sinusoidal filter

The utilisation of the sinusoidal filter extends itself to include the mains borne suppression of interference, from the frequency converter output to the shielded motor feed line with the alternating current motor attached to it, for clock frequencies from circa 500 Hz and higher.

The sinusoidal filter achieves a very high filtering effect as a result of its recise low-pass tuning to the clock frequency of the frequency converter. The wanted signal (the motor operation frequency) up to circa 120 Hz passes the sinusoidal filter with only a slight effective voltage drop, while the clock frequency (typically 8 kHz to 10 kHz) is already being reduced by circa 90 %.
Harmonic oscillations of the clock frequency are filtered out almost completely.

The special andvantages in summary:

• very high filtering effect throughprecise low-pass tuning
• practically the only edge steepness of the output voltage still remaining is that which is usual for mains
• clock frequency and harmonic oscillation of the frequency converter output voltage become severely attenuated
• long shielded motor feed line possible
• low-noise motor operation through high attenuation of the clock frequency
• reduction of leakage currents

 

 

Output voltage of a phase of the frequency converter

 

 

Output voltage of a phase of the sinusoidal filter

It can be seen in the oscillogram that the clock frequency of the frequency converter is present only in conjunction with a low-level amplitude superimposed on the wanted signal (motor operation frequency).