Output filters smooth out inverter waveforms

Edited by the Engineeringtalk editorial team Oct 21, 2002

Schaffner has developed a novel sinusoidal output filter solution based on its proprietary "Sinus Plus" concept.

Schaffner has developed a novel sinusoidal output filter solution based on its proprietary "Sinus Plus" concept.

The FN 5020 and FN 5030 filters increase the reliability of entire power drive systems and help to eliminate most problems related to modern frequency inverters.

Being a modular system, Sinus Plus can be arranged optimally according to system requirements and application.

As a symmetrical sinusoidal output filter module, the FN 5020 converts the PWM signal of frequency inverter outputs into a smooth sinusoidal curve, in between the phases.

This series of filters can be operated autonomously and offers a vast array of advantages.

Connected motors are afforded efficient protection from premature ageing or destruction, as the sinusoidal filter keeps dv/dt and overvoltage stress, in addition to magnetic losses inside the motor, within acceptable limits.

Furthermore, acoustic motor noise is minimised, a major consideration in air conditioning, ventilation and heating applications, where noise can be amplified and distributed throughout the entire building by means of air ducts and heating pipes.

In many applications, the FN 5020 symmetrical sinusoidal output filter provides a complete solution.

However, it may occasionally be necessary to satisfy even tougher requirements, in such applications, the FN 5030 can be additionally employed.

As an asymmetrical sinusoidal output filter, the FN 5030 significantly improves the voltage signal between the phases and earth (asymmetric).

It is an addon module, for use downstream of the FN 5020 module.

It incorporates innovative circuitry and, through a connection to the DC-link of the frequency inverter, provides a direct return path for common-mode interference currents to their origin inside the drive.

As a result, pulse currents to earth are virtually completely eliminated and therefore, both interference propagation coming from the shielded motor cable and detrimental bearing currents are eliminated.

By adopting the Sinus Plus output filter concept, the output signal of various frequency inverters is optimised, both symmetrically and asymmetrically, significantly reducing traditional downtime problems.

Efficiency, reliability, operational safety and continuity are all greatly enhanced by the new filters.

As the output signal beyond the two filter modules has a quality close to that of the mains supply, traditional considerations such as cable length and cable shielding become insignificant factors, opening up new, flexible deployment possibilities.

Sinus Plus filters are designed to be operated in 500V AC supply grids with current ratings from 25 to 120A and are suitable for switching frequencies from 6 to 15kHz.

With the ability to handle motor frequencies up to 600Hz, Sinus Plus has taken into account the growing market trend for motors with very high rotational speeds.