Variable-frequency drives generate high-frequency disturbances in the PWM output signal that cause EMI, motor load, and cable length limitations. Block’s SF4 all-pole sine wave filters convert this PWM signal into a virtually pure sine wave voltage on the motor side.
The filters suppress both differential-mode and common-mode components, resulting in lower EMC emissions on motor cables, reduced leakage currents to ground, lower bearing currents, and reduced thermal stress on the motor and cable. This increases reliability and extends the service life of the drive system.
In applications such as pumps, fans, and conveyor belts with long cables, surge spikes, reflections, and EMC issues occur without filtering. SF4 filters limit these effects and keep the motor voltage stable, allowing for longer cable runs. In certain configurations, this can also lead to approximately 5% higher system efficiency.
What sets the SF4 apart is that common-mode currents are internally fed back to the DC link rather than through ground. This reduces ground leakage currents and EMC loading and offers greater effectiveness than conventional du/dt filters or output chokes.
Electrical Specifications
- 3 × 500 VAC
- 5–150 Hz output frequency
- ≥4 kHz switching frequency
- 2.2–90 kW
- 5.2–165 A
Sinusoidal filtering is essential for long motor cables and stringent EMC requirements. The SF4 series reduces PWM-related interference and improves both EMC performance and the service life of the motor and system.
