How output reactors improve the EMC of frequency converters

Installing an output reactor at the inverter output terminal is a common and effective method to improve its EMC performance. The main functions of the output reactor include: limiting the dv/dt of the output current, smoothing the PWM pulse edges of the output voltage, thereby reducing the common-mode current generated by high-frequency voltage components through the parasitic capacitance of the motor cable. Together with the inductance of the motor cable, it can change the system's resonant frequency, avoiding resonant amplification at specific frequency points. It can reduce overvoltage on the motor terminals, protecting the motor insulation. Output reactors are usually used in conjunction with output dv/dt filters or sine wave filters to form a complete output filtering scheme.

When selecting a reactor, the inverter's rated current, carrier frequency, and the noise frequency band to be suppressed must be considered. The inductance of the reactor must be appropriate; too small an inductance will have little effect, while too large an inductance will lead to voltage drop and increased cost. During installation, the reactor should be placed close to the inverter's output terminals. Output reactors not only improve the inverter's own conducted and radiated emissions but also reduce interference to the motor and surrounding equipment, making them an important component of system-level EMC solutions. Eintech offers a variety of output reactors that can be used with filters.