Elimination of Common-Mode Choke Saturation Caused by Self-Resonance of the EMI Filter in a Variable-Frequency Drive System

The saturation of a common-mode (CM) choke is a practical problem in the electromagnetic interference filter application. As an important factor of the CM choke saturation, the self-resonance of the CM path is analyzed based on the low-frequency CM model of the variable-frequency drive system. Combining the analysis and the conducted emission test results of the system, the main cause of the CM choke saturation in our experiment is studied. Meanwhile, a novel online impedance measurement method is proposed to observe the saturation effect of the CM choke. To eliminate the saturation effect, a new method is proposed in this paper. A damping resistor is connected in parallel with Y capacitor of an electromagnetic interference filter to suppress the self-resonance. Through comparing the experimental results of the original filter and the improved filter, the effectiveness of the resonance suppression method is validated and the saturation of the CM choke is prevented.