Modeling and Suppression of Common-Mode Voltage Resonance in a Three-Level Inverter With Middle Line

In a high-power three-level inverter, a middle line is connected between an ac neutral point and a dc neutral point to construct a common-mode (CM) loop, which could reduce low-frequency electromagnetic interference (EMI). However, the stray inductance of the middle line may lead to CM voltage resonance, causing a new EMI problem. To address this challenge, this letter proposes an EMI model of the three-level inverter, which fully considers the neutral point to ground voltage fluctuation and the influence of the middle line stray inductance on resonance. Then, based on the EMI model, sensitivity analysis is performed to identify the primary CM resonance parameters, and the CM resonance mechanism is analyzed. According to the proposed EMI model, a new suppression method is developed. A capacitor is connected between the dc neutral point and the ground to eliminate the resonance, which could significantly reduce the size and cost of EMI filters. Both the accuracy of the EMI model and the effectiveness of the suppression method are validated through simulation and measurement.