Passive DC-input and DC-input/AC-output EMI filter for DC-AC inverter

This paper aims to compare the performance of an electromagnetic interference (EMI) direct current (DC)-input filter with a combined DC-input/alternating current (AC)-output filter. The EMI filters will be implemented in a DC-AC inverter to comply with regulatory standards. The DC-AC inverter has a two-level topology, with a defined switching frequency of 4 kHz. A theoretical model of the entire system, including the considered parasitic elements for cables, DC-AC inverter, and motor, is presented. Single-phase equivalent circuits for common mode (CM) and differential mode (DM) noises are derived from this circuit. The required transfer function to fulfill the standards for the two-level inverter is used to evaluate the influence of the EMI filter components and necessary filter stages. To accomplish this, the noise spectrum of the two-level topology without any EMI measures and the limit lines of two different regulatory standards are utilized. Considering this perspective, the passive components of the EMI filters are selected, with separate investigations conducted on CM and DM noises. Finally, conducted EMI measurements on a 55 kW DC-AC inverter prototype validate the proposed filter damping. Deviations between measured noise and the expected damping are discussed in detail.