Attenuation of Conducted EMI Emissions From an Inverter-Driven Motor

TLDR

Common‑mode voltage from the PWM inverter generates leakage current through parasitic motor capacitors, causing conducted EMI. The study investigates conducted EMI emissions from a 400 V, 15 kW inverter‑driven motor and the attenuation effects of line and motor EMI filters. The authors use theoretical analysis and experimental measurements to evaluate how a line EMI filter alone and in combination with a motor EMI filter attenuate conducted emission voltage. Without filters the drive fails Category 3 limits; a line filter alone meets Category 3; the motor filter eliminates common‑mode voltage and reduces leakage; together the two filters satisfy the stricter Category 2 limits.

Abstract

This paper provides theoretical and experimental discussions on conducted electromagnetic interference (EMI) emissions from an inverter-driven motor rated at 400 V and 15 kW. It focuses on a line EMI filter and its combination with a motor EMI filter, along with their effects on attenuation of conducted emission voltage. When no EMI filter is connected, the motor drive cannot meet the conducted emission limits prescribed by Category 3 in the IEC61800-3 regulations. The reason is that the common-mode voltage generated by a voltage-source pulse width modulation (PWM) inverter causes a common-mode leakage current flowing into the ground wire lead through parasitic capacitors inside the motor. When the line EMI filter is connected, the motor drive can meet Category 3. The motor EMI filter eliminates the common-mode voltage from the motor terminals, thus bringing a drastic reduction to the leakage current. The combination of the two EMI filters can comply with the limits prescribed by Category 2, which are much stricter than those by Category 3.