Impact of EMI components on conducted emissions in servo drives

This paper presents a methodology for assessing the impact of critical components in a PWM VSI servo drive on conducted electro-magnetic interference. Conducted emissions at the ac mains input are caused in part by the coupling and leakage of high frequency common-mode currents through complex return paths in the drive system. Common-mode currents are caused by switching of IGBTs at high slew rates which then charge and discharge various parasitic elements in a drive system such as motor cable capacitance, motor and other common-mode elements inside the drive hardware. Understanding the impact of critical components in a IGBT driven servo drive will help designers to focus on the design of these components which will help to minimize cost, size and design iterations. To understand the impact of various components on conducted emissions in PWM VSI servo drives, a servo drive system including drive, motor and cable is modeled in Matlab. Simulation results along with experimental results from an actual servo drive system for validation of models are presented. Methodology proposed in this paper can be used to design EMI filter components integrated into the servo drive.