A New Filter Concept for High Pulse-Frequency 3-Phase AFE Motor Drives

The size of back-to-back converters with active front end is significantly determined by the size of the passive filter components. This paper presents a new complete EMC filter concept for this type of converter system that is effective on the input and the output. This involves filtering the main common mode interferences from the grid and motor sides with a single CM choke. Since only the difference of the generated common mode voltage-time areas of both converters is absorbed by this component, the size of the required filter can be greatly reduced compared to conventional filter concepts. The concept is validated on a grid feeding inverter that can be connected to the public distribution network with an output power of 63 kW. The size reduction is demonstrated by means of a design example on a system with the same power and electrical requirements. It is elaborated why, applying the new filter concept, the impedance of the DC link potentials to ground and other electrical potentials should be as high as possible and therefore associated parasitic capacitances should be minimized. From this requirement, rules for the design of the power modules of PFC and motor converters for the application of this filter concept are derived.