An integrated DC link choke for elimination of motor common-mode voltage in medium voltage drives

An integrated DC link choke with common-mode voltage suppression is proposed for use in medium voltage (2300 V-7200 V) induction motor drives. The choke has an integrated magnetic core on which both differential and common-mode windings are placed. The differential winding is used to reduce the DC link current ripple while the common-mode winding is employed to suppress the motor common-mode voltage generated by the rectifier and inverter. The operating principle of the integrated DC choke is introduced. The calculation of the differential and common-mode inductances is presented. Experimental results based on a 5 hp induction motor drive are provided. A special issue concerning common-mode LC resonances is investigated. It is demonstrated that the proposed choke can be used to replace the isolation transformer normally used in medium voltage drives for common-mode voltage elimination, resulting in significant cost savings.