Optimized Filter Design for Common-Mode Current Reduction in Four-Wire Inverter-Fed Motors

Two optimized filter topologies for four-wire electric drive systems (EDSs) are proposed with smaller size, lower power loss, and larger common-mode (CM) current reduction than the usual filter topologies. It has been previously shown that using a four-wire topology reduces the CM current in a wide frequency range, when compared with the three-wire one. However, there still exist low- and high-frequency resonances in the transfer function between neutral and inverter output voltage, resulting in the increase of CM current. By means of the transfer function analysis, two types of optimized filter topology specified for the four-wire EDS are proposed. Unlike conventional CM filter (CMMF), the design of these two new filters also requires a serious consideration of the characteristics of motor and cable impedance. Based on the design procedure, these two filters are built with excellent performance of CM current reduction in the whole frequency range. Besides, compared with conventional CMMF used for three-wire EDS, they also show benefits, such as lower power loss and less implementation space. All theoretical analyses are validated by the experimental measurements and can benefit further studies.