MVDC Grounding and Common Mode Mitigation

Through existing STTR N16A-T012, Continuous Solutions (CS) and Purdue University are developing a product line which consists of Common Mode (CM) current-mitigating Bus-Bar Based Common Mode Inductors (B3CMI) and AC Common Mode Shorting Networks (ACSN). These products are installed on the DC (B3CMI) or AC (ACSN) interfaces of power converters. The DC-rail-inline B3CMI adds significant CM impedance at high frequencies, while passing DC differential mode current with negligible resistive impedance. The ACSN shorts CM currents to ground at a 3-phase AC interface, while providing a very high differential mode impedance that blocks AC current from flowing into ground. When employed in modern power systems using high-percentages of switching power converters, both devices promise significant reduction in CM currents emitted by switching-mode power converters (SMPS) and thus mitigate their adverse effects. In addition, Continuous Solutions is developing common mode test and characterization devices, termed the Active Line Impedance Stabilization Network (ALISN) and the precursor Passive Line Impedance Stabilization Network (PLISN). The PLISN is a simplified version of the ALISN that characterizes the CM behavior of power converters only considering the discrete frequencies generated by the converter itself. The ALISN characterizes the CM behavior of power converters over all continuous frequencies. The ALISN and PLISN are intended to 1) help diagnose problematic common mode behavior in power converters and 2) provide verification that installed power converters and system can comply with planned common mode specifications.