1. COMMON-MODE VOLTAGE REDUCTION METHODS FOR
CURRENT-SOURCE CONVERTERS IN MEDIUM-VOLTAGE DRIVES
ABSTRACT:
Common-mode voltages (CMVs) can lead to premature failure of the motor insulation system in
medium-voltage current-source-fed drives. By analyzing the CMV values at all switching states under
different operating conditions of a current-source-inverter (CSI)-based motor drive, this paper first indicates
that the CMV peaks are produced by the zero states in most of the cases. The nonzero-state (NZS)
modulation techniques employed in voltage-source converters are adapted for use in a space-vectormodulated current-source converter (CSC) to reduce the CMV magnitude. For NZS modulation in CSCs, the
nearest three-state (NTS) modulation sequences are designed with good low-order harmonic performances
in their linear modulation region of ma ≥ 0.67 and with no increase in the device switching frequency. A
combined active-zero-state (AZS) modulation technique is also proposed as compensation, for a lower
modulation index in the range of 0.4-0.67, when a compromise is made between the dc-link current
minimization and high input power factor control. The simulation and experimental results are provided to
validate the CMV reduction effects and harmonic performances of the NTS and combined AZS modulation
methods in CSI-fed drives.