Common mode voltage reduction methods for current-source converters in medium-voltage drives
Common-mode voltages in current-source converters used in medium-voltage drives can lead to insulation failure in the motor. This paper analyzes common-mode voltage values under different operating conditions and determines the voltage peaks are produced by the zero states. It adapts non-zero state modulation techniques used in voltage-source converters for use in current-source converters to reduce common-mode voltage magnitude. Specifically, it designs nearest three-state modulation sequences for good low-order harmonic performance when the modulation index is above 0.67 without increasing switching frequency, and proposes a combined active-zero-state modulation technique for indices between 0.4-0.67 to balance current ripple and power factor. Simulation and experimental results validate the
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Common mode voltage reduction methods for current-source converters in medium-voltage drives
- 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.