BENSHAW Rsi S Series, Instruction Manual, Page: 382 / 398

Applying Drives to Single-Phase Input Application
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12 Applying Drives to Single-Phase Input
Application
Introduction
The “S” Series inverter is a three-phase standard variable frequency drive(VFD). When applying
single-phase power to a three-phase VFD, there are several constraints that need to be considered.
Standard Pulse-Width-Modulated (PWM) VFDs use a 6-pulse diode rectifier. The 6-pulse
rectification results in 360 Hz DC bus ripple when used with a three-phase 60 Hz supply.
However, under single-phase use, the DC bus ripple becomes 120 Hz and the VFDs DC bus circuit is
subject to higher stress in order to deliver equivalent power.
Additionally, input currents and harmonics increase beyond those encountered with three-phase
input.
Input current distortion of 90% THD and greater can be expected under single-phase input
compared to approximately 40% with three-phase input as indicated in Figure 2.
Therefore, single-phase use requires the three-phase VFD power rating be reduced (derated) to
avoid over stressing the rectifier and DC link components.
Figure-1 Typical Three-Phase Configuration