Input filter pre-charge scheme for high power PWM-CSRs connected to a weak utility supply

High power PWM Current Source Rectifiers are normally connected to the utility supply by means of a lightly damped LC input filter. Pre-charge schemes employing pre-insertion resistors are typically used to mitigate the overvoltage across the filter capacitors during the connection to the utility grid. However noticeable distortion of the utility grid voltage may still occur during the insertion of the input filter to the grid, particularly at low ratios of the supply fault level to the converter rated power. This presentation proposes a pre-charge scheme which yields a smooth and controllable connection of the input filter to the utility grid along with total absence of overvoltage across the input filter capacitors.