RIDE-THROUGH METHOD AND SYSTEM FOR HVAC&R CHILLERS

摘要

A method of providing ridethrough capability in a chiller system employs a variable speed drive with an active converter stage, a DC link stage and an inverter stage for providing variable frequency and voltage to power at least one motor. An induction motor is coupled to the output of the inverter stage for driving a compressor in the chiller system. The ridethrough method comprises operating the active converter to regulate the DC link voltage of the DC link stage to a predetermined voltage level until the current through the active converter equals a predetermined current limit, then transferring regulation of the DC link to the inverter upon reaching the current limit of the converter. The compressor is unloaded, and the power flow through the inverter is reversed to maintain the voltage level of the DC link stage. Prerotation vanes, slide valve, or check valve are used to unload the compressor.