Patent ID: 9086070
Filing Date: 2015-07-21
Classification: F04D,Y02B

Abstract:
1. A method of controlling a centrifugal compressor to provide compressed gas at a required delivery pressure, said compressor having an impeller mounted on a shaft supported by an active magnetic bearing unit, said compressor being driven by a variable speed motor at a rotational speed under normal on-load conditions, said method comprising the steps of: operating a centrifugal compressor under a pre-determined speed at normal on-load conditions to result in a delivery of a compressed gas at a pre-determined delivery pressure; measuring and recording an actual rotational speed and an actual delivery pressure of the compressor repeatedly at high frequency; periodically surging the compressor after a preset re-calibration time; detecting said surge of said compressor at said preset re-calibration time; initiating a surge recovery cycle of the compressor when said surge is detected, wherein said surge recovery cycle comprises off-loading the compressor and reducing the actual rotational speed of the compressor; re-calibrating a pre-determined compressor pre-surge speed line during the surge recovery cycle for current operating conditions; increasing the actual rotational speed of the compressor after the reducing the actual rotational speed step of the surge recovery cycle; reloading the compressor when the actual rotational speed is increased to the greater of the re-calibrated compressor pre-surge speed line and a pre-set load speed; wherein the step of re-calibrating the pre-determined compressor pre-surge speed line includes adjusting the pre-determined compressor pre-surge speed line based upon a speed difference, the speed difference comprises a difference between a measured pressure rotational speed of the compressor which corresponds to a measured pressure delivery pressure, wherein both the measured pre-surge rotational speed and the measured pre-surge delivery pressure are obtained fractionally before the compressor surge is detected, and a pre-determined pre-surge rotational speed of the compressor for the measured pre-surge delivery pressure, wherein the pre-determined pre-surge rotational speed falls on the pre-determined compressor pre-surge speed line prior to the re-calibrating step; and wherein the pre-determined pre-surge speed for any delivery pressure is calculated using the formula wherein V