Abstract: There is provided a centrifugal compressor apparatus including a centrifugal compressor that centrifugally compresses a gas, an electric motor that rotatably drives the centrifugal compressor, a current detector that detects a drive current I of the electric motor, and an exhaust valve that discharges a compressed gas to a lower pressure section. The centrifugal compressor apparatus (A) detects the drive current I at a sampling cycle ts, (B) updates, as a current threshold, in real time, a value “(moving average)?n×(standard deviation)” for which a plurality of drive currents measured in a sampling period tp serves as a population, where n is a positive number in the range of 3 to 4 and, (C) determines that surging has occurred when the exhaust valve is closed and the drive current I is below the current threshold X, and (D) further opens the exhaust valve to discharge the compressed gas when determining that surging has occurred.

Abstract: There is provided a centrifugal compressor apparatus including a centrifugal compressor that centrifugally compresses a gas, an electric motor that rotatably drives the centrifugal compressor, a current detector that detects a drive current I of the electric motor, and an exhaust valve that discharges a compressed gas to a lower pressure section. The centrifugal compressor apparatus (A) detects the drive current I at a sampling cycle ts, (B) updates, as a current threshold, in real time, a value “(moving average)?n×(standard deviation)” for which a plurality of drive currents measured in a sampling period tp serves as a population, where n is a positive number in the range of 3 to 4 and, (C) determines that surging has occurred when the exhaust valve is closed and the drive current I is below the current threshold X, and (D) further opens the exhaust valve to discharge the compressed gas when determining that surging has occurred.