A centrifugal compressor for a chiller includes a casing, an inlet guide vane, an impeller downstream of the inlet guide vane, a motor and a diffuser. The casing has inlet and outlet portions with the inlet guide vane disposed in the inlet portion. The impeller is rotatable about a rotation axis defining an axial direction. A liquid injection passage is provided to inject liquid refrigerant into an area between the impeller and the diffuser. The motor rotates the impeller. The diffuser is disposed in the outlet portion downstream from the impeller with an outlet port of the liquid injection passage being disposed between the impeller and the diffuser. A controller is programmed to control an amount of the liquid refrigerant injected into the area between the impeller and the diffuser.