Control device for hydraulic turbines configured to adjust the resistant torque provided by the generator to the movement of the impeller of an hydraulic turbine so that a stable pressure is set at the inlet (Pi) and at the outlet (Po) regardless of the circulating flow rate (Q), and to adjust the electrical energy produced by the turbine to achieve the desired hydraulic behavior, the device comprising a controller and a power device; wherein said controller is connected to a pressure detector at the inlet (Pi) and at the outlet (Po) and to a flow-meter for obtaining the circulating flow rate (Q), as well as to a power sensor for measuring the power of the turbine; all this, in such a way that the controller acts on the power device for causing the application of the braking torque necessary to maintain a stable set-point value on the turbine.

A method for controlling multi-stage centrifugal compressors is provided. It allows an optimization of compressor head and efficiency at each compression stage and is specifically valuable at reduced compressor flow.