Abstract: A method and an apparatus for controlling a displacement-type fluid machine which handles fluid including gas and/or liquid for increasing or decreasing pressure of the fluid or transporting the fluid including the use of an alternating current motor for driving the displacement-type fluid machine and a frequency converter which is capable of conducting frequency conversion up to a range higher than the power source frequency to adjust the number of revolutions of the motor. Wherein the number of revolutions is adjusted so that input current to the motor is kept constant, regardless of any change in operating pressure of the displacement-type fluid machine, whereby the displacement-type fluid machine is operated maintaining the process values within an allowable limit without effecting repeated actuation and stopping of the machine.

Abstract: A system for controlling the operation of a turbo-type fluid machine driven by a variable speed prime mover, which enables the characteristics of the fluid machine to be improved so as to become favorable for actual use while allowing the prime mover to exhibit its capacity to the maximum even at an operating point other than the rated point. The operation control system includes a turbo-type fluid machine driven by a driving machine, and a device for detecting an operating head or operating pressure of the fluid machine.

Abstract: A pump control system has a pump unit composed of a turbo pump, a motor for operating the turbo pump, and a frequency/voltage converter for generating a frequency and a voltage to energize the motor. The rotational speed of the turbo pump is varied in order to equalize the current of the motor to a constant current irrespective of the head of the pump. The pump can be operated to take fully advantage of the current capacity of the motor.