Abstract: A control method for a compressor system includes a compressor connected to a pressure vessel and a frequency converter controlling an electric motor of the compressor. In the method, the present operating state is estimated on the basis of a monitored/estimated electrical quantity of the compressor system. The operating state may represent the pressure in the pressure vessel. The pressure in the pressure vessel causes a counter-torque to the motor. The counter-torque is proportional to the pressure and may be used for estimating the pressure inside the pressure vessel. An estimate of a counter-torque may be calculated on the basis of the monitored electrical quantity or quantities.

Abstract: The present disclosure describes a load/unload control method for a compressor system with a rotating compressor connected to a pressure vessel. In the method, the present operating state can be monitored on the basis of a monitored/estimated electrical quantity of the compressor system. The method comprises an identification phase and an operational phase. In the identification phase, the compressor is operated at a constant rotational speed to generate two known pressures to the pressure vessel. At least one electrical quantity is monitored, and values of the electrical quantity corresponding to the pressure limits are stored. In the operational phase, reaching of a pressure limit may then be detected by comparing the present value of the monitored electrical quantity to the stored values.

Abstract: The present disclosure describes a control method for a compressor system that comprises a compressor connected to a pressure vessel and a frequency converter controlling an electric motor of the compressor. In the method, the present operating state is estimated on the basis of a monitored/estimated electrical quantity of the compressor system. The operating state may represent the pressure in the pressure vessel. The pressure in the pressure vessel causes a counter-torque to the motor. The counter-torque is proportional to the pressure and may be used for estimating the pressure inside the pressure vessel. An estimate of a counter-torque may be calculated on the basis of the monitored electrical quantity or quantities.

Abstract: The present disclosure describes a load/unload control method for a compressor system with a rotating compressor connected to a pressure vessel. In the method, the present operating state can be monitored on the basis of a monitored/estimated electrical quantity of the compressor system, The method comprises an identification phase and an operational phase. In the identification phase, the compressor is operated at a constant rotational speed to generate two known pressures to the pressure vessel. At least one electrical quantity is monitored, and values of the electrical quantity corresponding to the pressure limits are stored. In the operational phase, reaching of a pressure limit may then be detected by comparing the present value of the monitored electrical quantity to the stored values.

Abstract: A method for controlling an electric drive, having an inverter, an electric motor and control means configured in a first operating state of the electric drive to control the electric drive to run in a constant operating point, determine and store a value of an output voltage of the inverter or a value of a flux reference of the inverter, and a value of a switching frequency of the inverter with which a determined input power of the electric drive is lowest. The controller is configured in a second operating state of the electric drive to control the electric drive to use the stored values to run in the operating point.

Abstract: A method for controlling an electric drive, having an inverter, an electric motor and control means configured in a first operating state of the electric drive to control the electric drive to run in a constant operating point, determine and store a value of an output voltage of the inverter or a value of a flux reference of the inverter, and a value of a switching frequency of the inverter with which a determined input power of the electric drive is lowest. The controller is configured in a second operating state of the electric drive to control the electric drive to use the stored values to run in the operating point.

Abstract: A method in connection with a pump drive connected to a container or the like, wherein a frequency converter is arranged to supply power to a pump in such a manner that a pump flow (Qp) is responsive to an estimated mean incoming flow (Qest) to the container. The method includes draining the container, allowing the container to fill during a predefined filling time (tfill) while the pump is inactive, draining the container again at a known pump flow (Qp,nom), defining the drainage time (tdrain), defining an estimated mean incoming flow (Qest) on the basis of the filling time (tfill), drainage time (tdrain) and known pump flow (Qp,nom), and setting the power supplied by the frequency converter to the pump to be such that the pump flow (Qp) corresponds to the produced estimated mean incoming flow (Qest).

Abstract: Exemplary embodiments relate to a method for verifying a leak situation in a liquid transfer system a system and a control unit for implementing the method. The liquid is transferred with a frequency-converter-controlled pump from a lower pressure to a higher pressure and where liquid is prevented from being transferred from a higher pressure to a lower pressure with one or more check valves positioned in a pipe system. The method includes generating, for the frequency converter, motion information on the motion of the pump between the motion operations, and indicating a leak situation of the check valve if the direction of operation of the pump is, in the motion information, opposite to the direction of operation during the use of the pump.

Abstract: A method in connection with a pump drive connected to a container or the like, wherein a frequency converter is arranged to supply power to a pump in such a manner that a pump flow (Qp) is responsive to an estimated mean incoming flow (Qest) to the container. The method includes draining the container, allowing the container to fill during a predefined filling time (tfill) while the pump is inactive, draining the container again at a known pump flow (Qp,nom), defining the drainage time (tdrain) defining an estimated mean incoming flow (Qest) on the basis of the filling time (tfill), drainage time (tdrain) and known pump flow (Qp,nom), and setting the power supplied by the frequency converter to the pump to be such that the pump flow (Qp) corresponds to the produced estimated mean incoming flow (Qest).

Abstract: The present invention relates to a method for verifying a leak situation in a liquid transfer system where liquid is transferred with a frequency-converter-controlled pump from a lower pressure to a higher pressure and where liquid is prevented from being transferred from a higher pressure to a lower pressure with one or more check valves positioned in a pipe system. The method is characterized by comprising the steps of comprising the steps of generating for the frequency converter motion information on the motion of the pump between the motion operations, and indicating a leak situation of the check valve if the direction of operation of the pump is, in the motion information, opposite to the direction of operation during the use of the pump. Further, the invention relates to a system and a control unit of a frequency converter for implementing the method.