COMPRESSORS CONTROL

• US 20120121440A1
• Filed: 07/18/2008
• Published: 05/17/2012
• Est. Priority Date: 08/21/2007
• Status: Active Grant

• Current Assignee: Gardner Denver Deutschland GmbH
• Original Assignee: Gardner Denver Deutschland GmbH
• Inventors: Powell, Geoffrey George
• Granted Patent: US 9,086,070 B2
• Time in Patent Office: Days
• US Class Current: 417/44.2
• CPC Class Codes: F04D 27/02 Surge control surge detection F04D27/001
• CPC Class Codes: F04D 27/0261 by varying driving speed
• CPC Class Codes: F04D 27/0284 Conjoint control of two or more different functions
• CPC Class Codes: Y02B 30/70 Efficient control or regulation technologies, e.g. for control of refrigerant flow, motor or heating

Abstract

The invention relates to improvements in compressors and, in particular, to improvements in a method of controlling centrifugal compressors to maximise their efficacy. The compressor has an impeller mounted on a shaft supported by an active magnetic bearing unit and is driven by a variable speed motor at a rotational speed under normal on-load conditions at a calculated pre-surge speed for the required delivery pressure. The actual rotational speed and delivery pressure of the compressor is repeatedly measured and recorded at high frequency. The compressor is allowed to surge periodically after a preset re-calibration time and the compressor is put into a surge recovery cycle when surge is detected, during which the compressor is off-loaded and the rotational speed reduced. The compressor pre-surge speed line is recalibrated during the surge recovery cycle for the current operating conditions and reloads the compressor when the shaft speed reaches the greater of the recalibrated presurge speed line or the load speed.

Claims

1. A method of controlling a centrifugal compressor to provide compressed gas at a required delivery pressure, said compressor having an impeller mounted on a shaft supported by an active magnetic bearing unit, said compressor being driven by a variable speed motor at a rotational speed under normal on-load conditions at a calculated pre-surge speed for the required delivery pressure, wherein

the actual rotational speed and delivery pressure of the compressor is repeatedly measured and recorded at high frequency;

the compressor is allowed to surge periodically after a preset re-calibration time;

the compressor is put into a surge recovery cycle when surge is detected, during which the compressor is off-loaded and the rotational speed reduced;

the compressor pre-surge speed line is recalibrated during the surge recovery cycle for the current operating conditions; and

reloads the compressor when the shaft speed reaches the greater of the recalibrated pre-surge speed line or the load speed.

2. A method as claimed in claim 1 in which the pre-surge line is recalibrated by calculating the pre-surge speed using a speed margin, which comprises the difference between the measured pre-surge rotational speed of the compressor immediately before the compressor surge and the calculated pre-surge speed for the measured pre-surge delivery pressure.

3. A method as claimed in claim 2 wherein the pre-surge speed for any given delivery pressure is calculated using the formula

V_s=mP_d+x

in which m is a gradient determined by operational characteristics of the compressor;

and x is a variable determined by the pre-surge line plus the speed margin and is recalculated after each surge cycle by adding the speed margin to it.

4. A method as claimed in claim 1 in which the rotational speed of the compressor is measured by the active magnetic bearing drive unit.

5. A method as claimed in claim 1 in which, if the measured delivery pressure is less than a preset load pressure, then the subsequent calculation of the surge line speed uses the load pressure as the delivery pressure.

6. A method as claimed in claim 1 in which, when a surge occurs whilst the compressor speed is increased after initially being put on-load, the recalibration time is set to a new value.

7. A compressor system comprising a centrifugal compressor having an impeller mounted on a shaft supported in an active magnetic bearing unit, a variable speed motor to drive the compressor and a control system, said control system including:

—

means for repeatedly measuring and recording delivery pressure of compressed air at an outlet of the compressor and rotational speed of the compressor;

means for presetting a recalibration time after which the compressor is allowed to enter a surge cycle;

means for transmitting signals to the motor to reduce or increase the speed of the compressor;

means for putting the compressor into a surge recovery cycle when surge is detected; and

means for recalibrating the compressor pre-surge line according to the method claimed in any one of the preceding claims.

8. (canceled)

9. (canceled)