Abstract:
A method for controlling a rotational speed of a compressor train that can be driven at an adjustable rotational speed using a drive unit, a corresponding arrangement and a compressor train with a frequency converter-guided drive unit that can drive the compressor train at an adjustable rotational speed, and a frequency converter guiding the drive unit is provided. A load value describing a dynamic torsion load in the compressor train is measured at a current rotational speed of the compressor train driven by the drive unit. The load value is compared to a predetermined limit value and, if the load value satisfies a predetermined condition relative to the predetermined limit value, the current rotational speed in the compressor train is adjusted using the drive unit. The arrangement has a detection device and a control unit, which are designed to perform the method.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to PCT Application No. PCT/EP2013 054311, having a filing date of Mar. 5, 2013, based off of DE 102012203426.9 having a filing date of Mar. 5, 2012, the entire contents of which are hereby incorporated by reference. 
     
    
     FIELD OF TECHNOLOGY 
       [0002]    The following relates to a method for controlling a rotational speed of a compressor train which can be driven at a variable rotational speed using a drive unit, and an arrangement for controlling a rotational speed of a compressor train which can be driven at a variable rotational speed using a drive unit. 
         [0003]    Furthermore, embodiments of the invention relates to a compressor train having a frequency-converter-controlled drive unit which can drive the compressor train at a variable rotational speed, and a frequency converter which controls the drive unit. 
       BACKGROUND 
       [0004]    Compressors or fluid-compressing devices are used in various industrial fields, for various applications which involve compression of fluids, especially (process) gases. 
         [0005]    Known examples of this are turbocompressors in mobile industrial applications, such as in exhaust gas turbochargers or in jet engines or else in stationary industrial applications, such as geared compressors or geared turbocompressors for chemical or petrochemical installations, for example, for air fractionation or natural gas liquefaction. 
         [0006]    In such turbocompressors which operate continuously in their method of operation, increase in pressure (compression) of the fluid is brought about by virtue of the fact that a rotational pulse of the fluid is increased from the inlet to the outlet by a rotating impeller, having radially extending blades, of the turbocompressor, as a result of the rotation of the blades. Here, i.e. in such a compressor stage, the pressure and temperature of the fluid increase, while the relative (flow) speed of the fluid in the impeller or turbo impeller drops. 
         [0007]    In order to achieve the greatest possible increase in pressure or greatest possible compression of the fluid, a plurality of such compressor stages can be connected in series. 
         [0008]    A differentiation is made between radial compressors, axial compressors and combined axial-radial compressors and between single-shaft compressors and geared compressors, as known designs of turbocompressors. 
         [0009]    In the case of the axial compressor, the fluid to be compressed, for example, a process gas, flows through the compressor in a parallel direction to the axis (axial direction). In the case of the radial compressor, the gas flows axially into the impeller of the compressor stage and is then deflected outward (radially, radial direction). In the case of multi-stage radial compressors, a flow deflection is therefore necessary downstream of each stage. 
         [0010]    Combined designs of axial compressors and radial compressors suck in large volume flows with their axial stages, which volume flows are compressed to high pressures in the subsequent radial stages. 
         [0011]    While mostly single-shaft machines (single-shaft turbocompressors) in which one or more compressor stages are implemented on or by means of the same shaft are used, in the case of (multi-stage) geared turbocompressors (also referred to below for short merely as geared compressors), the individual compressor stages are grouped around a large wheel, wherein a plurality of parallel (pinion) shafts, which are each fitted with one or two impellers (turbo impellers which are arranged at free shaft ends of the pinion shafts) accommodated in spiral casings implemented as housing attachments, are driven by a large drive gearwheel, a large wheel, mounted in the housing. 
         [0012]    A compressor is generally driven by means of a drive unit, for example an (electric) motor or a turbine, which is coupled mechanically to the compressor and can transmit a torque. 
         [0013]    The output or output shaft thereof is connected to the drive shaft of the compressor, indirectly, for example, with the intermediate connection of a transmission or of a clutch, or directly, for example, by means of a common output/drive shaft. 
         [0014]    This mechanical drive-output system of the compressor, i.e. the entire mechanical chain which transmits the torque, for example, the output shaft/shafts, clutch/clutches, (intermediate) transmission/transmissions, output shaft/shafts, at the compressor are referred to here as the compressor train. 
         [0015]    It is known to generate a variable compressor characteristic diagram using various methods of the compressor implementation and mode of operation such as, for example, throttling, adjustment of inlet guide vane cascades or adjustment of operating rotational speeds. 
         [0016]    In this context, converter-controlled electric motors which drive compressor trains are used to permit an operating rotational speed range of the installation or of the compressor (power range of the installation) and/or to generate the rotational speed characteristic diagram or compressor characteristic diagram. 
         [0017]    In this context, a change in rotational speed which is necessary, for example, for a required change or increase in power of the compressor or compressor train occurs in the compressor train by correspondingly actuating the electric motors, which drive the compressor train, by means of electronic frequency converters (referred to below only for short as frequency converter or only converter). 
         [0018]    Frequency converters are also known. A frequency converter is, for example, a current converter which generates, from an alternating current (either a single-phase alternating current or three-phase alternating current) with a specific frequency, a voltage which may vary in amplitude and frequency. This converted voltage is then used to operate a load, generally a three-phase motor. 
         [0019]    Torsion-exciting frequency components are also generated, in addition to a feed frequency of the electric motor, by dual conversion of an electric current or an electric voltage from the alternating current on one power system side, to the direct current within the converter, and finally to an alternating current on the side of the electric motor. 
         [0020]    These exciting frequency components, mainly harmonic and inter-harmonic excitations, can cause torsion resonances in the compressor train, i.e. in components and/or parts of the mechanical drive system or in the compressor train. 
         [0021]    These torsion resonances bring about oscillations in the components or parts of the compressor train, in particular torsional oscillations in shafts and/or radial oscillations in intermediate transmissions. 
         [0022]    Owing to such torsional oscillations or radial oscillations with resulting corresponding high component loads, component failures can occur in the components of the compressor trains. 
         [0023]    The removal and replacement or repair of the damaged components of the compressor train and necessary downtimes of the installations give rise to high costs. 
       SUMMARY 
       [0024]    An aspect relates to providing a compressor train which overcomes the disadvantages in the prior art. In particular, embodiments of the invention include preventing and reducing component damage and failures in compressor trains. 
         [0025]    Another aspect relates to a method for controlling a 
         [0026]    rotational speed of a compressor train which can be driven at a variable rotational speed using a drive unit, an arrangement for controlling a rotational speed of a compressor train which can be driven at a variable rotational speed using a drive unit, and a compressor train. 
         [0027]    In the method, a load value which describes a dynamic torsion load in the compressor train is detected at a current rotational speed of the compressor train which is driven by the drive unit. 
         [0028]    In this context, “detected” is understood to mean any type of, direct or indirect, detection, sensing or measurement of the load value which describes the dynamic torsion load in the compressor train. 
         [0029]    The load value is compared with a predefined limiting value, and, if the load value satisfies a predefined condition with respect to the predefined limiting value, the current rotational speed in the compressor train is changed using the drive unit. 
         [0030]    The arrangement has a detection device and a control unit. 
         [0031]    The detection device is configured such that the load value which describes the dynamic torsion load in the compressor train can be detected at a current rotational speed of the compressor train which is driven by the drive unit. 
         [0032]    The control unit is configured such that the load value can be compared with the predefined limiting value, and, if the load value satisfies the predefined condition with respect to the predefined limiting value, the drive unit can be actuated to change the current rotational speed in the compressor train. 
         [0033]    The compressor train has a frequency-converter-controlled drive unit which can drive the compressor train at a variable rotational speed, a frequency converter which controls the drive unit, and the arrangement. 
         [0034]    Expressed in simple terms, embodiments of the invention are based on monitoring or detection-technology-based/measuring-technology-based monitoring of the dynamic torsion load in the compressor train. 
         [0035]    For this purpose, a load variable, which represents the dynamic torsion load in the compressor train, i.e. the load value such as, in particular, a dynamic torsion torque in the compressor train, a dynamic shaft rotational speed in the compressor train, a dynamic relative shaft oscillation in the compressor train or a dynamic torque-forming current of the drive unit, is detected or measured. 
         [0036]    The dynamic torsion torque in the compressor train—or the other load variable which represents the dynamic torsion load, such as the dynamic shaft rotational speed in the compressor train, the dynamic relative shaft oscillation in the compressor train or the dynamic torque-forming current of the drive unit, is compared with a permissible limiting load or limiting value, usually a maximum load or a maximum value, to be defined beforehand. 
         [0037]    If, as can be correspondingly predicted in the case of a torsion resonance condition in the compressor train given a corresponding definition of the limiting value, the value of the maximum load or the maximum value is exceeded, operation of the compressor train is to be changed to a lower or higher rotational speed using the drive unit. The compressor or the compressor train is “moved out” of the resonance. 
         [0038]    The operating point of the compressor or of the compressor train will be typically shifted to a higher rotational speed, since this ensures that the requirements of the compressor process or installation process are met. 
         [0039]    Since torsion resonances in the compressor train are typically damped weakly, only a small change in the rotational speed is usually necessary to shift or move the operating point of the compressor out of the resonance range. 
         [0040]    Considered figuratively, for a specific compressor train in the case of embodiments of the invention, that rotational speed range or those rotational speed ranges in which a torsion resonance or the torsion resonances—with correspondingly high (relevant) torsion amplitudes—occur at the compressor train are therefore identified by detection or measurement of the dynamic torsion load at said specific compressor train. 
         [0041]    This rotational speed range or these rotational speed ranges can then be blocked with respect to steady-state and/or continuous operation of the compressor train or reduced to a necessary minimum. That is to say, corresponding rotational speed ranges or rotational speed bands in a compressor characteristic diagram of the compressor train are blocked with respect to steady-state operation or continuous operation of the compressor train. 
         [0042]    Continuously or continuous operation/operating state can be understood here to mean an (operating) state which is assumed for a predefinable time period and is maintained or persists for this time period. This time period in this context generally exceeds a time period of one second or a few seconds. 
         [0043]    Embodiments of the invention therefore reduces or prevents load-induced component damage on/in the compressor train—by avoiding torsion resonances with correspondingly high or relevant dynamic torsion amplitudes and therefore by reducing component loads in the compressor train—and thereby permits reliable and failsafe operation of the compressor train or compressor over a longer service life. 
         [0044]    A further particular advantage of the invention is that the selection from the converter, electric motor and train configuration can be made without any particular restrictions. 
         [0045]    This avoids operation of the compressor or of the compressor train in torsion resonance states with non-permanently transmissible dynamic torsion torques. 
         [0046]    In addition, the blocking continuous operation rotational speed range is reduced to a minimum. 
         [0047]    The effects or restrictions for the operation of the installation and also the additional power requirement of the compressor are therefore also reduced to a minimum. 
         [0048]    Further influencing variables, such as for example power system frequency fluctuations, power-dependent resonance amplitudes, changes in the torsion property frequencies etc., are also taken into account by means of this invention. 
         [0049]    Embodiments of the invention relate both to the method according to embodiments of the invention, to the arrangement according to embodiments of the invention and to the compressor train according to embodiments of the invention. 
         [0050]    Embodiments of the invention and the described developments can be implemented using software as well as hardware, for example using a specific electric circuit. 
         [0051]    In addition, fee-embodiments of the invention or any described development can be implemented by a computer-readable storage medium on which a computer program is stored, which computer program executes the invention or the development. 
         [0052]    Embodiments of the invention and/or any described development can also be implemented by means of a computer program product which has a storage medium on which a computer program is stored, which computer program executes embodiments of the invention and/or the development. 
         [0053]    In one preferred development, the load value is the dynamic torsion torque in the compressor train. 
         [0054]    That is to say, the dynamic torsion torque is preferably measured in the compressor train or on a component, in particular on a shaft or a clutch, of the compressor train. Torsion measurements on shafts or clutches are easy and cost-effective to implement. 
         [0055]    The detection device is then particularly preferably here a measuring device based on a strain gauge technology. 
         [0056]    That is to say, the measurement of the dynamic torsion torque is particularly preferably carried out by means of the strain gauge technology. This strain gauge technology is extensively tested, is, in particular, suitable for dynamic loads, is a mature technology and is reliable, easy and cost-effective to implement. 
         [0057]    Strain gauges, i.e. generally the detection unit for detecting the load value, can, in particular, be attached to a shaft or clutch of the compressor train by means of which the torsion torque, i.e. generally the load value, and therefore the dynamic torsion load in the compressor train, can be measured. A clutch is therefore particularly suitable since this is the location of the greatest twisting in the compressor train. 
         [0058]    The dynamic shaft rotational speed in the compressor train, the dynamic relative shaft oscillation in the compressor train or the dynamic torque-forming current of the drive unit can also be used as the load value. These variables also represent very well the dynamic torsion load in the compressor train. 
         [0059]    In a further preferred development, if the load value satisfies a predefined condition with respect to the predefined limiting value, the current rotational speed in the compressor train is increased. As a result, it is possible to ensure that the compressor meets the requirements of the compressor process, which is to say of the installation process. 
         [0060]    The predefined limiting value can be an upper limiting value, for example a maximum dynamic torsion torque, and the predefined condition can be the upper limiting value being reached or exceeded. 
         [0061]    The predefined limiting value can also be a lower limiting value, such as a minimum dynamic torsion torque, and the predefined condition can be the lower limiting value being reached or undershot. 
         [0062]    The limiting value is preferably detected or defined using a maximum, dynamically transmissible torque. Customary safety issues can be taken into account here and/or safety factors can be correspondingly included in the limiting value. 
         [0063]    The limiting value can also be defined using a rated torque. Safety issues or safety factors can also be taken into account here. 
         [0064]    Furthermore, the limiting value can also be defined using a predefinable permissible deviation, for example by specifying a percentage deviation such as +/−5%, +/−10% or +/−15%, from a reference value, such as a current drive torque or rated torque. 
         [0065]    The limiting value can be an absolute value or else a relative value with respect to a reference value, such as the current drive torque or the rated torque. 
         [0066]    In one particularly preferred development, an upper limiting value and a lower limiting value are defined, with both of which the load value is respectively compared. Considered figuratively, a permissible fluctuation range for the load value can therefore be “stretched” here so that in the event of the load value “moving out” of the permissible fluctuation range a torsion resonance is identified, and the change in the rotational speed is implemented. 
         [0067]    Such a permissible fluctuation range can be “static” here, i.e. the upper and lower limiting values are defined independently of an operating state of the compressor train here. Such a permissible fluctuation range can also be “dynamic”, i.e. the upper and lower limiting values change as a function of an operating state of the compressor train. Expressed in figurative terms, a band—with an upper and a lower limit—within which permissible load values are located, comes about here. If a load value is located outside the band, a torsion resonance is identified. 
         [0068]    In one further preferred development, the rotational speed is changed using a frequency-converter-controlled electric motor. The electric motor, which drives the compressor train here, can be controlled (actuated), in particular, using a frequency converter for changing the rotational speed. 
         [0069]    The method—with the inventive steps of “detecting”, “comparing” and, if appropriate, “changing the rotational speed”—is particularly preferably carried out at a multiplicity of successive times, for example in an operating phase of the compressor train, as in the case of starting or driving through a power ramp. 
         [0070]    As a result, embodiments of the invention can be used to monitor operating states of the compressor train, in particular to avoid a continuous operating state of the compressor train in a torsion resonance of the compressor train. 
         [0071]    Embodiments of the invention can especially be used to avoid continuous operation in a frequency-converter-excited torsion resonance of the compressor train. Here, the drive of the compressor train, with a variable rotational speed, is generated by means of a frequency-converter-controlled electric motor whose frequency converter generates torsion-exciting frequency components, which can then cause the torsion resonances in the compressor train. 
         [0072]    The dynamic torsion load in the compressor train is then monitored by fee-embodiments of the invention, such a frequency-converter-excited torsion resonance in the compressor train is identified—and the compressor train is then moved out of the resonance. A rotational speed (resonance rotational speed) which corresponds to the identified frequency-converter-excited torsion resonance or a corresponding rotational speed range (definable range around the resonance rotational speed) can also be blocked for the continuous operation. 
         [0073]    According to one preferred development, a turbocompressor, in particular a single-shaft turbocompressor or a transmission turbocompressor, has the compressor train, with the result that the turbocompressor or the operation of the turbocompressor can then be monitored by the embodiments of the invention or can be correspondingly controlled—while avoiding continuous operation in the torsion resonance. 
         [0074]    Embodiments of the invention can also be used in a large-scale technical installation, in particular in a chemical or petrochemical installation, such as an installation for air fractionation or an installation for (natural gas) liquefaction, which then has the compressor train. 
         [0075]    The previously provided description of advantageous refinements of the invention contains numerous features which are represented in the individual subclaims, a plurality thereof being combined in some cases. However, a person skilled in the art will expediently also consider these features individually and combine them to form further appropriate combinations. 
         [0076]    In particular, these features can each be combined individually and in any desired suitable combination with the method according to the invention, the arrangement and/or the compressor train according to the respective independent claim. 
     
    
     
       BRIEF DESCRIPTION 
         [0077]    Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein: 
           [0078]      FIG. 1  shows a schematic illustration of a compressor system having a compressor train driven by means of a converter-controlled electric motor, according to one exemplary embodiment; 
           [0079]      FIG. 2  shows a diagram with operating states BZ and measured loads of the compressor train in the case of a power ramp, according to the exemplary embodiment; 
           [0080]      FIG. 3  shows a compressor characteristic diagram with blocked rotational speed bands of continuous operation rotational speed ranges to be avoided on the basis of control technology, according to the exemplary embodiment; and 
           [0081]      FIG. 4  shows a method for controlling the rotational speed of the compressor train, according to the exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0082]    Exemplary embodiment: Avoiding continuous operation in frequency-converter-excited torsion resonances of a compressor train ( FIG. 1-FIG .  4 ). 
         [0083]      FIG. 1  shows—in schematic form—a compressor system  50 , for example for a natural gas liquefaction system, having a compressor train  1  with a single-shaft turbocompressor  51 , referred to for short merely as compressor  51 . 
         [0084]    In the case of the compressor train  1 , a converter-controlled electric motor  2  which 
         [0085]    drives this compressor train  1  at a variable rotational speed  6  is used to permit an operating rotational speed range of the compressor system  50  or of the compressor  51  (power range of the system  50 , cf.  FIG. 3  compressor characteristic diagram  52 ). 
         [0086]    Here, a change  130  in rotational speed—which is necessary, for example, for a requested change or increase in power (cf.  FIG. 2 , power ramp  53 ) of the compressor  51  or compressor train  1 —occurs in the compressor train  1  through corresponding actuation of the electric motor  2 , driving the compressor train  1 , by means of the electronic frequency converter  3 . 
         [0087]    Torsion-exciting frequency components are also generated, in addition to a feed frequency of the electric motor  2 , by dual conversion of an electric current from an alternating current on one power system side  13 , to a direct current within the converter  3 , and finally to an alternating current on the side  14  of the electric motor  2 . 
         [0088]    These exciting frequency components, mainly harmonic and inter-harmonic excitations, can cause torsion resonances  12  in the compressor train  1 , i.e. in components  4 ,  5  and/or parts  4 ,  5  of the mechanical drive system or in the compressor train  1 . 
         [0089]    These torsion resonances  12  bring about oscillations and loads in the components  4 ,  5  or parts  4 ,  5  of the compressor train  1  and can lead to component failures in the compressor train  1 . 
         [0090]    In order to ensure safe operation of the compressor train  1 , i.e. a steady-state operation (continuous operation) outside the torsion resonances  12 , the installation  50  provides monitoring of the dynamic torsion load  7  in the compressor train  1  on the basis of technical measuring means. 
         [0091]    For this purpose, as clarified in  FIG. 1 , strain gauges  15  are applied to a clutch  5  in the compressor train  1 , which can mechanically couple an output shaft  4  of the electric motor  2  to a driveshaft  4  of the compressor  51 , which strain gauges  15  measure the dynamic torsion torque  7 , acting at the clutch  5 , during the operation of the compressor system  50  ( FIG. 4 ,  100 ,  110 ). 
         [0092]    The measured torsion torques  7  are transferred to a controller  220 —in a process control system  54 —of the compressor system  50 , in addition to other operating parameters of the compressor system  50  which are present there, such as the current rotational speed  6  in the compressor train  1 , the rated rotational speed and the rated torque  16  of the compressor train  1 . 
         [0093]    The compressor system  50  is operated by means of the controller  220  in the process control system  54  of the compressor system  50  (cf.  FIG. 3  compressor or rotational speed characteristic diagram  52 ). 
         [0094]      FIG. 2  illustrates in a diagram (abscissa: time specified as point in time indication or in [min]  17 /ordinate: rotational speed 6 [rpm] and torsion torque 8 [kNm]) the operating states BZ and loads (dynamic torsion load  7 ) of the compressor train  1  when a power ramp (rotational speed ramp)  53  is passed through. 
         [0095]    Curve A (rotational speed curve)  18  shows here in the time profile  17 —over a time period of approximately 16 min—the rotational speeds  6  travelled at when passing through the power ramp (rotational speed ramp)  52  or the change  130  in rotational speed or increase  130  in rotational speed which is travelled at in the compressor train  1 . 
         [0096]    Starting from a first operating state BZ 1  at a first point in time t1 at which the compressor train  1  is operated with a first rotational speed DZ 1  of approximately 7300 rpm, the rotational speed  6  in the compressor train  1  is revved up  130  continuously—over a time period of approximately 12 min—to a second rotational speed DZ 2  of approximately 9300 rpm (operating state BZ 2  at a second point in time t2). 
         [0097]    Curve B (torsion load curve  7  with the rated torque curve  16 )  19  illustrates the dynamic torsion torques (dynamic torsion load)  7 ,  8  which are measured at the clutch  5  in the compressor train  1  when this power ramp  53  is passed through. 
         [0098]    In the case of a curve profile—approximately parallel to the rotational speed curve A  18 —of curve B  19 , the torsion torque  8  measured in the first operating state BZ 1  also increases, as  FIG. 2  shows, from approximately 54 kNm until it reaches the torsion torque  8  at the level of approximately  90  kNm in the second operating state BZ 2 . 
         [0099]    The increase  130  in rotational speed occurs here by means of the converter  3  which also produces torsion-exciting frequency components—in addition to the feed frequency of the electric motor  2  which is to be correspondingly raised. 
         [0100]    These torsion-exciting frequency components are transmitted via the electric motor  2  to the compressor train  1  and lead there, as shown by the torsion torque measurement or curve B  19  ( FIG. 2 , curve B  19 ), to oscillating fluctuations  20  in the torsion torque  8  and about the respective rated torque  16 . 
         [0101]    If these frequency components which are additionally transmitted to the compressor train  1  satisfy resonance conditions in the compressor train  1 , resonance states  12  occur in the compressor train  1 —at the corresponding rotational speeds  21  (resonance rotational speeds  21 ). 
         [0102]    These resonance states  12  are characterized by sudden increases  22  or a sudden drop  22  in the measured dynamic torsion torques  8  or the amplitudes thereof at or in the region of the resonance rotational speeds  21 . 
         [0103]    Since torsion resonances  12  are typically damped weakly, the sudden changes  22  in the torsion torque  8  (fluctuation widths) also suddenly decrease again, as shown also in  FIG. 2 , even when the respective resonance rotational speed  21  is slightly departed from. 
         [0104]      FIG. 2  illustrates four different resonance states RZ 1 , RZ 2 , RZ 3  and RZ 4 , which states are passed through when the power ramp  53  is passed through, and lead there to increased loads in the compressor train  1 . 
         [0105]    In order to monitor the dynamic torsion load  7  in the compressor train  1 , a (monitoring) band  23 —formed in a symmetrical fashion with respect to the rated torque  16  in this case—is positioned about the rated torque  16 , as is shown by  FIG. 2 . 
         [0106]    This band  23 , which defines the dynamic fluctuations  24  in the rated torque  16  which are permissible for safe operation of the compressor system  50 , is defined by an upper boundary line  25 , formed by an approximately 12% supplement to the respective rated torque  16  and by a lower boundary line  26 , formed by a corresponding 12% deduction from the respective rated torque  16 . 
         [0107]    By comparing ( FIG. 4   100 ,  120 ) the measured dynamic torsion torques with the boundaries or boundary lines  25 ,  26  of this band  23 , it is possible, as illustrated in  FIG. 2 , to identify four continuous operation rotational speed ranges DBB 1 , DBB 2 , DBB 3 , DBB 4  and  27 ,  28 ,  29 ,  30  which are to be avoided on the basis of control technology ( FIG. 4 ,  100 ,  120 ). 
         [0108]    These four continuous operation rotational speed ranges DBB 1 , DBB 2 , DBB 3 , DBB 4  and  27 ,  28 ,  29 ,  30  which are to be avoided on the basis of control technology occur in each case where the measured dynamic torsion torques are located outside the band  23 , in each case in the region of the respective resonance rotational speed  21 . 
         [0109]    The rotational speed ranges DBB 1 , DBB 2 , DBB 3 , DBB 4  and  27 ,  28 ,  29 ,  30  which can be identified in this way can then be avoided as continuous operating points during the control  220  of the compressor system  50 . 
         [0110]      FIG. 3  shows the influence of this monitoring of the dynamic torsion load  7  in the compressor train  1 —and avoidance of the continuous operation of the compressor system  50  in the frequency-converter-excited torsion resonances  12  or identified torsion resonance ranges TB 1 , TB 2 , TB 3 , TB 4  and  30 ,  31 ,  32 ,  33 —on the compressor characteristic diagram  52  of the compressor system  50 . 
         [0111]    As is shown by  FIG. 3 , four rotational speed bands DB 1 , DB 2 , DB 3 , DB 4 ,  37 ,  38 ,  39 ,  40  are characterized in the compressor characteristic diagram  52  (abscissa: (relative) throughput rate  35 /ordinate: (relative) outflow pressure  36 ), which rotational speed bands DB 1 , DB 2 , DB 3 , DB 4 ,  37 ,  38 ,  39 ,  40  correspond to the four identified torsion resonance ranges TB 1 , TB 2 , TB 3 , TB 4  and  31 ,  32 ,  33 ,  34  and the four continuous operation rotational speed ranges DBB 1 , DBB 2 , DBB 3 , DBB 4  and  27 ,  28 ,  29 ,  30  which are to be avoided on the basis of control technology, and which rotational speed bands DB 1 , DB 2 , DB 3 , DB 4 ,  37 ,  38 ,  39 ,  40  are blocked for steady-state operation of the compressor  51 . 
         [0112]    Operating states BZ which occur after the control  220  of the system  50 , within such a blocked rotational speed band DB 1 , DB 2 , DB 3 , DB 4  and  37 ,  38 ,  39 ,  40 , are moved out of the blocked rotational speed band DB 1 , DB 2 , DB 3 , DB 4 ,  37 ,  38 ,  39 ,  40  ( FIG. 4 ,  100 ,  130 ) or avoided by increasing  130  the rotational speed. 
         [0113]      FIG. 3  illustrates this on the basis of an operating point X, lying in the second blocked rotational speed band DB 2   38 , of the compressor system  50 . 
         [0114]    A torsion resonance (second identified torsion resonance range TB 2   32 ) occurs at this operating point X in the compressor train, which represents a high mechanical (component) load and can lead to damage to components in the compressor train. 
         [0115]    As a result of the increase  130  in the rotational speed—brought about by means of the converter  3 —, the operating point X is moved out of the blocked second rotational speed band  38  ( FIG. 4 ,  100 ,  130 ) as shown by the arrow Z in  FIG. 3 , and the compressor system  50  is moved into a permissible operating state BZ, operating point Y, for continuous operation, said operating state BZ being outside the resonance condition. 
         [0116]    The controller  220  therefore avoids the steady-state operation of the compressor system  50  in this frequency-converter-excited torsion resonance  12  or in the second identified torsion resonance range TB 2   32  and prevents component failure. 
         [0117]    Although the invention has been illustrated and described in more detail by means of the preferred exemplary embodiment, the invention is not restricted by the disclosed example and other variations can be derived therefrom by a person skilled in the art without departing from the scope of protection of the invention.