EP3472467B1 - Method and device for compensating pulsation of a compressor - Google Patents

Description

The invention relates to a method and a device for vibration compensation in a piston compressor, the piston compressor of which is driven by means of a crankshaft from a three-phase motor or the like controlled by a frequency converter. Furthermore, the invention also relates to a piston compressor which is equipped with such a device.

The field of application of the invention extends primarily to vehicles, in particular rail vehicles. Since the installation space in vehicles is limited in principle, very compact piston compressors are usually used for this purpose, on which an electric motor is flanged directly, usually multi-stage piston compressors, in order to drive the piston compressor. The load torque M _L of a piston compressor, in combination with the torque M _M of a driving motor, generates an exciter torque about the axis of rotation of the entire piston compressor, which leads to undesirable torsional vibrations. Since, in the case of piston compressors of the type of interest here, the torque M _M of the motor follows the load torque M _L of the piston compressor with a time delay, the excitation torque increases unfavorably.

From the DE 100 58 923 A1 a generic piston compressor emerges, the multi-stage piston compressor of which is driven by an electric motor flanged directly to it. The piston compressor is attached to the chassis of the vehicle by means of several vibration-damping wire rope springs in order to reduce the transmission of vibrations from the piston compressor to the vehicle.

Also the EP 1 242 741 A1 describes the problem of vibration excitation of piston compressors by load torque M _L and motor torque M _M and measures to reduce vibrations, which are part of the types of two-stage piston compressors lead to reduced vibration excitation. In order to minimize the influence of the engine on the excitation of vibrations, flywheel masses were used between the engine and the piston compressor, which counteract the excitation of vibrations. However, this technical solution requires a corresponding amount of material and generates an associated increase in weight.

the EP 3 098 448 A1 discloses a method for controlling an electric drive of an electrically driven air compressor. With this method, the load torque is estimated based on an operating parameter in order to reduce the control error on the control loop caused by the load torque.

From the DE 100 58 924 A1 a multi-stage piston compressor is known. In order to achieve a vibration reduction of the piston compressor, two connecting rods are arranged on each offset of the crankshaft, to which opposite pistons are assigned.

the EP 1 858 153 A2 discloses a method for controlling an electric drive. With this method, the system driven by the drive is to be protected against torsional vibrations of the drive. For this purpose, impermissible torsional vibrations are detected via a monitoring device and a control intervention is accordingly carried out via a control device.

From the U.S. 2006/125437 A1 a motor control method is known to avoid speed changes. For this purpose, an output voltage value or a command value of an inverter is detected and controlled so that the output voltage value or the command value does not exceed a predetermined value.

In practice, piston compressors are usually operated with three-phase motors, which are assigned a frequency converter. With the help of the frequency converter, the piston compressor can be controlled with variable speed, in particular to ensure a needs-based To realize compressed air generation within the framework of a corresponding regulation, taking into account minimum switch-on times, intermittent operation intervals and the like.

So far, frequency converters, especially those designed for rail vehicle operation, have had a very complex design and, above all, have been quite large. In addition, these so-called auxiliary converters on rail vehicles not only supply a single electrical consumer, but several, such as air conditioning systems, traction fans, device fans, compressors and the like. For this reason, such a conventional auxiliary converter could not previously be tuned to an individual consumer.

Due to further developments in converter technology and a high availability of power electronic components used here, there are currently boundary conditions that make it possible to assign frequency converters directly to a drive and also to place them there.

It is therefore the object of the present invention to create a method and a device for compensating for vibrations in a piston compressor, which enables effective vibration suppression in every operating situation of the piston compressor using simple technical means.

The object is achieved based on a method according to the preamble of claim 1 in conjunction with its characterizing features. The object according to claim 7 is achieved in terms of installation technology. The dependent claims refer back to advantageous developments of the invention.

The invention includes the procedural teaching that the current position of the crankshaft of the piston compressor is first determined for vibration compensation, and based on this, a torque M _M is specified for the driving three-phase motor by a frequency converter that the Load torque M _L of the piston compressor follows, that is, corresponds to this, in order to reduce the vibration excitation of the entire piston compressor. Since the oscillation excitation of the piston compressor arises from the difference between the torque M _M of the driving motor and the load moment M _L , the oscillation excitation resulting therefrom can be eliminated by a control based on the solution according to the invention. Flywheel masses between the motor and the piston compressor can be reduced or they can be dispensed with entirely.

A three-phase motor used within the scope of the solution according to the invention is preferably understood to be a three-phase asynchronous motor or a synchronous reluctance motor. Torque M _M specified for the three-phase motor preferably corresponds to the course of the load torque, including a phase length. The torque M _M specified for the three-phase motor corresponds to the first order of the load torque curve. Experiments have shown that a vibration compensation method that is quite easy to implement but very effective consists in simulating only the first-order component in the engine torque M _M . Higher orders are neglected. The basis for this is the elastic bearing of the piston compressor. This bearing is designed in such a way that excitations above a certain frequency are kept away from the adjacent structures. This has proved to be sufficient under the circumstances. Higher orders are largely kept away from the elastic bearings. For this reason it is sufficient to eliminate vibration excitations up to and including the first order with the method according to the invention.

It is also sufficient if the deviation of the load torque M _L of the piston compressor following the torque M _M for the three-phase motor is set in such a way that it is less than 30%. Within this deviation range, the torque M _M of the three-phase motor only approximately follows the load moment M _L of the piston compressor, which nevertheless results in effective vibration compensation. Within the framework of all structural boundary conditions, it has been shown that the entire vibration behavior can be improved by up to 70% by the electronic compensation according to the invention, with the vibration paths of the piston compressor being significantly reduced, particularly at low speeds.

According to a further measure improving the invention, it is proposed that, to compensate for speed fluctuations, the torque M _M generated by the three-phase motor is generated by varying the supply voltage and/or varying the pulse width in the converter. Thus, for example, an increase in the torque M _M can be achieved by briefly increasing the pulse width. As a result, the pulsating load torques usually generated by the piston compressor are smoothed out within the compressor, so that the resulting vibration excitation is further minimized. Since the torque M _M of the three-phase motor is proportional to the motor current, torque compensation is achieved by counter-regulating the motor current. The torque peak can be compensated for by controlling the IGBT pulse width accordingly and thus by changing the motor current at that moment. A correspondingly fast control and stable intermediate circuit voltage are required for this so-called «space vectoring modulation».

Preferably, the torque M _M for the three-phase motor can be increased in a simple manner by the frequency converter by a corresponding increase in the operating voltage. A control unit provided for carrying out the method for vibration compensation according to the invention can advantageously also be integrated directly in the frequency converter. The frequency converter itself is preferably arranged directly on the three-phase motor in order to ensure easy connection to the three-phase source. In addition, this electronic assembly can also have at least one sensor input, to connect a position sensor arranged in the area of the motor shaft or the crankshaft to measure the current angular position. The torque requirement to be readjusted depending on the speed is preferably stored in the logic of the control unit implemented in the frequency converter.

Fig. 1

eine Blockschaltbilddarstellung eines Kolbenkompressors mit hierin integrierter Einrichtung zur Schwingungskompensation,

Fig. 2

eine graphische Darstellung der von Motor und Verdichter erzeugten Drehschwingungen gemäß des Standes der Technik,

Fig. 3

eine graphische Darstellung der von Motor und Verdichter erzeugten Drehschwingungen gemäß der erfindungsgemäßen Lösung hinsichtlich einer ersten Ausführungsform, und

Fig. 4

eine graphische Darstellung des Drehzahlverlaufs bei der ersten Ausführungsform,

Fig. 5

eine graphische Darstellung des zeitlichen Verlaufs der Strangströme eines Drehstrommotors als Antrieb gemäß der ersten Ausführungsform,

Fig. 6

eine graphische Darstellung der von Motor und Verdichter erzeugten Drehschwingungen gemäß der erfindungsgemäßen Lösung hinsichtlich einer zweiten Ausführungsform

Fig. 7

eine graphische Darstellung des Drehzahlverlaufs bei der zweiten Ausführungsform,

Fig. 8

eine graphische Darstellung des zeitlichen Verlaufs der Strangströme eines Drehstrommotors als Antrieb gemäß der zweiten Ausführungsform.

Further measures improving the invention are presented in more detail below together with the description of a preferred exemplary embodiment of the invention with reference to the figures. It shows

1

a block diagram representation of a piston compressor with an integrated device for vibration compensation,

2

a graphical representation of the torsional vibrations generated by the engine and compressor according to the prior art,

3

a graphical representation of the torsional vibrations generated by the engine and compressor according to the solution according to the invention with regard to a first embodiment, and

4

a graphical representation of the speed curve in the first embodiment,

figure 5

a graphic representation of the time course of the phase currents of a three-phase motor as a drive according to the first embodiment,

6

a graphical representation of the torsional vibrations generated by the engine and compressor according to the solution according to the invention with regard to a second embodiment

7

a graphical representation of the speed curve in the second embodiment,

8

a graphical representation of the time course of the phase currents of a three-phase motor as a drive according to the second embodiment.

1 shows a piston compressor consisting essentially of a piston compressor 1 and a three-phase motor 2 . The piston compressor 1 is designed as a two-stage compressor unit and has two low-pressure cylinders 3a, 3b and a high-pressure cylinder 4 here. Coming from the atmosphere, the compressed air is first precompressed in the low-pressure cylinder 3a, 3b and then brought to an even higher pressure level by the high-pressure cylinder 4 before the compressed air produced is fed to the vehicle for further use.

The piston compressor 1 has a crankshaft 5, which is driven by the three-phase motor 2, for actuating the piston drive of the pistons—not shown in more detail—of the cylinders 3a, 3b and 4. The electric three-phase motor 2 is equipped with a frequency converter 6, via which the connection to a three-phase network 7 takes place. The frequency converter 6 is assigned an electronic control unit 8 which is structurally integrated therein. On the input side, the electronic control unit 8 receives the measurement signal from a position sensor 9 which is arranged in the area of the crankshaft 5 and which specifies the current angular position of the crankshaft 5 for the electronic control unit 8 .

2 shows a graphic representation of the torque curve in relation to an entire revolution of 0 to 360° of the crankshaft of a piston compressor of the prior art. The average torque of the drive is around 50 Nm (dotted line). In the course of the load torque _{M L} it can be seen that this has a maximum of about 140 Nm due to a pressure peak at an angular position of the crankshaft of about 200°. The curve of the load torque M _L shown is characteristic of two-stage piston compressors, as in figure 1 illustrated. The engine only reacts to the dominating pressure peak with a time delay and, as can be seen, builds up the engine torque M _M only out of phase at an angular position of the crankshaft of around 0°. Thus, the maximum engine torque _MM of approximately 75 _Nm only comes into effect when the load torque _ML of the piston compressor has already collapsed, here it has even reached its minimum. Due to this effect, three-phase motors even increase due to the design, the torsional vibration excitation in interaction with the piston compressors driven by it. The dominant pressure peak of the load torque _{M L} of around 150 Nm results from the compression of the second stage, namely the high-pressure cylinder. The three-phase drive reacts to this pressure peak and builds up its torque M _M of the curve shown. The area between the load moment M _L and the torque M _M of the engine is marked here as hatched and represents a measure of the vibration excitation around the crankshaft of the piston compressor. Due to the relatively large area of the hatched area, a relatively high disadvantageous vibration excitation can be assumed.

3 shows the torque curve of the torque M _M of the motor and the load moment M _L of the piston compressor for a full revolution of the crankshaft as a result of the vibration compensation according to the invention. In this embodiment, the motor is controlled in such a way that its torque M _M corresponds to the load moment M _L of the piston compressor follows. It follows from this that the content of the area between the load torque M _L and the engine torque M _M is minimal compared to the embodiment of the prior art explained above, so that very little vibration excitation takes place. Because of the control according to the invention, the driving motor builds up its torque M _M synchronously and in this respect in a demand-controlled manner with respect to the load torque M _L of the piston compressor to be mastered. Due to only minimal irregularities, there is an equally minimal vibration excitation.

4 consequently illustrates a uniform progression of the rotational speed n of the crankshaft over the entire revolution. This also roughly corresponds to the average course of the speed n'.

figure 5 shows the course of the phase currents over time with regard to the three phases of the three-phase motor, which here also turns out to be a fairly uniform respective sine curve due to the almost complete control-technical vibration compensation.

6 illustrated with respect to the second embodiment, the torque curve of the torque M _M and the load torque M _L for a full revolution of the Crankshaft, in contrast to the embodiment described above, here only a compensation with regard to the first order of the load torque curve of the piston compressor is carried out by the torque M _M of the three-phase motor. As a result, compared to the prior art explained above, a significantly smaller and evenly distributed surface area between the curves of the engine torque M _M of the variable-speed motor and the load torque M _L of the piston compressor contributes as a tightened area to excitation of vibrations. The vibration compensation achieved in this way can be regarded as sufficient for the application that is the subject of the invention.

7 consequently shows that the rotational speed n of the crankshaft fluctuates only slightly around the mean rotational speed n′. Extensive uniformity of the speed curve can be achieved here by compensating for the first order of the load torque curve of the piston compressor.

8 12 accordingly represents the time profile of the phase currents of the three phases of the three-phase motor, which, in contrast to the quasi-complete inventive compensation discussed above, reveals a slight non-uniformity. Nevertheless, the phase current progression is kept within narrow limits, which proves the effect of the solution according to the invention according to the second embodiment.

In a further exemplary embodiment, it is also possible, for example, to equip a single-stage piston compressor with the control-technical vibration compensation according to the invention instead of a two-stage piston compressor.

REFERENCE LIST

1

piston compressor

2

three-phase motor

3

low pressure cylinder

4

high pressure cylinder

5

crankshaft

6

frequency converter

7

three-phase source

8th

control unit

9

position sensor

ML

Load torque piston compressor

mm

Torque three-phase motor

n

rotation speed

n'

average speed

Claims (10)

1. Method for vibration compensation in a reciprocating compressor, the piston compressor (1) of which is driven by means of a crankshaft (5) of a three-phase motor (2) controlled by a frequency converter (6),
   characterised in that the current angular position of the crankshaft (5) of the piston compressor (1) is determined, and, based on this, a torque (M_M) that follows the load moment (M_L) of the piston compressor (1) is prescribed by the frequency converter (6) for the three-phase motor (2) in order to reduce the vibration excitation of the reciprocating compressor as a whole, wherein the torque (M_M) prescribed for the three-phase motor (2) corresponds to the first order of the load moment profile of the piston compressor (1).
2. Method according to claim 1,
   characterised in that the torque (M_M) prescribed for the three-phase motor (2) corresponds to the phase position and the load moment profile of the piston compressor (1).
3. Method according to claim 1,
   characterised in that the current angular position of the crankshaft (5) of the piston compressor (1) is determined by sensors
4. Method according to claim 1,
   characterised in that the deviation of the load moment (M_L) of the piston compressor (1) following the torque (M_M) for the three-phase motor (2) is set in such a way that it is less than 30%.
5. Method according to claim 1,
   characterised in that an increase of the torque (M_M) for the three-phase motor (2) is carried out by a corresponding increase of its operating voltage by the frequency converter (6).
6. Method according to any of the preceding claims,
   characterised in that, to compensate for fluctuations in speed, the torque (M_M) generated by the three-phase motor (2) is produced by the frequency converter (6) by a variation of the feed voltage and/or a variation of the pulse width.
7. Apparatus for vibration compensation in a reciprocating compressor, the piston compressor (1) of which is driven by means of a crankshaft (5) by a three-phase motor (2) controlled by a frequency converter (6),
   characterised in that the apparatus comprises a control unit (8) integrated into the frequency converter (6), wherein the current angular position of the crankshaft (5) of the piston compressor (1) can be determined by means of the control unit (8), and wherein, based on this, a torque (M_M) that corresponds to the load moment (M_L) of the piston compressor (1) for the three-phase motor (2) can be prescribed in order to reduce the vibration excitation of the reciprocating compressor as a whole.
8. Apparatus according to claim 7,
   characterised in that, in the region of the motor shaft or the crankshaft (5), there is arranged a position sensor (9) that measures its current angular position, in order to make the measured value available to the control unit (8).
9. Apparatus according to claim 7,
   characterised in that the frequency converter (6) is located in or at the three-phase motor (2)
10. Reciprocating compressor for producing compressed air, in particular for a vehicle, comprising a piston compressor (1), which drives a three-phase motor (2) flange-mounted thereon, and apparatus for vibration compensation according to any of the preceding claims 7 to 9.

Images