Method for operating and monitoring a motor

Abstract

The present invention relates to a method for operating a motor operatively connected to a compressor in an essentially noiseless and vibrationless manner, the method comprising the steps of providing a desired speed range for the motor, operating the motor at a number of selected speeds within the desired speed range, and determining, for each selected speed, a set of motor associated values, processing, for each selected motor speed, the determined set of motor associated values, and operating the motor at the speed or within a speed range in accordance with the processing of the determined set of motor associated values. The present invention further relates to a drive system configured for operating a motor operatively connected to a compressor in the essentially noiseless and vibrationless manner. The present invention further relates to a method for monitoring a motor operatively connected to a compressor, the method comprising the steps of comparing a predefined set of motor associated values with a determined set of motor associated values, and controlling the motor in according with a predetermined schedule in case the determined set of motor associated values deviate more than a certain amount from the predefined set of motor associated values.

Description

[0001] METHOD FOR OPERATING AND MONITORING A MOTOR

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a method, a drive system and motor system for operating a motor operatively connected to a compressor in an essentially noiseless and vibrationless manner using determined sets of motor associated values, such as a determined noise frequency spectrum in the audio band. The present invention further relates to a method for monitoring a motor operatively connected to a compressor by comparing predefined sets of motor associated values with determined or measured sets of motor associated values.

[0004] BACKGROUND OF THE INVENTION

[0005] Controlling and monitoring the operation of motor / compressor assemblies in a noiseless and vibrationless manner may be a rather complicated task in that vibration sensors may have to be secured to or integrated with the motor / compressor assemblies.

[0006] Vibration sensors secured to motor / compressor assemblies may potentially fall off, whereas integrated vibration sensors may increase the overall production cost of motor / compressor assemblies.

[0007] Thus, there is a need for a method that allows easy and reliable control and monitoring of motor / compressor assemblies so that they may be operated in an essentially noiseless and vibrationless manner.

[0008] It may be seen as an object of embodiments of the present invention to provide an easy way of controlling and monitoring a motor operatively connected to a compressor.

[0009] BRIEF DESCRIPTION OF THE INVENTION

[0010] The above-mentioned object is complied with by providing, in a first aspect, a method for operating a motor operatively connected to a compressor in an essentially noiseless and vibrationless manner, the method comprising the steps of a) providing a desired speed range for the motor, b) operating the motor at a number of selected speeds within the desired speed range, and determining, for each selected speed, a set of motor associated values, c) processing, for each selected motor speed, the determined set of motor associated values, and d) operating the motor at the speed or within a speed range in accordance with the processing of the determined set of motor associated values.

[0011] Thus, according to the first aspect the present invention relates to a method for operating a motor operatively connected to a compressor in an essentially noiseless and vibrationless manner. The motor may be a brushless DC motor / synchronous permanent magnet machine and the compressor may be a piston type compressor pump. The motor and compressor may be used in portable cooling devices for cooling for example pharmaceuticals.

[0012] The desired speed range for the motor may in principle be any speed range as long as the motor and the compressor are capable of handling the speed range. The desired speed range may be provided in various ways, such as via a look-up table. Typically, the speed range may be below 10000 rpm, such as between 2300 rpm and 4500 rpm with speed increments of for example 25 rpm, i.e. 2300 rpm, 2325 rpm, 2350 rpm etc.

[0013] The determined set of motor associated values for each selected motor speed may comprise a frequency spectrum originating from mechanical motor excitations. In the present context mechanical motor / compressor excitations are to be understood broadly including for example motor and / or compressor generated mechanical vibrations and / or generated pressure variations in the form of noise, such as noise within the audio range between 20 Hz and 20 kHz. In the case of generated mechanical vibrations a vibration sensor may be applied to determine the motor associated values, whereas in the case of generated pressure variations in the form of noise a microphone may be applied to determine the motor associated values.

[0014] As it will be discussed in further details below the origin of the measurable motor associated values (in the form of for example pressure variations) is mechanical vibrations of the motor and / or compressor during operation.

[0015] The set of motor associated values may be determined using one or more transducers, such as one or more pressure transducers, one or more accelerometers, one or more mechanical vibrations transducers etc. In one embodiment the set of motor associated values may be determined using one or more MEMS transducers. MEMS transducers are advantageous due to the limited dimensions of these transducers.

[0016] In one embodiment the set of motor associated values may comprise a noise frequency spectrum for each selected motor speed. The frequency spectrum may be determined using one or more microphones, such as MEMS microphones, in combination with a suitable processing algorithm where the noise generated by the motor and / or compressor is measured and subsequently processed using for example a Fast Fourier Transformation (FFT). Other suitable processing algorithms may involve Cepstrum analysis, waveform shape analysis, pulse countering or pass-band filtering with RMS calculation.

[0017] Determining the set of motor associated values using one or more microphones, such as MEMS microphones, is advantageous in that the one or more microphones may be positioned remote relative to the motor and / or compressor.

[0018] In order to account for unwanted disturbances method step b) may be repeated n times so that the set of motor associated values is repeatedly determined n times for each selected speed. Moreover, method step c) may involve that an average value of the determined n sets of motor associated values is calculated for each selected motor speed. Thus, in case each set of motor associated values involves a frequency spectrum a total of n frequency spectra (for each selected motor speed) is to be determined. The number of frequency spectra, n, may be 2, 5, 10, 25, 50, 100, 150, 200 or even higher.

[0019] An average value of the n frequency spectra may then be determined for each selected motor speed. The average value may be calculated by selecting a desired frequency range and finding the maximum acceleration within this range. It is in this respect noted that each motor / compressor speed has a corresponding „memory bin" that can store n-acceleration values. Thus, the maximum acceleration retrieved from the desired frequency range is „pushed" into this bin. In the present context „pushing" means the oldest acceleration value is discarded while the new is kept. Thus, the „memory bin" will always contain the newest n- acceleration values. Finally, an arithmetic average value is determined by summing the bin's n-acceleration values and dividing by n.

[0020] A low average value is advantageous in that a low average value represents a low noise level from the motor and compressor. In one embodiment, method step d) may involve operating the motor at the speed having the lowest average value, i.e. at the speed generating the smallest mechanical vibrations and generating the lowest noise level.

[0021] In a second aspect the present invention relates to a drive system configured for operating a motor operatively connected to a compressor in an essentially noiseless and vibrationless manner, the drive system comprising a controller configured for a) operating the motor at a number of selected speeds within a desired speed range, and determining, for each selected speed, a set of motor associated values, b) processing, for each selected motor speed, the determined set of motor associated values, and c) operating the motor at the speed or within a speed range in accordance with the processing of the determined set of motor associated values.

[0022] Thus, according to the second aspect the present invention relates to a drive system for operating a motor operatively connected to a compressor in an essentially noiseless and vibrationless manner, i.e. a drive system for performing the method according to the first aspect.

[0023] Again, the motor may be a brushless DC motor / synchronous permanent magnet machine and the compressor may be a piston type compressor pump. The motor and compressor may as already mentioned be used in portable cooling devices for cooling for example pharmaceuticals.

[0024] The desired speed range for the motor may in principle be any speed range as long as the motor and the compressor are capable of handling the speed range, and the desired speed range may be provided from for example a look-up table. Typically, the speed range may be below 10000 rpm, such as between 2300 and 4500 rpm with speed increments of for example 25 rpm, i.e. 2300 rpm, 2325 rpm, 2350 rpm etc.

[0025] Similar to the first aspect the determined set of motor associated values for each selected motor speed may comprise a frequency spectrum originating from mechanical motor excitations. In the present context mechanical motor / compressor excitations are to be understood broadly including for example motor and / or compressor generated mechanical vibrations and / or generated pressure variations in the form of noise, such as noise within the audio range between 20 Hz and 20 kHz. Again, in the case of generated mechanical vibrations a vibration sensor may be applied to determine the motor associated values, whereas in the case of generated pressure variations in the form of noise a microphone may be applied to determine the motor associated values.

[0026] The set of motor associated values may be determined using one or more transducers, such as one or more pressure transducers, one or more accelerometers, one or more mechanical vibrations transducers etc. In one embodiment the set of motor associated values may be determined using one or more MEMS transducers. As already mentioned MEMS transducers are advantageous due to the limited dimensions of these transducers. In one embodiment the set of motor associated values may comprise a noise frequency spectrum for each selected motor speed. The frequency spectrum may be determined using one or more microphones, such as MEMS microphones, in combination with a suitable processing algorithm where the noise generated by the motor and / or compressor is measured and subsequently processed using for example FFT. Other suitable processing algorithms may involve Cepstrum analysis, waveform shape analysis, pulse countering or pass-band filtering with RMS calculation.

[0027] Again, determining the set of motor associated values using one or more microphones, such as MEMS microphones, is advantageous in that the one or more microphones may be positioned remote relative to the motor and / or compressor.

[0028] In order to account for unwanted disturbances method step a) may be repeated n times so that the set of motor associated values is repeatedly determined n times for each selected speed. Moreover, method step b) may involve that an average value of the determined n sets of motor associated values is calculated for each selected motor speed. Thus, in case each set of motor associated values involves a frequency spectrum a total of n frequency spectra (for each selected motor speed) is to be determined. The number of frequency spectra, n, may be 2, 5, 10, 25, 50, 100, 150, 200 or even higher.

[0029] An average value of the n frequency spectra may then be determined for each selected motor speed. As already addressed, the average value may be calculated by selecting a desired frequency range and finding the maximum acceleration within this range. It is in this respect noted that each motor / compressor speed has a corresponding „memory bin" that can store n-acceleration values. Thus, the maximum acceleration retrieved from the desired frequency range is „pushed" into this bin. In the present context „pushing" means the oldest acceleration value is discarded while the new is kept. Thus, the „memory bin" will always contain the newest n-acceleration values. Finally, an arithmetic average value is determined by summing the bin's n-acceleration values and dividing by n.

[0030] A low average value is advantageous in that a low average value represents a low noise level from the motor and compressor. In one embodiment, method step c) may involve operating the motor at the speed having the lowest average value, i.e. at the speed generating the smallest mechanical vibrations and generating the lowest noise level.

[0031] In a third aspect the present invention relates to a motor system comprising a motor and the drive system according to the second aspect for driving the motor. In a fourth aspect the present invention relates to a method for monitoring a motor operatively connected to a compressor, the method comprising the steps of a) providing a predefined set of motor associated values, b) operating the motor at a selected speed and determining a set of motor associated values, c) comparing the predefined set of motor associated values with the determined set of motor associated values, and d) controlling the motor in according with a predetermined schedule in case the determined set of motor associated values deviate more than a certain amount from the predefined set of motor associated values.

[0032] Thus, according to the fourth aspect the present invention relates to a method for monitoring a motor operatively connected to a compressor.

[0033] The method according to the fourth aspect comprises the steps of comparing a predefined set of motor associated values with a determined set of motor associated values, and controlling the motor in according with a predetermined schedule in case the determined set of motor associated values deviate more than a certain amount from the predefined set of motor associated values. Such a deviation, i.e. more than a certain amount, may indicate a faulty motor and / or faulty compressor.

[0034] The certain amount, i.e. the limit of deviation between the determined set of motor associated values and the predefined set of motor associated values, may be in the range 1- 40%, such as in the range 2-30%, such as in the range 3-25%, such as in the range 4-20%, such as in the range 5-15%, such as in the range 5-10% or even a specific value. In case of a specific value a go / no go approach may be applied. Thus, if the average value is below a specified value, then no problem arises. If else, the algorithm may log an error message.

[0035] It should though be noted that by having different ranges is advantageous in that it may help identifying if the compressor is deteriorating over time. To determine this, the logging of the acceleration value vs. time should be continued.

[0036] Again, the motor may be a brushless DC motor / synchronous permanent magnet machine and the compressor may be a piston type compressor pump. The motor and compressor may as already mentioned be used in portable cooling devices for cooling for example pharmaceuticals.

[0037] In one embodiment the predetermined schedule of method step d) may involve changing the speed of the motor, such as increasing the speed of the motor, decreasing the speed of the motor or bringing the motor to a complete stillstand.

[0038] The motor may in principle be operated at any speed as long as the motor and the compressor are capable of handling the speed. Typically, the speed may be below 10000 rpm, such as between 2300 and 4500 rpm. The predefined set of motor associated values may be provided from for example a look-up table.

[0039] Similar to the first and second aspects the sets of motor associated values (both predefined and determined) may comprise a frequency spectrum originating from mechanical motor excitations. In the present context mechanical motor / compressor excitations are to be understood broadly including for example motor and / or compressor generated mechanical vibrations and / or generated pressure variations in the form of noise, such as noise within the audio range between 20 Hz and 20 kHz. Again, in the case of generated mechanical vibrations a vibration sensor may be applied to determine the motor associated values, whereas in the case of generated pressure variations in the form of noise a microphone may be applied to determine the motor associated values.

[0040] The set of motor associated values may be determined using one or more transducers, such as one or more pressure transducers, one or more accelerometers, one or more mechanical vibrations transducers etc. In one embodiment the set of motor associated values may be determined using one or more MEMS transducers. MEMS transducers are advantageous due to the limited dimensions of these transducers.

[0041] In one embodiment the set of motor associated values (both predefined and determined) may comprise a noise frequency spectrum. The frequency spectrum may be determined using one or more MEMS microphones in combination with a suitable processing algorithm where the noise generated by the motor and / or compressor is measured and subsequently processed using for example a FFT. Other suitable processing algorithms may involve Cepstrum analysis, waveform shape analysis, pulse countering or pass-band filtering with RMS calculation.

[0042] In order to account for unwanted disturbances method step b) may be repeated n times so that the set of motor associated values is repeatedly determined n times for the selected speed. In case each set of motor associated values involves a frequency spectrum a total of n frequency spectra is to be determined. The number of frequency spectra, n, may be 2, 5, 10, 25, 50, 100, 150, 200 or even higher.

[0043] In general, the various aspects of the invention may be combined and coupled in any way possible within the scope of the invention. These and other aspects, features and / or advantages of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0044] BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The present invention will now be described in further details with reference to the accompanying Figs, where

[0046] Fig. 1 illustrates a set up for determining sets of motor associated values using one or more microphones,

[0047] Fig. 2 shows a determined noise frequency spectrum,

[0048] Fig. 3 shows a flow-chart of a method for operating a motor operatively connected to a compressor in an essentially noiseless and vibrationless manner, and

[0049] Fig. 4 shows a flow-chart of a method for monitoring a motor operatively connected to a compressor according to the present invention.

[0050] DETAILED DESCRIPTION OF THE INVENTION

[0051] In general, the present invention relates to a method for operating a motor operatively connected to a compressor in an essentially noiseless and vibrationless manner. The method comprises the steps of operating the motor at a number of selected speeds within a desired speed range, and determining, for each selected speed, a set of motor associated values. For each selected motor speed, the determined set of motor associated values, is processed, and the motor is operated at the speed or within a speed range in accordance with the processing of the determined set of motor associated values. The present invention also relates to an associated drive system configured for operating a motor operatively connected to a compressor in the essentially noiseless and vibrationless manner.

[0052] Moreover, the present invention relates to a method for monitoring a motor operatively connected to a compressor. The method comprises the steps of comparing a predefined set of motor associated values with a determined set of motor associated values, and controlling the motor in according with a predetermined schedule in case the determined set of motor associated values deviate more than a certain amount from the predefined set of motor associated values.

[0053] Fig. 1 shows a motor 101 operatively connected to a compressor 102 via a rotatable shaft 103. During operation of the motor 101 and the compressor 102 mechanical vibrations are generated due to small mechanical imbalances in both the motor 101, the compressor 102 and the rotatable shaft 103. As already mentioned, the motor 101 may be a brushless DC motor / synchronous permanent magnet machine and the compressor 102 may be a piston type compressor pump. The motor 101 and compressor 102 may as also already mentioned be used in portable cooling devices for cooling for example pharmaceuticals. The motor 101 may be powered by a photovoltaic system (not shown) comprising a number of photovoltaic panels and / or a traditional AC power grid a available.

[0054] The mechanical vibrations generated by the motor 101, the compressor 102 and the rotatable shaft 103 in combination are, in Fig. 1, measured as pressure variations 105, 106 (noise) using a suitable microphone 104, such as a MEMS microphone with a suitable sensitivity and frequency response. The correlation between mechanical vibrations and the generated pressure variations is discussed in detail in relation to Fig. 2. In an alternative approach to Fig. 1 the mechanical vibrations generated by the motor 101, the compressor 102 and the rotatable shaft 103 could be measured using vibration sensors / accelerometers secured, or by other means mechanically coupled, to at least the motor 101 and the compressor 102.

[0055] Returning now to Fig. 1 the pressure variations 105, 106 measured by the microphone 104 are processed by an appropriate algorithm in the computer 107, such as a FFT algorithm. In this way a frequency spectrum representing mechanical motor / compressor excitations may be generated on the basis of measured pressure variations in the form of noise.

[0056] Turning now to Fig. 2a two mechanical motor vibration curves 201, 202 within the frequency range 100-1600 Hz are depicted. Vibration curve 201 is an average of 3 vibration curves, whereas vibration curve 202 is an average of 100 vibration curves. Vibration curves 201, 202 have both been measured using a vibration sensor secured to the PCB of the motor controller. Fig. 2a further shows an acoustical third curve 203 which has been measured with a MEMS microphone. A FFT algorithm has been applied to derive the vibration / acoustical curves 201, 202 and 203.

[0057] As seen in Fig. 2a the correlation between the vibration curves 201, 202 and the acoustical third curve 203 is almost perfect. Thus, from the acoustical third curve 203 alone the mechanical vibration spectrum of the motor, the compressor and / or the shaft connecting them can be determined.

[0058] Fig. 2b shows an enlarged portion of Fig. 2a in the frequency range 700-1100 Hz where the correlation between the vibration curves 201, 202 and the acoustical third curve 203 is more distinct and clear.

[0059] Fig. 3 shows a flow-chart of a method for operating a motor operatively connected to a compressor in an essentially noiseless and vibrationless manner. As depicted in Fig. 3 the following four steps: a) providing a desired speed range for the motor, b) operating the motor at a number of selected speeds within the desired speed range, and determining, for each selected speed, a set of motor associated values, c) processing, for each selected motor speed, the determined set of motor associated values, and d) operating the motor at the speed or within a speed range in accordance with the processing of the determined set of motor associated values.

[0060] The method steps depicted in Fig. 3 may for example be carried out by the computer shown in Fig. 1. Alternatively, the method may be carried out by a controller of a drive system configured to drive the motor and the compressor operatively connected thereto.

[0061] Again, the motor may be a brushless DC motor / synchronous permanent magnet machine and the compressor may be a piston type compressor pump. The motor and compressor may as already mentioned be used in portable cooling devices for cooling for example pharmaceuticals.

[0062] As already mentioned, the desired speed range for the motor may in principle be any speed range as long as the motor and the compressor are capable of handling the speed range. The desired speed range may be prestored and thus provided via a look-up table or similar storing arrangement. The speed range is typically up to 10000 rpm, such as between 2300 and 4500 rpm with speed increments (selected speeds) of for example 25 rpm, i.e. 2300 rpm, 2325 rpm, 2350 rpm etc. The determined set of motor associated values for each selected motor speed may be provided as depicted in Fig. 1 where a microphone (or microphones), such as a MEMS microphone (or microphones), measures mechanical motor / compressor excited pressure variations. As already mentioned, other types of transducers may also be applicable.

[0063] In the present context mechanical motor / compressor excitations are to be understood broadly including for example motor and / or compressor generated mechanical vibrations and / or motor and / or compressor generated pressure variations in the form of detectable noise. In a preferred embodiment the set of motor associated values is determined using one or more pressure transducers, such as one or more MEMS microphones. MEMS microphones are advantageous due to the limited dimensions of these microphones.

[0064] As depicted and discussed in relation to Fig. 2 the set of motor associated values comprises a FFT frequency spectrum of the measured pressure variations by one or more MEMS microphones. As already mentioned, other suitable processing algorithms may involve Cepstrum analysis, waveform shape analysis, pulse countering or pass-band filtering with RMS calculation.

[0065] As already discussed, method step b) is preferably repeated n times so that the set of motor associated values is repeatedly determined n times for each selected speed. Moreover, method step c) preferably involves that an average value of the determined n sets of motor associated values is calculated for each selected motor speed. The number of determined frequency spectra, n, may be 2, 5, 10, 25, 50, 100, 150, 200 or even higher. An average value of the n frequency spectra is then determined for each selected motor speed. The average value may be determined as outlined above, i.e. by using a memory bin.

[0066] A low average value is advantageous in that a low average value represents a low noise level from the motor and / or compressor, and consequently a low mechanical vibration level of the motor and / or compressor. Preferably method step d) involves that the motor and compressor are operated at the speed having the lowest average value, i.e. at the speed generating the lowest noise level due to the lowest mechanical vibration level.

[0067] Turning now to Fig. 4 a flow-chart of a method for monitoring a motor operatively connected to a compressor is depicted. As depicted in Fig. 4 the method comprises the following four steps: a) providing a predefined set of motor associated values, b) operating the motor at a selected speed and determining a set of motor associated values, c) comparing the predefined set of motor associated values with the determined set of motor associated values, and d) controlling the motor in according with a predetermined schedule in case the determined set of motor associated values deviate more than a certain amount from the predefined set of motor associated values.

[0068] The monitoring method steps depicted in Fig. 4 may also be carried out by the computer shown in Fig. 1. Alternatively, the method may be carried out by a controller of a drive system configured to drive the motor and the compressor operatively connected thereto.

[0069] Again, the motor may be a brushless DC motor / synchronous permanent magnet machine and the compressor may be a piston type compressor pump. The motor and compressor may as already mentioned be used in portable cooling devices for cooling for example pharmaceuticals.

[0070] As already mentioned, a deviation (between the determined set of motor associated values and the predefined set of motor associated values) that exceeds the certain amount may indicate a faulty motor and / or faulty compressor. The certain amount, i.e. the limit of deviation between the determined set of motor associated values and the predefined set of motor associated values, may be in the range 1-40%, such as in the range 2-30%, such as in the range 3-25%, such as in the range 4-20%, such as in the range 5-15%, such as in the range 5-10% or even a specific value. In case of a specific value a go / no go approach may be applied. Thus, if the average value is below a specified value, then no problem arises. If else, the algorithm may log an error message.

[0071] It should though be noted that by having different ranges is advantageous in that it may help identifying if the compressor is deteriorating over time. To determine this, the logging of the acceleration value vs. time should be continued.

[0072] The step of comparing the determined set of motor associated values and the predefined set of motor associated values, i.e. method step d) may involve changing the speed of the motor, such as increasing the speed of the motor, decreasing the speed of the motor or even bringing the motor to a complete stillstand. In relation to method step b) the motor may in principle be operated at any speed as long as the motor and the compressor are capable of handling the speed. Typically, the motor speed is below 10000 rpm, such as between 2300 and 4500 rpm.

[0073] The predefined set of motor associated values may be prestored and thus provided via a look-up table or similar storing arrangement.

[0074] Regarding the sets of motor associated values (both the predefined and the determined) these may comprise a frequency spectrum originating from mechanical motor excitations. In the present context mechanical motor / compressor excitations are to be understood broadly including for example motor and / or compressor generated mechanical vibrations and / or motor and / or compressor generated pressure variations in the form of detectable noise.

[0075] In a preferred embodiment the set of motor associated values is determined using one or more pressure transducers, such as one or more MEMS microphones. MEMS microphones are advantageous due to the limited dimensions of these microphones. As already mentioned, other types of transducers may also be applicable. As depicted and discussed in relation to Fig. 2 the set of motor associated values comprises a FFT frequency spectrum of the measured pressure variations by one or more MEMS microphones. As already mentioned, other suitable processing algorithms may involve Cepstrum analysis, waveform shape analysis, pulse countering or pass-band filtering with RMS calculation.

[0076] In order to account for unwanted disturbances method step b) may be repeated n times so that the set of motor associated values is repeatedly determined n times for the selected speed. In case each set of motor associated values involves a frequency spectrum a total of n frequency spectra is to be determined. The number of frequency spectra, n, may be 2, 5, 10, 25, 50, 100, 150, 200 or even higher.

[0077] Although the invention has been discussed in the foregoing with reference to exemplary embodiments of the invention, the invention is not restricted to these particular embodiments which can be varied in many ways without departing from the invention. The discussed exemplary embodiments shall therefore not be used to construe the appended claims strictly in accordance therewith. On the contrary, the embodiments are merely intended to explain the wording of the appended claims, without intent to limit the claims to these exemplary embodiments. The scope of protection of the invention shall therefore be construed in accordance with the appended claims only, wherein a possible ambiguity in the wording of the claims shall be resolved using these exemplary embodiments.

Claims

CLAIMS1. A method for operating a motor operatively connected to a compressor in an essentially noiseless and vibrationless manner, the method comprising the steps of a) providing a desired speed range for the motor, b) operating the motor at a number of selected speeds within the desired speed range, and determining, for each selected speed, a set of motor associated values, c) processing, for each selected motor speed, the determined set of motor associated values, and d) operating the motor at the speed or within a speed range in accordance with the processing of the determined set of motor associated values.

2. A method according to claim 1, wherein the determined set of motor associated values for each selected motor speed comprises a frequency spectrum of mechanical motor excitations.

3. A method according to claim 1 or 2, wherein the set of motor associated values are determined using one or more transducers, such as one or more MEMS transducers.

4. A method according to any of the preceding claims, wherein step b) is repeated n times so that the set of motor associated values is repeatedly determined n times for each selected speed, and wherein step c) involves that an average value of the determined n sets of motor associated values is calculated for each selected motor speed.

5. A method according to claim 4, wherein step d) involves operating the motor at the speed having the lowest average value.

6. A method according to any of the preceding claims, wherein the desired speed range for the motor is below 10000 rpm.

7. A drive system configured for operating a motor operatively connected to a compressor in an essentially noiseless and vibrationless manner, the drive system comprising a controller configured fora) operating the motor at a number of selected speeds within a desired speed range, and determining, for each selected speed, a set of motor associated values, b) processing, for each selected motor speed, the determined set of motor associated values, and c) operating the motor at the speed or within a speed range in accordance with the processing of the determined set of motor associated values.

8. A drive system according to claim 7, wherein the determined set of motor associated values for each selected motor speed comprises a frequency spectrum of mechanical motor excitations.

9. A drive system according to claim 7 or 8, further comprising one or more transducers, such as one or more MEMS transducers, for measuring the set of motor associated values.

10. A drive system according to any of claims 7-9, wherein the controller is configured for repeating step a) n number of times so that the set of motor associated values is repeatedly determined n times for each selected speed, and configured for calculating, in relation to step b) an average value of the determined n sets of motor associated values for each selected motor speed.

11. A drive system according to claim 10, wherein the controller is configured for operating, in relation to step d) the motor at the speed having the lowest average value.

12. A motor system comprising a motor and the drive system according to any of claims 7-11 for driving the motor.

13. A method for monitoring a motor operatively connected to a compressor, the method comprising the steps of a) providing a predefined set of motor associated values, b) operating the motor at a selected speed and determining a set of motor associated values, c) comparing the predefined set of motor associated values with the determined set of motor associated values, andd) controlling the motor in according with a predetermined schedule in case the determined set of motor associated values deviate more than a certain amount from the predefined set of motor associated values.

14. A method according to claim 13, wherein step d) involves changing the speed of the motor, such as bringing the motor to complete stillstand.

15. A method according to claim 13 or 14, wherein the determined set of motor associated values comprises a frequency spectrum of mechanical motor excitations.

16. A method according to any of claims 13-15, wherein the set of motor associated values are determined using one or more transducers, such as one or more MEMS transducers.

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