Method for prolonging the life of a rolling element bearing

Abstract

A method for extending the life of a rolling element bearing of an electric motor, the method comprising: a) defining a first set of control parameter values; b) estimating a first remaining service life (RUL) of the rolling element bearing based on a signal providing vibration measurements of the rolling element bearing obtained when the motor is controlled by the first set of control parameter values; c) changing at least one control parameter value in the first set of control parameter values ​​to obtain a second set of control parameter values; d) estimating a second RUL of the rolling element bearing based on a signal obtained when the motor is controlled by the second set of control parameter values; e) comparing the first RUL with the second RUL; f) if the second RUL is longer than the first RUL, replacing the control parameter values ​​in the first set of control parameter values ​​with the control parameter values ​​in the second set of control parameter values, and replacing the first RUL value with the value of the second RUL; and g) repeatedly performing steps c)-f) during operation of the motor.

Description

Technical Field

[0001] This disclosure generally relates to rolling element bearings used in electric motors. Background Technology

[0002] Electric motors are a key component for achieving modern, efficient production. For a company to remain competitive globally, its motors should operate 24 / 7.

[0003] More than half of electric motor failures are caused by bearing failure.

[0004] Improper handling of bearings during their service life is a major cause of early failure.

[0005] In academia and industry, many researchers are focusing on how to detect early-stage bearing failures. It is understood that due to the randomness of failure types, there are numerous types of failures, making identification very complex. Therefore, artificial intelligence algorithms are often employed. However, detecting bearing failures only provides the benefit of planning bearing replacement within the next maintenance cycle.

[0006] US6326758 discloses a model-based diagnostic method and qualitative / accidental model information. The aim is to monitor health status and then take action when an impending failure is detected. The goal is to change control parameters and verify that the system can operate reliably until the next planned maintenance. The method involves health assessment techniques to evaluate machine condition. A health indication is then given to the controller, where a model of the entire system is determined. Finally, a multi-objective optimization method is involved to optimize system performance. Different types of parameters are given as inputs to the optimization routines, such as control parameters, operating conditions, etc. The ultimate goal is to take action in the control system before an impending failure renders the control system inoperable. Summary of the Invention

[0007] The general objective of this disclosure is to provide a method for solving or at least mitigating problems in the prior art.

[0008] Therefore, according to a first aspect of this disclosure, a method for extending the life of a rolling element bearing of an electric motor is provided, the method comprising: a) defining a first set of control parameter values; b) estimating the remaining service life (RUL) of the first rolling element bearing based on a signal providing vibration measurements of the rolling element bearing obtained when the motor is controlled by the first set of control parameter values; c) changing at least one control parameter value in the first set of control parameter values ​​to obtain a second set of control parameter values; d) estimating a second RUL of the rolling element bearing based on a signal obtained when the motor is controlled by the second set of control parameter values; e) comparing the first RUL with the second RUL; f) if the second RUL is longer than the first RUL, replacing the control parameter value in the first set of control parameter values ​​with the control parameter value of the second set of control parameter values, and replacing the value of the first RUL with the value of the second RUL; and g) repeatedly performing steps c)-f) during operation of the motor.

[0009] This iterative method allows for the extension of the lifespan of rolling element bearings without requiring optimization routines. The optimization routines disclosed in US6326758 require the existence of a model. If this is not available, a signal must be injected, the system response must be analyzed, and the transfer function (stimulus-response) must be calculated. The transfer function is then considered in the optimization function.

[0010] For this method, only the trend direction estimated by RUL is needed to draw conclusions about the impact of changes in control parameter values.

[0011] This also allows for implementation with minimal hardware resources.

[0012] Furthermore, according to US6326758, the optimality of its solution depends on the chosen optimization function and its members. Constraints are also applied within the optimization routine, so the result is always optimal. However, this requirement makes the method difficult to implement in practice. According to this method, power converters / drivers can perform actions and decisions similar to humans, thus offering reasonable advantages and avoiding safety issues. On the other hand, if any member of the optimization function in US6326758 is faulty, the system will fail.

[0013] RUL is the amount of time that a group of obviously identical bearings completes or exceeds before fatigue spalling occurs.

[0014] The estimation of the first and second RUL can preferably be performed during steady-state conditions. This is because the estimation of RUL is complex and time-consuming, and may otherwise be affected by load or speed transients.

[0015] The method in step c) may involve progressively changing the value of at least one control parameter in each iteration. Therefore, this method can be search-based. The progressive changes can be performed incrementally or decrementally.

[0016] If the second RUL is longer than the first RUL, the same at least one control parameter value that was changed in the current step c) can be changed in the next iteration in step c).

[0017] If the second RUL is shorter than the first RUL, at least one control parameter value that remained unchanged in the current iteration of step c) can be changed in the next iteration of step c). A control parameter value that remained unchanged in the current iteration can be changed in the next iteration, provided that a new combination of control parameters is available.

[0018] The signal can originate from any sensor, and its processed or unprocessed output can be directly correlated with the level of mechanical vibration. The signal can be, for example, a vibration signal or a current signal. For current signals, the harmonic content increases in the event of a mechanical fault. Observing changes in the amplitude of certain harmonics can provide information about the vibration. Sensors can be, for example, one or more accelerometers such as a triaxial accelerometer, a current sensor, or one or more smart sensors such as ABB Ability. TM A smart sensor, or one or more capacitive sensors.

[0019] Control parameters can be, for example, torque reference, speed reference, switching frequency, or modulation. The switching frequency is the frequency of the switching semiconductors in a power converter configured to control the motor. The switching frequency is also the frequency of a pulse-width modulated carrier signal. The carrier signal can be a triangular wave. Modulation refers to the modulating signal, which is also used for pulse width modulation. The modulating signal can be a sine wave, but according to some examples, it can have a varying shape. Therefore, according to one example, the modulation of the modulating signal can be a control parameter.

[0020] Step c) may involve controlling a power converter that controls the motor using a second set of control parameter values.

[0021] According to one embodiment, the estimation involves using a degradation model of a rolling element bearing, using an extended Kalman filter, or using a neural network.

[0022] The estimation steps b) and d) can be performed using model-based or data-driven prediagnosis.

[0023] In model-based diagnostic methods, rolling element bearings and their degradation phenomena are represented by a set of mathematical laws used to estimate the resistance level (RUL). These mathematical laws / models can be, for example, L... 10 Predictive models.

[0024] In data-driven prediagnostic methods, sensor signals undergo a learning phase, during which they are transformed into a reliable model of degenerative behavior. This behavioral model is a degradation model. Features extracted from the sensor signals during the learning phase are used to obtain the degradation model. The degradation model can then be used in the development phase, either online with the signals mentioned in step a), or using the features extracted from the signals as input to the degradation model.

[0025] According to one embodiment, step f) involves replacing the control parameter value in the first set of control parameter values ​​only if the second RUL deviates from the first RUL by more than a threshold. In this way, the motor will be less disturbed by the control action in step c).

[0026] One embodiment includes, prior to step c): A) determining the harmonic content of the signal; B) changing at least one control parameter value from a third set of control parameter values ​​if there is an amplitude above a threshold in the harmonic content; and C) repeating steps A)-B) until a third set of control parameter values ​​is found that reduces the amplitude to below the threshold; and D) performing step cg), wherein the at least one control parameter value changed in step c) is at least one control parameter associated with at least one control parameter value used in step B), and wherein the change in at least one control parameter value in step B) is less than the change in step c).

[0027] Steps A) to C) are responsible for the dynamic conditions of the motor.

[0028] Furthermore, steps A) through C) perform an investigation into how to modify the control to increase the life of the rolling element bearing. Estimating the RUL is a complex task and therefore more time-consuming than the processing in steps A) through C). Step c) subsequently involves making significant changes to one or more control parameters found by performing steps A) through C). The changes performed in step c) may be large enough to alter the motor's operating point. The changes performed in step B) can preferably be small enough that they do not change the motor's operating point.

[0029] Step B) may involve comparing the amplitude of the harmonic content with the corresponding amplitude of the previously obtained harmonic content of the signal, and performing step D if the amplitude has decreased compared to the corresponding amplitude and is below a threshold.

[0030] According to one embodiment, at least one control parameter value in step B) is changed progressively in each iteration.

[0031] The gradual changes in step B can be performed incrementally or decrementally.

[0032] According to one embodiment, the change in step c) is based on at least one control parameter value selected in step B). The change in the control parameter value in step c) can be a gradual change from the control parameter value selected during the last execution of step B).

[0033] According to one embodiment, in the initial iteration of step B), the control parameter value of an individual control parameter is changed, and in subsequent iterations, when changes to all individual control parameters have been performed, the combination of control parameter values ​​is changed. Therefore, in the initial iteration of step B), only the control parameter value of a single control parameter is changed, while when / if all control parameters have been tested individually in different iterations, changes to the combination of control parameter values ​​for several control parameters are performed.

[0034] According to one embodiment, steps A)-C) form an internal control loop, and steps c)-g) form an external control loop. The internal and external control loops can operate independently of each other. However, the external control loop may sometimes receive information from the internal control loop regarding changes to a certain control parameter value.

[0035] Compared to external control loops, internal control loops can be high-speed control loops.

[0036] According to a second aspect of this disclosure, a computer program including computer code is provided, which, when executed by a processing circuit of a control system, causes the control system to perform the steps of the method of the first aspect.

[0037] According to a third aspect of this disclosure, a control system for extending the life of a rolling element bearing of an electric motor is provided. The control system includes: a storage medium containing computer code; and processing circuitry, wherein when the processing circuitry executes the computer code, the control system is configured to: a) define a first set of control parameter values; b) estimate a first remaining service life (RUL) of the rolling element bearing based on a signal providing vibration measurements of the rolling element bearing obtained when the motor is controlled by the first set of control parameter values; c) change at least one control parameter value in the first set of control parameter values ​​to obtain a second set of control parameter values; d) estimate a second RUL of the rolling element bearing based on a signal obtained when the motor is controlled by the second set of control parameter values; e) compare the first RUL with the second RUL; f) if the second RUL is longer than the first RUL, replace the control parameter value in the first set of control parameter values ​​with the control parameter value of the second set of control parameter values, and replace the first RUL value with the value of the second RUL; and g) repeatedly perform steps c)-f) during operation of the motor.

[0038] According to one embodiment, the processing circuit is configured to estimate the first RUL and the second RUL using a degradation model of the rolling element bearing or an extended Kalman filter.

[0039] According to one embodiment, the processing circuit is configured to, before step c),: A) determine the harmonic content of the signal, B) change at least one control parameter value in a third set of control parameter values ​​if there is an amplitude above a threshold in the harmonic content, and C) repeat steps A)-B) until a third set of control parameter values ​​is found that reduces the amplitude to below the threshold; D) perform step cg), wherein the at least one control parameter value changed in step c) is at least one control parameter associated with at least one control parameter value used in step B), and wherein the change of at least one control parameter value in step B) is less than the change in step c).

[0040] According to one embodiment, the processing circuit is configured to progressively change at least one control parameter value in step B) in each iteration.

[0041] According to one embodiment, the processing circuit is configured to perform the change in step c) based on at least one control parameter value selected in step B).

[0042] According to one embodiment, the processing circuit is configured to: change the control parameter value of an individual control parameter in the initial iteration of step B), and change the combination of control parameter values ​​of the control parameters in subsequent iterations when changes to all individual control parameters have been performed.

[0043] The processing circuit can be configured to change at least one control parameter value in step c) if the second RUL deviates from the first RUL by more than a threshold.

[0044] Generally, unless otherwise expressly defined herein, all terms used in the claims shall be interpreted according to their ordinary meaning in the art. Unless otherwise expressly stated, all references to “a / an / the element, device, assembly, component, etc.” shall be publicly interpreted as referring to at least one instance of the element, device, assembly, component, etc. Attached Figure Description

[0045] Specific embodiments of the inventive concept will now be described by way of example with reference to the accompanying drawings, in which:

[0046] Figure 1 An example of a control system for extending the life of rolling element bearings is illustrated schematically.

[0047] Figure 2 The illustration shows including Figure 1 The machine assembly of the control system and motor;

[0048] Figure 3 A flowchart of the internal control loop is shown; and

[0049] Figure 4 A flowchart of the external control loop is shown. Detailed Implementation

[0050] The inventive concept will now be described more fully below with reference to the accompanying drawings, in which exemplary embodiments are illustrated. However, the inventive concept can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete and will fully express the scope of the inventive concept to those skilled in the art. Throughout the description, similar numerals refer to similar elements.

[0051] Figure 1 A block diagram illustrating an example of control system 1 is provided. Control system 1 is configured to control a power converter that controls a motor. Control system 1 is configured to control the power converter in a manner that extends the life of the rolling element bearings of the motor.

[0052] The control system 1 includes an input unit 3 configured to receive signals from one or more sensors. These signals provide vibration measurements of the rolling element bearing. The one or more sensors may be, for example, an accelerometer configured to detect mechanical vibrations in the rolling element bearing, a current sensor configured to measure the phase current of a motor, one or more smart sensors measuring mechanical vibrations or key performance indicators (KPIs), or a capacitive sensor configured to detect radial displacement of the rolling element bearing.

[0053] The control system 1 includes a processing circuit 5 and may include a storage medium 7.

[0054] The storage medium 7 may include a computer program that, when executed by the processing circuitry 7, causes the control system 1 to perform the methods disclosed herein.

[0055] The processing circuit 5 may be one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), application-specific integrated circuit (ASIC), field-programmable gate array (FPGA), etc., and may be any combination thereof, capable of performing any operation related to motor control disclosed herein.

[0056] The storage medium 7 may be embodied, for example, as a memory such as random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM) or electrically erasable programmable read-only memory (EEPROM), and more specifically as a non-volatile storage medium of a device in an external memory such as a USB (Universal Serial Bus) memory or flash memory such as a compact flash memory.

[0057] Figure 2 An example of machine assembly 9 is shown. Machine assembly 9 includes a motor 11. Motor 11 is a rotary motor. Motor 11 can be a motor or a generator. Motor 11 in Figure 2 The image is shown in longitudinal section.

[0058] The motor 11 includes a stator 11a and a rotor 11b. The stator 11a and rotor 11b are configured to interact electromagnetically with each other. The rotor 11b includes a shaft 11c. The shaft 11c is rotatable about a longitudinal axis A.

[0059] The motor 11 includes rolling element bearings 13 and 15 attached to the shaft 11c. The rolling element bearings 13 and 15 enable the shaft 11c to rotate.

[0060] Rolling element bearing 15 has an inner bearing race 15a attached to shaft 11c. Bearing 15 has an outer bearing race 15b attached to a support structure (not shown) that supports rotor 11b. Rolling element bearing 13 is similar to or the same as rolling element bearing 15.

[0061] Machine assembly 9 also includes one or more sensors 17. The one or more sensors 17 may be, for example, accelerometers, current sensors, or capacitive sensors. If the sensors 17 are accelerometers, they generate signals that provide a measurement of mechanical vibrations in the rolling element bearings 13 and 15. If the sensors 17 are capacitive sensors, they may be arranged around shaft 11c to measure the radial displacement of shaft 11c and generate signals. Figure 2 In the example, sensor 17 is an accelerometer or a capacitive sensor, as it is placed on or around shaft 11c. If the sensor is a current transducer, it can be arranged to measure the phase current(s) and generate a signal.

[0062] Machine assembly 9 includes a control system 1. Machine assembly 9 includes a power converter 19. Power converter 19 can be a driver. Power converter 19 is configured to control the operation of motor 11. Control system 1 is configured to control the operation of power converter 19.

[0063] Control system 1 is configured to receive signals from one or more sensors 17. Control system 1 is configured to process the signals and, based on the signals, control power converter 19 and thus motor 11 in a manner that extends the lifespan of rolling element bearings 13 and 15. (See reference...) Figure 3 and Figure 4 Describe the operation.

[0064] Figure 3 A flowchart illustrating an example of an internal control loop executed by control system 1 is shown. Figure 4 A flowchart illustrating an example of an external control loop executed by control system 1 is shown. The external control loop can receive the output from the internal control loop as input, but the internal and external control loops can also execute independently.

[0065] like Figure 4 As shown, the method includes step a), in which a first set of control parameters is defined. This can be a set of control parameter values ​​selected for controlling the motor.

[0066] The method further includes step b) estimating the first RUL of the rolling element bearings 13, 15 based on signals received from one or more sensors 17. The signals obtained from the sensors are measured when the motor is controlled using a first set of control parameter values.

[0067] Features can be extracted from the signal, which can be used to estimate RUL.

[0068] As an example, the method disclosed in Medjaher et al.’s paper “Remaining Useful Life Estimation of Critical Components With Applications to Bearings” published in IEEE Transactions on Reliability (Vol. 61, No. 2, June 2012) can be used to estimate RUL.

[0069] Alternatively, one can use, such as L 10 Mathematical models, such as predictive models, are used to estimate RUL.

[0070] For example, a degradation model of rolling element bearings, an extended Kalman filter, or a neural network can be used to estimate the RUL.

[0071] refer to Figure 3 The internal control loop includes receiving signals from one or more sensors 17. These signals provide vibration measurements of the rolling element bearings 13, 15.

[0072] In step A), the harmonic content of the signal is determined. This can be done using frequency transforms, such as those from the Fourier transform family.

[0073] If the amplitude of the harmonic content is determined to be higher than the threshold, in step B), the control parameter value of at least one control parameter from a set of control parameters is changed. This set is also referred to herein as the "third set of control parameter values".

[0074] An amplitude exceeding the threshold indicates that there is higher-than-expected vibration in the rolling element bearings 13 and 15.

[0075] Step a) can be performed before steps A)-B). The first set of control parameter values ​​can, for example, be used as the set of control parameter values ​​in the first iteration of steps A)-B).

[0076] Step b) can be performed before steps A)-B).

[0077] In step C), steps A) and B) are repeated until a set of control parameter values ​​is found that reduces the amplitude below the threshold.

[0078] In each iteration, at least one control parameter value is gradually changed. When the amplitude decreases, the same at least one control parameter will undergo a change in value. If the amplitude increases, at least one different control parameter will cause its value to change.

[0079] In the initial iteration of step B), only one control parameter value is changed. In subsequent iterations, when changes to all individual control parameters have been performed and the amplitude is above the threshold, combinations of control parameter values ​​that change several or even all control parameters are changed.

[0080] The one or more control parameter values ​​changed in step B) are used to control the power converter 19. The control system 1 therefore changes one or more control parameter values ​​to obtain a new set of control parameters to control the power converter 19, which in turn controls the motor 11. The control parameters may be, for example, a torque reference, a speed reference, a switching frequency, or modulation.

[0081] Once steps A)-B) above have been performed and a set of control parameter values ​​has been found that reduce the amplitude below the threshold, the following steps can be performed in the external control loop.

[0082] In step c), at least one control parameter value that was changed in the last iteration of step B) is modified from the first set of control parameter values. This yields a second set of control parameter values. At least one control parameter value is changed by a larger increment or decrement than in step B). The direction of change, i.e., increment or decrement, is the same as in step B).

[0083] The second set of control parameter values ​​is then used to control motor 11. Control system 1 therefore uses the second set of control parameter values ​​to control power converter 19, which in turn controls motor 11. Control parameters may include, for example, torque reference, speed reference, switching frequency, or modulation.

[0084] In step d), the second RUL is estimated based on the signal obtained when the motor is controlled using the second set of control parameter values.

[0085] In step e), the first RUL is compared with the second RUL.

[0086] In step f), if the second RUL is longer than the first RUL, the control parameter value in the first set of control parameter values ​​is replaced with the control parameter value of the second set of control parameter values. The value of the first RUL is replaced with the value of the second RUL.

[0087] According to one example, step f) could involve replacing the control parameter values ​​in the first set of control parameter values ​​with control parameter values ​​from the second set of control parameter values ​​only if the second RUL is longer than the first RUL and the second RUL deviates from the first RUL by more than a threshold. If the second RUL deviates less than the threshold, the first set of control parameter values ​​can be used to control motor 11 because, in this case, according to one example, the improvement in RUL is small enough that, given the intrusive nature of the method, it will not produce a significant difference.

[0088] According to one variant, steps a)-g) can be performed without involving steps A)-C). Therefore, the steps referred to in this paper as the external control loop can be performed independently, i.e., as a standalone method.

[0089] If steps c)-g) follow steps A)-B) above, one or more control parameter values ​​selected in the last iteration of step B) are used as the starting values(s) being changed in step c). The change in step c) is greater than the change performed in step B).

[0090] Repeat steps a)-g) repeatedly during motor operation.

[0091] This can extend the life of rolling element bearings.

[0092] The internal control loop is faster than the external control loop. Therefore, while the external control loop is executing steps c)-f), the internal control loop continues executing steps A)-C). The internal and external control loops operate independently. For example, let's assume a first RUL estimated at 50,000 hours in step b) for the first set of control parameter values. Then the internal control loop runs. In this case, the external control loop does not run. Steps A) and B) are executed and repeated. For example, the control parameter value that might change in step B) is the speed reference. For example, in the first iteration of this internal control loop, the speed reference value might be 1500 rpm, and in each iteration, the speed reference value increases by 10 rpm. Therefore, in the second iteration, the speed reference is 1510 rpm, then in the third iteration it is 1520 rpm, and so on. Assume that steps A) and B) are repeated, gradually changing one or more control parameter values ​​until the amplitude in the harmonic content is below a threshold. The steps are small and may only be increased to a certain point, so they do not change the operating point of motor 11. In this scenario, as an illustrative example, we assume a speed reference of 1550 RPM when the amplitude in the harmonic content falls below a threshold. The process of running the internal control loop may take several minutes. In this case, in step c), the control parameter value associated with the speed reference is changed, thus obtaining a second set of control parameter values. This change could be, for example, 100, so the speed reference value changes to 1650 in step c). The operating point of motor 11 can thus be changed. In step d), a second RUL is estimated based on the speed reference of 1650 RPM. Assume the second RUL result is 51,000 hours. If improvement occurs, the change in RUL may be 3%-5% for a step change in one or more control parameter values. In this case, the control parameter values ​​in the first set of control parameter values ​​are replaced with the control parameter values ​​from the second set of control parameters. Furthermore, the first RUL value of 50,000 hours is replaced with the second RUL value of 51,000 hours. The external control loop may continue to change the control parameters in larger steps of 100, and all changes may be completed within several hours.

[0093] If the second RUL is shorter than the first RUL (e.g., 49,000 hours), the external control loop will change another control parameter value instead of the speed reference, regardless of the internal control loop which is not currently running. Once the external control loop has completed its operation, the internal control loop can iteratively execute steps A)-C) again to find a new set of control parameter values ​​that reduce vibration in the motor. For each set of second control parameter values ​​used in the external control loop, the corresponding RUL can be stored along with the second set of control parameter values. When all combinations of control parameter values ​​have been exhausted, the set of control parameters that gives the longest RUL can be selected to control motor 11.

[0094] The above examples primarily illustrate the inventive concept. However, as will be readily understood by those skilled in the art, other embodiments besides those disclosed above may also fall within the scope of the inventive concept defined by the appended claims.

Claims

1. A method for extending the life of rolling element bearings (13, 15) of an electric motor (11), the method comprising: a) Define the first set of control parameter values. b) Estimate the first remaining service life (RUL) of the rolling element bearings (13, 15) based on the vibration measurement signals of the rolling element bearings (13, 15) obtained when the motor is controlled by the first set of control parameter values. c) Change at least one control parameter value in the first set of control parameter values ​​to obtain the second set of control parameter values. d) Estimate the second RUL of the rolling element bearings (13, 15) based on the signal obtained when the motor is controlled by the second set of control parameter values. e) Compare the first RUL with the second RUL. f) If the second RUL is longer than the first RUL, replace the control parameter value in the first set of control parameter values ​​with the control parameter value in the second set of control parameter values, and replace the value of the first RUL with the value of the second RUL. g) Repeat steps c)-f) repeatedly during the operation of the motor (11).

2. The method of claim 1, wherein the estimation in steps b) and d) involves using a degradation model of the rolling element bearing, using an extended Kalman filter, or using a neural network.

3. The method of claim 1 or 2, wherein step f) involves replacing the control parameter value in the first set of control parameter values ​​only if the second RUL deviates from the first RUL by more than a threshold.

4. The method according to claim 1 or 2, comprising: Before step c): A) Determine the harmonic content of the signal. B) If the harmonic content contains amplitudes higher than the threshold, change at least one control parameter value from the third set of control parameter values, and C) Repeat steps A)-B) until a set of third control parameter values ​​is found that reduces the amplitude below the threshold; and D) Perform step cg), wherein the at least one control parameter value changed in step c) is at least one control parameter associated with the at least one control parameter value used in step B), and wherein the change of the at least one control parameter value in step B) is less than the change in step c).

5. The method of claim 4, wherein the change of the value of the at least one control parameter in step B) is performed incrementally in each iteration.

6. The method of claim 4, wherein the change in step c) is based on the at least one control parameter value selected in step B).

7. The method according to claim 4, wherein in the initial iteration of step B), the control parameter value of the individual control parameter is changed, and in subsequent iterations, when all changes to the individual control parameters have been performed, the combination of control parameter values ​​of the control parameters is changed.

8. The method according to claim 4, wherein steps A)-C) form an internal control loop, and steps C)-G) form an external control loop.

9. A computer program comprising computer code, which, when executed by a processing circuit (5) of a control system (1), causes the control system (1) to perform the steps of the method according to any one of claims 1-8.

10. A control system (1) for extending the life of rolling element bearings in an electric motor (11), the control system (1) comprising: Including storage media for computer code (7), and Processing circuit (5), When the processing circuit (5) executes the computer code, the control system (1) is configured as follows: a) Define the first set of control parameter values. b) Estimate the first remaining service life (RUL) of the rolling element bearings (13, 15) based on the vibration measurement signals of the rolling element bearings (13, 15) obtained when the motor is controlled by the first set of control parameter values. c) Change at least one control parameter value in the first set of control parameter values ​​to obtain the second set of control parameter values. d) Estimate the second RUL of the rolling element bearings (13, 15) based on the signal obtained when the motor is controlled by the second set of control parameter values. e) Compare the first RUL with the second RUL. f) If the second RUL is longer than the first RUL, replace the control parameter value in the first set of control parameter values ​​with the control parameter value in the second set of control parameter values, and replace the value of the first RUL with the value of the second RUL. g) Repeat steps c)-f) repeatedly during the operation of the motor (11).

11. The control system (1) according to claim 10, wherein the processing circuit (5) is configured to estimate the first RUL and the second RUL using a degradation model of the rolling element bearing, an extended Kalman filter, or a neural network.

12. The control system (1) according to claim 10 or 11, wherein the processing circuit (5) is configured to, before step c): A) Determine the harmonic content of the signal. B) If the harmonic content contains amplitudes higher than the threshold, change at least one control parameter value from the third set of control parameter values, and C) Repeat steps A)-B) until a set of third control parameter values ​​is found that reduces the amplitude below the threshold; and D) Perform steps c)-g), wherein the at least one control parameter value changed in step c) is at least one control parameter associated with the at least one control parameter value used in step B), and wherein the change of the at least one control parameter value in step B) is less than the change in step c).

13. The control system (1) according to claim 12, wherein the processing circuit (5) is configured to progressively change the value of at least one control parameter in step B) in each iteration.

14. The control system (1) according to claim 12, wherein the processing circuit (5) is configured to perform the change in step c) based on the at least one control parameter value selected in step B).

15. The control system (1) according to claim 12, wherein the processing circuit (5) is configured to: change the control parameter value of an individual control parameter in the initial iteration of step B), and change the combination of control parameter values ​​of the control parameters in subsequent iterations when changes to all individual control parameters have been performed.

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