Motor driving bearing damage testing device and method thereof

Abstract

The invention discloses a motor driving bearing damage testing device and method, and the method employs the motor driving bearing damage testing device to execute the following steps: measuring internal parasitic parameters of a motor; obtaining stray capacitance between a stator winding and a stator core in the motor, stray capacitance between the stator winding and a rotor and stray capacitance between the stator core and the rotor; testing the motor bearing under different working conditions, wherein the different working conditions comprise different bearing voltage amplitudes, different switching frequencies and different switching speeds; and the reducibility of the bearing operation environment can be maintained, and long-time testing and bearing observation can be conveniently carried out.

Description

Technical Field

[0001] The invention relates to a motor drive bearing damage testing device and a method thereof, belonging to the technical field of motor bearing damage testing. Background Art

[0002] The variable frequency drive (VFD) adjusts the speed of the motor by changing the input frequency and voltage of the motor, thereby improving the energy efficiency of the motor system. However, the use of the variable frequency drive also brings about an electromagnetic environment that is different from that of traditional DC or industrial frequency AC drives. Under the high-frequency pulses generated by the variable frequency drive, the electrical characteristics of the motor change, which easily forms a voltage difference on the motor bearings, resulting in the generation of bearing currents.

[0003] Typically, due to the switching operation of the inverter, the common mode voltage generated passes through the motor housing or grounding system, causing current to be generated in the bearing. When the current passes through the bearing, tiny electric sparks discharge between the bearing rolling elements and the inner and outer rings, causing local melting, ablation or pitting of the material surface. This electrical corrosion causes the lubrication performance of the bearing to deteriorate, increase friction and noise, and eventually cause premature failure of the bearing.

[0004] In order to analyze the impact of bearing current on bearing damage, an effective and reliable bearing test platform is needed for research. The traditional motor bearing test platform adopts an embedded design, the bearing is fixed inside the motor, and the bearing voltage is coupled through the high-frequency common-mode voltage output by the inverter. This type of platform has motor integrity. However, since the bearing is integrated inside the motor and has a tight fit or clearance fit with the shaft, it is impossible to remove the bearing from the motor for observation in a timely and effective manner during the experiment. This design brings inconvenience to long-term continuous testing and testing under different electrical conditions. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the defects of the prior art. To achieve this purpose, the present invention provides a motor-driven bearing damage testing device and method, which can not only maintain the restorability of the bearing operating environment, but also facilitate long-term testing and bearing observation.

[0006] Preferably, the present invention provides a motor-driven bearing damage testing device, comprising an asynchronous motor, a carbon brush, an inverter, a three-phase resistor and a parasitic capacitor network. The load of the inverter is a three-phase resistor, and the positive electrode of the common-mode voltage is drawn from the neutral point of the three-phase resistor and connected in series with the parasitic capacitor network, and finally introduced into the bearing with a carbon brush. The bearing to be tested is installed on the rotating shaft of the asynchronous motor by an interference connection using insulating material.

[0007] A motor drive bearing damage testing method, using the motor drive bearing damage testing device to perform the following steps:

[0008] The parasitic parameters inside the motor are measured to obtain the parasitic capacitance C between the stator winding and the stator core inside the motor. ws , parasitic capacitance C between stator winding and rotor wr And the parasitic capacitance C between the stator core and the rotor rs ;

[0009] Testing motor bearings under different operating conditions, including different bearing voltage amplitudes, different switching frequencies, and different switching speeds;

[0010] Adjust the amplitude ratio of the common mode voltage to the bearing voltage or the DC power supply of the inverter to obtain different bearing voltages;

[0011] Adjust the parasitic capacitance C between the stator winding and the rotor wr , different bearing voltage amplitudes are obtained.

[0012] Preferably, wide bandgap semiconductor GaN devices are used as switch tubes of the inverter.

[0013] Prioritize the measurement of the parasitic parameters inside the motor to obtain the parasitic capacitance C between the stator winding and the stator core inside the motor. ws , parasitic capacitance C between stator winding and rotor wr And the parasitic capacitance C between the stator core and the rotor rs ,include:

[0014] Disassemble the motor and take out the rotor, and short-circuit the three-phase input terminals of the motor's stator winding;

[0015] Measure the equivalent capacitance C1 between the neutral point of the stator winding and the body of the motor;

[0016] Measure and remove the equivalent capacitance C2 of the insulation layer in the bearing chamber of the motor end cover;

[0017] Reassemble the motor, keep the stator winding of the motor short-circuited, and short-circuit the insulation layers at both ends of the motor bearings, keep the shaft stationary, and measure the equivalent capacitance C3 between the neutral point of the stator winding and the body;

[0018] Calculate the parasitic capacitance C between the stator winding and the stator core inside the motor ws , parasitic capacitance C between stator winding and rotor wr And the parasitic capacitance C between the stator core and the rotor rs :

[0019] C ws =C1

[0020] C wr =C2-C1

[0021] C rs=C3-C wr

[0022] Preferably, the following conditions are met when testing motor bearings under different operating conditions:

[0023] Change any one of the bearing voltage amplitude, switching frequency and switching speed and keep the other two values ​​unchanged.

[0024] Preferably, the following conditions are met when testing motor bearings under different operating conditions:

[0025] The switching frequency covers the driving frequency range of commercial inverters.

[0026] Preferably, the following conditions are met when testing motor bearings under different operating conditions:

[0027] The switching speed is controlled by the driving resistor of the inverter, and the test range of the switching speed covers at least a switching speed of up to 30kV / μs.

[0028] Preferably, the following conditions are met when testing motor bearings under different operating conditions:

[0029] The bearing voltage variation range must cover the bearing voltage amplitude ratio BVR range of the actual motor.

[0030] The beneficial effects achieved by the present invention are:

[0031] 1. The present invention discloses a motor-driven bearing damage testing device and a motor-driven bearing damage testing method, which can conveniently disassemble the bearing to be tested and observe its damage condition under long-term continuous testing.

[0032] 2. The bearing voltage in the present invention is controllable, allowing the parasitic capacitance C to be adjusted. wr To change the bearing voltage ratio, the bearing voltage can be changed arbitrarily. When evaluating the impact of electrical parameters on bearing damage, this method comprehensively considers the theoretical analytical method and the thickness of each air gap inside the actual motor, and reasonably adjusts the BVR to generate a larger bearing voltage using a smaller DC bus voltage. Furthermore, after the BVR is adjusted, the DC bus voltage can be adjusted to achieve the effect of adjusting the bearing voltage.

[0033] 3. The present invention takes into account the parasitic capacitance parameters (C ws , C wr , C rs), so that the waveform of the bearing voltage during the test more truly reflects the actual situation. For bearings, bearing voltage is the main source of all excitations. Therefore, under the same bearing voltage excitation, the performance of bearing damage is closer to reality, ensuring the accuracy of the test results. By extracting the parasitic capacitance parameters in the real motor separately and connecting them to the loop, the coupling relationship of the shaft voltage can be better restored. This technology is not only applicable to this device, but also to other bearing test platforms that are separated from the complete motor, aiming to simplify the user's experimental use process. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solution of the present application, the drawings required for use in the embodiments are briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0035] Figure 1 A schematic diagram of a device in an embodiment of the present invention;

[0036] Figure 2 This is an example diagram of extracting internal parasitic capacitance parameters of a motor according to an embodiment of the present invention;

[0037] Figure 3 A topological structure diagram of a device in an embodiment of the present invention;

[0038] Figure 4 is the common mode voltage waveform;

[0039] Figure 5 is a schematic diagram of a device in an embodiment of the present invention;

[0040] Figure 6 A schematic diagram of a conventional invasive bearing testing platform according to an embodiment of the present invention;

[0041] Figure 7 In the embodiment of the present invention, V dc The comparison chart of the bearing voltage of this device and the traditional embedded test platform when the voltage is 20V;

[0042] Figure 8 A flow chart of adjusting bearing voltage according to an embodiment of the present invention.

[0043] Meaning of the reference numerals: 1-inverter; 2-three-phase resistor; 3-parasitic capacitance network; 4-current probe; 5-voltage probe; 6-carbon brush; 7-insulating material; 8-bearing to be tested; 9-deoxidized resin board; 10-commercial frequency converter; 11-junction box; 12-asynchronous motor. DETAILED DESCRIPTION

[0044] See also Figure 1 , a motor drive bearing damage testing method, comprising the following steps:

[0045] S1: By measuring the parasitic parameters inside the motor, the parasitic capacitance C between the stator winding and the stator core inside the motor is obtained. ws , parasitic capacitance C between stator winding and rotor wr And the parasitic capacitance C between the stator core and the rotor rs ;

[0046] S2: The input source of this device is a three-phase two-level inverter based on GaN HEMT devices, and the main load is a three-phase symmetrical resistor connected in star shape. The load draws the positive pole of the common-mode voltage from the neutral point, and the midpoint of the DC bus of the inverter is used as the negative pole of the common-mode voltage, and draws the positive pole of the common-mode voltage from the neutral point of the three-phase resistor, and connects the common-mode voltage to the subsequent parasitic capacitor network through a wire. In addition, a wire is connected to the midpoint of the capacitor of the GaN inverter to close the common-mode voltage loop. The magnitude of the common-mode voltage is only related to the amplitude of the DC bus voltage and is expressed by the following formula. The common-mode voltage is:

[0047]

[0048] S3: Control the change of bearing voltage by adjusting the amplitude ratio (BVR) of common mode voltage to bearing voltage. wr The size of the bearing voltage ratio can be effectively increased. In addition, adjusting the DC power supply of the inverter can also change the bearing voltage. The bearing voltage ratio (BVR) formula is:

[0049]

[0050] S4: Motor drive bearing voltage test steps: Use the traditional embedded motor bearing test platform and the simplified bearing test platform developed by the present invention for comparative testing to observe the difference in the bearing voltage waveform. For the bearing, the front-end loop serves as the voltage excitation source, so under the same voltage excitation conditions, the damage caused to the bearing by the two platforms should be the same. Therefore, the effectiveness of the present device can be verified by comparing the bearing voltage waveforms. After verifying the effectiveness, the motor bearings can be tested for a long time under different working conditions (different electrical parameters), and the electrical parameters include different bearing voltage amplitudes, switching frequencies, and switching speeds. In order to achieve a wide range of switching frequencies and switching speeds, wide bandgap semiconductor GaN devices are used as the switching tubes of the inverter.

[0051] By adjusting the BVR C wr The value of can be used to linearly adjust the inverter DC power supply and thus adjust the bearing voltage amplitude.

[0052] Specifically, the typical BVR value ranges from 2.5% to 7.5%. Therefore, even if a higher DC bus voltage is applied, the bearing voltage amplitude reflected to the bearing end is still small, and a wider range of bearing voltage amplitude tests cannot be achieved. In order to test the effect of bearing voltage on bearing damage, the C wr Increasing the value of BVR significantly increases the ratio of the bearing voltage to the common-mode voltage.

[0053] The extraction of the internal parasitic parameters of the motor requires the motor to be disassembled. The specific steps are as follows:

[0054] W1: Disassemble the motor and take out the rotor, short-circuit the three-phase input terminals of the stator winding; measure the equivalent capacitance between the neutral point of the stator winding and the body, recorded as C1;

[0055] W2: Measure and remove the equivalent capacitance of the insulation layer in the bearing chamber of the motor end cover, recorded as C2;

[0056] W3: Reinstall the motor, keep the stator winding short-circuited, and short-circuit the insulation layers of the bearings at both ends. Make sure the shaft is stationary, and measure the equivalent capacitance between the neutral point of the stator winding and the body again, which is recorded as C3.

[0057] W4: Based on the above measurement results, the coupling capacitance value is calculated as follows:

[0058] C ws =C1

[0059] C wr =C2-C1

[0060] C rs =C3-C wr

[0061] Based on this device, motor bearing tests can be performed under different working conditions. Specific parameters include: DC side voltage V dc , switching frequency f sw and switching speed.

[0062] In continuous testing, by changing one of the variables and keeping the other variables unchanged, the test conditions under the single electrical variable are obtained. During the test, the range of bearing voltage changes must cover the BVR range of the actual motor. For example, the BVR needs to be measured from a typical 2.5% to 7.5%, and the corresponding voltage range is 3V to 30V (the typical bearing voltage threshold when the breakdown current of EDM occurs).

[0063] The switching frequency should cover the driving frequency range of commercial inverters, from 4kHz to 20kHz. In order to study the relationship between bearing current and bearing damage and switching frequency, the bearing damage at higher frequencies can be further tested in the future.

[0064] The switching speed is controlled by the drive resistor of the inverter, and the test range should at least cover the switching speed up to 30kV / μs.

[0065] This device requires an additional asynchronous motor to support the rotation of the bearing. The additional asynchronous motor needs to lengthen the shaft to drag the external test bearing. In order to prevent the bearing voltage induced by the additional motor shaft from interfering with the experiment, an insulating material (such as polyurethane or other high dielectric constant materials) needs to be installed between the shaft and the bearing in an interference connection (the shaft radius is larger than the inner diameter of the insulating material).

[0066] This device uses an additional 1.1kW asynchronous motor to support the rotation of the bearing. The shaft of this motor is lengthened to 18cm and is used to pull the external test bearing. To prevent the bearing voltage induced by the 1.1kW motor shaft from interfering with the experiment, the shaft and the bearing are assembled by an interference fit using insulating materials (such as polyurethane or other high dielectric constant materials). The inner raceway of the bearing rotates with the insulating material and the shaft, while the outer raceway is fixed by a stainless steel bracket to access the wires of the test circuit.

[0067] The entire test bench is installed on a deoxidized resin board to ensure insulation. The bearing voltage measurement requires accurate access between the inner and outer raceways of the bearing. Since the inner raceway rotates with the shaft, a carbon brush is used to contact and connect to the positive pole of the common mode voltage; the outer raceway is fixed by a stainless steel cage, directly connected to the wire and returned to the midpoint of the DC bus of the GaN inverter, thus completing the closure of the entire test circuit. The bearing current is measured by clamping the current probe to the carbon brush wire, such as Figure 5 shown.

[0068] In addition, the bearing voltage to bearing voltage amplitude ratio BVR of the simplified device can be adjusted by adjusting the DC bus voltage or the capacitance value in the parasitic capacitor network. Specifically, C wr The amplitude of has a great influence on BVR, so it can be adjusted within a reasonable range. wr To improve the BVR value. In this example, several C wr The value of and the changed BVR, when C wr When it increases to 1nF, the BVR can reach 40.76%, but due to C wr The air gap is shorter, and the actual value is usually 60 to 100pF. However, in some higher power motors, due to the distribution of the air gap, C wr The value of can also break through hundreds of pF. Therefore, in this embodiment, considering the safety of the experiment and the rationality of the parameters, C wr Adjusting to 247pF, the BVR can be increased to 14.5%. This design ensures effective testing within reasonable parameters.

[0069] To verify the effectiveness of the device, the present embodiment intercepted the bearing voltage and bearing current waveforms from the asynchronous motor extracted from the parasitic capacitance parameters, and compared them with the traditional intrusive test platform (see Figure 6 ) are compared. Figure 7 The comparison of the bearing voltage and bearing current of this device and the traditional intrusive test platform shows that the bearing voltage waveform obtained by the simplified platform is roughly the same as that of the traditional method, and the bearing voltage amplitude can be flexibly adjusted. Compared with the traditional platform, this device has advantages in scalability, which shows that this device has high reproducibility and convenience.

[0070] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

[0071] Those skilled in the art will readily appreciate other embodiments of the invention after considering the specification and practicing the invention invented herein. This application is intended to cover any variations, uses or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art that are not invented by the present invention. The specification and examples are intended to be exemplary only, and the true scope and spirit of the invention are indicated by the claims.

[0072] The above specific implementation methods further illustrate the purpose, technical solutions and beneficial effects of the present application in detail. It should be understood that the above are only specific implementation methods of the present application and are not used to limit the protection scope of the present application. Any modifications, equivalent substitutions, improvements, etc. made on the basis of the technical solutions of the present application should be included in the protection scope of the present application.

Claims

1. A motor drive bearing damage testing device, characterized in that: It includes an asynchronous motor, carbon brushes, inverter, three-phase resistors and parasitic capacitor network. The positive pole of the common mode voltage is drawn from the neutral point of the three-phase resistor. The neutral point and the parasitic capacitor network are connected in series and finally introduced to the bearing with a carbon brush. The bearing to be tested is installed on the shaft of the asynchronous motor by interference connection using insulating materials.

2. A motor drive bearing damage testing method, characterized in that: The motor drive bearing damage testing device according to claim 1 is used to perform the following steps: The parasitic parameters inside the motor are measured to obtain the parasitic capacitance C between the stator winding and the stator core inside the motor. ws , parasitic capacitance C between stator winding and rotor wr And the parasitic capacitance C between the stator core and the rotor rs ; Testing motor bearings under different operating conditions, including different bearing voltage amplitudes, different switching frequencies, and different switching speeds; Adjust the amplitude ratio of the common mode voltage to the bearing voltage or the DC power supply of the inverter to obtain different bearing voltages; Adjust the parasitic capacitance C between the stator winding and the rotor wr , different bearing voltage amplitudes are obtained.

3. A motor drive bearing damage testing method according to claim 2, characterized in that: Wide bandgap semiconductor GaN devices are used as switching tubes of the inverter.

4. A motor drive bearing damage testing method according to claim 2, characterized in that: The parasitic parameters inside the motor are measured to obtain the parasitic capacitance C between the stator winding and the stator core inside the motor. ws , parasitic capacitance C between stator winding and rotor wr And the parasitic capacitance C between the stator core and the rotor rs ,include: Disassemble the motor and take out the rotor, and short-circuit the three-phase input terminals of the motor's stator winding; Measure the equivalent capacitance C1 between the neutral point of the stator winding and the body of the motor; Measure and remove the equivalent capacitance C2 of the insulation layer in the bearing chamber of the motor end cover; Reassemble the motor, keep the stator winding of the motor short-circuited, and short-circuit the insulation layers at both ends of the motor bearings, keep the shaft stationary, and measure the equivalent capacitance C3 between the neutral point of the stator winding and the body; Calculate the parasitic capacitance C between the stator winding and the stator core inside the motor ws , parasitic capacitance C between stator winding and rotor wr And the parasitic capacitance C between the stator core and the rotor rs : C ws =C1C wr =C2-C1 C rs =C3-C wr 5. A motor drive bearing damage testing method according to claim 2, characterized in that: The following conditions are met when testing motor bearings under different working conditions: Change any one of the bearing voltage amplitude, switching frequency and switching speed and keep the other two values ​​unchanged.

6. A motor drive bearing damage testing method according to claim 5, characterized in that: The following conditions are met when testing motor bearings under different working conditions: The switching frequency covers the driving frequency range of commercial inverters.

7. A motor drive bearing damage testing method according to claim 6, characterized in that: The following conditions are met when testing motor bearings under different working conditions: The switching speed is controlled by the driving resistor of the inverter, and the test range of the switching speed covers at least a switching speed of up to 30kV / μs.

8. A motor drive bearing damage testing method according to claim 7, characterized in that: The following conditions are met when testing motor bearings under different working conditions: The bearing voltage variation range must cover the bearing voltage amplitude ratio BVR range of the actual motor.

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